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  • 1985-1989  (6,023)
  • Organic Chemistry  (3,492)
  • Engineering  (2,531)
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  • 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.
    Additional Material: 1 Ill.
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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.
    Additional Material: 1 Ill.
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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.
    Additional Material: 2 Ill.
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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.
    Additional Material: 2 Ill.
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  • 12
    Electronic Resource
    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
    Type of Medium: Electronic Resource
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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.
    Additional Material: 3 Ill.
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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.
    Additional Material: 2 Ill.
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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
    Type of Medium: Electronic Resource
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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.
    Additional Material: 3 Ill.
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  • 17
    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
    Type of Medium: Electronic Resource
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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.
    Additional Material: 3 Tab.
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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.
    Additional Material: 2 Ill.
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  • 20
    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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  • 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
    Electronic Resource
    Electronic Resource
    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
    Electronic Resource
    Electronic Resource
    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
    Electronic Resource
    Electronic Resource
    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
    Electronic Resource
    Electronic Resource
    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
    Electronic Resource
    Electronic Resource
    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
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    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
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    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
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    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
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    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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  • 64
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    Helvetica Chimica Acta 72 (1989), S. 101-109 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Synthesis of Taxane DerivativesSubstituted racemic 4,8,12-trinortaxanes were prepared stereoselectively in several steps from the dienone 10. A variant of the de Mayo reaction with bicyclononenones 4 and cyclohexen produced the desired configuration at C(8) of the taxane framework. Retro-aldol cleavage of the tetracycle 5 led to the taxane skeleton 6. Stereoselective reduction followed by treatment with base afforded 7b. Hydrolysis of the acetal group and further reduction yielded 9 in which the relative configuration corresponds to the one of the natural products.
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  • 65
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    Helvetica Chimica Acta 72 (1989), S. 147-150 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Under O2, the Aspidosperma alkaloid tabersonine (1) was converted by a crude enzyme preparation from leaves of mature plants of Catharanthus roseus G DON into the trimeric 3-hydroxy-14′-(3α″-tabersonyl)voafrine B (4) which was easily reduced by NaBH4 to 14′-(3α″-tabersonyl)voafrine B ( = tertabersonine; 5). Compounds such as 4 and 5 are the first trimeric alkaloids in the series of monoterpenoid indole alkaloids.
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  • 66
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    Helvetica Chimica Acta 72 (1989), S. 158-164 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: μ-Carbonyl(Rh—Rh)di(η5-indenyl)[(2R,3S)-C,2,3,C-η-(2,3,4,5-tetramethylidenebicyclo[2.2.1]heptan-7-one)]]-dirhodium(I)(Rh—Rh) (7) and cis-μ-[(2R,3S,5R,6S))-C,2,3,C-η:C,5,6,C-η-(2,3,5,6-tetramethylidenebicyclo[2.2.1]heptan-7-one)]bis[μ-carbonyldi(η5-indenyl)dirhodium(I)(Rh—Rh)] (8) have been prepared. Complex 7 reacts with Fe2(CO)9 in hexane/MeOH and gives cis-μ-[(2R,3S,5R,6S] (9), trans-μ-[(2R,3S,5S,6R)-C,2,3,C-η: C,5,6, C-η-(2,3,5,6-tetramethylidenebicyclo[2.2.1]heptan-7-one)-μ-carbonyldi(η5-indenyl)dirhodium(I)(Rh—Rh)-(tricarbonyliron) (10), and, μ-carbonyl(Rh—Rh)[(2R,3S)-C,2,3,C-η-(2,3-dimethyl-5,6-dimethylidenebicyclo-[2.2.1]hept-2-en-7-one)]di(η5-indenyl)dirhodium(I)(Rh—Rh) (11). Treatment of 7-oxa[2.2.1]hericene (4) with Fe2(CO)9 or (cyclooctene)2Fe(CO)3 gave a 1:2 mixture of cis-μ-[(2R,3S,5R,6S)-] (12) and trans-μ-[(2R,3S,5S,6R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6-tetramethylidenebicyclo[2.2.1]heptan-7-one)]bis(tricarbonyliron)(13).
