Synthesis and biological evaluation of ambradiolic acid as an inhibitor of glycogen phosphorylase.

Ambradiolic acid (3) with oleanane skeleton is a natural pentacyclictriterpene. The first synthesis of 3 starting from 23-hydroxybetulinic acid (2) has been accomplished in 12-steps with a total yield of 18.1% in our study. Compound 3 was further biologically evaluated and found to exhibit significant inhibitory activity against rabbit muscle glycogen phosphorylase (GP) with an IC50 value of 12.4 μM, suggesting it could be a potential lead compound for the development of hypoglycemic drugs.