Synthesis of the tetrasaccharide residue of clarhamnoside,a novel glycosphingolipid isolated from the marine sponge Agelas clathrodes

摘要

A tetrasaccharide,alpha-L-Rhap-(1->3)-beta-D-GalpNAc-(1->6)-alpha-D-Galp-(1->2)-alpha-D-Galp,the carbohydrate moiety of clarhamnoside isolated from the marine sponge Agelas clathrodes,was synthesized as its propyl glycoside via a convergent approach.The key steps to the synthetic strategy were the stereoselective construction of the reducing-end disaccharide alpha-D-Galp-(1->2)-D-Galp (5) and efficient coupling with the terminal disaccharide alpha-L-Rhap-(1->3)-D-GalpNAc building block,in which the N-phthal-imido-protected trifluoroacetimidate 13 was proved to be an effective donor.