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  • 1
    Electronic Resource
    Electronic Resource
    Interaction of propafenone enantiomers with human α1-acid glycoprotein (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 30-34 
    Details
    ISSN: 0899-0042
    Keywords: propafenone ; enantiomers ; α1-acid glycoprotein ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of propafenone enantiomers with human α1-acid glycoprotein was studied using high-performance liquid chromatography. Each of the two optical antipodes interacted with one class of high-affinity binding sites characterized by Ka(R) = (6.18 ± 0.93) × 105 M-1, n(R) = 1.34 ± 0.09 for the (R)-isomer and Ka(S) = (8.93 ± 1.82) × 105 M-1, n(S) = 0.99 ± 0.08 for the (S)-isomer. Nonspecific binding to secondary low-affinity high-capacity binding site(s) was only slightly greater in the case of the (S)-enantiomer (n′k′(S) = (1.06 ± 0.09) × 104 M-1) compared to the (R)-enantiomer (n′k′(R) = (6.87 ± 0.72) × 103 M-1). It was concluded that both enantiomers interact with common single class of high-affinity binding sites on AAG (along with nonspecific binding) exhibiting only slight stereoselectivity for propafenone.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030107
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  • 2
    Electronic Resource
    Electronic Resource
    A molecular dynamics investigation of chiral discrimination complexes as chiral stationary-phase models: Methyl N-(2-naphthyl)alaninate with N-(3,5-dinitrobenzoyl)leucine n-propylamide (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 56-66 
    Details
    ISSN: 0899-0042
    Keywords: molecular recognition ; chiral recognition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations were performed on complexes of (S)-methyl N-(2-naphthyl)alaninate (NAP) with the enantiomers of N-(3,5-dinitrobenzoyl)leucine n-propylamide (DNB), which are used as models for chiral stationary-phase systems developed by Pirkle and co-workers. These studies were undertaken to qualitatively examine (pictorially) the role of entropic effects in these systems. The results of the dynamics calculations were used to refine the search for low-energy conformers. The structures were refined by the use of BioDesign's molecular mechanics method implemented in Biograf. The results of the structural refinements support our previous observation that the SR complex can achieve the same three primary interactions which are observed in the SS structure (i.e., two intermolecular hydrogen bonds and pi stacking) without a significant increase in energy. In addition, these primary interactions are conserved during molecular dynamics simulations with the occurrence of conformations which differ only in the rotational states of the alkyl side chains and ester group (which bears two potential hydrogen bond acceptors utilized in both the homo- and heterochiral complexes). The major difference in the two complexes is the relative position of the sec-butyl group and hydrogen atom on DNB's chiral center, both of which are outside the primary interaction region. All other local minima which have different relative pi orientations (“front-back,” “back-back,” and “back-front” as defined herein) are not sufficiently populated to make more than a negligible contribution to the statistical (time- or energy-averaged) analysis of the (SS)- and (SR)-NAP-DNB complexes. Thus the entropic effects observed in this study (e.g., alkyl side chain or ester group rotations) do not show evidence of qualitative differential effects on the maintenance of the same three primary interactions by both the homo- and heterochiral complexes. The reliability of the present study, which provides pictorial representations of the entropic effects, is not sufficient to determine whether the entropic effects observed herein are sufficient to achieve enantiomeric discrimination alone or in conjunction with other factors (e.g., conformational strain energy). Thus, all of the computational studies we have performed to date (i.e., our previous studies, which include strain energy and through-space field effects, and the present study, which includes entropic effects) show no evidence of any qualitative difference in the homo- and heterochiral complexes in terms of maintaining the same three “contact points”.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030110
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  • 3
    Electronic Resource
    Electronic Resource
    A highly enantioselective rhodium catalyst for the hydrogenation of aliphatic α-keto esters (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 370-375 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective catalysis ; (2S)-ethyl-2-hydroxy-4-phenylbutyrate ; (S)-ethyl lactate ; α-hydroxy esters ; (2S,3S)-NORPHOS ; rhodium diphosphine catalyst ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselective hydrogenation of several α-keto acid derivatives with rhodium diphosphine catalysts has been investigated using a random screening approach. The neutral rhodium catalyst prepared in situ from bis(2,5-norbornadiene rhodium chloride) and NORPHOS has been found to be an excellent catalyst for preparing aliphatic α-hydroxy esters in high optical purities. The reaction parameters for the hydrogenation of ethyl 2-oxo-4-phenyl-butyrate, an intermediate for the ACE inhibitor Benazepril, were optimized and the best optical yields obtained were 96%.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030423
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  • 4
    Electronic Resource
    Electronic Resource
    N,N-dimethylcarbamyl derivatives of oxazepam (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 212-219 
    Details
    ISSN: 0899-0042
    Keywords: oxazepam ; demoxepam ; 3-O-acyl-1-(N,N-dimethylcarbamyl)oxazepam ; 1-(N,N-dimethylcarbamyl)oxazepam ; 3-O-(N,N-dimethylcarbamyl)oxazepam ; camazepam ; norcamazepam ; 1,3-O-bis(N,N-dimethylcarbamyl)oxazepam ; kinetics of racemization ; enantioselectivity of esterases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three N,N-dimethylcarbamyl derivatives of oxazepam {1-(N,N-dimethylcarbamyl)oxazepam, 3-O-(N,N-dimethylcarbamyl)oxazepam, and 1,3-O-bis(N,N-dimethylcarbamyl)oxazepam} and a 3-O-acyl-1-(N,N-dimethylcarbamyl)-oxazepam were synthesized from either oxazepam or demoxepam. Enantiomeric pairs of these derivatives and of camazepam were resolved by high-performance liquid chromatography on at least two of three commercially available chiral stationary phase columns employed. Absolute configurations of resolved enantiomers were established by comparing their circular dichroism spectra to those of enantiomeric oxazepams with known absolute stereochemistry. Similar to those of oxazepam, enantiomers of 1-(N,N-dimethylcarbamyl)oxazepam undergo rapid racemization (t½ 1.9 min at 23°C and 0.9 min at 37°C) in an aqueous solution at pH 7.5. The (R)-enantiomer of rac-3-O-acyl-1-(N,N-dimethylcarbamyl)oxazepam was hydrolyzed ∼4.6-fold faster than the (S)-enantiomer by esterases in rat liver microsomes, whereas the (S)-enantiomer was hydrolyzed ∼43-fold faster than the (R)-enantiomer by esterases in rat brain S9 fraction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030313
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  • 5
    Electronic Resource
    Electronic Resource
    Prebiotic sources of biomolecular handedness (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 223-226 
    Details
    ISSN: 0899-0042
    Keywords: enantiomers ; diastereomers ; chirality ; circularly polarized radiation ; circular dichroism ; parity violation ; electroweak interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fischer demonstrated (1890-1919) that functional biomolecules are composed specifically of the D-sugars and the L-amino acids, and that in the laboratory synthetic reactions of such molecules propagate with chiral stereoselectivity. Given a primordial enantiomer, biomolecular homochirality followed without the intervention of the chiral natural force conjectured by Pasteur (1860), except prebiotically. Polarized solar radiation and other classical chiral forces were proposed as agencies generating a prebiotic enantiomeric excess, but the forces then known were found to be evenhanded on a time and space average, exemplifying parity conservation (1927). The weak nuclear force, shown to violate parity (1956), was unified with electromagnetism in the electroweak force (1970). Ab initio estimations including the chiral electroweak force indicate that the L-amino acids and the D-sugars are more stable than the corresponding enantiomers. The small energy difference between these enantiomer pairs, with Darwinian reaction kinetics in a flow reactor, account for the choice of biomolecular handedness made when life began.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030403
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  • 6
    Electronic Resource
    Electronic Resource
    Chiral aspects of drug action at ion channels: A commentary on the stereoselectivity of drug actions at voltage-gated ion channels with particular reference to verapamil actions at the Ca2+ channel (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 393-404 
    Details
    ISSN: 0899-0042
    Keywords: verapamil ; ion channels ; calcium channels ; 1,4-dihydropyridines ; state-dependent interactions ; channel activators ; channel antagonists ; local anesthetics ; sodium channels ; potassium channels ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion channels may be considered as pharmacological receptors possessing specific drug binding sites with defined structure-activity relationships. Accordingly drug binding to ion channels is stereoselective. Interpretation of this stereoselectivity may be complex because of the existence of differences in affinity and access to different channel states. Such state-dependent interactions may give rise to quantitative and qualitative differences in stereoselectivity. The implications of such differences are reviewed for drug action at Na+, K+ and Ca2+ channels. Detailed attention is paid to the actions of verapamil enantiomers in the cardiovascular system where activities differ in vascular and cardiac tissues because of state-dependent interactions and stereoselective first-oass metabolism.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030504
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  • 7
    Electronic Resource
    Electronic Resource
    Interaction of pirprofen enantiomers with human serum albumin (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 412-417 
    Details
    ISSN: 0899-0042
    Keywords: pirprofen enantiomers ; human serum albumin ; binding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of pirprofen enantiomers with human serum albumin (HSA) was investigated by means of high-performance liquid chromatography (HPLC), circular dichroism (CD), and 1H NMR spectroscopy. HPLC experiments indicated that both pirprofen enantiomers were bound to one class of high-affinity binding sites (n(+) = 1.91 ± 0.13, K(+) = (4.09 ± 0.64) × 105 M-1, n(-) = 2.07 ± 0.13, K(-) = (6.56 ± 1.35) × 105 M-1) together with nonspecific binding (n′K′(+) = (1.51 ± 0.21) × 104 M-1, n′K′(-) = (0.88 ± 0.13) × 104 M-1). Slight stereoselectivity in specific binding was demonstrated by the difference in product n(+)K(+) = (0.77 ± 0.08) × 106 M-1 vs. n(-)K(-) = (1.30 ± 0.21) × 106 M-1, i.e., the ratio n(-)K(-)/n(+)K(+) = 1.7. CD measurements showed changes in the binding sites located on the aromatic amino acid side chains (a small positive band at 315 nm and a pronounced negative extrinsic Cotton effect in the region 250-280 nm). The protein remains, however, in its predominantly alpha-helical conformation. The 1H NMR difference spectra confirmed that both pirprofen enantiomers interacted with HSA specifically, most probably with site II on the albumin molecule.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030506
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  • 8
    Electronic Resource
    Electronic Resource
    In vitro assessment of stereoselective hepatic metabolism of disopyramide in humans: Comparison with in vivo data (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 405-411 
    Details
    ISSN: 0899-0042
    Keywords: disopyramide ; enantiomers ; metabolism ; human hepatocyte cultures ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metabolism of disopyramide (DP) enantiomers has been investigated in primary cultures of adult human hepatocytes. Results were compared with in vivo data obtained from a previous pharmacokinetic study (Le Corre et al. Drug Metab. Dispos. 16:858-864 1988). Metabolism of DP enantiomers as a function of incubation time showed constant velocity over time. The intracellular/extracellular distribution of both DP and mono-N-desisopropyldisopyramide did not appear to be stereoselective. Metabolism of DP enantiomers as a function of substrate concentration followed a first order kinetics. The average fractions of (-)-(R)-DP and (+)-(S)-DP metabolized in vitro (4.7 ± 2.7 and 7.1 ± 4.2%, respectively, n = 4) were about 5-fold lower than the fractions metabolized in vivo (26.0 ± 6.0 and 40.2 ± 8.8%, respectively, n = 6). The stereoselective index [(+)-(S)/(-)-(R)] of the N-dealkylation pathway obtained in vitro (1.51 ± 0.11, n = 4) was very close to the one obtained in vivo (1.55 ± 0.10, n = 6). These results highlight the interest of hepatocyte cultures in the evaluation of drug metabolism and especially in the assessment of stereoselectivity.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030505
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  • 9
    Electronic Resource
    Electronic Resource
    Chiral separation of N-aminoalkylsuccinimides on an α1 - acid glycoprotein column: A quantitative structure - enantioselectivity relationship study (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 422-426 
    Details
    ISSN: 0899-0042
    Keywords: CHIRAL-AGP ; HPLC ; PLS ; principal components ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two quantitative structure-enantioselectivity models have been developed for a series of N-aminoalkylsuccinimides using the statistical method PLS. The models permit the prediction of enantioselectivity on an α1-acid glycoprotein column. The models are based on a physiocochemical description of the structures.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030508
