(-)-(7S,8R,10S,11R,12S)-7,8,12-Tris-(4-bromobenzoyloxy)-6,6, 10,11-tetramethyl-4-propyl-6,7,8,10,11,12-hexahydrodipyrano-[2,3-f':2',3'-h]chromen-2-one NSC683204