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  • Organic Chemistry  (68,935)
  • 1
    ISSN: 0899-0042
    Keywords: chiroptical properties ; Cotton effect ; atropisomerism ; quantum-mechanical calculation ; AM1 ; CNDO/S ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rotational strengths calculated on the basis of quantum-mechanically obtained minimum energy geometries were used to determine the absolute configurations of axially chiral 3-aryl-4(3H)-quinazolinones from the sign of the observed Cotton effects (CEs). For the spectral data, CNDO/S calculations were used; for the geometries, ab initio (RHF/6-31G) and semiempirical (AM1) theories were used. Oscillator and rotational strengths of all excited states down to 200 nm were compared to experimental absorption and circular dichroism (CD) data. It was found that the sign of the 1Lb Cotton effects obtained for the enantiomers of methaqualone and derivatives of 3-aryl-2-alkylthio-4(3H)-quinazolinones can be correlated unambiguously with the absolute configuration. Furthermore, the sign of the Cotton effect of the π-π* transition of the thiocarbonyl chromophore of 3-aryl-2-mercapto-4(3H)-quinazolinones is suitable for a successful stereochemical correlation. Chirality 10:253-261, 1998. © 1998 Wiley-Liss, Inc.
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  • 2
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    Chirality 10 (1998), S. 246-252 
    ISSN: 0899-0042
    Keywords: sulfoxides ; chloroperoxidase ; asymmetric oxidation ; enantioselective ; episulfide ; gas chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric sulfoxidation by means of a chloroperoxidase from Caldariomyces fumago and hydrogen peroxide as the oxygen source was studied for a series of sterically well-defined substrates. The stereochemistry of the sulfoxidation was the same for all substrates studied. While 2,3-dihydrobenzo[b]thiophene (1) is an excellent substrate (giving 99.5% yield and 99% e.e. of the (R)-sulfoxide), replacement of a methylene group by either a more sterically demanding group or a heteroatom caused a substantial decrease in reactivity or in reactivity as well as enantioselectivity. A further investigation of the lowered catalytic efficiency of chloroperoxidase with these substrates has been carried out in a series of competitive reactions. Thus, benzo[1,3]oxathiole (5) acted as a competitive inhibitor of the enzyme, whereas 1-thiochroman (2) and 1-thiochroman-4-one (3) were shown to be too sterically demanding to significantly compete for the active site. For the oxidation of 2, 3, and 5, it was found that in the low CPO concentration range the chemical yield after 60 min reaction time increased almost linearly with the amount of CPO used. The products from 2 and 3 could be obtained in over 80% yield with an e.e. exceeding 96%. Chloroperoxidase was also found to be an effective catalyst in the oxidation of labile episulfides, yielding the corresponding anti-sulfoxides quantitatively and giving 12% e.e. of (1R, 2R)-sulfoxide in the oxidation of propylene sulfide. Chirality 10:246-252, 1998. © 1998 Wiley-Liss, Inc.
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  • 3
    ISSN: 0899-0042
    Keywords: atropisomeric polychlorinated biphenyls (PCBs) ; Chirasil-Dex ; rotational barrier ; stopped-flow multidimensional gas chromatographic technique ; on-line enantiomerization kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational barriers ΔG
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  • 4
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    Chirality 10 (1998), S. 321-324 
    ISSN: 0899-0042
    Keywords: NSAID ; esterification ; resolution ; Candida antarctica lipase ; rac-Indoprofen ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lipase from Candida antarctica, commercially available immobilised on acrylic resin as Novozym® 435, allows for enantioselective esterification of rac-indoprofen (±)-1, with methanol in a dioxane-toluene solvent system. A double esterification process affords methyl ester (-)-(R)-2 in 85% e.e. and enantiopure (+)-(S)-1, both in good chemical yield. Chirality 10:321-324, 1998. © 1998 Wiley-Liss, Inc.
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  • 5
    ISSN: 0899-0042
    Keywords: chiral asymmetry generation ; chiral autocatalysis ; primary nucleation ; secondary nucleation ; chiral cobalt complex ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral asymmetry generation, the predominant production of one enantiomer in a non-chiral environment, could occur in the production of the chiral complex cis-[CoBr(NH3)(en)2]Br2 by the reaction of [Co(H2O)2{(OH)2Co(en)2}2](SO4)2 with ammonium bromide in an aqueous medium. The main kinetic steps in the reaction system have been determined. During the reaction, the product crystallizes at an early stage. When a very small amount of crystalline enantiomer was added to the reaction system at an early stage, the same enantiomer was produced preferentially; in addition, the enantiomeric excess of the product increased with increasing the stirring rate. Thus, it seems that each enantiomer generates chiral crystals that could self-replicate through secondary nucleation when the solution is stirred; these crystals in turn enhance the production of the same enantiomer. With a computer code that simulates such a kinetic mechanism, it is shown that enantiomeric excess observed in the experiments could be reproduced. Chirality 10:343-348, 1998. © 1998 Wiley-Liss, Inc.
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  • 6
    ISSN: 0899-0042
    Keywords: carbenicillin ; stereoselective ; secretion ; transport ; rabbit ; membrane vesicles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselectivity in the renal secretion of carbenicillin (CBPC) was studied in rabbits. Significant renal secretion of CBPC was observed in vivo, with the secretion of the S-epimer being greater than that of the R-epimer. Stereoselective transport of CBPC was further studied in vitro using basolateral and brush border membrane vesicles prepared from rabbit kidneys. The transport of CBPC by the organic anion transporter into the basolateral membrane vesicles (BLMV) was not stereoselective. In contrast, a distinct stereoselectivity was observed in the transport of CBPC by the organic anion transporter into the brush border membrane vesicles (BBMV), with the transport of the S-epimer being more favorable. Significant epimer-epimer interactions were also observed in the transport into BBMV. The stereoselectivity of the transport of CBPC was calculated from the kinetic parameters with consideration of epimer-epimer interactions and was similar to that observed in vivo. It was concluded that the observed stereoselectivity in the renal secretion of CBPC in vivo reflected that of transport via the organic anion transporter located at the brush border membrane. Chirality 10:349-357, 1998. © 1998 Wiley-Liss, Inc.
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  • 7
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    Chirality 10 (1998), S. 371-372 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 8
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    Chirality 10 (1998), S. 362-363 
    ISSN: 0899-0042
    Keywords: Jacobsen's catalyst ; enantiomeric purity determination ; chiral HPLC ; cyclodextrin chiral stationary phases ; enantioseparation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A HPLC method is described for the chiral analysis of the commercially available Jacobsen's catalyst. A hydroxypropyl β-cyclodextrin stationary phase was used in conjunction with a nonaqueous, polar-organic mobile phase. The method can be applied to control the enantiomeric purity of the catalyst, which is of great importance for quality control of that product. High accuracy in the determination of trace levels of the unwanted enantiomer in the presence of large amounts of the desired enantiomer is demonstrated. Chirality 10:362-363, 1998. © 1998 Wiley-Liss, Inc.
