Rationale on the High Radical Scavenging Capacity of Betalains.

Karina K. Nakashima,Erick L. Bastos

doi:10.3390/antiox8070222

Karina K. Nakashima, Erick L. Bastos

Open Access

https://doi.org/10.3390/antiox8070222

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Journal: Antioxidants	Publication Date: Jul 13, 2019
Citations: 20	License type: CC BY 4.0

Affiliation: Universidade de São Paulo

Abstract

Betalains are water-soluble natural pigments of increasing importance as antioxidants for pharmaceutical use. Although non-phenolic betalains have lower capacity to scavenge radicals compared to their phenolic analogues, both classes perform well as antioxidants and anti-inflammatory agents in vivo. Here we show that meta-hydroxyphenyl betalain (m-OH-pBeet) and phenylbetalain (pBeet) show higher radical scavenging capacity compared to their N-methyl iminium analogues, in which proton-coupled electron transfer (PCET) from the imine nitrogen atom is precluded. The 1,7-diazaheptamethinium system was found to be essential for the high radical scavenging capacity of betalains and concerted PCET is the most thermodynamically favorable pathway for their one-electron oxidation. The results provide useful insights for the design of nature-derived redox mediators based on the betalain scaffold.

Highlights

Oxidants play a major role in metabolism [1,2,3]
We have found that N-(3-hydroxylphenyl)betalain (m-OH-pBeet) is an adequate model to study the mechanism of antioxidant action of betanin because they share the same radical scavenging capacity [27]
Four model betalains were semisynthesized from betalamic acid (1) and the anilines 2 using a scaled up procedure based on the method of Schliemann and coauthors [28] (Figure 1a)

Summary

Introduction

Oxidants play a major role in metabolism [1,2,3] Despite their importance in several biological processes, such as cell signaling, proliferation and differentiation, the overproduction of oxidants has been linked to harmful health effects [4]. Antioxidants have been considered to be must-use food supplements against the deleterious effects of oxidants [6,7]. This idea was broadly advertised in the second-half of the 20th century and echoes in the 21st century [8,9]. Vitamin C and flavonoids, such as epicatechin gallate (ECG) from green tea, are examples of widely used antioxidants that show pro-oxidant action under certain conditions [10,11]

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