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  • 1
    Electronic Resource
    Electronic Resource
    Chiral separation of some 4a-methyl-1,2,3,4,4a,9a-hexahydro-fluoren-9-one derivatives as a probe for difference in solvation by 2-propanol of carbamate moiety in chiralcel OD-H, chiralpak AD, and chiralpak AS chiral stationary phases (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 770-777 
    Details
    ISSN: 0899-0042
    Keywords: chiral HPLC ; principal component analysis (PCA) ; hierarchical clustering ; hydrogen bonding ability ; solvation of carbamate phases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromatographic resolution of 12 derivatives in the 4a-methyl-2,3,4,4a-tetrahydro-1H-fluorene and 4a-methyl-1,2,3,4,4a,9a-hexahydrofluoren-9-one series differing by the framework around position 9 and substitution in position 6, are reported on Chiralcel OD, Chiralpak AD, and Chiralpak AS under two elution conditions and according to the two classes of enantiomers. Results from principal component analysis (PCA) as well as hierarchical clustering show a clustering of the actual compounds depending on properties around position 9, the effect of the substituent in position 6 (methyl, chloro or fluoro) not being strong enough to intermesh the data. Carbamate phases show very different properties when they are used in the separation of a series of ketones C and α-chloroketones D, which differ in basicity and the steric requirement around the carbonyl. Analysis of the effect of 2-PrOH content in hexane on the retention is consistent with a large difference in solvation of the carbamate moiety by 2-PrOH, in the order Chiralcel OD 〉 Chiralpak AD 〉 Chiralpak AS. 4a-Methyl-2,3,4,4a-tetrahydro-1H-fluorene derivatives, which lack hydrogen bonding sites, are not discriminated on these CSPs and show identical k′ responses to 2-PrOH content changes on the three CSPs. Chirality 10:770-777, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Separation of N-arylthiazoline-2-(thi)-one atropisomers on p-methylbenzoyl cellulose beads: A factorial design approach (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 207-212 
    Details
    ISSN: 0899-0042
    Keywords: chiral HPLC ; solvent effect ; quantitative substituent effects ; molecular recognition mechanism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A two level full factorial design has been applied to quantify the effect of three selected structural parameters on the capacity factors and chiral separation of atropisomers in N-arylthiazoline-2-(thi)-ones derivatives on tris(p-methylbenzoyl) cellulose beads. The behavior of the two enantiomers is influenced by different factors which might result from different retention sites within the same stationary phase. It appears that the two enantiomers behave independently on the CSP, the order of elution and separation being controlled by a minor steric modification in a very precise location in the molecule for one enantiomer. The methodology of the experimental design allows the comparison of equations generated from data issued from designed compounds. These equations afford much more information than the step by step comparison of individual molecules. In our case, the tris(p-methylbenzoyl)cellulose beads and microcrystalline cellulose triacetate appear as complementary CSPs for the resolution of atropisomers of the series studied. © 1993 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050403
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  • 3
    Electronic Resource
    Electronic Resource
    CHIRBASE, a graphical molecular database on the separation of enantiomers by liquid-, supercritical fluid-, and gas chromatography (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 213-219 
    Details
    ISSN: 0899-0042
    Keywords: enantiomer separation ; chiral recognition ; substructure search ; chemical information ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to cope with the increasing number of publications on the separation of enantiomers by chromatography on a chiral stationary phase, the graphical molecular database CHIRBASE was created. In the present state, the database package covers information (structural, bibiographic, and chromatographic data) on liquid-, supercritical fluid-, and gas chromatography; other methods will follow. CHIRBASE, running on the MDL software Chembase®, meets the requirements of contemporary information management in the chemical and pharmaceutical industry. (Detailed information including a demo-version of each part of CHIRBASE can be obtained from the authors on request.) © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050404
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  • 4
    Electronic Resource
    Electronic Resource
    γ-Cyclodextrin as chiral mobile phase additive in the HPLC separation of the atropisomers of some N-arylthiazoline-2-thiones and N-arylthiazoline-2-ones: Attempts to quantify the effect of selected structural parameters (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 471-478 
