Butanoic acid, 2-methyl-, 11-(acetyloxy)-1,4,5,6,7,7a,8,10a-octahydro-1,7a-dimethyl-5-methylene-4,8-dioxo-2,6-methano-2H-cyclopent[d]oxonin-7-yl ester NSC335754 PSEUDOGUAIANOLIDE