Practical synthesis of bredemolic acid, a natural inhibitor of glycogen phosphorylase.

Bredemolic acid (3) is a naturally occurring 2β,3α-isomer of maslinic acid (1) that is an allosteric site inhibitor of glycogen phosphorylase (GP). A practical synthesis of 3 was accomplished (18% yield) in five steps starting from the readily available 2β,3β-diol 6a. In a similar fashion, 2β,3α-dihydroxyurs-12-en-28-oic acid (4) was synthesized as a natural 2β,3α-isomer of corosolic acid (2). Compounds 3 and 4 exhibited significant inhibitory activity against rabbit muscle GPa with IC(50) values of 6.25 and 1.1 μM, respectively.