Abstract
BackgroundGraptopetalum paraguayense E. Walther is a popular traditional Chinese herb and possesses several health benefits. In earlier studies, we demonstrated that G. paraguayense showed no genotoxicity and showed several biological activities. However, the constituents of G. paraguayense have not been studied yet. In this present study, we isolated and identified the constituents of the leaves of G. paraguayense E. Walther.ResultsA total of seven flavonoid compounds were isolated from the methanolic extract of G. paraguayense. The four major compounds isolated were flavonoid glucoside derivatives of quercetin (1, 3) and kampferol (2, 4), each presenting a 3-hydroxyl-3-methylglutaroyl (HMG) substituent; compounds 3 and 4—the 2´´-acetyl derivatives of 1 and 2, respectively—are novel compounds isolated from nature for the first time. High-performance liquid chromatography for the quantitative analyses of the four major HMG-substituted flavonoid glycosides in G. paraguayense E. Walther were accomplished to acquire the high yields of 1–4 in the methanolic extract (4.8, 5.7, 4.3, and 2.5 mg/g, respectively). Furthermore, the antioxidant activities, including radical-scavenging, reducing power and lipid peroxidation inhibitory effects of these isolated flavonoids were also evaluated. All seven of the isolated flavonoid compounds possessed antioxdative activity.ConclusionsIn this study of the constituents of the leaves of G. paraguayense E. Walther, we isolated four major components from its methanolic extract and determined their structures to be (acetylated) HMG-substituted flavonol glycosides, which are rare in nature. All seven of the isolated compounds possessed antioxdative activity, and those flavonoid compounds may be responsible for the functional ingredients in G. paraguayense. Further investigation of their bioactivities or pharmacological activities will be continued.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-015-0088-4) contains supplementary material, which is available to authorized users.
Highlights
After successive normal and reversed-phase chromatography, we obtained a total of seven flavonoid compounds
We used ESI and FAB mass spectrometry and 1D and 2D NMR spectroscopy to elucidate the structures of the four HMG-substituted flavonoid glycosides 1–4
Through quantitative analysis based on triplicate injections into the high-performance liquid chromatography (HPLC) system, we found that the linearity of detection of the four compounds ranged from 2 to 500 ppm, with the squared correlation coefficient exceeding 0.999 in each case (Table 2)
Summary
A 50% aqueous ethanolic extract of G. paraguayense (GE50) acts as a mixed-type inhibitor of angiotensin-converting enzyme (ACE) (Chen et al 2007), and our in vivo study confirmed that daily oral administration of GE 50 (2.5 g/kg BW) for 4 weeks reduces blood pressure in spontaneously hypertensive rats (Chung et al 2009) and provide hepatoprotection against tert-butylhydroperoxide- and CCl4induced oxidative liver damage in rats (Chou et al 2008). G. paraguayense is useful against fibrosis or inflammation of tissues or organs other than the liver, in particular lung, kidney, and bladder. They mentioned in the patent that clinical trial results indicate almost all patients (14 persons) completely recovered from hepatic steatosis, G. paraguayense is effective in patients with fatty liver
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