New triterpenoid derivatives with various substituents at the C-17 position of 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) were synthesized. Among them, 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-onitrile (CNDDO), 1-(2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl) imidazole, 1-(2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl)-2-methylimidazole, 1-(2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl)-4-methylimidazole show extremely high inhibitory activity (IC₅₀=0.01-1 pM level) against production of nitric oxide induced by interferon- in mouse macrophages. These compounds can be used in the prevention or treatment of diseases such as cancer, Alzheimer's disease, Parkinson's disease, multiple sclerosis, rheumatoid arthritis, and other inflammatory diseases. All the new triterpenoid derivatives are more potent than previously known CDDO.