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 NaBH₄ afforded MPTP.