Selective Engineering of Linkage‐Specific α2,6‐N‐Linked Sialoproteins Using Sydnone‐Modified Sialic Acid Bioorthogonal Reporters

Abstract

The metabolic oligosaccharide engineering (MOE) strategy using unnatural sialic acids has recently enabled the visualization of the sialome in living systems. However, MOE only reports on global sialylation and dissected information regarding subsets of sialosides is missing. Described here is the synthesis and utilization of sialic acids modified with a sydnone reporter for the metabolic labeling of sialoconjugates. The positioning of the reporter on the sugar significantly altered its metabolic fate. Further in vitro enzymatic assays revealed that the 9‐modified neuraminic acid is preferentially accepted by the sialyltransferase ST6Gal‐I over ST3Gal‐IV, leading to the favored incorporation of the reporter into linkage‐specific α2,6‐N‐linked sialoproteins. This sydnone sugar presents the possibility of investigating the roles of specific sialosides.

Dynamic analysis of sugar metabolism reveals the mechanisms of action of synthetic sugar analogs

“…[14] In addition, specific sialic acid analogs were not accepted as substrate for CMP-sialic acid synthetase (CMAS). [15] Synthetic sugars are also developed as inhibitors of sugar metabolic pathways with the aim to develop novel therapeutics, [16] such as antimicrobial [17,18] and anticancer [19][20][21] drugs. Similarly, they are used to study the role of glycoconjugates in biological systems.…”

Chemical reporters to study mammalian O-glycosylation

“…This effect was shown to be dependent on cell type and the type of monosaccharide used. While initial MOE approaches relied on attachment of the unnatural tag at the N-acyl group of hexosamines, several more recent studies have explored the substitution of hydroxyl groups [40][41][42][43][44] or the N-acyl group in GlcNAc [45] with a bioorthogonal tag. In many cases, this strategy has led to the development of chemical reporters with enhanced selectivity towards specific classes of glycans.…”

“…For instance, 6-azido-6-deoxy-GlcNAc is selectively installed on O-GlcNAc modified proteins but not cell surface glycans [ 40 ]. Strikingly, selectivity within a glycan class was reported for a neuraminic acid derivative carrying a sydnone ligation handle at C9 [ 42 ]. In contrast with its C9-azide-tagged analogue, the sydnone probe selectively labels a subpopulation of sialylated glycoproteins in a glycosidic linkage-specific manner.…”

Bioorthogonal Ligations and Cleavages in Chemical Biology

“…[116] Isocyanides are stable in neutral pH aqueous media, and they show the advantage in bioorthogonal reaction for small size of isocyano group. [117] As shown in Figure 24, reactions of isonitriles with tetrazines can undergo the following process: [4 + 1] IEDDA cycloaddition of isonitrile (106) with tetrazine forms 107, release of N 2 in 107 leads to 108. Isomerization of 108 from primary, secondary isonitriles affords 110, and hydrolysis of 110 gives aldehyde or ketone 111 and amine 112.…”

“…via Michael addition of sulfydryl in 123 to maleimide in 122 to get 124, and rapid IEDDA of 124 with 1,2,4,5-tetrazine (106) provided conjugate 125 under physiological conditions (Figure 27). [6] The reaction was used in biorthogonal ligation for the first time without addition of catalyst, and it shows very high reaction rate and good biocompatibility and has been widely used in various fields.…”