75 (+)-Avermectin B_<1a>の全合成研究 : オキサヒドロインデン部の直截的合成

概要

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Avermectins are novel macrocyclic lactones produced by Streptomyces avermitilis and exhibit exceptionally potent actibity against a variety of parasites(nematodes and anthropods). Because of their unique structural features and bioactivity, we have lounched a synthetic studies toward avermectin B_<1a>, the most active member of the family, and recently achieved an enantiospecific synthesis of the spiro acetal unit(C11-C28). We present herein a straightforward and versatile route to the oxahydrindene(C1-C8) unit(1), which features the two sequential aldol type condensations: in the first intermolecular reaction of ketone C with aldehyde A, contrary to that with benzaldehyde, a remarkably high diastereoselectivity(5,6-anti) has been observed while the diastereofacial selectivity turned out to be moderate. The second intramolecular cyclization of ketoaldehyde 15 completed the stereocontrolled construction of the functionalized cyclohexene ring. Thus, the four chiral centers embodied in the unit 1 were expeditiously introduced by the aldol condensations; the asymmetric center placed at C8 in the ketone C has been a clue for the asymmetric induction. The remaining task for the synthesis of 1 is protecting group adjustments and concomitant oxolanone ring formation. The work along this line from the compound 18 and 19 will be reported.
天然有機化合物討論会の論文
1986-09-09