Absolute stereochemistry of amphidinolide Q.

The absolute configurations at five chiral centers in amphidinolide Q (1), a cytotoxic 12-membered macrolide isolated from a marine dinoflagellate Amphidinium sp., were elucidated to be 4R, 7R, 9S, 11R, and 13R on the basis of NMR analyses and a modified Mosher's method.