title: Phenolic and enolic hydroxyl groups in curcumin: which plays the major role in scavenging radicals?
abstract: The aim of this work is to clarify the antioxidant abilities of phenolic and enolic hydroxyl groups in curcumin. 1,7-bis(4-benzyloxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (BEC), 1,7-bis(4-hydroxy-3-methoxyphenyl)heptane-3,5-diol (OHC), 1,7-bis(4-hydroxy-3-methoxyphenyl)heptane-3,5-dione (THC), and 1,7-bis(3,4-dihydroxyphenyl)-1,6-heptadiene-3,5-dione (BDC) are synthesized to determine the antioxidant activities by using antiradical assays against 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical, galvinoxyl radical, and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cation radical (ABTS*+) and by protecting DNA and erythrocyte against 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) induced oxidation. The phenolic hydroxyl is the main group for curcumin to trap DPPH, galvinoxyl, and ABTS*+ radicals. The conjugative system between enolic and phenolic hydroxyl groups is beneficial for curcumin to protect erythrocytes against hemin-induced hemolysis and to protect DNA against AAPH-induced oxidation, but is not beneficial for curcumin to protect erythrocytes against AAPH-induced hemolysis. More hydroxyl groups enhance the antioxidant effectiveness of curcumin in the experimental systems employed herein. Therefore, curcumin acts as an antioxidant through the phenolic hydroxyl group.
authors.affiliation: Department of Organic Chemistry, College of Chemistry, Jilin University, Changchun 130021, China.
authors.forename: Jian-Ying
authors.initials: JY
authors.lastname: Feng
authors.forename: Zai-Qun
authors.initials: ZQ
authors.lastname: Liu
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology; D001559:Benzhydryl Compounds / Q000737:chemistry; D052160:Benzothiazoles / Q000737:chemistry; D001713:Biphenyl Compounds / Q000737:chemistry; D003474:Curcumin / Q000737:chemistry* / Q000494:pharmacology; D004247:DNA / Q000737:chemistry / Q000187:drug effects; D016166:Free Radical Scavengers / Q000737:chemistry*; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D010851:Picrates / Q000737:chemistry; D013451:Sulfonic Acids / Q000737:chemistry
chemical_list: D000975:Antioxidants; D001559:Benzhydryl Compounds; D052160:Benzothiazoles; D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D010636:Phenols; D010851:Picrates; D013451:Sulfonic Acids; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D004247:DNA; C004931:1,1-diphenyl-2-picrylhydrazyl; D003474:Curcumin; C020338:galvinoxyl