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  • 1985-1989  (3,492)
  • Organic Chemistry  (3,492)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 2-6 
    ISSN: 0899-0042
    Keywords: optical isomers ; stereochemistry ; enantiomers ; Food and Drug Administration ; drug development ; drug regulation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The current regulatory position of the Food and Drug Administration is discussed with regard to the approval of racemates and pure stereoisomers. Circumstances in which stereochemically sensitive analytical methods are necessay to ensure the safety and efficacy of a drug are described. Regulatory guidelines are interpreted for applications for the approval of a pure enantiomer in which the racemate is marketed, for the approval of eitehr a racemate or a pure enantiomer in which neither is marketed, and for clinical investigations to compare the safety and efficacy of a racemate and its enantiomers. Examples of te basis for such regulation are drawn from historical situations (thalidomide, benoxaprofen) as well as currently marketed drugs (arylproionic acids, disopyramide, indacrinone).
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 10-13 
    ISSN: 0899-0042
    Keywords: (S)-, (R,S)-propranolol ; pharmacokinetic ; human study ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pharmacokinetics of (S)-propranolol were compared after the oral administration of a 40 mg dose of the pure enantiomer and an 80 mg dose of a racemic mixture of (R,S)-propranolol. The results of this study indicate that the bioavailability of (S)-propranolol, as expressed by the mean area uner the concentration-time curve (AUC) and maximum serum concentration, is lower after 40mg of the optically pure drug than after the racemic drug.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 89-91 
    ISSN: 0899-0042
    Keywords: asmmetric induction ; bacterial cell wall ; D-Ala-D-Ala ; dipeptide ; peptidoglycan ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute stereochemical control is employed in the synthesis of isosteres for dipeptide subunits 1; see Fig. (1) in which the amide linkage has been replaced by a trans carbon-caron double bond. The synthesis affords access to the four stereoisomers of 1 in which R and R' = CH3, including the isostere of D-alanine-d-alanine (D-ala-D-Ala), 2.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 7-9 
    ISSN: 0899-0042
    Keywords: substrate enantioselectivity ; product enantioselectivity ; Michaelis-Menten analysis ; intrinsic activity ; potency ; receptor affinity ; efficacy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 178-179 
    ISSN: 0899-0042
    Keywords: CD spectra ; optical rotation ; phthalideisoquinoline base and salts ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The appearance of positive charge on the nitrogen moiety of phthalideisoquinoline alkaloids brings about a strong change in the intensities of CD Cotton effects. Hence the optical rotations of enantiomeric salts and their parent base of identical configuration are often of opposite sign. Thus, the name (+)-bicuculline-methiodide for the methiodide salt of (+)-bicuculline is false.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 170-173 
    ISSN: 0899-0042
    Keywords: phenglutarimide enantiomers ; enantioselectivity ; antiparkinsonian drugs ; M1-selective antagonists ; rabbit vas deferens ; pirenzepine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The affinity of the enantiomers of phenglutarimide at three muscarinic receptor subtypes was examined in vitro using field-stimulated rabbit vas deferens (M1 receptors) and guinea pig atria (M2α receptors) and ileum (M2β receptors). Extremely high stereoselectivity was observed and higher affinities (up to 6000-fold) were found for the (+)-S-enantiomer. The stereoselectivity ratios were different at the three subtypes, and the stereochemical demands made by the muscarinic receptors were most stringent at M1 receptors. (+)-(S)-Phenglutarimide was found to be a potent M1-selective antagonist (pA2 at M1 = 8.53). Its receptor selectivity profile is qualitatively similar to that of pirenzepine. (-)-(R)-Phenglutarimide showed no comparable discriminatory properties.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 174-177 
    ISSN: 0899-0042
    Keywords: pharmacokinetics ; terbutaline ; enantiomers ; human ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Terbutaline is a β2-agonist and administered as the racemic mixture. The pharmacokinetics of the separate enantiomers differ with respect to degree of absorption and clearance. In the present study, repeated doses of racemic terbutaline were given to six healthy volunteers. Plasma was analyzed for the concentrations of the two enantiomers. The observed plasma concentrations at steady state differed from those predicted from the values observed after single dose administration of the separate enantiomers. The difference between the observed and predicted values can be tentatively explained by a combined influence of (-)-terbutaline on the absorption of (+)-terbutaline and the influence of (+)-terbutaline on the elimination of (-)-terbutaline. The results have implications for the interpretation of effect/concentration studies with terbutaline, but do not affect the doses used in clinical practice.
