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  • Organic Chemistry  (6,898)
  • Engineering General  (3,850)
  • 1985-1989  (5,965)
  • 1980-1984  (4,783)
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Keywords
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Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    The FDA perspective on the development of stereoisomers (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 2-6 
    Details
    ISSN: 0899-0042
    Keywords: optical isomers ; stereochemistry ; enantiomers ; Food and Drug Administration ; drug development ; drug regulation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The current regulatory position of the Food and Drug Administration is discussed with regard to the approval of racemates and pure stereoisomers. Circumstances in which stereochemically sensitive analytical methods are necessay to ensure the safety and efficacy of a drug are described. Regulatory guidelines are interpreted for applications for the approval of a pure enantiomer in which the racemate is marketed, for the approval of eitehr a racemate or a pure enantiomer in which neither is marketed, and for clinical investigations to compare the safety and efficacy of a racemate and its enantiomers. Examples of te basis for such regulation are drawn from historical situations (thalidomide, benoxaprofen) as well as currently marketed drugs (arylproionic acids, disopyramide, indacrinone).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010103
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  • 2
    Electronic Resource
    Electronic Resource
    Pharmacokinetic data of propranolol enantiomers in a comparative human study with (S)- and (R,S)-propranolol (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 10-13 
    Details
    ISSN: 0899-0042
    Keywords: (S)-, (R,S)-propranolol ; pharmacokinetic ; human study ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pharmacokinetics of (S)-propranolol were compared after the oral administration of a 40 mg dose of the pure enantiomer and an 80 mg dose of a racemic mixture of (R,S)-propranolol. The results of this study indicate that the bioavailability of (S)-propranolol, as expressed by the mean area uner the concentration-time curve (AUC) and maximum serum concentration, is lower after 40mg of the optically pure drug than after the racemic drug.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010105
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  • 3
    Electronic Resource
    Electronic Resource
    Stereocontrolled synthesis of peptide bond isosteres (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 89-91 
    Details
    ISSN: 0899-0042
    Keywords: asmmetric induction ; bacterial cell wall ; D-Ala-D-Ala ; dipeptide ; peptidoglycan ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute stereochemical control is employed in the synthesis of isosteres for dipeptide subunits 1; see Fig. (1) in which the amide linkage has been replaced by a trans carbon-caron double bond. The synthesis affords access to the four stereoisomers of 1 in which R and R' = CH3, including the isostere of D-alanine-d-alanine (D-ala-D-Ala), 2.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010116
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanisms of chiral recognition in xenobiotic metabolism and drug-receptor interactions (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 7-9 
    Details
    ISSN: 0899-0042
    Keywords: substrate enantioselectivity ; product enantioselectivity ; Michaelis-Menten analysis ; intrinsic activity ; potency ; receptor affinity ; efficacy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010104
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  • 5
    Electronic Resource
    Electronic Resource
    Methiodide of the GABA antagonist (+)-bicuculline is levorotatory (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 178-179 
    Details
    ISSN: 0899-0042
    Keywords: CD spectra ; optical rotation ; phthalideisoquinoline base and salts ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The appearance of positive charge on the nitrogen moiety of phthalideisoquinoline alkaloids brings about a strong change in the intensities of CD Cotton effects. Hence the optical rotations of enantiomeric salts and their parent base of identical configuration are often of opposite sign. Thus, the name (+)-bicuculline-methiodide for the methiodide salt of (+)-bicuculline is false.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010214
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  • 6
    Electronic Resource
    Electronic Resource
    Stereoselectivity at muscarinic receptor subtypes: observations with the enantiomers of phenglutarimide (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 170-173 
    Details
    ISSN: 0899-0042
    Keywords: phenglutarimide enantiomers ; enantioselectivity ; antiparkinsonian drugs ; M1-selective antagonists ; rabbit vas deferens ; pirenzepine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The affinity of the enantiomers of phenglutarimide at three muscarinic receptor subtypes was examined in vitro using field-stimulated rabbit vas deferens (M1 receptors) and guinea pig atria (M2α receptors) and ileum (M2β receptors). Extremely high stereoselectivity was observed and higher affinities (up to 6000-fold) were found for the (+)-S-enantiomer. The stereoselectivity ratios were different at the three subtypes, and the stereochemical demands made by the muscarinic receptors were most stringent at M1 receptors. (+)-(S)-Phenglutarimide was found to be a potent M1-selective antagonist (pA2 at M1 = 8.53). Its receptor selectivity profile is qualitatively similar to that of pirenzepine. (-)-(R)-Phenglutarimide showed no comparable discriminatory properties.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010212
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  • 7
    Electronic Resource
    Electronic Resource
    Pharmacokinetics of the enantiomers of terbutaline after repeated oral dosing with racemic terbutaline (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 174-177 
    Details
    ISSN: 0899-0042
    Keywords: pharmacokinetics ; terbutaline ; enantiomers ; human ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Terbutaline is a β2-agonist and administered as the racemic mixture. The pharmacokinetics of the separate enantiomers differ with respect to degree of absorption and clearance. In the present study, repeated doses of racemic terbutaline were given to six healthy volunteers. Plasma was analyzed for the concentrations of the two enantiomers. The observed plasma concentrations at steady state differed from those predicted from the values observed after single dose administration of the separate enantiomers. The difference between the observed and predicted values can be tentatively explained by a combined influence of (-)-terbutaline on the absorption of (+)-terbutaline and the influence of (+)-terbutaline on the elimination of (-)-terbutaline. The results have implications for the interpretation of effect/concentration studies with terbutaline, but do not affect the doses used in clinical practice.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010213
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  • 8
    Electronic Resource
    Electronic Resource
    Stereochemistry of tissue distribution of racemic propranolol in the dog (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 192-196 
    Details
    ISSN: 0899-0042
    Keywords: propranolol enantiomers ; enantiomers ; propranolol ; β-receptor-blocking drugs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Only limited information is available on the stereochemistry of the in vivo distribution of β-receptor-blocking drugs. In this study we determined the levels of the propranolol enantiomers in plasma, cerebrospinal fluid (CSF) and central nervous system (CNS), and peripheral tissues in the dog following an intravenous dose of a deuterium-labeled pseudoracemate. The appearance of the propranolol enantiomers in the CSF was rapid and nonstereoselective, with maximum concentrations reached at 15 min after dosing. The levels of the enantiomers in both CSF and plasma then declined in a parallel biphasic fashion, with a terminal t1/2 of about 125 min. Except for an early high CSF/plasma concentration ratio of 0.35, the CSF propranolol levels corresponded to the unbound concentration in plasma, CSF/plasma 0.20. All areas of the brain showed a similar uptake of propranolol, with a tissue concentration exceeding that in plasma about 10-fold during the terminal phase of elimination. The uptake of propranolol by peripheral tissues varied widely, ranging from a 50-fold accumulation by the lungs compared to plasma to no accumulation by adipose tissue. However, as for the CSF, there was no evidence of stereoselective uptake of propranolol by any CNS or peripheral tissue except for the liver. A significantly higher level of (+)- vs. (-)-propranolol in liver tissue presumably was a reflection of stereoselective hepatic metabolism of (-)-propranolol by this tissue. The slight stereoselectivity in plasma binding of propranolol known to exist in the dog had no significant influence on tissue or CSF distribution.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010303
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  • 9
    Electronic Resource
    Electronic Resource
    The development of concepts of chiral discrimination (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 183-191 
    Details
    ISSN: 0899-0042
    Keywords: enantiomorphism ; dissymmetry ; chirality ; enantioselectivity ; diastereoselectivity ; steric complementarity ; asymmetric induction ; three-point contact ; circularly polarized radiation ; circular dichroism ; parity nonconservation ; electroweak interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pasteur's conjecture (1860) that biomolecular homochirality arose from a chiral natural force as yet inaccessible in the laboratory was supplanted by Fischer's (1894) “key and lock” hypothesis of stereoselection in enantiomer to diastereomer conversions, whether in the laboratory or in living organisms. Elaborations of the “key and lock” hypothesis by Haldane (1930) and Pauling (1948) have been illustrated and supported with modification by X-ray diffraction crystal structures of enzyme-substrate complexes over the past quarter century.Two types of mechanism for the product diastereoselectivity in the reactions of an enantiomer with an achiral reagent, early proposed, have recent support: one proposes a quasidiastereomeric structure for the enantiomer attacked in the ground state, the other for the corresponding transition state of the reaction. Approaches to the differential biological activity of two enantiomers postulate either the complete binding of each isomer to a chiral receptor site, resulting in diastereomeric complexes with inequivalent bioactivities, or the differential binding of the two isomers to a set of three sites, with which only one isomer is sterically congruent.Biochemical homochirality, based on the chiral stereoselectivity of both biosynthetic and metabolic reactions, derives from the evolutionary pressure for a progressive enhancement of the kinetic efficiency and economy of those reactions. Recently Pasteur has been vindicated in part, and the problem of the original prebiotic enantiomeric excess left outstanding by Fischer has been solved. The unification of the electromagnetic with the weak interaction provided a universal chiral natural force, the electroweak interaction, which favours the chiral series selected during the course of biochemical evolution, both the D-sugars and the L-amino acids.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010302
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  • 10
    Electronic Resource
    Electronic Resource
    Stereochemical influences upon the opioid ligand activities of 4-alkyl-4-arylpiperidine derivatives (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 202-208 
    Details
    ISSN: 0899-0042
    Keywords: opioid ligand ; 4-arylpiperidines ; conformation, NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and stereochemistry (configuration and preferred solute conformation) of some 4-alkyl (methyl, n-propyl, isobutyl)-4-(3-hydrxyphenyl)-1-methylpiperidines and corresponding 3-methyl diastereoisomeric pairs are reported, together with their in vivo and in vitro activities as opioid ligands. All potent agonists exhibit a preference for axial 4-aryl chair conformations when protonated, and stereochemical analogies with rigid opioids of the benzomorphan class are discussed. Antagonist properties are found in compounds with preference for equatorial 4-aryl chairs, notably the cis 3,4-dimethyl derivative.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010305
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  • 11
    Electronic Resource
    Electronic Resource
    Species differences in the chirality of the carbonyl reduction of [14C] fenofibrate in laboratory animals and humans (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 197-201 
    Details
    ISSN: 0899-0042
    Keywords: fenofibrate ; chiral reduction ; species differences ; prochiral to chiral transformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The prochiral carbonyl group of fenofibrate (isopropyl 2-[4-(4-chlorobenzoyl)phenoxy]-2-methyl propionate) is reduced during its metabolism giving rise to a chiral secondary alcohol, “reduced fenofibric acid.” Chiral and diastereomeric HPLC methods have been developed for the determination of its enantiomeric composition and these have been applied to the measurement of the “reduced fenofibric acid” enantiomers in urine of rats, guinea pigs, dogs, and human volunteers given [14C]fenofibrate. In the three animal species, the reduction is markedly enantioselective for the (-)-isomer, the enantiomeric ratios (-/ +) being 95:5. This was not due to differences in the excretion of the enantiomers, since when racemic “reduced fenofibric acid” was given to rats it was recovered in the urine with the same enantiomeric composition as the dose form. In humans the ratio was 52:48 showing the lack of stereoselectivity of reduction in this species.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010304
