Structural characterisation of a novel bioactive polysaccharide from Ganoderma atrum

The structure of a novel bioactive polysaccharide fraction from Ganoderma atrum (PSG-1) was characterised by methylation analysis and 1D/2D nuclear magnetic resonance (NMR) spectroscopy. Sugar analysis revealed that PSG-1 was composed of glucose (Glc), mannose (Man), galactose (Gal) and galacturonic acid (GalA) in molar ratio of 4.91:1:1.28:0.71. Methylation and GC-MS analysis indicated that the main linkage type was 1,3-linked-Glcp (21.08%), followed by T-Glcp (18.68%), 1,3,6-Glcp (12.97%), 1,4-Galp (12.70%), 1,6-Glcp (12.33%), 1,2-Manp (8.06%), 1,4-GalpA (6.15%), 1,4-Manp (4.55%) and 1,4,6-Glcp (3.24%). Combined the methylation analysis results with 1D (H-1, C-13) and 2D (DQF-COSY, TOCSY, HSQC and HMBC) NMR spectroscopy, a preliminary structure of PSG-1 was proposed as follows: 1)-alpha-Galp-(4 <- 1)-alpha-GalpA-(4 <- 1)-beta-Glcp-(6 <- 1)-beta-Glcp-(3 <- 1)-beta-Glcp down arrow 6 down arrow -> 3)-beta-Glcp-(1 -> 6)-beta-Glcp-(1 -> 4)-beta-Glcp-(1 -> 2)-alpha-Manp-(1 -> 3)-beta-Glcp-(1 -> 6)-beta-Glcp-(1 -> 6)-beta-Glcp-(1 -> 4)-alpha-Manp-(1 -> 4)-alpha-Galp-(1 -> 3)-beta-Glcp-(1 -> down arrow 6 up arrow 1)-alpha-Galp-(4 <- 1)-beta-Glcp down arrow 3 up arrow 1)-beta-Glcp-(3 <- 1)-beta-Glcp (C) 2012 Elsevier Ltd. All rights reserved.