Flavonoids from Nitraria tangutorum

Abstract

Nitraria tangutorum Bobr. belongs to the Zygophyllaceae family and is widely distributed from Europe to East Asia. It is mainly grown in deserted and semideserted areas and is a very important sand-fixing plant. In China it has been used in the Uyghur Autonomous Region as medicine for more than a thousand years. It is reported to have antigastralgia, antidiabetes, and antihypertensive effects [1]. However, there are few reports on the chemical constituents of this plant. Only a few alkaloids and phenolics, including flavonoids, have been isolated from the plant [2–4]. In order to find more bioactive compounds, we carried out an investigation of the chemical constituents of Nitraria tangutorum Bobr. The air-dried leaves of Nitraria tangutorum Bobr. (4.0 kg) were powdered and extracted with methanol three times under reflux, each time for 30 min. The solvent was removed under reduced pressure to give a crude extract (1000 g). The crude extract was subjected to 200–300 mesh silica gel column chromatography eluting with a gradient of chloroform–methanol (40:1 to 1:1) to yield 50 fractions. Subfractions 20–24 were combined and purified by Sephadex LH-20 to yield compound 1, subfractions 26–27 were combined and recrystallized in methanol to yield compound 6, and subfractions 35–38 were purified by Sephadex LH-20 and semipreparative HPLC to yield compounds 2–5 and 7. Their structures were identified to be acacetin (1), apigenin 7-O-rutinoside (2), kaempferol 3-O-rutinoside (3), chrysoeriol 7-O-rutinoside (4), isorhamnetin 3-O-rutinoside (5), quercetin (6), and rutin (7) on the basis of spectral data and by comparison with published data [5–11]. Compounds 1–4 were isolated from the genus Nitraria for the first time. Acacetin (1), C16H12O5, yellow needles. UV spectrum (MeOH, max, nm): 330, 267. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [5]. Apigenin 7-O-rutinoside (2), C27H30O14, yellow powder. UV spectrum (MeOH, max, nm): 337, 266. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [6]. Kaempferol 3-O-rutinoside (3), C27H30O15, yellow powder. UV spectrum (MeOH, max, nm): 348, 266. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [7]. Chrysoeriol 7-O-rutinoside (4), C28H32O15, yellow powder. UV spectrum (MeOH, max, nm): 349, 265. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [8]. Isorhamnetin 3-O-rutinoside (5), C28H32O16, yellow powder. UV spectrum (MeOH, max, nm): 356, 254. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [9]. Quercetin (6), C15H10O7, yellow needles. UV spectrum (MeOH, max, nm): 375, 255. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [10]. Rutin (7), C27H30O16, yellow powder. UV spectrum (MeOH, max, nm): 355, 255. 1H NMR (600 MHz, DMSO-d6) and 13C NMR (150 MHz, DMSO-d6) data are as in [11].