Stereoselectivein-vitro aromatic-ring oxygenations of chiral 1,4-benzodiazepin-2-ones

Biotransformations and plasma-level curves of chiral 1,4-benzodiazepine-2-ones

Biotransformations of chiral 1,4-benzodiazepine-2-ones, (S)- and (R)-1 (7-chloro-1,3-dihydro-3 (S and R)-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one) in untreated and phenobarbital-pretreated rats were investigated. In urine, a 4'-oxygenated metabolite (compound 2) was identified as the biotransformation product from both enantiomers, (S)-2 being present in much higher amounts than (R)-2. Unchanged parent compounds were not found in urine. In plasma, 3'- and 4'-oxygenated metabolites were identified after administration of (S)-1 and (R)-1, respectively. The metabolite possessing an R-configuration was present in much lower amounts. The maximum concentrations of (R)-1 in plasma, following a single dose, was about 6 time as high as the maximum plasma concentration of (S)-1. Faster biotransformation and elimination of (S)-1 is assumed to be the explanation of these findings.

Metabolism and pharmacokinetics of metaclazepam (Talis), Part III: Determination of the chemical structure of metabolites in dogs, rabbits and men

The metabolism of 7-bromo-1-methyl-2-methoxymethyl-5-(2'-chlorophenyl)-2, 3-dihydro-1H-1,4-benzodiazepine (metaclazepam, Talis) in animals and men is described. Based upon mass spectrometry fifteen metabolites could be identified. Qualitative and quantitative differences in the biotransformation products of metaclazepam in comparison with the well known metabolites of other drugs in the 1,4-benzodiazepine class could be demonstrated. Metabolites with a benzodiazepine-2-one structure representing the most characteristic feature of other 1,4-benzodiazepines and their metabolites, were found in trace amounts only. The major metabolic pathways of metaclazepam led via stepwise demethylation of the O-methyl and/or the N-methyl group to O-demethyl-metaclazepam (M 2), N-demethyl-metaclazepam (M 7) and bis-demethyl-metaclazepam (M 6). Further aromatic hydroxylation yielded the metabolite M 1. Two metabolites with amino-benzophenone structure (M 5, M 8) which are in general known to result from other 1,4-benzodiazepines could be detected. Additionally a 3-oxo-benzodiazepine (M 4) was found. Minor biotransformation pathways led to a chlorophenyl-bromo-benzodiazepine (M 9) by loss of the side chain from bis-demethyl-metaclazepam and N-demethyl-metaclazepam. By further oxidation and degradation the 2-oxo-benzodiazepine M 10 and the dihydro-quinazoline M 12 were formed. The respective N-methylated metabolites M 13 and M 16 were possibly generated by the same pathway. Still open is the formation of M 15, a 1-methyl-3-hydroxy-4-(2'-chlorophenyl)-6-bromo-1,2-dihydroquinoline and M 11, a 2-methyl-4-(2'-chlorophenyl)-6-bromo-quinazoline. The substitution of bromine by a hydroxyl group during the formation of M 14 can be explained by a NIH-shift mechanism. Quantitative investigations show that the methoxymethyl side chain in the benzodiazepine ring system of metaclazepam acts as an effective barrier with respect to the metabolic attack at position two. We assume that this barrier only can be overcome by complete side chain degradation. This multi-step reaction can hardly compete with more favourable and faster conjugation and elimination processes.

Stereochemical characterization of interactions of chiral 1,4-benzodiazepine-2-ones with liver microsomes

Microsomal P-450 cytochrome are stereoselective toward 7-Chloro-1,3-dihydro-3(S)-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one. (S)-1, and 7-chloro-1,3-dihydro-3(S)-isopropyl-5-phenyl-2H-1,4-benzodiazepin-2-one, (S)-2. (S)-enantiomers bind to a substrate binding site which accomodates the stable M-conformation (Ks =0.01 to 0.018 mmol/l). (R)-enantiomers, however, undergo a ligand type of interaction (Ks = 0.036 to 0.12 mmol/l). Prochiral desmethyldiazepam behaves similarly to the (S)-enantiomers of the above compounds. The ligand binding site does not differentiate between M- and P-conformers.

Comparison of dihydrodiazepam enantiomers: metabolism, serum binding and brain receptor binding

Dihydrodiazepam is a diazepam prodrug, as shown by its in vitro metabolism by rat and mouse liver and brain microsomal fractions, and its displacing activity on brain diazepam binding. The mechanism of bioactivation is discussed. Stereoselectivity of metabolism and of binding to specific benzodiazepine binding sites in brain synpatosomes and serum albumin were studied.