AAPH or Peroxynitrite-Induced Biorelevant Oxidation of Methyl Caffeate Yields a Potent Antitumor Metabolite

Abstract

Hydroxycinnamic acids represent a versatile group of dietary plant antioxidants. Oxidation of methyl-p-coumarate (pcm) and methyl caffeate (cm) was previously found to yield potent antitumor metabolites. Here, we report the formation of potentially bioactive products of pcm and cm oxidized with peroxynitrite (ONOO¯), a biologically relevant reactive nitrogen species (RNS), or with α,α′-azodiisobutyramidine dihydrochloride (AAPH) as a chemical model for reactive oxygen species (ROS). A continuous flow system was developed to achieve reproducible in situ ONOO¯ formation. Reaction mixtures were tested for their cytotoxic effect on HeLa, SiHa, MCF-7 and MDA-MB-231 cells. The reaction of pcm with ONOO¯ produced two fragments, an o-nitrophenol derivative, and a new chlorinated compound. Bioactivity-guided isolation from the reaction mixture of cm with AAPH produced two dimerization products, including a dihydrobenzofuran lignan that exerted strong antitumor activity in vitro, and has potent in vivo antimetastatic activity which was previously reported. This compound was also detected from the reaction between cm and ONOO¯. Our results demonstrate the ROS/RNS dependent formation of chemically stable metabolites, including a potent antitumor agent (5), from hydroxycinnamic acids. This suggests that diversity-oriented synthesis using ROS/RNS to obtain oxidized antioxidant metabolite mixtures may serve as a valid natural product-based drug discovery strategy.

Oxidized Resveratrol Metabolites as Potent Antioxidants and Xanthine Oxidase Inhibitors

“…Resveratrol was transformed by a variety of oxidative reagents. These included hypervalent iodine (III) reagents PIFA/PIDA and AAPH that were found in our previous studies to reasonably mimic reactions that could occur via ROS scavenging by an antioxidant [ 20 , 21 ]. To further increase the explorable chemical complexity, periodic acid was also selected with oxone or iron (III) chloride as a co-oxidant.…”

Scavengome of an Antioxidant

“…In our previous work, we investigated the possible formation of III/6 in HeLa, SiHa, MCF-7 and MDA-MB-231 cancer cells treated with III and incubated with or without t-BuOOH-induced oxidative stress. While no direct evidence was found for an in-situ formation of III/6, the cytotoxic activity of III was altered by oxidative stress in a way that coincided with the cell line specificity of compound III/6 (Fási et al, 2020).…”

“…Among the oxidized metabolites of caffeic acid derivatives, perhaps the most significant bioactivity changes were observed for compound III/6. This dihydrobenzofuran lignan was formed when methyl caffeate (III) was oxidized in biorelevant (Fási et al, 2020) or biomimetic (Pieters et al, 1999) experimental setups. Compound III/6 was identified as a highly promising antitumor agent in various in vitro and in vivo experimental models.…”

Preparation and Evaluation of 6-Gingerol Derivatives as Novel Antioxidants and Antiplatelet Agents

“…Peroxynitrite was synthesised by a continuous flow system using syringe pumps as published previously [ 45 ]. Briefly, an acidic solution of hydrogen peroxide (0.6 M H 2 O 2 , 0.7 M HCl) was pumped to a junction alongside of sodium nitrite solution (0.6 M) at a flow rate of 1.5 mL/min.…”

“…Compounds’ structures were drawn and saved in PDB format using ChemDraw 12.0.2 software (ACD/LABS, Advanced Chemistry Development, Inc.) [ 45 ]. The h -COX-1 enzyme structure was retrieved from the PDB database.…”