Implication of tyramine in the biosynthesis of morphinan alkaloids in Papaver.
Doubly-labeled [(3)H, (14)C]tyrosines, [1-(13)C-]tyramine or [2-(14)C]tyramine, administered to the stems of intact Papaver somniferum L. plants, were found to be incorporated into the morphinan alkaloids of the plant with comparable efficiency. (3)H/(14)C ratios of alkaloids from plants fed the tyrosines were consistent with an almost equal conversion of this amino acid into the tetrahydroisoquinoline (TIQ) and benzyl-derived segments. Nuclear magnetic resonance (NMR) analyses of morphine isolated after administration of [1-(13)C]tyramine demonstrated selective labeling of C-16 of the alkaloid, indicating the conversion of this amine primarily into the TIQ-derived moiety. Morphine and thebaine labeled by [2-(14)C]tyramine were degraded to phenanthridines and N,N'-dimethyl ethylamines. Of the total radioactivity in the alkaloids 97% was found to be associated with the ethylamines, a distribution consistent with the NMR data. This preferential utilization of tyramine in the biosynthesis of morphinan alkaloids can be explained by the compartmentalization of intermediates and enzymes of the pathway.
Department of Pharmacognosy, London University, WCIN 1AX, London, UK.
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Roberts
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Kutchan
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Brown
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Coscia