The metabolic fate of camazepam in rats

Qualitative structure-metabolism relationships in the hydrolysis of carbamates

The aims of this review were 1) to compile a large number of reliable literature data on the metabolic hydrolysis of medicinal carbamates and 2) to extract from such data a qualitative relation between molecular structure and lability to metabolic hydrolysis. The compounds were classified according to the nature of their substituents (R³OCONR¹R²), and a metabolic lability score was calculated for each class. A trend emerged, such that the metabolic lability of carbamates decreased (i.e., their metabolic stability increased), in the following series: Aryl-OCO-NHAlkyl >> Alkyl-OCO-NHAlkyl ~ Alkyl-OCO-N(Alkyl)₂ ≥ Alkyl-OCO-N(endocyclic) ≥ Aryl-OCO-N(Alkyl)₂ ~ Aryl-OCO-N(endocyclic) ≥ Alkyl-OCO-NHAryl ~ Alkyl-OCO-NHAcyl >> Alkyl-OCO-NH₂ > Cyclic carbamates. This trend should prove useful in the design of carbamates as drugs or prodrugs.

Achiral and chiral analysis of camazepam and metabolites by packed-column supercritical fluid chromatography

Supercritical fluid chromatography, using carbon dioxide as the mobile phase and ethanol as a modifier, has been applied to the analysis of products formed in rat liver microsomal metabolism of racemic camazepam, a hypnotic/anxiolytic drug in clinical use. An achiral (amino) column and a chiral (Chiralcel OD-H) column were used. The results suggest that achiral and chiral packed-column supercritical fluid chromatography gives a shorter analysis time and higher selectivity and efficiency than achiral and chiral stationary-phase high-performance liquid chromatography in the analysis of camazepam and its derivatives.

Enantiomer resolution of camazepam and its derivatives and enantioselective metabolism of camazepam by human 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. Enantiomer resolution of CMZ and 11 of its derivatives was studied by high-performance liquid chromatography (HPLC) using 5 different chiral stationary phase (CSP) columns. Enantiomers of 10 compounds were resolved by at least one of the 5 CSP's tested. Enantiomers of two other compounds, which have either one or two hydroxymethyl groups at the carbamoyl nitrogen, were either not resolved or resolved with very low efficiency. However, enantiomers of the hydroxymethyl derivatives were resolved via base-catalyzed dehydroxymethylation. In vitro metabolism of racemic CMZ by human liver microsomes was found to be enantioselective. Major metabolites were isolated by normal-phase and reversed-phase HPLC and further characterized by ultraviolet absorption and circular dichroism spectral analyses, and by chiral stationary phase HPLC analysis. Following an in vitro incubation of rac-CMZ, the unmetabolized CMZ was found to be enriched in (S)-CMZ, indicating that the R-enantiomer was enantioselectively metabolized. Metabolites were formed primarily by hydroxylation and demethylation of the methyl groups at the C3 side chain. All metabolites were found to be optically active, enriched in either the S-enantiomer or the R-enantiomer.

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.

N,N-dimethylcarbamyl derivatives of oxazepam

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 (t1/2 1.9 min at 23 degrees C and 0.9 min at 37 degrees C) in an aqueous solution at pH 7.5. The (R)-enantiomer of rac-3-O-acyl-1-(N,N-dimethylcarbamyl)oxazepam was hydrolyzed approximately 4.6-fold faster than the (S)-enantiomer by esterases in rat liver microsomes, whereas the (S)-enantiomer was hydrolyzed approximately 43-fold faster than the (R)-enantiomer by esterases in rat brain S9 fraction.