Conversion of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (mptp) and its 5‐methyl analog into pyridinium salts

Monoamine oxidase B metabolizes 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP; 1 ) first to 1‐methyl‐4‐phenyl‐2,3‐dihydropyridinium salt (MPDP + ; 5 ), and then to 1‐methyl‐4‐phenylphridinium salt (MPP + ; 7 ). Chemical synthesis of MPDP + and its 5‐methyl analog 6 was accomplished from the N ‐oxides 3 and 4 of MPTP and its 5‐methyl analog, respectively, by a Polonovski reaction. Oxidation of MPDP + to MPPM + was accomplished with air, and greatly accelerated by Pt catalyst. Reduction of MPDP + and MPP + with NaBH 4 afforded MPTP.