93 アバーメクチン類の合成研究 : 直登型ストラテジーによるミルベマイシンα_1の全合成(口頭発表の部)

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The avermectins (1) and the milbemycins (2) have attracted a considerable interest in the natural product synthesis due to their unique structures and potent antiparasitic activities.^<1,2> Construction of hexahydrobezofuran moiety with both the correct stereochemistries (particularly at C2) and the C3-C4 double bond is the most important aspect in their total synthesis, because this structure prone to undergo C2-epimerization and double bond-migration as well as aromatization is essential for their biological activity. Therefore, successful total syntheses have adopted secure strategies introducing the crucial 3,4-double bond at the final stages after constructing the whole macrolactone structures.^3 Such approaches utilizing the deconjugation-epimerization^3 (Scheme 1) or the selenenylation-elimination process, however, are still less than satisfactory in terms of stereo- and regio-control. Thus, we have attempted a more simple but apparently more difficult approach through the macrolactonization of the genuine seco-acid 6 (Scheme 2) on the working hypothesis that it could be executed without serious epimerization/conjugation problem probably via β-lactone intermediate 7. We describe herein the straightforward synthesis of milbemycin α_1 (2a) on this line.
天然有機化合物討論会の論文
1990-09-25