摘要:

AbstractOptically active enamines of 2‐(2′‐pyrido)acetophenone or 2‐(2′‐quinolino)acetophenone with (R)‐1‐phenylethylamine, (R)‐1‐(1‐naphthyl)ethylamine, (R)‐cyclohexylethylamine, and (R)‐phenylglycinol were prepared and their copper(I) complexes used in the enantioselective cyclopropanation of styrene with ethyl‐ and menthyldiazoacetate. Enantioselectivities of up to 42% enantiomeric excess were obtained forcis/trans2‐phenylcyclopropan‐1‐carboxylic acid ethyl esters, as determined by gas‐liquid chromatography (GLC) on chiral chromatograp

ISSN:0899-0042    

DOI:10.1002/chir.530070302

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe hydroformylation of (+)‐(R)‐limonene (1), (+)‐(1R)‐isolimonene (2), camphene (3), and (+)‐β‐cedrene (4) resulted in the regiospecific formation of the corresponding linear aldehyde in the presence of homogeneous platinum and, in some cases, rhodium catalysts. The epimeric composition could be influenced slightly by optically active catalysts formed with chiral bidentate phosphines. The relative configurations of newly formed stereogenic centers were analyzed by1H and13C NMR. The primarily formed aldehydes of (+)‐8(15)‐cedren‐9‐ol (5) and γ‐gurjunene (6) underwent cyclization, giving a mixture of epimers of tetracyclic terpenes. Despite the moderate diastereoselection, the products are of practical importance due to their highly regioselective formation.

ISSN:0899-0042    

DOI:10.1002/chir.530070303

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThere are cases in which exciton coupling between two chromophores does not occur because the two electric transition moments which should interact are coplanar. This is seen with cyclohexane‐1,4‐diols (both ee or ea) and a wide variety of 3‐hydroxy carotenoids, 3‐hydroxyretinoids, etc. A general approach to deal with such cases is to acylate one of the hydroxyl groups with a chiral allenic acid substituted with a suitable chromophore, e.g., CHROMCHCCH‐COOH. The allenic bond introduces a 90° twist at the italicized central carbon so that the allenic CHROM now couples with the second chromophore. This concept of introducing an auxiliary allenic center should be of general applicability in other similar cases. © 199

ISSN:0899-0042    

DOI:10.1002/chir.530070304

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe chiral recognition property of poly[(1→6)‐2,5‐anhydro‐3,4‐di‐O‐alkyl‐D‐glucitol] (1) toward racemic RCH (CO2CH3)NH3+· PF6−(2· HPF6) has been studied using a transport system involving an aqueous source and receiving phases separated by a chloroform phase containing1. Transport rates for aromatic guests2a(R = Ph) and2b(R = CH2Ph) were faster than those for aliphatic guests,2c(R = CH(CH3)2) and2d(R = CH2CH(CH3)2), using the polymer substituted with methyl groups (1a). The enantiomeric excess (e.e.) was 10.9% for2aas a maximum value and decreased in the order of2a>2c>2b=2d. When the transport of2a· HPF6was carried out using the polymers with 3,4‐di‐O‐methyl (1a), ethyl (1b), allyl (1c), and pentyl (1d) groups, the e.e. was 22.0% for1das a maximum value and increased in the order of1a<1b<1c<1d. The formation of a complex between1aand2a· HPF6was confirmed by1H and13C NMR spectral measure

ISSN:0899-0042    

DOI:10.1002/chir.530070305

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of structural features of six pairs of enantiomers of cannabimimetic compounds on their chromatographic resolution on an amylose tris(3,5‐dimethylphenylcarbamate) chiral stationary phase was studied using various compositions of n‐hexane with 2‐propanol and ethanol. Structural analysis by molecular mechanics was also performed to verify that the 3D conformation within this family of compounds was preserved with substitution. The homologous enantiomeric pairs showed better resolution when there was an additional OH group near the chiral centers (position 7 on the cannabinoid structure). Better resolution was observed also for the enantiomeric pair that had the smaller alkyl side chain. These differences indicated that the additional OH group contributed to a better discrimination of the enantiomers by the chiral sites of the stationary phase and that the bulkier alkyl side chain reduced it. The chromatographic resolution of two enantiomeric pairs of nonclassical cannabinoids HU‐249 and HU‐250, HU‐255 and HU‐256, was compared both in ethanol and 2‐propanol. Both enantiomeric pairs showed relatively high resolution and selectivity, but the rigid benzofuran analogs (HU‐249 and HU‐250) exhibited better resolution using 2‐propanol, in spite of the flexibility of the open chain analog (HU‐255 and HU‐256) and its additional OH group. The elution order of all the cannabinoids was (+)/(−) using both solvents. Unusual solvent effects were displayed by one enantiomeric pair, Δ6‐THC, which was resolved easily using 2‐propanol, but whose elution order reversed with 1% ethanol in the mobile phase. Partial separation was obtained at 5% ethanol [elution order (+)/(−)] and full separation was obtained at 0.5% ethanol [elution orde

