Synthetic Neoglycoconjugates of Hepta‐ and Nonamannoside Ligands for Eliciting Oligomannose‐Specific HIV‐1‐Neutralizing Antibodies

Oligomannose‐type glycans on the spike protein of HIV‐1 constitute relevant epitopes to elicit broadly neutralizing antibodies (bnAbs). Herein we describe an improved synthesis of α‐ and β‐linked hepta‐ and nonamannosyl ligands that were subsequently converted into BSA and CRM 197 neoglycoconjugates. We assembled the ligands from anomeric 3‐azidopropyl spacer glycosides from select 3‐O‐protected thiocresyl mannoside donors. Chain extensions were achieved using [4+3] or [4+5] block synthesis of thiocresyl and trichloroacetimidate glycosyl donors. Subsequent global deprotection generated the 3‐aminopropyl oligosaccharide ligands. ELISA binding data obtained with the β‐anomeric hepta‐ and nonamannosyl conjugates with a selection of HIV‐1 bnAbs showed comparable binding of both mannosyl ligands by Fab fragments yet lesser binding of the nonasaccharide conjugate by the corresponding IgG antibodies. These results support previous observations that a complete Man 9 structure might not be the preferred antigenic binding motif for some oligomannose‐specific antibodies, and have implications for glycoside designs to elicit oligomannose‐targeted HIV‐1‐neutralizing antibodies.