NOVEL CARBAMATE METABOLITES OF MOFEGILINE, A PRIMARY AMINE MONOAMINE-OXIDASE-B INHIBITOR, IN DOGS AND HUMANS

Mofegiline or MDL 72,974A ((E)-4-fluoro-beta-fluoromethylene benzene b utanamine hydrochloride) is a selective enzyme-activated irreversible inhibitor of monoamine oxidase B, which is under development for use i n the treatment of Parkinson's disease. Male beagle dogs were given si ngle po (20 mg/kg) and iv (5 mg/kg) doses of [C-14]-Mofegiline. Total radioactivity excreted in urine and feces over 96 hr was, respectively , 75.5 +/- 3.8 and 6.3 +/- 3.4% of the dose after po and 67.9 +/- 0.5 and 3.9 +/- 2.4% after iv administration. Unchanged drug in urine repr esented 3% of the dose after po and less than 1% after iv administrati on. Mofegiline was thus extensively metabolized in dogs, and urinary e xcretion was the major route of elimination of metabolites. HPLC, with on-line radioactivity detection, showed the presence of four major pe aks (M(1), M(2), M(3), and M(4)), representing respectively 50, 9, 5, and 0.5% of the administered dose excreted in 0-24 hr urine. TSP-LC-MS , FAB MS, and NMR spectra of the purified metabolites were obtained. M (1), the major metabolite in dogs, was shown to have undergone defluor ination of the beta-fluoromethylene moiety, and one carbon addition. I ts structure was confirmed to be a cyclic carbamate. M(2) was a N-carb amoyl O-beta-D-glucuronide conjugate of parent drug. The formation of M(1) and M(2) is likely to involve initial reversible addition of CO2 to the primary amine function. M(3) was a N-succinyl conjugate of the parent drug. M(4) had also undergone defluorination to yield a urea ad duct of an unsaturated alpha, beta aldehyde. Structures of M(1) end M( 3) were further confirmed by comparing their MS and NMR spectra with t hose of authentic reference compounds. TSP-LC-MS ion chromatograms of human urine, obtained from two male volunteers after po administration of 24 mg of drug, showed selected molecular ion peaks with the same r etention time as the metabolites identified in dogs. In humans, these common metabolites represented a similar percentage of the administere d dose to that in dogs. The present study demonstrates that NMR, TSP-L C-MS, and FAR-MS are complementary analytical techniques, which allow structural identification of unhydrolyzed drug conjugates. The formati on of carbamates of amine-containing drugs may be more common than pre viously reported.