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  • 67
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    Helvetica Chimica Acta 72 (1989), S. 172-179 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Aminoazirine Reaction. Formation of 3,6-Dihydropyrazin-2(1H)-onesThe reaction of 3-(dimethylamino)-2H-azirines 1 and 2-(trifluoromethyl)-1,3-oxazol-5(2H)-ones 5 in MeCN or THF at 50-80° leads to 5-(dimethylamino)-3,6-dihydropyrazin-2(1H)-ones 6 (Scheme 3). Reaction mechanisms for the formation of 6 are discussed: either the oxazolones 5 react as CH-acidic heterocycles with 1 (Scheme 4), or the azirines 1 undergo a nucleophilic attack onto the carbonyl group of 5 (Scheme 6). The reaction via intermediate formation of N-(trifluoroacetyl)dipeptide amide 8 (Scheme 5) is excluded.
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  • 68
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 18-O-Methylchaenorpine (1a) and iso-18-O-methylchaenorpine (1b) two novel stereoisomeric spermine alkaloids were isolated from the roots of Aphelandra tetragona (VAHL) NEES. Their structures were established by chemical and spectroscopic studies.
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  • 69
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    Helvetica Chimica Acta 72 (1989), S. 185-195 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,5,7-Triazabicyclo[4.4.0]dec-5-ene as Reaction Medium: An Efficient One-Step Formation of Etioporphyrine from ProtoporphyrineHeating the commercially available protoporphyrine (4) in molten 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) at 200° for 4 h under exclusion of O2 produces etioporphyrine (6) in 60-70% yield by bisdecarboxylation and concomitant reduction of the two vinyl groups. Mesoporphyrine (5) is bisdecarboxylated to 6 in over 80% yield under these conditions in TBD as well as in DBU as the reaction medium.
    Additional Material: 7 Ill.
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  • 70
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    Helvetica Chimica Acta 72 (1989), S. 213-223 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The β-C-lithiated acrylamide 3A has been proven to be an ideal pyruvate β-carbanion equivalent useful in a highly diastereoselective KDO synthesis. The starting material 3 was prepared from pyruvate diethyl acetal in four convenient steps. Direct lithiation with 2 equiv. of LDA generated the dilithiated species 3A quantitatively. Reaction with 2,3:4,5-di-O-isopropylidene-D-arabinose (11) was highly D-manno-selective. The product 12 was obtained readily from the reaction mixture via crystallization. Ring closure to the butenolide 13, subsequent PhS-group removal with Bu3SnH and pyridinium bromide, and hydrogenolytic debenzylation afforded the known butenolide 19; this KDO precursor gives KDO in two convenient steps. Butenolide 19 was also transformed via two high-yielding steps into the 4,5:7,8-di-O-cyclohexylidene-KDO derivative 22, a valuable starting material for KDO α-glycoside syntheses.
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  • 71
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polarized optical absorption and emission (spectra, decay times) of single crystals of [Pd(thpy)2] and [Pt(thpy)2] (thpy ≡ C(3′)-deprotonated form of 2-(2-thienyl)pyridine) at temperatures 1.9 K ≤ T ≤ 80 K are reported. The emission of [Pt(thpy)2] can be influenced strongly by applied magnetic fields (0 ≤ H ≤ 6 T). Depending on the central ions Pd and Pt, the lowest excited electronic states of the single complexes are ligand-centered (LC) states and metal-to-ligand charge transfer (MLCT) states, respectively. This difference leads to distinctly dissimilar properties of the emission of both compounds. The experimental data show that the emission of single crystals of [Pd(thpy)2] and [Pt(thpy)2] at T ≤ 30 K originates from several types of traps (defect states of symmetry 3B2-stabilized below the exciton band) with LC and MLCT character, respectively. In the Pt compound, the 3B2 is split by spin-orbit coupling into three states. The states B1′ and A2′, which determine the emission properties, are separated by Δv ∼ 13 cm-1. Both states can mix under the influence of an applied magnetic field yielding an increase of the emission intensity by a factor of ∼ 1.5 at H = 6 T.
    Additional Material: 14 Ill.
