Cytotoxic indolocarbazoles alkaloids from the streptomyces sp. A65

Abstract Three new indolocarbazoles alkaloids together with nine known compounds were isolated from the rice solid fermentation of the marine-derived Streptomyces sp. A65. Their structures were elucidated by interpretation of spectroscopic and spectrometric data (1D and 2D NMR, IR, and HRESIMS). The absolute configurations of compounds 1 and 2 were determined by single-crystal X-ray crystallographic analysis, and 3 was assigned on the basis of experimental and calculated electronic circular dichroism spectra. All of these compounds were evaluated for cytotoxic activity assay. Compounds 6 and 10 exhibited significant cytotoxicity against PC3 cell lines with IC 50 values of 1.96 and 2.92 μM, respectively; Compounds 2 and 3 showed moderate cytotoxic activity with IC 50 values of 9.67 and 6.79 μM, respectively. Additionally, compounds 1 – 4 also were also tested for enzyme inhibition activities of Protein kinase C and Brution tyrosine kinase. They showed moderate activity with IC 50 values ranging from 0.25 μM to 1.91 μM except for compound 1 , which has no inhibition activity for protein kinase C.