Synthesis of a boronic acid-based oligosaccharide receptor using a porphyrin scaffold

Abstract

The multi-step synthesis of a boronic acid-based oligosaccharide receptor is described. The proposed molecule was synthesized with the aim of developing a sensor that could be tuned to bind specific oligosaccharides on the cell surface. This receptor consisted of a meso-substituted tetraphenylporphyrin scaffold. 5,15-bis(4-cyanophenyl)-10,20-bis(4-hydroxyphenyl) porphyrin was first coordinated to a zinc ion. Polyethylene glycol chains were then added to the phenols of the porphyrin with hopes of increasing water solubility. The alcohol groups of the PEG chains were then protected from base by dihydropyran, and reduction of the cyano groups with LiAlH4 followed. Subsequent refluxing in acid resulted in the removal of the alcohol-protecting groups and the zinc as well as the oxidation of any reduced porphyrin. The reductive amination of formylphenylboronic acid by the porphyrin resulted in the incorporation of two boronic acid functional groups. Upon purification, this porphyrin will be used in saccharide binding experiments to test the specific porphyrin-sugar interactions. These interactions will possibly be studied through the use of affinity chromatography, utilizing a solid phase such as Sephadex. This study may also ultimately provide a method for purification of the boronic acid porphyrin, which has not yet been easily conducted using conventional column chromatography.