Patent ID: 7579460

Claim:
A method for tagging a carbohydrate, selected from an N-linked oligosaccharide and an O-linked oligosaccharide of a glycoprotein with N-acetylglucosamine as a reducing sugar moiety and unprotected hydroxyl groups in the sugar backbone, with an active methylene compound with two carbanion-stabilizing groups composed of carbonyl and/or nitrile group, said method comprising preparing a α, β-unsaturated carbohydrate-tagged conjugate that converts to ring closure form by the conjugate addition to hydroxyl group in the carbohydrate chain under basic conditions in which the carbohydrate and the methylene compound are combined by mixing carbohydrate mixture and the methylene compound under aqueous polar aprotic solvent containing amine base catalyst, whereby an elimination and addition reaction between the carbohydrate and the methylene compound is carried out.