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  • 9
    ISSN: 0899-0042
    Keywords: cyclic imides ; barbiturates ; piperidine-2,6-diones ; mephenytoin ; chiral recognition ; enantioselectivity ; vancomycin chiral stationary phase ; normal-phase mode ; reversed-phase mode ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several cyclic imidic compounds (barbiturates, piperidine-2,6-diones, and mephenytoin) are enantiomerically resolved via high-performance liquid chromatography (HPLC) on a macrocyclic antibiotic covalently bonded to a silica gel support. The Chirobiotic V chiral stationary phase (CSP) column contains the antibiotic vancomycin as the chiral selector. The results of the analysis show that the substituents at the chiral carbon position of the racemic drugs affect chiral resolution. In addition, ring size may also play a role when considering the formation of analyte-CSP inclusion complexes. Contrary to the piperidine-2,6-diones, the chromatographic parameters for the barbiturates are much the same under normal- or reversed-phase conditions. The details of these results are discussed. Chirality 10:358-361, 1998. © 1998 Wiley-Liss, Inc.
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  • 10
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    Chirality 10 (1998), S. 373-374 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 11
    ISSN: 0899-0042
    Keywords: (±)nicotine ; (±)nornicotine ; chiral separation ; enantiomers ; normal phase HPLC ; mobile phase additive ; cellulose-based chiral stationary phase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper describes the enantiorecognition of (±)nicotine and (±)nornicotine by high-performance liquid chromatography using two derivatized cellulose chiral stationary phases (CSPs) operated in the normal phase mode. It was found that different substituents linked to the cellulose backbone significantly influence the chiral selectivity of the derivatized CSP. The results showed that, in general, the tris(4-methylbenzoyl) cellulose CSP (Chiralcel OJ) surpasses tris(3,5-dimethylphenyl carbamoyl) cellulose CSP (Chiralcel OD). On the former column, the resolution (±)nicotine and (±)nornicotine enantiomers depended largely on mobile phase compositions. For the separation of the nicotine enantiomers, the addition of trifluoroacetic acid to a 95:5 hexane/alcohol mobile phase greatly improved the enantioresolution, probably due to enhanced hydrogen bonding interactions between the protonated analytes and the CSP. For (±)nornicotine separation, a reduction in the concentration of alcohol in the mobile phase was more effective than the addition of trifluoroacetic acid. Possible solute-mobile phase-stationary phase interactions are discussed to explain how different additives in the mobile phase and different substituents on the cellulose glucose units of the CSPs affect the separation of both pairs of enantiomers. Chirality 10:364-369, 1998. Published 1998 Wiley-Liss, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.
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  • 12
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    Chirality 10 (1998), S. iii 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 13
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    Chirality 10 (1998), S. 722-725 
    ISSN: 0899-0042
    Keywords: R- and S-isomer ; chiral compound ; enthalpy of mixing ; propane-1,2-diol ; methyllactate ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enthalpies of mixing of chiral isomers R- and S- of propane-1,2-diol and methyllactate, respectively, have been measured over the whole range of mole fraction at 298.15 K. All the enthalpies of mixing measured are very small. The enthalpic differences between the interactions of molecules of like-configuration and those of opposite configuration have been evaluated precisely. Mixing of R- and S-enantiomers of propane-1,2-diol gives slight enthalpic stabilisation over the whole range of mole fraction, however methyllactate has shown the opposite effect on mixing. Chirality 10:722-725, 1998. © 1998 Wiley-Liss, Inc.
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  • 14
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    Chirality 10 (1998), S. 173-179 
    ISSN: 0899-0042
    Keywords: chirality at low and high resolution ; functional groups ; fuzzy density fragments ; continuum models ; fuzzy sets ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mislow's Label Paradox and the chirality preserving or abandoning properties of deformation paths of polyhedral models are extended to simple representations of electron density continua of molecules. Chirality 10:173-179, 1998. © 1998 Wiley-Liss, Inc.
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  • 15
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    Chirality 10 (1998), S. 405-414 
    ISSN: 0899-0042
    Keywords: chiral-discrimination ; homochirality ; stereospecificity ; self-assembly ; supercoiling ; cholesteric mesophase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleic acids are characterized by a predominant right-handed helical configuration that derives from the chirality of the sugar moiety. Hitherto, only “local” effects of this helical asymmetry, exemplified by DNA interactions with small compounds, have been documented. The results described in this study indicate that an enhanced asymmetry is required for the manifestation of chiral effects in DNA self-assembly processes or for chiral discrimination upon interactions with peptides. Two cases in which the intrinsic DNA asymmetry is enhanced are reported: rod-like superhelical species derived from linear DNA molecules, and topologically constrained supercoiled DNA. In the first case, the superhelical grooves within the DNA rods allow for a stereospecific complexation with peptides, resulting in chiral discrimination. In the second case, it is shown that the properties of cholesteric assemblies derived from supercoiled DNA are strictly determined by the enhanced asymmetry associated with molecular supercoiling. The results allow for new reflections on the concept of molecular complementarity, and indicate that spontaneously obtained chiral DNA mesophases might have played a key role in determining terrestrial homochirality. Chirality 10:405-414, 1998. © 1998 Wiley-Liss, Inc.
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  • 16
    ISSN: 0899-0042
    Keywords: chiral separation ; two- and three-dimensional crystals ; grazing incidence X-ray diffraction ; atomic force microscopy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spontaneous separation of enantiomers in two- and three-dimensional crystals is driven by the same thermodynamic and kinetic factors. However, amphiphilic crystalline monolayers at an interface cannot possess a center of inversion, the most common symmetry element in bulk crystals. This fact should, in principle, lead to better chances for spontaneous separation in the Langmuir or Langmuir-Blodgett monomolecular films. On the other hand, the monolayers of most amphiphiles studied to date incorporate long aliphatic chains that have an intrinsic tendency to pack in a herring-bone motif requiring glide plane symmetry, thus creating a bias towards racemate formation. Moreover, 2-D crystals supposedly have a much higher degree of molecular and therefore enantiomeric disorder compared to bulk crystals. All these factors necessitate a careful choice of molecules to guarantee enantiomeric separation in two dimensions. Unambiguous detection of spontaneous resolution in 2-D appears to require atomic resolution of molecular packing arrangement, which can in principle be obtained by grazing incidence X-ray diffraction or atomic force microscopy, whereas in bulk solids spontaneous resolution can be easily detected by various macroscopic methods. This short review provides analogies between spontaneous separation in 3-D and recent examples in 2-D, showing that spontaneous separation generally depends upon subtle differences in molecular structure. Chirality 10:415-424, 1998. © 1998 Wiley-Liss, Inc.
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  • 17
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    Chirality 10 (1998), S. 430-433 
    ISSN: 0899-0042
    Keywords: Whelk-O 1 ; chromatography ; HPLC ; enantiodifferentiation ; heterocycles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In concert with a larger study of the processes by which chiral stationary phase CSP 1 differentiates between enantiomers, we have investigated the chromatographic separation of the enantiomers of a series of aryl-substituted heterocycles of systematically varied structure. A mechanistic picture of how these and similar resolutions occur is emerging. The mechanistic hypothesis described herein is of predictive value. Chirality 10:430-433, 1998. © 1998 Wiley-Liss, Inc.
