Design,Synthesis,and Activity Of Novel Benzofuranone Cyanide As Sortase A Inhibitors

Staphylococcus aureus is a major pathogen causing infections in humans and animals.The current main therapy strategy is antibiotic treatment.However,drug-resistant bacteria have emerged which then leads to clinical antibiotic deficiency.The emergence of drug-resistant bacteria is the result of the constant evolution of antibiotic stress.For above reason,it is expected to seek new bacterial infection drug entities to avoid the problem of resistance due to stress.The virulence factors on the surface of bacteria can promote the formation of bacterial biofilms,help bacteria to escape the lethality of antibiotics and help bacteria to enter the host,which are the main cause of the bacterial infection and drug resistance.The therapeutic strategy of targeting key virulence factors can not only block infection of bacteria but also avoid the occurrence of bacterial resistance by stress.Thus,this therapeutic strategy has greater advantages than antibiotics.Studies have shown that these virulence factors are anchored to the bacterial cell wall by the enzyme Sortase A.The Sortase A can efficiently recognize the conserved LPXTG pentapeptide in bacteria and catalyze the virulence factors with LPXTG pentapeptide structure to be anchored on the surface of the bacteria and help the connection of bacteria to host.Theoretically,if the Sortase A gene is knocked out or the activity of the Sortase A can be inhibited,the infection of the host by the bacteria can be effectively prevented.Therefore,the Sortase A enzyme has become a new target for the development of new anti-infective drugs.In this study,we summarized the structure-activity relationship of the reported Sortase A inhibitors.The 3-isopropionylbenzofuran mimics the L-shape configuration consisted by leucine and proline residues.The cyanohydrin is a Michael acceptor that binds to the cysteine thiol group in the active pocket of Sortase A to inhibit enzyme activity.Based on our previous results,the benzoxazole derivatives and benzofuran derivatives showed potent inhibitory activivy on Sortase A.A new benzofuranyl cyanide derivative was designed and synthesized to get more potent Sortase A inhibitors.For the purpose of the target compound,salicylaldehyde was used as raw material to get 2-acyl-3-phenylethylcyano-benzofuran intermediate by Wittig reaction,iodine-catalyzed ring closure,Vilsmeier formylation,oxidation,esterification,bromination,hydrolysis,chlorination and cyano substitution.Then,36 target compounds are obtained by condensation of 2-acyl-3-phenylethylcyano-benzofuran with different substituted aromatic aldehydes.The Sortase A inhibitory activity of the target compounds was evaluated by Fluorescence resonance energy transfer method.The results showed that most of the compounds showed excellent inhibitory activity against Sortase A and their IC₅₀0 values range from 3 uM to100μM,among them,XII-1,XII-6,XII-11,XII-13,XII-14,XII-18 and XII-28 exihibited excellent activity with IC₅₀ less than 10 uM.The structure-activity relationship analysis showed that the introduction of group to the benzofuran ring reduced the inhibitory activity.The main reason was that steric hindrance affects the binding of benzofuran ring of with His120 and Trp194 in the active pocket.The phenyl acrylonitrile structure plays an important role in the inhibition of the enzyme activity.The cyano cyanide structure can effectively attack the thiol structure of Cys184 as a Michael acceptor to inhibit the activity of nzyme.If the double bond configuration of the cyano cyanide is destroyed,the enzyme inhibitory activity of the entire compound is significantly reduced.The chlorine substitution at the 3-position benzene ring of cyano cyanide can significantly increase the activity of compound.The study of structure-activity relationship provides good reference for further design of potent Sortase A inhibitors.