Structure-activity relationship of natural flavonoids in hydroxyl radical-scavenging effects
AIM: To study the relationship between the structure and hydroxyl radical ('OH)-scavenging activity of twelve natural flavonoids. METHODS: The hydroxyl radicalgenerating chemiluminescence system with ascorbateCuSO4-yeast-H2O2 was used to determine the hydroxyl radical-scavenging activity of twelve natural flavonoids.RESULTS: Guereetin, heliosin, hyperoside, kaempferal, 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. CONCLUSION: ( 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.
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