58 グリシノエクレピンAの合成(口頭発表の部)

概要

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Glycinoeclepin A (1) is a degraded triterpenoid isolated from kidney bean roots as a hatching stimulus for soybean cyst nematode. Its unusual structure as well as its strong activity made us to attempt its synthesis. Two (S)-hydroxyketones (E and F) readily available by reducing the corresponding symmetrical 1,3-diketones (G and H) with baker's yeast were employed as chiral starting materials. One of the key intermediates (C≡7) possessing the bridged-ether ring was synthesized from E in 14 steps and the other (D≡15) was obtained from F after 12 step-conversion including the introduction of the methyl groups and the methylene insertion. Aldol condensation of 15 with 7 gave 17 as a sole product, which has all chiral centers of glycinoeclepin A correctly. The aldol product 17 was converted to the key-intermediate, diketo lactone 24, via the intramolecular Horner-Wittig reaction to introduce a two-carbon unit and the following transformation. Reductive C-ring formation was accomplished by treatment of 24 with Me_2CuLi to give 31 in high yield after esterification. Finally, dehydration and deprotection yielded glycinoeclepin A (1). The overall yield of 1 was 3.0% in 32 steps from E or 2.6% in 31 steps from F.
1988-09-26