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  • 72
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convergent diastereoselective synthesis of racemic aristoserratine ((±)-24) via an intramolecular iminium-ion cyclization is described. The pivotal imine (±)-19 was prepared by condensation of the two building blocks (± )-trans-8-amino-3-(2,6-difluorobenzyloxy)-1-p-menthene ((±)-11) and N-(p-methoxybenzenesulfonyl)-3-indo-leacetaldehyde (18) which were synthesized from (±)-trans-1-p-menthene-3,8-diol ((±)-7) and 3-indoleacetic acid, respectively. On the route to the target (±)-24, two previously unknown indole alkaloids have been characterized, namely (±)-‘anti’-hobartin-15-ol ((±)-22) and (±)-‘anti’-aristotelin-15-ol ((±)-23).
    Additional Material: 1 Tab.
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  • 73
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (1S, 4R, 5S, 6S)-5-exo, 6-exo-(Isopropylidenedioxy)-7-oxabicyclo[2.2.1]heptan-2-one ((-)-1) was transformed with high stereoselectivity to L-allose. Similarly, enantiomer (+)-1 was transformed into L-talose. The ketones (+)-1 and (-)-1 were derived from furan and 1-cyanovinyl (1S)-camphanate and 1-cyanovinyl (1R)-camphanate, respectively.
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  • 74
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Absolute Configuration of Iridals and Cycloiridals of Different OriginNatural irones are known to occur in enantiomeric forms within Iris oils of different origin. They are formed by oxidative degradation of the cycloiridals (C31-triterpenoids) found in rhizomes of various Iris species. The absolute configuration of iridals from different varieties is determined by ozonolysis of the triterpenoids and comparison of their degradation products with authentic samples of known configuration. It is shown that the initial cyclization of squalene resulting in the formation of a monocyclic seco-ring-A iridal has the same stereo-chemical course throughout all Iris species studied. The subsequent cyclization of the homofarnesyl side chain of the iridals, however, produces cycloiridals with enantiomeric irone moieties within different subspecies of the sword lilies.
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  • 75
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The potentiometric study of the complexation of 1,4,7-triazacyclononane-l-acetic acid (1) with Cu2+ (I = 0.5 (KNO3), T = 25°) indicates the presence of the species [Cu(1)], [Cu(1)OH], [Cu(1)2], and [(Cu(1))2OH], the stability constants of which are determined. The two complexes [Cu(1)]ClO4 and [(Cu(1)2)OH]ClO4 were also characterized by X-ray structure analysis. In both cases, the Cu2+ ion is in a distorted square-pyramidal arrangement, penta-coordinated by the three N-atoms of the macrocycle, an O-atom of the carboxylate, and an additional O-atom either from a second carboxylate or from an OH-, acting as a bridge between two metal centres.
    Additional Material: 3 Ill.
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  • 76
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The epimeric alkoxides 6a and 6b, generated in the gas phase by deprotonation of the stereospecifically deuterated isoborneols 5a and 5b, undergo loss of H2 and HD in a 1:1 ratio. This result, ruling out a concerted one-step process, establishes the intermediacy of an ion/molecular complex (‘solvated’ hydride ion) in the course of formation of enolates from the alkoxide anions in the gas phase.
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  • 77
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    Helvetica Chimica Acta 72 (1989), S. 323-337 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution chemistry of Cu(II) with a series of five planar tridentate nitrogen ligands, 2,6-bis(benzimidazol-2-yl)pyridine (bzimpy, 1), 2,6-bis(l-methylbenzimidazol-2-yl)pyridine (mbzimpy, 2) 2,6-bis(benzothiazol-2-yl) pyridine (bzthpy, 3), 2,6-bis(benzoxazol-2-yl)pyridine (bzoxpy, 4), and 2,2′, 6′, 2″-terpyridyl (terpy, 5) is reported. Electronic and EPR spectra are consistent with the complexes [CuL]2+ having essentially tetragonal structure in solution, with the fourth coordination site in the plane of the ligand occupied by solvent. bzthpy and bzoxpy show smaller ligand-field splittings than bzimpy, mbzimpy, and terpy, and are easily decomplexed from the copper. Substitution of the coordinated solvent molecule in the plane of the ligand is observed with Cl- and OH- (provided that the ligand has no acidic protons) for all ligands except terpy. The reaction between [Cu(mbzimpy)]2+ and imidazole has been studied by potentiometric titration in MeCN/H2O 1:1 and shows strong binding of the imidazole in the plane (log K = 4.5 at 25°), and also the formation of an imidazolate-bridged dinuclear species.
