K-252b, c and d, potent inhibitors of protein kinase C from microbial origin

Nocardiopsis sp. K-290 was found to produce novel metabolites, designated K-252b, c and d, which were structurally related to K-252a. These compounds were isolated from the culture broth and the physico-chemical and biochemical properties were examined. The compounds strongly inhibited protein kinase C. IC50 values (the concentrations causing 50% inhibition) for the effects of K-252b, c and d on the rat brain enzyme were 38.3, 214, and 337 nM, respectively.