Stereocontrolled synthesis of α-d-allulofuranosides using α-selective d-fructofuranosidation reaction

Stereocontrolled synthesis of rare sugar derivatives, namely α-d-allulofuranosides, was achieved using d-fructose, one of the most abundant carbohydrates in nature. The following are the key steps of the α-d-allulofuranosides' synthesis. (1) An α-selective glycosidation reaction of 1,3,4,6-tetra-O-benzoylated d-fructofuranosyl donor to obtain α-d-fructofuranosides with 98 %-75 % isolated yields. (2) A regioselective 1,4,6-tri-O-pivaloylation reaction of the tetraol of α-d-fructofuranosides with the C3-hydroxy group remaining intact. (3) The oxidation of the C3-hydroxy group followed by the stereoselective reduction of the C3-carbonyl group. Primary and secondary alcohols and sugars can be used as glycosyl acceptors and aglycones for the following pivaloylation and stereoinversion reactions to obtain α-d-allulofuranosides.

Stereoselective synthesis of (+)-5-thiosucrose and (+)-5-thioisosucrose

(+)-5-Thiosucrose 1, a novel isosteric sulfur analog of sucrose, was synthesized stereoselectively for the first time via indirect β-d-fructofuranosidation involving selective β-d-psicofuranosidation, followed by stereo-inversion of the secondary hydroxy group at the C-3 position on the furanose ring. Glycosidation of protected 5-thio-d-glucose with a d-psicofuranosyl donor provided β-d-psicofuranosyl 5-thio-α-d-glucopyranoside and that with d-fructofuranosyl donor gave α-d-fructofuranosyl 5-thio-α-d-glucopyranoside. Two anomeric stereocenters of the glycosyl donor and acceptor were controlled correctly to provide a single disaccharide among four possible anomeric isomers in the glycosylation. Conversion of the resulting disaccharides afforded (+)-5-thiosucrose 1 and (+)-5-thioisosucrose 2 in excellent yields, respectively. Inhibitory activities of 1 and 2 against α-glucosidase in vitro were also examined.

(+)-5-Thiosucrose and (+)-5-thioisosucrose were stereoselectively synthesized among four possible anomeric isomers using 5-thio-d-glucose as an α-directing glycosyl acceptor.