The biosynthesis of β-carboline and quinolizidine alkaloids of Alangium lamarckii

The incorporation of tryptamine, dopamine, N-deacetylisoipecoside, N-deacetylipecoside into alangimarckine, deoxytubulosine and ankorine and of strictosidine and vincoside into alangimarckine and deoxytubulosine in young Alangium lamarckii Thw. (Alangiaceae) has been studied and specific utilisation of N-deacetylisoipecoside demonstrated. Parallel experiments with nordeoxytubulosine and deoxytubulosine suggested that O-methylation precedes condensation of protoemetine with tryptamine and further the reduction of ethylene side chain takes place before condensation. Hydroxylation at C-8 in the trans-quinolizidine moiety is the terminal step in the biosynthesis of alangimarckine. Incorporation of labelled precursors into 17, 20 and 6 in Alangium lamarckii Thw. is reported. It is shown that O-methylation precedes condensation of protoemetine nucleus with tryptamine, reduction of the ethylene side chain occurs before condensation and C-8 hydroxylation in transquinolizidine part is the terminal step in the biosynthesis of 17.