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  • 12
    Electronic Resource
    Electronic Resource
    Joining hands (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 1-1 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010102
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  • 13
    Electronic Resource
    Electronic Resource
    Pharmacologic implications of α-adrenocreceptor interactive parameters for epinephrine enantiomers in the rat vas deferens (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 14-19 
    Details
    ISSN: 0899-0042
    Keywords: affinity ; efficacy ; dissociation ; constants ; steroselectivity ; entropy ; enthalpy ; receptor ; interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: After alkylation of a fraction of the total α-adrenoreceptors by phenoxybenzamine in rat vas deferens, the dissociation constants of (-)- and (+)-epinephrine in functional studies were 7 × 10-7 M and 2 × 10-5 M, respectively. In the adrenoreceptor-containing tissue fraction, when 3H-labeled WB4101 was used as the interacting ligand, for each enantiomer who affinity sites were found. Only the low-affinity dissociation consant for each isomer correlates with the constant obtained from the functional studies. If the change in Gibb's free energy. ΔG°, is calculated from the low-affinity binding constants, the values -8.1 and -6.2 kcal/mol for (-)- and (+)-isomer, respectively, are obained. The small difference in the value between isomers forms a hydrogen bond with the receptor. The interaction of epinephrine with this receptor appears to be driven largely by the entropy of the drug-receptor interaction with only a small nonsteroselective contribution from the enthalpy of ineraction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010106
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  • 14
    Electronic Resource
    Electronic Resource
    Preparation of chiral statonary phase from an α-amino phosphonate (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 57-62 
    Details
    ISSN: 0899-0042
    Keywords: chiral stationary phase ; α-amino phosphonate ; chromatographic separation of enantiomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral statonary phase (CSP) derived from an N-(3,5-dinitrobenzoyl)-α-aminobenzylphosphonate has been prepared and evaluated for its utility in the direct separation of enantiomers. This CSP, 2, is structurally related to earlier N-(3,5-dinitrobenzoyl)-α-acids acid-derived phases (e.g., CSP 1), but the mode of attachment to the support is different. In scope; CSP 2 is qualitaively similar to CSP 1. However, it differs quantitatively from CSP 1, showing either greater or lesser selectivity for different pairs of enantiomers.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010111
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  • 15
    Electronic Resource
    Electronic Resource
    Masthead (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010101
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  • 16
    Electronic Resource
    Electronic Resource
    The stereochemical resolution of enantiomeric free and derivatized amino acids using and hplc chiral stationary phase based on immobilized α-chymotrypsin: Ciral separation due to solue structure or enzyme activity (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 38-44 
    Details
    ISSN: 0899-0042
    Keywords: column liquid chromatography ; chiral separations ; chymotrypsin on silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical separation of free and derivatized amino acids on active α-chymotrypsin bonded to silica is governed by two mechanisms based on the structure of the solutes or on the enzymatic activity of the enzyme. Te deactivation of the hydrolytically active site of the enzyme demonstrated that a significant portion of the retention on this support is due to hydrophobic interactions at other sites. These sites appear to be stereoselective for the ester derivatives of amino acids but not for the other studied solutes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010109
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  • 17
    Electronic Resource
    Electronic Resource
    Masthead (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010201
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  • 18
    Electronic Resource
    Electronic Resource
    Implications of chirality and geometric isomerism in some psychoactive drugs and their metabolites (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 99-120 
    Details
    ISSN: 0899-0042
    Keywords: asymmetry ; enantiomers ; geometric isomers ; (+)- (-)-isomers ; D- and L-isomers ; R- and S-isomers ; Z- and E-isomers ; drug metabolism ; stereoselectivity and stereospecificity in drug action ; stereoselectivity and stereospecificity in drug metabolism ; psychotropic drugs ; stimulants ; antidepressants ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Many drugs contain a chiral centre, or such a centre is introduced during metabolism of the drug in man and in animals. If a single chiral centre is present, the drug will normally exist as a mixture of two enantiomers, of which one may have quite different pharmacologic and/or toxic effects than the other. Chiral drugs that are used in psychiatry, and some other pharmacologically related drugs are identified, and the implications of the presence of one or two chiral centres in these drugs are discussed. Differences in pharmacologic properties of drug and metabolite enantiomers are identified and discussed. Also reviewed are the properties of some drugs used in psychiatry that both are chiral and display geometric isomerism.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010204
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  • 19
    Electronic Resource
    Electronic Resource
    Optical enrichment of dansyl-rac-amino acids by formation of crystalline inclusion complexes with cyclodextrins (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 137-141 
    Details
    ISSN: 0899-0042
    Keywords: resolution by crystallization ; racemic mixture ; dansyl-D-leucine ; dansyl-L-leucine ; dansyl-D-norleucine ; dansyl-L-norleucine ; dansyl-D-phenylalanine ; dansyl-L-phenylalanine ; β-cyclodextrin ; γ-cyclodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical enrichment from racemic dansyl-leucine, dansyl-norleucine, and dansyl-phenylalanine with both β- and γ-cyclodextrins in water is reported. Initial crystallization yielded the dansyl-L-leucine isomer complexed in excess with β-cyclodextrin with an optical purity of 62-78% depending on experimental conditions. The optical purities obtained for L-norleucine and L-phenylalanine were 71 and 64%, respectively. The optical purity can be increased with continued recrystallization. The dansyl-D-leucine isomer was obtained in the mother liquor with an optical purity of 54-93% depending on experimental conditions. The optical purities obtained for D-norleucine and D-phenylalanine were 72 and 58%. The optical purity of the isomer depended on the molar ratio of host:guest and the pH value of the solution. Optimum enrichment of both enantiomers was achieved with host:guest ratios of 2 : 1 and 3 : 1. Although maximum crystalline yield of the dansyl-leucine/CD inclusion complex was obtained at a pH of 3.5, optical purity of both enantiomers was less than that obtained at other pHs. The influence of the molar ratio of host:guest and the pH value of the solution are discussed. This method is suitable for large-scale enantiomeric separations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010207
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  • 20
    Electronic Resource
    Electronic Resource
    Masthead (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010301
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  • 21
    Electronic Resource
    Electronic Resource
    Masthead (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010401
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  • 22
    Electronic Resource
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    St. Mary's discussion forum: “Racemates and enantiomers: Scientific and regulatory aspects” (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 249-250 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010402
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  • 23
    Electronic Resource
    Electronic Resource
    The interaction of the enantiomers of carvedilol with α1- and β1-adrenoceptors (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 265-270 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselectivity of carvedilol, a novel β-adrenoceptor antagonist and vasodilator with one asymmetric carbon atom, was examined at α1- and β1-adrenoceptors in vitro and in vivo. (-)-(S)-Carvedilol is a potent, competitive antagonist of the β1-adrenoceptor-mediated positive chronotropic response to isoproterenol in guinea pig atrium, with a dissociation constant (KB) of 0.4 nM. (+)-(R)-Carvedilol was more than 100-fold less potent than the (-)-S-enantiomer as an antagonist of β;1-andrenoceptors, having a KB of approximately 45 nM. Consistent with these findings (-)-(S)-carvedilol (0.1 mg/kg, i.v.) produced a 25-fold rightward shift in the β1-adrenoceptor-mediated positive chronotropic response to isoproterenol in pithed rats, whereas the (+)-R-enantiomer had no β1-adrenoceptor blocking activity in vivo at this dose. In contrast to the marked degree of stereoselectivity observed at βl1-adrenoceptors, both (-)-(S)- and (+)-(R)-carvedilol produced equal antagonism of the α1----adrenoceptor-mediated vasoconstrictor response to norepinephrine in rabbit aorta, with KB values of 14 and 16 nM, respectively. Furthermore, in the pithed rat, the α1-adrenoceptor-mediated pressor dose-response curve to cirazoline was shifted approximately 6-fold to the right by both the (+)-R- and (-)-S-enantiomers of carvedilol at a dose of 1 mg/kg, i.v. In anesthetized spontaneously hypertensive rats, (-)-(S)-carvedilol was 6-fold more potent as an antihypertensive than (+)-(R)-carvedilol. The vasodilator and acute antihypertensive activity of carvedilol results from α1-andrenoceptor blockade produced by both enantiomers, and the concomitant β1-adrenoceptor blockade produced by the (-)-S-enantiomer, which prevents reflex tachycardia that can offset the antihypertensive response, leading to greater overall antihypertensive potency of (-)-(S)-carvedilol relative to the (+)-R-enantiomer. These data also suggest that distinct regions of the carvedilol molecule are responsible for blocking α1- and β1-adrenoceptors, with β1-adrenoceptor blockade resulting from an area of the molecule containing the asymmetric carbon atom, specifically the carbazolyloxy propanolamine moiety, and α1-adrenoceptor blockade resulting from a part of the molecule that does not contain the asymmetric carbon atom, most likely the phenoxyethylamine moiety.
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    Crystal structure and absolute configuration of (+)546-[copy4Cl2]HDBT: An example of torsional isomerism (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 284-292 
    Details
    ISSN: 0899-0042
    Keywords: absolute configuration ; crystal structure ; resolution ; solid-state circular dichroism ; torsional isomerism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure and absolute configuration of the (-)589-dibenzoylmonohydrogentartrate salt of the cation [Co(pyridine)4Cl2]+ have been determined from a three-dimensional X-ray analysis. Single crystals were grown from dimethylsulfoxide: space group P212121, Z = 4, and cell dimensions a = 21.463(4), b = 23.112(3), and c = 7.490(1) Å. Full-matrix least-squares refinement on F converged at R = 0.075, 196 variables and 2029 observations. The cation has pseudotetragonal coordinate geometry, with axial Cl and equatorial N atoms. The dihedral angles between the pyridine ligands and the equatorial plane are 47(1), 39(1), 50(1), and 45(1)° and torsional isomerism is responsible for the solid-state chiroptical properties of the cation. The preferential crystallization of the P atropisomer of the cation is attributed to a general electrostatic attraction between cation and anion.
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    Announcements (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 94-95 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010118
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    Response to letter to the editor (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 98-98 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chir.530010203
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    Determination of terbutaline enantiomers in biological samples using liquid chromatography with coupled columns (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 20-26 
    Details
    ISSN: 0899-0042
    Keywords: terutaline ; enantiomers ; determination ; liquid ; chromatography ; coupled columns ; cyclodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of this work was to develop and validate a method for the separation and determination of the enantiomers of terbutaline in plasma and intestinal juice. Terbutaline was extracted from plasma and intestinal juice by liquid-solid extraction on small C18 cartridges. The extract was then analyzed by coupled column liquid chromatography with amperometric detecton. For ciral separation a β-cyclodextrin phase was used.The within-day variation (Cv) on spiked plasma samples was in the rane 0.8-6.4% at 3.8-33.8 nmol/liter for the (-)-enantiomer, and 2.6-23.0% at 1.3-11.3 nmol/liter for the (+)-enantiomer. The between-day variation on spiked plasma samples was 5.5% at 10.7 nmol/liter and 13.6% at 4.3 nmol/liter for the (-)- and (+)-enantiomers, respectively. The within-day variation for inestinal juice was i the range 0.7-1.5% at 5.6-30.0 μmol/liter for the (+)-enantiomer.