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  • 18
    ISSN: 0899-0042
    Keywords: atropisomeric polychlorinated biphenyls (PCBs) ; Chirasil-Dex ; rotational barrier ; stopped-flow multidimensional gas chromatographic technique ; on-line enantiomerization kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational barriers ΔG† (T) of the four atropisomeric polychlorinated biphenyls (PCBs) 2,2′,3,5′,6-pentachlorobiphenyl (PCB 95), 2,2′3,3′,4,6′-hexachlorobiphenyl (PCB 132), 2,2′,3,3′,6,6′-hexachlorobiphenyl (PCB 136), and 2,2′,3,4′,5′,6-hexachlorobiphenyl (PCB 149) were determined via on-line enantiomerization kinetics by a new stopped-flow multidimensional gas chromatographic technique (stopped-flow MDGC) employing Chirasil-Dex as chiral stationary phase for enantiomer separation. The calculated rotational barriers ΔG† (T) of the trichloro-ortho-substituted atropisomers are 184 ± 2 kJ/mol for PCB 95, 189 ± 4 kJ/mol for PCB 132, and 184 ± 1 kJ/mol for PCB 149 at 300°C. The rotational barrier ΔG† (T) of tetrachloro-ortho-substituted PCB 136 is at least (or higher than) 210 kJ/mol at 320°C. Chirality 10:425-429, 1998. © 1998 Wiley-Liss, Inc.
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  • 19
    ISSN: 0899-0042
    Keywords: chiral CE ; maltooligosaccharides ; cellooligosaccharides ; cis-diltiazem ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Twelve different disaccharides and a series of noncyclic malto- and cello-oligosaccharides were used as chiral selectors in capillary electrophoresis (CE). Most saccharides resolved the enantiomers of atropisomeric 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (BDHP) depending on the type (α or β) and position of the linkage between monosaccharides. The effect of chain length of malto- and cello-oligosaccharides on enantioseparation of BDHP was also investigated. The nature of cations in background electrolytes affected significantly the separation of BDHP enantiomers. Chirality 10:134-139, 1998. © 1998 Wiley-Liss,Inc.
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  • 20
    ISSN: 0899-0042
    Keywords: salbutamol ; chiral separation ; validated assay ; fluorescence detection ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A sensitive enantioselective high-performance chromatographic (HPLC) method was developed and validated to determine low levels of (-)-R and (+)-S-albuterol in plasma. Baseline resolution was achieved by using a teicoplanin-based chiral stationary phase with a polar organic mobile phase consisting of methanol/acetonitrile/glacial acetic acid/diethylamine, 40:60:0.3:0.2, (v/v/v/v) and a flow-rate of 1.0 ml/min. Enantioselectivity (α) equaled 1.18 and resolution (Rs) equaled 1.8. By using fluorescence detection maximized at 230 and 310 nm for excitation and emission, respectively, concentrations of each enantiomer could be measured down to 125 pg/ml from a 1-ml plasma sample. Initially, the method was applied to plasma samples from a small single-dose inhalation study of racemic albuterol in a human volunteer and, later, to in vivo samples from a canine inhalation study of the single enantiomer, (-)-R-albuterol. Results from the canine study showed that no chiral inversion of (-)-R-albuterol occurs in the dog. Chirality 10:484-491, 1998. © 1998 Wiley-Liss, Inc.
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  • 21
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    Chirality 10 (1998), S. 499-504 
    ISSN: 0899-0042
    Keywords: enantioselective capillary gas chromatography ; cyclodextrin derivatives ; stereochemistry of terpenes ; monoterpenes ; essential oils ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Capillary gas chromatography employing the unique selectivities of specifically substituted cyclodextrins is highly suited for stereochemical investigations of terpenoid compounds. The analysis of many essential oils have shown that monoterpene derivatives regularly occur as enantiomeric mixtures. In the case of sesquiterpene hydrocarbons, liverworts (Hepaticae) and other lower organisms usually biosynthesize compounds of opposite stereochemistry as compared to higher plants and enantiomeric mixtures occur only occasionally. The investigation of diterpene hydrocarbons has so far shown no indication of the presence of both enantiomers in the same plant. Chirality 10:499-504, 1998. © 1998 Wiley-Liss, Inc.
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  • 22
    ISSN: 0899-0042
    Keywords: chloroquine ; enantiomers ; synthesis ; pyroglutamic acid ; ferriprotoporphyrin IX ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chloroquine (CQ) enantiomers were prepared by a novel synthesis starting from either (S)- or (R)-pyroglutamic acid. Light-absorption spectra of CQ and of complexes of ferriprotoporphyrin IX (FP) with CQ were measured in dilute aqueous solutions at pH 7.3 and 11.3. Spectrophotometric titrations at these pH values indicated a mole ratio of FP:CQ of 2:1 for the FP-CQ aggregated complexes. Aqueous solutions of each of the CQ enantiomers (pH 7.3) and of their complexes with FP (pH 11.3) were investigated by circular dichroism (CD). At pH 11.3, the complexes of the two enantiomers showed CD-band extrema of opposite sign at 409-410 nm. CD-titrations at pH 11.3 confirmed a predominant mole ratio of FP:CQ of 2:1 in the complex. The possible origin of the optical activity of the FP-CQ complexes is discussed. Chirality 10:556-563, 1998. © 1998 Wiley-Liss, Inc.
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  • 23
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    Chirality 10 (1998), S. 587-591 
    ISSN: 0899-0042
    Keywords: snuff ; chewing tobacco ; Turkish tobacco ; Burley tobacco ; Virginia tobacco ; transdermal patches ; gum ; nasal spray ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric composition of nicotine in 18 smokeless tobaccos, 3 strains of tobacco leaf, 8 pharmaceutical products, and 4 commercial reagents was determined. The relative amount of the minor enantiomeric component, (R)-(+)-nicotine, ranged from ∼0.1% to ∼1.2% of the total nicotine in all samples. In some cases it appears that (R)-(+)-nicotine may be considered one of the five most common alkaloids in tobacco products. The highest level of (R)-(+)-nicotine was found in a commercial transdermal patch. The extraction and purification processes used in obtaining commercial (S)-(-)-nicotine supplies from tobacco do not appear to decrease the amount of (R)-(+)-nicotine present. Chirality 10:587-591, 1998. © 1998 Wiley-Liss, Inc.
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  • 24
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    Chirality 10 (1998), S. 747-753 
    ISSN: 0899-0042
    Keywords: pantoprazole ; proton pump inhibitor ; chiral inversion ; stereoselective pharmacokinetics ; rats ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (±)-Pantoprazole ((±)-PAN), (±)-5-(difluoromethoxy)-2-[[(3.4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole is a chiral sulfoxide that is used clinically as a racemic mixture. The disposition kinetics of (+)-PAN and (-)-PAN given separately has been studied in rats. Serum levels of (+)- and (-)-PAN and its metabolites, pantoprazole sulfone (PAN-SO2), pantoprazole sulfide (PAN-S), 4′-O-demethyl pantoprazole sulfone (DMPAN-SO2), and 4′-O-demethyl pantoprazole sulfide (DMPAN-S) were measured by HPLC. Following single intravenous or oral administration, both enantiomers were rapidly absorbed and metabolized, resulting in similar serum concentrations, suggesting that the two enantiomers have approximately the same disposition kinetics. The major metabolite of both (+)- and (-)-PAN was PAN-SO2, while DMPAN-SO2 was also detected as a minor metabolite. Serum levels of PAN-S and DMPAN-S could not be quantified after intravenous or oral administration of either enantiomer.Significant chiral inversion occurred after intravenous and oral administration of (+)-PAN. The AUCs of (-)-PAN after intravenous and oral dosing of (+)-PAN were 36.3 and 28.1%, respectively of those of total [(+) + (-)] PAN. In contrast, the serum levels of (+)-PAN were below quantitation limits after intravenous or oral administration of (-)-PAN. Therefore, chiral inversion was observed only after administration of (+)-PAN, supporting the hypothesis that stereoselective inversion from (+)-PAN to (-)-PAN occurs in rats. Chirality 10:747-753, 1998. © 1998 Wiley-Liss, Inc.
