| Coix lacryma-jobi L.var.ma-yuen Stapf,belong to the cultivated crop of Gramineae family,is used both as medicine and food,with different pharmacological effects of various parts.Coix seeds,as the directly edible part,has been studied their biological activities widely.The earlist attention of their biological activity is the effect of antidiabetics,and the polysaccharide from coix seed is considered as the bioactive constituents,using alloxan diabetic mice as a model,studies have shown that intraperitoneal injection of Coix seed polysaccharide can effectively reduce blood sugar in mice,while whether other more constituents involved are still not clear..In order to explore other chemical components in Coix Seed contributed to antidiabetics effect,and provide scientific guidance for further development of related products,the experiment on the screening of α-glucosidase inhibitory constituents was carried out,which is one of the important targets for the treatment of type II diabetes in the clinic.Two different methods are used to extract different parts of the Coix lacryma-jobi(seed,shell,bran,spikelet,leaf and stem),respectively.The chemical constituents were analyzed by high performance liquid chromatography(HPLC)and gas chromatography-mass spectrometry(GC-MS),and theα-glucosidase inhibitory activity of each extract was screened by the optimized pNPG method.Based on above,the main components from the low-polarity part of ethanol extract of coix seed(palmitic acid,trans-oleic acid,cis-linoleic acid,cis-oleic acid methyl ester and cis-linoleic acid methyl ester)were tested for α-glucosidase inhibitory activity and enzyme kinetics.The results were showed as following:palmitic acid(IC50=163.46±10.01μM),trans-oleic acid(IC50=4.05±0.00μM),cis-linoleic acid(IC50=3.83±0.00μM),cis-methyl oleate(IC50=16.75±0.07μM),cis-linoleic acid methyl ester(IC50=3.59±0.00μM).Most of the compounds showed significantly strongerα-glucosidase inhibitory effect than that of the positive control(acarbose,IC50=581.94±0.26μM),and palmitic acid was the weakest one.The results of enzyme kinetics showed that the α-glucosidase inhibition type of cis-methyl oleate and methyl cis-linoleate were competitive inhibition,while palmitic acid,trans-oleic acid,cis-linoleic acid showed mixed inhibition on α-glucosidase.In order to study more chemical constituents in the coix seed on α-glucosidase inhibitory activity,a variety of column chromatography techniques were used to separate and purify the petroleum ether and ethyl acetate fractions of the ethanol extract of Coix seed.By structure elucidation,eleven compounds were isolated and identified:soybean meal-5-ene-3β-ol-7-one(stigmast-5-en-3β-ol-7-one)(1),soybean meal-3β,6α-diol(stigmastane-3β,6α-diol)(2),carotin(daucosterol)(3),β-sitosterol(β-sitosterol)(4),single oil Glycerol monooleate(5),monopalmitate(6),palmitic acid(7),linoleic acid(8),(6Z)-epoxyeicos-6-ene(9),N-((2S,3R,4E,8E)-1,3-dihydroxyoctadecyl-4,8-dien-2-yl)-hexade canamide(10),methyl dihydrophaseate(11).Among them,compounds 1,2,3,9,10 and 11 were isolated from coix seed for the first time.The α-glucosidase inhibitory activity test of the isolated compound was carried out by the optimized pNPG method.And the results showed that the steroidal compound carotenoid and the olefin compound(6Z)-epoxyeicos-6-ene had good inhibitory activity,with the IC50 values are 100.22±0.09 μM and 29.41±0.12μM,respectively.Thus,trans-oleic acid,cis-linoleic acid,cis-oleic acid methyl ester and cis-linoleic acid methyl ester have stronger inhibitory effects on α-glucosidase than(6Z)-epoxyeicos-6-ene,relatively speaking,carotenoids and palmitic acid have a poor inhibitory effect on α-glucosidase,and the main volatile component in coix seed is the main component that inhibits α-glucosidase. |
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