Isolation and structural characterization of a neutral polysaccharide from the stems of Dendrobium densiflorum

A novel neutral heteropolysaccharide (DDP-1-D) was purified from hot water extracts of dried stem of Dendrobium densiflorum by DEAE-52 and Sephacryl S-200 High-Resolution Chromatography. The heteropolysaccharide had an average molecular weight about 9440 Da. It was composed mainly of glucose and mannose in the ratio of 3.01:1. Structural features of DDP-1-D were elucidated by a combination of chemical and instrumental techniques, including FT-IR, GC-MS, periodate oxidation-Smith degradation, H-1 and C-13 NMR spectroscopies (including COSY, TOCSY, HSQC, and HMBC spectra). The results indicated that DDP-1-D is a mannoglucan and has a backbone consisting of (1 -> 4)-linked alpha-D-Glcp, (1 -> 6)-linked alpha-D-Glcp, (1 -> 2)-linked alpha-D-Manp and (1 -> 4)-linked beta-Manp. This is the first study to provide clear evidence for the structure of the polysaccharide in D. densiflorum. (C) 2012 Elsevier B.V. All rights reserved.