Approaches towards the core pentasaccharide in N-linked glycans

All eukaryotic cells share a common core pentasaccharide, Man3GlcNAc2 (M3), which is found in both dolichol-linked oligosaccharides (DLOs) and N-linked glycoproteins. A pentasaccharide M3 can be elongated and elaborated by various glycosyltransferases and is thus considered as the key intermediate in the in vitro synthetic pathway of N-glycans. In this review, we describe the progresses in the preparation of M3 by chemical and chemoenzymatic methods. We first draw a brief schematic view of the typical N-glycan biological pathway and then focus on the requirements and challenges in obtaining core pentasaccharides. Representative methods and recent reported findings, especially research progress in chemoenzymatic synthesis, are highlighted. In addition, the opportunities in exploiting novel methods for constructing N-glycans, as well as their applications, are discussed.