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    Letter to the editor (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 97-97 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010202
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    Stereoselective sulfation of terbutaline by the rat liver cytosol: evaluation of experimental approaches (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 121-126 
    Details
    ISSN: 0899-0042
    Keywords: stereoselective metabolism ; sulfate conjugation ; in vitro sulfation ; sympathomimetic amines ; chiral separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Little is known about the stereochemistry of sulfation of chiral phenolic drugs. In this study we examined several in vitro approaches to this question, using (+)-, (-)-, or (±)-terbutaline as the substrate and the rat liver cytosol as the phenolsulfotransferase enzyme source. The cosubstrate PAPS was either generated by the cytosol from inorganic sulfate and ATP or added to the cytosol. The intact sulfate conjugates formed were determined by HPLC. Using the PAPS generating system, which is best suited for the production of relatively large quantities of sulfate conjugates, with the individual enantiomers as substrates, (+)-terbutaline was conjugated to a much greater extent than (-)-terbutaline; the (+)/(-)-enantiomer ratio was 7.3 ± 0.3 (mean ± SE). When (±)-terbutaline was the substrate and chiral derivatization was employed to separate the sulfate enantiomers formed, a similar (+)/(-)-enantiomer ratio of 7.9 ± 0.2 was obtained. With PAP35S added to the cytosol, an approach best suited for kinetic studies, the substrate concentration dependence of sulfation could be determined. The Km app for this reaction was identical for (+)- and (-)-terbutaline. However, the Vmax app was 8.1 ± 0.4 times greater for (+)-terbutaline. This study for the first time shows enantioselectivity in sulfation of a chiral phenolic drug. The experimental approaches used should be valuable for human studies of stereoselectiven sulfation of terbutaline and other chiral drugs.
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    Cytochrome P-450-catalyzed asymmetric epoxidation of simple prochiral and chiral aliphatic alkenes: species dependence and effect of enzyme induction on enantioselective oxirane formation (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 127-136 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective epoxidation ; cytochrome P-450-dependent monooxygenases ; species dependence of microsomal epoxidation ; product enantioselectivity ; substrate enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity of the in vitro conversion of simple prochiral and chiral aliphatic alkenes into oxiranes by liver microsomes of untreated or induced (phenobarbital) rats, of untreated or induced (phenobarbital, benzo[α] pyrene) mice, and of humans was determined by complexation gas chromatography. The enantiomeric excess (ee) of the epoxides extends from 0 (trimethyloxirane) to 50% (ethyloxirane). The configuration (R or S) of the enantiomers formed in excess is consistent for homologous oxiranes but is species dependent and in some cases influenced by enzyme induction. Enantioselectivity differences of aliphatic alkene epoxidation by human liver microsomes of four individuals are negligible.
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    Optical resolution of some biologically active compounds by chiral liquid chromatography on BSA-silica (resolvosil) columns (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 154-160 
    Details
    ISSN: 0899-0042
    Keywords: enantiomers ; chiral discrimination ; drugs ; hydrophobic interaction ; biopolymers ; elution order ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution on the analytical scale of a number of racemic pharmaceuticals and some other biologically active compounds has been studied using immobilized bovine serum albumin (BSA) as the stationary phase. For some of the compounds the elution order was determined by the use of optically enriched fractions obtained from a preceding passage of a sample through a preparative column containing microcrystalline triacetylcellulose (MCTA). The reversal in the sign of optical rotation shown in the polarimetric elution profile from the latter, combined with the integrated peak area ratio obtained on resolution on the analytical column, gave directly the order of elution. For one of the benzothiadiazines studied (bendroflumethiazide), increasing the pH of the mobile phase produced opposite effects on the retention of the two enantiomers, leading to a large effect on the separation factor. For many of the compounds studied, high separation factors (α 〉 2) could be achieved.
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    Direct separation of albendazole sulfoxide enantiomers by liquid chromatography on a chiral column deriving from (S)-N-(3,5-dinitrobenzoyl)tyrosine: application to enantiomeric assays on plasma samples (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 142-153 
    Details
    ISSN: 0899-0042
    Keywords: enantiomeric separations ; chiral stationary phase ; Pirkle-type phases ; HPLC ; anthelmintics ; benzimidazole sulfoxides ; albendazole ; fenbendazole ; oxfendazole ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct enantiomeric resolution of albendazole sulfoxide (SOABZ), an anthelmintic drug belonging to the benzimidazole class, is reported on a chiral stationary phase (CSP) synthesized by covalent binding of (S)-N-(3,5-dinitrobenzoyl)tyrosine-O-(2-propen-1-yl) methyl ester on a γ-mercaptopropylsilanized silica gel. A comparison with the resolution achieved on commercially available Pirkle-type CSPs obtained from N-(3,5-dinitrobenzoyl) derivatives of (R)-phenyglycine or (S)-phenylalanine is described. Some structurally related chiral sulfoxides including oxfendazole (SOFBZ) are also studied. Optimization of the mobile phase nature and composition is investigated showing that a hexane-dioxane-ethanol ternary mixture affords an almost baseline resolution (Rs = 1.25); however, in this case, albendazole sulfone (SO2ABZ) is eluted between the two sulfoxide enantiomers; accordingly, a hexane-ethanol mobile phase would be preferred for biological samples containing both metabolites. The influence of temperature on the resolution is depicted with a hexane-ethanol mobile phase. Finally, application to the enantiomeric assays of SOABZ in plasmatic extracts of rat, sheep, bovin, and man after oral administration of albendazole (sulfoxidized to SOABZ and SO2ABZ) is reported. Some distortions in the enantiomeric ratios are evidenced depending on the species.
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    A vivid model of chiral recognition (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 167-169 
    Details
    ISSN: 0899-0042
    Keywords: enantioselectivity ; three-point model ; chiral receptors ; chiral separations ; didactic model ; elusion of the three-point model ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hands can be used to demonstrate the three-point model of chiral recognition. The points of attachment are thumb, forefinger, and middle finger. This vivid model has the advantages of simplicity, perspicuity, and availability at any time, although two persons are necessary. It can be shown that two interactions are not sufficient for chiral recognition but that three attractive or two attractive and one repulsive attraction are needed. It can also be used to explain some possibilities of weakening or elusion of the three-point model.
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    Resolution of some β-hydroxyphenethylamines as N-(3,5-dinitrobenzoyl) amides on chiral stationary phases derived from cinchona alkaloids (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 161-166 
    Details
    ISSN: 0899-0042
    Keywords: chromatography ; chirality ; chiral recognition ; β-aminoalcohols ; stereochemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three chiral stationary phases, obtained by derivatizing γ-mercaptopropylsilanized silica gel with quinine, quinidine, and cinchonidine, have been employed in the resolution of N-acyl derivatives of β-hydroxyphenethylamines. The use of circular dichroism for detection and NMR analysis of analyte-selector mixtures provides an experimental basis for preliminary assignment of a recognition mechanism.
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    Announcements (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 178-179 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chir.530010215
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    First announcement and call for papers (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 246-248 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chir.530010312
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    Direct chromatographic separation of 2-arylpropionic acid enantiomers using tris(3,5-dimethylphenylcarbamate)s of cellulose and amylose as chiral stationary phases (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 239-242 
    Details
    ISSN: 0899-0042
    Keywords: optical resolution ; HPLC ; chromatography ; antiinflammatory drug ; ibuprofen ; ketoprofen ; flurbiprofen ; tiaprofenic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct optical resolution of antiinflammatory drugs such as ibuprofen, ketoprofen, flurbiprofen, and tiaprofenic acid were attempted by high-performance liquid chromatography using tris(3,5-dimethylphenylcarbamate)s of cellulose and amylose as chiral stationary phases. Although ibuprofen was not sufficiently resolved, the other three 2-arylpropionic acids were completely resolved by amylose tris(3,5-dimethylphenylcarbamate). Ibuprofen was resolved as anilide derivative.
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    Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl series: Synthesis of (6,6′-dimethylbiphenyl-2,2′-diyl)bis(diphenylphosphine) (‘BIPHEMP’) and analogues, and their use in Rh(I)-catalyzed asymmetric isomerizations of N,N-diethylnerylamine (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 897-929 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The axially dissymmetric diphosphines (-)-(R)- and (+)-(S)-(6-6′-dimethylbiphenyl-2,2′-diyl)bis(diphenyl-phosphine) ((-)-(R)-10 and (+)-(S)-10; ‘BIPHEMP’) have been synthesized, starting from (R)- and (S)-6,6′-dimethylbiphenyl-2,2′-diamine ((R)- and(S)-16), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′- dimethyl- and 4,4′-bis(dimethylamino)-substituted analogues 11 and 12 respectively, and the 6,6′-bridged analogues 1,11-bis(diphenylphosphino)-5,7-dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)- and(S)-enantiomers via complexation with di-μ-chlorob is {(R)-2-[1-(dimethylamino)ethyl]pheny-C—N}dipalladium(II) ((R)-18). The molecular structures of the diphosphines (S)-10 and (R)-13 and of two derived cationic Rh(I) complexes,[Rh((S)- 10)(nbd)]BF4 and [Rh((R)- 13)(nbd)]BF4 were determined by x-ray analyses. Absolute configurations were established for (+)-(S)- 10 by X-ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (-)-(R)- 13 by X-ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 11 12 were achieved by means of 1H-NMR comparisons. The BIPHEMP ligand 10 and analogues 11, 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry-inducing ligands in Rh(I)-catalyzed isomerizations of N,N-diethylnerylamine affording citronellat enamine of 98-99% ee.
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    Isolation from the Mediterranean Stolonifern Coral Sarcodictyon roseum of Sarcodictyin C, D, E, and F, novel diterpenodic alcohols esterified by (E)- or (Z)-N(1)-methylurocanic acid. Failure of the carbon-skeleton type as a classification criterionPresented by F. P. as a part of a lecture at the University of Hawaii at Manoa, Honolulu, December 9th, 1987. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 964-976 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown here that the stoloniferan coral Sarcodictyon roseum of east Pyrenean waters contains four novel diterpenoids, sarcodictyin C ((-)-3), D ((-)-4), E ((+)-5), F ((+)-6), which are related to sarcodictyin A ( = (-)-(4R,4aR,7R,10S,11S,12aR,1Z,5E,8Z-7,10-epoxy-3,4,4a,7,10,11,12,12a-octahydro-7-hydroxy-6-(methyoxycarbonyl)-1,10-dimethyl-4-(1-methylethyl)-benzocyclodecen-11-yl (E)-N1-methylyrocanate; ((-)-1), previously isolated from the same coral. Sarcodictyin C ((-)-3) and D ((-)-4) and the 3α-hydroxy and 3α-acetoxy derivatives of (-)-1), sarcodictyin E ((+)-5) is the (Z)-urocanate isomer of (-)-3), and sarcodictyin F ((+)-6) is the 1α-hydroxy-2-ene isomer of (-)-3. In all cases, the nine-membered ring is locked, and the molecule stabilized, by the urocanic appendage; when this is removed in MeOH/KOH, the C(11)-O- function is free to attack at C(5), and retro-condensations then lead to the ring-contracted butenolides 11 (from (-)-3) or 10 (from(-)-1) with extrusion of the hydroxyfuran nucleus (Scheme 3). Under the same conditions, with (-)-3, the C(3)-O- group competitively attacks at C(5), the hydroxyfuran nucleus is expelled, and aldehyde 14 is formed. Peculiarly, in the reaction of (-)-3 with MeOD/KOD, the ring-contracted butenolide 17 contains D at the 4′-ax position. The sarcodictyins are unique in these chemical properties, not shared by the cladiellanes which have the same C-skeleton.
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    EPC synthesesFor definition and discussion of the term, see [1]. from bicyclic dixoanones; (-)-5-epidehydrofukinone (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 977-980 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (-)-5-Epidehydrofukinone ((-)-15) has been synthesized from (2S,4aS,5S,8aS)-4a,5-dimethyl-2-(tert-butyl)-perhydro-4H-1,3-benzodioxan-4-one (4a), a counpound readily available by yeast reduction of ethyl 2-oxocyclohexanecarboxylate.