    Additional Material: 2 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 192-196 
    ISSN: 0899-0042
    Keywords: propranolol enantiomers ; enantiomers ; propranolol ; β-receptor-blocking drugs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Only limited information is available on the stereochemistry of the in vivo distribution of β-receptor-blocking drugs. In this study we determined the levels of the propranolol enantiomers in plasma, cerebrospinal fluid (CSF) and central nervous system (CNS), and peripheral tissues in the dog following an intravenous dose of a deuterium-labeled pseudoracemate. The appearance of the propranolol enantiomers in the CSF was rapid and nonstereoselective, with maximum concentrations reached at 15 min after dosing. The levels of the enantiomers in both CSF and plasma then declined in a parallel biphasic fashion, with a terminal t1/2 of about 125 min. Except for an early high CSF/plasma concentration ratio of 0.35, the CSF propranolol levels corresponded to the unbound concentration in plasma, CSF/plasma 0.20. All areas of the brain showed a similar uptake of propranolol, with a tissue concentration exceeding that in plasma about 10-fold during the terminal phase of elimination. The uptake of propranolol by peripheral tissues varied widely, ranging from a 50-fold accumulation by the lungs compared to plasma to no accumulation by adipose tissue. However, as for the CSF, there was no evidence of stereoselective uptake of propranolol by any CNS or peripheral tissue except for the liver. A significantly higher level of (+)- vs. (-)-propranolol in liver tissue presumably was a reflection of stereoselective hepatic metabolism of (-)-propranolol by this tissue. The slight stereoselectivity in plasma binding of propranolol known to exist in the dog had no significant influence on tissue or CSF distribution.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 183-191 
    ISSN: 0899-0042
    Keywords: enantiomorphism ; dissymmetry ; chirality ; enantioselectivity ; diastereoselectivity ; steric complementarity ; asymmetric induction ; three-point contact ; circularly polarized radiation ; circular dichroism ; parity nonconservation ; electroweak interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pasteur's conjecture (1860) that biomolecular homochirality arose from a chiral natural force as yet inaccessible in the laboratory was supplanted by Fischer's (1894) “key and lock” hypothesis of stereoselection in enantiomer to diastereomer conversions, whether in the laboratory or in living organisms. Elaborations of the “key and lock” hypothesis by Haldane (1930) and Pauling (1948) have been illustrated and supported with modification by X-ray diffraction crystal structures of enzyme-substrate complexes over the past quarter century.Two types of mechanism for the product diastereoselectivity in the reactions of an enantiomer with an achiral reagent, early proposed, have recent support: one proposes a quasidiastereomeric structure for the enantiomer attacked in the ground state, the other for the corresponding transition state of the reaction. Approaches to the differential biological activity of two enantiomers postulate either the complete binding of each isomer to a chiral receptor site, resulting in diastereomeric complexes with inequivalent bioactivities, or the differential binding of the two isomers to a set of three sites, with which only one isomer is sterically congruent.Biochemical homochirality, based on the chiral stereoselectivity of both biosynthetic and metabolic reactions, derives from the evolutionary pressure for a progressive enhancement of the kinetic efficiency and economy of those reactions. Recently Pasteur has been vindicated in part, and the problem of the original prebiotic enantiomeric excess left outstanding by Fischer has been solved. The unification of the electromagnetic with the weak interaction provided a universal chiral natural force, the electroweak interaction, which favours the chiral series selected during the course of biochemical evolution, both the D-sugars and the L-amino acids.
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 202-208 
    ISSN: 0899-0042
    Keywords: opioid ligand ; 4-arylpiperidines ; conformation, NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and stereochemistry (configuration and preferred solute conformation) of some 4-alkyl (methyl, n-propyl, isobutyl)-4-(3-hydrxyphenyl)-1-methylpiperidines and corresponding 3-methyl diastereoisomeric pairs are reported, together with their in vivo and in vitro activities as opioid ligands. All potent agonists exhibit a preference for axial 4-aryl chair conformations when protonated, and stereochemical analogies with rigid opioids of the benzomorphan class are discussed. Antagonist properties are found in compounds with preference for equatorial 4-aryl chairs, notably the cis 3,4-dimethyl derivative.
    Additional Material: 3 Tab.
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  • 11
    ISSN: 0899-0042
    Keywords: fenofibrate ; chiral reduction ; species differences ; prochiral to chiral transformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The prochiral carbonyl group of fenofibrate (isopropyl 2-[4-(4-chlorobenzoyl)phenoxy]-2-methyl propionate) is reduced during its metabolism giving rise to a chiral secondary alcohol, “reduced fenofibric acid.” Chiral and diastereomeric HPLC methods have been developed for the determination of its enantiomeric composition and these have been applied to the measurement of the “reduced fenofibric acid” enantiomers in urine of rats, guinea pigs, dogs, and human volunteers given [14C]fenofibrate. In the three animal species, the reduction is markedly enantioselective for the (-)-isomer, the enantiomeric ratios (-/ +) being 95:5. This was not due to differences in the excretion of the enantiomers, since when racemic “reduced fenofibric acid” was given to rats it was recovered in the urine with the same enantiomeric composition as the dose form. In humans the ratio was 52:48 showing the lack of stereoselectivity of reduction in this species.
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  • 12
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    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 1-1 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 13
    ISSN: 0899-0042
    Keywords: affinity ; efficacy ; dissociation ; constants ; steroselectivity ; entropy ; enthalpy ; receptor ; interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: After alkylation of a fraction of the total α-adrenoreceptors by phenoxybenzamine in rat vas deferens, the dissociation constants of (-)- and (+)-epinephrine in functional studies were 7 × 10-7 M and 2 × 10-5 M, respectively. In the adrenoreceptor-containing tissue fraction, when 3H-labeled WB4101 was used as the interacting ligand, for each enantiomer who affinity sites were found. Only the low-affinity dissociation consant for each isomer correlates with the constant obtained from the functional studies. If the change in Gibb's free energy. ΔG°, is calculated from the low-affinity binding constants, the values -8.1 and -6.2 kcal/mol for (-)- and (+)-isomer, respectively, are obained. The small difference in the value between isomers forms a hydrogen bond with the receptor. The interaction of epinephrine with this receptor appears to be driven largely by the entropy of the drug-receptor interaction with only a small nonsteroselective contribution from the enthalpy of ineraction.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 57-62 
    ISSN: 0899-0042
    Keywords: chiral stationary phase ; α-amino phosphonate ; chromatographic separation of enantiomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral statonary phase (CSP) derived from an N-(3,5-dinitrobenzoyl)-α-aminobenzylphosphonate has been prepared and evaluated for its utility in the direct separation of enantiomers. This CSP, 2, is structurally related to earlier N-(3,5-dinitrobenzoyl)-α-acids acid-derived phases (e.g., CSP 1), but the mode of attachment to the support is different. In scope; CSP 2 is qualitaively similar to CSP 1. However, it differs quantitatively from CSP 1, showing either greater or lesser selectivity for different pairs of enantiomers.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 16
    ISSN: 0899-0042
    Keywords: column liquid chromatography ; chiral separations ; chymotrypsin on silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical separation of free and derivatized amino acids on active α-chymotrypsin bonded to silica is governed by two mechanisms based on the structure of the solutes or on the enzymatic activity of the enzyme. Te deactivation of the hydrolytically active site of the enzyme demonstrated that a significant portion of the retention on this support is due to hydrophobic interactions at other sites. These sites appear to be stereoselective for the ester derivatives of amino acids but not for the other studied solutes.
