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

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.