Accordingly a bioassay guided approach was

Accordingly, a bioassay-guided approach was been used to study the bioactive compounds in VAS contribute to the α-glucosidase inhibitory and antioxidant activity. The 95% ethanol extraction of VAS was successively partitioned with petroleum ether, ethyl acetate and n-butanol. Ethyl acetate fraction was further isolated because of its high radical scavenging ability and α-glucosidase inhibition. Finally, 16 compounds including a new Quinacrine hydrochloride hydrate and a compound from natural source firstly were isolated from ethyl acetate fraction by using silica gel, Sephadex LH-20, C18 reversed-phase silica gel and semi-preparative high performance liquid chromatography (Semi-HPLC). The structures of isolated compounds were identified by nuclear magnetic resonance (NMR) and high resolution electrospray ionization mass spectrometry (HR-ESI-MS). Radical scavenging and α-glucosidase inhibitory ability of the compounds were measured.
Materials and methods
Results and discussion
Conclusions Bioassay orientated approach is an effect method for isolating the active ingredients from VAS. Finally, 16 compounds were isolated from the ethyl acetate partition of 95% ethanol extract, including 8 compounds isolated in genus Vigna for the first time. Compound 1 was a new compound and compound 2 was isolated from natural source for the first time. The majority of the ingredients shown excellent ABTS radical scavenging activity and α-glycosidase inhibitory activity. Furthermore, the structure-activity relationships had been discussed. Then compounds 1 and 2 were identified as competitive inhibitor for α-glucosidase with result of Lineweaver-Burk double-reciprocal-plot method. Molecular docking was performed to simulate the binding of compounds 1 and 2 with α-glucosidase. In general, this study explained ingredients with antioxidant and α-glucosidase inhibitory activity in VAS, and provide basic information for the further development of VAS as an industrial product or new medicine resource.
Conflicts of interest
Acknowledgements
Introduction Bark and young shoots of Quercus coccifera L. are used for the treatment of diabetes, diarrhea, and wounds in different parts of Anatolia [1], [2], [3]. Moreover, Quercus extracts applied for the treatment of hyperpigmentation in Persian Traditional Medicine [4]. The presence of tannins, flavonoids, and saponins in genus Quercus were reported before [5], [6], [7]. Some hydrolysable tannins were isolated from the leaves of Q. coccifera. Previously, we isolated two simple phenols, [kermesoside, (3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-propan-1-one) and 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)- propan-1-one], a megastigmane (cocciferoside), a tannin precursor [(-)-8-chlorocatechin], a stilbene derivative (polydatin), and two lignans (lyoniresinol-9-O-β-xylopyranoside and lyoniresinol-9-O-β-glucopyranoside) from bark of Q. coccifera [8]. Diabetes mellitus (DM) is a progressive degenerative disease characterized by abnormally high levels of glycemia. Diabetes dramatically increases the risk of cardiovascular problems, nephropathy, retinopathy, neuropathy, and some other neurodegenerative conditions like Alzheimer disease [9]. α-Glucosidase inhibitors are used for the treatment of type 2 DM. They affect carbohydrate digestion by inhibiting their conversion to monosaccharides thus limiting absorption by the intestines. Hence, α-glucosidase inhibitors reduce postprandial blood glucose and insulin levels [10]. The enzyme tyrosinase catalyzes the oxidation of simple phenols, which is the first step of the melanin biosynthetic pathway [11]. Melanin protects the skin from ultraviolet radiation but overproduction of melanin triggers several pigmentation disorders such as freckles, melanoma, and age spots in humans [12]. Tyrosinase also plays a key role in Parkinson’s disease (PD) by converting dopamine to neuromelanin and its oxidation products, which are neurotoxic compounds associated with neurodegeneration in PD. Thus, it is important to limit tyrosinase to inhibit development of PD [13]. Furthermore, tyrosinase induces undesirable browning side effects in fruits and vegetables thereby cause loss of nutritional quality and value in the food industry [14]. Since tyrosinase inhibitors have potential applications in cosmetics, agriculture, and medicine, developing novel inhibitors with lower side effects is desirable [15].