Structure and Absolute Configuration of Malyngolide, an Antibiotic from the Marine Blue-Green Alga Lyngbya majuscula Gomont

The δ-lactone malyngolide, an antibiotic effective against Mycobacterium smegmatis and Streptococcus pyogenes, was isolated from the dichloromethane extract of a shallow-water variety of the blue-green alga Lyngbya majuscula Gomont. Its skeletal structure and relative stereochemistry were established by spectral analysis, chemical degradation, and a lanthanide-induced proton chemical shift study. The absolute configuration was determined by a circular dichroism study and by converting malyngolide to levorotatory methyl 2-methyl-5-oxotetradecanoate which had an optical rotation comparable with that of methyl 2(R)-methyl-5-oxoheptanoate. The structure was verified by X-ray crystallographic analysis of the levorotatory saponification product, (2/?, 5S)-5-hydroxy-5-(hydroxymethyl)-2-methyltetradecanoic acid.