12 シガトキシンの絶対構造決定への合成化学的アプローチ(口頭発表の部)

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Twenty thousand of people in subtropical and tropical regions have suffered annually from ciguatera caused by poisonous fishes dwelling in coral reefs. In 1989 Yasumoto et al. established the whole structures including relative stereochemistry of the causative principle, ciguatoxin (CTX, 1), isolated from moray eel, Gymnothorax javanicus, and its congener, gambiertoxin 4B (GT4B, 2), from epiphytic dinoflagellate, Gambierdiscus toxicus (Fig. 1). Extremely low accessibility of these toxins, however, hampers further studies on their absolute configuration, pharmacological studies at the molecular level and development of immunoassay for differentiating poisonous fishes. Therefore, determination of the absolute stereochemistry and the chemical syntheses are critical and of great interest. The AB ring framework of gambiertoxin 4B (3) which has a butadienyl substituent on the tetrahydrooxepin ring A has been synthesized stereoselectively (Scheme 2) and its CD spectrum (Fig. 2) suggests that gambiertoxin 4B (2) and ciguatoxin (1) have 5R configuration.
1991-09-07