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  • 25
    ISSN: 0899-0042
    Keywords: optically active oxiranes ; liquid crystals ; epichlorohydrin ; glycidol ; chiral HPLC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of racemic and optically active oxiranes, bearing mesogenic groups, precursors of liquid crystalline polyethers, has been synthesized from epichlorohydrin or glycidol. The enantiomeric excess of the optically active oxiranes has been determined by chiral stationary phase HPLC. Compounds bearing 4-cyanobiphenyl mesogenic group exhibit monotropic liquid crystalline behavior. A transfer of chirality to the mesophase has been observed for the optically active oxiranes, which present a cholesteric phase. Chirality 10:779-785, 1998. © 1998 Wiley-Liss, Inc.
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  • 26
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    Chirality 10 (1998), S. 28-34 
    ISSN: 0899-0042
    Keywords: collagen ; nuclear magnetic resonance (NMR) ; nuclear Overhauser effect (NOE) ; stereospecific assignment ; triple-helix ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved model-based method for the stereospecific assignment of prochiral centers in collagen-like triple-helical molecules is introduced. Using the concepts of reporter atoms and of ensemble NOEs, the proposed methodology extracts the stereochemical information contained in the chiral elements of triple-helices and transfers it to prochiral centers with nondegenerate proton resonances. The improved approach has been successfully validated using -(Gly-Pro-Hyp)n- triple-helices for which the stereospecific assignment was previously obtained with established techniques. We have applied our stereochemical characterization to novel peptoid containing triple-helices for which existing methods of stereospecific assignment can not be used for all the prochiral centers. In our approach, several different NOE measurements are employed to make a given stereospecific assignment. The multiple NOE comparisons allow internal cross checks, which reduce the chance of erroneous assignments caused by experimental artifacts including spin diffusion and bias from anisotropic rotational motions. In addition, the multiple NOE comparisons are useful in overcoming problems associated with resonance overlap often encountered in the 1H-NMR spectra of collagen-like molecules. Our stereochemical analysis is anticipated to improve the precision and accuracy of the characterization of collagen-like triple-helices through a better correlation of structures with their 1H-NMR spectra. Chirality 10:28-34, 1998. © 1998 Wiley-Liss, Inc.
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  • 27
    ISSN: 0899-0042
    Keywords: polymers ; polyisocyanates ; helical conformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A class of polymers synthesized at DuPont in the late 1950's, the polyisocyanates, are the simplest analogs of the Nylons and have proven valuable as experimental models for theories of wormlike macromolecules. The macromolecular dimensional properties associated with all wormlike polymers arise from a strongly preferred local conformation of the chain and in the polyisocyanates this conformation is helical with an interesting additional property in that the mirror helical senses are of equal probability. Recent experiments have shown that discrimination between the helical senses can be accomplished with surprisingly small chiral influences indicating high cooperativity which arises from a conformational state in which long sections of one helical sense are separated from the other sense by infrequent helical reversals. This can be seen to be analogous to theoretical ideas about one-dimensional paramagnetic materials in which the spin states and the domain boundaries are analogs to the helical sense and the helical reversals in the polyisocyanates. The mathematical formalisms of the one-dimensional magnetic materials precisely describe the chiral properties of the polyisocyanates. Chirality 10:41-45, 1998. © 1998 Wiley-Liss,Inc.
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  • 28
    ISSN: 0899-0042
    Keywords: amylose ; 3,5-dimethylphenyl-carbamate ; polysaccharide phase ; tert-butyl 2-tert-butyl-4-methoxy-2,5-dihydro-1,3-imidazole-1-carboxylate; amino acid ester synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparative separation of the enantiomers of the title compound, a versatile chiral building block for the synthesis of unnatural amino acid esters, by high performance liquid chromatography on a chiral stationary phase (CSP), is reported for the first time. The CSP consists of amylose-(3,5-dimethylphenyl-carbamate), which has been coated onto the surface of macroporous aminopropyl-functionalized silica gel. The effect of mobile phase composition and the amount of amylose derivative on the silica gel has been thoroughly investigated. Using 2-propanol as organic modifier in hexane as mobile phase, on a semi-preparative column (200 mm × 40 mm ID, containing 192 g of stationary phase) about 200 mg of the racemate was separated per injection. Running the equipment under automatic conditions with repetitive injection mode allowed for the separation of 30 g per day. Both enantiomers were obtained with enantiopurities 〉99.75:0.25. Chirality 10:217-222, 1998. © 1998 Wiley-Liss, Inc.
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  • 29
    ISSN: 0899-0042
    Keywords: deuterium labelling ; menthocitronellol ; citronellol ; enantioselective multidimensional gas chromatography-mass spectrometry (enantio-MDGC-MS) ; dynamic headspace analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mechanistic aspects of the biogenesis of the chiral monoterpenoid rose oxide in Pelargonium graveolens L'Héritier are investigated using deuterium-labelled precursors. After administration of the precursors using the cut-stem method, the dynamic headspace extracts of the plants are analysed using multidimensional gas chromatography-mass spectrometry (enantio-MDGC-MS). It is unequivocally shown that this plant is able to convert citronellol and menthocitronellol into cis-/trans-rose oxide. Menthocitronellol is converted into rose oxide with a clearly detectable enantiodiscrimination. These facts may be explained with the presence of an oxidase, which is able to oxidize citronellol and menthocitronellol in allylic position. A photooxygenation mechanism including singlet oxygen as the oxidizing agent is rather unlikely. Chirality 10:229-237, 1998. © 1998 Wiley-Liss, Inc.
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  • 30
    Electronic Resource
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    Chirality 10 (1998), S. 238-245 
    ISSN: 0899-0042
    Keywords: chiral selectivity ; amino acid crystallization ; molecular recognition ; stochastic kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of chirally selective interaction in the stirred crystallization of glutamic acid and lysine is presented. The crystallization of S-glutamic acid is influenced by the presence of S-lysine but not R-lysine. Crystal nuclei in stirred systems are produced due to secondary nucleation. Secondary nucleation is an autocatalytic process in which a crystal produces secondary nuclei due to fluid motion, and due to crystal stirrer and crystal-crystal collisions. As a result of this autocatalysis, small fluctuations in the nucleation rates are amplified and the kinetics show a marked stochastic behavior. We investigate the stochastic behavior in detail and propose a kinetic mechanism that explains both the increase and the statistical distribution of the crystallization times of S-glutamic acid due to the presence of S-Lysine. Chirality 10:238-245, 1998. © 1998 Wiley-Liss, Inc.
