SECONDARY METABOLITES BY CHEMICAL-SCREENING .2. OASOMYCINS, NEW MACROLACTONES OF THE DESERTOMYCIN FAMILY

New macrolactones, named oasomycin A to D (1 to 4), were discovered by a chemical screening in the culture broth of Streptoverticillium bald acii subsp. netropse (strain FH-S 1625). The structures were establish ed by detailed spectroscopic analysis. The fundamental 42-membered lac tone moiety of oasomycin A and B (1 and 2) is analogous to that of des ertomycin A (5), while the oasomycins C and D (3 and 4) are the first representatives of macrolactones bearing a 44-membered skeleton. These metabolites can be distinguished by side chain modifications at C-41 or C-43 as well as the presence of an alpha-linked D-Mannose moiety at tached to 22-OH. Due to the structural similarities the oasomycins are integrated into the desertomycin family. In vitro testing by using th e HEP-G2 cell assay showed oasomycin A (1) to be an inhibitor of de no vo cholesterol biosynthesis.