Absolute stereochemistry of neohalicholactone from the brown alga Laminaria sinclairii.

Phytochemical analysis of an extract from the brown alga Laminaria sinclairii led to the isolation of neohalicholactone, a cyclopropyl-containing oxylipin previously isolated from a marine sponge, Halichondria okadai. Unequivocal stereochemical analysis of the C-15 hydroxyl group showed this isolate to be of opposite overall absolute stereochemistry compared to that proposed for halicholactone, a related compound from the sponge, and by our inference, sponge-derived neohalicholactone. Comparison of chiroptical data for all three compounds indicates the absolute stereochemistry of the sponge compounds is most probably opposite to that previously proposed.