Practical Synthesis of α-Amyrin, β-Amyrin, and Lupeol: The Potential Natural Inhibitors of Human Oxidosqualene Cyclase.

A practical synthesis of α-amyrin (1), β-amyrin (2), and lupeol (3) was accomplished in total yields of 32, 42, and 40% starting from easily available ursolic acid (4), oleanolic acid (5), and betulin (6), respectively. Remarkably, these three natural pentacyclic triterpenes exhibited potential inhibitory activity against human oxidosqualene cyclase.