Efficient access to isomeric 2,3-dihydroxy lupanes: first synthesis of alphitolic acid

Alphitolic acid (3) is a naturally occurring lupane type of pentacyclic triterpene, which possesses various pharmacological properties. Efficient synthesis of 3 has been accomplished in 10 steps with an overall yield of 19% starting from the readily available diketone 11. An alternative approach to the key intermediate 17 has also been developed, and based on this approach, 3 could be obtained in 10 steps with an overall yield of 26% starting from 11. Moreover, seven other isomeric 2,3-dihydroxy lupanes 4–10 have been synthesized. The synthesized triterpenes 3–10 were evaluated for their inhibitory activity against rabbit muscle GPa (RMGPa), and some of them exhibited moderate inhibitory activity against RMGPa.