title: Structure-activity relationship of natural flavonoids in hydroxyl radical-scavenging effects.
abstract: OBJECTIVE
  To study the relationship between the structure and hydroxyl radical (*OH)-scavenging activity of twelve natural flavonoids.
  
  
  METHODS
  The hydroxyl radical-generating chemiluminescence system with ascorbate-CuSO4-yeast-H2O2 was used to determine the hydroxyl radical-scavenging activity of twelve natural flavonoids.
  
  
  RESULTS
  Guercetin, heliosin, hyperoside, kaempferol, baicalin, corylifolin, lysionotin, matteucinol, corylifolinin, and genistein could effectively scavenge. OH and inhibit the chemiluminescence of the system. The IC50 values (95 % confidence limits) of the flavonoids were 12.1 (9.9-14.5) g/L, 15.8(14.0-19.2) g/L, 19.5 (16.8-27.4) g/L, 20.1 (13.6-29.0) g/L, 34.6 (28.4-43.4) g/L, 66.8 (63.2-74.4) g/L, 187 (147-235) g/L, 211 (165-284) g/L, 262 (190-346) g/L, and 708 (498-994) g/L, respectively; whereas nobilelin and corylifolin-Ac could not scavenge *OH.
  
  
  CONCLUSIONS
  (1) Phenolic hydroxyls in flavonoids were the main active groups capable of scavenging *OH; (2) Hydroxyl groups in ring B and A were important *OH-scavenging active groups; (3) The ortho-dihydroxyl groups in ring A and/or B could greatly enhance the *OH-scavenging activity of the rings; (4) Comparing the IC50 values of guercetin, heliosin, hyperoside, baicalin, lysionotin, and matteucinol, it was suggested that the hydroxyl groups on 3',4' position of ring B possessed high *OH-scavenging activity and the scavenging activity of hydroxyl groups in ring B was higher than that of hydroxyl groups in ring A. The hydroxyl group or glucoside on 3 position of ring C of the above mentioned 6 flavonoids was also related to the. OH-scavenging ability. (5) The structural types of flavonoids themselves could influence their *OH-scavenging activity.
authors.affiliation: School of Life Science, East China Normal University, Shanghai 200062, China. ecnuchenjw@sohu.com
authors.forename: Ji-Wu
authors.initials: JW
authors.lastname: Chen
authors.forename: Zhen-Qin
authors.initials: ZQ
authors.lastname: Zhu
authors.forename: Tian-Xi
authors.initials: TX
authors.lastname: Hu
authors.forename: Da-Yuan
authors.initials: DY
authors.lastname: Zhu
mesh_terms: D005419:Flavonoids / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology*; D017665:Hydroxyl Radical; D010946:Plants, Medicinal / Q000737:chemistry; D011794:Quercetin / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D005419:Flavonoids; D016166:Free Radical Scavengers; D017665:Hydroxyl Radical; C038044:baicalin; D011794:Quercetin