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  • 1
    ISSN: 1434-1948
    Keywords: Copper ; Nickel ; Amides ; Polynuclear complexes ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New homo- and heterometallic hexanuclear complexes of formula {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}(ClO4)4 ·2 H2O [Cu6-tmen] {[Cu(pmdien)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu6-pmdien] and {[Ni(cyclam)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu2Ni4-cyclam] [H8L = tetrakis(aminomethylene)methanetetrakis(oxamic acid), tmen = N,N,N′,N′-tetramethylethylenediamine, pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine, and cyclam = 1,4,8,11-tetraazacyclotetradecane] have been synthesized. The crystal structure of [Cu6-tmen] has been determined by single-crystal X-ray diffraction. The structure consists of cationic {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}4+ hexanuclear units. The hexanuclear cation is made up of two symmetry-related oxamato-bridged trinuclear units connected through the central carbon atom C(6) of the L8- ligand. Variable-temperature magnetic susceptibility measurements (1.8-300 K) have been performed for these series of complexes including the dinuclear precursors of formula Na4[Cu2L] · 10.5 H2O [Cu2-Na], (NMe4)4[Cu2L] · 4 H2O [Cu2-NMe4] and (PPh4)4[Cu2L] · 6 H2O [Cu2-PPh4]. The magnetic data have been interpreted. Evidence of a weak intramolecular ferromagnetic interaction between the two CuII ions in [Cu2L]4- has been observed. For the hexanuclear species, the interaction through the oxamato bridge was found to be equal to -6790, -2650, and -1643 yJ (-342, -133, and -82 cm-1) for [Cu6-tmen], [Cu6-pmdien], and [Cu2Ni4-cyclam], respectively. In these complexes, the weak intramolecular ferromagnetic coupling between the two CuII ions within the dinuclear synthon was masked by intermolecular interactions or local anisotropy.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0947-3440
    Keywords: Indazolols ; Indazolinones ; Indoxyls ; Cytostatic agents ; HeLa cells ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The remarkable cytostatic activity of 1-substituted indazolols 2a,b, condensed indazolinones 4a-c and indoxyl derivatives 5a, b against HeLa cells is reported. Three different approaches to the synthesis of indazolophthalazinone 4a, representing alternatives to those previously reported, were studied. Several compounds related to the mentioned indazolols and indazolinones were obtained and their cytostatic activity against HeLa cells was tested. Among them we can mention the tetracyclic SO2 analogue 14 and the condensed pyridine derivative 18, the tricyclic pyrazolophthalazinone 22 and the bicyclic pyrazolodiazepinone 25, which were prepared by taking advantage of the reactivity of heterocyclic spiro aminimides.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 527-532 
    ISSN: 0947-3440
    Keywords: Centaurea paui ; Sesquiterpenes ; Heliangolides ; Elemanolides ; Terpenoids ; Natural products ; Phytochemistry ; Lactones ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aerial parts of Centaurea paui afforded, in addition to several known sesquiterpene lactones, the two new elemanolides 2-4, the new elemane derivative 5 as well as the five new heliangolides 14-18. Their structures were elucidated by spectroscopic methods, especially high-field NMR spectroscopy. The structure of the heliangolide 12 previously isolated from this plant, has been confirmed by X-ray diffraction.
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  • 4
    ISSN: 0947-3440
    Keywords: Intramolecular reductive coupling ; Aluminium amalgam ; Bridgehead polycyclic 1,2-diamines ; Bridgehead polycyclic 2-amino alcohols ; Rigid acetylcholine analogs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of dioxime 2a with NBS gave 3 and 4. A chair-boat conformation has been established for 3 by X-ray diffraction analysis, while 4 seems to exist in a chair-chair conformation on the basis of NMR data. m-Chloroperbenzoic acid oxidation of dioximes 2 gave polycyclic dinitro compounds 7. In some oxidations of 2a, nitroso dimer 8 was isolated, its structure being established by X-ray diffraction analysis. Reduction of 7 with aluminium amalgam gave in good yields diamines 6, that were also obtained by reductive coupling from dioximes 2. Amino alcohols 14 were obtained by reductive coupling from monooximes 11. While 11a could be obtained in pure form from diketone 1a via 9a and 10a; hydrolysis of 10b to 11b failed. Azapolycyclic compounds 12 were obtained by hydrolysis of 10. Amino alcohol 14b was more appropriately prepared by reduction of nitro alcohol 15 obtained together with 7b by m-chloroperbenzoic acid oxidation of a mixture containing monooxime 11b and dioxime 2b. From the oxidation of a mixture containing 11a, nitro ketone 16 was isolated in low yield. Amino alcohols 14 and diamines 6 were also characterized as cyclic carbamates 13 or ureas 5. Rigid analogs of acetylcholine 20 and 21 were obtained from 14 by standard procedures, compounds 17 and 18 being detected as intermediates. Neither muscarinic nor antiacetyl-cholinesterase activity has been observed for compounds 20 and 21.
    Additional Material: 2 Ill.
