Elucidação estrutural de heterogalactanas parcialmente metiladas obtidas de Grifola frondosa (“Maitake”) e Pleurotus ostreatus (“Shimeji”)

Abstract

Partially methylated heterogalactans were isolated from the fruiting bodies of the medicinal mushroom Pleurotus ostreatus (mannogalactan) and Grifola frondosa (mannofucogalactan), via successive cold aqueous extraction, followed by fractionation through freeze-thawing, precipitation with Fehling solution of soluble material, and dialysis using membranes with different exclusion limits (MWCO 50, 100, and 500 kDa). Their chemical structures were established based on monosaccharide composition, methylation analysis and NMR studies. The mannogalactan (Mw = 50.7 x 103 g.mol-1) had a main chain of (1→6)-linked α-D-galactopyranosyl and 3-O-methyl-α-D-galactopyranosyl units, both of which are partially substituted at O-2 by -D-mannopyranosyl nonreducing ends.The other was a mannofucogalactan (Mw = 15.9 x 103 g.mol-1), which had a similar main-chain, being a part of the galactopyranosyl units substituted at O-2 mainly by 3-O-α-D-mannopyranosyl-α-L-fucopyranosyl groups and in a minor proportion with α-L-Fucp single-unit side chains. Recently, the heterogalactans are also recognized for their relevant biological activities, such as antitumor, immunomodulatory, anti-inflammatory and antinociceptive effects. Thus, the heterogalactans obtained from G.frondosa and P. ostreatus could present itself as a good candidate to be evaluated for its biological potential.