Synthesis of C2-Regioselectively Substituted Curdlan Acetate Propionate and the Effect of C2 Substituent on Their Properties

A new C2-regioselective synthetic strategy for Curdlan hetero esters was developed using benzaldehyde to protect the Curdlan C4 and C6 hydroxyl groups as a cyclic acetal structure. After esterification and deprotection reactions, two C2-regioselectively substituted Curdlan acetate propionates, 2-O-acetyl-4,6-di-O-propionyl-Curdlan (CD2Ac46Pr) and 4,6-di-O-acetyl-2-O-propionyl-Curdlan (CD46Ac2Pr), were successfully obtained. Through differential scanning calorimetry and wide-angle X-ray diffraction analysis, the C2 ester was confirmed as the decisive substituent over the melting behavior and crystal structure of Curdlan esters.