Highly Efficient Synthesis of Kaempferol-5-O-rhamnopyranoside

Abstract

Kaempferol-5-O-α-L-rhamnopyranoside (1) and kaempferol-3,5-di-O-α-L-rhamnopyranoside (2) are representative flavonol 5-O-rhamnopyranoside. Because of the strong intramolecular H-bond, the 5-O-glucosidic linkage could not be efficiently constructed via conventional glycosylation method. In this paper, a novel glycosylation method was used which is gold(I)-catalyzed glycosylation method with glycosyl ortho-alkynylbenzoates as donor to efficiently achieve the formation of the challenging kaempferol-5-O-glycosidic linkages, and finally leading to naturally occurring compounds 1 and 2.