Flavonoids and Hydroxycinnamic Acids from Leonurus quinquelobatus

Abstract

Little information is available in the literature on the composition and contents of phenolic compounds in Leonurus quinquilobatus Gilib. A coumaroylapigenin glycoside was isolated and called quinqueloside [1]. Plants of other species of the genus Leonurus L. contained 8-hydroxyflavone 7-allosylglucoside, p-coumaroylglucoside, quercetin, rutin, hyperoside, epicatechin, procyanidin B2, quercetin-3-O-[3,4-hydroxy-3,5-dimethoxybenzyl-L-rhamnopyranosyl]-D-galactopyranoside, quercetin-3-O-arabinoside, isoquercitrin, hyperoside, apigenin, genkwanin, quercetin-O-hexosylhexoside, quercetin-Odeoxyhexosylhexoside [2–10], leonuriside A and B, lavandulifolioside and verbascoside, leucosceptoside A, eugenylrutinoside, and kaempferol-3-O-glucoside [10, 11] and ferulic, caffeic, and chlorogenic acids [10, 12–15]. The goal of the present work was to define the composition of phenolic compounds in L. quinquelobatus grown in western Siberia. HPLC-MS analysis used an Agilent 1200 SL liquid chromatograph (with a diode-matrix detector) and a Bruker micrOTOFQ hybrid quadrupole–time-of-flight mass spectrometer. The herb (medicinal raw material) of L. quinquilobatus growing in the three western Siberian regions: Novosibirsk, Kemerovo, and Kamlak village (Gornyi Altai) was studied. Raw material was collected in early July (flowering of lower verticils) according to requirements of the State Pharmacopoeia (1990) and extracted with aqueous EtOH (70%) [16, 17]. An aliquot was passed through a Diapak C16 cartridge and eluted with MeOH. The sample was analyzed by reversed-phase HPLC-MS with elution by HCOOH (2%)–MeOH with a stepped gradient using a Zorbax SB-C18 column (2.1 150 mm, 3.5 m) at 25°C and flow rate 0.2 mL/min. Chromatograms were recorded at 340 50 nm. Electrospray ionization (ESI) used 2 bar, 8 L/min, 240°C; 4 kV, m/z 100–1200; and mass accuracy 0.01 Da. MS-MS spectra were obtained at 20 and 40 eV. The qualitative compositions of extracts of raw material from the various regions did not differ. Nine principal constituents were detected. Comparison with a mixture of standards identified in the extracts chlorogenic acid and rutin. The other compounds were identified using UV and mass spectra. Chlorogenic (caffeoylquinic) acid (1), tR 16.9 min, C7H11O6 –. The UV spectrum was identical to that of the standard. Ester of caffeic and malic acids (2), tR 20.8 min, C13H12O8, MW 296.053 Da (MeOH, max = 330 nm, 304sh nm). The UV spectrum was similar to that of chlorogenic acid but shifted by 4 nm. The MS-MS spectrum had three fragment ions at 179 (caffeic acid anion, C9H7O4 –), 135 (loss of CO2 from caffeic acid anion, [C9H7O4 – CO2] –), and 133 (malic acid anion, C4H5O5 –). Tetrosodipentoside of caffeoylquinic acid (3), tR 22.5 min. UV spectrum (MeOH, max = 332 nm, 304sh nm). C30H44O22. MW 756.228 Da [M – H] – 755. MS-MS spectrum m/z: 461, 315, 297; 191 (quinic acid anion); 179 (caffeic acid anion); 161 (fragment ion C9H5O3 –, [X – ROH – H+]–, formed by decomposition of caffeic acid derivative [X – H+]–, where X = [C9H7O3 – O – R]); and 135 (fragment ion after loss of CO2 from caffeic acid anion); 133 (fragment ion after loss of CO from the anion with m/z 161). The difference of m/z values for anions of this derivative (755) and caffeoylquinic acid (353) was 402, which corresponded to the trisaccharide C14(H2O)13, a dipentosotetrose.