Enzymic Dealkylation of a Substituted Aminoacetamidobenzophenone and Cyclization to the Corresponding Benzodiazepine in vitro

Abstract

1. The metabolism of the substituted aminoacetamidobenzophenone C 72 0045 to nimetazepam has been studied in rat, mouse and dog liver slices and microsomes.

2. Whereas in dog and mouse liver slices [¹⁴C]C 72 0045 was metabolized to material chromatographically identical to nitrazepam and nimetazepam in rat liver slices more polar products were formed.

3. In microsomal preparations, from all three species, fortified with an NADPH-regenerating system, two products were formed simultaneously, one of which was further metabolized to nimetazepam.

4. Rat liver microsomes performed the transformation much faster than liver microsomes of dog or mouse, as reflected in kinetic parameters (K_m, F_max).

5. Formaldehyde was produced concomitantly with the formation of one initial metabolite and concomitantly with the further metabolism of the second initial metabolite to nimetazepam.

6. The enzyme required to initiate the metabolism of C 72 0045 was located in the microsomal fraction, required NADPH and air, was induced two-fold by pre-treating rats with phenobarbitone and was inhibited by CO, SKF 525-A, and 8-hydroxyquinoline but not by iproniazid or cysteine.

7. Transformation of one metabolite to nimetazepam required microsomes and an NADPH-regenerating system incubated aerobically. No further intermediate was detected.

8. A possible route is proposed for the formation of nimetazepam from C 72 0045 by dealkylation and cyclization via a specific intermediate metabolite.