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  • 78
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (1R, 2R, 4R)-2-endo-Cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl acetate ((-)-7) has been transformed into the all-cis-configurated 4L-4,5,6/0-trihydroxycyclohex-2-en-1-one derivatives (-)-12 and (-)-19. (-)-Conduritol C ((-)-3) was derived in a stereospecific manner from (-)-12.
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  • 79
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    Helvetica Chimica Acta 72 (1989), S. 348-352 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diels-Alder Reactions with 3-Cyclopropylideneprop-1-enyl Ethyl Ether as 1,3-DieneThe title compound undergoes readily Diels-Alder reactions with various dienophiles, especially with quinones. The resulting adducts constitute key intermediates in the synthesis of labdane diterpenoids.
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  • 80
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    Helvetica Chimica Acta 72 (1989), S. 370-376 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New Approaches to Some Aromatic RetinoidsStarting from 2,3,5-trimethylphenol (2), two pathways to ethyl (all-E)-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethylnona-2,4,6,8-tetraenoate (1) and to some of its (Z)-isomers have been developed. The first one is based on a Pd(O)-catalyzed arylation of (Z)-3-methylpent-2-en-4-yn-l-ol (6) with 4-bromo-2,3,5-trimethylanisol (5). The acetylenic C15-alcohol 9 was transformed into the corresponding acetylenic phosphonium salt 10, which was catalytically hydrogenated to the olefinic Wittig salt. Wittig olefination led, then, to the (6Z, 8Z)- and (4Z, 6Z, 8Z)-isomers, 7 and 8, respectively. In a second approach, Friedel-Crafts reaction of 3-methylpent-l-en-4-yn-3-ol with the 2,3,5-trimethylanisol gave a C15-intermediate with a terminal C=C bond in the side chain. After deprotonation and reaction with a C5 aldehyd, the corresponding C20-intermediate could be isolated in high yield. Finally, further conversion led predominantly to the (all-E)-retinoid, accompanied by its (9Z)- and (13Z)-isomers.
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  • 81
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    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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  • 82
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Incubation of the geraniols (R)-(8-2H1)[8-3H1]-1 and (S)-(8-2H1)[8-3H1]-1 with microsomal cytochrome P-450Cath. from the subtropical plant Catharanthus roseus (L.)G. DON resulted in the formation of the chiral 8-hydroxygeraniols (S)-(8-2H1)[8-3H1]-2 and (R)-(8-2H1)[8-3H1]-2. Their absolute configuration was assigned on the basis of the 1H-decoupled 3H-NMR Spectra of the corresponding dicamphanates (S)-(8-2H1)[8-3H1]-9 and (R)-(8-2H1)[8-3H1]-9, of which the configurations are established in relation to the synthetic reference samples. The results clearly indicate retention of configuration during the allylic oxidation of 1.
    Additional Material: 2 Ill.
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  • 83
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hormaomycin, a Novel Peptide Lactone with Morphogenetic Activity on StreptomycesA culture identified as Streptomyces griseoflavus (strain W-384) has been found to produce a novel peptide-lactone antibiotic designated hormaomycin (6). The empirical molecular formula of the compound is established to be C55H69ClN10O14. The constituent amino acids of the antibiotic are suggested to be allothreonine (1; 1), isoleucine (2; 1), 3-methyl-phenylalanine (3; 2), and, for the first time identified from a natural source, 4-[(Z)-prop-1-enyl]-proline (4; 1) and 3-(2-nitrocyclopropyl)-alanine (5; 2). The amino acids were delivered by acidic hydrolysis and assigned by high-resolution- GC/MS analysis (after transformation to derivatives) in combination with extended 2D-NMR experiments of the antibiotic itself. From the latter, it became plausible that the N-terminus of the peptide chain is acylated by a Cl-containing derivative of 1H-pyrrol-2-carboxylic acid. Hormaomycin is active against some Gram-positive bacteria. In addition, the antibiotic exhibits potent aerial mycelium-inducing activity and effects the production of antibiotics.
