Efficient Convergent Synthesis of Bi-, Tri-, and Tetra-antennary Complex Type N-Glycans and Their HIV-1 Antigenicity

Abstract

The structural diversity of glycoproteins often comes from post-translational glycosylation with heterogeneous N-glycans. Understanding the complexity of glycans related to various biochemical processes demands a well-defined synthetic sugar library. We report herein a unified convergent strategy for the rapid production of bi-, tri-, and tetra-antennary complex type N-glycans with and without terminal N-acetylneuraminic acid residues connected via the α-2,6 or α-2,3 linkages. Moreover, using sialyltransferases to install sialic acid can minimize synthetic steps through the use of shared intermediates to simplify the complicated procedures associated with conventional sialic acid chemistry. Furthermore, these synthetic complex oligosaccharides were compiled to create a glycan array for the profiling of HIV-1 broadly neutralizing antibodies PG9 and PG16 that were isolated from HIV infected donors. From the study of antibody PG16, we identified potential natural and unnatural glycan ligands, which may facilitate the design of carbohydrate-based immunogens and hasten the HIV vaccine development.

Modular synthesis of N-glycans and arrays for the hetero-ligand binding analysis of HIV antibodies

“…The strategy was designed on the basis that diversity can be created by assembly of the so-called ‘D1 and D2/D3 arm modules’, followed by the α-specific mannosylation at the O3 and/or O6 position of the mannose residue of the common core trisaccharide. Previously, the versatility of the glycosyl fluoride strategy was combined with enzymatic sialylation to build a library of symmetric bi-, tri- and tetra-antennary complex-type glycans 50 . Here, we extend the scope of this modular strategy to prepare high-mannose, hybrid and, more importantly, asymmetrically sialylated multi-antennary glycans (Fig.…”

“…To illustrate this strategy, oligomannose-type (mono- to pentasaccharides, 1–5 ), complex-type (di- to heptasaccharides, 6–13 ) and core trisaccharide ( 14 , 15 ) building blocks were first chemically synthesized on multigram scales (Supplementary Schemes 1–8), with temporary anomeric protecting groups installed before transformation into fluorides. For the high-mannose series (Man 3 /Man 4 /Man 5 /Man 9 GlcNAc 2 ) glycans, donors 1 and 2 , and for the hybrid series glycans, donors 6 and 7 were stereoselectively linked to the O3 position of 14 50 . The benzylidene ring was then removed to obtain 4,6-diol, and finally a regioselective glycosylation was achieved at the O6 position with donors 1–7 .…”

“…In this process we observed that the removal of N-phthalimide protection from glycans with preinstalled sialic acid under strong heating conditions often provided undesirable side products, so the more versatile NH-Troc protection was installed at all GlcNAc residues. Fluoride donors 8–13 were then used for glycosidation of core 15 50,54 under the promotion of AgOTf/Cp 2 HfCl 2 . Surprisingly, all these complex conjugations were found to be very clean, albeit in moderate yields (Supplementary Schemes 14–19), and the stereoselectivity was excellent, except for glycan G18 (Supplementary Scheme 14), where the glycosylation of 8 resulted in a mixture of isomers, suggesting that non-participating mannosylations are complex in terms of selectivity in some cases.…”

Efficient routes toward the synthesis of the D-rhamno-trisaccharide related to the A-band polysaccharide of Pseudomonas aeruginosa

“…We began our synthesis targeting two pivotal intermediates 1a and 1b which were obtained using previously reported methods [40–41] and then proceeding forward to the monomeric building blocks required according to the retrosynthetic analysis (Fig. 2).…”

Corrigendum to “The neoglycolipid (NGL)-based oligosaccharide microarray system poised to decipher the meta-glycome” [Curr Opin Chem Biol 18 (2014) 87–94]

“…These are in accord with X-ray crystal structures. Wong and colleagues recently reported the recognition of multi-antennary complextype N-glycans by another bNAb PG16 using a synthetic N-glycan array [38 ].…”