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  • 17
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    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 99-120 
    ISSN: 0899-0042
    Keywords: asymmetry ; enantiomers ; geometric isomers ; (+)- (-)-isomers ; D- and L-isomers ; R- and S-isomers ; Z- and E-isomers ; drug metabolism ; stereoselectivity and stereospecificity in drug action ; stereoselectivity and stereospecificity in drug metabolism ; psychotropic drugs ; stimulants ; antidepressants ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Many drugs contain a chiral centre, or such a centre is introduced during metabolism of the drug in man and in animals. If a single chiral centre is present, the drug will normally exist as a mixture of two enantiomers, of which one may have quite different pharmacologic and/or toxic effects than the other. Chiral drugs that are used in psychiatry, and some other pharmacologically related drugs are identified, and the implications of the presence of one or two chiral centres in these drugs are discussed. Differences in pharmacologic properties of drug and metabolite enantiomers are identified and discussed. Also reviewed are the properties of some drugs used in psychiatry that both are chiral and display geometric isomerism.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 137-141 
    ISSN: 0899-0042
    Keywords: resolution by crystallization ; racemic mixture ; dansyl-D-leucine ; dansyl-L-leucine ; dansyl-D-norleucine ; dansyl-L-norleucine ; dansyl-D-phenylalanine ; dansyl-L-phenylalanine ; β-cyclodextrin ; γ-cyclodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical enrichment from racemic dansyl-leucine, dansyl-norleucine, and dansyl-phenylalanine with both β- and γ-cyclodextrins in water is reported. Initial crystallization yielded the dansyl-L-leucine isomer complexed in excess with β-cyclodextrin with an optical purity of 62-78% depending on experimental conditions. The optical purities obtained for L-norleucine and L-phenylalanine were 71 and 64%, respectively. The optical purity can be increased with continued recrystallization. The dansyl-D-leucine isomer was obtained in the mother liquor with an optical purity of 54-93% depending on experimental conditions. The optical purities obtained for D-norleucine and D-phenylalanine were 72 and 58%. The optical purity of the isomer depended on the molar ratio of host:guest and the pH value of the solution. Optimum enrichment of both enantiomers was achieved with host:guest ratios of 2 : 1 and 3 : 1. Although maximum crystalline yield of the dansyl-leucine/CD inclusion complex was obtained at a pH of 3.5, optical purity of both enantiomers was less than that obtained at other pHs. The influence of the molar ratio of host:guest and the pH value of the solution are discussed. This method is suitable for large-scale enantiomeric separations.
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  • 20
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    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 22
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 249-250 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 23
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselectivity of carvedilol, a novel β-adrenoceptor antagonist and vasodilator with one asymmetric carbon atom, was examined at α1- and β1-adrenoceptors in vitro and in vivo. (-)-(S)-Carvedilol is a potent, competitive antagonist of the β1-adrenoceptor-mediated positive chronotropic response to isoproterenol in guinea pig atrium, with a dissociation constant (KB) of 0.4 nM. (+)-(R)-Carvedilol was more than 100-fold less potent than the (-)-S-enantiomer as an antagonist of β;1-andrenoceptors, having a KB of approximately 45 nM. Consistent with these findings (-)-(S)-carvedilol (0.1 mg/kg, i.v.) produced a 25-fold rightward shift in the β1-adrenoceptor-mediated positive chronotropic response to isoproterenol in pithed rats, whereas the (+)-R-enantiomer had no β1-adrenoceptor blocking activity in vivo at this dose. In contrast to the marked degree of stereoselectivity observed at βl1-adrenoceptors, both (-)-(S)- and (+)-(R)-carvedilol produced equal antagonism of the α1----adrenoceptor-mediated vasoconstrictor response to norepinephrine in rabbit aorta, with KB values of 14 and 16 nM, respectively. Furthermore, in the pithed rat, the α1-adrenoceptor-mediated pressor dose-response curve to cirazoline was shifted approximately 6-fold to the right by both the (+)-R- and (-)-S-enantiomers of carvedilol at a dose of 1 mg/kg, i.v. In anesthetized spontaneously hypertensive rats, (-)-(S)-carvedilol was 6-fold more potent as an antihypertensive than (+)-(R)-carvedilol. The vasodilator and acute antihypertensive activity of carvedilol results from α1-andrenoceptor blockade produced by both enantiomers, and the concomitant β1-adrenoceptor blockade produced by the (-)-S-enantiomer, which prevents reflex tachycardia that can offset the antihypertensive response, leading to greater overall antihypertensive potency of (-)-(S)-carvedilol relative to the (+)-R-enantiomer. These data also suggest that distinct regions of the carvedilol molecule are responsible for blocking α1- and β1-adrenoceptors, with β1-adrenoceptor blockade resulting from an area of the molecule containing the asymmetric carbon atom, specifically the carbazolyloxy propanolamine moiety, and α1-adrenoceptor blockade resulting from a part of the molecule that does not contain the asymmetric carbon atom, most likely the phenoxyethylamine moiety.
