Synthesis and characterization of regioselectively substituted curdlan hetero esters via an unexpected acyl migration

• Published in: Carbohydrate polymers Vol. 155; pp. 440 - 447
• Main Authors: Chien, Chih-Ying, Enomoto-Rogers, Yukiko, Takemura, Akio, Iwata, Tadahisa
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 02.01.2017
• Subjects: Acyl migration; Curdlan; Hetero ester; Regioselectively; Regioselectively; Acyl migration; Curdlan; Hetero ester
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2016.08.067

[Display omitted] ⿢Regioselectively substituted curdlan ester was synthesized.⿢An unexpected acyl migration was found in the detritylation.⿢Regioselectively substituted ester groups promoted the crystallization. Regioselectively substituted curdlan esters were synthesized by protecting the C6 primary hydroxyl group with a triphenylmethyl group followed by the acylation of the secondary hydroxyl groups at C2 and C4. The subsequent detritylation of C6 trityl group under acidic conditions revealed an unexpected acyl migration from C4 to C6. This unique acyl migration in curdlan was first observed, which haven⿿t been reported in other polysaccharides such as cellulose. The rate of this migration was found to be dependent on the length of the acyl group, leading to the proposal of a new mechanism for this transformation. Based on these results, we synthesized 2,6-di-O-acetyl-4-O-propionyl-curdlan, which was fully characterized by 1H NMR, 13C NMR, COSY, HSQC and HMBC analyses. Thermogravimetric analysis and differential scanning calorimetry measurements revealed that the regioselective esterification to curdlan promoted its crystallization compared with randomly mixed ester derivatives.