    Notes: No abstract.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 84
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetylenic acetals of type I (Scheme 1) and acetylenic ketones of type III (Scheme 1), 37 and 38 (Scheme 7) are versatile synthetic precursors for the synthesis of various heterocycles by acid-catalyzed cyclization reactions. By this way, substituted 3-halofurans of type II and IV (Scheme 1) and flavones and styrylchromones (Scheme 7) can be synthesized in good-to-excellent yields. The high degree of regioselectivity in the synthesis of the 3-halofurans (Scheme 4) is the result of the regioselective β-addition of HX (X = Cl, Br, I) to the acetylenic aldehyde and acetylenic ketone moieties. A possible mechanism is depicted in Scheme 5. Since 3-halofurans can easily be metalated and substituted, this approach constitutes a new synthesis of highly substituted furans.
    Additional Material: 3 Tab.
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  • 85
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Electrochemical Decarboxylation of L-Threonine and Oligopeptide Derivatives with Formation of N-Acyl-N, O-acetals: Preparation of Oligopeptides with Amide or Phophonate C-TerminusDerivatives of α-amino acids with two stereogenic centers (cf. L-threonine) and of di-, tri-, and tetrapeptides are electrolyzed in MeOH or AcOH, with formation of N-acyl-N, O-acetals (1b-15b, 20b), in an anodic oxidative substitution of the COOH by an OR group. The amine ends of the oligopeptides may be benzyloxycarbonyl(Z)- or (tert-butoxy)carbonyl(Boc)-protected. With unprotected dipeptides, an electrolytic decarboxylative cyclization to imidazolidinones (18c, 19c) may also occur (in H2O/NH4OAc). The electrolyses are carried out in simple flasks with cooling jackets (‘undivided cell’), using constant current conditions and anodes of Pt or glassy C. The electrolyte is generated in situ by adding 10-20 mol-% of a tertiary amine. Mild acidic hydrolysis of electrolysis products thus obtained may lead to amino-acid amides or peptide amides (10c, 11c, 12c, 17c) with one amino acid less than the starting material. The N, O-acetals from L-threonine and the oligopeptides also react with organometallic nucleophiles such as Grignard compounds (→21-26, 29), with formation of products in which the original COOH group has been replaced by alkyl or allyl (sometimes even with moderate stereoselectivity). By treatment of the peptide-derived (open-chain) N, O-acetals with trialkyl or triaryl phosphites/TiCl4 the RO group is replaced by a phosphodiester group in a (non-diastereoselective) Michaelis-Arbuzov-type reaction (1d, 1e, 2d-9d, 5e). Thus, the two-step sequence of electrolysis and phosphonation converts an oligopeptide derivative to an analogue with a phosphonic-acid end group. The diastereoisomeric N-protected dimethyl and diethyl dipeptidephosphonates (also prepared from the corresponding diaryl esters by Ti(OR)4-mediated transesterification) could be separated by preparative HPLC (SiO2, Lichrosorb Si 60, 10 μm); the dextrorotatory isomers of 1d-3d were assigned L, D-, the laevoratory ones L, L-configuration by hydrolysis to and identification of the known amino and aminophosphonic acids. The results described demonstrate a new simple route leading, from a given oligopeptide, to pure peptide analogues of known configuration.
    Notes: No abstract.
    Additional Material: 2 Ill.