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    A Vibrational Study of Some 1,2,4-Trioxanes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 992-999 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vibrational spectra of some 1,2,4-trioxanes present two characteristic bands at 790 and 880 cm-1. On the basis of 18O-isotopic substitution and comparison with analogous compounds, these bands have been assigned to coupled C—O and O—O stretching modes of the C—O—O element.
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    NorbornanesThe IUPAC name for norbornane: 8,9,10-trinorbornane.. Part 21. Bridging strain in norbornyl and oxanorbornyl cations (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1017-1024 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Further evidence is presented that the 2-norbornyl cation is stabilized primarily by C(2)-C(6) bridging, and that C(2)-C(7) bridging leads to prohibitive strain. Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicyclo[3. 2. 0. 0.2,7]heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher that that of 17. Furthermore, 6-exo-2-oxabicyclo[2. 2. 1]heptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12. In contrast, 2-endo-7-oxabicyclo[2.2.1]heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15.
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    Preparation of 3-Oxo- and 3-Ethylideneazetidine DerivativesThis work is part of the Ph. D. thesis of H. B. [1] (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1035-1041 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of 3-azetidinones with different N-substituents and their transformation to 3-ethylideneazetidines has been studied in relation with a projected synthesis of 3-ethylideneazetidine-2-carboxylic acid (= polyoximic acid; 1). The stable crystalline 3-azetidinone hydrochloride (18), obtained by hydrogenolysis of the known 1-(diphenylmethyl)-3-azetidenone (4), is described for the first time, From this key intermediate, 3-oxoazetidine-derived amides, exemplified by benzamide 12,urethanes (e.g. 17), and ureas (e.g. 20) can be prepared in good yield (Scheme 3). The olefination of 3-azetidinones with alkylidene(triphenyl)phosphoranes is a perparatively useful process only for derivatives with a pyramidal N-atom, e.g. the diphenylmethyl derivative 4, and not for the amide 12 or the urethane 17 (Scheme 4). 3-Alkylidene-azetidines with an amide N-atom should, therefore, be prepared by exchange of the N-substituent after the introduction of the double bond.
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    The Radical Cation of Cyclobutene and its Photoproduct. Preliminary communication (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1069-1072 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hitherto unknown radical cation of cyclobutene (2) has been generated in a CFCl3 matrix by γ rays at 77 K. The coupling constants, as determined from the ESR spectrum of 2+, are 2.80 and 1.11 mT for the four CH2 and the two CH = protons, respectively. Photo-induced ring opening of 2+ yields a radical cation which exhibits the same ESR and ENDOR spectra as those observed upon direct ionization of s-trans-buta-1, 3-diene (s-trans-1). The radical cation s-trans-1+, should, therefore, be the final product of this conversion.
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  • 45
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    Dreifach-Diamantstruktur von. 2,6-Dioxoadamantan-1,3,5,7-tetracarbonsäure (Hydrat) als Wirtsgitter für Essigsäure (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1084-1093 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Triple-Diamond Structure of 2,6-Dioxoadamantane-1,3,5,7-tetracarboxylic Acid (Hydrate) as Host Lattice for Acetic AcidA novel solid-state channel-inclusion compound characterized by X-ray methods is based on three interpenetrating, translationally equivalent super-diamond network as host structure and AcOH as guest. The diamondoid host network are fromed by the 2,6-dioxoadamantane-1,3,5,7-tetracarboxylic acid tied together via pairwise H-bonds. The channels embedding the AcOH molecules may be viewed as symmetric triple helices winding about the guest species. Prospects regarding design and potentialities of diamondoid inclusion compounds are exemplified and appear promising.
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  • 46
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    Ruthenium(II) Complexes with Three Different Diimine Ligands (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1108-1115 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of tri-heteroleptic complex of Ru(II) with diimine ligands is describe. Ten compounds [Ru(R2bpy) (biq) (L)][PF6]2 (R = H, CH3); L = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), 2,2′-bipyrimidine (bpm), 2,2′-biisoquinoline (biiq), 1,10-phenanthroline (phen), dipyrido[3,2-c:2′,3′-e]pyridazine (taphen), 2,2′-biquinoline (biq), 6,7-dihydrodipyrido[2,3-b:3,2-j][1,10]-phenanthroline (dinapy), 2-(2[pyridyl)quinoline (pq), 1-(2-pyrimidyl)pyrazole] (pzpm), 2,2′-biimidazole (H2biim) are characterized by elemental analysis, electronic and 1H-NMR spectroscopy. The relative photosustitution rates of biq in MeCN are given at three temperatures.
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  • 47
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    Design and Synthesis of 5-Lipoxygenase Inhibitors (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1156-1176 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on the substrate specificity for 5-lipoxygenase and the known stereochemical course of the reaction, a hypothetical model of the enzyme active site was developed and used to design 2 types of selective inhibitors of 5-lipoxygenase. Both inhibitor types used aromatic rings in place of (Z)-olefins of the substrate and were designed to mimic the nonpolar end of arachidonic acid. One inhibitor type used a carboxylic-acid interaction with the O-binding centre of the enzyme in analogy with known cyclooxygenase inhibitors, whereas a second type employed a hydroxylamine function to interact with a presumed tyrosine or cysteinyl radical predicted to be in the enzyme active site. Selective 5-lipoxygenase inhibitors were 7-(hexyloxy) naphthalene-2-acetic acid (1) and N-methyl;-N(7-propoxynaphthalene-2-ethyl)hydroxylamine (2). Structure-activity relationships for both types of inhibitors are discussed.
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  • 48
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    Colchicine Models: Synthesis and Binding to Tubulin of Tertamethoxybiphenyls (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1199-1209 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheis of tetramethoxybiphenyl 21 was accomplished from 4-phenylcylohexane-1,3-dione 13 by aromatization to biphenyl 19 and reductive removal of the phenolic OH group as phenyltetrazolyl ether. Tertramethoxybiphenyls 34 and 40 were obtained from 4-phenylcyclohexenone 26 via ester 27. The tetramethoxybiphenyls 21, 34, and 40, and analogs 28, 29, and 31 were evaluated for antitubulin activity and as antimitotic agents with L1210 murine leukemia cells. Compounds 31 and 34 had significant effects on the in-vitro polymerization of tubulin. Compound 31 was the most cytotoxic of the six new biphenyls studied (IC50 for cell growth, 0.6M) and caused the accumulation of cells in metaphase arrest.
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  • 49
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    Antifungal Polyphenols from Cordia goetzeiGürke (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1210-1219 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four highly oxygenated polyphenols 1-4, have been isolated from the stem bark of Cordia goetzei Gürke (Boraginaceae) and their structures elucidated by a combination of one- and two-dimensional (including COLOC) NMR spectroscopic techniques, mass spectroscopy, and chemical methods. The first new compound, cordigone (1), is a tetrahydrofuran derivative and the second one, cordigol (2), a furobenzopyran derivative. The benzofurans 3 and 4 are orange pigments, responsible for the coloration of the stem bark of the tree. All four polyphenols are fungicidal against cladosporium cucumerinum.
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  • 50
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    Die röntgenstrukturanalysen von (E)- und (Z)-2-Buten-1,4-diyl-dithiocyanat bei 93 K (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1235-1241 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-Ray Diffraction Analysis of (E)- and (Z)-2-Butene-1,4-diyl DithiocyanateThe crystal structure of the (E)- and (Z)-2-butene-1,4-diyl dithiocyanate (1 and 2, respectively) which have been used as substrates for an E′ reaction, has been determined by X-ray analysis. The SCN groups are for both molecules in an anticlinal conformation relative to the double bond. A remarkable intermoecular contact has been observed between the N-atom of one molecule and the S-atom of its neighbour.
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    Tandem Diels-Alder Reactivity Controlled by Remote Substituents. Regioselective synthesis of linearly annellated six-membered ring systems from (1RS,5SR,6RS,7SR)-6,7-bis(chloromethyl)-8,9-dimethylidene-2-oxabicyclo[3.2.2]nonan-3-one. Crystal structure of (1RS,5RS,6SR,11RS)-6,7-bis(chloromethyl)-3-oxo-2-oxatricyclo[7.4.0.1,5]tridec-8-en-11-yl methyl ketoneFor a preliminary communication, see [1].Part of the planned Ph. D. thesis of Bernard Demarchi, University of Lausanne. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1249-1267 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthess of 6,7,8,9-tetramethylidene-2-oxabicyclo[3.2.2]nonan-3-one (12), 6,7,8,9-tetramethylidene-2-azatricyclo[3.2.2]nonan-3-one (13), and (1RS,5SR,6RS,7SR)-6,7-bis(chloromethyl)-8,9-dimethylidene-2-oxabicyclo-[3.2.2]nonan-3-one (14) are presented. The rate constants of the two successive Diels-Alder additions of a given dienophile to 12 and 13 were nearly the same. Lewis-acid-catalyzed Diels-Alder addition of methyl vinyl ketone to 14 gave adduct 39 with high regio- and stereoselectivity. Lewis acids isomerized 39 into(1RS,5RS,6SR,7SR,11RS)-6,7-bis(chloromethyl)-3-oxo-2-oxatricyclo[7.4.0.01,5]tridec-8-en-11-yl methyl ketone (40) whose structure was determined by single-crystal X-ray crystallography. Heating 39 with CsF/Cs2CO3 in DMF/HMPT gave (1RS,5RS,11RS)-6,7-dimethylidene-3-oxo-2-oxatricycl. [7.4.0.01,5]tridec-8-en-11-yl methyl ketone (42). The exocyclic butadiene moiety of triene 42 added to methyl propynoate and 2,3-didehydroanisole with good regioselectivity giving polysubstituted anthracenyl and naphthacenyl derivatives, respectively.
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    Conformational Flexibility of the Acetoxyphenyl Group Studied by Statistical Analysis of Crystal Structure Data (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1281-1290 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformation of the acetoxyphenyl fragment shows a planar acctoxy (AcO) group perpendicular to the Ph ring. Steric hindrance strongly limits and affects rotation about the C—OCOCH3 bond: if the AcO group twists away from its perpendicular conformation, the carbonyl oxygen moves to keep the nonbonded distance to the atoms in ortho-position maximal. This is achieved by some twisting about the O—COCH3 bond correlated with angle bending at the ipso-C-atom and ester O-atom. The maximum observed deviation away from the perpendicular conformation is ∼ 47°. In the case of one or two ortho-hydrogens, deviations of the AcO group from the perpendicular conformation tend to be larger than in the case of two substituents.
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    Präparative chromatographische Enantiomerentrennung von synthetisch nützlichen cyclischen AcetalenTeil der Doktorarbeiten von St. M. (Dissertation Nr. 8616, ETH Zürich, 1988), J. Z. (Dissertation Nr. 8518, ETH Zürich, 1988) und der geplanten Dissertation von U. G. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1303-1318 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparative Chromatographic Resolution of Synthetically Useful Cyclic AcetalsRacemic cyclic acetals derived from aldehydes and glycine, glycolic acid, thioglycolic acid, formylacetic acid, and acetoacetic acid (oxazolidinones 4-13, dioxolanones 14, 15, oxathiolanone 16, dioxinones 17-23) are resolved by preparative high-pressure liquid chromatography on silica gel coated with the polymer from N-acryloylphenylalanine ethyl ester (Chiraspher®). The separation factors α range from1,1 to 2,4. Use of a Prepbar®-chromatography system allows injection of several grams at a time. The enantiomeric acetals thus obtained are fully characterized. First application to amino-acid synthesis are mentioned.
