Synthesis of dl-pumiliotoxin C hydrochloride and its crystal structure.

Abstract

Racemate of pumiliotoxin C which is a toxic constituent of skin extracts of Neotropical frogs, Dendrobates pumilio and Dendrobates auratus, was synthesized. The epoxy-lactam (8) was synthesized from octahydroquinolone (4) via the N-benzyl-cis-octahydroquinolone (7). The bromohydrin (9) from 8 was successively subject to Jones' oxidation, dehydrobromination, and the conjugated addition to give the methyl-ketone (14). The thio-lactam (40) was obtained from the methyl-ketone (14) via the decahydroquinolone (39). Using the Eschenmoser's procedure, the thio-lactam (40) was transformed to the vinylogous amide (42). Catalytic hydrogenation of 42, followed by Jones' oxidation, gave the aminoketone (44). Reductive desulfurization of the thioacetal (45) gave dl-pumiliotoxin C (46), the stereochemistry of which was confirmed by a single crystal X-ray analysis. Three stereoisomers, (17), (19), and (36), of the methyl-ketone (14) were also prepared.