Synthesis and Antioxidant Activity of 2-Amino-5-methylthiazol Derivatives Containing 1,3,4-Oxadiazole-2-thiol Moiety

A series of new 5-(2-amino-5-methylthiazol-4-yl)-1,3,4-oxadiazole-2-thiol derivatives 6(a–j) were designed and synthesized with various substituted aldehydes. The chemical structures were confirmed by elemental analyses, FT-IR, 1H NMR, and mass spectral studies. The antioxidant activity of the synthesized compounds was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, nitric oxide, and superoxide radical scavenging assay methods. Compounds 6a, 6e, and 6c showed significant radical scavenging potential due to the presence of electron donating substituent on substituted aldehydes. 1. Introduction Compounds containing azomethine group (–C=N–) in the structure are known as Schiff bases which are usually synthesized by the condensation of primary amines and active carbonyl groups. Schiff bases are found to exhibit multifunctional properties, and they are able to improve various biological and pharmacological activities such as antitumor, antioxidant, and antibacterial activities [1]. Schiff bases bearing heterocyclic residues possessing excellent biological activity have attracted the attention of many researchers in recent years [2]. Due to the great flexibility and diverse structural aspects of Schiff bases, a wide range of these compounds have been synthesized and their activities have been studied [3, 4]. Many Schiff bases are known to be medicinally important and are used to design medicinal compounds [5]. 1,3,4-Oxadiazoles and thiazoles are versatile leading molecules for designing potential bioactive agents. The derivatives of these molecules constitute an important family of heterocyclic compounds. Compounds bearing 1,3,4-oxadiazole nucleus are known to exhibit remarkable biological activities such as antimalarial, anticancer, anticonvulsant, and anti-inflammatory [6–12]. Thiazole nucleus is also an integral part of all the available penicillins which have revolutionized the therapy of bacterial diseases [13]. The applications of thiazoles were found in the drug development for the treatment of allergies, hypertension, inflammation, schizophrenia, bacterial, HIV infections, hypnotics, and so forth [14]. Free radicals such as superoxide, hydroxyl, and nitric oxide are the oxygen centered free radicals, and they are also called reactive oxygen species (ROS). They are generated in the human body and would cause damage to lipids, proteins, and DNA and thus may lead to various diseases such as carcinogenesis, drug-associated toxicity, and inflammation. Furthermore, radical reactions play a significant role in the development of life limiting