Facile cleavage of some 2-acetamido-2-deoxy-β-D-gluco- and galactopyranosides using aqueous HF

Abstract

Treatment of pneumococcal C-substance (PnC) with 48% aqueous HF resulted in not only the intended removal of all the phosphate esters but also in the highly specific hydrolysis of the glycosidic bond between the 2-acetamido-2-deoxy-β-D-galactopyranose and ribitol residues. Some of the structural features associated with this facile hydrolysis were elucidated from studies on the treatment of model methyl glycosides and oligosaccharides with the same reagent. These studies indicate that an increase in the rate of hydrolysis is associated with glycosides of 2-acetamidohexapyranoses having a trans diequatorial disposition of the aglycon and 2-acetamido groups. These studies also indicate that the nature of the aglycon is also a contributing factor, because although simple alkoxy and terminal open-chain glycitols are readily cleaved from glycosides satisfying the above criteria, hydrolysis does not occur where the aglycon is another cyclized sugar moiety. Thus chitotriose can only be degraded to chitobiose using this reagent following the reduction of its terminal reducing moiety.