title: Glycosyl trifluoroacetimidates. 2. Synthesis of dioscin and xiebai saponin I.
abstract: Two trisaccharide steroidal saponins, dioscin (1) and Xiebai saponin I (2) with various bioactivities, were efficiently synthesized using the newly developed glycosyl N-phenyl trifluoroacetimidates (10-13) as glycosylation donors. Thus, dioscin was synthesized in five steps and a 33% overall yield from diosgenin and glycosyl trifluoroacetimidates (10 and 11). Xiebai saponin I was synthesized in eight steps and a 32% overall yield from laxogenin and glycosyl trifluoroacetimidates (10, 12, and 13), whereupon, the rare steroid laxogenin was prepared from diosgenin in four steps and an overall 69% yield. All the glycosylation reactions involved in the present syntheses demonstrated that glycosyl trifluoroacetimidates were successful donors comparable to the corresponding glycosyl trichloroacetimidates.
authors.affiliation: State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, China. byu@pub.sioc.ac.cn
authors.forename: Biao
authors.initials: B
authors.lastname: Yu
authors.forename: Houchao
authors.initials: H
authors.lastname: Tao