Calphostins, novel and specific inhibitors of protein kinase C. II. Chemical structures.

Abstract
The structures of new antitumor antibiotics, calphostins (UCN-1028) A, B, C, D and I, which are specific and potent inhibitors of protein kinase C, were determined by spectral and chemical studies. All of the antibiotics have a 3,10-perylenequinone skeleton and calphostin D was revealed to be an antipode of isophleichrome.