摘要:
Methyl (RS)-[1,2-C-13(2),1-C-14]-4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoate was synthesized from a mixture of sodium [1,2-C-13(2)]- and (1-C-14]acetate. This beta-keto ester was administered to intact Erythroxylum coca plants, resulting in the formation of labeled cocaine and methyl ecgonine. The presence of contiguous C-13 atoms in these alkaloids at C-2 and C-9 was established by C-13 NMR spectroscopy, and the presence of C-14 at C-9 was established by a chemical degradation. These results are consistent with our new hypothesis for the biosynthesis of cocaine, which involves the intermediacy of 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoate (rather than 2-(1-methyl-2-pyrrolidinyl)-3-oxobutanoate) in the formation of the tropane moiety of cocaine. Support for this biogenetic scheme was also obtained by a biomimetic synthesis of 2-carbomethoxy-3-tropinone by the oxidation of methyl 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoate with mercuric acetate. The formation of labeled cocaine and methyl ecgonine in leaf cuttings of Erythroxylum coca was observed after incubation with. [9-C-14]-2-carbomethoxy-3-tropinone. The degree of incorporation of this precursor into cocaine was significantly increased by the concomitant administration of the N-acetylcysteamine thioester of benzoic acid, with a corresponding reduction in the degree of incorporation into methyl ecgonine.