Biosynthesis of slaframine, (1S,6S,8aS)-1-acetoxy-6-aminooctahydroindolizine, parasympathomimetic alkaloid of fungal origin. 4. Metabolic fate of ethyl pipecolylacetate, 1,3-dioxooctahydroindolizine, and 1-hydroxyoctahydroindolizine in Rhizoctonia leguminicola
Known or suspected intermediates in the biosynthesis of slaframine and 3,4,5-trihydroxyoctahydro-1-pyrindine, piperidine alkaloids of the phytopathogenic fungus Rhizoctonia leguminicola, were prepared and tested for biological conversions. Ethyl pipecolylacetate, an analogue of the postulated condensation product of pipecolic and malonic acids (two previously identified alkaloid precursors), was insufficiently stable for feeding experiments. The lactam of pipecolylacetate, 1,3-dioxooctahydroindolizine, was degraded by the fungus without direct incorporation into alkaloids. The known slaframine precursor 1-hydroxyoctahydroindolizine was prepared by a novel route which permitted high levels of deuterium enrichment at C-1 and C-3. Mass spectrometric examination of the slaframine biosynthesized from cis- and trans-[1,3,3-2H]-1-hydroxyoctahydroindolizine strengthened arguments that 1-oxooctahydroindolizine is an intermediate in slaframine biogenesis.