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    The Reaction of 3-(Dimethylamino)-2H-azirines with 2,3-Pyridinedicarboximide (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1319-1327 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2,2-dialkyl-3-(dimethylamino)-2H-azirines 1a and 1b with 2,3-pyridinedicarboximide (4) in MeCN or DMF at room temperature yielded two regioisomeric tricyclic 1:1 adducts, the azacyclols 11/12 and 16/17, respectively (Schemes 3 and 4). The structure of 12 was established by X-ray crystallography. Methanolysis of 11/12 and 16/17 led to mixtures of methyl [4, 4-dialkyl-5-(dimethylamino)-4H-imidazol-2-yl] pyridine carboxylates 13/14 and 18/19, respectively. The structure of compound 14 is closely related to that of the powerful herbicide 9 (Scheme 9), i.e. the described reactions offer a new synthetic approach to this class of compounds. A mechanistic interpretation for the formation of regioisomeric 1:1 adducts as well as methyl (imidazol-2-yl) pyridine carboxylates is depicted in Scheme 5.
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    Stereoselectivity in Reactions of Metal Complexes. Part XPart IX: [1]. Kinetics and stereoselectivity of the inner-sphere electron-transfer reaction between [Co(bamap)H2O]+ (bamap = 2,6-bis(3-carboxy-1,2-dimethyl-2-azapropyl)pyridine) and optically active iron(II) complexes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1339-1348 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the electron-transfer reaction between racemic or optically active [Co(bamap)H2O]+ and optically active Fe2+ complexes of the three new pentadentate ligands bamap, alamp, and valmp has been investigated. All the reacting species show C2 symmetry. With respect to aquo-Fe2+, the reaction rate for the Fe2+ complexes is enhanced by a factor of 104 to 105, and the observed kΔΛ/kΛΛ ratio is 1.0, 1,9, and 1.2, respectively. In all cases where stereoselectivity is observed, the reaction is faster between the complexes of opposite absolute configuration (ΔΛ or ΛΔ) than between species with the same configuration (ΛΛ or ΔΔ). The stereoselectivity effects are discussed of the basis of the structure of the transition state and the interatomic distances between the two metal centers at the moment of electron transfer.
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    Mitteilungen (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1379-1381 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    The Reaction of Water with Iron- and Rutheniuncarbonyl Complexes of Polyolefins: 1,2- and 1,4-hydrogenation of 1,3-dienes. hydrogenolysis of allylic ethereal bonds and deoxygenation of 7-oxabicyclo[2.2.1]hept-2-enes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1354-1366 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Under basic conditions, H2O reacts with tricarbonyl[(1R,2R,3S,4S,5R,6S)-C,5,6,C-η-(2-exo,3-exo-bis-(chloromethyl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]heptane)]iron) (1), and -ruthenium (4), with tricarbonyl-[(1R,2R,3S,4S)-C,2,3,C-η-(2,3,5,6-teramethylidene)-7-oxabicyclo[2.2.1]heptane)]iron (6) and -ruthenium (7), and with cis-η-[1S,2S,3R,4S,5S,6R)-C,2,3,C-η : C-η-(2,3,5,6-tetramethylidene-7-oxabicyclo)[2.2.1]heptane)bis-(tricarbonyliron) (11)] to give products of demetallation and 1,2- or/and 1,4-hydrogenation. Reductive demetallation of tricarbonyl[C,5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidenecylohexa-1,3-diene]iron (14) required heating under acidic conditions, giving 2,3-dimethylbenzaldehyde (16). H2O reacted under neutral conditions with cis-heptacarbonyl-μ-[(1RS,2SR,3RS,4SR,5RS,6SR)-2,3-η : C,5,6,C-η-(1-(dimethyoxymethyl)-5,6,-(dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene]diiron (17) and with tricaboyl[(1RS,2SR,3RS,4SR,5RS,6SR)-C-η5,6,C-η-(1-(dimethyoxymethyl)-5,6-dimethyldidene-7-oxabicyclo[2.2.1]hept-2-ene)]iron (18) to give the orthoquinodimethane complex 14 as major product. This reaction was accompanied by hydrogenolysis of the allylic ethereal C(4)—O(7) bond in 17 and 18 and gave tricarbonyl[(1RS,5RS,6SR)-C,5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidenecylohex-2-en-1-ol)]iron (21) as minor product. The latter was not an intermediated of reaction 17 → 14. Reactions with D2O allowed one to discuss the possible mechanism of this deoxygenation process. With Trans-heptacarbonyl-μ-[(1RS,2SR,3RS,4SR,5RS,6SR)-2,3-η : C,5,6,C-η-(1-(dimethoxymethyl-5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene)diiron (38)], the reaction with THF/H2O gave 14 nearly quantitatively, with no D-incorporation in the presence of D2O.
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    Pteridines. Part LXXXVIIPart LXXXVI [1].. Synthesis and Properties of 8-Substituted 2-Thiolumazines (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1379-1391 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various 8-substituted 2,8-dihydro-2-thioxopteridin-4(3H)-ones (14-21) and 2-(methylthio)pteridin-4(8H)-ones (27-32) have been synthesized by condensation of the appropriate 5-amino-6-(substituted amino)-1,2-dihydro-2-thioxopyrimidin-4(3H)-ones (22-34) and 5-amino-6-(substituted amino)-2-(methylthio)pyrimidin-4(3H)-ones (25, 26), respectively, with glyoxal, biacetyl, and benzil. The presence of a quinonoid cross-conjugated π-electron system makes this type of compounds susceptible to nucleophilic additions in position 7, which leads to intramolecular (43, 45) and intermolecular (44) covalent adducts. The newly synthesized compounds have been characterized by elemental analyses, pKa determinations, 1H-NMR and UV spectra. UV-Spectral changes in dependence of the pH are associated with the most appropriate molecular species including the monocations, neutral forms, covalent adducts, mono- and dianions.
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    Synthesis of (+)-1,3:2,5-dianhydroviburnitol ((+)-(1R,2R,3S,5R,6S)-4,7-dioxatricyclo[3.2.1.03,6]octan-2-ol) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1399-1405 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epoxidation of (-)-(1R,2R,4R)-2-endo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl acetate ((-)-5) followed by saponification afforded (+)-(1R,4R,5R,6R)-5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ((+)-7). Reduction of (+)-7 with diisobutylaluminium hydride (DIBAH) gave (+)-1,3:2,5-dianhydroviburnitol ( = (+)-(1R,2R,3S,4R,6S)-4,7-dioxatricyclo[3.2.1.03,6]octan-2-ol; (+)-3). Hydride reductions of (±)-7 were less exo-face selective than reductions of bicyclo[2.2.1]heptan-2-one and its derivatives with NaBH4, AlH3, and LiAlH4 probably because of smaller steric hindrance to endo-face hydride attack when C(5) and C(6) of the bicyclo-[2.2.1]heptan-2-one are part of an exo oxirane ring.
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    The solution structure and reactivity of decavanadate (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1406-1420 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxygen-exchange reaction of V10O286- with bulk water has been followed by time-dependent 17O-NMR spectroscopy (buffered solutions, pH ∼ 5.5, [V10]total ∼ 0.17m, T = 298 K). It is shown that all seven structurally different sites of O-atoms are kinetically similar but, in contrast to earlier studies, not identical (6 h ≤ ‘t1/2’ ≤ 11 h). The kinetic similarity of the various structural sites implies the some (but not full) O scrambling is involved. Two possible mechanisms with a ‘half-bonded’ and an ‘open’ intermediate are discussed in detail to interpret the experimental results. A computer simulation of the exchange reaction based on these models is presented. It is shown that the ‘half-bonded-intermediate’ mechanism is consistent with the experimental data and the following parameters are calculated: formation of the intermediate: k1 = 5.8 · 10-3 s-1, k-1 = 6.7 · 10-2 s-1, [intermediate]∞ ≈ 8%; all activated O-atoms exchange within the lifetime of the intermediate (τ ∼ 15 s), and the calculated exchange rate of the intermediate (k2 ≥ 0.60 s-1) is consistent with earlier assumptions (k2 ≈ 0.5 s-1). It is shown that a simulation based on the ‘open-intermediate’ mechanism results in kinetic parameters which are not consistent with the kinetics of the formation of cyclic metavanadates ((VO3-)n, n = 4,5) from decavanadate, since the required formation rate is by a factor ∼ 102 too fast, and the equilibrium concentration of metavanadates is by a factor of ∼ 2 too large (under the conditions of the O-exchange experiments of decavanadate (T = 298 K, [V10]total ≈ 0.17m, pH ∼ 5.55) the total amount of metavanadates present is ∼ 8%, with [(VO3-)4]/[(VO3-)5] ∼ 4:1; a qualitative analysis of the kinetics of the formation of metavanadates (vo kinetics; the exact mechanism of the back-reaction (at least second-order) is not known with certainty) leads to k1 ≥ 4·10-5 s-1). O exchange of decavanadates via equilibrated metavanadates would lead to full scrambling of the O sites and is not consistent with the observed differences in the exchange rates. From the qualitative kinetic parameters of the metavanadate formation kinetics, it can be concluded that any contribution of an ‘open’ or an ‘metavanadate’ mechanism is of the order of 1-2% at most.
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    Synthesis and Steroidogenic Activity of Covalently Dimerized Corticotropin (ACTH) FragmentsAbbreviations for amino acids and derivatives follow the recommendations of the IUPAC-IUB Joint Commission on Biochemical Nomenclature [1]. Further abbreviations: DMF = N, N′-dimethylformamide, DCCI = N, N′ -dicyclohexylcarbodiimide, SDS = sodium dodecyl sulfate, FPLC = fast protein liquid chromatography. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1421-1428 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical synthesis by classical methods in solution of a dimer of the sequence 1 to 24 of adrenocorticotropin(ACTH) is described. The two monomers were covalently linked through their C-termini, using lysine amide as spacer. Dimerization did not improve significantly the potency of the agonist ACTH-(1-24), while it strongly potentiated the antagonistic effect of the fragments ACTH-(11-24) and ACTH-(7-24) in the stimulation of steroidogenesis in isolated adrenal cells. The results seem to imply a microaggregation of the receptors at the adrenal cell surface.
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    Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. Part XVIIPart XVI: see [1].. Some platinum(II) complexes with anionic ligands such as methoxide, formate, carboxylate, hydride, and borohydride, and the X-ray crystal structure of [PtHCl()] (PP = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1442-1457 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes trans-[PtXY(2] (X = H or Me; Y = OMe, OCHO, CO2H, and BH4; 2 = 2,11-bis{bis[3-(trifluoromethyl)phenyl]phosphinomethyl}benzo[c]phenanthrene) were prepared, and their decompositions to trans[PtHX(2)] were studied. Some binuclear hydrido-bridged complexes, e.g.[(2)HPt(μ-H)PtH(2)]+, were also obtained. The preparation of complexes trans-[PtHX(28)2] (X = H or Me, 28 = bis[3-(trifluoromethyl)phenyl]benzylphosphine) is also reported. The X-ray crystal structure of trans-[PtHCl1)] (1 = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene) was carried out.