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  • 10
    Electronic Resource
    Electronic Resource
    An evaluation of ibuprofen bioinversion by simulation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 418-421 
    Details
    ISSN: 0899-0042
    Keywords: chiral bioinversion ; pharmacokinetics ; (+)-(S)-ibuprofen ; (-)-(R)-ibuprofen ; rac-ibuprofen ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a pharmacokinetic model recently proposed to explain ibuprofen disposition in man,1 plasma concentrations of pure ibuprofen enantiomers were simulated following oral administration of (-)-(R)-ibuprofen, (+)-(S)-ibuprofen, or rac-ibuprofen. Simulated and literature values for AUC's were used to compare S/R ratios for different cases of the model and for different methods of calculating the fraction of R bioinverted to S. Numerical simulation using STELLA confirmed previous results for different cases of bioinversion. Simulated S/R AUC ratios, for administration of the racemate, ranged from 4.0 (presystemic bioinversion) to 1.66 (systemic bioinversion). Literature values for S/R AUC ratios averaged 1.53±0.2 for administration of the racemate; therefore, systemic bioinversion was concluded to be representative of ibuprofen disposition. Additional simulations of S/R AUC ratios, for administration of (-)-(R)-ibuprofen only, ranged from 1.5 (presystemic bioinversion) to 0.66 (systemic bioinversion). Literature values for S/R AUC ratios averaged 0.50±0.9 for administration of (-)-(R)-ibuprofen only, which again supported conclusions of systemic bioinversion. Using different equations for estimation of fraction of R inverted to S (FR→S), results based on simulated data were identical; however, FR→S values based on literature data were different. Therefore, assumptions made for different FR→S equations do not appear to be rigorous. Calculations of FR→S, based on literature data, averaged 0.52 overall, indicating bioavailability of (+)-(S)-ibuprofen may be similar for a 150 mg dose of (+)-(S)-ibuprofen compared to a 200 mg dose of racemate.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030507
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  • 11
    Electronic Resource
    Electronic Resource
    The absolute configuration of the enantiomers of 6-chloro-9-(4′-diethylamino-1′-methylbutyl)-amino-2-methoxyacridine (quinacrine) (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 436-437 
    Details
    ISSN: 0899-0042
    Keywords: stereochemistry ; quinacrine ; enantiomers ; enantioselectivity ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute configurations have been assigned to the enantiomers of the antimalarial drug quinacrine dihydrochloride. Condensation of (-)-(R)-4-amino-1-diethylaminopentane (from L-glutamic acid) with 6,9-dichloro-2-methoxyacridine gave (-)-(R)-6-chloro-9-(4′-diethylamino-1′-methylbutyl) amino-2-methoxyacridine [(-)-(R)-quinacrine] while (+)-(S)-quinacrine was obtained from the enantiomeric diamine.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030510
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  • 12
    Electronic Resource
    Electronic Resource
    Steric hindrance influence on the enantiorecognition ability of tyrosine-derived chiral stationary phases (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 427-435 
    Details
    ISSN: 0899-0042
    Keywords: enantiomeric separations ; chiral stationary phases ; tyrosine chiral selector ; HPLC ; reversal of elution order ; chiral recognition mechanisms ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four chiral stationary phases (CSPs) derived from N-(3,5-dinitrobenzoyl)tyrosine have been synthesized. They differ by the substituent nature (methyl, ethyl, isopropyl, tert-butyl) of the aliphatic amide function. The enantiorecognition ability of these CSPs was evaluated with 10 racemates. For the majority of them, the stereoselectivity increases with the steric hindrance of the substituent. The chiral selector enantiomeric separation on the resulting CSPs has evidenced a reversal of elution order only for CS 4 on CSP 4 (tert-butyl substituent), suggesting a change in its conformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030509
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  • 13
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030601
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  • 14
    Electronic Resource
    Electronic Resource
    Editorial: Notes from the editor-in-chief (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 439-439 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030602
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  • 15
    Electronic Resource
    Electronic Resource
    Letter to the editors (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 440-440 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030603
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  • 16
    Electronic Resource
    Electronic Resource
    Letter to the editors (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 441-441 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030604
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  • 17
    Electronic Resource
    Electronic Resource
    Letter to the editors: Should the terminology used in chirality be more precise? (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 442-442 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030605
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  • 18
    Electronic Resource
    Electronic Resource
    Steric aspects of agonism and antagonism at β-adrenoceptors: Synthesis of and pharmacological experiments with the enantiomers of formoterol and their diastereomers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 443-450 
    Details
    ISSN: 0899-0042
    Keywords: chiral separation ; enantiomeric purity ; tracheal smooth muscle ; skeletal muscle ; cardiac muscle ; guinea pig ; in vitro ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of formoterol (R;R and S;S) and their diastereomers (R;S and S;R) were synthesized and purified using a new procedure which required the preparation of the (R;R)- and (S;S)-forms of N-(1-phenylethyl)-N-(1-(ρ-methoxyphenyl)-2-propyl)-amine as important intermediates. The enantiomeric purity obtained was greater than 99.3%, usually 〉 99.7%. The four stereoisomers were examined with respect to their ability to interact in vitro with β-adrenoceptors in tissues isolated from guinea pig. The effects measured were (1) relaxation of the tracheal smooth muscle (mostly β2), (2) depression of subtetanic contractions of the soleus muscle (β2), and (3) increase in the force of the papillary muscle of the left ventricle of the heart (β1). All enantiomers caused a concentration-dependent and complete relaxation of the tracheal smooth muscle which was inhibited by propranolol. The order of potency was (R;R) 〉 〉 (R;S) = (S;R) 〉 (S;S). There was a 1,000-fold difference in potency between the most and the least potent isomer. The presence of the (S;S)-isomer did not affect the activity of the (R;R)-isomer on the tracheal smooth muscle. Also on the skeletal and cardiac muscles (R;R)-formoterol was more potent than its (R;S)-isomer. The selectivity for β2-adrenoceptors appeared to be slightly higher for the (R;R)-isomer than for the (R;S)-isomer. The potency of the (S;R)- and (S;S)-isomers on the papillary muscle was too low to be determined accurately. The present study shows that determination of enantiomeric ratios and conclusions regarding structure-effect relationships are critically dependent on a very high degree of stereochemical purity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030606
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  • 19
    Electronic Resource
    Electronic Resource
    Stereoselective accumulation of the β-receptor blocking drug atenolol by human platelets (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 451-453 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective ; stereoisomers ; β-blockers ; adrenergic β-receptor blockaders ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied the stereochemistry of accumulation of the hydrophilic β-adrenoceptor antagonist rac-atenolol by human platelets in vitro. The accumulation was slow, not reaching equilibrium until 90 min at 37°C. The uptake was temperature dependent with the accumulation at 37°C being 3-4 times greater than at 4°C. The accumulation was also stereoselective at 37°C, favoring the active (-)-enantiomer over the (+)-enantiomer by 2.3-fold. Reserpine, but not desipramine, inhibited the platelet accumulation of rac-atenolol enantiospecifically. This uptake profile is different from the platelet uptake of lipophilic β-blockers, which is characterized by nonspecific membrane binding, but similar to the carrier-mediated accumulation of the neurotransmitter norepinephrine by storage granules within the platelet.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030607
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  • 20
    Electronic Resource
    Electronic Resource
    Stereoselective inhibition of diphenylhydantoin metabolism by p-hydroxyphenyl-phenylhydantoin enantiomers in rats (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 454-459 
    Details
    ISSN: 0899-0042
    Keywords: phenytoin ; product inhibition ; p-HPPH ; rat liver microsomes ; ligand-exchange chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different doses of rac-p-HPPH (0.4 and 4 mg/h) were given repeatedly to rats infused with [14C]phenytoin. The serum levels of 14C-labeled and unlabeled p-HPPH, and [14C]phenytoin were measured by an HPLC method and radiometric analysis. The clearance of phenytoin and p-HPPH was determined by rate of dosing divided by the steady-state concentration. The phenytoin clearance was significantly lower in the high dose p-HPPH injection group than in the low dose group (87 versus 262 ml/h), whereas p-HPPH clearance showed no difference. The formation clearance of [14C]p-HPPH was also significantly lower in rats injected with high dose of p-HPPH (35 versus 169 ml/h). The clearance of other elimination pathways was also lower in rats with high dose of p-HPPH (53 versus 89 ml/h). The serum protein binding of phenytoin was lower in rats injected with high dose of p-HPPH. The result indicated that injections of rac-p-HPPH mainly inhibited on the formation of p-HPPH itself. The formation of (R)-p-HPPH and (S)-p-HPPH in microsomal preparation was measured by a ligand-exchange chromatographic method. The formation of (S)-p-HPPH or (R)-p-HPPH was not only inhibited by the enantiomer itself, but also cross-inhibited by the other enantiomer. To the formation of either (S)-p-HPPH or (R)-p-HPPH, (S)-p-HPPH showed a higher inhibitory activity. The use of rac-p-HPPH to inhibit phenytoin metabolism in vivo involved several mechanisms. In addition to binding displacement on the serum proteins, one is the product inhibition by the respective p-HPPH metabolite, the other is the competitive inhibition by the other p-HPPH enantiomer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030608
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    Stereoselectivity of (R)- and (S)-hexahydro-difenidol binding to neuroblastoma M1, cardiac M2, pancreatic M3, and striatum M4 muscarinic receptors (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 118-123 
    Details
    ISSN: 0899-0042
    Keywords: hexahydro-difenidol enantiomers ; muscarinic receptor subtypes M1, M2, M3 and M4 ; stereoselective interaction ; difenidol ; dicyclidol ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (R)-Hexahydro-difenidol has a higher affinity for M1 receptors in NB-OK 1 cells, pancreas M3 and striatum M4 receptors (pKi 7.9 to 8.3) than for cardiac M2 receptors (pKi 7.0). (S)-Hexahydro-difenidol, by contrast, is nonselective (pKi 5.8 to 6.1). Our goal in the present study was to evaluate the importance of the hydrophobic phenyl, and cyclohexyl rings of hexahydro-difenidol for the stereoselectivity and receptor selectivity of hexahydro-difenidol binding to the four muscarinic receptors. Our results indicated that replacement of the phenyl ring of hexahydro-difenidol by a cyclohexyl group (→ dicyclidol) and of the cyclohexyl ring by a phenyl moiety (→ difenidol) induced a large (4- to 80-fold) decrease in binding affinity for all muscarinic receptors. Difenidol had a significant preference for M1, M3, and M4 over M2 receptors; dicyclidol, by contrast, had a greater affinity for M1 and M4 than for M2 and M3 receptors. The binding free energy decrease due to replacement of the phenyl and the cyclohexyl groups of (R)-hexahydro-difenidol by, respectively, a cyclohexyl and a phenyl moiety was almost additive in the case of M4 (striatum) binding sites. In the case of the cardiac M2, pancreatic M3, or NB-OK 1 M1 receptors the respective binding free energies were not completely additive. These results suggest that the four (R)-hexahydro-difenidol “binding moieties” (phenyl, cyclohexyl, hydroxy, and protonated amino group) cannot simultaneously form optimal interactions with the M1, M2, and M3 muscarinic receptors. When each of the hydrophobic groups is modified, the position of the whole molecule, relative to the four subsites, was changed to allow an optimal overall interaction with the muscarinic receptor.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030207
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  • 22
    Electronic Resource
    Electronic Resource
    Björn Ringdahl: A remembrance (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 156-156 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030214
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  • 23
    Electronic Resource
    Electronic Resource
    Synthesis of the [8] gingerol enantiomers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 151-155 
    Details
    ISSN: 0899-0042
    Keywords: (-)-(R) and (+)-(S) [8] gingerol ; enantiomers synthesis ; chiral stationary phase ; HPLC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (+)-(S)-5-Hydroxy-1-(4-hydroxy-3-methoxyphenyl)-3-dodecanone 1a commonly named (+)-(S)-[8] gingerol is a natural product known to have cardiotonic activity.1-5 A total synthesis of both enantiomers is described with details for the first time using a general synthetic scheme which was recently outlined in the literature.6 This synthesis relies both on the separation of the diastereoisomers 4a and 4b by simple column chromatography on silica gel and on an HPLC analysis on a chiral phase to determine the optical purity of the enantiomers 8a and 8b of protected [8] gingerol. The gingerol isomers were thus obtained in good chemical yields in greater than 96% enantiomeric excess.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030213
