Combinatorial Library of Low Molecular‐Weight Organo‐ and Hydrogelators Based on Glycosylated Amino Acid Derivatives by Solid‐Phase Synthesis

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Abstract
A combinatorial approach for the synthesis of supramolecular gelators as new organic materials is described herein. In the course of the development of a convenient and flexible solid‐phase synthesis of the artificial glycolipids, some of these compounds were accidentally found to act as low molecular‐weight gelators toward organic solvents. Using this combinatorial solid‐phase synthesis of glycosylated amino acetates, screening and optimization of low molecular‐weight organo/hydro‐gelators were efficiently carried out. We found that an N‐acetyl‐galactosamine‐appended amino acid ester (GalNAc‐aa) efficiently gelates a broad spectrum of organic solvents. More interestingly, some GalNAc‐aa derivatives displayed an excellent hydrogelation capability. Transmission electron microscopy, scanning electron microscopy, confocal laser scanning microscopy, and FT‐IR were used for characterization of the gel structure. It is indicated that supramolecular fibers supported by strong hydrogen‐bonding networks are entangled so that the resulting spaces can immobilize a number of solvent molecules effectively. In addition, the supramolecular hydrogel consisting of GalNAc‐suc‐glu(O‐methyl‐cyc‐pentyl)2 is stable even under high salt concentrations probably due to its nonionic character and as a result, a native protein is successfully entrapped in the gel matrix without denaturation.