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  • 86
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Further investigation of global extracts from cultures of the marine deuteromycete Dendryphiella salina leads to the isolation of three novel trinor-eremophilanes esterified by branched C9-carboxylic acids, dendryphiellin B(= (+)-(1R*,2S*,7R*,8aR*)-1,2,6,7,8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*, 2E, 4E)-6-hydroxy-6-methylocta-2,4-dienoate; (+)-2), dendryphiellin C (=(+)-(1R*, 2S*, 7R*, 8aR*)-1,2,6,7,8,8a-hexa-hydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6S, 2E, 4E)-6-methylocta-2,4-dienoate; (+)-3)), and dendryphiellin D (=(+)-(1R*, 2S*, 7R*, 8aR*)-1,2,6,7(8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*,2E,4E)-6-(hydroxymethyl)octa-2,4-dienoate; (+)-4). An intact eremophilane, dendryphiellin E (5), and its ethanolysis product dendryphiellin F whose absolute configuration is represented by structural formula (+)-6 are also isolated from the above extracts. Dendryphiellin E exists as an open form 5a in equilibrium with a closed form 5b. A similar equilibrium exists between the open form 8a and the closed form 8b of a non-esterified eremophilane, dendryphiellin G (8), which is isolated too from the above extracts and proves structurally related to the cyclic portion of 5. Finally, the free, branched C9-carboxylic acids dendryphiellic acid A ((+)-9) and B ((+)-10) which correspond to side chains of the above esterified terpenes are also isolated from the above extracts.
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  • 87
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 457-463 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: A New Azepine-Ring SynthesisA new one-step synthesis of an azepine ring is described. The 2H-pyran-2-one ring of methyl cumalate (8) or cumalaldehyde (2) upon reaction with an 1-aminoacryl derivative, e.g. 1 or 6, is opened with subsequent decarboxylation to give a 1-aminobutadiene derivative that undergoes an electrocyclic ring closure to the azepine ring (Schemes 1 and 2).
    Notes: No abstract.
    Additional Material: 1 Ill.
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  • 88
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present study, it is confirmed that the deuteration of C—H groups is accompanied by a small but genuine decrease in lipophilicity. The lipophilicity of deuterated isotopomers of caffeine was measured by reversed-phase HPLC. Overall, lipophilicity was shown to decrease when going from unlabelled caffeine to the three isomeric trideuterated caffeines, then to the three isomeric hexadeuterated caffeines, and finally to nonadeuterated caffeine. In addition, position-specific effects were also proven. E.g. (7-methyl-2H3)caffeine experienced a smaller isotope effect than its two positional isomers. Both a cavity factor (decreased volume of deuterated isotopomers) and intramolecular electronic effects are postulated to operate.
    Additional Material: 2 Tab.
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  • 89
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crude petroleum-ether extract of the root bark of Hypericum revolutum VAHL (Guttiferae) exhibited in vitro growth-inhibitory activity against the Co-115 human colon carcinoma cell line. Activity-guided fractionation of this extract resulted in the isolation of two new hyperforin derivatives 1 and 2. The structure of 1 (hyperevolutin A) was established by X-ray analysis as the 4-hydroxy-8-exo-methyl-5,7-exo-bis(3-methylbut-2-enyl)-1-(2-methyl-1-oxopropyl)-8-endo-(4-methylpent-3-enyl)bicyclo[3.3.1]non-3-ene-2,9-dione. The structure of the homologue 2 was deduced by comparison of its UV and 1H- and 13C-NMR spectra with those of 1.
    Additional Material: 2 Ill.
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  • 90
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new linear triamine 2,6-bis(pyrrolidin-2-yl)pyridine (II) has been synthesized, and the (R, S)-, (R, R)-, and (S, S)-isomers have been separated. Compared to other triamines showing a similar structure, these new ligands form very stable Cu2+ complexes. No significant difference is observed between the meso and the racemic forms for their binary or ternary mixed-ligand complexes with the amino acids alanine and proline.
    Additional Material: 1 Ill.
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  • 91
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 482-486 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from sultam 1, the chiral dienophile (2R)-N-glyoxyloylbornane-10,2-sultam (4) was readily prepared. Non-catalyzed atmospheric- and high-pressure as well as [Eu(fod)3]-promoted [4 + 2] cycloadditions of 1-methoxy-buta-1,3-diene (5) to chiral dienophile 4, leading with high asymmetric induction to 6-methoxy-3,6-dihydro-2H-pyran-2-yl derivatives 6-9, are described. The extent and direction of asymmetric induction in these reactions were established by 1H-NMR analysis and chemical correlation, respectively. Stereochemical models for both non-catalyzed and [Eu(fod)3]-promoted reactions are proposed.
    Additional Material: 1 Tab.
