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Abstract
Enantiomers of temazepam (TMZ), an anxiolytic drug in clinical use, were resolved and stabilized by the use of aprotic solvents in chiral stationary phase high-performance liquid chromatography (CSP-HPLC). The enantiomers were used to study racemization and heteronucleophilic substitution (alcoholysis) reactions in anhydrous acidic methanol and ethanol. Kinetics of spontaneous racemization and stereoselective conversions to 3-O-methyltemazepam (MeTMZ) and 3-O-ethyltemazepam (EtTMZ) were determined by circular dichroism (CD) spectropolarimetry and CSP-HPLC. The rates of conversion of rac-TMZ to rac-MeTMZ (or rac-EtTMZ) were determined by ultraviolet-visible spectrophotometry. The results indicated that, for example, both N4-protonated and unprotonated forms of (S)-TMZ underwent spontaneous racemization and its 3S-hydroxyl group was highly stereoselectively substituted at C3 position by the ethoxy group of ethanol to form EtTMZ enriched in (S)-EtTMZ. Similar stereoselective reactions occurred for TMZ enantiomers in acidic methanol. Chirality 11:179–186, 1999. Published 1999 Wiley-Liss, Inc.
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