Preparation of oligomeric β-glycosides from cellulose and hemicellulosic polysaccharides via the glycosyl transferase activity of a Trichoderma reesei cellulase

Abstract

Oligoglycosyl (allyl, 2,3-dihydroxypropyl, ethyl, 2-hydroxyethyl, and methyl) β-glycosides were generated by endotransglycosylation reactions catalyzed by commercially available Trichoderma reesei cellulase. A polymeric donor substrate (xyloglucan or cellulose) was incubated with the enzyme in an aqueous solution containing 20% of the acceptor alcohol (allyl alcohol, glycerol, ethanol, ethylene glycol, and methanol, respectively). The products of these reactions included oligomeric alkyl β-glycosides and reducing oligosaccharides. The high yield of alkyl β-glycosides may be explained by the resistance of the xyloglucan β-glycosides to cellulase-mediated hydrolysis. The resistance of the oligoxyloglucan β-glycosides to endoglucanase catalyzed hydrolysis supports the hypothesis that productive binding of the glycan substrate depends on its interaction with enzyme subsites on both sides of the cleavage point, leading to distortion of the ring geometry of the residue whose glycosidic bond is cleaved. Oligoxyloglucan β-glycosides were purified by a combination of gel-permeation and reversed-phase HPLC and were structurally characterized by MS and NMR spectroscopy. These results demonstrate that novel oligosaccharide β-glycosides can be efficiently produced by enzyme-catalyzed fragmentation/transglycosylation reactions starting with a polysaccharide donor substrate. This class of reactions may represent a convenient source of β-glycosides to be used as synthons for the rapid synthesis of complex glycans.