Chapter 7 Boronated saccharides: potential applications

Abstract

This chapter discusses several applications of boronated saccharides. The chapter discusses the interaction of boronic acids with saccharides and the usefulness of this kind of interaction in chemosensing, transport, chromatography, diabetes, cancer, drug delivery, and few other miscellaneous applications. Boronic acids react covalently and reversibly with 1,2- or 1,3-diols to form five- or six-membered cyclic esters in nonaqueous or basic aqueous media. The adjacent rigid cis diols of saccharides form stronger cyclic esters than trans diols. The formation of cyclic ester of saccharides is complicated by the possibility of pyranose to furanose isomerization of the saccharide moiety. On saccharide binding and formation of a cyclic boronate ester, the p K a of the boronic acid is enhanced and the “ester” is more acidic than the “acid.” The enhanced acidity is because of a bond angle compression on formation of a cyclic boronate ester. Boronic acids have a 120° ( sp 2 ) bond angle, but in a cyclic ester the bond angle is reduced to 108°. The change in the bond angle from 120° to 108° facilitates the change in hybridization from sp 2 to sp 3 on deprotonation.