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    Intramolecular Dynamics of Five-coordinate iron Carbonyl Complexes with olefinic ligands as studied by variable-pressure 1H-NMR spectroscopy (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1458-1466 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variable-pressure 1H-NMR Spectroscopy has been used to study the fluxionality of some five-coordinated Fe complexes in solution. For [Fe(CO)2 1,3-cyclooctadiene (PPh3)], the CO site exchange is known (by analogy with [Fe(CO)3(1,3-cyclooctadiene)]) to be a non-dissociative process, and an activation volume of ca. 0 cm3.mol-1 was indeed obtained. However, for [Fe(CO2){2,3-η:O-σ-(7,7-dimethoxybicyclo[2.2.1]hept-2-ene)}(PPh3)], the activation volume of +5 cm3 mol-1 suggests that an unprecedented dissociation process is responsible for the CO site exchange. The molecular structure of [Fe(CO)2(1,3-cyclooctadiene)(PPh3)] was ascertained by single-crystal X-ray diffractometry. The crystals are triclinic, space group P1, a = 9.606(3), b = 16.795(2), c = 7.743(8) Å, α = 97.83(4), β = 109.63(4), γ = 83.37(2)°. The structure determination has shown that the complex possesses a tetragonal pyramidal coordination, with the endocyclic C=C bond and PPh3 occupying basal sites.
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    Lavandulifolioside: A New Phenylpropanoid Glycoside from Stachys lavandulifolia (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1483-1490 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new phenlypropanoid glycoside has been isolated from the methanolic extract of the aerial parts of Stachys lavandulifolia (Lamiaceae), lavandulifolioside (1). On the basis of chemical and spectral data the structure of the new compound 1 has been elucidated as β-(3,4-dihydroxyphenyl)ethyl O-α-L-arabinopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→3)-4-O-caffeoyl-β-D-glucopyranoside.
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    Polar Effects. Part 15. Twin γ-substituent effects in the formation of adamantyl-1-cations (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1502-1507 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvolysis rates of several adamant-1-yl ( = tricyclo[3.3.1.13,7]dec-1-yl) p-toluenesulfonates and bromides 2 identically substituted at C(3) and C(5) (twin substitution) have been determined and compared with the rates of the corresponding 3-monosubstituted compounds 1. As expected, the rate factors for twin substitution are much larger, but less than the square of the rate factors for single substitution. Also the rates factors per substitutent in 2 are considerably smaller than those for one substituent in 1. This attenuation is attributed to electron repulsion which limits the convergence of electron density to the cationic center. On the other hand, the inductivity for twin substitution (ρ1 = -2.55) is ca. twice as high as for mono-substitution (ρ1 = -1.26).
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    The mild bromination of adamantane and (trimethylsilyl) adamantanes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1508-1510 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Small amounts of H2O or MeOH catalyze the reaction of Br2 with adamantane and its 1-(trimethylsilyl) and 1,3-bis(trimethylsilyl) derivatives.
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    Efficient Synthesis of 1,2-Bis(2,2′-bipyridinyl)ethane and 1,2-bis(1,10-phenanthrolinyl)ethane ligands by oxidative coupling of the corresponding monomeric methylene carbanions (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1511-1516 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several dimeric 1,2-bis (2,2′-bipyridinyl)ethane (1,2,6,7, and 9 and 1,2-bis(1,10-phenanthrolinyl)) ethane (3,4, and 5) ligands have been synthesized in high yield by oxidative coupling of the corresponding monomeric methylene carbanions using as oxidating agents Br2, I2, and 1,2-dibromoethane. The structure of the compounds obtained from three tetramethyl-2,2′-bipyridines and one tetramethyl-1,10-phenanthroline have been assigned on the basis of their 1H-NMR spectra. The electronic absorption and emission properties of these new ligands are reported. They display intense fluorescence spectra.
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    Stoffwechselprodukte von Mikroorganismen. 250. Mitteilung249. Mitteilung: [1].. Maduraferrin, ein neuartiger Siderophor aus Actinomadura madurae (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1528-1540 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Maduraferrin, a Novel Siderophore from Actinomadura maduraeFrom a strain of Actinomadura madurae, a new siderophore was isolated. Maduraferrin is the Fe complex of an oligopeptide composed of salicylic acid, β-alanine, glycine, L-serine, Nδ-hydroxy-Nα-methyl-L-ornithine, and L-hexahydropyridazine-3-carboxylic acid. The complexing centers are a salicylamide moiety, a hydroxamic-acid group and an acid hydrazide group.
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    Semicorrin Metal Complexes as Enantioselective Catalysts. Part 1. Synthesis of chiral semicorrin ligands and general conceptsTaken in part from the Ph.d. thesis of H. F., ETH-Zürich (in preparation); for a preliminary communication, see [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1541-1552 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient synthesis of chiral semicorrin ligands is described (see 6-9, Schemes 2 and 3). Both enantiomers are readily obtained in enantiomerically pure form starting either from D-or L-pyroglutamic acid (1). Semicorrins of this type possess several features that make them attractive ligands for enantioselective control of metal-catalyzed reactions. Their structure is characterized by C2 symmetry, a conformationally rigid ligand system, and two stereogenic centers adjacent to the coordination sphere. In a metal complex, the two substituents at the stereogenic centers shield the metal atom from two opposite directions and, therefore, are expected to have a pronounced effect on the stereochemical course of a reaction occurring in the coordination sphere. The structure of these two substituents can be easily modified in a variety of ways. A series of (semicorrinato)copper(II) complexes (see 10-14, Scheme 4) has been prepared, and in one case (14), the three-dimensional structure has been determined by X-ray analysis (Fig. 1).
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    Synthesis and Characterization of DNA Fragments Bearing an Adenine Radiation Product: 7,8-Dihydroadenin-8-one (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1566-1572 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 7,8-dihydroadenin-8-one is one of the base derivatives formed by the action of ionizing radiation upon DNA. In order in investigate the mutagenic effects and the repair of DNA lesions induced by gamma rays, the synthesis of oligonucleotides bearing this damage has been performed by the phosphoramidite methodology. The preparation of the corresponding protected mononucleotide 6 (see Scheme) and its insertion into a DNA fragment are described. The modified oligonucleotide was purified by HPLC, characterized by DNA sequencing, enzymatic hydrolysis, and FAB mass spectrometry. In the experimental conditions used herein, no basic or acidic degradation was observed. In the DNA chain, the lesion is stable on piperidine heating under the usual DNA sequencing conditions.
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    β-Cleavage of Bis(homoallylic) Potassium Alkoxides. Synthesis of γ-damascone (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1587-1597 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the γ-lactone cis-1, two new syntheses of γ-damascone ((E)-4) are described. In both syntheses, the key step involves the β-cleavage of a bis(homoallylic) potassium alkoxide, viz. the transformation of 3a to 20 and (E/Z)-4, and the conversion of 21a to 23 and (E/Z)-24.
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    Synthesis, Structure Elucidation, and Pharmacological Evaluation of 5-Methyl-oxymorphone (= 4,5α-epoxy-3,14-dihydroxy-5,17-dimethylmorphinan-6-one) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1801-1804 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 5-methyl-oxymorphone (3) was accomplished by oxidation of 5-methylthebaine (4) with performic acid, followed by catalytic hydrogenation and cleavage of the 3-MeO group. X-Ray analysis confirmed that the 14-OH group has, like the one in oxymorphone (1), β-orientation. Pharmacological studies in vivo and in vitro showed 3 to possess slightly less opioid agonistic properties than 1.
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    Synthese des Flechtenmakrolids (+)-Aspicilin mit Photolactonisierung als SchlüsselreaktionAus den Dissertationen oder Diplomarbeiten von N. H. [1], J. G. [2], U. D. [3], M. E. [4], U.-M. B. [5].Die Essenz dieser Mitteilung ist in Zuschriften [6] sowie in Vortragsreferaten [7] enthalten.In dieser Mitteilung werden folgende Abkürzungen verwendet: BHT: 2,6-Di(tert-butyl)-4-methylphenol, DABCO: 1,4-Diazabicyclo[2.2.2]octan, DBU: 1,8-Diazabicyclo[5.4.0]undec-7-en, DHP: 3,4-Dihydro-2H- pyran, DIBAH: Diisobutylaluminium-hydrid, DMAP: 4-(Dimethylamino)pyridin, MAD: Methylaluminiumbis[2,6-di(tert-butyl)-4-methylphenoxid], MCPBA; m-Chlorperbenzoesäure, MOM: Methoxymethyl, MTPA: α-Methoxy-α-(trifluoromethyl)phenylessigsäure, NBS: N-Bromsuccinimid, NMI: N-Methylimidazol, NOE: ‘nuclear Overhauser enhancement’, PPTS: Pyridinium-p-toluolsulfonat, THP: Tetrahydropyranyl, TMEDA: N,N,N′,N′,-Tetramethylethylendiamin.Sir Derek Barton zum 70. Geburtstag gewidmet (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1719-1794 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of the Lichen Macrolide (+)-Aspicilin Using Photolactonization as a Key Reaction(+)-Aspicilin, obtained from a lichen source of the Black Forest, has been proven to have the absolute configuration depicted by formula la. It is easily built up from phenol (14a), 1,9-nonanediol (13a), and (-)-(S-) methyloxiarane (6) (cf. Scheme 2). The latter building block provides the first stereogenic center C(17). The heterocycle is produced by photolactonization, fairly early during the course of the synthesis. The second stereogenic center is generated diastereoselectively at C(6) in compound 8, conveniently available from photolactone 9a or 9b/9c. Its absolute configuration depends on the kind of reducing agent and is controlled by long-range conformational transmission of chiral information. To explore the cause of stereoselection, 2D-NMR spectroscopy, X-ray structural analysis, and/or computer-aided conformational search followed by energy minimization have been used extensively, revealing the importance of the local conformation of the lactone moiety. Compound 8, on treatment with Yamamoto's reagent, affords pre-target compound 7a almost exclusively. The latter compound, on pyridine-accelerated dihydroxylation with OsO4, gives preferentially (+)-Aspicilin.
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    Synthesis of New unnatural Macrocyclic Trichothecenes: 4-epiverrucarin A. 47th Communication on verrucarins and roridins46th Commun.: [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1904-1913 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 4-epiverrucarin A (24), a new unnatural macrocyclic trichothecene, was synthesized starting from 4-epiverrucarol (20). The latter was obtained by metal-hydride reduction of the 4-oxo derivative 19. Subsequent conversion of 20 into the monoester 30 and then the diester 32 followed by macrolactonization of the latter yielded 4-epiverrucarin A (24). Attempts to invert the configuration of the naturally occuring 3α-OH group of a trichothecene were unsuccessful. The cytostatic (P-815) and immunosuppressive (MLR) activity of several natural and unnatural trichothecenes was determined in vitro.
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    The Structure of the Polycyclic Nonadecapeptide Ro 09-0198In memoriam Prof. Dr. Rolf Geiger (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1924-1929 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conventional determination of the amino-acid sequence of the peptide antibiotic Ro 09-0198 was prevented by four cyclizations via side chains. The joint application of NMR spectroscopy at highest field and automated Edman degradation yielded a complete determination of the connectivity pattern. The three-dimensional structure derived from NOE data exhibits an interesting separation of amino acids with hydrophilic and hydrophobic side chains.
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    The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene, syntheses, photolyses, X-ray-structure analysis, and PE spectra (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1937-1965 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The propensity of the N=N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1-3, no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray (1: d = 2.71 Å, ω = 129°) and PE measurements (1: I1 = 8.00, I2 = 9.05 eV; 2; I1 = 8.00, I2 = 9.25eV). The steric/stereoelectronic demands for the participation of the N=N bond in pericyclic reactions are clearly more stringent than those for the C=C bond.
