Abstract
The research was conducted in the “logical series” of seven ligands: chromone, flavone, 3-hydroxyflavone, 3,7-dihydroxyflavone, galangin, kaempferol and quercetin. Each subsequent ligand differs from the previous one, among others by an additional hydroxyl group. The studied chromone derivatives are plant secondary metabolites which play an important role in growth, reproduction, and resistance to pathogens. They are important food ingredients with valuable pro-health properties. The studies of the relationships between their molecular structure and biological activity facilitate searching for new chemical compounds with important biological properties not by trial and error, but concerning the impact of specific changes in their structure on the compound properties. Therefore several pectroscopic methods (FT-IR, FT-Raman, 1H and 13C NMR) were applied to study the molecular structure of the compounds in the series. Moreover the quantum-chemical calculations at B3LYP/6-311++G** were performed to obtained the theoretical NMR spectra, NBO atomic charge, global reactivity descriptors and thermodynamic parameters. The antioxidant activity of the compounds was tested in the DPPH and FRAP assays and the mechanism of antioxidant activity was discussed based on the results on theoretical calculations. The cytotoxicity of the ligands toward human epithelial colorectal adenocarcinoma Caco2 cells was estimated and correlated with the lipophilicity of the compounds. The principal component analyses (PCA) and hierarchical cluster analysis were used to study the dependency between the molecular structure of ligands and their biological activity. The experimental data were related to the theoretical ones. The found regular changes in physicochemical properties correlated well with the systematic changes in antioxidant and biological properties.
Highlights
Chromone (1-benzopyran-4-one) is the backbone of many flavanols, flavones, isoflavones and flavonoids found in the plant kingdom and dietary products
The DPPH assay is considered as having a mixed mechanism which depends on the structure of an antioxidant, pH and solvent polarity, i.e.: (a) hydrogen atom transfer (HAT), (b) PCET, (c) sequential proton loss electron transfer (SPLET) and ET-PT [20, 21]
The antioxidant activity of the studied ligands increased with the number of hydroxyl substituents in the ring, i.e. in the series: chromone ! flavone ! 3-hydroxyflavone ! 3,7-dihydroxyflavone ! galangin ! kaempferol ! quercetin
Summary
Chromone (1-benzopyran-4-one) is the backbone of many flavanols, flavones, isoflavones and flavonoids found in the plant kingdom and dietary products. The chromone structural system is used to synthesize many anti-HIV, anti-inflammatory, antibacterial and anticancer drugs as well as those used in neurodegenerative diseases, inflammatory diseases and diabetes [1]. Investigations of this class of compounds showed that they have promising properties as inhibitors of tyrosine kinases, carbonate anhydrases, NF-κB factor, sirtuins, topoisomerases, adenosine A3 receptors, as well as modulators in Keap1-Nrf signaling pathway. Scavenging of free radicals can occur through rapid hydrogen transfer In this regard, the high reactivity of hydroxyl substituents influences to the greatest extent the antioxidant capacity of a given compound [3]. The total antioxidant capacity and redox potential are defined by several conformation factors (substitution pattern of functional groups including hydroxyl groups), phenoxyl radical stabilization and electron delocalization in the molecule (energy of the HOMO and the LUMO molecular orbital) [4]
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