Sialic acids cap the termini of many mammalian glycoproteins and glycolipids, where they govern immune recognition, host–pathogen interaction, brain development, and tumor progression. Yet accessing homogeneous sialoglycans—the glycans that carry these residues—remains a long-standing bottleneck in carbohydrate chemistry. A recent study by Zhang et al. (2026) introduces a practical solution: a one-pot α-sialylation protocol built on sialyl ortho-(1-phenylvinyl)benzoate (PVB) donors, an approach that dovetails with modern Glycomics workflows for sialoglycan characterization.
Why α-Sialylation Is Hard
Unlike α-glycosylation of simple hexoses, α-sialylation targets the sterically hindered tertiary anomeric center of a 2-keto-3-deoxy-nononic acid. Neighboring-group participation—the usual trick for steering α-selectivity—is unavailable because sialic acid lacks an equatorial C3 hydroxyl. Competing 2,3-elimination and the glycerol side chain at C6 further complicate stereocontrol, so many classical donors (chlorides, thio-, xanthates, phosphites, and others) still deliver modest yields or poor selectivity.
Deciphering the biological roles of these structures depends on reliable Glycan Profiling and Glycomic Characterization, which in turn require ample, well-defined material. Faster synthetic access therefore benefits not only chemistry but also downstream Sialic Acid Analysis and Glycoprotein Structure Analysis.
A Reactivity-Based One-Pot Strategy
The key insight is a large reactivity gap between the new PVB sialyl donor and conventional thioglycoside acceptors. Under N-iodosuccinimide (NIS) and triflic acid (TfOH) promotion, the sialyl PVB donor activates first and couples to a thioglycoside acceptor; the resulting thioglycoside-bearing sialoside can then be activated by the same promoter to couple with a second acceptor—all in one pot. The differential reactivity lets the sequence self-sort, avoiding extensive protective-group manipulations and intermediate purifications.
With optimized conditions (often −60°C to −20°C), the method shows remarkably broad scope: primary, secondary, and even tertiary alcohols are sialylated with α/β ratios exceeding 20:1 and yields of 55–95% in single-step reactions, while one-pot assemblies reach 72–98%. Natural motifs fall out cleanly, including 6′-sialyllactose (a human milk oligosaccharide), the epidermal-growth-factor tetrasaccharide found in coagulation factor IX, and sialic acid dimers relevant to polysialic acids (which can be retrieved through Enzymatic Release of Sialic Acid after conjugation studies).
Fig. 1 Design plan for one-pot assembly of α-sialoglycans. (A) Representative example of sialic acids containing glycan STN antigen. (B) Previous α-sialylation methods with different leaving groups and current method with PVB as the leaving group. (C) Reactivity-based one-pot synthesis of various α-sialoglycans. (Zhang, et al. 2026)
From Disaccharides to Natural Products
The protocol scales up to elaborate full sialoglycans. The team assembled type-I antenna motifs present in N-glycoproteins, mannose- and rhamnose-containing sialoglycans, and furanose-linked structures—all in a single pot with 72–98% yields.
Fig. 2 One-pot synthesis of natural product ganglioside Hp-s1 11 and STN-antigen 13. (Zhang, et al. 2026)
Two headline natural products underscore the efficiency gain. Ganglioside Hp-s1, a monomethylated ganglioside with neuritogenic activity, was prepared in just three linear steps (67% overall)—versus longer stepwise routes reported previously. The tumor-associated STN antigen was assembled in three steps with 59% overall yield, again cutting the step count of prior syntheses. Both outcomes illustrate how the one-pot design shortens synthetic routes to biologically active sialoglycoconjugates.
What DFT Reveals About Reactivity
Density functional theory calculations explain why PVB outpaces thiosialosides. The rate-determining iodonium addition has a lower barrier for the PVB donor (15.2 versus 17.1 kcal/mol for the thioglycoside), and the two phenyl groups of the PVB moiety stabilize the key carbocation intermediate while reinforcing favorable noncovalent interactions with the promoter. A competition experiment confirmed the selectivity: when both donors were present, the thioglycoside was recovered nearly quantitatively while the PVB donor reacted.
Outlook
By marrying a highly reactive sialyl donor with reactivity-based one-pot assembly, this work removes a major obstacle to obtaining homogeneous sialoglycans. That, in turn, should accelerate both fundamental glycobiology and the development of carbohydrate-based therapeutics built on sialic-acid-terminated structures.
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Reference
- Zhang, Y., et al. (2026). Highly efficient α-sialylation with ortho-(1-phenylvinyl)benzoates as leaving groups: One-pot assembly of α-sialoglycans. Science Advances. DOI: 10.1126/sciadv.aeb0711.
