Development of Method for Determination the Total Flavonoids in Sophora Japonica Fruits

Japanese sophora (Sophora japonica L., Fabaceae family) is a unique source of biologically active compounds of natural origin, including flavonoids. In scientific medicine, flowers and fruits of Sophora japonica are used to obtain medicinal herbal preparations. In the flowers of this plant, the dominant flavonoid is rutin (3-O-rutinoside of quercetin), whose content reaches 20–30%. In the fruits of Sophora japonica, the predominant flavonoids are isoflavone glycoside sophoricoside (4’-O-β-D-glucopyranoside of genistein) and flavone derivative kaempferol-3-O-sophoroside. Rutin, as a pharmaceutical substance with an angioprotective effect, is widely used for the production of combined medicines. The flavonoids of the fruits of Sophora japonica have bactericidal, anti-inflammatory, wound-healing activity and are used to produce tinctures. The purpose of this study is to develop a technique for quantifying the amount of flavonoids in the fruits of Sophora japonica. The XV edition of the State Pharmacopoeia of the Russian Federation includes a pharmacopoeia article on raw materials «Sophora japonica fruits» FS.2.5.0130 (instead of FS 42-452-72), according to which the identification of fruits of this plant is carried out by determination of the main groups of biologically active substances by thin-layer chromatography relative to the pharmacopoeial standard sample of sophoricoside. The section «Quantitative determination» of this pharmacopoeia article provides for the determination of the total of phenolic compounds by direct spectrophotometry at an analytical wavelength of 260 nm calculated on genistein (5,7,4'-trihydroxyisoflavone). In our opinion, this technique is not selective enough, since the fruits of Sophora japonica, along with flavonoids, contain phenolic compounds such as chlorogenic, caffeic and gallic acids, which differ in spectral characteristics from flavonoids. In addition, the calculation of the amount of phenolic compounds is carried out on genistein, which has an aglycone nature, while flavonoid glycosides predominate in the fruits of Sophora japonica. As a result of the conducted research, it is proved that for the purposes of standardization of the fruits of Sophora Japonica, it is advisable to use differential spectrophotometry, which allows more selectively determination of the content of the total flavonoids. A technique has been developed for the quantitative determination of the total flavonoids in the fruits of Sophora japonica by differential spectrophotometry at an analytical wavelength of 400 nm using a pharmacopoeial standard sample of cynaroside (3-O-β-D-glucopyranoside of luteolin) having similar spectral characteristics with flavonoids of this raw material (flavone derivatives). It was determined that the content of the total flavonoids in the fruits of Sophora japonica varies from 8.52±0.21 to 13.45±0.33% (calculated on cynaroside). The error of a single determination of the total flavonoids in the fruits of Sophora japonica with a 95% confidence probability is ±2.48%.