    Details
    ISSN: 0899-0042
    Keywords: chiral additive ; cyclodextrin ; RP-HPLC ; atropisomers ; experimental design ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the position and type of the substituent on the chromatographic separation of N-arylthiazoline-2-thione and arylthiazoline-2-one atropisomers are described in reversed-phase HPLC using β- or -β-cyclodextrin as chiral mobile phase additive. A quantitative approach to experimental design has been developed. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050613
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of alkyl substituents on chiral separation of N-arylthiazolin-2-(thi)-one atropisomers on tris (p-methylbenzoyl)cellulose beads and cellulose triacetate: Lipophilicity aspects (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 251-260 
    Details
    ISSN: 0899-0042
    Keywords: chiral HPLC ; experimental design ; quantitative substituent effects ; recognition mechanism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The determination of lipophilicity of the title compounds allowed treatment of the data for chiral separation (capacity factors) on CTA and CTPB according to these parameters. A linear correlation between In k′(+) and log k′w was found on both CTA and CTPB, as far as the substituents are situated in the plane of the aryl ring or the heterocycle. This correlation with a nonchiral descriptor allows treatment of capacity factors for (-)-enantiomers as deviations from the lipophilicity line or derived parallels. It results in a clear description of the molecular area affecting enantioselectivity. Application to larger alkyl derivatives shows that the effect of the substituent should be treated on a basis of attractive effect in the case of CTA and on the basis of attractive and repulsive effects for CTPB. © 1994 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530060407
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  • 6
    Electronic Resource
    Electronic Resource
    Conversion of a racemate into a single enantiomer in one step by chiral liquid chromatography: Studies with rac-2,2′-diiodobiphenyl (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 610-611 
    Details
    ISSN: 0899-0042
    Keywords: axially chiral biphenyl ; rotational energy barrier ; enantiomeric separation ; high-performance liquid chromatography ; triacetylcellulose ; deracemization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of rac-2,2′-diiodobiphenyl were separated by liquid chromatography on microcrystalline triacetylcellulose. The conformational lability, a large separation factor α, and a suitable capacity factor k′(+) of this biphenyl allowed us to convert the racemate into 90% of enantiomerically pure (-)-2,2′-diiodobiphenyl and 10% of pure (+)-2,2′-diiodobiphenyl, respectively, by a series of in situ racemization-elution cycles. The much better retained (+)-enantiomer was racemized on the chromatographic column at 50°C after the less retained (-)-enantiomer has already been eluted at 8°C. © 1995 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070809
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  • 7
    Electronic Resource
    Electronic Resource
    Structure and substituent effect on chiral separation of some 4a-methyl-2,3,4,4a-tetrahydro-1H-fluorene derivatives and 4a-methyl-1,2,3,4,4a,9a-hexahydro-fluoren-9-one derivatives on CTA-I and chiralcel OJ chiral stationary phases (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 522-527 
    Details
    ISSN: 0899-0042
    Keywords: chiral HPLC ; quantitative substituent effect ; recognition mechanism ; fluorene derivative-chiral separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chromatographic parameters for 12 structurally related compounds in the 4a-methyl-2,3,4,4a-tetrahydro-1H-fluorene and 4a-methyl-1,2,3,4,4a,9a-hexahydro-fluoren-9-one series are reported on CTA-I and Chiralcel OJ chiral stationary phases. Arrangement of the k' values according to configurationally related enantiomer series (Class I and Class II) and not according to the actual order of elution, allows the treatment of the data by linear correlation with structure and substituent effect. A detailed analysis of the capacity factor variation with respect to the structural changes shows clearly that the framework and substitution effects do not result in the same response on the two cellulose ester chiral stationary phases. More interestingly, it emerges that chiral discimination may be attributed to certain areas of the molecule, these areas being different in the interaction within CTA-I and Chiralcel OJ. Furthermore, our analysis points out the relevance of attempting to develop quantitative relationships for configurationally related series of enantiomers (in our case Class I and Class II), the main effort being devoted to the understanding of the capacity factor variation in each class rather than of the α values, which are derived entities. Chirality 10:522-527, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of substituents on the rotational energy barrier of atropisomeric biphenyls  -  studies by polarimetry and dynamic gas chromatography (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 781-786 
