A new inhibitor of protein kinase C, RK-1409B (4'-demethylamino-4'-hydroxy-3'-epistaurosporine).

RK-1409B, a new inhibitor of protein kinase C, was isolated from the culture broth oi Streptomyces platensis subsp.malvinus RK-1409.The structure was elucidated on the basis oi spectroscopic analyses.RK-1409B inhibited protein kinase C in vitro and the morphological change of a human chronic leukemia cell line, K-562, induced by phorbol 12,13-dibutyrate with IC50 value of0.4juM.Protein kinase C (PKC) has a crucial role in signal transduction, cellular regulation, proliferation, and tumor promotion1'2).Specific inhibitors of PKCwere expected to be excellent tools for understanding the roles of PKC.Previously, we reported the PKCinhibitors, sangivamycin3), RK-286C4), RK-286D5), and RK-1409 (7-oxostaurosporine)6'7) by using a convenient assay system for PKCinhibitors, named bleb forming assay8).This assay is based on the morphological change of a humanchronic leukemia cell line K-562.Wefound that Streptomyces platensis subsp.malvinus RK-1409, the RK-1409 (7-oxostaurosporine)producing strain6), produced an additional novel inhibitor of PKC, RK-1409B.In this paper, we report isolation, physico-chemical properties, structural elucidation and biological activities of the novel indolocarbazole antibiotic RK-1409B. Experimental GeneralMPwas measured with a Yanaco micro melting point apparatus.Optical rotation and CDspectrum were measured by a Perkin-Elmer 241MCpolarimeter and a Jasco J-20A spectropolarimeter, respectively.UVana IK spectra were taken on a Hitachi 220A spectrometer and a Shimadzu IR27G recording IR spectrometer, respectively.EI-MS spectra were obtained with a Hitachi M-80 mass spectrometer.NMR spectra were recorded on a Jeol GX-400 and GSX-500 spectrometers.