Virtual screening identification of novel severe acute respiratory syndrome 3C-like protease inhibitors and in vitro confirmation

The 3C-like protease (3CL(pro)) of severe acute respiratory syndrome associated coronavirus (SARS-CoV) is vital for SARS-CoV replication and is a promising drug target. Structure based virtual screening of 308 307 chemical compounds was performed using the computation tool Autodock 3.0.5 on a WISDOM Production Environment. The top 1468 ranked compounds with free binding energy ranging from −14.0 to −17.09 kcal mol(−1) were selected to check the hydrogen bond interaction with amino acid residues in the active site of 3CL(pro). Fifty-three compounds from 35 main groups were tested in an in vitro assay for inhibition of 3CL(pro) expressed by Escherichia coli. Seven of the 53 compounds were selected; their IC(50) ranged from 38.57 ± 2.41 to 101.38 ± 3.27 μM. Two strong 3CL(pro) inhibitors were further identified as competitive inhibitors of 3CL(pro) with K(i) values of 9.11 ± 1.6 and 9.93 ± 0.44 μM. Hydrophobic and hydrogen bond interactions of compound with amino acid residues in the active site of 3CL(pro) were also identified.