Linear and Cyclic Carbohydrate Receptors Based on Peptides Modified with Boronic Acids

In this article we report the synthesis of boronic acid functionalized fluorenylmethoxycarbonyl (Fmoc) protected amino acids and their use in solid phase peptide synthesis to synthesize tripeptides with the motif Cys-X-Cys (X= boronic acid functionalized amino acid). The interaction of these peptides with a set of carbohydrates in aqueous solution was studied by using a competitive indicator displacement assay as well as by isothermal titration calorimetry. We determined carbohydrate binding constants ranging from 2 x 10(1) M-1 up to 3 x 10(3) M-1 from these measurements. Moreover, the formation of cyclic hexapeptides was accomplished by oxidation of the thiols of the Cys to disulfides and the interactions between these cyclic receptors and carbohydrates were studied by using a competitive indicator displacement assay and isothermal titration calorimetry. The binding constants observed for these cyclic receptors are similar to the linear receptors.