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  • 24
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 284-292 
    ISSN: 0899-0042
    Keywords: absolute configuration ; crystal structure ; resolution ; solid-state circular dichroism ; torsional isomerism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure and absolute configuration of the (-)589-dibenzoylmonohydrogentartrate salt of the cation [Co(pyridine)4Cl2]+ have been determined from a three-dimensional X-ray analysis. Single crystals were grown from dimethylsulfoxide: space group P212121, Z = 4, and cell dimensions a = 21.463(4), b = 23.112(3), and c = 7.490(1) Å. Full-matrix least-squares refinement on F converged at R = 0.075, 196 variables and 2029 observations. The cation has pseudotetragonal coordinate geometry, with axial Cl and equatorial N atoms. The dihedral angles between the pyridine ligands and the equatorial plane are 47(1), 39(1), 50(1), and 45(1)° and torsional isomerism is responsible for the solid-state chiroptical properties of the cation. The preferential crystallization of the P atropisomer of the cation is attributed to a general electrostatic attraction between cation and anion.
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  • 25
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 94-95 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 26
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 98-98 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 27
    ISSN: 0899-0042
    Keywords: terutaline ; enantiomers ; determination ; liquid ; chromatography ; coupled columns ; cyclodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of this work was to develop and validate a method for the separation and determination of the enantiomers of terbutaline in plasma and intestinal juice. Terbutaline was extracted from plasma and intestinal juice by liquid-solid extraction on small C18 cartridges. The extract was then analyzed by coupled column liquid chromatography with amperometric detecton. For ciral separation a β-cyclodextrin phase was used.The within-day variation (Cv) on spiked plasma samples was in the rane 0.8-6.4% at 3.8-33.8 nmol/liter for the (-)-enantiomer, and 2.6-23.0% at 1.3-11.3 nmol/liter for the (+)-enantiomer. The between-day variation on spiked plasma samples was 5.5% at 10.7 nmol/liter and 13.6% at 4.3 nmol/liter for the (-)- and (+)-enantiomers, respectively. The within-day variation for inestinal juice was i the range 0.7-1.5% at 5.6-30.0 μmol/liter for the (+)-enantiomer.
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  • 28
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 97-97 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 29
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 121-126 
    ISSN: 0899-0042
    Keywords: stereoselective metabolism ; sulfate conjugation ; in vitro sulfation ; sympathomimetic amines ; chiral separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Little is known about the stereochemistry of sulfation of chiral phenolic drugs. In this study we examined several in vitro approaches to this question, using (+)-, (-)-, or (±)-terbutaline as the substrate and the rat liver cytosol as the phenolsulfotransferase enzyme source. The cosubstrate PAPS was either generated by the cytosol from inorganic sulfate and ATP or added to the cytosol. The intact sulfate conjugates formed were determined by HPLC. Using the PAPS generating system, which is best suited for the production of relatively large quantities of sulfate conjugates, with the individual enantiomers as substrates, (+)-terbutaline was conjugated to a much greater extent than (-)-terbutaline; the (+)/(-)-enantiomer ratio was 7.3 ± 0.3 (mean ± SE). When (±)-terbutaline was the substrate and chiral derivatization was employed to separate the sulfate enantiomers formed, a similar (+)/(-)-enantiomer ratio of 7.9 ± 0.2 was obtained. With PAP35S added to the cytosol, an approach best suited for kinetic studies, the substrate concentration dependence of sulfation could be determined. The Km app for this reaction was identical for (+)- and (-)-terbutaline. However, the Vmax app was 8.1 ± 0.4 times greater for (+)-terbutaline. This study for the first time shows enantioselectivity in sulfation of a chiral phenolic drug. The experimental approaches used should be valuable for human studies of stereoselectiven sulfation of terbutaline and other chiral drugs.
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  • 30
    ISSN: 0899-0042
    Keywords: enantioselective epoxidation ; cytochrome P-450-dependent monooxygenases ; species dependence of microsomal epoxidation ; product enantioselectivity ; substrate enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity of the in vitro conversion of simple prochiral and chiral aliphatic alkenes into oxiranes by liver microsomes of untreated or induced (phenobarbital) rats, of untreated or induced (phenobarbital, benzo[α] pyrene) mice, and of humans was determined by complexation gas chromatography. The enantiomeric excess (ee) of the epoxides extends from 0 (trimethyloxirane) to 50% (ethyloxirane). The configuration (R or S) of the enantiomers formed in excess is consistent for homologous oxiranes but is species dependent and in some cases influenced by enzyme induction. Enantioselectivity differences of aliphatic alkene epoxidation by human liver microsomes of four individuals are negligible.
    Additional Material: 2 Ill.
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  • 31
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 154-160 
    ISSN: 0899-0042
    Keywords: enantiomers ; chiral discrimination ; drugs ; hydrophobic interaction ; biopolymers ; elution order ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution on the analytical scale of a number of racemic pharmaceuticals and some other biologically active compounds has been studied using immobilized bovine serum albumin (BSA) as the stationary phase. For some of the compounds the elution order was determined by the use of optically enriched fractions obtained from a preceding passage of a sample through a preparative column containing microcrystalline triacetylcellulose (MCTA). The reversal in the sign of optical rotation shown in the polarimetric elution profile from the latter, combined with the integrated peak area ratio obtained on resolution on the analytical column, gave directly the order of elution. For one of the benzothiadiazines studied (bendroflumethiazide), increasing the pH of the mobile phase produced opposite effects on the retention of the two enantiomers, leading to a large effect on the separation factor. For many of the compounds studied, high separation factors (α 〉 2) could be achieved.
    Additional Material: 7 Ill.