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    The Reaction Volume for the Equilibrium between the Lanthanide (III) ennea- and octaaqua lons as a diagnostic aid for their water-exchange mechanisms. Preliminary Communication (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1971-1973 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium between [Ce(H2O)9]3+ and [Ce(H2O)8]3+ has been followed in aqueous solution at 298 K by variable-pressure UV spectroscopy at 295 nm. The dervied volume of reaction for the dissociation of this enneaaqua ion is ΔV0 = +10.9 cm3. mol-1. This value, together with the previously determined activation volume, ΔV≠ = -6 cm3. mol-1, for H2O exchange on [Ln(H2O)8]3+ (Ln = Tb to Tm), allows the assignment of an associative interchange Ia mechanism on these octaaqua ions.
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    Synthesis und thermisches Verhalten von exo-3-Methylidentricyclo[3.2.1.02,4]oct-6-en (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2022-2025 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Thermal Behaviour of exo-3-Methylidenetricyclo[3.2.1.02,4]oct-6-eneThe title compound 3 has been prepared in 16% yield starting from 8,9,10-trinorborna-2,5-diene. Heating 3 at 140° for 4 h does not give triafulvene and cyclopentadiene by Diels-Alder cycloreversion, instead the tetracyclic compound 10 has been isolated (81%), which is presumably formed via the diradical 11.
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    A New Method for the Preparation of (E)-3-Acylprop-2-enoic AcidsPresented in part at the autumn meeting of the Swiss Chemical Society in Bern on October 21, 1988.Dedicated to Prof. R. E. Ireland on the occasion of his 60th birthday (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 117-122 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the preparation of (E)-3-acylprop-2-enoic acids ( = (E)-3-acylacrylic acids) of type II via acid-catalyzed isomerization of the corresponding 3-acylprop-2-ynal acetals of type I (Scheme 1) has been found. The described reaction gives a rapid and quite general access to these compounds known to exhibit a number of interesting biological activities. Some studies toward the elucidation of the reaction mechanism have been made, and a hypothetical mechanism is proposed.
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    Metal Complexes with Macrocyclic Ligands. Part XXVIIPart XXVI. Cu2+-promoted hydrolysis of carboxylic- and phosphonic-acid esters in the side chain of tetraazamacrocycles (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 131-138 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structures of the Cu2+ complexes of 1,4,8,11-tetraazacyclotetradecane derivatives with an ethylpro-pionate and diethylphosphonate group, 5 and 6, respectively, indicate that the metal ion is pentacoordinated by the four N-atoms of the macrocycle and one O-atom. In the case of 5, it is the carbonyl O-atom of the carboxylate group, whereas for 6 it is the phosphonyl O-atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu2+ complexes with the 1,4,8,11-tetraazacyclotetradecanes 3-6 have been measured by pH-stat and stopped-flow techniques. The rate law for the hydrolysis of the carboxylates 3-5 is proportional to the complex concentration and to [OH-] up to pH 13, whereas that of the phosphonate 6 is proportional to [OH-] up to pH 11.5, becoming independent of [OH-] at pH 〉 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra- or an intermolecular OH- attack and the results of the X-ray structure analyses.
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  • 81
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    Oberflächenmodifikation von Kohlenstoff-Elektroden durch Zweikomponenten-Polymere, aufgebaut aus Epoxidharzen und einem Derivat von Vitamin B1217. Mitt. über Synthese und Reaktionen porphinoider Metallkomplexe. 16. Mitt. s. [1].Herrn Prof. Dr. Albert Eschenmoser zu seinem sechzigsten Geburtstag gewidmet (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1301-1311 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Surface Modification of Carbon Electrodes by Polymers Consisting of Epoxy Resins and a Derivative of Vitamin B12A derivative of vitamin B12 containing a 3,5-diaminobenzoyl group in the c side-chain has been synthesized. It was used as the amine component in the formation of an optically active cross-linked epoxy-polymer. Surface modification of carbon electrodes (basal plane graphite and carbon felt) has been achieved by impregnating them with solutions of the monomers followed by thermal curing at 120°C. Electrochemical responses of the Co(II)/Co(I) redox system from sub-mono to multilayer coverages have been observed. The polymer exhibits catalytic activities typical for monomeric vitamin B12 as shown by spectroscopic and electrochemical techniques. Polymermodified electrodes with large specific surfaces have been used in organic electrosynthesis, i.e. the exclusive formation of valeronitrile by reductive cross-coupling of ethyl iodide and acrylonitrile.
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    Direct Observation of Acetophenone Enol Formed by Photohydration of Phenylacetylene (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1331-1332 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photohydration of phenylacetylene yields acetophenone enol as a transient primary product which was detected by flash photolysis. The identification of the transient intermediate rests on a quantitative comparison of its decay kinetics with that of authentic acetophenone enol generated by Norrish type-II photoelimination from γ-hydroxybutyrophenone in aqueous HCl and aqueous AcOH buffer solutions.
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    Structural isomerism in Polycondensates. Part IVPart III: [1].. Synthesis and characterization of liquid crystalline poly(azomethines) and low molecular weight model compounds (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1349-1355 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the aim to investigate the influence of structural isomerism on the mesomorphic thermal stability in main chain thermotropic polycondensates, a series of poly(azomethines) and low molecular weight models have been prepared. The model compounds exhibit smectic and/or nematic mesophases whose stabilites are very sensitive to structural modifications. On the basis of the above results, monomers 2, 5, 6, 8, 9, 23, 25, and 26 were selected to synthesize oligomers 27-23. The oligomer 33 obtained from the nonsymmetric diamine 23 has a lower melting point than the symmetric oligomer 28, but a similar liquid crystalline range.
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  • 84
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    Photochemical reactions. 148th communication147th Communication: [1].. Photochemistry of acylsilanes: Preparation, photolyses, and thermolyses of α,β-unsaturated silyl ketones (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1378-1394 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses, photolyses, and thermolyses of the α,β-unsaturated silyl ketones (E/Z)-7, (E)-8, and (E)-9 are described. On n,π*-excitation (λ 〉 347 mm), the aforementioned compounds undergo (E/Z)-isomerization followed by γ-H abstraction. The intermediate enols are trapped intermolecularly by siloxycarbenes leading to the dimeric acetals 27A + B, 30A + B, and 31A + B. In addition, the acylsilanes (E/Z)-7 undergo photoisomerization by δ-H abstraction furnishing the acylsilanes 29A + B. Flash vacuum thermolyses (FVT) of (E/Z)-7, (E/Z)-8, and (E)-9 give rise to intramolecular reactions of the siloxycarbene intermediates. Thus, FVT (520°) of (E)- and (Z)-7 selectively leads to the enol silyl ethers 32 and (E)-33, respectively, arising from carbene insertion into an allylic C--H bond. FVT of (E/Z)-8 (560°) and (E)-9 (600°) affords the trienol silyl ethers 34A + B and the cyclic silyl ethers 37A + B, respectively, which are formed by CH insertion of the siloxycarbenes. As further products of (E)-8 and (E)-9, the bicyclic enol ethers 35 and 36 are formed, presumably via siloxycarbene addition to the cyclohexene C=C bond.
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    Synthese von (Methylthio)penam-Derivaten durch Keten-Addition an 4,5-Dihydro-5-(methylthio)-1,3-thiazole (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1424-1434 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of (Methylthio)penam Derivatives via Keten Addition onto 4,5-Dihydro-5-(methylthio)-1,3-thiazolesThe 4,5-dihydro-5-(methylthio)-2-phenyl-1,3-thiazoles 3a and 3b, easily prepared from the corresponding 1,3-thiazol-5(4H)-thiones and MeLi, react with dichloroacetyl chloride (5a) and acidoacetyl chloride (5b) in the presence of Et3N to give (methylthio)penam derivatives 6 (Table 1). The reaction mechanism is either a [2 + 2] cycloaddition of in situ generated ketene or a two-step reaction (Scheme 2). The structure of 6f has been confirmed by X-ray crystallography (Fig. 2). The relative configuration of 6a-e follow from comparison of their 1H-NMR spectra with those of 6f (Fig. 1). The 6-azidopenams 6d and 6f have been reduced to aminopenams 8a and 8b, respectively. Acylation of 8a with phenacetyl chloride yields 9 (Scheme 4).
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    Triaziridines. Part VPart IV, see [1].. A semiempirical MNDO study of nitrogen inversion and amide rotation in Formyltriaziridines (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1461-1468 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Since we found certain structural features of triaziridine (1) obtained by MNDO calculations to be in qualitative agreement with those derived earlier from ab initio calculations, we used the MNDO method to derive properties of formyltriaziridine (2) and 1-formyl-2,3-diisopropyltriaziridine (3) as models for the preparatively known 2,3-dialkyl-triaziridine-1-carboxylates 4 and 5. The main results are: (a) The triaziridine N-atoms with H, alkyl, or formyl as substituents (see 2 and 3) are pyramidal. N(1) carrying the formyl group is flatter than N(2) and N(3) with H or alkyl substitent. Bond lengths and angles at N(2) and N(3) are almost identical with those calculated for the N-atoms of 1. (b) The MNDO inversion barriers at the H-substituted N(2) and N(3) of 2 are higher than those at the formyl-substituted N(1), but similar to the ab initio barriers at the N-atoms of 1. (c) The MNDO inversion barriers at N(1) of 2 and 3 are 53 to 92 kJ/mol, whereas the rotation barriers around the N(1)-C(4) bond are 7 to 23 kJ/mol; thus, the previously observed dynamic NMR phenomena in trans-2,3-diisopropyltriaziridine-carboxylates (5) can now be assigned to the slowing down of N(1) inversion rather than N(1)-C(4) rotation.
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    Synthese und Strukturaufklärung von Merucathinon und Synthese von Cathinon. Inhaltsstoffe von Catha edulis FORSK (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1498-1504 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Structure Elucidation of Merucathinone and Synthesis of Cathinone. Constituents of Catha edulis FORSK.Starting from L-alanine, two constituents of Catha edulis FORSK., (S)-4-amino-1-phenylpent-1-en-3-on ((S)-3; merucathinone) and (S)-2-amino-1-phenylpropan-1-on ((S)-1; cathinone) were synthesized.
    Additional Material: 4 Ill.
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    The Relative Stabilities of Substituted cis- and trans-1,2,3,4,4a,9,10,10a-Octahydrophenanthrenes, Including Configurational Corrections in the Elad-Ginsburg Morphine Synthesis (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1559-1566 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative configuration of the title compounds has been determined by 1H-NMR measurements at 300 MHz. In contradistinction to prevailing opinion, it was found that 4-oxo derivatives prefer the cis-configuration. While the cis/trans ratio is 82:18 for the parent 1,2,3,4,4a,9,10,10a-octahydrophenanthrene-4,9-dione, the trans-isomers of C(5)-substituted derivatives cannot be detected under the conditions of equilibration. The cis-configuration is retained upon acetalization of the 4-oxo derivative. A warning is issued regarding the assigned configurations of certain intermediates in the Elad-Ginsburg synthesis of morphine.
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    Sarcodictyeone, a ring-reduced, optically active linear tetraprenylquinone from the mediterranean stolonifer Sarcodictyon roseum ( = Rolandia rosea) (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1581-1584 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Mediterranean stolonifer Sarcodictyon roseum ( = Rolandia rosea) (Cnidaria, Anthozoa, Alcyonaria, Stolonifera, Clavulariidae) contains the first example of a chiral, optically active prenyl derivative of a reduced benzoquinone, sarcodictyenone (= (+)-(4R*,5R*)-5-geranylgeranyl-4-hydroxy-2-methylcyclohex-2-en-1-one; (+)-1a).
