Comparison of phenolic compounds of rhubarbs in the section deserticola with Rheum palmatum by HPLC-DAD-ESI-MSⁿ

A sophisticated LC-ESI-MSⁿ method was utilized for the analysis of the phenolic compounds in five unofficial Rheum species for the first time. These species belong to the section deserticola Maxim. of the Polygonaceae family, including Rheum racemiferum Maxim., R. nanum Siev. ex Pall., R. delavayi Franch., R. sublanceolatum C. Y. Cheng et T. C. Kao and R. pumilum Maxim. A total of 101 phenolic compounds, including senno-sides, anthraquinones, stilbenes, glucose gallates, naphthalenes, procyanidins and chromones were identified or tentatively characterized based on their UV and mass spectral data from the methanol extracts. These chemical constituents were compared with those of an official species (R. palmatum L.). The results showed that most sennosides and procyanidin derivatives were only present in R. palmatum rather than in the unofficial species; stilbenes and chromones were only found in the sect. deserticola species; while anthraquinones, glucose gallates and naphthalenes could be detected in all studied species. For an-thraquinone glycosides, only emodin O-glucosides were detected in the sect. deserticola species. Moreover, remarkable difference was observed among unofficial species. These results may be useful for the quality control of rhubarb in order to guarantee its clinical effects, and may also be helpful for the further clarification of the taxonomic relationship of the plants in the sect. deserticola.