Design And Synthesis Benzofuran Derivatives As Potent Sortase A Inhibitors

Staphylococcus aureus（S.aureus）is one of the most common pathogenic bacteria leading to purulent infection clinically,such as pneumonia,pseudo membranous enteritis,pericarditis,septicemia and sepsis systemic infection.With the wide application of antibiotics in clinical,staphylococcus aureus resistant strains appear constantly,especially methicillin-resistant S.aureus（MRSA）,being the main pathogenic bacteria of nosocomial infections and multiple drug resistance.It is a strain with resistance to antibiotics currently in clinical use,including vancomycin which was once considered the best therapies for MRSA.Therefore,in order to cope with the increasingly serious pathogen infection and its drug resistance problems,it is urgent to develop new antibacterial targets and corresponding inhibitors.Under this serious situation,anti-virulence strategy has become today’s new way for the treatment of bacterial infections.Compared with traditional antibacterial way,anti-virulence strategy’goal is not to kill bacteria directly,but to block the synthesis or secretion of virulence factors,which will diminish the rate of clinical infection and bacterial drug-resistance.Sortase A is a cysteine transpeptidase exsiting widely in Gram-positive bacteria and responsible for anchoring many surface virulence proteins to the cell wall layer of bacteria.These surface proteins display a critical role in infection process,including adherence,invasion,evasion of the host immune system,involved in the formation of biofilms and other biological function.When the expression genes of Sortase A are knocked out,bacterial infection ability declines obviously,but it does not affect the growth of bacteria.Therefore,Srt A is considered an ideal target for the design of novel anti-infective drugs.Previously,a large number of compounds were screened for Srt A inhibitors,but only a few compounds exhibited excellent inhibitory activity at the low micromolar range because of poor specificity to Sortase A.Usually,Srt A can specifically recognize substrate with L-shape mode,which is afforded by Leu and Pro side chains.Compounds with kink forming propensity to L-shape like Leu/Pro residues can be tolerated by Srt A.Here we designed and synthesized a family of novel2-phenyl-benzofuran-3-carboxamide derivatives with functional module arrangement similar to that of SrtA substrate LPXTG,as potential Srt A inhibitors.Commercially available salicylalcdehyde was used as the starting material,which was conducted firstly via Wittig reaction and intra-molecular cyclization to get 2-substituented benzofuran.Following the Vilsmeier reaction,oxidation,esterification,hydrolysis and amidation reaction,2,3-substituented intermediate was obtained,and eventually,the40 target molecules were facilely synthesized with aromatic acid or phenol by substitution reaction.The design route has only 11 steps,economically and high production rate.It has vital signification for further research of such benzofuran-based structure.All the synthesized compounds were evaluated for their in vitro inhibitory activities against Sortase A using a high-performance liquid chromatography（HPLC）assay.Most compounds exhibited great inhibitory activity against Sortase A.Specially,compounds:Ia-7,Ia-22,I-38 exihibited excellent activity with IC₅₀0 value ranging from 28.6μM to39.6μM.Structure-activity relationgship（SAR）revealed:a)3-substituented i-butyl amine side chain was essential to activity;b)the free hydroxyl group also made great influence on the activity,andreplacement with methoxyl,methoxyl,trifluoromethyl,halogen or nitro group led to decrease of the inhibitory activity.c)The length of linker had slight influence on the inhibitory against Sortase A,and the activity will be slightly decreased as the increase of length of linker.The present study is of considerable importance as it provides insights into the design and development of potent and selective Sortase A inhibitors.