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    Nukleophile Addition von Lithiumorganylen an das N,N-Diethyl-10-(trimethylsilyl)-1, 6-methano[10]annulen-2-carboxamid (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1597-1601 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic Addition of Lithiumorganyles to N,N-Diethyl-10-(trimethylsilyl)-1,6-methano[10]annulene-2-carboxamideReaction of lithiumorganyles with N,N-diethyl-10-(trimethylsilyl)-1,6-methano[10]annulene-2-carboxamide followed by quenching with H2O or MeI yields 2,3-dihydro derivatives of 1,6-methano[10]annulene.
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    Synthese von 3-Nitro-1,1-bis(triisopropylsilyl)-1H-cyclopropabenzol und Azocyclopropabenzol-Derivaten (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1623-1626 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 3-Nitro-1,1-bis(triisopropylsilyl)-1H-cyclopropabenzene and Derivatives of Azocyclopropabenzene1,1-Bis(triisopropylsilyl)-1H-cyclopropabenzene (4) can be nitrated at C(3) without opening of the three-membered ring. Further functionalized cyclopropabenzenes are available in this way.
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    Triazene: An ab initio Molecular-Orbital Study of Structure, Properties, and Hydrogen-Transfer Reaction Pathways (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1627-1637 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations of structure, properties, and tautomerization reactions of triazene (1) at the HF/3-21G//3-21G, HF/6-31G*//6-31G*, HF/6-31G**//6-31G*, and MP2/6-31G*//6-31G* levels led to the following conclusions and predictions: (a) Calculations of the ground-state structure of (E)- and (Z)-triazene (1a and 1b, respectively) at various levels of theory show for both isomers C1 geometry with a rather flat pyramidal configuration at N(3), and small energy differences (0.2-7.2 kJ/mol) between C1 and Cs geometry, i.e. inversion at N(3) is a quasi-free process. With all levels of calculations, 1a is found to be of lower energy than 1b by 23-30 kJ/mol. (b) Comparison of vibrational frequencies of (E)-diazene (3) calculated at the HF/3-21G level with experimental values reveals that HF/3-21G calculations are reliable for the prediction of vibrational frequencies of polyaza compounds, if corrected by a factor of 0.91. On this basis, the harmonic vibrational frequencies of 1a and 1b were predicted. (c) For the rotation around the N(2) - N(3) bond of 1a two conceivable transition states, 5a (syn) and 5b (anti) were located (HF/3-21G). The energy differences between 5a or 5b, and 1a are in the order of magnitude of 50-56kJ/mol and show a slight preference for the anti-mode, i.e. energy barriers for the N(2) - N(3) rotation are obtained comparable to those observed experimentally with substituted (E)-triazenes (4). (d) Protonation of 1a at N(1), N(2), or N(3) leads to 6a, 6b, and 6c, respectively -the last one resembling an intermediate of formation of 1 from hydrogendiazonium ion (7) and ammonia (8). Energetically, the conjugate acids of 1a follow the sequence 6a 〈 6c 〈 6b. (e) The preference of N(1) protonation of 1a is also reflected in the relatively high gain of energy in the formation of H-bonded dimers of 1a with H-bonds from N(3) - H to N(1). Calculations of three different H-bonded dimers 9a-c of 1a with the 3-21G basis show that an eight-membered cyclic dimer 9c with two H-bonds from N(3)—H to N(1) is energetically most favoured (67.5 kJ/mol below two separate molecules of 1a). This dimer might well be the starting situation of double intermolecular H-transfer leading to an automeric dimer 9c via an energetically low-lying transition state 12, thus offering a low-energy pathway for the known easy tautomerization of mono- or disubstituted (E)-triazenes. For 9c⇄9c, the activation energy including correction for polarization and correlation effects as well as for vibration zero-point energy is estimated to be ca. 54kJ/mol. (f) A six-membered cyclic dimer 9b of 1a with two H-bonds from N(3)—H to N(2) might be involved for double H-transfer via a transition state 11 to a dimer 10 of (E, Z)-azimine (2). This process, however, turns out to be energetically highly disfavoured (estimated energy barrier for 9b→10: 232 kJ/mol) in contrast to the reverse reaction (10→9b via 11: 4 kJ/mol). This leads to the prediction that azimines bearing an H-atom at N(2) might be kinetically too instable for isolation, being, instead, easily tautomerized to triazenes by bimolecular H-transfer.
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    Carbophile Additionen von Organocupraten mit 1,3-Thiazol-5(4H)-thionen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1837-1843 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbophilic Additions of Organocuprates and 1,3-Thiazole-5(4H)-thionesOrganocuprates and 1,3-thiazole-5(4H)-thiones 1 react in THF at 0° via carbophilic addition onto the C—S bond to give 4,5-dihydro-1,3-thiazole-5-thiols 3 (Scheme 3). This observation is in marked contrast to the previously described reaction of organolithium compounds and 1, which undergo a thiophilic addition onto the exocyclic S-atom. As an exception, treatment of the 1,3-thiazole-5(4H)-thione 1a with tert-butyl cuprate leads to 7a (Scheme 3).
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    Highly Stereoselective Photochemical Oxidative Addition Reactions. Preliminary Communication (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1855-1857 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclometallated complexes of the type cis-bis(2-phenylpyridine)platinum(II) (C22H16N2Pt) and cis-bis(2-(2′-thienyl)pyridine)platinum(II) (C18H12N2S2Pt) undergo thermal or photochemical oxidative addition (TOA or POA) reactions with a number of substrates. TOA (with CH3I, CH3CH2I etc.) yield mixtures of several isomers which rearrange slowly (within ca. one week at room temperature) to one of the possible cis-isomers. CH2Cl2, CHCl3, or (E)—ClCH=CHCl, e.g., do not react thermally. POA yield directly complexes of Pt(IV) with the halide and a σ-bonded C-atom in cis-position. The configuration, as assigned by extensive use of 1H-NMR data, can be characterized for the two chelating ligands C … N and C′ … N′ by C,C′-cis; N,N′-cis and C(chelate), Cl-trans.
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    Zur Photochemie von (Z,Z)-2,7-Cyclodecadien-1-on und 4,8-Cyclododecadien-1-on. Synthese und Eigenschaften von Tricyclo[5.3.0.02,8]decan-Systemen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1872-1886 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Photochemistry of (Z,Z)-2,7-Cyclodecadien-1-one and 4,8-Cyclododecadien-1-one. Synthesis and Properties of Tricyclo[5.3.0.02,8]decane SystemsIrradiation of (Z,Z)-2,7-cyclodecadien-1-one (3) yields (Z,Z)-3,7-cyclodecadien-1-one (12) or tricyclo-[5.3.0.02,8]decan-4-one (16), depending on the reaction conditions. Irradiation of 4,8-cyclododecadien-1-one (28) results also in a light-induced transannular [2 + 2] cycloaddition, yielding tetracyclo[7.3.0.02,1003,6]dodecan-1-one (30). Starting from 16, the preparation of tricyclo[5.3.0.02,8]dec-4-ene (19), tricyclo[5.3.0.02,8]dec-4-ene (21) and tricyclo[5.3.0.02,8]deca-3,5-diene (24) is described. The 1H-NMR and 13C—NMR spectra of the newly prepared compounds are discussed. In the case of 19, 21, and 24, the electronic structure is discussed on hand of their PE spectra.
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    Metaboliten der 1,5-Dihydroimidazo[2,1-b]chinazolin-2(3H)-one. Synthese und Reaktionen einiger 1,5-Dihydro-3-hydroxyimidazo[2,1-b]chinazolin-2(3H)-one (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1887-1897 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metabolites of 1,5-Dihydroimidazo[2,1-b ]quinazolin-2(3H)-ones. Preparation and Reactions of Some 1,5-Dihydro-3-hydroxyimidazo[2,1-b]quinazolin-2(3H)-onesHydroxylated 1,5-dihydroimidazo[2,1-b]quinazolin-2(3H)-ones 2-4 and 6 were isolated as metabolites of imidazoquinazolinones 1a and 1b, respectively. The synthesis of 1,5-dihydro-3-hydroxy-3-methylimidazo[2,1-b]quinazolin-2(3H)-ones 3, 4, and 6, and the preparation of some derivatives thereof is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690816
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  • 97
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    Enantioselective Syntheses of α-Amino Acids from 10-(Aminosulfonyl)-2-bornyl Esters and Di(tert-butyl) Azodicarboxylate. Preliminary CommunicationPresented (W.O.) in part at the IASOC II Meeting, Ischia, May 1986. At the same occasion, C. Gennari presented an independent approach to amino acids via asymmetric addition of ephedrine-derived ketene silyl acetals to di(tert-butyl) azodicarboxylate. (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1923-1926 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Succesive treatment of chiral esters 1 with LiN(i-Pr)2/Me3SiCl and di(tert-butyl) azodicarboxylate/TiCl4/Ti(i-PrO)4 gave N,N′ -di[(tert-butoxy)carbonyl]hydrazino esters 9 which on deacylation, hydrogenolysis, transesterification, and acidic hydrolysis furnished (2S)-α-amino acids 6 in high enantiomeric purity with efficient recovery of the auxiliary alcohol 7.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690819
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  • 98
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    Regioselectivity and Deuterium Isotope Effects in Geraniol Hydroxylation by the Cytochrome P-450 Monooxygenase from Catharanthus roseus (L.) G. DON (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1959-1970 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydroxylation of geraniol (8) by cytochrome P-450 (P-450Cath.) from the subtropical plant Catharanthus roseus (L.) G. DON was optimised to give 8-hydroxygeraniol (9) as the single product in 35% yield. Incubations of different 13C- and 2H-labelled geraniols revealed that H-abstraction is completely regioselective in favour of the CH3 group trans to the chain at C(6) of 8. An intramolecular isotope effect kH/kD = 8.0 was determined, suggesting that H-abstraction is one of the major rate-contributing steps; however, the intermolecular isotope effect was surprisingly inverse at low conversion kH/kD = 0.50, indicating the existence of rate-contributing steps preceding the first irreversible, isotope-sensitive reaction in the sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690822
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  • 99
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    Intermolecular [4 + 2]-Cycloadditions of Nitroalkenes with Cyclic Olefins. Transformations of Cyclic Nitronates (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1971-1989 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitrocyclohexene undergoes facile SnCl4-induced, [4 + 2]-cycloadditions with simple cycloalkenes to produce nitronates. The nitronates can be transformed sterospecifically into a number of other functional groups (alcohol, ketone, oxime, amine) by hydrolytic, reductive, and oxidative processes. The mechanism of the [4 + 2]-cycloaddition is believed to involve formation of a zwitterionic intermediate which can collapse via competing pathways to form the observed products. 1,3-Dipolar cycloadditions of the nitronates are described.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690823
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  • 100
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    Kombinierte NOE- und Entkopplungsexperimente zur selektiven H-NMR-Detektion: Anwendung auf ein stereochemisches Problem (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 2062-2066 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Combined NOE and Decoupling Experiments for the Selective H-NMR Detection: Application to a Stereochemical ProblemThe successful solution of complex stereochemical problems by NMR methods often requires scalar (J) and dipolar (NOE) data. A modern method, improved with respect to sensitivity and selectivity, which yields both scalar and dipolar informations is proposed, and an application to configurational analysis is demonstrated. The method is based on NOE effects for the detection of selected protons and homonuclear decoupling for improved resolution.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690829
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