Isolation, Identification and Cytotoxic Activity of Triterpenes and Flavonoids from Green Walnut (Juglans regia L.) Pericarps

Three alpha-amyrine type triterpenes (1-3) in addition to oleanolic acid (4) and six known flavonoids, namely apigenin (5) and its 7-O-beta-D-glucuronide (9), 5,6,4'-trihydroxy-7,3'-dimethoxy-flavone (6), cirsilineol (7), sudachitin (8) and cilicione-b (10) were isolated from the dichloromethane extract of the pericarps of Juglans regia. The structures of the compounds were established on the basis of spectroscopic analyses (UV, IR, HRESIMS and 1D & 2D NMR). Compounds 2, 3 and 6-10 were isolated from J. regia for the first time. To the best of our knowledge, compound 3 is a new natural product. All isolated compounds, as well as the dichloromethane extract were evaluated for their cytotoxic activity against the human cancer cell lines, MCF-7, HCT-116, HeLa, K562, Raji and THP-1. Compounds (1) and (5) showed the most potent anticancer activity against the cancer cells assessed. Interestingly, the concentration of compound (5) that was cytotoxic to cancer cells did not induce human peripheral blood mononuclear cell apoptosis. These results suggest that the structure of compound (5) may eventually serve as a lead for developing novel anticancer drugs with limited side effects against normal cells.