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  • 31
    ISSN: 0899-0042
    Keywords: chiral separation ; chiral selector ; separation of enantiomers ; liquid chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral stationary phase (CSP 1) prepared starting from (R)-4-hydroxyphenylglycine and then grafting (R)-N-butanoyl-4-allyloxyphenylglycine N-propyl amide to silica gel was found to be very effective in separating the enantiomers of N-(3,5-dinitrobenzoyl)-α-amino amides. From the chromatographic behaviors of the resolution of N-propyl amides, N,N-diethyl amides and ethyl esters of N-(3,5-dinitrobenzoyl)-α-amino acids and the resolution of various N-(substituted benzoyl)leucine N-propyl amides, the hydrogen bonding and the π-π donor-acceptor sites of the analyte for the interaction with the CSP have been proposed. Similarly, the hydrogen bonding donor and acceptor sites of the CSP for the interaction with the analyte have been proposed from the comparison of the chromatographic behaviors of the resolution of various N-(3,5-dinitrobenzoyl)-α-amino N-propyl amides on modified CSPs (CSP 7 containing trifluoroacetyl group instead of the butanoyl group of CSP 1 and CSP 8 containing N,N-diethyl group instead of the N-propyl group of CSP 1) with those on CSP 1. By correlating the interaction sites of the CSP and their complementary interaction sites of the analyte, a chiral recognition mechanism which utilizes the two hydrogen bonding interactions and the π-π donor-acceptor interaction between (R)-CSP 1 and more retained analytes, (S)-N-(3,5-dinitrobenzoyl)-α-amino amides, has been proposed. Chirality 10:592-599, 1998. © 1998 Wiley-Liss, Inc.
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  • 32
    ISSN: 0899-0042
    Keywords: configurational stability ; pH ; temperature ; ionic strength ; phosphate buffer concentration ; plasma protein affinity ; native cyclodextrins ; cyclodextrin derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational stability of (+)- and (-)-diethylpropion [(+)- and (-)-2-(diethyl)-1-phenyl-1-propanone or (+)- and (-)-DEP] was investigated systematically from chemical, pharmaceutical, and pharmacological aspects. The enantiomeric ratio was monitored directly with a recently developed stability-indicating enantioselective HPLC method.In aqueous solutions, the rate of racemization increased non-linearly with increasing pH and with increasing phosphate buffer concentration. The racemization rate showed a positive slope with increasing temperature and decreasing ionic strength.The racemization rates of (+)- and (-)-DEP in the presence of cyclodextrins (CDs) did not differ significantly. CDs that were added to (+)- and (-)-DEP in a molar ratio 5:1 showed the following effects after dissolution in 10 mM phosphate buffer (final pH 6.7): sulfobutyl ether-β-CD (SBE-β-CD) and methylated-β-CD (Me-β-CD) retarded racemization; whereas hydroxypropyl-β-CD (HP-β-CD), acetyl-γ-CD (Ac-γ-CD), acetyl-β-CD (Ac-β-CD), γ-CD, and β-CD showed a weak destabilising effect. In contrast to the described CDs, α-CD distinctly accelerated the rate of racemization.The configurational stability of (+)- and (-)-DEP was also studied under physiological conditions. The half-life of racemization in heparinised human plasma was for both enantiomers determined to be approximately 23-25 min.In phosphate buffer (10 mM, pH 7.4), rac-DEP showed a high, but unselective affinity towards human α1-acid glycoprotein (orosomucoid) immobilised on silica (Chiral AGP).The rate of racemization of the free base of (-)-DEP dissolved in organic solutions generally increases with the polarity of the solvating agent. Chirality 10:307-315, 1998. © 1998 Wiley-Liss, Inc.
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  • 33
    Electronic Resource
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    Chirality 10 (1998), S. 661-666 
    ISSN: 0899-0042
    Keywords: chiral dendrimers ; dendrimers ; axial chirality ; (R)-(+)-1,1′-bi-2,2′-naphthol ; optical rotation ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and optical activity of novel chiral dendrimers with axial chirality are reported. The dendrimers were constructed by coupling of the polyether dendritic bromides with (R)-(+)-1,1′-bi-2-naphthol (1). The uniform (2, 3, 4) and non-uniform double-O-alkylated (8, 9, 10) as well as mono-O-alkylated (5, 6, 7) products were thus obtained. These chiral molecules were characterized by 1H- and 13C-NMR, elemental analysis, optical rotation, adsorption spectra, and circular dichroism. It was found that the specific rotation decreases with the increase of the number of generation for each group of dendrimers (2-4, 5-7, and 8-10, respectively). In terms of the molar rotation, it was quite different; the molar rotation increased sharply for dendrimers, 2-4, but only slightly for dendrimers 5-7. The dihedral angle change of bi-naphthyl in the synthesized dendrimers was discussed based on the CD spectra. Chirality 10:661-666, 1998. © 1998 Wiley-Liss, Inc.
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  • 34
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    Chirality 10 (1998), S. 325-337 
    ISSN: 0899-0042
    Keywords: diastereomeric salts ; molecular recognition ; hydrogen bonding ; thermal analysis ; crystallography ; solubility ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (+)-(1S;2S)-Pseudoephedrine and racemic mandelic acid form three distinct diastereomeric salts from solutions in 95% ethanol. The least-soluble phase, a hemihydrate, contains the (2R)-mandelate. A salt phase of intermediate solubility is the unsolvated double salt, containing both the (2R)- and the (2S)-mandelate. The most-soluble salt phase contains the (2S)-mandelate. Mandelate configuration and order of solubility (based on the heats of fusion) is inverted from that found in the same system synthesized from chiral base and acid, and then crystallized from benzene solution. The (2R)-mandelate hemihydrate (-H2O at 349.5K, mp 391K), monoclinic, P21, a = 6.788(5), b = 29.415(35), c = 9.488(10)Å, β = 108.91(8)°, Z = 4 (2 ion-pairs/asymmetric unit). Intermediate double salt (2S)- and (2R)-mandelate, mp 377.6K, anorthic, P1, a = 7.758(4), b = 9.966(5), c = 13.366(6)Å, α = 72.99(4), β = 79.98(4), γ = 70.51(4)°, Z = 1 (2 ion-pairs/asymmetric unit). The (2S)-mandelate (mp 386.2K), orthorhombic, P212121, a = 7.079(6), b = 13.443(10), c = 18.820(14)Å, Z = 4 is identical to a salt made from a combination of enantiomeric moieties from benzene solution. While differing from ephedrine mandelates in configuration at one center, solubilities of pseudoephedrine mandelates in 95% ethanol are much larger. A comparison of molecular structure (non-polar and H-bonding) regions of pseudoephedrine and ephedrine mandelates shows similarities and differences that are tentatively linked to crystal properties. This study reemphasizes the necessity for consistency in solvent use in resolution and in phase identification and comparison because the phases produced are frequently dependent upon the solvent. Chirality 10:325-337, 1998. © 1998 Wiley-Liss, Inc.
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  • 35
    ISSN: 0899-0042
    Keywords: additive ; selectivity ; efficiency ; modifier ; subcritical fluid chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Subcritical fluid chromatography (SubFC) using a carbon dioxide-methanol mobile phase is used for the chiral resolution of IIb/IIIa receptor antagonist enantiomers. The chiral resolution of three analogs, each containing two chiral centers, is optimized using various mobile phase additives. The effects that acidic, basic, and neutral additives have on retention, efficiency, and resolution are examined. The additive that gives the best resolution was found to be dependent upon the functionality and charge of the chiral analyte. For charged analytes, additives that act as competing ions of the same charge as the chiral analyte dramatically improve efficiency and resolution. Resolution of neutral chiral analyte enantiomers is also greatly affected by the choice of mobile phase additive. Chirality 10:338-342, 1998. © 1998 Wiley-Liss, Inc.
