•Ultrasonic-assisted synthesis of new sulfonamide schiff base derivatives.•New oxazepine derivatives were synthesized using Microwave-technique.•Low-Cytotoxic, hemolytic Antimicrobial, and antioxidant agents were observed.•Molecular docking and DFT computational analyses have been predicted.•Identification of pharmacokinetic properties, bioactivity scores and pharmacophore site by POM analyses. The eco-friendly sonication and microwave irradiation techniques were used for the straight forward synthesis of the Schiff base platform from sulfathiazole. Herein, Schiff bases were developed and converted to oxazepane derivatives. Compounds were tested for their antimicrobial, antioxidant, in vivo cytotoxicity activity. Moreover, density functional theory (DFT) and molecular docking studies were also carried out to explore the structural prpoperties and interaction of compounds with the receptor molecules. In vitro antimicrobial activity was determined against Gram-positive and Gram-negative strains via microdilution technique, which showed that the synthesized derivatives exhibit significant antimicrobial activity. Furthermore, in vivo cytotoxicity activity of the compounds were carried out via intravenous injection in rats. The results were compared with negative controls and it was observed that most of the synthesized compounds displayed excellent antimicrobial activity and low toxicity in comparison to references and negative controls, respectively. Hemolysis test was carried out for bioactive compounds, and results showed higher hemolysis values of the Schiff bases than the correponding oxazepines and lower hemolytic effects. The free radical inhibittion and antioxidant activity was carried out by using 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH) and ferric reducing antioxidant power (FRAP) methods which suggested that the free radical scavenging activity increases with the presence of hydroxyl group. The Spectral measurements fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and high resolution electrospray ionization mass spectrometry (HRESIMS) confirmed the structure of the compounds. Display omitted