Stereoselective synthesis of marine antibiotic (-)-malyngolide and its stereoisomers.

A convenient synthetic method for the marine antibiotic (-)-malyngolide and its stereoisomers was accomplished from a chiral alpha-alkoxyketone (4), which was readily available as a chiron. Chiral quaternary carbon synthons (5a) and (5b) as the key intermediates were constructed by the chelation controlled addition of Grignard reagent to 4. The diastereomeric mixture of 5a and 5b was readily transformed into a separable mixture of lactones (7a) and (7b), each of which could be easily separated by silica-gel column chromatography. (-)-Malyngolide and its three stereoisomers were obtained in optically pure form without the need for optical resolution.