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Structural characterization of a xylomannan and a b-glucan, isolated from the edible mushroom Flammulina velutipes (Curt. ex Fr.) Sing.
Smiderle, F. R.; Carbonero, E. R.; Mellinger, C. G.; Sassaki, G. L.; Gorin, P. A. J.; Iacomini, M.
Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, CP – 19046, CEP – 81531-990, Curitiba, PR, Brazil
Edible mushrooms have, since ancient times, been consumed with the hope of maintaining health and promotion of longevity. Nowadays, following nutritional investigations, they are well known as a very rich food supplement, due to their favorable protein, carbohydrate and dietary fiber contents. Based on the increase consumption of mushrooms by the population, a chemical investigation was carried out with the basidiomycete Flammulina velutipes. The dried and milled fungus was submitted to hot aqueous and alkaline (KOH 2%, 25%) extractions. The resulting extracts were treated with excess of ethanol, and the resulting precipitated were submitted to purification via freeze-thawing and fractionated by exclusion membranes. Two polysaccharides, present in different fractions (PK2 and XM), were obtained. The structures of these polymers were determined by GC-MS, mono- (RMN-13C and -1H) and bidimensional (HMQC) spectroscopy experiments, besides methylation analysis, and controlled Smith degradations. One of the polysaccharides was a branched b-glucan, with a main chain of (1®3)-linked-Glcp residues, substituted at O-6 by b-Glcp units. From 13C NMR and HMQC spectra, a b-configuration was shown by H-1 signals at high field and C-1 signals at low field. The signals at d 86.7, 86.3 and 68.5 indicate substitutions at O-3 and O-6, respectively. The other polymer was an uncommon xylomannan, that was homogeneous (HPSEC: molar mass 30.8 x 104 g/mol). 13C-NMR and HMQC spectra showed a complex structure with a main chain composed by (1®3)-linked-a-Manp units, substituted, mainly at O-4, by b-Xylp, and/or probably by 3-O-b-D-Xylp-b-D-Xylp branches. The anomeric region contained signals (C-1/H-1) at d 103.9/4.88, corresponding to b-Xylp units, low field C-1 signals being typical of a b-configuration and others at d 101.7/5.59; 101.5/5.61; 99.7/5.72 arising from C-1/H-1 of a-Manp units. Such low field H-1 signals are typical of a-configurations in the pyranosyl series. These data agree with those of methylation analysis.
Supported by CNPq, Fundação Araucária, and Pronex-Carboidratos.
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