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

Oligoglycosyl (allyl, 2,3-dihydroxypropyl, ethyl, 2-hydroxyethyl, and methy l) beta-glycosides were generated by endotransglycosylation reactions catal yzed by commercially available Trichoderma reesei cellulase. A polymeric do nor substrate (xyloglucan or cellulose) was incubated with the enzyme in an aqueous solution containing 20% of the acceptor alcohol (allyl alcohol, gl ycerol, ethanol, ethylene glycol, and methanol, respectively). The products of these reactions included oligomeric alkyl beta-glycosides and reducing oligosaccharides, The high yield of alkyl beta-glycosides may be explained by the resistance of the xyloglucan beta-glycosides to cellulase-mediated h ydrolysis. The resistance of the oligoxyloglucan beta-glycosides to endoglu canase 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 geomet ry of the residue whose glycosidic bond is cleaved. Oligoxyloglucan beta-gl ycosides were purified by a combination of gel-permeation and reversed-phas e HPLC and were structurally characterized by MS and NMR spectroscopy, Thes e results demonstrate that novel oligosaccharide beta-glycosides can be eff iciently produced by enzyme-catalyzed fragmentation/transglycosylation reac tions starting with a polysaccharide donor substrate, This class of reactio ns may represent a convenient source of beta-glycosides to be used as synth ons for the rapid synthesis of complex glycans.