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  • 32
    ISSN: 0899-0042
    Keywords: enantiomeric separations ; chiral stationary phase ; Pirkle-type phases ; HPLC ; anthelmintics ; benzimidazole sulfoxides ; albendazole ; fenbendazole ; oxfendazole ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct enantiomeric resolution of albendazole sulfoxide (SOABZ), an anthelmintic drug belonging to the benzimidazole class, is reported on a chiral stationary phase (CSP) synthesized by covalent binding of (S)-N-(3,5-dinitrobenzoyl)tyrosine-O-(2-propen-1-yl) methyl ester on a γ-mercaptopropylsilanized silica gel. A comparison with the resolution achieved on commercially available Pirkle-type CSPs obtained from N-(3,5-dinitrobenzoyl) derivatives of (R)-phenyglycine or (S)-phenylalanine is described. Some structurally related chiral sulfoxides including oxfendazole (SOFBZ) are also studied. Optimization of the mobile phase nature and composition is investigated showing that a hexane-dioxane-ethanol ternary mixture affords an almost baseline resolution (Rs = 1.25); however, in this case, albendazole sulfone (SO2ABZ) is eluted between the two sulfoxide enantiomers; accordingly, a hexane-ethanol mobile phase would be preferred for biological samples containing both metabolites. The influence of temperature on the resolution is depicted with a hexane-ethanol mobile phase. Finally, application to the enantiomeric assays of SOABZ in plasmatic extracts of rat, sheep, bovin, and man after oral administration of albendazole (sulfoxidized to SOABZ and SO2ABZ) is reported. Some distortions in the enantiomeric ratios are evidenced depending on the species.
    Additional Material: 10 Ill.
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  • 33
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 167-169 
    ISSN: 0899-0042
    Keywords: enantioselectivity ; three-point model ; chiral receptors ; chiral separations ; didactic model ; elusion of the three-point model ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hands can be used to demonstrate the three-point model of chiral recognition. The points of attachment are thumb, forefinger, and middle finger. This vivid model has the advantages of simplicity, perspicuity, and availability at any time, although two persons are necessary. It can be shown that two interactions are not sufficient for chiral recognition but that three attractive or two attractive and one repulsive attraction are needed. It can also be used to explain some possibilities of weakening or elusion of the three-point model.
    Additional Material: 6 Ill.
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  • 34
    ISSN: 0899-0042
    Keywords: chromatography ; chirality ; chiral recognition ; β-aminoalcohols ; stereochemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three chiral stationary phases, obtained by derivatizing γ-mercaptopropylsilanized silica gel with quinine, quinidine, and cinchonidine, have been employed in the resolution of N-acyl derivatives of β-hydroxyphenethylamines. The use of circular dichroism for detection and NMR analysis of analyte-selector mixtures provides an experimental basis for preliminary assignment of a recognition mechanism.
    Additional Material: 4 Ill.
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  • 35
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 178-179 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 36
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 246-248 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 37
    ISSN: 0899-0042
    Keywords: optical resolution ; HPLC ; chromatography ; antiinflammatory drug ; ibuprofen ; ketoprofen ; flurbiprofen ; tiaprofenic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct optical resolution of antiinflammatory drugs such as ibuprofen, ketoprofen, flurbiprofen, and tiaprofenic acid were attempted by high-performance liquid chromatography using tris(3,5-dimethylphenylcarbamate)s of cellulose and amylose as chiral stationary phases. Although ibuprofen was not sufficiently resolved, the other three 2-arylpropionic acids were completely resolved by amylose tris(3,5-dimethylphenylcarbamate). Ibuprofen was resolved as anilide derivative.
    Additional Material: 2 Ill.
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  • 38
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the preparation of (E)-3-acylprop-2-enoic acids ( = (E)-3-acylacrylic acids) of type II via acid-catalyzed isomerization of the corresponding 3-acylprop-2-ynal acetals of type I (Scheme 1) has been found. The described reaction gives a rapid and quite general access to these compounds known to exhibit a number of interesting biological activities. Some studies toward the elucidation of the reaction mechanism have been made, and a hypothetical mechanism is proposed.
    Additional Material: 2 Tab.
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  • 39
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structures of the Cu2+ complexes of 1,4,8,11-tetraazacyclotetradecane derivatives with an ethylpro-pionate and diethylphosphonate group, 5 and 6, respectively, indicate that the metal ion is pentacoordinated by the four N-atoms of the macrocycle and one O-atom. In the case of 5, it is the carbonyl O-atom of the carboxylate group, whereas for 6 it is the phosphonyl O-atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu2+ complexes with the 1,4,8,11-tetraazacyclotetradecanes 3-6 have been measured by pH-stat and stopped-flow techniques. The rate law for the hydrolysis of the carboxylates 3-5 is proportional to the complex concentration and to [OH-] up to pH 13, whereas that of the phosphonate 6 is proportional to [OH-] up to pH 11.5, becoming independent of [OH-] at pH 〉 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra- or an intermolecular OH- attack and the results of the X-ray structure analyses.
    Additional Material: 5 Ill.
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  • 40
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 41
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 353-360 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two gossypol analogues 2a and 2b were synthesized for biological evaluation as male contraceptive agents. The naphthol 8c was prepared by analogy with a known procedure starling from 3-isopropylcatechol (3). (t-Bu)2O2-Mediated phenolic coupling of 8c furnished the binaphthol 9c which, after pyrane ring closure, deprotection. and selective bisformylation with SnCl4/Cl2CHOCH3, gave the target compound 2a. The corresponding tetrahydroxy analogue 2b was prepared in a similar way.
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  • 42
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    Helvetica Chimica Acta 72 (1989), S. 361-364 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of (+)-Abscisic Acid.Starting from (4S)-4-hydroxy-2,6,6-trimethylcyclohex-2-enone (2), a short synthesis of the natural (+)-abscisic acid ((+)-1) has been accomplished.
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  • 43
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    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 365-369 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Access to 2,6,6-Trimethylcyclohexa-2,4-dienone from 4-Oxoisophorone2,6,6-Trimethylcyclohexa-2,4-dienone (1), a versatile starting material for the preparation of some carotenoids and several natural products, was efficiently (73% yield) prepared from oxoisophorone 3. After conversion of 3 to the alcohol 4 or the acetate 5, H2O was eliminated (4→1) under acidic distillative conditions, whereas AcOH could be eliminated (5→l) under Pd(O) catalysis.
