Expedient syntheses of neoglycoproteins using phase transfer catalysis and reductive amination as key reactions

Abstract

Starting from peracetylated chloro- or bromo-glycosyl donors of N-acetylneuraminic acid, N-acetylglucosamine, glucose and lactose, the corresponding p-formylphenyl glycosides were synthesized stereospecifically under phase transfer catalysed conditions at room temperature in yields of 38-67%. After Zemplén de-O-acetylation, the formyl groups were directly and chemoselectively coupled to the lysine residues of bovine serum albumin by reductive amination using sodium cyanoborohydride. The conjugation reactions were followed as a function of time and under a series of different molar ratios of the reactants to provide glycoconjugates of varying degree of antigenicities. Thus, carbohydrate protein conjugates were made readily available using essentially two key reactions.

Carbohydrate protein interactions. Syntheses of agglutination inhibitors of wheat germ agglutinin by phase transfer catalysis

“…In continuation of our efforts (10,13) to utilize phase transfer '~uthor to whom correspondence may be addressed. catalysis in glycoside syntheses of aryl2-acetamido-2-deoxy-P-D-glucopyranosides, it was hypothesized that formation of the expected 2-methyl-(3,4,6-tri-0-acetyl-1 ,2-dideoxy-a-D-glucopyrano)-[2,1-4-oxazoline 2 could be prevented if nucleophilic attack by the phenoxides at the anomeric center could occur at a faster rate than the attack by the catalyst counteranions.…”

Chemistry, biochemistry and biology of sialic acids

“…These polymers containing multivalent sialic acid are in principle useful for various applications related with recognitionhindinglinhibition processes. Using the strategy of reductive amination, p-formylphenyl glycoside of a-NeuSAc was also conjugated with proteins [488], and starting from the p-nitrophenyl 0and S-glycosides, p-N-acryloylamino analogues were synthesized, which could be copolymerized with acrylamide, yielding water-soluble pseudopolysaccharides with Neu5Ac and acrylamide in different ratios [489], or directly coupled with polylysine [490]. Copolymerization of the allyl glycoside with acrylamide generated a water-soluble pseudopolysaccharide [484].…”

Per‐glycosylation of the Surface‐Accessible Lysines: One‐Pot Aqueous Route to Stabilized Proteins with Native Activity

“…[10][11][12][13][14][15][16] Highly successful in their own right, these methods are labor-intense and only suited for low-level protein modification (in view of the low frequency of Cys or engineered residues in proteins). In stark contrast, extensive prior art illustrates that reductive amination at lysine (Lys) amines [17][18][19][20][21][22][23][24] is a facile tool and achieves protein modification to a very high degree of surface modification, without apparent detriment to the protein structure or catalytic output (for enzymes). [17][18][19][20] These prior reports strongly suggest that indiscriminate modification at the surface-accessible Lys amines (and the N-terminus) may present a facile alternative to the site-specific glycosylation, and open formidable opportunities in the synthesis of glycoconjugates.…”