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  • 36
    ISSN: 0899-0042
    Keywords: optically active ; epichlorohydrin ; 3-chloro-1,2-propanediol ; microbial resolution ; dehalogenation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Production of highly optically active C3 and C4 chlorohydrins was developed by using the bacteria stereoselectively dehalogenating and assimilating the racemic substrate: Pseudomonas sp. and Alcaligenes sp. These bacteria stereoselectively assimilate (RS)-2,3-dichloro-1-propanol (DCP) and (RS)-3-chloro-1,2-propanediol (CPD) followed by microbial preparation of (R)- and (S)-DCP, and (R)- and (S)-CPD with 〉99% ee. A novel dehalogenating enzyme, halohydrin dehydro-dehalogenase from one of the above strains, Alcaligenes sp. DS-S-7G, was applicable for preparation of optically active 1,2-diols with 60-99% ee. Moreover, microbial resolution of C4 chlorohydrins with whole cells of Pseudomonas sp. was carried out. This resolution reaction using the resting cells gave (R)- and (S)-4-chloro-3-hydroxybutyrate (CHB) and (S)-4-chloro-3-hydroxybutyronitrile (BN) with 〉98% ee. In the case of the resting cells of Enterobacter sp., both (R)-CHB (〉99% ee) and (S)-3-hydroxy-γ-butyrolactone (95% ee) with excellent yield were obtained. Also, some typical synthetic applications using the above chiral C3 and C4 synthons were introduced: ferroelectric liquid crystals, optically active β-blockers, and other chiral pharmaceuticals. Chirality 10:682-692, 1998. © 1998 Wiley-Liss, Inc.
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  • 37
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    Chirality 10 (1998), S. 180-189 
    ISSN: 0899-0042
    Keywords: hypercoordinate silicon in naphthylsilanes ; X-ray structures ; NMR spectra ; reinterpretation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hexacoordinate silicon has been claimed to occur in bis(8-dimethylamino-naphth-1-yl)silanes on the basis of X-ray data and NMR spectra. Very much the same effects are shown by a bis(8-dimethylamino-naphth-1-yl)carbinol, pointing to essentially the same bonding in the Si and C compounds. Faced with the choice that either the carbon in the carbinol is hexacoordinate, too, or that the silicon in the silanes is, in fact, tetracovalent, we prefer the latter conclusion. Chirality 10:180-189, 1998. © 1998 Wiley-Liss, Inc.
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  • 38
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    Chirality 10 (1998), S. 190-193 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 39
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    Chirality 10 (1998), S. 169-172 
    ISSN: 0899-0042
    Keywords: stereochemistry ; chirality ; circular dichroism ; isoquinoline ; enantiomers ; alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Circular dichroism (CD) spectra were determined for the bioactive (+)-enantiomers of 1 · HCl, 3 · HCl, and 4 · HBr to characterize the chiroptical properties of these pyrroloisoquinoline antidepressants. The compounds showed a low-intensity negative CD band with much fine structure between 252 and 272 nm, a medium negative CD band with fine structure between 215 and 225 nm, and a high-intensity negative CD maximum between 198 and 203 nm. Except for amplitude variation, the three CD spectra were essentially superimposable in sign and position of the bands. The CD curves for the (-)-enantiomers of 1 · HCl and 4 · HBr were opposite in sign and comparable within 5% to the (+)-enantiomers. The results are consistent with the previously assigned (Maryanoff et al. J. Med. Chem. 30:1433-1454, 1987) absolute configurations of (6S, 10bR) for 1 and 3, and (6R, 10bR) for 4. Chirality 10:169-172, 1998. © 1998 Wiley-Liss, Inc.
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  • 40
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    Chirality 10 (1998), S. 147-153 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the chiral 9,12-dimethyl-4-oxa[7]paracyclophane 3 was achieved by the dithia route with subsequent sulfone pyrolysis. The conformational flexibility of the oxamethylene bridge with local Cs symmetry is evident from low temperature NMR experiments. Experimentally, an activation enthalpy of 11.4 kcal/mol is found for this process, which is in good agreement with the rotational barrier derived from semiempirical AM1 calculations (10.2 kcal/mol). Ab initio Hartree-Fock geometry optimizations have been performed for 3 and the corresponding hydrocarbon 9,12-dimethyl[7]paracyclophane 4. The distance of the O-atom to the center of the benzene ring in the structure of 3 is only 2.784 Å, i.e., significantly closer than the analogous C4-benzene ring distance in the slightly more strained 4 (3.112 Å). The enantiomeric separation of (±3) has been achieved by HPLC and the circular dichroism (CD) spectrum is reported. Ab initio all-electron DFT/SCI calculations of the CD spectrum are in good agreement with the experimental data and reveal the importance of p(O-atom)→ π* charge-transfer type excited states at relative low energies (6.6 eV, 188 nm) responsible for an intense negative CD band. The benzene type π → π* states are energetically lowered by 0.4-0.8 eV due to the boat-type deformation of the benzene moiety. By comparison of theoretical and experimental CD data the absolute configuration of 3 is assigned as (-)-(S). Chirality 10:147-153, 1998. © 1998 Wiley-Liss, Inc.
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  • 41
    ISSN: 0899-0042
    Keywords: capillary electrophoresis ; enantiomer separation ; chiral drugs ; γ-cyclodextrin ; gamma-cylcodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Following an extended chiral drug screening program by capillary zone electrophoresis (CZE), the enantioseparation of 86 racemic drugs was tested with γ-cyclodextrin as a chiral solvating agent. Unified conditions were applied to all experiments. In total, 18 drug racemates were separated, 13 entries thereof that had not been separated at the lower CSA concentration applied in an earlier stage of the project. A comparison of the data with the results obtained for α- and β-cyclodextrin points to the significance of partial penetration (“side-on binding”) of aryl groups into the cyclodextrin cavity. Chirality 10:548-554, 1998. © 1998 Wiley-Liss, Inc.
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  • 42
    ISSN: 0899-0042
    Keywords: asymmetric hydrogenation ; aminophosphine phosphinites ; rhodium complexes ; dehydro aminophosphonic acids ; NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral α-aminophosphonic acid derivatives are efficiently synthesized by asymmetric hydrogenation of the prochiral N-acyl-α,β-dehydroaminophosphonates. PROPRAPHOS-Rh-catalysts from readily available (S)- and (R)-Propranolol proved to be suitable in the homogenous reaction affording an enantiomeric excess of 87-92% with high rate. The aminophosphonic acid derivatives and precursors were fully characterized by 1H, 13C, and 31P NMR spectroscopy. Chirality 10:564-572, 1998. © 1998 Wiley-Liss, Inc.
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  • 43
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    Chirality 10 (1998), S. 578-586 
    ISSN: 0899-0042
    Keywords: bark beetle pheromone ; drugstore beetle pheromone ; enantioselective synthesis ; frontalin ; stegobinone ; stereochemistry-pheromone activity relationships ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective synthesis is a central component of research on the effect of chirality on the relationships between pheromone structure and pheromone bioactivity. The syntheses of stegobinone, the drugstore beetle pheromone, and frontalin, a bark beetle pheromone, are reported as examples of stereocontrolled synthesis. Chirality governs the biodiversity of pheromone perception, as illustrated by the discussion on the relationships between absolute configuration and pheromone activity. Chirality 10:578-586, 1998. © 1998 Wiley-Liss, Inc.
