NAPHTHOPYRANQUINONE ANTIBIOTICS - NOVEL ENANTIOSELECTIVE SYNTHESES OFFRENOLICIN-B AND SOME OF ITS STEREOISOMERS

Two new enantioselective syntheses of the naphthopyranquinone antibiot ic frenolicin B (1), of its enantiomer 2, and ofits diastereoisomers 3 and 4 were accomplished using two different routes from optically act ive beta-hydroxy esters (R)- and (S)-11 and 18. beta-Hydroxy esters (R )- and (S)-ll were prepared stereoselectively from optically active su lfenylacetates (S)- and (R)-10, respectively (Scheme 2, Method A). Alt ernatively, compound 18 was obtained in excellent yield by enantiosele ctive hydrogenation of the corresponding beta-keto ester 17, using a c hiral ruthenium-complex catalyst (Scheme 3, Method B). Subsequently, c ompounds (S)-ll and 18 were transformed into frenolicin B (1). In anal ogy, stereoisomers 2-4 were prepared from (S)- and (R)-ll in good yiel ds.