Abstract
Deep eutectic solvents, as green and environmentally friendly media, were utilized in the synthesis of novel coumarinyl Schiff bases. Novel derivatives were synthesized from 2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide and corresponding aldehyde in choline chloride:malonic acid (1:1) based deep eutectic solvent. In these reactions, deep eutectic solvent acted as a solvent and catalyst as well. Novel Schiff bases were synthesized in high yields (65–75%) with no need for further purification, and their structures were confirmed by mass spectra, 1H and 13C NMR. Furthermore, their antioxidant activity was determined and compared to antioxidant activity of previously synthesized derivatives, thus investigating their structure–activity relationship utilizing quantitative structure-activity relationship QSAR studies. Calculation of molecular descriptors has been performed by DRAGON software. The best QSAR model (Rtr = 0.636; Rext = 0.709) obtained with three descriptors (MATS3m, Mor22u, Hy) implies that the pairs of atoms higher mass at the path length 3, three-dimensional arrangement of atoms at scattering parameter s = 21 Å−1, and higher number of hydrophilic groups (-OH, -NH) enhanced antioxidant activity. Electrostatic potential surface of the most active compounds showed possible regions for donation of electrons to 1,1-diphenyl-2-picryhydrazyl (DPPH) radicals.
Highlights
Coumarins are a class of compounds widely distributed in the plant kingdom [1], but lots of synthetic studies have been done on them in the last few decades
Synthesis of Schiff bases is often performed by a reaction of amine with aldehyde, usually with the addition of catalysts such as acetic acid
We describe a synthesis of Schiff bases from
Summary
Coumarins are a class of compounds widely distributed in the plant kingdom [1], but lots of synthetic studies have been done on them in the last few decades. We have been investigating the antioxidant activity of different synthetic coumarin derivatives for years and showed that different synthetic modifications on the basic coumarin core can increase its antioxidant activity [2,3,4,5] For this purpose, a series of Schiff bases were synthesized [2] conventionally; we have noticed their formation when deep eutectic solvents (DESs) are applied as well. DESs have proven to be a convenient media for many synthetic routes and are often characterized as environmentally friendly [6,7,8] Their application in organic synthesis and extraction, as well as an extensive analysis of their properties, were described in some good reviews published in the last few years [6,7,8,9,10,11]
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