Synthesis and characterization of a tetramer, propyl 6- O-β- d-galactopyranosyl-(1→6)- O-β- d-galactopyraosyl-(1→6)- O-β- d-galactopyranosyl-(1→6)-β- d- galactopyranoside

Abstract

6- O-Acetyl-2- O-benzoyl-3,4-di- O-benzyl-α- d-galactopyranosyl chloride ( 1a) was converted into the 1-sulfonate ( 1b), which was allowed to react with allyl alcohol in acetonitrile to give allyl 6- O-acetyl-2- O-benzoyl-3,4-di- O-benzyl-β- d-galactopyranoside ( 2). Compound 2 was O-deacetylated with ammonium hydroxide in methanol to give 3. Reaction of 1b with 3 under the same conditions of glycosidation gave the corresponding disaccharide 4. O-Deallylation of 4 gave with methanesulfonyl chloride or (chloromethylene)dimethylimminium chloride in N, N-dimethylformamide, to form the 1-chloro derivative 7. Compound 7 was converted into the 1- O-[(2,2,2-trifluoroethyl)sulfonyl] derivative ( 8). O-Deacetylation of 4 followed by glycosidation with 8 gave the corresponding tetrasaccharide derivative 9 in 77% yield. Appropriate deprotection sequences gave the title tetramer. The structures of the glycosides were determined with the aid of both 1H- and 13C-n.m.r. spectroscopy. No evidence of α- d linkages was found.