Synthesis and Characterization of Multi-Reducing-End Polysaccharides
Zhai, Zhenghao; Zhou, Yang; Korovich, Andrew G.; Hall, Brady A.; Yoon, Hu Young; Yao, Yimin; Zhang, Junchen; Bortner, Michael J.; Roman, Maren; Madsen, Louis A.; Edgar, Kevin J.
Department of Sustainable Biomaterials, Macromolecules Innovation Institute, Virginia Tech, Blacksburg, Virginia 24061, United States
Site-specific modification is a great challenge for polysaccharide scientists. Chemo- and regioselective modification of polysaccharide chains can provide many useful natural-based materials and help us illuminate fundamental structure–property relationships of polysaccharide derivatives. The hemiacetal reducing end of a polysaccharide is in equilibrium with its ring-opened aldehyde form, making it the most uniquely reactive site on the polysaccharide molecule, ideal for regioselective decoration such as imine formation. However, all natural polysaccharides, whether they are branched or not, have only one reducing end per chain, which means that only one aldehyde-reactive substituent can be added. We introduce a new approach to selective functionalization of polysaccharides as an entrée to useful materials, appending multiple reducing ends to each polysaccharide molecule. Herein, we reduce the approach to practice using amide formation. Amine groups on monosaccharides such as glucosamine or galactosamine can react with carboxyl groups of polysaccharides, whether natural uronic acids like alginates, or derivatives with carboxyl-containing substituents such as carboxymethyl cellulose (CMC) or carboxymethyl dextran (CMD). Amide formation is assisted using the coupling agent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM). By linking the C2 amines of monosaccharides to polysaccharides in this way, a new class of polysaccharide derivatives possessing many reducing ends can be obtained. We refer to this class of derivatives as multi-reducing-end polysaccharides (MREPs). This new family of derivatives creates the potential for designing polysaccharide-based materials with many potential applications, including in hydrogels, block copolymers, prodrugs, and as reactive intermediates for other derivatives.
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Supporting Information | 1H NMR spectra for hydrolyzed carboxymethyl cellulose, carboxymethyl dextran, partially hydrolyzed alginate, 1,3,4,6-tetra-O-acetyl-d-glucosamine (acetyl-GlcN), CMC-acetyl GlcN, N-acetylglucosamine, and neutralized d-2-amino-2-deoxyglucose; 13C NMR spectra for 1,3,4,6-tetra-O-acetyl-d-glucosamine (acetyl-GlcN), alginate, and alginate-acetyl GlcN; HSQC NMR spectra for alginate-GlcN and GlcNAcCMD; 1H DOSY spectra for CMD-acetyl GlcN, CMC-acetyl GlcN, and alginate-acetyl GlcN; silver mirror reaction pictures of CMD and CMD-GlcN; and table for the reaction parameters and aldehyde concentration of MREPs using fluorometric method (PDF) | 1.11 MB | Login to download |