Use of the methylsulfenyl cation as an activator for glycosylation reactions with alkyl (aryl) l-thioglycopyranosides: synthesis of methyl O-(2-acetamido-2-deoxy-β- d-glucopyranosyl)-(1→ 2)-α- d-glucopyranoside, a derivative of the core trisaccharide of E. coli K12

Abstract

Methylsulfenyl bromide (MSB) and methylsulfenyl trifluoromethanesulfonate (MST) have been used to prepare 1,2- cis-linked disaccharides. Ethyl (phenyl) l-thio-β- d-gluco- and galacto-pyranosides having non-participating (benzyloxy) protecting groups were used as the donors. The αβ-ratio of the products depended on the promoter and conditions of reaction. Intimate ion-pairs, formed initially, may be responsible for the steric outcome of the glycosylations. Thus, with ethyl 2,3,4,6-tetra- O-benzyl-α- d-mannopyranoside as a donor, moderate quantities of the β- linked disaccharide could be produced using MSB as the activator. The synthesis of the title trisaccharide glycoside that contains 1,2- cis and 1,2- trans-linkages is described.