Hydroxycinnamic acids (HCAs) are important phytochemicals possessing significant biological properties. Several investigators have studied in vitro antioxidant activity of HCAs in detail. In this review, we have gathered the studies focused on the structure-activity relationships (SARs) of these compounds that have used medicinal chemistry to generate more potent antioxidant molecules. Most of the reports indicated that the presence of an unsaturated bond on the side chain of HCAs is vital to their activity. The structural features that were reported to be of importance to the antioxi-dant activity were categorized as follows: modifications of the aromatic ring, which include alterations in the number and position of hydroxy groups and insertion of electron donating or withdrawing moieties as well as modifications of the car-boxylic function that include esterification and amidation process. Furthermore, reports that have addressed the influence of physicochemical properties including redox potential, lipid solubility and dissociation constant on the antioxidant activ-ity were also summarized. Finally, the pro-oxidant effect of HCAs in some test systems was addressed. Most of the investigations concluded that the presence of ortho-dihydroxy phenyl group (catechol moiety) is of significant importance to the antioxidant activity, while, the presence of three hydroxy groups does not necessarily improve the activity. Optimiza-tion of the structure of molecular leads is an important task of modern medicinal chemistry and its accomplishment relies on the careful assessment of SARs. SAR studies on HCAs can identify the most successful antioxidants that could be use-ful for management of oxidative stress-related diseases.Keywords: Antioxidant, hydroxycinnamic acids, in vitro, ROS, structure-activity relationships. OXIDATIVE STRESS AND ANTIOXIDANTSReactive oxygen species (ROS) are oxygen derived molecules that readily react with other compounds and macromolecules and oxidize them. Some representative exam-ples of these species include superoxide (O2•-), hydroxy (HO • ) and peroxy (ROO • ) radicals, hydrogen peroxide (H2O2) and singletROS are involved in important physiological processes such as immune response, gene expression, signal transduc-tion and growth regulation [5,6]; however if they are not kept under tight control by physiological antioxidant systems they will be able to oxidize and damage various biological molecules leading to a condition called oxidative stress [1,7,8]. In this regard, oxidative stress has been reported to be in-volved in the pathogenesis of diseases such as cancer [9], neurodegenerative diseases [10], stroke [11], and others [12,13].Since an important source of ROS comes from environment [14], with the industrial development and the change in life style, oxidative stress related diseases need a special attention [15].Antioxidants operate by preventing or slowing the progression of oxidative damage reactions [16,17]. An antioxidant has been defined as "any substance that delays, p...

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Isatin is an important compound from the biological aspect of view. It is an endogenous substance and moreover; various pharmacological activities have been reported for isatin and its derivatives. In-vitro cytotoxic effects of the prepared isatin Schiff bases toward HeLa, LS180 and Raji human cancer cell lines has been reported in our previous work. 3-(2-(4-nitrophenyl)hydrazono) indolin-2-one was found to be the most potent one among the studied compounds (IC(30) =12.2 and 21.8 μM in HeLa and LS-180 cell lines, respectively). Obtained biological data could be well interpreted using docking binding energies toward vascular endothelial growth factor receptor (VEGFR-2); a key anticancer target being biologically investigated against various isatin derivatives. In the present work, quantum mechanical (QM) method including functional B3LYP in association with split valence basis set using polarization functions (Def2-SVP) was used to estimate individual ligand-residue interaction energies for the docked 3-(2-(4-nitrophenyl)hydrazono) indolin-2-one into VEGFR-2 active site. Results were further interpreted via calculated polarization effects induced by individual amino acids of the receptor active site. A fairly good correlation could be found between polarization effects and estimated binding energies (R(2) =0.7227). Conformational analysis revealed that 3-(2-(4-nitrophenyl) hydrazono) indolin-2-one might not necessarily interact with the VEGFR-2 active site in its minimum energy conformation.

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