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  • 24
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    Synthesis and effects on peripheral thyroid hormone conversion of (R)-4-hydroxypropranolol, a main metabolite of (R)-propranolol (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 145-150 
    Details
    ISSN: 0899-0042
    Keywords: hyperthyroidism ; (R)-4-hydroxypropranolol ; peripheral conversion ; metabolites of propranolol ; negative chronotropic effect ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The inhibiting effect of (R,S)-propranolol on peripheral T4/T3 conversion can be related to the (R)-isomer. The intention of this study is to clarify if (R)-4-hydroxypropranolol, a main metabolite of (R)-propranolol, develops the same or even a stronger effect on peripheral thyroxine metabolism as the parent drug. (R)-4-hydroxypropranolol was synthesized via (R)-4-methoxypropranolol and their optical purity was checked chromatographically. Twenty patients suffering from hyperthyroidism were divided into five groups and treated with (R)-4-hydroxypropranolol · HCl in dosages from 12 to 75 mg per day in a placebo controlled study over a period of 5 days. The serum hormone levels and resting pulse rate were measured. No significant changes of thyroid parameter could be observed but a significant decrease of resting pulse rate under treatment with 75 mg (R)-4-hydroxypropranolol occurred. It could be concluded that (R)-4-hydroxypropranolol possesses negative chronotropic effects but develops no changes in thyroid hormone metabolism in hyperthyroid patients.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030212
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  • 25
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030101
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  • 26
    Electronic Resource
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    Second international symposium on Chiral discrimination (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 157-157 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030215
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  • 27
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    Molecular graphic and modelling training course intensive four-day course with “hands-on” training (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 158-158 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030216
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  • 28
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030301
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  • 29
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    On flying wedges, crashing wedges, and perspective-blind stereochemists (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 159-160 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030302
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  • 30
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    Drug chirality: Impact on pharmaceutical regulation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 161-164 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030303
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  • 31
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    Optical resolution of two isomeric naphthylalanines by immobilized enyzmes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 170-173 
    Details
    ISSN: 0899-0042
    Keywords: β-(1-naphthyl)alanine ; β-(2-naphthyl)alanine ; alumina ; α-chymotrypsin ; subtilisin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution of β-(1-naphthyl)alanine and β-(2-naphthyl)alanine have been efficiently carried out through enzymatic hydrolysis of their methyl ester and/or N-acetyl ester derivatives by immobilized enzymes. Difficulties related to the lipophilic character of these amino acids were overcome by using emulsions of n-butyl acetate-water as reaction medium. The use of an automatic recirculating apparatus allowed reproducible and repetitive use of the immobilized biocatalysts.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030305
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  • 32
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    N-(n-Butylamide) of (S)-2-(phenylcarbamoyloxy)propionic acid: A new chiral solvating agent, derived from L-lactic acid, for the enantiomeric purity determination of derivatized amino acids (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 174-176 
    Details
    ISSN: 0899-0042
    Keywords: chiral ; chiral solvating agent ; stereochemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-(n-butylamide) of (S)-2-(phenylcarbamoyloxy)propionic acid, easily prepared starting from the inexpensive L-ethyl lactate, can be used as convenient chiral solvating agent (CSA) to determine the enantiomeric composition of N-(3,5-dinitrobenzoyl)amino acid methyl esters.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030306
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  • 33
    Electronic Resource
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    Pharmacokinetics of ibuprofen enantiomers in dogs (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 165-169 
    Details
    ISSN: 0899-0042
    Keywords: ibuprofen ; enantiomer ; stereoselectivity ; chiral inversion ; pharmacokinetics ; dog ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Inversion of inactive (R)-ibuprofen to active (S)-ibuprofen has been suggested to occur presystemically only. In order to investigate the site of inversion in dogs we administered both enantiomers either intravenously or intraduodenally (10 mg/kg) to adult, male beagle dogs (n = 3) in a crossover design. Plasma, urine, and bile were collected for up to 6 h and analyzed stereospecifically by HPLC, according to a previously published method. Pharmacokinetic parameters were calculated using a linear computer program. Absorption after intraduodenal administration occurred rapidly, resulting in maximum plasma concentrations 0.2 h after giving the enantiomer. Approximately 70% of the (R)-enantiomer (according to AUC) was inverted to the S-enantiomer independent of route of administration. No R-ibuprofen could be detected in plasma after (S)-ibuprofen administration. Mean residence time was found to be 2 to 3 times longer for (S)-than for (R)-ibuprofen. Total systemic clearance from plasma was twice as high for (R)- than for (S)-ibuprofen. There were no differences between plasma clearances after intravenous and intraduodenal administration. Between 8 and 17% of dose was recovered in bile [especially as free and conjugated (S)-ibuprofen] and 3-12% in urine [as (S)-ibuprofen, hydroxy- and carboxyibuprofen, free and conjugated forms]. Small amounts of (R)-ibuprofen were detected in bile after intraduodenal administration of (R)-ibuprofen only (1.8% of dose). In short, the unidirectional inversion of R-ibuprofen appears to occur systemically rather than presystemically in dogs.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030304
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  • 34
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    Pharmacokinetic studies with the lipid-regulating agent beclobrate: Enantiospecific assay for beclobric acid using a new fluorescent chiral coupling component (S-FLOPA) (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 35-42 
    Details
    ISSN: 0899-0042
    Keywords: chiral derivatization ; pharmacokinetics ; enantiospecific assay ; fluorescent derivatization ; flunoxaprofen ; acyl glucuronides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The major biotransformation pathway for the chiral lipid-regulating agent beclobrate is conversion to the corresponding carboxylic acid, which is then metabolized to the acyl glucuronide. An enantiospecific assay for biological material was developed that is based on chiral derivatization with N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide (EDAC) and the primary amine S-FLOPA, a new chiral coupling component for carboxylic acids derived from the 2-arylpropionic acid S-flunoxaprofen. Conversion of beclobric acid to the acyl chloride prior to coupling with the amine is also feasible. From plasma or urine beclobric acid was extracted into n-hexane/ethanol (9:1) at pH 4 after addition of sodium chloride. Clofibric acid was used as internal standard. Derivatization with EDAC/FLOPA was performed under addition of 1-hydroxybenzotriazole in anhydrous dichloromethane containing trace amounts of pyridine (ambient temperature/2 h reaction time). The chromatographic separation was performed on a silica gel stationary phase (Zorbax Sil) using n-hexane-chloroform-ethanol (100:10: 0.75, by vol) as mobile phase [flow rate, 2 ml/min; fluorescence detection, 305/355 nm; elution order of the derivatives, (-) before (+)]. Coefficients of variation were between 1.3 and 9.3% for both plasma and urine. Limit of quantification was 20-25 ng/ml for plasma based on a sample volume of 0.2 ml. Application of the assay in a pilot pharmacokinetic study showed significant differences between the kinetics of the two enantiomers. In plasma and urine, the concentrations of the dextrorotatory enantiomer exceeded those of the levorotatory enantiomer significantly.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030108
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  • 35
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    A chiral stationary phase which affords unusually high levels of enantioselectivity (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 183-187 
    Details
    ISSN: 0899-0042
    Keywords: (S)-N-(1-naphthyl)leucine ; N-(3,5-dinitrobenzoyl) ; amino acids ; derivatives ; 3,5-dinitroanilides of chiral acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral stationary phase (CSP) derived from N-(1-naphthyl) leucine has been prepared. This CSP is conceptually similar to the CSP derived from N-(2-naphthyl)alanine and was expected to separate the enantiomers of the same clientele of analytes as does the latter. The magnitudes of the separation factors observed on the two CSPs may differ markedly for a given analyte, the new CSP often affording much greater enantioselectivity.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030308
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  • 36
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    Fast liquid chromatography for the resolution of chiral compounds (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 188-195 
    Details
    ISSN: 0899-0042
    Keywords: fast analysis times ; enantiomers ; chiral stationary phase ; Pirkle-concept ; achiral derivatization ; rapid screening ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Pirkle-concept chiral stationary phase (CSP) derived from N-(1-naphthyl)leucine was evaluated for developing methods to reduce analysis times and investigating techniques in the rapid screening of a variety of chiral compounds over a given chiral selector. The effects of reduced column lengths and elevated temperatures were studied to shorten analysis times.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030309
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  • 37
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    Electronic Resource
    Solid angle as steric parameter of acyclic saturated groups (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 242-253 
    Details
    ISSN: 0899-0042
    Keywords: steric effects ; geometric model ; ester hydrolysis ; ester conformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the early aim of quantifying steric consequences of chirality, efforts to define a nonempirical steric parameter of chemical groups are reported. Steric hindrance of a reacting center by any acyclic saturated R group has been characterized by a geometric “axial steric parameter”: the solid angle of R. When the group is a “symmetric top substituent” (i.e., when all the terminal atoms are equivalent), the solid angle matches the solid angle of a cone envelope of R. The definition of this cone is compared with Tolman's definition of a ligand cone in organometallic complexes. The chemical significance of this parameter is shown by an excellent correlation with the Dubois' experimental steric parameter E′s. Modeling steric repulsion by the cone of R, and correcting solid angles for conformational effects, only 3 empirical coefficients are needed to calculate 33 values of E′s with less than 10% error. The cone model is suggested to be relevant within the limits of random and independent free rotations about all the bonds in the C-R group. A separation between “axial cone steric hindrance” and other steric effects is proposed. The basic model and the corrections proposed allow the conformational features of esters to be discussed.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030406
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  • 38
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    Direct measurement of enantiomeric ratios of enzymatic resolution by chiral high-performance liquid chromatography (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 67-70 
    Details
    ISSN: 0899-0042
    Keywords: enzymatic resolution ; chiral HPLC ; enantiomeric ratio ; enantiomeric excess ; 2-(phenoxy)propionate ; 2-(4-chlorophenoxy)propionate ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (R)- and (S)-Methyl 2-(phenoxy)propionate and their acids could be separated simultaneously by a Chiralcel OD or OK column, while (R)- and (S)-methyl 2-(4-chlorophenoxy)propionate and their acids were separated concurrently only by an OK column. This is a novel and facile way to measure the enantiomeric excesses of the remaining substrate and product in the reaction of enzymatic resolution; enantiomeric ratios could then be calculated.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030111
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  • 39
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    Chirality of isomers of aldosterone formed in dilute alkali (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 71-75 
    Details
    ISSN: 0899-0042
