Isolation and Structure-Activity Relationship of the Antioxidant Chemical Constituents from the Flowers of Rosa chinensis Jacq

The objective of this study was to investigate the antioxidant activity, chemical constituents, and structure-activity relationship from the flowers of Rosa chinensis Jacq. The antioxidant activity of the different polar solvent extracts were assayed by a 1,1-diphenyl-2-picrylhydrazyl scavenging experiment. The extract with the strongest 1,1-diphenyl-2-picrylhydrazyl scavenging capacity was further isolated and purified by column chromatography. The structures of the isolated compounds were elucidated on the basis of spectral analysis and physiochemical properties. The antioxidant activity of these compounds was assayed by a 1,1-diphenyl-2-picrylhydrazyl scavenging experiment and ascorbic acid was chosen as the positive control. The ethyl acetate fraction had the strongest 1,1-diphenyl-2-picrylhydrazyl scavenging activity. Ten compounds were obtained, represented as: 3,4,8,9,10-pentahydroxydibenzob,d]pyran-6-one (1), quercetin (2), kaempferol (3), 3,5,7,4′-tetrahydroxy-8-methoxy-flavone (4), isoquercetrin (5), kampferol 3-O-β-D-glucoside (6), tiliroside (7), kampferol 3-O-(6′′-galloyl)-β-D-glucoside (8), kampferol 3-O-(2′′,6′′-digalloyl)-β-D-glucoside (9), quercetin 3-O-(2′′,6′′-digalloyl)-β-D-glucoside (10). The 1,1-diphenyl-2-picrylhydrazyl scavenging capacity for these compounds, in descending order, were as follows: 10 > 9 > 1 ≈ 8 > 5 > ascorbic acid ≈ 2 > 6 > 7 > 3 > 4. Compounds 1, 8, 9, and 10 have the stronger antioxidant activity. Our results suggested the antioxidant activities of these compounds might be influenced by the number and position of hydroxyl groups in their aromatic rings.