Synthetic and metabolic studies on 1-methyl-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridine, a neurotoxic analog of the Parkinsonian inducing agent MPTP
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1-Methyl-4-(1-methylpyrrol-2-yl)-1 ,2,3,6-tetrahydropyridine (TMMP) is a neurotoxic analog of the parkinsonian inducing agent MPTP. TMMP and its putative metabolites 1-methyl-4-(1-methylpyrrol-2-yl)-2,3-dihydropyridinium (MMDP+) and 1-methyl-4-(1-methylpyrrol-2-yl)pyridinium (MMP+) were synthesized and fully characterized. Substrate/inactivation properties of TMMP and its analog N-propargyl-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridine with MAO-B were investigated. Kinetic data was obtained, including Km and Vmax for TMMP as an MAO-B substrate, and KI and kinact values for N-propargyl-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridine. The metabolic studies of TMMP and MMDP+ were conducted with an HPLC diode array assay. Both in-vivo and in-vitro metabolic studies showed that TMMP is oxidized to its dihydropyridinium species (MMDP+) in a reaction catalyzed by MAO-B. MMDP+ undergoes autoxidation to form the pyridinium species (MMP+), the mechanism of this conversion is not clear. In-vitro studies show that MAO-B is not responsible for this conversion and the oxidation of MMDP+ to MMP+ is likely to be enzyme catalyzed. Toxicity investigations include dopamine depletion studies of TMMP and MMDP+, mitochondrial respiration and microdialysis studies of MMDP+ and MMP+. The above studies show that TMMP is an MPTP-type neurotoxin.
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