Investigations on the regioselective hydrolysis of a branched beta-1,3-glucan

Schizophyllan, an extracellular polysaccharide secreted by the fungus Schizophyllum commune ATCC 38548, shows interesting technical and pharmaceutical applications. Especially in the degraded form, this homoglucan is applicable as an antitumor, antihepatitis, anti-HIV and antiviral agent. Due to the fact that the side chains of the biopolymer are essential for its activities, a regioselective degradation of the beta-1,3 basic chain by maintaining the beta-1,6 side chains is necessary. This paper covers investigations which deal with the regioselective cleavage of the basic chain. It was found that the hydrolysis of aqueous polysaccharide solutions by incubation in DURAN glass bottles al 121 degrees C and 1 bar was the most successful method. A slight decrease of pH, a rapid loss of viscosity, a constant increase in reducing end groups and a continual release of glucose over an incubation time of 100 h indicated a degradation especially at the basic chain. Stepwise ultrafiltration of degraded solutions yielded fractions with varying molar masses and the ratio of the fractions depended on the total incubation time. The maintenance of the side chains was verified by C-13-NMR spectra. The regioselectivity of this degradation method can explained by a pore theory. One attempt to justify this theory is the suppression of hydrolysis after hydrophobization of the glass surface by using dichloromethylsilane.