Structure of onchidione, a bis-gamma-pyrone polypropionate from a marine pulmonate mollusk.

The chemical investigation of the marine pulmonate Onchidium sp. and of its defensive mucous secretion led us to the isolation of a novel polypropionate, onchidione (4), containing two g-pyrone rings. The structure of 4 was elucidated by spectroscopic methods, mainly NMR techniques, and secured by X-ray analysis on a single crystal.