Component analysis of <i>Cucumis melo</i> L. leaves and their antioxidant activity

<i>Cucumis melo var. reticulatus</i> Ser. (or netted melon 'Earl's Favourite'), a variety of <i>Cucumis melo</i> L., is widely cultivated in Shizuoka, Japan. However, the leaves and stems are discarded after harvest. Therefore, we investigated the chemical constituents of melon leaves to suggest potential applications. Air-dried melon leaves were extracted using methanol. The methanol extract was suspended in water and successively partitioned using <i>n</i>-hexane, ethyl acetate, and to yield each fraction. Eight flavone glycosides (<b>1 </b>-<b> 8</b>) and three terpenes (<b>9 </b>-<b> 11</b>) were obtained. The chemical structures of these compounds were determined <i>via</i> nuclear magnetic resonance and mass spectrometry. The antioxidant activity of compounds <b>1 </b>-<b> 8</b> was evaluated using a 2,2-diphenyl-1-picrylhydrazyl radical assay. All compounds showed radical-scavenging activity in the range of IC₅₀, 24.2 - 129.5 μM, which depended on the number of hydroxyl groups on the benzene ring and <i>ortho</i>-substitution. Therefore, the leaves of <i>C. melo</i> may be considered valuable material for developing antioxidants.