Enantiomers of 3-O-methyloxazepam and 3-O-ethyloxazepam were resolved by chiral stationary phase high-performance liquid chromatography (CSP-HPLC). Temperature-dependent and acid-catalysed racemization of 3-O-methyloxazepam enantiomers in methanol and 3-O-ethyloxazepam enantiomers in ethanol were studied by quenching reaction products at various times by neutralization. Enantiomeric contents of reaction product were determined by CSP-HPLC. Thermodynamic parameters in the formation of the activated complex (Eact, delta H++, delta S++ and delta G++) were consistent with those determined by a spectropolarimetric method. A nucleophilically solvated and transient C3 carbocation intermediate resulting from an N4-protonated enantiomer is proposed to be an intermediate and responsible for the acid-catalysed stereoselective homonucleophilic substitution and the resulting racemization.

Acids↗

PubMedDate not supplied

Enantioselective metabolism of camazepam by rat liver microsomes.

Camazepam [3-(N,N-dimethyl)carbamoyloxy-7-chloro-1-methyl-1, 3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, CMZ] possesses anxiolytic, anticonvulsant, muscle relaxant and hypnotic properties. CMZ is clinically used as a racemate. The enantioselective metabolism of racemic CMZ by rat liver microsomes was studied. Major metabolites were isolated by normal-phase and reversed-phase liquid chromatography (LC) and further characterized by UV absorption, mass, and circular dichroism spectral analyses, and by chiral stationary phase LC analysis. Following an in vitro incubation of rac-CMZ, the unmetabolized CMZ was found to be enriched (S)-CMZ, indicating that the R-enantiomer was enantioselectively metabolized. Two of the most abundant metabolites, formed by hydroxylation and demethylation of a methyl group of the N,N-dimethylcarbamyloxy side chain, were found to be enriched in the R-enantiomer. The results indicated that the (R)-CMZ was metabolized at a faster rate than (S)-CMZ by rat liver microsomes.

Animals↗

PubMedDate not supplied

Stereoselective metabolism of prazepam and halazepam by human liver microsomes.

Metabolism of prazepam [PZ, 7-chloro-1,3-dihydro-5-phenyl-1- (cyclopropylmethyl)-2H-1,4-benzodiazepin-2-one] and halazepam [HZ,7- chloro-1,3-dihydro-5-phenyl-1-(2,2,2-trifluoroethyl)-2H-1,4- benzodizepin-2-one] was investigated in microsomes prepared from the livers of two male and one female subjects who died of head injuries. PZ (or HZ) and its metabolites were analyzed by normal phase and chiral stationary phase HPLC. The relative amount of products formed in the metabolism of PZ was found to be N-desalkylprazepam (NDZ, also known as N-desmethyldiazepam and nordiazepam) greater than 3-hydroxy-PZ (3-OH-PZ) much greater than oxazepam (OX). In contrast, the relative amount of products formed in the metabolism of HZ was found to be 3-OH-HZ much greater than NDZ greater than OX. Enantiomers of 3-OH-PZ and 3-OH-HZ were resolved by HPLC on an analytical column packed with the chiral stationary phase R-N-(3,5-dinitrobenzoyl)phenylglycine covalently bound to spherical particles of gamma-aminopropylsilanized silica. The 3-OH-PZ formed in the metabolism of PZ by three human liver microsomal preparations were found to have 3R/3S enantiomer ratios of 65:35, 61:39, and 62:38. In the metabolism of HZ, the enzymatically formed 3-OH-HZ had 3R/3S enantiomer ratios of 67:33, 60:40, and 62:38. N-Dealkylations of racemic 3-OH-PZ and 3-OH-HZ by human liver microsomal preparations were substrate-enantioselective; 3S-OH-PZ and 3R-OH-HZ were each N-dealkylated slightly faster than the corresponding antipode. The results indicated that both C3-hydroxylation of PZ and HZ as well as N-dealkylation of 3-OH-PZ and 3-OH-HZ catalyzed by human liver microsomes were stereoselective, resulting in the formation of a C3-hydroxylated product enriched (60-67%) in the 3R-enantiomer.

Adolescent↗