RK-1355A and B, novel quinomycin derivatives isolated from a microbial metabolites fraction library based on NPPlot screening

Two novel quinomycin derivatives, RK-1355A ( 1 ) and B ( 2 ), and one known quinomycin derivative, UK-63,598 ( 3 ), were isolated from a microbial metabolites fraction library of Streptomyces sp. RK88-1355 based on Natural Products Plot screening. The structural elucidation of 1 and 2 was established through two-dimensional NMR and mass spectrometric measurements. They belong to a class of quinomycin antibiotics family having 3-hydroxyquinaldic acid and a sulfoxide moiety. They are the first examples for natural products as a quinoline type quinomycin having a sulfoxide on the intramolecular cross-linkage. They showed potent antiproliferative activities against various cancer cell lines and they were also found to exhibit moderate antibacterial activity.