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  • 44
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 377-382 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic route leading to bis-heteroleptic cyclometalated complexes is described. The complexes [2-(2′-thienyl)pyridinato-N, C-3′]{2-[3′-(trimethylsilyl)2′-thienyl]pyridinato-N, C3′}platinum(II) ([Pt(thpy) (TMS-thpy)]; I) and (l-phenylpyrazolato-N2, C2′)[2-(2′-thienyl)pyridinato-N, C3′]platinum ([Pt(Phpz)(thpy)]; II) are characterized by UV/VIS, NMR, and mass spectroscopy. Thermal and photochemical oxidative addition reactions yield two out of the 10 possible pairs of enantiomers of octahedral Pt(IV) compounds.
    Additional Material: 1 Ill.
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  • 45
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical cation of bicyclo[2-2.1]hepta-2,5-diene (8,9,10-trinorborna-2,5-diene; 1) in CF2ClCFCl2, and CF3CCl3 matrices and that of bicyclo[2.2.2]octa-2,5-diene (2,3-dihydrobarrelene; 2) in CFCl3 and CF3CCl3 matrices have been studied by ESR and ENDOR spectroscopy. For \documentclass{article}\pagestyle{empty}\begin{document}${\bf 1}^{+ \atop \dot{}}$\end{document}, the coupling constants of the olefinic, methano-bridge, and bridgehead protons are -0.780 ±0.005, +0.304±0.002, and -0.049±0.002 mT, respectively. The hyperfine tensor for the methano-bridge protons is axial, Ax = +0.263 ± 0.002 and Ay = +0.386 ± 0.002 mT, while that for the olefinic protons is orthorhombic, Ax = -0.594 ± 0.005, Ay= -0.913 ± 0.005, and Az = -0.834 ± 0.005 mT (x parallel to C—H- z parallel to 2pπ axis). For \documentclass{article}\pagestyle{empty}\begin{document}${\bf 2}^{+ \atop \dot{}}$\end{document}, the coupling constants of the olefinic, ethano-bridge, and bridgehead protons are -0.68 ± 0.01, +0.162 ± 0.005, and -0.108 ± 0.005 mT, respectively. The hyperfine data for \documentclass{article}\pagestyle{empty}\begin{document}${\bf 1}^{+ \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}${\bf 2}^{+ \atop \dot{}}$\end{document} fully support the presentation of their singly occupied orbitals as antisymmetric combinations, b2(π), of the two bonding ethene π-MO's.
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  • 46
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    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 401-402 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 47
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present the application of several homo- and heteronuclear 1D- and 2D-NMR techniques to assign the 1H-NMR chemical shifts of the dominant conformation of didemnin B (2; three different conformations in (D6)DMSO solution in the ratio 8:1:1) and its conformational analysis, as well as the solution conformation of didemnin A (1). The conformations were refined by restrained molecular-dynamics calculations using the GROMOS program and by MOMO, a novel personal-computer-based interactive molecular-graphics and molecular-mechanics package, using experimental distances (via a H…H pseudo potential function) as restraints. The solution structures of 1 and 2 obtained by GROMOS and MOMO calculations were compared with each other and related to the recently solved crystal structure of 2. Focusing on the main conformer, the two kinds of the distance-restrained conformational calculations for 2 yielded a ‘solution structure’ close to the crystal structure. Almost all of the 40 restrained H…H distances coincided (within the estimated standard deviations) with those observed in the crystal structure. One more hydrogen bond was detected in solution involving the lactoyl OH group (disordered in the crystal structure) and the dimethyltyrosine (Me2Tyr5) carbonyl O-atom. The macrocyclic ring system in the modeled solution structure of 1 exhibited a topology close to those of the solution and crystal structures of 2. The main difference between 1 and 2 could be traced back to a significant change in the Ψ angle of the N-methyl-D-leucine (MeLeu7) residue. In 1, the N-methyl moiety of MeLeu7 points inward within the macrocyclic ring toward the 1st and Hip region. We also tested the suitability of structures obtained from NMR data as ‘search fragments’ in the ‘Patterson search approach’ of crystal-structure analysis. It proved possible to resolve the crystal structure of 2 a posteriori with the Patterson search program PATSEE, in this way.
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  • 48
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    Helvetica Chimica Acta 72 (1989), S. 570-593 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transformations of 12 bicyclo[2.2.2]oct-5-en-2-ols (V or VI) to 3-(cyclohex-3-enyl)-2-alkanones (III or IV), via β-cleavage of their potassium alkoxides in HMPA, has been investigated (cf. Table 1). As an illustration of this synthetic methodology, a stereoselective synthesis of (±)-trichodiene ((±)-1) is described which involves the β-cleavage of the tricyclic potassium alkoxides 46a and 47a to cyclopentanone 4 (cf. Scheme 7).
    Additional Material: 1 Ill.
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  • 49
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: About 65 diverse phenyl benzoates incorporating a trans-1,4-disubstituted cyclohexane ring and at least one lateral substituent have been synthesised. The dependence of the liquid-crystal transition temperatures of these materials on various lateral substituents (F, Cl, CN, and Br) in different positions of the esters has been investigated systematically. The influence of up to four F-atoms in various positions of a standard ester has been thoroughly studied and the optimum combination for a broad smectic C mesomorphic range established. In consequence, three homologous series incorporating the 4-alkoxy-2,3-difluorobenzoic-acid moiety were prepared. An additional C=C bond was introduced into the alkyl chain attached to the cyclohexane ring of some of these esters and the resulting modifications of the transition temperatures determined. Three ester series incorporating a lateral substituent and the optically active (+)-(S)-(1-methylheptyl)oxy substituent have also been synthesised, and similar effects have been observed. These materials can be used as important components of commercial chiral smectic C mixtures for electro-optic display device applications.
