Determination of the phenolic content and antioxidant potential of crude extracts and isolated compounds from leaves of Cordia multispicata and Tournefortia bicolor

Abstract

In this work, the total phenolic content and antioxidant activity of extracts and four flavonoids isolated from leaves of two Boraginaceae species (Cordia multispicata Cham. and Tournefortia bicolor Sw.) were evaluated using Folin-Ciocalteu reagent, DPPH free radical scavenging and inhibition of peroxidation of linoleic acid by FTC method. For comparison, ascorbic acid, α-tocopherol and BHT were used. In general, extracts from T. bicolor (68.8 ± 0.001 to > 1000 mg/g) showed higher phenolic content than C. multispicata (66.1 ± 0.009 to 231 ± 0.07 mg/g), and also scavenged radicals (IC50 12.8 ± 2.5 to 437 ± 3.5 mg/L) and inhibited lipid peroxide formation (IC50 51.2 ± 2.29 to 89 ± 0.59 mg/L). For these extracts a good correlation between the phenolic content and antioxidant activity was observed, suggesting that T. bicolor is richer in phenolic compounds and that it could serve as a new source of natural antioxidants or nutraceuticals with potential applications. Chromatographic procedures monitored by antioxidant assays afforded seven compounds, which were identified by spectral analyses (IR, MS and 1D and 2D NMR) and comparison with reported data as being trans-phytol (1), taraxerol (2), 3,7,4’-trimethoxyflavone (3), 5,3’-dihydroxy-3,7,4’-trimethoxyflavone (4), quercetin (5), tiliroside (6), and rutin (7). Compounds (4-7) were also evaluated and were effective as DPPH quenching (IC50 7.7 ± 3.6 to 79.3 ± 3.4 mg/L) and as inhibition of lipid peroxidation (IC50 80.1 ± 0.98 to 88.7 ± 3.62 mg/L). This is the first report on the total phenolic content, radical-scavenging and antioxidant activities of these species.