Relative and absolute configuration of the 3,12-dihydroxypalmitic acids

Article abstract of DOI:10.1002/jlac.199619961226

The relative and absolute configuration of (+)-3,12-dihydroxypalmitic acid, a constituent of the Ipomea operculata M. resin, has been determined by synthesis. Dimethyl L-malate was converted via (S)-(+)-1 into the oxirane (S)-(-)-2. Reaction of (-)-2 with the Grignard reagent of 8-benzyloxybromooctane provided (S)-(+)-3 in 84% yield, and this was converted into the aldehyde (S)-(-)-6 via (S)-(-)-4 and (S)-(-)-S. Reaction with the lithium enolate of methyl acetate gave 7 and 8, which could be converted via 9 and 10, 11 and 12, 13 and 14 into the lactones (4S,13S)-(+)-15 and (4R,13S)-(+)-16 and finally into the methyl esters (3S,12S)-(+)-17 and (3R,12S)-(+)-18 and acids (-)-19 and (+)-20. The errthro configuration of (+)-17 was established by a stereoselective synthesis starting from (S)-(-)-2 via (S)-(+)-21, (+)-22, (+)-23, the Grignard reagent of (+)-24 and (R)-(+)-2-(2-benzyloxyethyl)oxirane to give (3S,12S)-(-)-25, (-)-26, (+)-27 and (+)-28, which could be oxidized to the diacetoxy acid (3S,12S)-(+)-29. Saponification and esterification gave (3S,12S)-(-)-19 and (3S,12S)-(+)-17, with properties identical to those of (+)-17 obtained from the resin glycoside. VCH Verlagsgesellschaft mbH, 1996.