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  • 50
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermolysis of steroidal 5α, 8α- peroxides of type 3a-d generates as major products the corresponding diseco compounds containing a 14-membered ring instead of the standard A-B-C-ring skeleton. Depending on the reaction conditions, either the primary products of type 9 or the α, β-unsaturated ketones of type 4, formed by subsequent elimination of AcOH, are isolated. The latter, configurationally uniform compounds undergo epoxidation of the C(9)=C(10) bond followed by a Baeyer-Villiger oxidation to give, as final products, the 15-membered cyclic epoxyenol lactones of type 20 and 21. The structures of the various products were determined by 1H- and 13C-NMR spectroscopy. The conformations of the 14- and 15-membered rings were established by X-ray structure analyses of 7 and 21a. A reaction mechanism for the above transformations is discussed.
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  • 51
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    Helvetica Chimica Acta 72 (1989), S. 631-631 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 52
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    Helvetica Chimica Acta 72 (1989), S. 624-630 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: X-Ray Crystal-Structure Analysis of 2,4,6-Tri(tert-butyl)phenyllithium · N,N,N′,N′-Tetramethylpropane-1,2-diamine: a Monomeric Organolithium CompoundTri(tert-butyl)phenyllithium is an important reagent for the preparation of derivatives of main-group elements with low coordination state as well as a highly hindered base for the generation of amine-free Li-enolates. Its monomeric nature in solution was previously deduced from NMR measurements. While Et2O, THF, and N,N,N′,N′-tetramethylethylene-1,2-diamine (tmen) led to crystalline samples which were not suitable for structure analysis, the N,N,N′,N′-tetramethylpropane-1,2-diamine (tmpn) gave good single crystals of the title compound from Et2O/hexane (disorder along the two-fold crystallographic axis running through Li—C(1) and C(4) of the Ph ring. The structure (Fig. 1, Table 1) has some remarkable features: (i) it is one of the very few monomeric organolithium compounds so far, (η1-Li on aromatic ring); (ii) it has the rare trigonal-planar coordination of the Li-atom; iii) there are close contacts between the Li-atom arid one of the Me groups in each ortho-position (Fig. 3). The internal angle on the Ph-ring ipso-C-atom is 114°. This angle as well as those of the other known phenyllithium (Table 2), -magnesium, and -aluminum structures are included in a plot of ipso-angles against Pauling electronegativities (Fig. 2).
    Notes: No abstract.
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  • 53
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    Helvetica Chimica Acta 72 (1989), S. 1-13 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloartenol (4), a natural plant sterol, was shown to be an effective membrane reinforcer; this was attributed to its conformation. We now present a conformational analysis of 4 by molecular modeling and NMR. Molecular modeling suggests that two conformations I and II coexist, differing mainly at the level of ring C, and of nearly equal energy, I and II each having ring A and B in a chair and half-chair conformation, respectively, with ring C 1,3-diplanar in I (solid-state structure as determined by X-ray crystallography) and in chair conformation in II. A complete assignment of the 1H- and 13C-NMR spectra of 4 and the entire coupling network in rings A and B is determined by various modern NMR techniques. The conformation of rings A and B thus determined is in agreement with conformations I and II. Low-temperature NMR experiments show a fast equilibrium between two conformations, presumably I and II. It is concluded, therefore, that the cyclopropane ring of 4 produces a flexibility at the level of ring C which may be important for the membrane properties.
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  • 54
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    Helvetica Chimica Acta 72 (1989), S. 17-28 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Influence of the Acceptor Part of the Chromophor of Dimethinemerocyanine Dyes upon the Aggregation Tendency in Aqueous SolutionA series of novel long-chain alkyl-dimethinemerocyanine dyes containing sulfonate groups is synthesized in good yield and their aggregation tendency in H2O and in organic solvent/H2O mixtures investigated. The merocyanine dyes 11 and 15 only exhibit an intense, red-shifted absorption band due to J-aggregation in H2O without addition of salt. The influence of cationic and anionic tensides and other compounds as urea, glucose, and polysaccharides upon the J-aggregation tendency is investigated.
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  • 55
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    Helvetica Chimica Acta 72 (1989), S. 59-64 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between the chiral allenic acid (+)-(S)-1 and the carbodiimides 2a-d and the keten-imine 6 gives, under mild conditions, the tricyclic compounds 3-5, 7, and 8. Low diastereoselectivity and a partial loss of optical activity are observed. A stepwise mechanistic pathway via a biradical intermediate is postulated.
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  • 56
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Attempted Synthesis of Calicene from Trisubstitued Cyclopropanes and CyclopentenoneThe Li carbenoids 4, prepared by treatment of substituted 1,1-dihalocyclopropanes with BuLi, are reacted with cyclopent-2-enone under thermodynamic and kinetic control (Scheme 1). In general, the latter procedure gives better yields of cyclopropylcyclopentenols 5a-e, but the reaction seems to be controlled mainly by the steric and electronic properties of the substituent Y. So, with 4b and 4e, the main reaction is the attack of the carbenoid at C(1) of cyclopent-2-enone, while 4a (Y = PhS) predominantly deprotonates the ketone (Scheme 4). Whereas 5d and 5e can easily be converted to the dihydrocalicenes 6d and 6e (Scheme 6), the attempted elimination of H2O from 5a-c leads to the rearranged products 13-2 due to the opening of the cyclopropane ring (Scheme 5). Finally, the generation of the parent compound 2 from the silylated precursor 6d is attempted: treatment with MeO- gives the addition products 18A/18B, while the reaction with Br2 provides 19 by a bromination/dehydrobromination sequence (Scheme 7).
