Direct Synthesis of para-Nitrophenyl Glycosides from Reducing Sugars in Water

Reducing sugars may be directly converted into the corresponding para-nitrophenyl (pNP) glycosides using 2-chloro-1,3-dimethylimidazolinium chloride (DMC), para-nitrophenol, and a suitable base in aqueous solution. The reaction is stereoselective for sugars with either a hydroxyl or an acetamido group at position 2, yielding the 1,2-trans pNP glycosides. A judicious choice of base allows extension to di- and oligosaccharide substrates, including a complex N-glycan oligosaccharide isolated from natural sources, without the requirement of any protecting group manipulations.