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  • 5
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the stability of the Schiff bases formed between pyridoxal 5′-phosphate (PLP) and leucine in the presence of (hexadecyl)trimethylammonium bromide (CTAB) over a wide pH range by determining the kinetic constants of formation and hydrolysis of these compounds. The results show that the stability of the Schiff bases is increased by the presence of CTAB as a result of increased rates of formation and decreased hydrolysis rate constants. The ionic head groups of CTAB favour the formation of the bases, while its hydrophobic rests protect the imine double bond from hydrolysis. This model system permits one to obtain partially hydrophobic media with no need for any non-aqueous solvents.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1619-1625 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A kinetic study on the alkaline hydrolysis of cephaloridine (1) at pH 10.5 and 37° was carried out using ion-pair reversed-phase HPLC. The main resulting degradation products, the 7-epimer 2 of 1, the Δ2-isomer 3 of 1, and the 3-methylidene compound 4 were identified. The presence of a pyridinio group at C(31) results in a slightly increased formation constant for the 3-methylidene compound 4 and the 7-epimer 2, and introduces a new reaction: the isomerization of the double bond at C(3) in the dihydrothiazine ring to C(2).
    Additional Material: 3 Ill.
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  • 7
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase basic hydrolysis of clavulanic acid (a) was studied by using the AM1 semi-empirical method. The results obtained show that the hydroxyethylidene side chain at C(2) is pivotal to the stability of the different reaction products involved. The products with an open oxazolidine ring are more stable than those with a closed ring fused to the β-lactam ring. This behaviour differs from that of penicillins and cephalosporins where the most stable degradation products are those with an intact thiazolidine or dihydrothiazine ring, respectively, fused to the β-lactam ring. The different chemical reactivity of clavulanic acid relative to penicillins and cephalosporins could explain the disparate behaviour of the latter two types of compound towards β-lactamases. Once the acyl-enzyme intermediate of clavulanic acid has been formed, it can evolve with cleavage of the oxazolidine ring to form a difficult to deacylate compound.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1793-1802 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The degradation of cefaclor (1), an oral cephalosporin antibiotic, was studied at 37° in a neutral aqueous medium by HPLC and 1H-NMR. Under these conditions, 1 underwent intramolecular aminolysis by the 7-side-chain NH2 group on the β-lactam moiety to give a piperazine-2,5-dione. The most prominent peak in the HPLC profile of a degradation solution from 1 was isolated by prep. HPLC. Mechanistically, the formation of this degradation product cis-11 from 1 involves the contraction from a six-membered cephem ring to a five-membered ring, which presumably takes place via a common episulfonium ion intermediate 9 (see Scheme). Loss of the Cl-atom from 3-chloro-3-cephem is a general reaction subsequent to β-lactam ring opening.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We used semi-empirical and ab initio calculations to investigate the nucleophilic attack of the OH- ion on the β-lactam carbonyl group. Both allowed us to detect reaction intermediates pertaining to proton-transfer reactions rather than the studied reaction. We also used the PM3 semi-empirical method to investigate the influence of the solvent on the process. The AMSOL method predicts the occurrence of a potential barrier of 20.7 kcal/mol due to the desolvation of the OH- ion in approaching the β-lactam carbonyl group. Using the supermolecular approach and a H2O solvation sphere of 20 molecules around the solute, the potential barrier is lowered to 17.5 kcal/mol, which is very close to the experimental value (16.7 kcal/mol).
    Additional Material: 6 Ill.
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Natural free carboxylic acids from the hadromerid sponge Diacarnus levii (Kelly-Borges and Vacelet) were esterified to yield the new cyclic norditerpene peroxides ent-muqubilin benzyl ester (= (αR,3S,6R)-α,6-dimethyl-6-[(E)-4-methyl-6-(2,6,6-trimethyl-cyclohex-1-en-1-yl)hex-3-enyl]-1,2-dioxan-3-acetic acid benzyl ester; 6, diacarnoate B methyl ester(= (αS,3R,6R)-α,6-dimethyl-6-{2-(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-3-oxo-2,5,5,8a-tetramethylnaphthalen-1-yl)ethyl}-1,2-dioxan-3-acetic acid methyl ester; 9), and deoxydiacarnoate B benzyl ester (= (αS,3R,6R)-α,6-dimethyl-6-{2-[(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethyl-1-naphthalenyl]ethyl}-1,2-dioxan-3-acetic acid benzyl ester; 10), which were isolated following extensive chromatography. The relative configuration of the peroxide/α-methylacetate moiety of 6, 9, and 10, was directly determined from their NMR spectra. The absolute configurations of the peroxide/α-methylacetate moiety was deduced from comparative 1H-NMR data of the (S)- and (R)-phenylglycine methyl ester derivatives 7 and 8 as well as 11/13 and 12/14, all obtained from a mixture of the precursors of 3, 6, and 10. The absolute configuration at the carbobicyclic moiety of enone 9 and of 10, is identical, as established by chemical interconversion, 9 and 10 belong to the normal labdane series according to empirical CD rules, applied either directly to 9 or to the parent (+)-sclareolide-derived enone 20. In contrast, molar rotation additivity rules suggest the ent-labdane configuration for 9 and 10. The epidioxides 1-3, 6, and 10 proved active in vitro against the malaria parasite Plasmodium falciparum; especially the previously isolated methyl 3-epinuapapuanoate (2) was active against a chloroquine-resistant strain, and this with a good security index.
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