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  • 44
    ISSN: 0899-0042
    Keywords: hexahelicene ; sulphoxides ; carbohydrate carbamate ; chiral preparative ; silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparative enantiomeric resolutions of hexahelicen-7-yl acetic acid methyl ester and two sulphoxides were performed on cellulose tris(3,5-dimethylphenylcarbamate) coated onto aminopropylated 5-μm silica with 120-Å diameter pore. High enantiomeric purity was obtained for both enantiomers. The enantioselectivity of the amylose tris(3,5-dimethylphenylcarbamate), cellulose and amylose tris(phenylcarbamate) phases for the hexahelicen-7-yl acetic acid derivative were also investigated. Chirality 10:573-577, 1998. © 1998 Wiley-Liss, Inc.
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  • 45
    ISSN: 0899-0042
    Keywords: calcium antagonist ; stereoselective analytical method ; isradipine enantiomers ; Chiral OJ ; HPLC ; GC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: rac-Isradipine is a dihydropyridine type calcium antagonist. Its calcium entry blocking effect is due primarily to the (+)-(S)-enantiomer. This study describes a sensitive enantioselective method for the determination of isradipine in human serum. Following alkaline extraction into hexane, the enantiomers of isradipine are separated quantitatively by high-performance liquid chromatography on a Chiralcel OJ column at 39°C. The collected fractions were evaporated and assayed using capillary gas chromatography on a HP 50+ column with nitrogen selective detection. Using 2.0 ml of serum, 0.7 nmol/1 (0.26 ng/ml) of each enantiomer could be determined with acceptable precision. The method has successfully been used to measure (+)-(S)- and (-)-(R)-isradipine concentrations in samples from volunteers after intravenous and oral administration of isradipine. Chirality 10:808-812, 1998. © 1998 Wiley-Liss, Inc.
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  • 46
    ISSN: 0899-0042
    Keywords: quinuclidine derivatives ; chromatographic separation ; borane complexes ; fractional crystallization ; resolution ; X-ray crystallography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The four stereoisomers of the antimuscarinic 3-(2,3-dihydrobenzofuran-2-yl)quinuclidine have been prepared by a method involving chromatographic separation of the racemic diastereoisomers as borane complexes. The relative and absolute configurations of the stereoisomers were determined by X-ray crystallographic methods. The crystal structure of (2′R,3R)-3-(2,3-dihydrobenzofuran-2-yl)quinuclidine · HCl · H2O contains two independent molecules with different conformations of both the quinuclidine moiety and the dihydrofuran ring. Chirality 10:813-820, 1998. © 1998 Wiley-Liss, Inc.
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  • 47
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    Chirality 10 (1998), S. 1-2 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 48
    ISSN: 0899-0042
    Keywords: α-hydroxy acids ; chiral stationary phases ; enantiomer resolution ; copper ternary complexes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct separation of several α-hydroxy acid racemic mixtures was performed by the aid of ligand exchange chromatography using L-hydroxyproline chemically bound to silica stationary phase and aqueous solutions of copper (II) sulphate as a mobile phase. The elution order of the D- and L-enantiomers of α-hydroxy acids is interpreted in terms of a modified Davankov's rule. Several aspects of the Davankov's model of selectand-Cu(II)-selector ternary complexes are discussed based on the theoretical calculations within the quantum mechanical semiempirical and density functional theories. Chirality 10:821-830, 1998. © 1998 Wiley-Liss, Inc.
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  • 49
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    Chirality 10 (1998), S. 3-7 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 50
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 8-13 
    ISSN: 0899-0042
    Keywords: stereochemistry ; ion channel proteins ; nAChR ; K+ channels ; subunit arrangement ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of ion channel proteins present many special challenges, including the potential for novel stereochemical phenomena. Here we describe several examples in which modern studies of ion channels have involved or made use of stereochemistry. Chirality 10:8-13, 1998. © 1998 Wiley-Liss, Inc.
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  • 51
    ISSN: 0899-0042
    Keywords: direct chiral separation ; mobile phase composition ; NSAIDs ; retention model ; vancomycin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fused silica-packed capillary columns containing vancomycin immobilized by reductive amination on an aldehyde-silica were used to separate enantiomers of some non-steroidal anti-inflammatory drugs. Attempts have been made to qualitatively explain the influence of various mobile phase compositions on the enantioselective retention. The effects of mobile phase pH, buffer, and organic modifier concentrations were investigated as well as the influence of salts of hydrophobic ions added to the mobile phase to induce ion pair retention. Chirality 10:273-280, 1998. © 1998 Wiley-Liss, Inc.
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  • 52
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 262-272 
    ISSN: 0899-0042
    Keywords: airway ; beta2-agonist ; racemic ; eutomer ; distomer ; hyperreactivity ; bronchospasm ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Airways of asthma patients can become hyperresponsive to airway spasmogens following regular use of isoprenaline or β2-selective sympathomimetics. Hyperreactivity that results from acute exposure of animals to these drugs is pre-empted by vagal section (a procedure which does not influence spasmolytic efficacy of sympathomimetics), is not diminished by antagonism of β2-adrenoceptors and is not associated with loss of responsivity of β2-adrenoceptors in the airways. Since activation, modulation, or blockade of β2-adrenoceptors does not determine this form of hyperreactivity, the possibility that distomers may induce hyperreactivity must be considered. Ocular and vascular responses to distomers of sympathomimetics have long been recognised and, more recently, comparable observations have been made for the airways. Thus, reactivity of guinea-pig airways to spasmogens was increased following exposure to S-isoprenaline, S-salbutamol, or S-terbutaline and exposure to S-isoprenaline or S-salbutamol can intensify symptoms in asthmatics. Regular exposure to the racemate, especially during or following an allergic reaction, predisposes to expression of hyperreactivity, which is nullified, acutely, by the eutomer. These observations imply that biological effects of sympathomimetic distomers may contribute to morbidity and mortality in asthma patients. Chirality 10:262-272, 1998. © 1998 Wiley-Liss, Inc.
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  • 53
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 600-618 
    ISSN: 0899-0042
    Keywords: steroidal bile acids ; inclusion compounds ; crystal structures ; facial molecules ; amphiphilic molecules ; amphiphilic sheets ; hydrogen-bonding networks ; head-to-tail ; head-to-head ; tail-to-tail ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral compounds, N-methyl-, N-ethyl-, and N-n-propylcholamides, form crystalline inclusion compounds with water or small organic substances. The compounds were analyzed by X-ray diffraction methods. It was found that the crystals have bilayered structures accumulated by chiral molecular sheets. The chiral molecules associate in a unique head-to-head/tail-to-tail and right-to-left motif to give chiral and amphiphilic sheets. Such sheets stack by adhesions between the hydrophilic sides and between the lipophilic sides. The alkyl groups of the amides prompt the formation of a hydrogen-bonding network between the tails instead of a cyclic one between the head and tail. The guest molecules are accommodated into small cavities between the steroidal side chains. Chirality 10:600-618, 1998. © 1998 Wiley-Liss, Inc.