ISSN:0899-0042    

DOI:10.1002/chir.530070306

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA direct chiral chromatographic reversed phase method for the determination of the enantiomers of felodipine is described. The influence of charged and uncharged modifiers as well as the effect of the mobile phase pH on the enantiomeric resolution is discussed. A high mobile phase pH and the addition of 2‐propanol as organic modifier gave the highest separation factor (α = 1.3). The high mobile phase pH (pH = 7.6) is outside the recommended pH limit of silica based columns but was necessary to achieve baseline resolution of (R)‐ and (S)‐felodipine. Improvement of column efficiency by increasing column temperature was utilized for optimization of the enantiomeric resolution (Rs = 1.7). The enantiomers of felodipine and three related compounds were separated within 15 min. The enantiomeric purity of (R)‐ and (S)‐felodipine in injections and (R)‐felodipine in bulk substance was higher than 99.5% and no racemization was observed after storage at accelerated conditions. A poor Chiral‐AGP® column used for a long period was restored using a simple wash step together with repacking the top of the chromatographic column. © 1995

ISSN:0899-0042    

DOI:10.1002/chir.530070307

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe perchlorotriphenylmethyl radical (PTM) shows enantiomerism due to restricted internal rotations. Several chiral stationary phases have been tested in different conditions for the resolution of PTM by HPLC. Only poly(triphenylmethyl methacrylate) provided sufficient resolution for carrying out a micropreparative scale separation. Racemization of (+)‐ and (−)‐PTM was monitored polarimetrically as a function of time. The process was found to follow strict first‐order kinetics. The value of ΔG#303.8= 23.6 Kcal · mol−1agrees with that determined previously by HPLC with the stopped flux technique (Crespo, Doctoral Thesis, CETS Institut Químic de Sarrià, 1991). Following the helicity rules in the circular dichroism spectrum, (+)‐PTM can be assumed to have (P) configuration and (−)‐PTM (M) configuration. ©

ISSN:0899-0042    

DOI:10.1002/chir.530070308

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA direct, isocratic, and simple chromatographic method is described for the resolution of racemic albuterol using the α1‐acid glycoprotein chiral stationary phase (AGP‐CSP) under reverse phase conditions. The effect of various organic modifiers, temperature, and phosphate buffer ionic strength on the separation factor (α) and stereochemical resolution factor (Rs) has been studied. The enantiomeric separation of albuterol was also achieved using a urea‐type CSP of (S)‐indoline‐2‐carboxylic acid and (R)‐1‐(α‐naphthyl)ethylamine, known as Chirex 3022, running in the normal phase mode. The effect of different organic acids added to the mobile phase was examined and the chiral recognition mechanism(s) is discussed. Solid phase extraction with C18Sep‐Pak cartridges was applied as a clean‐up step to determine the enantiomeric ratio between (−)‐R and (+)‐S‐albuterol in pharmaceutical formulations and in huma

ISSN:0899-0042    

DOI:10.1002/chir.530070309

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe extent of myocardial accumulation of tocainide, administered as single enantiomers and as well as racemate, was determined in the isolated, spontaneous beating rabbit heart. The heart was retrogradely perfused at a constant rate and fractions of the perfusate were collected during and after infusion. Kinetic parameters for myocardial accumulation and disposition of tocainide were indirectly determined from drug concentration/time course in the outflow perfusate. No stereoselectivity in myocardial accumulation was observed. A two compartment model with mean half‐lives for distribution and elimination of 0.60 and 3.78 min, respectively, was fitted to the accumulation and disposition data. At steady‐state, tocainide enantiomers were accumulated about three times in the myocardium relative to the perfusion liquid. © 1995 Wiley‐Lis

ISSN:0899-0042    

DOI:10.1002/chir.530070310

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIsradipine (PN 200–110) is a highly potent calcium entry blocker with an asymmetrically substituted dihydropyridine ring (methyl‐ and isopropylester, respectively). The binding of the (+)‐(S)‐isradipine and (−)‐(R)‐isradipine to isolated human serum albumin (HSA, 30 μmol/l) and α1‐acid glycoprotein (AAG, 10 μmol/l) has been studied in vitro over a wide range of isradipine concentrations (0.06–20 μmol/l) using high‐performance liquid chromatography (HPLC). HPLC experiments revealed that both isradipine enantiomers were bound to one class of high‐affinity binding sites on the AAG molecule (n(S)= 0.83 ± 0.05,Ka(S)= (1.33 ± 0.25) × 1061/mol,n(R)= 0.85 ± 0.07,Ka(R)= (1.17 ± 0.44) × 107l/mol). The (R)‐enantiomer also exhibited an interaction with the secondary low‐affinity binding sites (n′K′a (R)= (2.66 ± 0.65) × 104l/mol). In contrast, the pharmacologically more potent (+)‐(S)‐enantiomer was more strongly bound to HSA than its optical antipode (n(S)= 1.07 ± 0.07,Ka(S)= (1.76 ± 0.26) × 105l/mol,nKa(R)= (3.62 ± 0.06) × 104l/mol). In general, the resulting binding characteristics of individual isradipine enantiomers showed stereoselectivity, but this was opposite for the two most important plasma binding proteins. The process of accumulation of isradipine by human platelets in the therapeutically relevant range (10–80 ng/ml) at 37°C wa

ISSN:0899-0042    

DOI:10.1002/chir.530070311

出版商:Alan R. Liss, Inc.    

年代:1995

数据来源: WILEY