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  • 92
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 496-501 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of (R)-β, β-Caroten-2-ol and (2R, 2′R)-β, β-Carotene-2,2′-diolStarting from geraniol, the two carotenoids (R)-β, β-caroten-2-ol (1) and (2R, 2′R)-β, β-carotene-2,2′-diol (3) were synthesized. The optically active cyclic building block was obtained by an acid-catalysed cyclisation of the epoxide (R)-4. The enantiomeric excess of the product was 〉 95 %.
    Notes: No abstract.
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  • 93
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a search for further synthetic routes to substituted [5.5.5.5] fenestranes, compound 1a, a derivative of 7-methoxyindane, was photolyzed. Two of the three photoproducts, viz. the [3.5.5.5]fenestrane 3a and the isomer 4a, are formed according to the expected intramolecular meta-cycloaddition. A different mechanism is suggested for the formation of the major component 2a.
    Additional Material: 4 Tab.
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  • 94
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2-azatricyclo[5.2.2.01,5]undeca-4,8,10-trien-3-ones 1a and 1b gave on irradiation the 2-azatricyclo-[6.2.1.01,5]undeca-4,6,9-trien-3-ones 2a and 2b, respectively. The rearrangement was found to be solvent-, oxygen-, and wavelength-independant.
    Additional Material: 2 Ill.
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  • 95
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 8-substituted xanthines 1-21 (including compound S 9795), caffeine (22), and the three isomeric dimethyl-xanthines 23-25 (see Table 1), were examined for their lipophilic behaviour using a reversed-phase HPLC technique. A number of flexible compounds showed a smaller-than-expected lipophilicity which based on conformational and tautomeric calculations were ascribed to the predominance of folded forms. A QSAR analysis of the phosphodiesterase-inhibitory potency of several compounds showed favourable factors to be a low lipophilicity and the absence of a substituent on the N7 position.
    Additional Material: 5 Ill.
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  • 96
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total synthesis of racemic cis-2,3,181, 182, -tetrahydroprotobiliverdin IXα dimethyl ester (19b), which is identical with the dimethyl ester of rac-4, is described (Scheme 2). Under virtually neutral conditions, in solution, this bile pigment isomerized within a few min to racemic Z-phycocyanobilin dimethyl ester (rac-5b). Likewise, acid-catalyzed allyl rearrangement of 3-vinyl-substituted cis- and trans-2,3-dihydrodipyrrin-1(10H)-ones 11c and 13c, respectively, yielded the corresponding ethylidene derivatives. In this case, however, the E-isomer was formed stereo selectively from both substrates. The above results prove that, if protobiliverdin IXα (2) is transformed enzymatically to its 2,3,181, 182-tetrahydro derivative, the latter would isomerize spontaneously to phycocyanobi-lin. The biosynthesis of bacteriochlorophyll a and b from a common precursor bearing a vinyl group at C(8)may be straightforwardly explained in the same way.
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  • 97
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation of Substituted 2-Aminooxazole-4-carbonitrilesDuring our synthetic programme to convert 4-isoxazolylthioureas 3 into the corresponding carbodiimides 5, a side reaction leading to the hitherto unknown 2-aminooxazole-4-carbonitriles 6 was observed. By selecting appropriate reaction conditions, it was possible to improve the yields of the carbodiimides 5 as well as of the novel oxazole-carbonitriles 6 at will, thus allowing the synthesis of 6 to be conducted in very good yields. To overcome the difficulty of isolating unstable carbodiimides, the synthesis of 6 is best carried out in a one-pot procedure. A limited mechanistic study showed that the formation of 6 proceeds via 5 as the only intermediate. The stability of the N=C=N bonds against base attack (depending strongly on both sterical hindrance and electronic-density factors) forms the only limitation of this new synthetic pathway to oxazole-4-carbonitriles.
    Notes: No abstract.
    Additional Material: 4 Tab.
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  • 98
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 632-633 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    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
    Type of Medium: Electronic Resource
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  • 100
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Evidence is presented for the first time that ‘naked’ Fe+ ions, complexed to the NH2 group of primary amines, are capable of intramolecularly activating C—C bonds in a highly specific mode without preceding C—H activation.
    Additional Material: 2 Tab.
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