Abstract
The relative and absolute configuration of (+)β3,12βdihydroxypalmitic acid, a constituent of the Ipomea operculata M. resin, has been determined by synthesis. Dimethyl Lβmalate was converted via (S)β(+)β1 into the oxirane (S)β(β)β2. Reaction of (β)β2 with the Grignard reagent of 8βbenzyloxybromooctane provided (S)β(+)β3 in 84% yield, and this was converted into the aldehyde (S)β(β)β6 via (S)β(β)β4 and (S)β(β)β5. 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 (4__S__,13__S__)β(+)β15 and (4__R__,13__S__)β(+)β16 and finally into the methyl esters (3__S__,12__S__)β(+)β17 and (3__R__,12__S__)β(+)β18 and acids (β)β19 and (+)β20. The erythro configuration of (+)β17 was established by a stereoselective synthesis starting from (S)β(β)β2 via (S)β(+)β21, (+)β22, (+)β23, the Grignard reagent of (+)β24 and (R)β(+)β2β(2βbenzyloxyethyl)oxirane to give (3__S__,12__S__)β(β)β25, (β)β26, (+)β27 and (+)β28, which could be oxidized to the diacetoxy acid (3__S__,12__S__)β(+)β29. Saponification and esterification gave (3__S__,12__S__)β(β)β19 and (3__S__,12__S__)β(+)β17, with properties identical to those of (+)β17 obtained from the resin glycoside.