Discovery of Sortase A covalent inhibitors with benzofuranene cyanide structures as potential antibacterial agents against Staphylococcus aureus

Sortase A (SrtA) is a cysteine transpeptidase of most gram-positive bacteria that is responsible for the anchoring of many surface protein virulence factors to the cell wall. SrtA ablation has demonstrated to alleviate the infection without affecting the viability of bacteria. Herein, a series of benzofuran cyanide derivatives were synthesized and evaluated. Several compounds exhibited excellent inhibitory activity against SrtA with IC50 values from 3.3 μM to 21.8 μM compared with the known SrtA inhibitor pHMB (IC50 = 130 μM). Ⅲ-1, Ⅲ-15, Ⅲ-34 and V-1 showed potent inhibitory effects on biofilm formation with IC50 values from 2.1 μM to 54.2 μM. Invasion assays showed the four compounds caused a decrease of 4%-24.0% in the uptake of the S. aureus strain by 293T cells. Further assay showed that compound Ⅲ-15 decreased the amount of cell wall-associated protein A by 26.5%. Structure-activity relationship and docking studies demonstrated that the acrylonitrile moiety of the compounds played an important role in enhancing the activity. When the double bond of acrylonitrile changed to single bond, the activity was decreased significantly. This indicates that acrylonitrile, which is a Michael receptor, can inhibit the activity of SrtA by covalent binding effectively to the thiol group of Cys184.