Isolation and Identification of Aglicones of Flavonoids of Some Species of the Genus <i>Astragalus</i> L. of the Volga Region Flora

Abstract

Introduction. Promising sources of biologically active compounds (BAS) are extracts obtained from various morphological parts of plants of the numerous genus Astragalus L. One of the main groups of BAS isolated from plants of this genus are flavonoids, saponins, and polysaccharides. Sufficiently studied are Astragalus membranaceus (Fisch.) Bunge) and Astragalus mongholicus Bge., whose extracts have a wide range of pharmacological activity. Expansion of the nomenclature of medicinal plant materials and the study of BAS groups that determine the main pharmacological effects are topical studies in pharmacognosy. From this point of view, little-studied species of Astragalus (Astragalus henningii (Stev.) Klok., Astragalus testiculatus Pall., Astragalus varius S.G. Gmel., Astragalus dasyanthus Pall.), massively growing in the Volga region, are of interest.Aim. Isolation and identification of 5 aglycones of flavonoids in hydrolysates of water-alcohol extracts from Astragalus herb: A. henningii, A. testiculatus, A.varius, A. dasyanthus by HPLC/UV.Materials and methods. The objects of the study were the herb of four types of Astragalus (A. henningii, A. testiculatus, A.varius, A. dasyanthus), harvested during the period of mass flowering in the Saratov region and dried to an air-dry state. To study the composition of phenolic compounds, extraction was carried out with 70 % ethanol in the ratio of raw material : extracting agent 1 : 10 by infusion for 7 days. Acid hydrolysis was carried out with hydrochloric acid 37 % with heating for 40 min. The resulting hydrolysates were analyzed on an Agilent 1260 chromatograph (Agilent Technologies, USA) with a diode array detector, manual sample injection (Agilent G1328C manual injector, Agilent Technologies, USA) and an Agilent OpenLab CDS chromatographic data collection and processing system using an individually selected elution gradient of the mobile phase (0.1 % solution of orthophosphoric acids/acetonitrile). Compounds in the hydrolysates were identified by the retention times and UV spectra of a mixture of reference standards (RS) of quercetin, isorhamnetin, luteolin, kaempferol, and apigenin.Results and discussion. An elution gradient was selected for one time determination of 5 aglycones of flavonoids with a single analysis time of 13 minutes. These conditions made it possible to identify compounds in the hydrolyzates of water-alcohol extracts of four types of Astragalus. Luteolin, quercetin and apigenin were found in hydrolyzates of A. henningii, A. testiculatus and A. varius; isorhamnetin and kaempferol were found in A. henningii and A. varius. None of the analyzed aglycones was found in the A. dasyanthus hydrolyzate.Conclusion. After preliminary selection of the optimal conditions for the chromatographic separation of a mixture of 5 aglycones of flavonoids, hydrolysates of four types of Astragalus were analyzed. The data obtained indicate the prospects for further study of the chemical composition of Astragalus and confirm the expediency of their use for obtaining of new herbal remedies.