BIOSYNTHESIS OF SLAFRAMINE, (1S,6S,8AS)-1-ACETOXY-6-AMINOOCTAHYDROINDOLIZINE, A PARASYMPATHOMIMETIC ALKALOID OF FUNGAL ORIGIN .3. ORIGIN OF THE PYRROLIDINE RING

The phytopathogen Rhizoctonia leguminicola has previously been shown to incorporate pipecolic acid into the piperidine alkaloids l-acetoxy-6-aminooctahydroindolizine (slaframine) and 3, 4, 5-trihydroxyoctahydro-l-pyrindine. In the experiments described here, resting cultures of R. leguminicola were incubated with [1-14C]- and [2-14C]malonic acid and with [1-14C]- and [2-2H]acetic acid. Both acids were incorporated into the ring systems of both alkaloids. Mass spectrometric analysis of 2H-enriched slaframine showed that the label resides in the five-membered ring and that the methyl carbon of acetate is joined to the carboxyl carbon of pipecolate. A pipecolate-dependent decarboxylation of [l-14C]malonate was demonstrated in cell-free extracts of R. leguminicola. The results account for previously unattributed carbons in the two alkaloids arid suggest the formation of an eight-carbon intermediate common to both alkaloids by acylation of malonate with pipecolic acid. © 1979, American Chemical Society. All rights reserved.