26 大環状ピロリジジンアルカロイド,(±)-インテゲリミンの全合成

概要

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A total synthesis of a 12-membered bislactonic pyrrolizidine alkaloid, (±)-integerrimine (1), has been achieved. Integerrinecic acid monoester (6), the acid part of integerrimine, was synthesized stereoselectively starting from 2-methyl-2-cyclopentenone. Retronecine (3) was prepared according to a modified method of the Geissman's route, and the primary alcohol was protected as silyl ether (7). The acid component (6) was converted to an acid anhydride (8), and then 8 was treated with lithium salt of 7 and a catalytic amount of N,N-dimethylaminopyridine to give a desired ester (9). This ester (9) was too unstable under acidic conditions to be deprotected selectively to yield the hydroxy acid (10). Therefore, new esterification reaction was developed based on the concept of activatable protective group, and it was found that treatment of alkylsulfonylalkyl esters of carboxylic acids with lithium alkoxides afford the corresponding esters in good yields. (±)-Integerrimine (1) was synthesized successfully by the application of this method to the lactonization step.
天然有機化合物討論会の論文
1982-09-10