Abstract:Two new caprolactones, (R)-10-methyl-6-undecanolide (1) and (6R,10S)-10-methyl-6-dodecanolide (2), were identified in thelipid extract of a marine streptomycete (isolate B6007). Their structures were proposed on the basis of GC-MS experimentsand proved by synthesis. The absolute configuration of the compounds was established by comparison of the natural andsynthetic stereoisomers using chiral gas chromatography. These caprolactones show a moderate phytotoxicity and apromising activity against cancer cells with concomitant low general cytotoxicity.