The Design of Boronic Acid Spectroscopic Reporter Compounds by Taking Advantage of the pK a-Lowering Effect of Diol Binding:  Nitrophenol-Based Color Reporters for Diols

• Published in: Journal of organic chemistry 2004-03, Vol.69 (6), p.1999-2007
• Main Authors: Ni, Weijuan, Fang, Hao, Springsteen, Greg, Wang, Binghe
• Format: Article
• Language: English
• Subjects: Boronic Acids - chemical synthesis; Carbohydrates - analysis; Colorimetry; Cyclopentanes - chemistry; Drug Design; Fructose - chemistry; Glucose - chemistry; Glycols - analysis; Hydrogen-Ion Concentration; Molecular Structure; Nitrophenols - chemistry; Polymers - chemistry; Spectrophotometry, Ultraviolet - methods
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0350357

The complex that forms between a boronic acid and a diol is often much more acidic than the starting boronic acid. In conditions where the solution pH is between the two pK a values, the boron atom will convert from a neutral trigonal form to an anionic tetrahedral form upon complexation. Such a change is likely to dramatically alter the electron density of neighboring groups. Utilizing this effect, we have designed and synthesized two nitrophenol-based boronic acid reporter compounds that change ionization states and therefore spectroscopic properties upon diol binding. Both compounds show significant UV changes upon addition of saccharides. For example, a blue shift of the absorption max from 373 to 332 nm was observed with the addition of d-fructose to 2-hydroxy-5-nitrophenylboronic acid at neutral pH. Such a reporter compound can be used as a recognition and signaling unit for the construction of polyboronic acid sensors for the selective and specific recognitions of saccharides of biological significance.