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COVID-19 pandemic caused by the SARS-CoV-2 virus has led to a worldwide crisis. In view of emerging variants time to time, there is a pressing need of effective COVID-19 therapeutics. Setomimycin, a rare tetrahydroanthracene antibiotic, remained unexplored for its therapeutic uses. Herein, we report our investigations on the potential of setomimycin as COVID-19 therapeutic. Pure setomimycin was isolated from Streptomyces sp. strain RA-WS2 from NW Himalayan region followed by establishing in silico as well as in vitro anti-SARS-CoV-2 property of the compound against SARS-CoV-2 main protease (M pro ). It was found that the compound targets M pro enzyme with an IC 50 value of 12.02 ± 0.046 μM. The molecular docking study revealed that the compound targets Glu166 residue of M pro enzyme, hence preventing dimerization of SARS-CoV-2 M pro monomer. Additionally, the compound also exhibited anti-inflammatory and anti-oxidant property, suggesting that setomimycin may be a viable option for application against COVID-19 infections. Graphical abstract

Consistent production of bioactives from microbial sources remains a big challenge for fermentation based bio-processes. Setomimycin, a rare 9,9'-bianthrylanthracene antibiotic reported to be active against Gram positive bacteria i.e. Staphyloccocus aureus, Bacillus subtilis, Bacillus cereus, and Mycobacterium smegmatis, including mycobacteria is one of the least exploited antibiotic. Present work aims to enhance and maximize setomimycin production using One Factor at a Time (OFAT) approach, followed by Taguchi L9 orthogonal array (OA) design in 30L fermenter. Four most influential parameters, namely carbon source, nitrogen source, air and agitation were selected for optimization studies. The optimized production medium supplemented with 150 g/L glycerol and 7.5 g/L soyabean meal with an agitation rate of 100 RPM and air flow rate of 20 LPM (Liters Per Minute) resulted in 675 mg/L setomimycin production within 96–108 h of fermentation as compared to the initial production i.e. 40 mg/L. Thus, an overall enhancement of 16.8 folds was achieved in setomimycin production after optimization in 30L fermenter. Graphical Abstract