One new indolocarbazole alkaloid from the Streptomyces sp. A22

One new indolocarbazole alkaloid, 12-N-methyl-k252c, together with eight known indolocarbazoles were isolated from the rice solid fermentation of the marine-derived Streptomyces sp. A22. Their structures were elucidated on the basis of spectroscopic methods (UV, IR, HRESITOF MS, 1D NMR and 2D NMR). All of these compounds were evaluated for bromodomain-containing protein 4 (BRD4) inhibitory activities and cytotoxic activity assay, respectively. Compounds 4 and 5 showed moderate cytotoxic activity with an IC₅₀ value of 3.52 and 3.93 μM, respectively. Additionally, compound 1 also was tested for enzyme inhibition activities of protein kinases and showed moderate activity with IC₅₀ values of 0.91-1.84 μM.