Basic Study On Antioxidant Active Substances In The Aboveground Parts Of Rheum Tanguticum Maxim.ex Balf.

The Chinese herb rhubarb is the underground rhizomes and roots of three plants of the Rheum officinale Baill.,Rheum palmatum L.and Rheum tanguticum Maxim.ex Balf.of Rheum in Polygonaceae.The above-ground parts of rhubarb are generally classified as non-medicinal parts and are often discarded when collecting herbs.However,according to literature and folk recipes,the above-ground stems and leaves of rhubarb are also useful in clearing heat and drain fire,cooling blood and resolving stasis,and clear the meridians and detoxifying,and are traditionally consumed in Qinghai,Gansu,and other regions.In order to make full use of rhubarb plant resources,this study was carried out the above-ground parts of Rheum tanguticum to investigate the material basis of antioxidant activity and to lay the foundation for the comprehensive utilization and development of the authentic medicinal herb.1.The aboveground part of Rheum tanguticum were dried and extracted with 95%ethanol,and the samples were initially separated by microporous resin to obtain a total of 6 fractions,which were separated and prepared using semi-preparative liquid chromatography and HPLC to obtain 13 compounds,the purity of which reached over95%after purification.2.Using the DPPH method,the antioxidant activities of the ethanolic extract of the above-ground parts of Rheum tanguticum,6 fractions and 13 compounds were determined.The results showed that the ethanolic extract of the above-ground parts of Rheum tanguticum had certain antioxidant activities,and the antioxidant activities of Fr3,Fr4,Fr5 and Fr6 in fractions 1-6 were better,while the activities of Fr1 and Fr2were weaker;then from the more active compounds,Fr311,Fr321,Fr331,Fr431,Fr451,Fr521,Fr531 and Fr62l showed well antioxidant activity as determined by the DPPH method,with IC₅₀ values of 47.39μg/m L,87.53μg/m L,47.43μg/m L,46.53μg/m L,35.53μg/m L,146.48μg/m L,91.23μg/m L and 74.55μg/m L respectively.3.¹H-NMR,¹³C-NMR and MS were used to structurally identify the 8 compounds with antioxidant activity among the 13 compounds isolated,and the 8 compounds were determined to be:Myricetin-3-O-α-L-rhamnopyranoside,Myricetin-3’-α-L-rhamnopy ranoside,Isomyricitrin,Quercitrin,Quercetin,Quercetin-3-O-α-L-arabinopyranoside,Quercetin-3-O-β-D-glucopyranoside-7-O-α-L-rhamnopyranoside,Quercetin-3-O-β-D-xylopyranosy（1→2）-β-D-gluco pyranoside.