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.