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Open AccessArticle

A Null B-Ring Improves the Antioxidant Levels of Flavonol: A Comparative Study between Galangin and 3,5,7-Trihydroxychromone

by Xiaojian Ouyang 1,2,†, Xican Li 1,2,*,†, Wenbiao Lu 1,2, Xiaojun Zhao 1,2 and Dongfeng Chen 3,4,*
1
School of Chinese Herbal Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
2
Innovative Research & Development Laboratory of TCM, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
3
School of Basic Medical Science, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
4
The Research Center of Basic Integrative Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editors: Susana M. Cardoso and Alessia Fazio
Molecules 2018, 23(12), 3083; https://doi.org/10.3390/molecules23123083
Received: 6 November 2018 / Revised: 22 November 2018 / Accepted: 23 November 2018 / Published: 26 November 2018
(This article belongs to the Special Issue The Antioxidant Capacities of Natural Products 2019)
To clarify the role of the B-ring in antioxidant flavonols, we performed a comparative study between galangin with a null B-ring and 3,5,7-trihydroxychromone without a B-ring using five spectrophotometric assays, namely, O2-scavenging, 1,1-diphenyl-2-picrylhydrazyl radical (DPPH)-scavenging, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical-scavenging, 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) radical-scavenging, and Fe3+-reducing activity. The DPPH-scavenging reaction products of these assays were further analyzed by ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) technology. In the five spectrophotometric assays, galangin and 3,5,7-trihydroxychromone dose-dependently increased their radical-scavenging (or Fe3+-reducing) percentages. However, galangin always gave lower IC50 values than those of 3,5,7-trihydroxychromone. In the UPLC-ESI-Q-TOF-MS/MS analysis, galangin yielded galangin-DPPH adduct MS peaks (m/z 662, 434, 301, 227,196, and 151) and galangin-galangin dimer MS peaks (m/z 538, 385, 268, 239, 211, 195, and 151). 3,5,7-Trihydroxychromone, however, only generated m/z 3,5,7-trihydroxychromone-DPPH adduct MS peaks (m/z 586, 539, 227, 196, and 136). In conclusion, both galangin and 3,5,7-trihydroxychromone could similarly undergo multiple antioxidant pathways, including redox-dependent pathways (such as electron transfer (ET) and ET plus proton transfer (PT)) and a non-redox-dependent radical adduct formation (RAF) pathway; thus, the null B-ring could hardly change their antioxidant pathways. However, it did improve their antioxidant levels in these pathways. Such improvement of the B-ring toward an antioxidant flavonol is associated with its π-π conjugation, which can provide more resonance forms and bonding sites. View Full-Text
Keywords: antioxidant; galangin; 3,5,7-trihydroxychromone; flavonol; structure–activity; B-ring antioxidant; galangin; 3,5,7-trihydroxychromone; flavonol; structure–activity; B-ring
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Ouyang, X.; Li, X.; Lu, W.; Zhao, X.; Chen, D. A Null B-Ring Improves the Antioxidant Levels of Flavonol: A Comparative Study between Galangin and 3,5,7-Trihydroxychromone. Molecules 2018, 23, 3083.

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