Acetolysis of Pichia pastoris IFO 0948 strain mannan containing α-1,2 and β-1,2 linkages using acetolysis medium of low sulfuric acid concentration

Abstract

To obtain manno-oligosaccharides containing β-1,2-linked nonreducing terminal groups from the mannan of Pichia pastoris IFO 0948 strain by acetolysis, an attempt was made to establish the reaction conditions under which cleavage of the α-1,6 linkage took place preferentially leaving manno-oligosaccharides composed largely of β-1,2 linkages. By the action of an ordinary acetolysis medium, a 10/10/1 ( v v ) mixture of acetic anhydride, acetic acid, and sulfuric acid at 40 °C for 13 h or at 25 °C for 120 h, the O-acetyl derivative of this mannan gave mannose, mannobiose, mannotriose, and mannopentaose. However, treatment of the same O-acetyl mannan with a 50/50/1 ( v v ) acetolysis medium at 40 °C for 15 h gave a mannotetraose in addition to mannose, mannobiose, mannotriose, and mannopentaose. Use of a 100/100/1 ( v v ) acetolysis medium at 40 °C for 36 h gave a more satisfactory result, a mixture of oligosaccharides, from mannose to mannopentaose, which contained more mannotetraose than mannopentaose. Because both mannotetraose and mannopentaose contained α-1,2 and β-1,2 linkages, it was concluded that an acetolysis medium containing a low concentration of sulfuric acid, up to 0.5% ( v v ), facilitates the preferential cleavage of the α-1,6 linkage, leaving manno-oligosaccharides containing the β-1,2 linkage which was found to be labile to the action of the 10/10/1 ( v v ) acetolysis medium.