We initially randomly synthesized about 60 oleanane and ursane triterpenoids as potential anti-inflammatory and cancer chemopreventive agents. Preliminary screening of these derivatives for inhibition of production of nitric oxide induced by interferon-gamma in mouse macrophages revealed that 3-oxooleana-1, 12-dien-28-oic acid (B-15) showed significant activity (IC(50) = 5.6 microM). On the basis of the structure of B-15, 19 novel olean- and urs-12-ene triterpenoids with a 1-en-3-one functionality having a substituent at C-2 in ring A have been designed and synthesized. Among them, 3-oxooleana-1,12-diene derivatives with carboxyl, methoxycarbonyl, and nitrile groups at C-2 showed higher activity than the lead compound B-15. In particular, 2-carboxy-3-oxooleana-1, 12-dien-28-oic acid (3) had the highest activity (IC(50) = 0.07 microM) in this group of triterpenoids. The potency of 3 was similar to that of hydrocortisone (IC(50) = 0.01 microM), although 3 does not act through the glucocorticoid receptor. Interesting structure-activity relationships of these novel synthetic triterpenoids are also discussed.