    Details
    ISSN: 0947-3440
    Keywords: Atropisomers ; Biphenyls, axially chiral ; Enantiomerization ; Dynamic gas chromatography ; Polarimetry ; Energy barriers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have synthesized a series of 2,2′-substituted biphenyls and particularly derivatives of 2,2′-bis(trifluoromethyl)biphenyl (4) with either one or two fluoro, chloro, bromo, amino, nitro or methoxy substituents in the para positions for investigating the influence of these substituents on the rotational energy barrier of the biphenyls by polarimetry and dynamic gas chromatography (DGC). Axially chiral biphenyls with at least two bulky substituents in the ortho positions were separated by gas chromatography on selectively modified cyclodextrins. Due to competition between resolution and enantiomerization in the gas chromatographic column 2-tert-butyl-2′-isopropyl- (2), 2-isopropyl-2′-(trifluoromethyl)biphenyl (5), and some para-substituted derivatives of 4 show temperature-dependent interconversion profiles and coalescence phenomena in analogy to dynamic NMR studies. The accelerating effect on the rate of enantiomerization of electron-donating groups in the para positions and the decelerating effect of electron-accepting groups has been determined. Dynamic gas chromatography is shown to be a useful supplement to studies of thermal enantiomerization kinetics of optically enriched or separated compounds by polarimetry for the investigation of energy barriers of atropisomeric biphenyls.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199505114
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  • 9
    Electronic Resource
    Electronic Resource
    An Anomalous Oxidation of β-Pinene (1975)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 58 (1975), S. 2151-2160 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of β-pinene with aqueous alkaline potassium periodate and catalytic amounts of potassium permanganate gave, in addition to the expected oxidation product nopinone, a β-ketol. The structure of the latter was shown to be 1-(2-hydroxyisopropyl)bicyclo[3.1.0]hexan-2-one. The formation of this anomalous side-product represents a new type of rearrangement of the pinane skeleton.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19750580727
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  • 10
    Electronic Resource
    Electronic Resource
    Unexpected Configurational and Conformational Preference in Bicyclo [3.2.0]heptane Systems (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 703-720 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Einige 7endo-monosubstituierte Bicyclo[3.2.0]hept-2-en-6-one and Bicyclo-[3.2.0]heptan-6-one zeigen eine unerwartete thermodynamische Stabilität gegenüber den entsprechenden 7exo-Isomeren. Die basenkatalysierte Epimerisierung (NaOH oder N(CH2CH3)3) verschiedener 7-monosubstituierter Bicyclo[3.2.0]-hept-2-en-6-one (1-7) und Bicyclo[3.2.0]heptan-6-one (8-10) führt je nach Substituent (R) zu folgenden endo/exo-Gleichgewichtsgemischen: (a) Bicyclo[3.2.0]-hept-2-en-6-one: R = F: 89/11, R = C1: 87/13, R = CH3: 76/24, R = CH2CH3: 65/35, R = CH (CH3)2: 57/43, R= C (CH3)3: 10/90, R= C6H5: 66/34; (b) Bicyclo[3.2.0]-heptan-6-one: R = C1: 85/15, R = CH3: 45/55, R= C (CH3)3: 0,4/99,6. In jedem Fall wurde das gleiche Epimerengemisch erhalten, ausgehend sowohl vom endo- wie auch vom exo-Isomeren.Die bemerkenswerte endo-Stabilität wird einer Bevorzugung der Konformation 11 des Cyclobutanonringes zugeschrieben, verursacht durch geringere Pitzer-Spannung. So kann ein endo-Substituent an C(7) eine pseudoäquatoriale Lage am Cyclobutanonring einnehmen. Bei sehr sperrigen Substituenten mit zunehmender Raumerfüllung nimmt eine 1,2-abstossende Wechselwirkung langsam überhand, bis im Falle des t-Butylsubstituenten die exo-Konfiguration die stabilere wird.Die Dehalogenierung von 7-Halo-substituierten Bicyclo [3.2.0]hept-2-en-6-onen (15 bis 21) mit Zink und Eisessig und mit Tributylzinnhydrid führte zu den folgenden endo/exo-Epimerengemischen der entsprechenden 7-monosubstituierten Bicyclo [3.2.0]hept-2-en-6-one (2 bis 7): R = C1: 92/8, R = CH3: 93/7, R = CH2CH3: 93/7, R = CH(CH3)2: 92/8, R = C(CH3)3: 93/7, R = C6H5: 93/7. In allen Fällen, also unabhängig vom Substituenten R, war das endo-isomere stark bevorzugt. Es muss sich also um eine kinetische Kontrolle im isomerenbestimmenden Schritt handeln: Die Reduktion verläft über das Enolat, bzw. über eine Radikalspezies mit trigonal-planarer Anordnung am C(7), so dass die (irreversible) Wasserstoff-Anlagerung von der weniger behinderten Site, der exo-Seite her erfolgt.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650308
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