A new series of asymmetric bis-isatin derivatives containing urea/thiourea moiety: Preparation, spectroscopic elucidation, antioxidant properties and theoretical calculations

Abstract

In the present study, design, synthesis, characterization, and investigation of antioxidant properties of novel asymmetric bis-isatin derivatives (1-8) containing urea/thiourea moiety are reported for the first time. FT-IR, 1H-NMR, and 13C-NMR spectroscopic methods and elemental analysis were used to elucidate the structures of the synthesized compounds. Their CUPRAC and ABTS cation radical scavenging abilities were investigated for antioxidant activity. The bis-isatins containing urea moiety (compounds 1-4) did not show ABTS activity, while those containing the thiourea moiety (compounds 5-8) showed moderate ABTS activity. Besides, all bis-isatins were observed to exhibit CUPRAC activity at a low micromolar level The 1-(5-chloro-2-oxoindolin-3-ylidene)-5-(2-oxoindolin-3-ylidene)thiocarbonohydrazide (compound 5) showed the highest ABTS activity with IC50 value of 18.44 µM; on the other hand, the 1-(5-chloro-2-oxoindolin-3-ylidene)-5-(5-methoxy-2-oxoindolin-3-ylidene)carbonohydrazide (compound 2) had the strongest CUPRAC activity with A0.50 value of 0.600 µM. Both spectroscopic and antioxidant properties of the compounds were examined computationally, and the structure-activity relationship was investigated theoretically by comparing with experimental data. The ground state geometries and chemical reactivity parameters of the compounds were calculated using the B3LYP hybrid functional with 6-311++g(2d,2p) and 6-31g(d) basis sets. After determining the local electron affinity of the compounds, the Laplacian bond order and intrinsic bond strength indexes (independent gradient model-δgIGMH and IBSIIGMH descriptors based on Hirshfeld approach) of hydrogen bonds at possible reactive sites were calculated and associated with the antioxidant properties of the compounds.