STUDY OF THE FLAVONOID COMPOSITION OF JUGLANS NIGRA L. BARK

Abstract

Juglans nigra L. is a species of trees of the Juglandaceae family. This representative of the genus Walnut (Juglans L.) has not been sufficiently studied in comparison with other species, including Juglans regia L., but J. nigra is promising type of medicinal plant material, which the preparations have an antimicrobial, restorative effect. In our opinion, the contribution to the main antimicrobial effect, along with naphthoquinones, is also made by the flavonoids, contained in the raw material of this plant. There are insufficient data in the literature to substantiate the chemical composition of the black walnut bark. There is a possibility of standardizing the leaves of black walnut when quantitative determination of the amount of naphthoquinones by photocolorimetry method in terms of juglone is carried out. This article discusses the results of a study of the flavonoid composition of the bark of black walnut (Juglans nigra L.) as a promising source of biologically active compounds. As a result of the comparative chromatographic study, the presence of flavonoids was detected using detection at a wavelength of 365 nm, after treatment with 3% ethanolic solution of aluminum chloride (AlCl3) and diazobenzenesulfonic acid. In all water-alcohol extracts from the bark of the black walnut, the presence of rutin was not confirmed. Using column chromatography on silica gel L 40/100, the dominant flavonoid compound, myricitrin (3-О-α-L-rhamnopyranoside of myricetin), which has chloroform-ethanol-water (26 : 16 : 3) and n-butanol-acetic acid (glacial) in the solvent systems: water of Rf value about 0.4 and 0.65, respectively. Myricitrin was identified as 3-O-α-L-rhamnopyranoside of myricetin based on UV, 1H-NMR, 13C-NMR spectroscopy, mass spectrometry, and acid hydrolysis results. It was determined that in all UV spectra of extracts from the bark of black walnut, a bathochromic shift of the long-wavelength band is observed in the presence of a 3% ethanolic solution of AlCl3, which confirms the presence of flavonoids. Under the conditions of differential spectrophotometry, an absorption maximum is observed in the 410-416 nm area, which indicates the advisability of using myricitrin in the analysis procedure, which has an absorption maximum at a wavelength of 416 nm. As a result of the study, a method was developed for the quantitative determination of the total flavonoids in the bark of black walnut. The optimal parameters have been determined: extractant is 80% water- ethanolic solutions; the ratio "raw material-extractant" – 1 : 30; time of extraction - extraction on a boiling water bath for 60 min, the degree of grinding of the raw material – 2 mm, analytical wavelength at 416 nm. It was determined that the content of the total flavonoids calculated on myricitrin in all studied samples is varied from 2.38% to 3.02%.