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    Antioxidant and Tyrosinase Inhibitory Activities of Flavonoids from Trifolium nigrescens Subsp petrisavi
    (Amer Chemical Soc, 2013) Demirkiran, Ozlem; Sabudak, Temine; Ozturk, Mehmet; Topcu, Gulacti
    Trifolium nigrescens was researched for its chemical constituents for the first time. Bioassay-guided isolation of the EtOAc extract from the leaves of T. nigrescens resulted in the purification of a new biflavone, 4',5,5 '',7,7 ''-pentahydroxy-3',3'-dimethoxy-3-O-beta-D-glucosyl-3 '',4'-O-biflavone (1) along with eleven known compounds consisting of three phenolics (2-4), and eight flavonoid glycosides (5-12). Their structures were determined by extensive ID and 2D NMR, and MS data analyses. The isolated compounds were evaluated for their antioxidant activity and inhibitory activity on mushroom tyrosinase. Highly potent inhibitions Were found by compounds 7 (IC50 = 0.38 mM), 8 (IC50 = 0.19 mM), and 12 (IC50 = 0.26 mM) when compared with standard tyrosinase inhibitors kojic acid (IC50 = 0.67 mM) and L-mimosine (IC50 = 0.64 mM). The antioxidative effect of the isolated compounds and the extracts were determined by using, beta-carotene-linoleic acid, DPPH center dot scavenging, ABTS(+center dot) scavenging, superoxide scavenging, and CUPRAC assays. The experimental findings indicated that all the compounds demonstrated activity in all antioxidant activity tests employed except for the compounds 2-6. Compounds 2-6 showed moderate activity only in ABTS(+center dot) scavenging assay. The new compound 1 exhibited better activity than standard alpha-tocopherol in DPPH center dot scavenging, and ABTS(+center dot) scavenging assays. The results show that T. nigrescens can be regarded as a potential source of antioxidant compounds and tyrosinase inhibitors of significance in both the pharmaceutical and food industries.
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    Phenolic compounds from Trifolium echinatum Bieb. and investigation of their tyrosinase inhibitory and antioxidant activities
    (Pergamon-Elsevier Science Ltd, 2013) Sabudak, Temine; Demirkiran, Ozlem; Ozturk, Mehmet; Topcu, Gulacti
    Two bischromones, 3,3'-dimethoxy-2'-oxychromone (1), 3,3'-dihydroxy-2,2'-oxychromone (2) and a biflavone, 5,7,4',5 '',3''',4''''-hexahydroxy-3 ''-O-beta-glucosyl-3',7 ''-O-biflavone (3) have been isolated from whole plant of Trifolium echinatum Bieb. together with five known fiavonoids. The structures of the compounds were elucidated by 1D and 2D NMR analysis as well as HRESIMS. The isolated compounds were investigated for their antioxidant activity and tyrosinase inhibitory activity. Highly potent inhibition was found for compounds 1 (IC50 = 0.41 mM), 5 (IC50 = 0.47 mM) and 8 (IC50 = 0.45 mM) compared to those of standard tyrosinase inhibitors kojic acid (IC50= 0.67 mM) and L-mimosine (IC50 = 0.64 mM). The antioxidative effect of the extracts was determined by using beta-carotene-linoleic acid, DPPH. scavenging, ABTS(+-) scavenging, and CUPRAC assays. The experimental findings indicated that the compounds 2 and 8 were found to be active in radical scavenging and CUPRAC assays. (C) 2013 Elsevier Ltd. All rights reserved.