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  • 54
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 693-698 
    ISSN: 0899-0042
    Keywords: Pseudomonas cepacia ; lipase PS ; transesterification ; kinetic resolution ; 2-substituted 3-hydroxy ester ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic resolution of 2-substituted 3-hydroxy esters was examined by lipase PS catalyzed transesterification using vinyl acetate as an acyl donor. Resolution of (±)-syn- and -anti-1a, -1e possessing a small methyl group at the C-3 position was accomplished enantioselectively. The outcome of the resolution seems to be related to the differences in size of the substituents at the stereocenter bearing a secondary hydroxy group. Chirality 10:693-698, 1998. © 1998 Wiley-Liss, Inc.
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  • 55
    ISSN: 0899-0042
    Keywords: preferential enrichment ; enantiomeric enrichment ; mixed crystal ; solid solution ; racemic compound crystals ; X-ray crystallography ; chiral ammonium sulfonate ; reversal of chirality ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal structure of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl]dimethylammonium p-nitrobenzenesulfonate [(±)-NNMe2], which shows the novel enantiomeric resolution phenomenon Preferential Enrichment, has been compared with that of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy) phenylcarbamoyl]ethyl]dimethylammonium p-toluenesulfonate [(±)-NTMe2], which does not show the phenomenon. The stable crystalline form of (±)-NNMe2 is a racemic compound, while that of (±)-NTMe2 is a mixed (disordered) crystal composed of the two enantiomers. The intermolecular hydrogen bonding mode in the crystal of (±)-NNMe2 was very different from that of (±)-NTMe2. Chirality 10:705-710, 1998. © 1998 Wiley-Liss, Inc.
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  • 56
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 699-704 
    ISSN: 0899-0042
    Keywords: ormeloxifene ; chiral separation ; sulfated cyclodextrin ; enantiomers ; capillary electrophoresis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (-)-Ormeloxifene, a drug candidate under development, was separated from (+)-ormeloxifene using capillary electrophoresis (CE) with sulfated β-cyclodextrin as chiral buffer additive. With conventional long-end injection the method showed high efficiency, since the theoretical plate number for (-)-ormeloxifene was over 1 million per m and the enantiomeric resolution was more than 100. However, the relatively long separation time of ∼22 min was a limiting factor. In order to reduce separation time, short-end injection experiments were carried out. By using the instrumental limits for capillary dimensions and field strength, the separation time was reduced to 〈40 sec. A further and significant reduction was achieved by applying extended short-end injection, which is a novel injection technique presented in this paper. With the extended short-end injection procedure, a plug of run buffer is injected after the sample has been injected, thus moving the sample closer to the detector and resulting in very short effective capillary lengths. Using the extended short-end injection technique, the separation was performed on 1.8 cm capillary (effective length) and the enantiomers were separated within 10 sec, which is a reduction of the original separation time by a factor of ∼155. Chirality 10:699-704, 1998. © 1998 Wiley-Liss, Inc.
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  • 57
    ISSN: 0899-0042
    Keywords: zirconium ; binaphthol (BINOL) ; allylation ; asymmetric activation ; enantioselective carbon-carbon bond formation ; chiral high-performance liquid chromatography ; induction period ; product-like activator ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The asymmetric activation of binaphthol (BINOL)-zirconium catalysts is described on the enantioselective allylation of benzaldehyde with allyltin reagents. This model reaction has been used with the intention of establishing a protocol for a zirconium-based catalyst system, to be followed by structural studies. Initial results are reported that characterise a number of interesting features, namely the influence of an induction period and a high level of asymmetric activation obtained after addition of a product-like activator. Chirality 10:717-721, 1998. © 1998 Wiley-Liss, Inc.
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  • 58
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 711-716 
    ISSN: 0899-0042
    Keywords: stereospecific polymerization ; chiral α-substituted acrylate ; stereoregularity ; chiroptical property ; isotactic polymer ; regular arrangement ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel chiral monomer, benzyl α-[(1-phenylethoxy)methyl]acrylate was synthesized, and the stereoregularity and chiroptical property of the polymers obtained by radical and anionic polymerizations were investigated. Anionic polymerization in toluene provided a polymer with high isotacticity regardless of optical purity of the monomer and difference of counter cations, Li+ and Mg2+, while radical polymerization appears to yield an atactic polymer. The isotactic copolymers anionically obtained from a mixture of (R)- and (S)-monomers showed peak splitting probably due to the triad arrangement of (R) and (S) groups of side chains in the resonance of 13C-NMR spectra. The isotactic polymer prepared from enantiomerically pure (R)-monomer ([α] 25 365 = +157°) with n-BuLi in toluene exhibited higher specific rotation ([α] 25 365 = +262°) than that of the radical polymer ([α] 25 365 = +162°). This may be explained by regular arrangement of optically active groups along the polymer chain of the isotactic polymer. Chirality 10:711-716, 1998. © 1998 Wiley-Liss, Inc.
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  • 59
    ISSN: 0899-0042
    Keywords: grazing-incidence X-ray diffraction ; topochemical photodimerization ; 4-alkoxycinnamic acid ; 4-alkoxycinnamamide ; 2-D crystallites on water surfaces ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A direct relationship between the structures of two-dimensional (2-D) crystallites of 4-octadecyloxy-E-cinnamic acid and 4-octadecyloxy-E-cinnamamide amphiphiles at the air-water interface and their photochemical behavior, is presented. The detailed packing arrangements of the monolayers were determined, close to the atomic level, from the diffraction pattern measured, in situ on the water surface, by the grazing incidence X-ray diffraction (GID) technique using synchrotron radiation. The products of the photochemical reaction, performed by irradiating the monolayer films directly on the water surface, were collected and analyzed. While the acid crystallites yield a β-truxinic acid product together with the cis-isomer, the amide undergoes only trans-cis isomerisation, in full agreement with the 2-D crystalline packing arrangements of the two amphiphiles on the water surface. Chirality 10:60-65, 1998. © 1998 Wiley-Liss,Inc.
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  • 60
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    Electronic Resource
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    Chirality 10 (1998), S. 66-77 
    ISSN: 0899-0042
    Keywords: logwood ; hematoxylin ; dyes ; crystals ; enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hematoxylin, C16H14O6, from the extract of logwood, crystallizes as a trihydrate with the water molecules inside helical channels. It was the first organic compound used to deliberately stain a salt crystal and as such played a central role in the general development of the subject of dyeing crystals. We discuss this development and, moreover, show that efforts to stain (NH4)H2PO4 crystals with hematoxylin in 1879 provided evidence of enantioselective crystal chemistry recognizable with the unaided eye. What motivated nineteenth century chemists to dye crystals? Why and how was hematoxylin selected as the first colorant, and what were the consequences of this selection? In order to answer these questions, we offer an integrated history of hematoxylin. We trace logwood extract from the height of the Mayan civilization, through the development of the baconian scientific method, during the Atlantic slave trade, and in supramolecular stereochemical associations while dyeing crystals. Along this journey we endeavour to reflect upon the science and conscience of a stereochemist. Chirality 10:66-77, 1998. © Wiley-Liss, Inc.
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  • 61
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 88-90 
    ISSN: 0899-0042
    Keywords: allylic oxidation ; dihydroxylation ; chiral lactam ; chiral indolizidines ; phenyl glycinol ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The concise and highly diastereoselective synthesis of the titles azasugars was accomplished using nonracemic bicyclic lactams. Chirality 10:88-90, 1998. © 1998 Wiley-Liss, Inc.
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  • 62
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 78-87 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: