Pentacyclic triterpenes. Part 1: the first examples of naturally occurring pentacyclic triterpenes as a new class of inhibitors of glycogen phosphorylases.

The semi-synthesis, in vitro and in vivo biological evaluation of corosolic acid (1) and maslinic acid (2) are described. Compounds 1 and 2 represent a new class of inhibitors of glycogen phosphorylases. Both 1 and 2 inhibit the increase of fasted plasma glucose of diabetic mice induced by adrenaline. It is therefore proposed that naturally occurring pentacyclic triterpenes 1 and 2 might reduce blood glucose, at least in part, through inhibiting hepatic glycogen degradation.