Abstract
The batrachotoxins are a unique class of steroidal alkaloids isolated in minute quantities from the skins of poison arrow frogs (genus Phyllobates) as well as from the skins and feathers of New Guinea birds (genus Pitohui and Iflita) and exhibit various unique structural features, including a steroid-based pentacyclic core skeleton, an intramolecular 3-hemiketal, and a seven-membered oxazapane ring. These compounds are extremely potent neurotoxins (batrachotoxin (2), LD50 in mice 2 μg/kg) that act as selective and irreversible Na+-channel activators. In this paper, we review historical background of isolations and structure determinations of batrachotoxins and our studies on the total synthesis of (-) -batrachotoxinin A (1). Strategic bond-forming events include the stereospecific epoxidation of the double bond (9→10), a new Garst-Spencer protocol to construct 3, 4-disubstituted furan (14b→17b), the stereoselective intramolecular furan Diels-Alder reaction to assemble the steroidal skeleton (20d→22d), a novel intramolecular oxy-Michael reaction to close the oxazapane ring (31→33), an organocerium addition to form the α-enone (39b→40), and the simultaneous reduction and optical resolution of the racemic ketone to provide both enantiomers of a molecule (rac-41→43, 44).
