Chemically induced Parkinson's disease. II: Intermediates in the oxidation and reduction reactions of the 1-methyl-4-phenyl-2,3-dihydropyridinium ion and its deprotonated form

The one-electron reduction product of 1-methyl-4-phenyl-2,3-dihydropyridinium ion has been generated by pulse radiolysis and its absorption spectrum recorded. This radical was found to decay by second-order kinetics (2k = 9.5 x 10(8) M-1 s-1) to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 1-methyl-4-phenyl-2,3-dihydropyridinium ion. Reactions of the above radical species and that formed by one-electron reduction of 1-methyl-4-phenylpyridinium ion, which can also be generated by one-electron oxidation of 1-methyl-4-phenyl-1,2-dihydropyridine, with a number of molecules of biochemical interest have been studied. The one-electron reduction product of oxidised nicotinamide adenine dinucleotide efficiently reduced 1-methyl-4-phenyl-2,3-dihydropyridinium ion (k = 2.2 x 10(9) M-1 s-1). The relevance of these results in relation to redox cycling, a possible mechanism for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity, is discussed.