    Keywords: crystal structure ; aldosterone conformation ; correction of assigned configuration ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of dilute alkali at room temperature aldosterone undergoes rearrangement to form 11β,18:18,21-diepoxy-20,21-dihydroxy-4-pregnen-3-one (V). X-Ray crystallographic analysis demonstrates that isomers of both 18R, 20S, 21S and 18R, 20S, 21R configuration are formed rather than the 18R, 20R, 21R isomer postulated on the basis of examination of 1H-NMR spectra. The spectra appears to be consistent with the major component of the mixture. The 20S configuration observed is in agreement with the chirality assigned to the degradation product obtained when the same alkaline solution of aldosterone is subjected to reflux. The crystals of (V) are monoclinic P21, Z = 4 with a = 20.891(2), b = 6.3848(5), c = 16.067(2)Å, β = 122.09°(1) with two molecules in the asymmetric unit. Molecule A has the 20S,21S configuration and the molecules in the second site are a mixture of the 20S, 21S and 20S, 21R configuration in the ratio of 3:2.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030112
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  • 40
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    Separating enantiomers by HPLC on silica dynamically coated with a chiral stationary phase of permethylated β-cyclodextrin (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 136-138 
    Details
    ISSN: 0899-0042
    Keywords: solvent generated HPLC systems ; β-cyclodextrin derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The paper demonstrates that the technique of solvent generated liquid--solid chromatography can be used to create normal phase systems for chiral separations. The chiral adsorption layer was generated by pumping a binary hexane:ethanol eluent containing a small fraction of permethylated β-cyclodextrin through a column packed with microparticulate silica. This technique leads to columns with good time stability and reproducibility. The possibility of generating normal phase systems with permethylated β-cyclodextrin as chiral component via the mobile phase broadens the range of phase system which can be used to separate enantiomers by HPLC.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030210
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  • 41
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    Stereospecific HPLC method for the quantitation of the enantiomers of MK-0571, a potent leukotriene D4 receptor antagonist, in biological specimens (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 129-135 
    Details
    ISSN: 0899-0042
    Keywords: chiral separation ; diastereomer ; racemate ; (+)-α-(1-naphthyl)ethylamine derivatives ; enantioselective ; drug disposition ; toxicokinetic studies ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A stereospecific HPLC bioanalytical method was developed for quantitation of the enantiomers of MK-0571, a leukotriene D4 receptor antagonist. The procedure involves the addition of an internal standard analog to the biological matrix followed by extraction of the free acids into ethyl acetate. The acids are subsequently reacted with the homochiral reagent, (+)-(R)-α-(1-naphthyl)ethylamine (NEA) to form diastereomers. Following removal of excess reagent and side products by a dilute acid wash, the NEA-MK-0571 diastereomers are separated on a phenyl urea chiral column using a mobile phase containing hexane, isopropanol, and acetonitrile and are detected with a fluorescence detector. The sensitivity of the method is such that 50 ng of each enantiomer can be quantitated. In the 0.05 to 10 μg range the recoveries of the enantiomers of MK-0571 from plasma were 100.4 ± 7.9% and 100.0 ± 7.2%. NMR and mass spectral data confirmed the structure of the derivative. The method has been utilized in drug safety evaluation studies to demonstrate enantioselectivity in disposition of the enantiomers of MK-0571 in rats and monkeys but not in mice.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030209
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    A method for the quantitative enantioselective HPLC analysis of ethambutol and its stereoisomers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 139-144 
    Details
    ISSN: 0899-0042
    Keywords: benzoylation ; Pirkle phase ; absolute stereochemistry ; antituberculosis drug ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A rapid, quantitative, enantioselective HPLC method, using N,N′-dibenzylethylenediamine as internal standard, for the analysis of the three stereoisomers of the antituberculosis drug ethambutol and 2-aminobutan-1-ol is described. The derivatisation and chromatographic procedures and their reproducibility, durability, and sensitivity are discussed. Application to assays of raw material, tablet content, and synthetic reactions are illustrated. The method involves perbenzoylation, in pyridine, followed by direct HPLC on a “Pirkle covalent bonded column” containing a 3,5-dinitrobenzoyl-D-phenylglycine as chiral stationary phase (CSP) using hexane/IPA as mobile phase and detection at 230 nm.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030211
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    The circular dichroism of tumor necrosis factor-α: Measurement into the vacuum UV and analysis for secondary structure (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 254-256 
    Details
    ISSN: 0899-0042
    Keywords: tumor necrosis factor-α ; secondary structure ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism (CD) spectrum of tumor necrosis factor-α has been measured into the vacuum UV to 168 nm. Analysis of the CD for secondary structure is in good agreement with X-ray diffraction results, but the analysis is somewhat unstable. Adding the CD of this protein together with its X-ray determined secondary structure to the basis set should improve subsequent analyses of CD spectra for other all-β proteins.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030407
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  • 44
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    Evaluation of chiroptical properties of molecules by asymmetric photochemistry (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 257-262 
    Details
    ISSN: 0899-0042
    Keywords: chiral photochemistry ; excitation transfer ; optical activation ; circular dichroism ; dissymmetry factor ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The physics involved in photochemistry with circularly polarized light, the warnings on its inherent limitations, as well as some examples of application on organic molecules are briefly reviewed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030408
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  • 45
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    Absolute configuration of feroxidin: An experimental support to snatzke's helicity rules for tetralins (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 263-267 
    Details
    ISSN: 0899-0042
    Keywords: aloe ; feroxidin ; absolute configuration ; tetralins ; helicity ; Cotton effect ; conformation ; half-chair cyclohexene ring ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configuration of carbon-8 in feroxidin (1) was proven to be (S) by chemical correlation with (S)-methylsuccinic acid. Previous demonstration that 6-hydroxy and 8-methyl groups are equatorial and pseudoaxial, respectively, in a half-chair conformation of the cyclohexene ring (relative configuration) allowed the absolute stereochemistry of the whole molecule to be established (Fig. 3). The CD spectrum of feroxidin represents the first experimental test confirming the applicability of Snatzke's helicity rules to tetralins m-disubstituted on the aromatic ring.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030409
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  • 46
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    Helix-sense-selective polymerization of diphenyl-2-pyridylmethyl methacrylate with chiral anionic initiators (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 277-284 
    Details
    ISSN: 0899-0042
    Keywords: asymmetric polymerization ; stereospecific polymerization ; optically active polymer ; helix ; (+)-tartaric acid ; L-proline ; (+)-(S)-2-(1-pyrrolidinylmethyl)pyrrolidine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymerization of diphenyl-2-pyridylmethyl methacrylate was carried out with the complexes of organolithium compounds with 22 chiral ligands. Helix-sense-selectivity of the polymerization was largely affected by a slight structural difference of chiral ligands. (+)-(S)-2-(1-Pyrrolidinylmethyl)pyrrolidine was the most effective ligand in producing a one-handed helical polymer with narrow molecular weight distribution.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030411
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  • 47
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    Cooperation in a deep helical energy well (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 285-291 
    Details
    ISSN: 0899-0042
    Keywords: macromolecular ; optical activity ; polyisocyanate ; deuterium ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast to random coil polymers, polyisocyanates maintain a highly extended helical conformation in solution. This structural characteristic causes unusually large chiral optical properties to arise from copolymerization of tiny proportions of optically active monomer isocyanates with achiral isocyanates or even from stereospecific placement of deuterium in the side chain of poly(n-hexyl isocyanate). These effects can be understood as phenomenologically related to the optical activity amplification properties of vinyl polymers studied by Pino and his co-workers and ascribed to breaking the energetic degeneracy of the otherwise equally populated left- and right-handed helical states of the backbone. Statistical thermodynamic calculations, based on this model, and analogous to those carried out earlier on the vinyl polymers, allow matching the temperature and molecular weight dependence of the optical activity in poly((R)-1-deuterio-1-hexyl isocyanate) to the approximate responsible energy terms.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030412
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  • 48
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    Absolute configuration for peptidomimetic residues in bioactive peptides (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 268-276 
    Details
    ISSN: 0899-0042
    Keywords: absolute configuration ; peptidomimetics ; retro-inverso modifications ; 2-aminocyclopentanecarboxylic acid ; nuclear magnetic resonance (NMR) ; nuclear Overhauser effect ; bioactive peptides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modern method is reported for the assignment of absolute configuration for peptidomimetics in bioactive peptides by use of 1H-NMR parameters in solution. Four peptide systems incorporating either retro-inverso modifications or 2-aminocyclopentanecarboxylic acid (2-Ac5c) as a peptidomimetic for proline are discussed. (1) Two 14-membered cyclic dermorphin analogs Tyr-c[D-A2bu-Phe-gPhe-(S and R)-mLeu] with a reverse amide bond between gPhe and mLeu residues where gPhe denotes a gem-diamino analog of Phe and mLeu refers to a malonyl analog of Leu. (2) Two cyclic hexapeptides related to somatostatin, c[gSar6-(S and R)-mPhe7-D-Trp8-Lys9-Thr10-Phe11], with a reverse amide bond between the gSar and mPhe residues where the gSar and mPhe denote the gem-diamino and malonyl analogs of the Sar and Phe residues, respectively. The superscript numbers refer to positions in native somatostatin. (3) Cyclic hexapeptide somatostatin analogs containing 2-Ac5c [trans-(1S,2S)-2-Ac5c, trans-(1R,2R)-2-Ac5c, cis-(1R,2S)-2-Ac5c, and cis-(1S,2R)-2-Ac5c] in place of proline c[(2-Ac5c)6-Phe7-D-Trp8-Lys9-Thr10-Phe11]. (4) Morphiceptin related analogs incorporating a cis-2-Ac5c residue as shown in Tyr-cis-2-Ac5c-Phe-Val-NH2. The methodology described in this investigation could be applied to a wide variety of peptide systems.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030410
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    Chiroptical and photochromic properties of stereoregular copolymers of 4-methacryloxyethylenoxyazobenzene with (-)-menthyl methacrylate (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 292-298 
    Details
    ISSN: 0899-0042
    Keywords: photochromic polymers ; chiral polymers ; stereoregular polymers ; 4-methacryloxyethylenoxyazobenzene ; (-)-menthyl methacrylate ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copolymers of the photochromic monomer 4-methacryloxyethylenoxyazobenzene with the optically active comonomer (-)-menthyl methacrylate, having different stereoregularity, were investigated in order to obtain a better understanding of the relationship between microstructure and photochromism in synthetic macromolecules. No appreciable effect was observed by copolymer composition, sequence distribution, and microtacticity on the photoinduced trans → cis isomerization of the azobenzene side chains. This last, however, is reflected in changes of the chiroptical properties, type and entity of the photoinduced variation being dependent on chain structure. The long spacer separating the azo chromophore from the main chain limits the extent of chiroptical properties dependence on irradiation.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030413
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  • 50
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    An alternative to Urry's model for the gramicidin transmembrane channels (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 315-317 
    Details
    ISSN: 0899-0042
    Keywords: ↕ β6.3-model ; ↕ β-model ; ↕ β7.2-structures ; closed structures ; open structures ; non-conducting dimers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is suggested that the conducting transmembrane channels formed by the linear gramicidins A, B and C may be head-to-head (formyl end-to-formyl end) dimers of double-stranded parallel β-helices. This possibility is not in conflict with any of the various experimental findings bearing on the molecular organization of the channels and represents a plausible alternative to Urry's model of a head-to-head dimer of single-stranded β6.3-helices.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030416
