-Hydroxyoctahydroindolizine in Rhizoctonia leguminicolat

Known or suspected intermediates in the biosynthesis of slaframine and 3,4,5-trihydroxyoctahydro-1pyrindine, 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 L y s i n e is converted by the phytopathogenic fungus Rhizoctonia leguminicola to two unusual piperidine alkaloids: 1-acetoxy-6-aminooctahydroindolizine (slaframine, 1) and 3,4,5-trihydroxyoctahydro-l-pyrindine (2) (Aust & Broquist, 1965; Guengerich et al., 1973a). As indicated by the heavy lines in the structural drawings in Scheme I, six of the eight carbons in both compounds are derived from the six carbons of lysine via pipecolic acid (Guengerich et al., 1973a,b). In From the Departments of Biochemistry (E.C.C. and H.P.B.) and Chemistry (P.W. and T.M.H.), Vanderbilt University, Nashville, Tennessee 37232. Received November 16, 1978; revised manuscript received May 2, 1979. This work was supported by U S . Public Health Service Grants AM-05441, GM-24831, and ES-00267 and was in part taken from the Ph.D. dissertation of E.C.C. and the M.S. thesis of P.W., which were submitted to the Graduate School of Vanderbilt University in partial fulfillment of degree requirements. 0006-2960/79/0418-3663$01 .OO/O 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 cisand trans[ 1 ,3,3-2H]1 -hydroxyoctahydroindolizine strengthened arguments that 1-oxooctahydroindolizine is an intermediate in slaframine biogenesis. isotope incorporation experiments described in the previous communication in this series (Clevenstine et al., 1979), it has been shown that the remaining two carbons in the fivemembered rings of both 1 and 2 are derived from acetate via malonate. These observations are incorporated in the proposed biosynthetic pathway to slaframine shown in Scheme I. This paper describes two attempts to define further the early stages of slaframine biosynthesis. The first involves feeding ethyl pipecolylacetate (7), which is closely related to 3, the hypothetical common precursor of alkaloids 1 and 2. The second involves the lactam 1,3-dioxooctahydroindolizine (4), which might itself be an intermediate in the pathway or, alternatively, might be able to enter the pathway by conversion to 3. During the course of this work a facile synthesis of the 1 -hydroxy derivatives (5a and 5b) of octahydroindolizine