Chemical and chemo-enzymatic synthesis of the alpha-Neu p5Ac-(2-->6)- beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp element that is part of N-linked carbohydrate chains of human lutropin

Chemical Synthesis of Human Milk Oligosaccharides: para-Lacto-N-hexaose and para-Lacto-N-neohexaose

Human milk oligosaccharides (HMO) have emerged as a very active area of research in glycoscience and nutrition. HMO are involved in the early development of infants and may help to prevent certain diseases. The development of chemical methods for obtaining individual HMO aids the global effort dedicated to understanding the roles of these biomolecules. Reported herein is the chemical synthesis of two common core hexasaccharides found in human milk, i. e. para-lacto-N-hexaose (pLNH) and para-lacto-N-neohexaose (pLNnH). After screening multiple leaving groups and temporary protecting group combinations, a 3+3 convergent coupling strategy was found to work best for obtaining these linear glycans.

Systematic synthesis of bisected N-glycans and unique recognitions by glycan-binding proteins

Bisected N-glycans represent a unique class of protein N-glycans that play critical roles in many biological processes. Herein, we describe the systematic synthesis of these structures. A bisected N-glycan hexasaccharide was chemically assembled with two orthogonal protecting groups attached at the C2 of the branching mannose residues, followed by sequential installation of GlcNAc and LacNAc building blocks to afford two asymmetric bisecting "cores". Subsequent enzymatic modular extension of the "cores" yielded a comprehensive library of biantennary N-glycans containing the bisecting GlcNAc and presenting 6 common glycan determinants in a combinatorial fashion. These bisected N-glycans and their non-bisected counterparts were used to construct a distinctive glycan microarray to study their recognition by a wide variety of glycan-binding proteins (GBPs), including plant lectins, animal lectins, and influenza A virus hemagglutinins. Significantly, the bisecting GlcNAc could bestow (PHA-L, rDCIR2), enhance (PHA-E), or abolish (ConA, GNL, anti-CD15s antibody, etc.) N-glycan recognition of specific GBPs, and is tolerated by many others. In summary, synthesized compounds and the unique glycan microarray provide ideal standards and tools for glycoanalysis and functional glycomic studies. The microarray data provide new information regarding the fine details of N-glycan recognition by GBPs, and in turn improve their applications.

Rapid clearance of sialylated glycoproteins by the asialoglycoprotein receptor

The asialoglycoprotein-receptor (ASGP-R) located on liver parenchymal cells was originally identified and characterized on the basis of its ability to bind glycoproteins bearing terminal galactose (Gal) or N-acetylgalactosamine (GalNAc); however, endogenous ligands for the ASGP-R have not to date been definitively identified. We have determined that the rat ASGP-R specifically binds oligosaccharides terminating with the sequence Siaalpha2,6GalNAcbeta1,4GlcNAcbeta1,2Man. Bovine serum albumin chemically modified with 10-15 tetrasaccharides with the sequence Siaalpha2,6GalNAcbeta1,4GlcNAcbeta1,2Man is cleared from the blood of the rat with a half-life of <1 min by a receptor located in the liver. We have isolated the receptor and identified it as the ASGP-R. Furthermore, we have determined that subunit 1 of the ASGP-R accounts for the binding of terminal Siaalpha2,6GalNAcbeta. Based on the newly defined specificity of the rat ASGP-R we hypothesize that glycoproteins bearing structures that are selectively modified with terminal Siaalpha2,6GalNAcbeta and are released into the blood may be endogenous ligands for the rat ASGP-R.