Complexation of boronic acids with saccharides

Scheme 17 In addition to the pair-wise interaction of boronic acids with polyhydroxyl species discussed, boronic acids also form stable complexes with buffer conjugate bases. These complexes can be formed between both the free boronate anion and Lewis bases as well as between saccharide boronate complexes and Lewis bases. Not recognised until 2004, these species persist into acidic solution and under certain stoichiometric conditions can become the dominant component in the solution. The two modes of interaction between the phenylboronate anion and phosphate are illustrated here.

Shinkai et al. described the synthesis of dendritic saccharide sensors based on a PAMAM dendrimer labeled with eight boronic acid residues [183]. The dendritic compound showed enhanced binding affinity for D-galactose and d-fructose. The fact that the dendritic boronic acid functions as a saccharide sponge is ascribed primarily to the cooperative action of two boronic acids to form an intramolecular 2 1 complex. When one boronic acid binds a saccharide, its counterpart cannot participate in dimer formation and seeks a guest. 

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