Controlled silylation of friedelin (1) from cork smoker wash solids, a byproduct generated during processing of corkboard by steam baking, gave 3-trimethylsiloxyfriedel-2-ene (3) in high yields. Oxidation of 3 with OsO(4)/NMMO produced 2alpha-hydroxyfriedelan-3-one (cerin) (5), from which the new 2,3-secofriedelan-2-al-3-oic acid (6) was obtained quantitatively by periodic acid oxidation. Oxidation of 3 with DDQ afforded friedel-1-en-3-one (8). Reductive ozonolysis of 3 gave 2alpha,3beta-dihydroxyfriedelane, pachysandiol A (7). Compound 6 proved to be a potent inhibitor of human lymphocyte proliferation (IC(50) = 10.7 microM) and of the growth of a human cancer cell line (GI(50) = 5.4-17.2 microM). (13)C NMR data for compounds (3, 4, 5, 6a,7, and 8) are described for the first time.