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    Chiral liquid-crystalline side chain polymers by enantioselective modification of prochiral parent polymers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 307-314 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation is reported of two side chain polyacrylate samples 1a,b containing a sulfide group linked to the mesogenic core. By oxidation with a preferentially chiral oxaziridine, samples 1a,b were chemoselectively and enantioselectively converted to the corresponding sulfoxide containing polymers 2a,b with an estimated 20% asymmetric induction. The mesophasic behaviour of the parent and oxidized polymer samples is analyzed by thermal and optical techniques. The modification of the prochiral sulfide groups into chiral sulfoxide groups slightly depresses the propensity of the resulting polymers to give stable and persistent mesophases.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030415
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  • 52
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    Polypeptide models of elastin: CD and NMR studies on synthetic poly(X-Gly-Gly) (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 318-323 
    Details
    ISSN: 0899-0042
    Keywords: nuclear magnetic resonance ; circular dichroism ; β-turn conformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(X-Gly-Gly), simple structural models for the hydrophobic, proline-devoid, regions of elastin, have been synthesized and studied by circular dichroism and NMR spectroscopies. The results gave evidence of type II β-turns as the only ordered structure present in the polymers. The stability of the turns has been shown to decrease on hydration and to increase in the series Leu 〈 Ala 〈 Val 〈 Ile.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030417
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  • 53
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    A model for the homogeneous isospecific Ziegler-Natta polymerization of olefins: Enantioselectivity in the deuteration and deuteriooligomerization of 1-alkenes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 299-306 
    Details
    ISSN: 0899-0042
    Keywords: conformational analysis ; nonbonded interactions ; metallocene/methylalumoxane systems ; 1-pentene ; styrene ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity found in homogeneous isospecific Ziegler-Natta catalysts for the insertion of 1-alkenes in metal-deuterium or in metalisobutyl bonds is discussed from a theoretical point of view. Nonbonded energy calculations, based on a model of the catalytic site previously proposed by us, indicate that the strong enantioselectivity found in the insertion of 1-alkenes in a metal-isobutyl bond is drastically reduced in the presence of a metal-deuterium bond. In particular, a weak enantioselectivity in favour of a monomer coordinated with the opposite chirality (lower for the case of 1-butene, higher for the case of styrene) is shown to occur in the latter case.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030414
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  • 54
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    Control of asymmetric induction in the organometallic synthesis of 3-methyl-(E)-4-hexen-2-one (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 324-330 
    Details
    ISSN: 0899-0042
    Keywords: bis(μ-methyl-1,3-dimethyl-η3-allylnickel) ; menthyl phosphines ; menthoxy phosphines ; carbon monoxide ; parity control ; complementarity control ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(μ-methyl-1,3-dimethyl-η3-allylnickel) reacts in the presence of phosphorus(III) ligands (phosphines, phosphites) with CO to give 3-methyl-(E)-4-hexen-2-one. Systematic experiments were performed using chiral ligands containing menthyl or menthoxy groups and different achiral groups on the P atom to determine the influence of ligand structure and concentration on the direction and extent of chiral induction in this ketone synthesis. It could be shown that reversion of enantioselectivity can be obtained not only by the obvious method of reversing the absolute configuration of the ligand (“parity control”) but also by modifying the nonchiral substituents of the phosphorus ligand (“complementarity control”). The synthesis, physical, and spectroscopic properties of several new menthyl phosphines and phosphites are reported.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030418
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  • 55
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    Enantioselective carbonylation reactions of para-substituted 2-phenylpropenes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 341-344 
    Details
    ISSN: 0899-0042
    Keywords: enantioselectivity ; carbonylation ; hydroformylation ; hydroalkoxycarbonylation ; para-substitution ; 2-phenylpropene ; platinum catalyst ; palladium catalyst ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselective hydroformylation catalyzed by [(R,R)-Diop]Pt(SnCl3)Cl7 and the enantioselective hydroisopropoxycarbonylation catalyzed by [(R,R)-Diop]PdCl28 or by [(R,R)-Diop-dbp]PdCl29 of some para-substituted 2-phenylpropenes (para substituents = NO2, H, CH3O, Cl, CF3) was investigated in order to recognize possible electronic influences on the regioselectivity and on the enantioface selection which take place in such carbonylation reactions. The catalytic systems used gave no carbonylation products when the nitro compound was the substrate. 7 and 8 show similar regioselectivities, the less branched isomer being exclusively formed for all substrates except p-methoxy-2-phenylpropene which gave small amounts of the alternative regioisomer. The enantioselectivity depends on the σp effect of the substituent in both cases; the differences are, however, rather small and the trend is opposite in the two cases. The regioselectivity displayed by 9 is still in favour of the less branched isomer but it is high only in the case of p-trifluoromethyl-2-phenylpropene. Larger differences with respect to the other catalytic systems were also observed for enantioselectivity but the trend for both regioselectivity and enantioselectivity is not linear.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030420
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  • 56
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    Cooperativity of chirality in homogeneous catalysis: The gold(I)-catalyzed aldol reaction and the vanadium(IV)-catalyzed hetero Diels-Alder cycloaddition (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 331-340 
    Details
    ISSN: 0899-0042
    Keywords: asymmetric synthesis ; enantioselectivity ; diastereoselectivity ; double stereodifferentiation ; chiral ferrocenyl ligands ; bis(1,3-diketonato)oxovanadium(IV) complexes ; oxazolines ; dihydropyrones ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The notion of internal (or intramolecular) cooperativity of chirality is reviewed on the basis of various examples of diastereoisomeric ferrocenylphosphine ligands used in the gold(I)-catalyzed aldol reaction. It was found that the stereochemical outcome of this reaction strongly depends on the specific combination of the absolute configuration of the different stereogenic centers present in the ligand. Thus, individual chirotopic segments in these ligand molecules can act either in a cooperative or noncooperative manner in determining both diastereo-and enantioselectivity. Furthermore, several examples of application of the strategy of double stereodifferentiation (external, or intermolecular cooperativity of chirality) in the gold(I)-catalyzed aldol reaction and the vanadium(IV)-catalyzed hetero Diels-Alder condensation are presented. Based on our work it is apparent that, whether the diastereoselectivity of these two reactions is controlled by the catalyst or by a chiral substrate, cannot be predicted and very much depends on the nature of every individual reactant. Thus, it was found that in both reactions the chiral aldehyde substrate usually has a strong impact on the diastereoselectivity, leading to interesting patterns of double asymmetric induction. On the other hand, chiral isocyanoacetate and chiral-activated dienes, respectively, showed little or no effect on the stereochemical outcome of the reactions.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030419
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    Iridium complexes of dehydroamino acids: The kinetic resolution of racemic diphosphines and their application in catalytic asymmetric hydrogenation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 345-354 
    Details
    ISSN: 0899-0042
    Keywords: iridium ; asymmetric hydrogenation ; dehydroamino acid esters ; enamide complexes ; resolution ; homogeneous catalysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of chiral diphosphines with a configurationally pure cationic bis-enamide complex of iridium, bis(menthyl (Z)-α-benzamidocinnamate)-iridium tetrafluoroborate, is described. When the reactant ligand is racemic then kinetic resolution occurs with high specificity under the appropriate conditions. Since the iridium diphosphine complex is catalytically inactive in homogeneous hydrogenation, the residual enantiomer may be reacted with bis(norbornadiene)-rhodium tetrafluoroborate to produce an active catalyst. This effects the hydrogenation of methyl (Z)-α-acetamidocinnamate in optical yields comparable with those obtained separately with the enantiomerically pure ligand rhodium complex. The reaction of pure (+)- or (-)-enantiomer of bis(menthyl (Z)-α-benzamidocinnamate)-iridium tetrafluoroborate with enantiomerically pure diphosphines has been studied. Invariably one hand of the diphosphine reacts rapidly with a given enantiomer of the iridium complex to give a stable diphosphine iridium enamide complex in which the original configuration of the coordinated olefin is maintained. The other combination of enantiomers reacts much more slowly, in keeping with the kinetic resolution work, and produces an enamide complex which is unstable in solution, isomerising to a second diastereomer. Since the absolute configuration of the iridium bis-enamide complex has been established by X-ray crystallography, this experiment affords a method of determining the configuration of rhodium enamide complexes in asymmetric hydrogenation (assuming structural homology between Rh and Ir). In all cases the disfavoured enamide complex was the one involved in the catalytic pathway.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030421
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    IBC technical services Ltd. Presents the 2nd international conference on drug chirality: Strategies for decision making in the development of stereoisomeric drugs: October 28-29, 1991 - the royal Lancaster hotel, London (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 386-386 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030425
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  • 59
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    The asymmetric hydroformylation in the synthesis of pharmaceuticals (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 355-369 
    Details
    ISSN: 0899-0042
    Keywords: enantiomerically pure compounds ; chiral drugs ; enantioselective hydroformylation ; enantioselective catalysts ; biologically active compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The asymmetric hydroformylation reaction represents a potential powerful synthetic tool for the preparation of large number of different chiral products to be used as precursors of several organic compounds endowed with therapeutic activity. Essential and nonessential amino acids, 2-arylpropanoic acids, aryloxypropyl- and β-phenylpropylamines, modified β-phenylethylamines, pheniramines, and other classes of pharmaceuticals are available through enantioselective oxo-reaction of appropriate functionalized olefins; this process is catalyzed by rhodium or platinum complexes with chiral ligands, mainly chelating phosphines, and sometimes affords very high enantiomeric excesses. Furthermore, the application of many simple optically active aldehydes arising from asymmetric hydroformylation as chiral building blocks for the synthesis of complex pharmacologically active molecules such as antibiotics, peptides, antitumor macrocycle compounds, and prostaglandins is conveniently emphasized. The possibility of a future application of this asymmetric process for the production of many synthons to obtain other valuable pharmaceuticals is widely discussed too.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030422
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  • 60
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    Plasma protein binding of ketoprofen enantiomers in man: Method development and its application (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 460-466 
    Details
    ISSN: 0899-0042
    Keywords: ketoprofen ; stereoisomers ; plasma binding ; binding linearity and competition ; ketoprofen glucuronides ; 2-arylpropanoic acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protein binding of ketoprofen enantiomers was investigated in human plasma at physiological pH and temperature by ultrafiltration. 14C-labelled (RS)-ketoprofen was synthesized and purified by high-performance liquid chromatography and utilized as a means of quantifying the unbound species. In vitro studies were conducted with plasma obtained from six healthy volunteers. The plasma was spiked with (R)-ketoprofen alone, (S)-ketoprofen alone, and (RS)-ketoprofen in the enantiomeric concentration range of 1.0 to 19.0 μg/ml. The plasma protein binding of ketoprofen was nonenantioselective. At a racemic drug concentration of 2.0 μg/ml the mean (± SD) percentage unbound of (R)-ketoprofen was 0.80 (± 0.15)%. The corresponding value for (S)-ketoprofen, 0.78 (± 0.18)%, was not statistically different (P 〉 0.05). At this racemic drug concentration (2.0 μg/ml) the percentage unbound of each enantiomer was unaffected (P 〉 0.05) by the presence of the glucuronoconjugates of ketoprofen (10 μg/ml) in plasma. At clinically relevant concentrations, the plasma binding of ketoprofen did not exhibit enantioselectivity or concentration dependence nor was the binding of either enantiomer influenced by its optical antipode (P 〉 0.05).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030609
