On the other hand, withanolide A displayed strong binding to SARS-CoV spike glycoprotein (Table 6; BE: −9.78 kcal/mol, Kd: 67.23 nM), SARS-CoV-2 spike glycoprotein (Table 7; BE: −7.18 kcal/mol, Kd: 5.48 µM), SARS-CoV 3CL-pro main protease (Table 9; BE: –8.93 kcal/mol, Kd: 285.01 nM) and SARS-CoV-2 Nsp10/Nsp-16 complex (Table 11; BE: −10.38 kcal/mol, Kd: 24.67 nM). Interestingly, withanolide A exhibited almost 1000× times stronger binding to SARS-CoV main protease as compared to standard reference drugs arbidol (Table 6; BE: −4.91 kcal/mol, Kd: 251.65 µM) and hydroxychloroquine (Table 6; BE: −5.25 kcal/mol, Kd: 142.18 µM). The same binding profile was observed for withanolide A with respect to SARS-CoV-2 spike glycoprotein as compared to standard reference drugs arbidol (Table 7; BE: −3.14 kcal/mol, Kd: 4.99 mM) and hydroxychloroquine (Table 7; BE: −2.48 kcal/mol, Kd: 15.11 mM). Withanolide A also displayed a 1000× stronger binding to Nsp-10/Nsp-16 complex from SARS-CoV-2 in comparison to losartan (Table 11; BE: −6.49 kcal/mol, Kd: 17.54 µM) and hydroxychloroquine (Table 11; BE: −4.93 kcal/mol, Kd: 244.14 µM)