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Structure identification of α-glucans from Dictyophora echinovolvata by methylation and 1D/2D NMR spectroscopy.

Food chemistry (2018-09-22)
Xiao-Dan Shi, Ou-Ye Li, Jun-Yi Yin, Shao-Ping Nie
ABSTRACT

Dictyophora echinovolvata is a kind of edible mushroom in the Dictyophora genus, of which polysaccharide is an important chemical substance. Herein, three polysaccharide fractions (DEP-4P, DEP-6P and DEP-8P) were prepared from water extract of D. echinovolvata using gradient ethanol precipitation method. Their chemical structures were analyzed by methylation analysis and 1D/2D NMR spectroscopy. Molecular weights were determined by multi-angle laser light scattering combined with size-exclusion chromatography (HPSEC-MALLS). HPSEC data showed that DEP-4P had the highest values of molecular weight, intrinsic viscosity and hydrodynamic radius. DEP-6P and DEP-8P had lower molecular weights, which contributed to their easily distinguished 1D and 2D NMR spectra. Methylation and NMR analysis suggested that the three fractions were linear α-(1 → 4)-glucans with α-Glcp residues linked to the backbone at C-6. Differences among the three fractions were the molar ratios of the identified glycosidic bonds. Repeating units of polysaccharides from D. echinovolvata were proposed as follows.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Deuterium oxide, 99.9 atom % D
Sigma-Aldrich
Sodium borodeuteride, 98 atom % D, 90% (CP)
Sigma-Aldrich
Iodomethane solution, 2.0 M in tert-butyl methyl ether, contains copper as stabilizer