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    Enantiomeric analysis of terfenadine in rat plasma by HPLC (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 467-470 
    Details
    ISSN: 0899-0042
    Keywords: antihistamines ; chromatography ; stereoisomers ; chiral HPLC ; ovomucoid ; HI blockers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric pairs of the antihistaminic drug terfenadine and its carboxylic acid derivative were directly separated by HPLC using an ovomucoid protein column. Absolute configurations of terfenadine enantiomers were assigned by comparing their circular dichroism spectra with those of 1-phenyl-1-butanol enantiomers of known absolute stereochemistry. Terfenadine and its major carboxylic acid metabolite extracted from blood plasma following an oral administration of a racemic terfenadine to rats were found to be enriched in the (S)- and (R)-enantiomers, respectively. The results indicated that the (R)-enantiomer of an orally administered racemic terfenadine was preferentially oxidized in rats to form a carboxylic acid metabolite enriched in the (R)-enantiomer.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030610
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    The kinetics of diastereomeric amino acids with o-phthaldialdehyde (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 471-475 
    Details
    ISSN: 0899-0042
    Keywords: amino acids ; kinetics ; epimers ; OPA ; postcolumn reaction detection ; fluorescence detection ; amino acid racemization ; dating methods ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reaction of the amino acid epimers L-isoleucine, D-alloisoleucine, L-threonine, and D-allo-threonine with o-phthaldialdehyde and mercaptoethanol were determined at 25°C. L-Isoleucine reacts faster than its D-epimer whereas L-threonine reacts slightly slower than its D-epimer. In the case of isoleucine, the consequence can be an allo/iso ratio which in the worst case is 25% too low if these amino acids are quantified by liquid chromatography and o-phthaldialdehyde fluorescence detection. The effect on dating of fossils by amino acid racemization is discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030611
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    Enantiomeric separation of 2-(phenoxy)propionate derivatives by chiral high-performance liquid chromatography (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 476-479 
    Details
    ISSN: 0899-0042
    Keywords: chiral HPLC ; 2-(phenoxy)propionate derivatives ; Chiralcel OD column ; Chiralcel OK column ; chiral-2 column ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-(Phenoxy)propionate derivatives were separated on three chiral columns, OD, OK, and chiral-2 columns. The chlorine substitution in the phenyl ring and the alcohol moiety of the ester groups of the derivatives had great influence for separation on the OD and OK columns, but little effect on the chiral-2 column.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/chir.530030612
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    Chiral resolution of α,α′-bis[3-(N,N-diethylcarbamoyl)piperidino]-p-xylene, a novel antiplatelet compound (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 480-483 
    Details
    ISSN: 0899-0042
    Keywords: biscarbamoylpiperidine ; stereoisomer separation ; enantioselectivity ; circular dichroism ; α1-acid glycoprotein ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α,α′-Bis[3-(N,N-diethylcarbamoyl)piperidino]-p-xylene dihydrobromide, a novel antiplatelet agent, was resolved into three isomers A, B, and C, on a chiral α1-acid glycoprotein analytical column using a mobile phase of 0.025 M phosphate buffer containing 0.025 M tetrabutylammonium hydrogen sulfate, at a pH of 6.5. The effect of molarity, temperature, pH, flow rate, and organic modifiers on the enantioselectivity was examined. Based on circular dichroic spectra at 220 nm, A and C appear to be the (-)- and (+)-enantiomers, respectively, and B the meso diastereomer. Attempts at resolution using Pirkle type columns gave unsatisfactory results. It appears that both hydrophobic and polar interactions between the compound and the stationary phase are important determinants of resolution.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030613
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    Production of a chiral polyester by Pseudomonas oleovorans grown with 5-phenyl-2,4-pentadienoic acid (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 492-494 
    Details
    ISSN: 0899-0042
    Keywords: bacterial polyesters ; Pseudomonas oleovorans ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pseudomonas oleovorans has been previously shown to produce a polyester containing a phenyl pendant group when grown with 5-phenylpentanoic acid under nutrient-limiting conditions. The same polyester was produced when 5-phenyl-2,4-pentadienoic acid was the only carbon source, and a mixture of two different polymers was produced when this bacterium was grown on a mixture of 5-phenyl-2,4-pentadienoic acid and nonanoic acid. The polymer blend obtained was separated by fractional crystallization to yield poly(3-hydroxy-5-phenylpentanoate) and the copolymer which is normally produced with nonanoic acid alone.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030615
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    Living enantiosymmetric and enantioasymmetric polymerization of methylthiirane in homogeneous phase (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 484-491 
    Details
    ISSN: 0899-0042
    Keywords: propylene sulfide ; cadmium thiolate ; stereospecific polymerization ; living polymerization ; anionic polymerization ; ring-opening polymerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of racemic methylthiirane in homogeneous phase, initiated by bis(isopropyl-S-cysteinato) cadmium is a living process. The resulting polymers are isotactic and optically active at partial conversion. The optical purity of the residual monomer may reach 27% at half conversion. The propagation occurs mainly on one valency of Cd, however oligomers grow slowly on the second valency. The stereoregularity of the polymer chain appears only when the length of the oligomer becomes high enough, making possible a bicoordination of the Cd counterions. The stereoregularity of the polymer is characterized by the molar fraction σ of isotactic diads which varies from 0.5 for atactic chains - formed at the beginning - to about one for isotactic segments formed for longer chains. The stereospecifictity also depends on temperature of propagation and on initiator concentration. The kinetics observed (zero order in monomer and one-half in Cd) are explained by monomer coordination before insertion and dimeric association of the thiolate end groups. The enantioasymmetric process observed results from an unbalance in the number of the two different types of active sites and possibly from a difference in their reactivities. Enantioasymmetry has been found to decrease significantly when the dielectric constant ε of the medium increases.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030614
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    Racemization of the aqua-{N-salicylidene-(S)-alaninato}copper(II) by reaction with potassium cyanate (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 503-505 
    Details
    ISSN: 0899-0042
    Keywords: racemisation of an S-enantiomeric Schiff base ligand ; potassium isocyanato-{N-salicylidene-(RS)-alaninato}cuprate(II) ; EPR spectrum ; basalcrystallographic data ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) N-salicylidene-(S)-alaninate trihydrate reacting as the S-enantiomeric parent compound with KOCN in hot diluted methanol yielded by slow crystallisation from the cooled reaction mixture (in the course of 1 day) the racemic product K[Cu{sal-(RS)-ala}(NCO)]. The parameters of the axial type EPR spectrum in X-band region and the LF band position in the electronic spectrum are typical of an axially distorted square pyramidal coordination of the Cu(II) atom in this complex. The spectral properties of the complex cuprate prepared and its basal crystallographic data are consistent with those of the earlier studied15 K2[Cu2{sal-(RS)-ala}2(μ-NCO)2] synthetized by using [Cu{sal-(RS)-ala}(H2O)].H2O as the racemic parent complex in the reaction mixture with KOCN.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030617
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    Chiroptical properties of lecithin reverse micelles and organogels (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 495-502 
    Details
    ISSN: 0899-0042
    Keywords: circular dichroism ; spectroscopy ; surfactant ; optical activity ; phosphatidylcholine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ultraviolet absorbance and circular dichroism (CD) spectra of lecithin reverse micelles and gels were investigated in order to establish whether the formation of these noncovalent macromolecular aggregates, which was induced by the addition of water to solutions of lecithin in organic solvents, was accompanied by specific spectroscopic changes. Systems containing the synthetic short-chain lecithins, 1,2-hexanoyl-, 1,2-diheptanoyl-, 1,2-dioctanoyl-, and 1,2-dinonaoyl-sn-glycero-3-phosphatidylcholines were used as models for the long-chain lecithins, soybean phosphatidylcholine and palmitoyl-oleoyl-phosphatidylcholine. All the molecules studied had asymmetric centres, formed reverse micelles under appropriate conditions, and, while both the long-chain lecithins also formed gels, none of the short-chain molecules did. As well as having CD spectra that were simpler to interpret, spectroscopic observations on solutions of the short-chain lecithins could be carried out over a large water content range. The ester chromophore of these compounds was shown to be highly sensitive to variation in both the solvent environment and the temperature, and components of both direct solvent effects and conformational change upon the addition of water were detected in the spectra.The spectra of the longer chain lecithins were complicated by the presence of double bonds although, here again, it was found that significant changes occurred as the water content increased, as monitored by the ester chromophore. However, no specific effect that could be ascribed to gelation alone was detected.The overall picture that emerged was that the ester chromophore of anhydrous micelles gave rise to a specific negative band in the CD spectrum (λmax ≈ 210 nm) whereas a positive CD signal (λmax ≈ 233 nm) was associated with the same chromophore in filled (i.e., hydrated) micelles. The two signals correspond to two different conformational states of the lecithin molecule, the hydrated state being not only more conformationally restricted but also providing a less polar environment for the ester groups, while the addition of water to the system shifts the conformational equilibrium. These observations have been interpreted as showing that only a limited range of lecithin conformation is compatible with the formation of the micellar structure and that it is this constraint, together with those introduced by the overall geometry of the aggregated state, that gives rise to the changes observed in the CD spectrum.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030616
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    Short cource on chromatographic separation of enantiomers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 506-506 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030618
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    New chiral fluoroanthryl derivatives: Resolution of the enantiomers by chromatography on cellulose esters and their evaluation as chiral solvating agents in NMR spectroscopy (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 177-182 
    Details
    ISSN: 0899-0042
    Keywords: cellulose triacetate ; tribenzoylcellulose ; methylbenzoylcellulose ; chiral phase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,2,2-Trifluoro-1-(9-anthryl)ethanol (TFAE) has now been widely used as a powerful chiral solvating agent for NMR spectroscopy. In connection with the development of a new general synthesis of halogenoalkylalkanols, starting from the corresponding ketone or aldehyde, we synthesized some halogenoalkyl-1-(9-anthryl)methanol derivatives liable to work as chiral solvating agents. The racemic anthryl derivatives were preparatively resolved into their corresponding enantiomers by chromatography on triacetyl cellulose (CTA I) or on meta-methylbenzoyl cellulose beads as chiral stationary phases. Their effectiveness as chiral solvating agents was measured as the magnitude of the splitting induced in the 1H-NMR spectra of 1-phenylethylamine and of (1-phenylethyl)methyl ether in comparison with splitting caused by TFAE. While TFAE induced the largest splitting for 1-phenylethylamine, 2,2,3,3,3-pentafluoro-1-(9-anthryl)propanol 2 was more effective in the case of (1-phenylethyl)methyl ether, pointing out that depending on the substrate, other derivatives of the TFAE type can be very useful as chiral solvating agents.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030307
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    Benzoyl cellulose beads in the pure polymeric form as a new powerful sorbent for the chromatographic resolution of racemates (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 43-55 
    Details
    ISSN: 0899-0042
    Keywords: beads ; polymer ; enantiomer ; chiral phase ; interaction ; alcohol ; diol ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cellulose-based stationary phases are known to be very efficient and versatile chiral sorbents for the chromatographic resolution of racemates. Except for microcrystalline cellulose triacetate (CTA I), basically all other cellulose-based phases have been prepared by coating of ca. 20% weight polymer on a wide pore silica gel used as a carrier. In this work we describe the preparation of benzoylcellulose (TBC) beads in the pure polymeric form (without inorganic carrier) from an emulsion of the organic polymer. The new material has been fully characterized and used as a chiral stationary phase for the resolution of various classes of racemic compounds such as benzylic alcohols or acetate derivatives of aliphatic alcohols and diols. The structural variety of the separated solutes as well as the irrational influence of the aromatic substituent in different classes of aryl compounds suggest that multiple interaction sites are involved in the complexation, making a prediction of the separation difficult. The benzoyl cellulose beads exhibit a very high loading capacity, which is particularly useful for preparative purposes as demonstrated for selected examples.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030109
