生物活性アルカロイドの集団的供給を志向した生合成中間体の全合成および(－)-ルベニンの全合成

Abstract

The first enantioselective total syntheses of the biosynthetic intermediates of the monoterpenoid indole alkaloids, (—)- secologanin (1), (—)-5-carboxystrictosidine (2), and (—)-strictosidine (3), were accomplished. In addition, (—)-rubenine (4) with a hexa-continuous fused ring was synthesized. The key reactions to form a dihydropyran ring of 1 was a sequential anti- and enantioselective organocatalytic Michael reaction/Fukuyama reduction. The secologanin tetraacetate (15), which is a key intermediate for our bioinspired collective syntheses of monoterpenoid indole alkaloids, was prepared in multigram scales. In the bioinspired Pictet-Spengler reaction for the synthesis of 2 and 3, it was important to use L-tryptophan methyl ester and cyanotryptamine derived from D-tryptophan, respectively, as substrate to achieve the desired diastereoselectivity. The total synthesis of 4 were achieved by epoxidation and nucleophilic cyclization of secondary amine followed by a lactonization reaction as in biosynthesis.