N-methylputrescine oxidation during cocaine biosynthesis: Study of prochiral methylene hydrogen discrimination using the remote isotope method

[GRAPHICS] The stereoselectivity of N-methylputrescine (3) oxidation to pyrrolinium io n 4 in Erythroxylum coca during cocaine (1) biosynthesis was studied, The r emote isotope method was used to advantage. Each enantiomer of 4-monodeuter ated N-methylputrescine served as a precursor for plant feeding. To facilit ate mass-spectrometric analysis of products, a (H3C)-H-2-C-13-methyl group was also incorporated into the 4-deuterio-N- methylputrescines. Oxidative d eamination of N-methylputrescine was found to be stereoselective; the pro-S hydrogen atom is removed with 6-10:1 selectivity.