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    Direct chromatographic resolution of racemic cyclohexylaminoglutethimide and its acetylated metabolite using cellulose-based chiral stationary phase (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 204-207 
    Details
    ISSN: 0899-0042
    Keywords: chiral chromatography ; cellulose-based chiral stationary phase ; aromatase inhibitor ; cyclohexylaminoglutethimide and metabolite ; enantiomeric separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic cyclohexylaminoglutethimide (±ChAG) and its acetylated metabolite (±ChAG) were resolved by a direct chromatographic method using a Chiracel OD column without derivatization. Maximum resolutions (R) of 4.89 and 0.74 were obtained for the enantiomers of cyclohexylaminoglutethimide and its acetylated metabolite, respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030311
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    A new model to account for the order in which enantiomers of alkylarylcarbinols elute from a pirkle chiral HPLC column: Preparation, absolute stereochemistry, and chromatographic properties of (+)-1,2-benzocyclononen-3-ol and (+)-1,2-benzocyclodecen-3-ol (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 196-203 
    Details
    ISSN: 0899-0042
    Keywords: (R)- ; (S)-1,2-benzocyclononen-3-ol ; (R)-1,2-benzocyclodecen-3-ol ; separation of enantiomers of Pirkle HPLC columns ; chiral recognition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Samples enriched in (-)- and (+)-1,2-benzocyclononen-3-ol were prepared by microbially mediated reactions. An enriched sample of (+)-1,2-benzocyclodecen-3-ol was prepared by fractional crystallization of the diastereoisomeric camphanates, followed by hydrolysis. The absolute stereochemistry of both alcohols was established by chemical transformations. The elution order of their enantiomers from a chiral Pirkle HPLC column [(R)-N-(3,5-dinitrobenzoyl)phenyl glycine ionically bound to γ-aminopropyl silanized silica] was determined. The information in conjunction with other data was used to formulate a rule to predict the configuration of an enantiomer of an alkylarylcarbinol from its elution order from this column.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030310
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    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030401
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    Relative configuration of thioridazine enantiomers (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 208-211 
    Details
    ISSN: 0899-0042
    Keywords: neuroleptic ; dopamine ; receptor ; enantioselectivity ; schizophrenia ; stereochemistry ; isomers ; racemate ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative configuration of the enantiomers of thioridazine was defined to explore the stereochemistry associated with the selective binding of (-)-thioridazine to dopamine D-1 receptors and (+)-thioridazine to D-2 receptors. Using a seven-step stereoconservative synthesis, (-)-(S)-2-piperidinecarboxylic acid was converted to (-)-(S*)-2-(2-chloroethyl)-1-methylpiperidine, a literature (-)-thioridazine synthetic precursor. Accordingly, (-)- and (+)-thioridazine are the (S)- and (R)-enantiomers, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030312
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    Dedication: In memory of Piero Pino (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 221-222 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030402
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    Circular dichroism detection in HPLC (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 376-385 
    Details
    ISSN: 0899-0042
    Keywords: circular dichroism ; detection system ; chromatography ; chiral discrimination ; enantiomeric excess ; elution order ; dissymmetry factor ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A circular dichroism-based detection system presents several advantages in the HPLC analysis of chiral compounds because of the selective monitoring of optically active molecules. Its use allows reliable determination of enantiomeric excesses and elution order. To this end, the application of empirical, semiempirical, and nonempirical methods to get stereochemical information from the CD signal is reported. Furthermore, recording the CD spectra on line and evaluation of the dissymetry factor make the CD detection very powerful in characterizing the stereochemistry of chiral eluates.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030424
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    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030501
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    Stereochemical confusion with computer literature searches (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 387-388 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030502
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    Benzylic alcohols as stereospecific substrates and inhibitors for aryl sulfotransferase (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 104-111 
    Details
    ISSN: 0899-0042
    Keywords: stereochemistry ; sulfation ; enantioselectivity ; inhibition ; chiral ; mechanism ; stereoselective ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aryl sulfotransferase IV catalyzes the 3′-phosphoadenosine-5′-phosphosulfate (PAPS)-dependent formation of sulfuric acid esters of benzylic alcohols. Since the benzylic carbon bearing the hydroxyl group can be asymmetric, the possibility of stereochemical control of substrate specificity of the sulfotransferase was investigated with benzylic alcohols. Benzylic alcohols of known stereochemistry were examined as potential substrates and inhibitors for the homogeneous enzyme purified from rat liver. For 1-phenylethanol, both the (+)-(R)-and (-)-(S)-enantiomers were substrates for the enzyme, and the kcat/Km value for the (-)-(S)-enantiomer was twice that of the (+)-(R)-enantiomer. The enzyme displayed an absolute stereospecificity with ephedrine and pseudoephedrine, and with 2-methyl-1-phenyl-1-propanol; that is, only (-)-(1R,2S)-ephedrine, (-)-(1R,2R)-pseudoephedrine, and (-)-(S)-2-methyl-1-phenyl-1-propanol were substrates for the sulfotransferase. In the case of 1,2,3,4-tetrahydro-1-naphthol, only the (-)-(R)-enantiomer was a substrate for the enzyme. Both (+)-(R)-2-methyl-1-phenyl-1-propanol and (+)-(S)-1,2,3,4-tetrahydro-1-naphthol were competitive inhibitors of the aryl sulfotransferase-catalyzed sulfation of 1-naphthalenemethanol. Thus, the configuration of the benzylic carbon bearing the hydroxyl group determined whether these benzylic alcohols were substrates or inhibitors of the rat hepatic aryl sulfotransferase IV. Furthermore, benzylic alcohols such as (+)-(S)-1,2,3,4-tetrahydro-1-naphthol represent a new class of inhibitors for the aryl sulfotransferase.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chir.530030205
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    Nucleotides. Part XXXVIPart XXXV:[1]. Syntheses and biological characterization of phosphorothioate analogues of (3′-5′)adenylate trimer (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 892-898 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The four protected diastereoisomcrs 7a/7b and 8a/8b P-thioadenylyl-(3′-5′)-P-thioadenylyI-(3′-5′)-adenosine were synthesized, separated, and deblocked to the free oligonucleotides (Scheme). Biochemical characterization of these (3′-5′)phosphorothioate analogues of adenyiate trimer indicate that these compounds, and the corresponding 5′-monophosphates, neither bind to nor activate RNase L, and are considered to be valuable control compounds in screening experiments.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740420
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    Errata (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 904-904 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740422
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    [5-Leucin]enkephalin-Related Glycoconjugates: Structurally Novel Agents Effective against HIV-1 (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 951-955 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of [Leu5]enkephalin-related glycoconjugates with an ester-, ether-, or amide-type linkage were synthesized and evaluated for antiviral activity against HIV-1 in a cell-culture system using peripheral blood lymphocytes. All tested glycoconjugates exhibited a certain antiviral activity which was significantly higher than the activity of the parent peptide compound itself. These results indicate that synthetic glycoconjugates of opioid peptides are good candidates for the development of anti-HIV agents.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19910740505
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  • 84
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    Synthesis of the Bretonins, Polyolefinic Esterified Glyceryl Ethers of an Unidentified Sponge from the North-Brittany Sea: Absolute Configuration and Novel Structure Assignment (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 941-950 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The absolute configurations of acetylated bretonin A (= (+}-(R)-1-[(acetoxy)methyl]-2-{[(4E,6E,8E)-dodeca-4,6,8-trienyl]oxy}ethyl 4-acetoxybenzoate; (-)-1b) and isobretonin A (= (+)-(S)-3-{[(4E,6E,8E)-do-deca-4,6,8-trienyl]oxy}-2-hydroxypropyl 4-hydroxybenzoate; (+)-2), previously isolated from an undetermined sponge of the North Brittany sea, were established by comparison with synthetic (+)-lb and (+)-2, obtained from the condensation of commerical (-)-(R)-2,2-dimethyl-1,3-dioxolan-4-yl p-toluenesuifonate ((-)-(R)-15) with a mixture of (4E,6E,8E)- (14e) and (4E,6Z,8E)-dodeca-4,6,8-trien-1-ol (14z). This also allowed confirming the structure and configuration of bretonin B (= (S)-2-{[(4E,6Z,8E)-dodeca-4,6,8-trienyl]oxy}-1-(hydroxy-methyl)ethyl 4-hydroxybenzoate; 3) which was also isolated from the same sponge, albeit in a too small amount for a complete study. As concerns the glyceryl ethers precursors of the bretonins, co-occurrence of the usual (S)-con-figuration (from 1a) with the unusual (R)-configuration (from (+)-2)) poses intriguing biogenetic problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740504
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  • 85
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    Ionization Behavior and Ionization-Dependent Conformation of Raclopride, a Dopamine D2 Receptor Antagonist (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 956-968 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Raclopride, an antipsychotic 6-methoxysalicylamide (= 2-hydroxy-6-methoxybenzamide) derivative, was shown by titrimetry and UV-pholometry to exist in zwitterionic form at physiological pH. Calculations revealed that the neutral and zwitterionic forms differ considerably in their conformational behavior, the latter form being energetically favored by an intramolecular phenolate-ammonium ionic bond. These findings indicate that raciopride and other halogenated 6-melhoxysalicylamides with a highly acidic phenolic group may not resemble other ortho-methoxybenzamides in their stereoelectronic structure and mode of binding to the dopamine D2 receptor.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19910740506
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  • 86
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    Synthesis, Isolation, and Full Spectroscopic Characterization of Eleven (Z)-Isomers of (3R,3′R)-Zeaxanthin (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 969-982 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Developmental efforts to improve the yield of the chemical synthesis of (3R,3′R)-zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by 1H-NMR, UV/VIS, and CD spectrosocpy of eleven (Z/E)-isomers of zeaxanthin: (7Z)-, (9Z), (13Z)-, (15Z)-, (7Z,7′Z)-, (9Z,9′Z)- (7Z,9Z,7Z)-, (7Z,11Z,7′Z)-, (9Z,13Z,9′Z)-, (7Z,9Z,7′Z,9′Z)-, and (7Z,9Z,11Z,7′Z,9′Z)-zeaxanthin. Five of these isomers were obtained by specific synthesis, namely the (7Z)-, (7Z,7′Z)-, (9Z,9′Z)-, (7Z,9Z,7′Z)-, and (7Z,9Z,7′Z-9Z)-isomers.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740507
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  • 87
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    Synthesis and X-Ray Crystal Structure of an Optically Pure Tripodal C3-Symmetric Tritertiary Phosphine Bearing Chirality on Phosphorus (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 983-988 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of the optically pure tritertiary phosphine (RRR)-MeSi(CH2P(t-Bu)Ph)3 (2) is reported. The route followed involves deprotonation of optically pure (R)-P(BH3)Me(t-Bu)PH (2) the reaction of the resulting carbanion with MeSiCl3, followed by removal with morpholine of the BH3-protecting groups from the triertiary phosphine-borane 3. The latter's X-ray crystal structure and that of [Rh(NBD)((RRR)-1]TOf)(4), are also rported. Furthermore, it is shown that the separation of the racemic phosphine-borane 2 can be conveniently carried out using medium-pressure liquid chromatgrapy with cellulose-riacetate as a chiral stationary phase.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740508
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  • 88
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    The Lewis basicity of the [Pt3(μ-CO)3(PR3)3] clusters and the X-ray crystal structure of [{ZnI2}{Pt3(μ-CO)3(PPh(i-Pr)2)3}]Dedicated to Prof, Hans-Georg von Schnering on the occasion of his 60th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 989-992 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cluster compounds [Pt3(μ-CO)3(PR3)3] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX2, and Group XIII, MX3, to form cluster compounds of the composition [{MXn}{Pt3(μ-CO)3(PR3)3}]. The X-ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt3(μ-CO)3(PPh(i-Pr)2)3}].
