Investigation and synthetic studies of bioactive Mitragyna alkaloids.

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The leaves of Mitragyna speciosa Korth. have been known as an opium substitute in traditional use by Thai and Malay natives. Reinvestigation of the alkaloidal constituents in the leaves of the plant resulted in the isolation of a major indole alkaloid, mitragynine, and a new minor alkaloid 7alpha-hydroxy-7H-mitragynine. Starting from an optically pure alcohol, an enantioselective total synthesis of mitragynine was attained. Mitragynine was converted into the pseudoindoxyl derivative and its stereochemistry of C2, C3 was elucidated. The structure of nauclefidine, having a basic skeleton in the new type of Mitragyne alkaloids, was revised based on the total synthesis and biomimetic transformation from the vincoside lactam. The crude alkaloid mixture and mitragynine showed non-narcotic antinociceptive activities and inhibited contraction of smooth muscle.