Controlled Acetylation Of Glucomannan From Bletilla Striata

A convenient method for controlled acetylation of glucomannan from Bletilla striata was established in this paper, and the optimized process of water-soluble products with regioselectivity was thus developed.Glucomannan acetates were synthesized in DMF solvent with acetic anhydride. The optimized preparation parameters of glucomannan acetates were determined as follows: molar ratio of glucomannan, acetate anhydride and DMF was 1:3:65, reaction temperature was set at 100℃. The degree of acetylation substitution of glucomannan acetates could be achieved between 0.2～0.8. The kinetic equation of the esterification was established according to the second-order reaction mechanism, and the apparent activation energy of the reaction was 120.6 kJ·mol-1 The determination of degree of acetylation substitution was established by a UV spectrophotometric method, usingβ-D-Glucose pentaacetate as the reference compound, the line range was between 15.4～92.4μg·mL^-1 (r = 0.9996), the detection limit is 11.1μg·mL^-1, the average recovery was 101.4 % (n = 9), and the precision (RSD) was 0.08 %. The structures of glucomannan acetates have been characterized using HPGPC, infrared spectra and 1H NMR analysis of their perpropanoyl abbreviates, ¹H NMR results of the perpropanoyl abbreviates of the glucomannan acetates revealed that the acetyl group was mainly substituted at C6- OH of the hexose group, less preferred at C2- OH and not occurred at C3- OH of the polysaccharide.In this paper, a novel acetylation method of glucomannan from Bletilla striata was achieved in DMF solvent media, and the substitution group was characterized to locate dominantly at C6- OH of the hexose group. The method developed is simple, economic and can be easily controlled, and the process of water-soluble products with selective acetylation was developed with success.