Farnesyl-protein transferase (FPTase) catalyses the specific transfer of farnesyl to Ras-peptides that is essential for oncogenic activity in oncogene-mediated tumors. Specific inhibition of FPTase activity has been shown to reduce tumor development in nude mice challenged with oncogenic forms of ras, thereby establishing FPTase as a viable therapeutic target. Our continued efforts to discover inhibitors of FPTase has led to the discovery of a triterpenoidal inhibitor, clavaric acid (1). This compound inhibits rHFPTase with an IC50 value of 1.3 microM. Structure elucidation, structure modifications, and biological activity of clavaric acid are herein described.