Synthesis of a tri- and a tetradeoxy analogue of methyl 3,6-di-O-α-d-mannopyranosyl-α-d-mannopyranoside for investigation of the binding site of various plant lectins

The synthesis of the 2,4,3′-trideoxy and 2,4,3′,4′-tetradeoxy analogues of the trimannoside part of the core structure of N-linked glycoproteins, methyl 3,6-di-O-α-d-mannopyranosyl-α-d-mannopyranoside, is described. A 2,4-dideoxy (1⃗6)-linked disaccharide was used as a common intermediate acceptor, which was coupled with a 3-deoxy and a 3,4-dideoxy benzochlorosugar donor, the latter prepared from methyl α-d-mannopyranoside in five steps. Despite the acid-sensitive donors and acceptor, acceptable glycosylation yields were obtained of both the trideoxy- and the tetradeoxy trisaccharide using silver triflate as a promoter (65 and 51%, respectively). Deprotection in one step then gave the target products.