π-π Conjugation Enhances Oligostilbene's Antioxidant Capacity: Evidence from α-Viniferin and Caraphenol A.

Xican Li,Dongfeng Chen,Yulu Xie,Hong Xie,Jian Yang

doi:10.3390/molecules23030694

Abstract

α-Viniferin and caraphenol A, the two oligostilbenes, have the sole difference of the presence or absence of an exocyclic double bond at the π-π conjugative site. In this study, the antioxidant capacity and relevant mechanisms for α-viniferin and caraphenol A were comparatively explored using spectrophotometry, UV-visible spectral analysis, and electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC–ESI–Q–TOF–MS/MS) analysis. The spectrophotometric results suggested that caraphenol A always gave lower IC50 values than α-viniferin in cupric ion-reducing antioxidant capacity assay, ferric-reducing antioxidant power assay, 1,1-diphenyl-2-picryl-hydrazl radical (DPPH•)-scavenging, and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical-scavenging assays. In UV-visible spectra analysis, caraphenol A was observed to show enhanced peaks at 250–350 nm when mixed with Fe2+, but α-viniferin exhibited no similar effects. UPLC–ESI–Q–TOF–MS/MS analysis revealed that α-viniferin mixed with DPPH• produced radical adduct formation (RAF) peak (m/z = 1070–1072). We conclude that the antioxidant action of α-viniferin and caraphenol A may involve both redox-mediated mechanisms (especially electron transfer and H+-transfer) and non-redox-mediated mechanisms (including Fe2+-chelating or RAF). The π-π conjugation of the exocyclic double bond in caraphenol A can greatly enhance the redox-mediated antioxidant mechanisms and partially promote the Fe2+-chelating mechanism. This makes caraphenol A far superior to α-viniferin in total antioxidant levels.

Highlights

In natural product chemistry, the term “stilbene” refers to the trans-1,2-diphenylethene core (Figure 1)
Accumulative evidence suggests that antioxidation is a complicated process involved in several pathways
Redox-mediated pathways are characterized by electron transfer (ET), through which electrons are transferred from a antioxidant to reactive oxygen species (ROS) or reactive nitrogen species (RNS) [12]

Summary

Introduction

The term “stilbene” refers to the trans-1,2-diphenylethene core (Figure 1). The 1,2-double bond (C=C) can induce polymerization to form oligostilbenes, mainly dimeric stilbene, trimeric stilbene, and tetrameric stilbene. At least 200 natural oligostilbenes have been discovered [1,2]. Almost all of these natural oligostilbenes are documented to bear phenolic. -OH [2], and they can be regarded as the members of natural phenolics and function as phenolic Molecules. 2 of29of 9 antioxidants [3]. 22,22, x x Figure1.1.The. Thetrans-1,2-diphenylethene trans-1,2-diphenylethene core. Three dimers of resveratrol have been found in grape wine, including parthenocissin

Methods

Results

Conclusion