ORIGINAL RESEARCH published: 23 March 2018 doi: 10.3389/fchem.2018.00056 Frontiers in Chemistry | www.frontiersin.org 1 March 2018 | Volume 6 | Article 56 Edited by: Rajeev K. Singla, Netaji Subhas Institute of Technology, India Reviewed by: Abdul Sadiq, University of Malakand, Pakistan Lhassane Ismaili, Université Bourgogne Franche-Comté, France Rohit Gundamaraju, University of Tasmania, Australia *Correspondence: Dharmendra Kumar Yadav dharmendra30oct@gmail.com Sandeep Chaudhary schaudhary.chy@mnit.ac.in † These authors have contributed equally to this work. Specialty section: This article was submitted to Medicinal and Pharmaceutical Chemistry, a section of the journal Frontiers in Chemistry Received: 25 November 2017 Accepted: 23 February 2018 Published: 23 March 2018 Citation: Sharma V, Jaiswal PK, Saran M, Yadav DK, Saloni, Mathur M, Swami AK, Misra S, Kim M and Chaudhary S (2018) Discovery of C-3 Tethered 2-oxo-benzo[1,4]oxazines as Potent Antioxidants: Bio-Inspired Based Design, Synthesis, Biological Evaluation, Cytotoxic, and in Silico Molecular Docking Studies. Front. Chem. 6:56. doi: 10.3389/fchem.2018.00056 Discovery of C-3 Tethered 2-oxo-benzo[1,4]oxazines as Potent Antioxidants: Bio-Inspired Based Design, Synthesis, Biological Evaluation, Cytotoxic, and in Silico Molecular Docking Studies Vashundhra Sharma 1† , Pradeep K. Jaiswal 1† , Mukesh Saran 2 , Dharmendra Kumar Yadav 3 *, Saloni 3 , Manas Mathur 2 , Ajit K. Swami 2 , Sanjeev Misra 4 , Mi-hyun Kim 3 and Sandeep Chaudhary 1 * 1 Laboratory of Organic and Medicinal Chemistry, Department of Chemistry, Malaviya National Institute of Technology, Jaipur, India, 2 Department of Advance Molecular Microbiology, Seminal Applied Sciences Pvt. Ltd., Jaipur, India, 3 College of Pharmacy, Gachon University of Medicine and Science, Incheon, South Korea, 4 Department of Biochemistry, All India Institute of Medical Sciences (AIIMS), Jodhpur, India The discovery of C-3 tethered 2-oxo-benzo[1,4]oxazines as potent antioxidants is disclosed. All the analogs 20a-20ab have been synthesized via “on water” ultrasound-assisted irradiation conditions in excellent yields (upto 98%). All the compounds have been evaluated for their in vitro antioxidant activities using DPPH free radical scavenging assay as well as FRAP assay. The result showed promising antioxidant activities having IC 50 values in the range of 4.74 ± 0.08 to 92.20 ± 1.54 μg/mL taking ascorbic acid (IC 50 = 4.57 μg/mL) as standard reference. In this study, compounds 20b and 20t, the most active compound of the series, showed IC 50 values of 6.89 ± 0.07 μg/mL and 4.74 ± 0.08 μg/mL, respectively in comparison with ascorbic acid. In addition, the detailed SAR study shows that electron-withdrawing group increases antioxidant activity and vice versa. Furthermore, in the FRAP assay, eight compounds (20c, 20j, 20m, 20n, 20r, 20u, 20z, and 20aa) were found more potent than standard reference BHT (C 0.5FRAP = 546.0 ± 13.6 μM). The preliminary cytotoxic study reveals the non-toxic nature of active compounds 20b and 20t in non-cancerous 3T 3 fibroblast cell lines in MTT assay up to 250 μg/mL concentration. The results were validated via carrying out in silico molecular docking studies of promising compounds 20a, 20b, and 20t in comparison with standard reference. To the best of our knowledge, this is the first detailed study of C-3 tethered 2-oxo-benzo[1,4]oxazines as potential antioxidant agents. Keywords: 2-oxo-benzo[1, 4]oxazines, antioxidant, DPPH, FRAP, ascorbic acid, BHT INTRODUCTION “Antioxidant” are primarily reducing agents/compounds which refer to the activity of numerous vitamins, minerals and phytochemicals (such as vitamin E, vitamin C and glutathione etc.) by providing protection against the damage caused by reactive oxygen species (ROS) (Park and Pezzutto, 2002; Trombino et al., 2004; Govindarajan et al., 2005; Zhang et al., 2006). Antioxidants