title: Identification of six phenylpropanoids from garlic skin as major antioxidants.
abstract: The extract of garlic skins (peels) showed strong antioxidant activity, and some responsible constituents were isolated and identified. Garlic (Allium sativum L.) has been used as an herbal medicine, but there is no report on the health benefits of the skin or peel. In this study, the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of garlic skin extract was evaluated. Using chromatographic techniques, the active constituents were isolated and subsequently identified. Analyses by high-performance liquid chromatography coupled with a photodiode array detector (HPLC-PDA) suggested that these compounds were phenylpropanoids, which had a characteristic absorbance at 300-320 nm. Liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance analyses allowed the chemical structures of the isolated constituents to be postulated. The proposed compounds were subsequently synthesized and compared with the constituents in the extract using HPLC-PDA and LC-MS. N-trans-Coumaroyloctopamine, N-trans-feruloyloctopamine, guaiacylglycerol-beta-ferulic acid ether, and guaiacylglycerol-beta-caffeic acid ether were identified as were trans-coumaric acid and trans-ferulic acid. Also, the antioxidant activities of these compounds were determined.
authors.affiliation: Healthcare Research Institute, Wakunaga Pharmaceutical Company, Ltd., 1624 Shimokotachi, Kodacho, Takatagun, Hiroshima 739-1195, Japan. ichikawa_m@wakunaga.co.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Ichikawa
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Ryu
authors.forename: Jiro
authors.initials: J
authors.lastname: Yoshida
authors.forename: Nagatoshi
authors.initials: N
authors.lastname: Ide
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Kodera
authors.forename: Takashi
authors.initials: T
authors.lastname: Sasaoka
authors.forename: Robert T
authors.initials: RT
authors.lastname: Rosen
mesh_terms: D000975:Antioxidants / Q000032:analysis* / Q000737:chemistry; D001713:Biphenyl Compounds; D002851:Chromatography, High Pressure Liquid; D002934:Cinnamates / Q000032:analysis* / Q000737:chemistry; D003373:Coumaric Acids; D000431:Ethanol; D005737:Garlic / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D010851:Picrates / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry*; D018514:Plant Structures / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D002934:Cinnamates; D003373:Coumaric Acids; D010851:Picrates; D010936:Plant Extracts; D000431:Ethanol; C004999:ferulic acid; C004931:1,1-diphenyl-2-picrylhydrazyl