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  • 57
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular cations of 1,3,5-cyclooctatriene (COT+·) and bicyclo[4.2.0]octa-2,4-diene (BCO+·) can be observed intact in γ-irradiated Freon glasses, as opposed to Ar matrices where ionization is accompanied by extensive rearrangements. This proves the superiority of the Freon-glass method for the generation of metastable primary cations. The electronic absorption (EA) spectra reveal a) that a previous analysis of the BCO+· electronic structure on the basis of the ultraviolet photoelectron (UP( spectrum of BCO was incomplete, and b) that COT undergoes planarization upon ionization, in accord with qualitative expectations and MNDO calculations. A previously proposed LCBO model was used to assess the influence of the above geometry change on the electronic structure of COT+·.
    Additional Material: 2 Ill.
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  • 58
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and complexation properties of 1,4-dimethyl-8-[2-(2-pyridyl)ethyl]-1,4,8,11-tetraazacyclotetra-decane (2) are described. This ligand forms with Cu2+ two complexes, one of which has been characterized by X-ray structure analysis. The structural, spectral, and kinetic studies indicate that the two Cu2+ complexes are isomers with the macrocycle in the trans-III and trans-I configuration. The rate of the interconversion of the trans-I isomer to the thermodynamically more stable trans-III species is proportional to [OH-]. A mechanism for this reaction is proposed.
    Additional Material: 2 Ill.
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  • 59
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dienyl acetates 2 lacking a geminal disulfone or a malonate group cyclize selectively to (E)-l-methylidene-2-styrylcyclopentanes 4 in the presence of 7 mol-% of [Pd(PPh3)4].
    Additional Material: 1 Tab.
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  • 60
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 29-40 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted methylidenecyclopropanes 12a-d, being easily available from 1,1-dibromo-2-(phenylthio)-cyclopropane (9a), are attractive precursors of triafulvene (2-methylidene-1-cyclopropene; 1). Both the sulfoxide 12b and the sulfone 12c react with an excess of alkoxides (t-BuOK and NaOMe) to give 12e and 12f, respectively, while the sulfinyl group of 12b may be replaced by the PhCH2S substituent in the presence of PhCH2SH/t-BuOK. These reactions (Scheme 4) may be explained by assuming 1 as a reactive intermediate, although an alternative sequence including carbene 20 (Scheme 6) is not completely ruled out. D-labelling experiments (Scheme 5) do not give conclusive evidence due to D scrambling, but deprotonation/methylation sequences show that H—C(2) of 12a-c is the most acidic proton. Final evidence for 1 results from the reaction of 12d with cyclopentadienide (Scheme 7): the reaction of 1 with cyclopentadiene produces the expected [4 + 2]-cycloaddition product 23, while some mechanistic insight results from the sequence 12d → 24 → 25.
    Additional Material: 1 Ill.
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  • 61
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 51-58 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Competition of Endoperoxide and Hydroperoxide Formation in the Reaction of Singlet Oxygen with Cyclic, Conjugated DienesRose-bengal-sensitized photooxygenation of (-)-(R)-α-phellandrene (1) in MeOH at room temperature yielded a complex mixture of products, contrary to previous reports describing cis-(3S, 6R)-epidioxy-p-menthene (2) and trans-(3R, 6S)-epidioxy-p-menthene (3) as the only products. The mixture was separated by prep. HPLC (silica gel, pentane/Et2O 9:1). Besides the known endoperoxides 2 (yield 39%) and 3 (26%), all those hydroper-oxides, which can be deduced from an ene reaction of 1O2 with 1, were isolated, i.e. 4β-p-mentha-2,5-dien-1β-yl hydroperoxide (4) (14%), 4β-p-mentha-2,5-dien-1α-yl hydroperoxide (5) (9%), (2R, 4R)-p-mentha-1(7), 5-dien-2-yl hydroperoxide (6) (2,1%), (2S, 4R)-p-mentha-1(7),5-dien-2-yl hydroperoxide (7) (1,5%) and (1R)-p-mentha-3,6-dien-yl hydroperoxide (8; 1,5%; Scheme 1). Furthermore, the constant cis/trans ratio for all diastereoisomeric pairs (2/2, 4/2, 6/2) was striking. With the help of the two possible conformers 1a and 1b of the starting material a model of a common first step for endoperoxide as well as for hydroperoxide formation is developed. A photooxygenation at -50° supports this model. The absolute value of the cis/trans ratio changes in the same way for the endoperoxides and the hydroperoxides.
    Additional Material: 2 Ill.
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  • 62
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Vinylindole (1a) and its donor- and acceptor-substituted (E)-derivatives 1b-e react highly locoselectively with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate (3) to form the novel (indol-2-yl)-1,4-dihydropyridazines 4a and 7 as well as the heterocyclic annellated pyridazines 4b, 5, and 6. The reactions of the structurally related 3-vinylindoles 2a-e with 3 also gave rise to new indol-3-ylpyridazines 8, 9, and 10. The locoselectivities of these Diels-Alder reactions were controlled mainly by steric effects.
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  • 63
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 83-92 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mechanistic evidence for the light-induced ring opening of thiophen-2(5H)-ones 1 in alcohols affording α, β-unsaturated mercapto esters 2 is presented. Regio-and stereochemical aspects of the ring closure of alkenylthio (type 3) radicals 15 and 17 to S-heterocycles 16 and 18, of 3-thiahex-5-enyl radicals 4 to (tetrahydrothien-3-yl)methyl radicals 6 and of (2,3-dihydrothien-3-yl)methyl radicals 30 (type 7, but-3-enyl radicals) to cyclopropane-methyl radicals 29 are discussed. Irradiation (λ 350 nm) of 1 in cyclohexane in the presence of 2,3-dimethylbut-2-ene affords [2 + 2] cycloadducts 14 albeit in very low yields.
    Additional Material: 1 Tab.
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