New bhimamycins from Streptomyces sp. AK 671.

From the wild-type strain Steptomyces sp. AK 671, three nitrogen-containing octaketides were isolated, bhimamycins F, H and I, besides the known azaanthraquinone utahmycin A and polyketide shunt products SEK 4, SEK 4b, mutactin, dehydromutactin and EM18. The structures were characterized by MS and NMR experiments. The hitherto unknown absolute configuration of the two enantiomers of EM18 was determined by online-CD spectroscopy and quantum-chemical CD calculations. Bhimamycins H and I show weak antibacterial activities, whereas the enzyme phosphodiesterase 4 is strongly inhibited by bhimamycins H and I, which has never been reported for nitrogen-containing octaketides. In addition, bhimamycin H inhibits the enzyme glycogen synthase kinase-3β.