title: Study on Dendrobium officinale O-acetyl-glucomannan (Dendronan®): part II. Fine structures of O-acetylated residues.
abstract: Main objective of this study was to investigate the detailed structural information about O-acetylated sugar residues in Dendronan(®). A water solution (2%, w/w) of Dendronan(®) was treated with endo-β-mannanase to produce oligosaccharides rich in O-acetylated sugar residues. The oligosaccharides were partly recovered by ethanol precipitation (70%, w/w). The recovered sample (designated Hydrolyzed Dendrobium officinale Polysaccharide, HDOP) had a yield of 24.7% based on the dry weight of Dendronan(®) and was highly O-acetylated. A D2O solution of HDOP (6%, w/w) generated strong signals in (1)H, (13)C, 2D (1)H-(1)H COSY, 2D (1)H-(1)H TOCSY, 2D (1)H-(1)H NOESY, 2D (1)H-(13)C HMQC, and 2D (1)H-(13)C HMBC NMR spectra. Results of NMR analyses showed that the majority of O-acetylated mannoses were mono-substituted with acetyl groups at O-2 or O-3 position. There were small amounts of mannose residues with di-O-acetyl substitution at both O-2 and O-3 positions. Minor levels of mannoses with 6-O-acetyl, 2,6-di-O-acetyl, and 3,6-di-O-acetyl substitutions were also identified. Much information about sugar residue sequence was extracted from 2D (1)H-(13)C HMBC and 2D (1)H-(1)H NOESY spectra. (1)J(C-H) coupling constants of major sugar residues were obtained. Evidences for the existence of branches or O-acetylated glucoses in HDOP were not found. The major structure of Dendronan(®) is shown as follows: [Formula: see text] M: β-D-mannopyranose; G: β-D-glucopyranose; a: O-acetyl group.
authors.affiliation: Department of Food Science, University of Guelph, Guelph, ON, Canada N1G 2W1; Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, ON, Canada N1G 5C9.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Xing
authors.affiliation: Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, ON, Canada N1G 5C9. Electronic address: stevewcui@gmail.com.
authors.forename: Steve W
authors.initials: SW
authors.lastname: Cui
authors.affiliation: State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, Jiangxi, China.
authors.forename: Shaoping
authors.initials: S
authors.lastname: Nie
authors.affiliation: Glyn O. Phillips Hydrocolloid Research Centre, Glyndŵr University, Wrexham LL11 2AW, UK; Phillips Hydrocolloids Research Ltd., 45 Old Bond Street, London W1S 4QT, UK.
authors.forename: Glyn O
authors.initials: GO
authors.lastname: Phillips
authors.affiliation: Department of Food Science, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: H Douglas
authors.initials: HD
authors.lastname: Goff
authors.affiliation: Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, ON, Canada N1G 5C9.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
mesh_terms: D000107:Acetylation; D009682:Magnetic Resonance Spectroscopy; D008351:Mannans / Q000138:chemical synthesis / Q000737:chemistry*; D009844:Oligosaccharides / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D008351:Mannans; D009844:Oligosaccharides; C000602098:dendronan
keywords: 2,3-Di-O-acetyl-β-d-mannopyranose; Dendrobium officinale; Detailed structure; Glucomannan; Mannanase; NMR