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740509
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  • 89
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    Stereo and Face Selectivity in Cycloadditions of 1,2,3-Trichloro-3-fluorocyclopropenes to Acyclic Dienes and FuransDedicated to Prof. Kurt Schaffner on the occasion of his 60th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 993-1001 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereo and face selectivities of the cycloaddition of 1,2,3-trichloro-3-fluorocyclopropene (1a) with acyclic dienes and furans has been re-investigated by X-ray determination and correlation of 19F-NMR data. The isolated adducts of dienes exclusively have exo-configuration, and exo-Configuration predominates with furans. The Cl substituents of the resulting cyclopropane ring are cis-oriented. The face selectivity of the reaction with both types of substrates is attributed to electrostatic interactions between the F and the bridgehead Cl substituents, which destabilize the F-cis-transition state (13 (F-cis)) over 13 (F-trans).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740510
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  • 90
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    Zur Oxidation von 1,2-Thiazolen: Ein einfacher Zugang zu 1,2-Thiazol-3(2H)-on-1,1-dioxidenHerrn Prof. Dr. Siegfried Hauptmann zum 60. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1059-1070 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of 1,2-Thiazoles; A Convenient Approach to 1,2-Thiazol-3(2H)-one 1,1-DioxidesThe 1,2-thiazoles obtained from 3-chloroalk-2-enals and ammonium thiocyanate (7 → 9, Scheme 1) are easily transformed to 1,2-thiazol-3(2H)-one 1,1-dioxidcs 10 on treatment with H2O2 in AcOH at 80°. Hydrogenation of 10 in AcOH yields the corresponding saturated 1,2-thiazolidin-3-one 1,1-dioxides 16 (Scheme 3). Cycloalka[c]-1,2-thiazoles 18 are prepared from 2-[(thiocyanato)methyliden]cycloalkan-1-ones and ammonia (Scheme 4). Surprisingly, oxidation of 18a with H2O2 in AcOH yields the tricyclic oxaziridine 19.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740515
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  • 91
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    Nitroacetyl Group as a Peptide Synthon: Synthesis of Dipeptides with an α,α-Bisallylglycine Residue at the N-TerminusNCL Communication No. 5185. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1071-1080 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Nitroacetyl derivatives of L-proline, L-valine, and L-phenylalanine esters were prepared in two steps under mild conditions (Scheme 2). Regiospecific mono- and bis-allylation of these nitroacetyl derivatives were accomplished in presence of a Pd(0) catalyst. The bis-allyl derivatives 7-9 were obtained in 40-75% yield. The tertiary NO2 group in these compounds could be transformed into an acetylamino group by Zn/AcOH/Ac2O. The final products 11-13 are dipeptides in which the N-terminal glycine residue bears two α-allyl substituents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740516
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  • 92
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    3′-Substituted and 2′,3′-Unsaturated 7-Deazaguanine 2′,3′-Dideoxynucleosides: Syntheses and Inhibition of HIV-1 Reverse Transcriptase (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1081-1090 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of 2′,3′-dideoxy-2′,3′-didehydro-β-D-ribofuranoside 1 and 2′,3′-dideoxy-3′-fluoro-β-D-ribo-furanoside 5 of 7-deazaguanine as well as 7-deaza-2′-deoxyxyloguanosine (3) are described. The corresponding 2,4-diamino compounds 2 and 4 were also prepared. Thus, silytation of 2-amino-4-chloro-7-(2-deoxy-β-D-erythro-pentofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine (6) afforded 7, which gave the oxo-nucleoside 13 after oxidation with CrO3. NaBH4 reduction yielded 14 which, upon deprotection (Bu4NF) and nucieophific displacement, afforded 3 and 4. On the other hand, the N2-formyl derivative of 7 was mesylated (→ 10), treated with Bu4NF, and deprotected with NH3 yielding the 2′,3′-dideoxy-2′,3′-didehydro-nucleoside 12, Nucleophilic displacement reactions on 12 yielded 1 and 2. The fluoro-nucleoside 5 was obtained from 14 after methoxytritylation of the NH2 group (→ 16), fluorination with DAST (→ 17), and treatment with 2M NaOH. The 5′-triphosphates of 5 and other pyrrolo[2,3-d]pyrimidine 2′,3′-dideoxy-3′-fluoro-nucleosides were found to be highly active inhibitors of HIV-1. reverse transcriptase, similar to those of 1 and 2.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19910740517
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  • 93
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    Zur Synthese von Derivaten des Pyrido[1,2-a]azepinsProf. Horst Prinzbach zum 60. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1095-1101 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Synthesis of Derivatives of Pyrido[1,2-a]lazepineThe conjugated pyridinium ylides of type 4 undergo 8π -electrocyclisation affording the heterobicyclic allenes 5 which, in the presence of H2O and H2O2, are subsequently transformed into the substituted pyrido[1,2-a]-azepinones 6, a novel heterocyclic system. The chemical behaviour of 6a,b is dominated by cleavage of the lactam bond and subsequent reaction to pyridinc and isoquinoline derivatives, respectively; e.g. reaction of 6a, b with 4,5-dihydro-4-methyl-3H-1,2,4-triazole-3,5-dione affords the cycloadducts 11 and 12 almost quantitatively. The successful transformation of 6b into 15 is described, the latter being the first representative of the presently unknown, potentially antiaromatic pyrido[1,2-a]azepine (1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740519
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  • 94
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    Regioselectivity, Stereoselectivity, and Isotopically Sensitive Branching in the Fe(I)-Mediated Dehydrogenation of Octane-1,8-diol in the Gas PhaseDedicated to Prof. Jürgen Sauer on the occasion of his 60th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1127-1134 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regio- and stereospecific labeling experiments are conducted to unravel the mechanistic features of the Fe+-induced dehydrogenation of octane-1,8-diol in the gas phase. With regard to the regioselectivity, ca. 20% of molecular hydrogen originates from the C(3)/C(4) or the equivalent C(5)/C(6) positions. The remaining 80% are, provided by the C(4)/C(5) methylene units. The steps, preceding the reductive elimination of hydrogen, are irreversible, and the overall reaction follows a 1,2-elimination mode. The loss of HD from C(3)/C(4) is associated with a kinetic isotope effect KH2/KHD = 1.68. Formation of D2 from the positions C(4)/C(5) has an isotope effect of KH2/KD2 = 4.7; this figure is slightly dependent on the configuration at C(4)/C(5). Most interesting is the finding that the configuration at C(4)/C(5) in [4,5-D2]octane-1,8-diol, i.e. 5c vs. 5d, plays a pivotal role in the dehydrogenation of the central C(4)/C(5) part. This unexpected and unprecedented result is explained in terms of conformational analysis. A staggered-like conformation serves as a precursor to generate a trans-fused bicyclic intermediate 6. It is this very intermediate from which most of the molecular hydrogen is eliminated. Of minor importance is the as-fused chelate 7, which is formed from an eclipsed-like conformation of the octane-1,8-diol/Fe+ complex. The contribution of 6 and 7 to the product formation is controlled by the relative configuration at the labeled positions C(4)/C(5). For the D,L-form 5c, we estimate a ratio of ca. 9:1 for the contribution of 6 vs. 7; due to an isotope effect, this ratio drops to 1:85:1 for the meso-form 5d. This finding constitutes the first example for the existence of isotopically sensitive branching (‘metabolic switching’) in gas-phase organometallic chemistry.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19910740522
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  • 95
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    Mitteilungen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1156-1156 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740525
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  • 96
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740601
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  • 97
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    C—C Bond Formation via Carbon-Centered Radicals Generated from Dicarbonyl(η5-cyclopentadienyl) organoiron Complexes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1143-1155 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of benzyldicarbonyl(η5-cyclopentadienyl)iron complex (2) leads to hemolytic cleavage of the Fe—C bond. In the presence of activated alkenes, radical addition occurs and both saturated and unsaturated addition products 7-9 are formed. Photolysis of alkyliron complexes 2,3 and 20 in the presence of acrylonitrile leads to the same products as the irradiation of the respective acyliron complexes 28-30. This indicates that, under photolytical conditions, alkyl and acyl complexes are in equilibrium with each other.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19910740524
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  • 98
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    Crystal Structures of the Lithium Cryptates of Two Macrobicyclic Ligands Containing Pyridine, Bipyridine, and Biisoquinoline Units (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1157-1162 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of the LiBr complexes of two macrobicyclic ligands, [py.py.bpy]1 and [py.biqi.biqi] 2, have been determined. They confirm the cryptate nature of these species. In 3, the Li+ cation is bound in the shallow cavity of a ligand of flattened shape, whereas in 4, it is buried inside the macrobicycle and surrounded by its three bridges.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740602
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  • 99
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    Site-Selectivity in the Fe+-Mediated C—H/C—C Bond Activation of Aldimines Short CommunicationDedicated to Prof. Gerhard Spiteller on the occasion of his 60th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1171-1174 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is demonstrated for the first time that the site-selectivity for the Fe+-mediated C—H bond activation of aldimines R1N=CHR2 (R1, R2 = alkyl) involves the alkyl chain R1 by a factor ≥ 12 in comparison to the alkenyl part R2. This finding explains previous observations that dehydrogenation of intermediates formed by alkene loss from either R1 or R2 of R1N=CHR2/Fe+ preferentially involves the alkyl part.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19910740604
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  • 100
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    Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1163-1170 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of the LaIII, EuIII, and TbIII complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La3+ ⊂ 1]3 Cl- ( = 3-La), [Tb3+ ⊂ 1]3 Cl- ( = 3-Tb), and [Eu3+ ⊂ 2]3 C1- ( = 3-Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl- ions or H2O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the EuIII and TbIII cryptates, which indicated residual coordination of H2O molecules.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19910740603
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