New Indolocarbazoles from a Mutant Strain of the Marine-Derived Actinomycete Streptomyces fradiae 007M135

Fradcarbazoles A–C (1–3), three new indolocarbazoles, were isolated from a mutant strain of the marine-derived actinomycete Streptomyces fradiae 007M135. Their structures were established by spectroscopic analysis, quantum chemical calculation, CD spectra, and chemical transformation. Fradcarbazole A (1) possessed a unique skeleton consisting of a staurosporine core, a thiazole ring, and an indole fragment. Compounds 1–3 displayed significant cytotoxicity against HL-60, K562, A-549, and BEL-7402 cell lines and inhibitory effects on the kinase PKC-α with IC50 values of 0.001–4.58 μM.