Studies On Acid Hydrolysis And Antioxidant Activities Of Flavonoids C-glycosides From Trollius Chinensis

Trollflowers, flowers of Trollius chinensis Bunge are one of traditional Chinesemedicine possessing antibacterial, anti-virus, antioxidant and other pharmacologicalactivities. Previous researches of our group have revealed orientin, vitexin and theirderivates are antioxidants rich in trollflowers. The present study focuses on acid hydrolysismechanisms and kinetic processes of flavone C-glycosides from trollflowers, andantioxidant activities of their fractions and acid hydrolysates. This is helpful for elucidatingfunctional ingredients in trollflowers and developing new drugs based on thesecompounds.Acid hydrolysis mechanisms and kinetic processes of flavone C-glycosides fromtrollflowers were studied at first. Orientin-2-O-galactopyranoside （OGA） could behydrolyzed to orientin after losing its terminal galactopyranosyl group, and orientin maynot be hydrolyzed in certain condition. However, in stronger condition, some amount oforientin would turn to isoorientin following the known Wessely-Mose rearrangement. Thiscould happen for isoorientin, vitexin and isovetexin. A fraction rich in OGA fromtrollflowers, TC-1was thus undertaken acid hydrolysis to elucidate its kinetic process.Different conditions, including solvent concentration, acidity, temperature, substrateconcentration were investigated in detail. The optimal condition was established to obtainorientin-rich fraction as follows: TC-1was solved in20%ethanol, and reacted with0.5mol/L sulfuric acid at80°C for7h. The acid hydrolysis of TC-1followed first orderreaction, the activation energy was calculated to be126.7±8.89KJ/mol. Finally, bycontrolled acid hydrolysis, OGA could turn to orientin and stop to transfer to isoorientin atthe same time, which could be applied to preparation of orientin-rich fraction from TC-1.Antioxidant capacities of different fractions （TC-1–TC-3; and their hydrolytesTC-1h–TC-3h） and compounds from trollflowers were further assessed by2,2-diphenyl-1-picrylhydrazyl radical and2,2′-azinobis-（3-ethylbenzothiazoline-6-sulphonate） radical cation scavenging assays. The contents and antioxidant properties ofOGA, orientin and vitexin among these fractions were determined by HPLC analysis. They all possessed notable concentration-dependent antioxidant activities. By comparisons oftheir IC50（g/mL） data, the order of the antioxidant activity against DPPH^●was as follow:TC-1TC-3h﹥TC-1h﹥TC-3﹥TC-2h TC-2; the order of the antioxidant activityagainst ABTS^●+was TC-1﹥TC-3TC-3h﹥TC-1h TC-2, TC-2h.. TC-1showed strongcapacities even higher than orientin. These results demonstrated that flavone C-glycosidesfrom trollflowers showed good antioxidant capacities, which provide insights for betterusages of these ingredients.