New biologically active rubiginones from Streptomyces sp.

Four new polyketides, named rubiginone D-2 (2), 4-O-acetyl-rubiginone D-2 ( 3), rubiginone H (6) and rubiginone I (7) were isolated from the cultures o f Streptomyces sp. (strain Go N1/5). Their structures were established by a detailed spectroscopic analysis. The absolute configuration of 3 was deter mined by derivatization with chiral acids (Helmchen's method). The rubigino nes inhibit the growth of some Gram-positive bacteria and are cytostaticall y active against different tumor cell lines.