Oligosaccharide analysis of the backbone structure of the characteristic polysaccharide of Dendrobium officinale

Natural polysaccharides occur as complex mixtures and are hardly isolated as a single molecule, challenging the current analytical methods. Dendrobium officinale polysaccharide, the characteristic active ingredient, is an example. The backbone of Dendrobium officinale polysaccharide (DOP) was reported to be glucomannan. But the dispute continues due to the limitations of conventional analysis methods (e.g. the overlapped NMR signals). Herein, we describe an oligosaccharide sequencing analysis that successfully corrects the backbone to mannan as shown in [Fig. 1]. This analysis involves producing oligosaccharide fragments from mild acid hydrolysis of DOP followed by p-aminobenzoic ethyl ester (ABEE) derivatisation. Then, a series of oligosaccharides with varied polymerisation degrees (DP=2–10) were isolated and identified by LC-MS profiling, monosaccharide composition analysis, linkage analysis and 1D-/2D-NMR elucidation. Finally, we conclude that the backbone of DOP is a β-D-1,4-mannan which is confirmed by other analysis such as comparison with reference mannan. This oligosaccharide analysis is more straightforward and reliable by transforming the complicated polymers into oligomers which have more accurate and convincing MS and NMR data.

Fig. 1 Structural characterization of the backbone of Dendrobium officinale polysaccharide (DOP) using an oligosaccharide analysis strategy. With the aid of sugar sequence analysis by LC-MS profiling, monosaccaride composition, linkage analysis and NMR spectroscopy.

 

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Conflict of Interest

The authors declare no conflict of interest.

Publication History

Article published online:
16 November 2023