Abstract
A series of rhodanine derivatives was synthesized in the Knoevenagel condensation of rhodanine and different aldehydes using choline chloride:urea (1:2) deep eutectic solvent. This environmentally friendly and catalyst free approach was very effective in the condensation of rhodanine with commercially available aldehydes, as well as the ones synthesized in our laboratory. All rhodanine derivatives were subjected to 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activity investigation and quantitative structure-activity relationship (QSAR) studies were performed to elucidate their structure-activity relationship. The best multiple linear QSAR model demonstrate a stability in the internal validation and Y-randomization (R2 = 0.81; F = 24.225; Q2loo = 0.72; R2Yscr = 0.148). Sphericity of the molecule, ratio of symmetric atoms enhanced atomic mass along the principle axes in regard to total number of atoms in molecule, and 3D distribution of the atoms higher electronegativity (O, N, and S) in molecules are important characteristic for antioxidant ability of rhodanine derivatives. Molecular docking studies were carried out in order to explain in silico antioxidant studies, a specific protein tyrosine kinase (2HCK). The binding interactions of the most active compound have shown strong hydrogen bonding and van der Waals interactions with the target protein.
Highlights
Deep eutectic solvents (DESs) are often characterized as environmentally friendly and acceptable, due to their low vapor pressure, non-toxic properties, reusability, and cheapness [1,2]
The deep eutectic solvent formed of the choline chloride and urea was found to be very suitable for this type of condensation, since no catalyst was required, and the yields of the compounds were moderate to excellent
This method is characterized by a simplicity of post synthetic procedures, which includes the addition of water into reaction mixture followed by product precipitation
Summary
Deep eutectic solvents (DESs) are often characterized as environmentally friendly and acceptable, due to their low vapor pressure, non-toxic properties, reusability, and cheapness [1,2]. DESs are formed by the interaction of different hydrogen bond acceptors (HBA), like quaternary ammonium salts, and hydrogen bond donors (HBD), like urea, carboxylic acids, sugars or amides [1]. They have been proven to be efficient in many applications, such as organic synthesis, extraction, electrochemistry, etc. Yarovenko et al [18] studied Knoevenagel condensation of rhodanine with various aldehydes in different solvents and with different catalysts. They found that methanol as a solvent and ethylenediammonium diacetate at ambient temperature gave high yield of the product, sodium acetate in acetic acid or acetic anhydride gave moderate yields, while ethanol and piperidine as a catalyst gave no product
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