New Flavonoid Glycoside from Thalictrum minus
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NEW FLAVONOID GLYCOSIDE FROM Thalictrum minus
B. D. Komilov, M. A. Agzamova, I. M. Isaev, and K. A. Eshbakova*
The new flavonoid diglycoside thamiflaside was isolated from the aerial part of Thalictrum minus. The chemical structure of this glycoside was determined as apigenin 7-O-α-L-2″′-methoxyrhamnopyranosyl(1→6)-β-D-glucopyranoside based on PMR and 13C NMR (DEPT, HSQC, HMBC) physicochemical methods. Keywords: flavonoid glycoside, Thalictrum minus, meadow rue, glucose, rhamnose, NMR spectra. Plants of the genus Thalictrum are widely used in folk medicine owing to their rich composition that includes biologically active compounds such as alkaloids [1–6], flavonoids [7], triterpene glycosides and saponins [8–11], vitamins [12], steroids, and fatty [13] and organic acids [14]. Triterpene saponins [10] with antitumor and contraceptive activity [8, 9] were isolated from T. minus L. and T. foetidum L. growing in Irkutsk Region, Russia. Little information is available on the chemical composition and structure of flavonoids from plants of this genus. Alkaloids [5] and cycloartane glycosides [11] were isolated for the first time from plants of this genus during research conducted at the Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan. T. minus plants were collected in Surxondaryo Region, Uzbekistan (Kyzylkum, Peter I ridge). The ground aerial part of the air-dried plant (6 kg) was exhaustively extracted with EtOH at room temperature. The obtained total extracted substances were successively extracted with hexane and CHCl3 to remove nonpolar constituents and then with BuOH. The BuOH extract was separated by column chromatography over silica gel. Compound 1 was isolated by elution with CHCl3–EtOH–H2O (70:23:1.5). Compound 1 was a light-yellow powder of formula C28H32O14, m/z 593.300 [M + 1]+. The chemical structure of 1 was established using PMR and 13C NMR spectral data and two-dimensional HSQC and HMBC experiments. The PMR spectrum of 1 (Table 1) showed resonances characteristic of glycosylated flavones. The region of aromatic protons exhibited two 1H doublets at δ 6.40 and 6.77 ppm with spin–spin coupling constant (SSCC) J = 2 Hz and meta splitting that were attributed to H-6 and H-8. Resonances of two 2H doublets at δ 7.08 and 7.98 with SSCC J = 9 Hz and ortho splitting were indicative of a substituent in the 4′-position of ring B. The H-3 resonance appeared as a singlet at δ 6.88 ppm and confirmed that the isolated compound was a flavone. A 1H singlet at δ 12.86 ppm corresponded to a chelated OH on C-5. The weak-field 13C NMR spectrum also had resonances for aromatic C atoms of the aglycon part of the molecule. The presence of these resonances indicated that apigenin was the aglycon [15]. The PMR spectrum of 1 contained additional resonances for 10 protons as multiplets at δ 3.10–3.62 ppm that were characteristic of carbohydrates. The anomeric protons resonated at δ 5.01 and 4.50 ppm as clear doublets with SSCC J = 7.22 and 1.6 Hz. The strong-field spectrum exhibited
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