Component analysis of Cucumis melo L. leaves and their antioxidant activity

Cucumis melo var. reticulatus Ser. (or netted melon 'Earl's Favourite'), a variety of Cucumis melo 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 n-hexane, ethyl acetate, and to yield each fraction. Eight flavone glycosides (1 - 8) and three terpenes (9 - 11) were obtained. The chemical structures of these compounds were determined via nuclear magnetic resonance and mass spectrometry. The antioxidant activity of compounds 1 - 8 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 ortho-substitution. Therefore, the leaves of C. melo may be considered valuable material for developing antioxidants.