Oxidative stress, a result of an overproduction and accumulation of free radicals, is the leading cause of several degenerative diseases such as cancer, atherosclerosis, cardiovascular diseases, ageing and inflammatory diseases. Polyphenols form an important class of naturally occurring antioxidants, having innumerable biological activities such as anticancer, antifungal, antibacterial, antiviral, antiulcer and anticholesterol, to name a few. Among various polyphenols, gallic acid (3,4,5-trihydroxybenzoic acid), a naturally occurring low molecular weight triphenolic compound, has emerged as a strong antioxidant and an efficient apoptosis inducing agent. Starting from the bioavailability and the biosynthetic pathway of gallic acid, this review includes various in vitro, in vivo and in silico studies providing the mode of action, radical scavenging activity, ability to inhibit lipid peroxidation, maintenance of endogenous defense systems and metal ion chelation by this triphenolic molecule, along with a comprehensive overview of factors responsible for its high antioxidant activity. Gallic acid derivatives have also been found in a number of phytomedicines with diverse biological and pharmacological activities, including radical scavenging, interfering with the cell signaling pathways and apoptosis of cancer cells. The diverse range of applications of this simple polyphenol is due to a fine amalgam between its antioxidant and prooxidant potential. The existing literature on this dual behavior of gallic acid and its derivatives is reviewed here. This is followed by an account of their potential clinical and industrial applications.

Isatin (1H-indole-2,3-dione) and its derivatives represent an important class of heterocyclic compounds that can be used as precursors for drug synthesis.

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Pyruvic acid and its isomers, including the enol tautomers and enantiomeric lactone structures, have been investigated at the B3LYP/6-311 + + G(3df,3pd) level, and it is found that a keto form with trans C(methyl)C(keto)C(acid)O(hydroxyl) and cis C(keto)C(acid)OH, and with one methyl hydrogen in a synperiplanar position with respect to the keto oxygen, is the most stable. This agrees with previous theoretical and experimental determinations. However, no minimum corresponding to protonated pyruvate could be located, although previous semiempirical calculations had found such structures. Decarboxylation by different possible routes was then studied. It was found that the direct formation of acetaldehyde, the most stable of the resulting C2H4O isomers, via a four-center-like transition state is the most feasible, although there is a high activation barrier of 70 kcal mol(-1). In contrast to semiempirical calculations, it is found that no hydroxyethylidene-carbon dioxide complex exists as a product, and no transition state leading to the dissociation to hydroxethylidene could be located.

Thiazolidinone is a biologically important five‐membered heterocyclic ring having almost all types of biological activities. This review covers various types of thiazolidinones, such as 2‐thiazolidinones, 4‐thiazolidinones, 5‐thiazolidinones, 2‐thioxo‐4‐thiazolidinones, and thiazolidiene‐2,4‐dione. The literature related to the physical properties, chemical reactions, and synthesis for these derivatives has been included. Recent advances in the biological activities reported for 4‐thiazolidinone derivatives, such as peroxisome proliferator‐activated receptor γ binders, follicle‐stimulating hormone agonists, cystic fibrosis transmembrane conductance regulator inhibitors, and antioxidants, have been covered in this review. Thus, this study may help in further optimizing these thiazolidinone derivatives as more effective drug agents.