Antioxidant Phenolics from the Green Husks of Juglans sigillata

Juglans sigillata Dode (Juglandaceae), a fast growing hardwood species, is indigenous to the mountain regions of southwest China. The green husks have long been used in traditional medicines for the treatment of various diseases, such as esophageal, gastric, cardiac and lung cancer [1]. However, its antioxidant activity has never been reported to date. In this work, repeated Sephadex LH-20 column chromatography of an EtOAc soluble fraction from the 95% EtOH extract of J. sigillata green husks yielded five phenolic compounds: (+)-catechin (1), (+)-catechin(4α→8)-(+)-catechin (2), (–)-epicatechin (3), ellagic acid (4) and 1,2,3,4,6-penta-O-galloyl-β-D-glucose (5). Structures of the five compounds were elucidated on the basis of a combination of spectroscopic analyses and other physiochemical data. Assessing by DPPH free radical scavenging assay, EtOAc soluble fraction (IC₅₀ value of 7.90µM) and compounds 1–5 (IC₅₀ values of 6.87, 6.68, 6.87, 6.71 and 6.55µM, respectively) inhibited strong antioxidant activities, comparing with that of α-tocopherol (positive control, IC₅₀ value of 7.0µM). Sturcture-and-activity relationship analysis suggested that the galloyl groups could be mainly responsible for the significant antioxidant potency of compounds 1–5. This investigation substantially indicated that the hydroalcoholic extracts and phenolics 1–5 might be exploited as good source for antioxidants. Acknowledgements: Natural Science Foundation of Tianjin City (09JCYBJC15800, 09JCZDJC21800) and China Postdoctoral Science Foundation is gratefully acknowledged.