Abstract:

Purpose: To develop a rapid and efficient method to synthesize galactan and analyze the structure of the synthetic
product. Methods: For preparation of galactan, galactose was allowed to undergo a dehydration-condensation reaction
initiated by sodium chloride solution and catalyzed by heteropolyacid under microwave irradiation. The synthetic product
was precipitated by addition of anhydrous ethanol and purified/fractionated by Sepherdex G-25 column chromatography. The
purity and degree of polymerization (DP) were analyzed by high performance gel permeation chromatography (HPGPC), the
monosaccharide composition by high performance anion exchange chromatography (HPAEC), and the structure by IR and NMR
spectroscopy. Results: The optimal conditions for synthesizing galactan were determined as follows: initiator concentration
0.25 mol/L, catalyst dosage 1.1%, reaction temperature 130 ℃ and microwave irradiation time 4.5 min. Under these conditions, the
conversion rate of galactose was 97.22%, and the synthesized product had an average molecular weight of 2.853 kD and a degree
of polymerization of 17 and was composed of monosaccharide components such as galactose and trace glucose. IR and 1H-NMR
analysis showed that the sugar residues in the galactan were dominated by β-configuration. Conclusion: Galactan can be rapidly
and efficiently synthesized by microwave irradiation under the catalysis of heteropolyacid.

Key words: microwave, galactan, structural analyses