Sporangimicins A-D, acylated maltose derivatives from a rare actinomycete of the genus Pseudosporangium.

Abstract

Sporangimicins A-D (1-4), four anomeric pairs of diacyl disaccharides that represent a new metabolite class, were discovered from the culture extract of an actinomycete Pseudosporangium sp. RD061809. Compounds 1-4 caused peak separation in the HPLC chromatogram and partial duplication of the NMR resonances by anomeric interconversion of a maltose core modified at the two sugar 6-positions with an isobutanoyl and a methyl-branched long-chain dienoyl groups. A highlight of the structure elucidation was application of Ohrui-Akasaka's method to a chromatographically inseparable mixture of 3 and 4, which proved the composition ratio of 3 and 4 to be 82:18 and the R/S ratio at the anteiso-methyl bearing chiral center in 3 to be 66:34. Compounds 1-4 showed antimicrobial activity against Gram-positive bacteria and modest cytotoxicity toward P388 murine leukemia cells.