50 (±)-Amarolideの全合成

概要

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Amarolide (2), one of the representative quassinoids, is a tetracyclic terpenoid having a picrasane skeleton (1) with 10 chiral centers. The first total synthesis of (±)-amarolide (2) has been accomplished stereoselectively from a known tricyclic compound (5). The main synthetic pathway is shown in Schemes 2-7. Orthoester Claisen rearrangement (from 13 to 14) and lead tetraacetate oxidation (from 19 to 20) were utilized as key reactions to prepare 12β-hydroxypicrasan-3-one (26), a compound which has the correct relative stereochemistry of all the six ring-juncture chiral centers of the picrasane skeleton (1). The compound (26) was transformed into (±)-amarolide (2) by 18 step reactions, including the 1,3-carbonyl transposition reactions (from 26 to 38), introduction of two hydroxyl groups at C-2 and C-11 positions, respectively, (from 38 to 40), and an oxidation of the ether ring to afford the δ-lactone. The NMR spectral data of synthetic amarolide (2) and amarolide diacetate (42) were completely identical with those of natural ones. Overall yield of the synthesis of (±)-2 from 5 by 35-step reactions was 0.2%. As the transformation of amarolide (2) into quassin (3) has already been known, this synthesis of (±)-2 constitutes also a formal total synthesis of (±)-quassin.
天然有機化合物討論会の論文
1986-09-09