Study On The Design, Synthesis And 3D-QSAR Of P.aeruginosa Quorum-sensing Inhibitors

As an important opportunistic pathogen, Pseudomonas aeruginosa (P. aeruginosa, PA) was the most prevalent bacterial pathogens in infectious diseases, such as respiratory tract infections, bacteremia, pneumonia, urinary tract infections, cystic fibrosis, infections of burn, catheter infections and infections of heart valve. Owing to mass usage of antibiotic agents, P. aeruginosa has shown multi-drug resistance (MDR) that always causes failure in clinical therapy. The quorum sensing system of P. aeruginosa is currently the most intensively researched.Bacterial cell-to-cell communication mediated by small diffusible signal molecules is a common phenomenon referred to as quorum sensing (QS), which is an important mechanism controlling and coordinating a number of bacterial behaviors, such as antibiotic production, biofilm formation, hydrolytic enzyme production and the generation of virulence factors in several pathogenic bacteria. QS system has been regarded as a promising target for developing novel approaches to controlling bacterial infections.The P. aeruginosa quorum-sensing network consists of two LuxIR circuits, termed LasIR and RhlIR. Lasl produces an AHL autoinducer that binds to LasR. The LasR-autoinducer complex activates a variety of target genes including lasl and also activates the expression of rhlR and rhlI encoding another quorum-sensing circuit. The crystal structure of the P. aeruginosa LasR-autoinducer complex was reported, but the crystal structure of LasR-QSIs has not been obtained yet so far.The object of the present work is to study Quorum-sensing inhibitors by ligand-based drug design (LBDD), including quantitative structure-activity relationship (QSAR) statistical model construction and database search using Surflex-Sim molecular shape similarity approach, to guide the design of novel QS inhibitors with potent activity. The main contents are as follows:(1) 3D-QSAR analysis based on N-phenylacetanoyl-L-homoserine lactones as inhibitors of bacterial quorum sensing by using CoMFA approach. The results showed that electron-donating groups at the 5-position of lactone ring are preferred, and additional steric interaction at 4-position in lactonic ring would lead to a decreased activity. (2) 3D-QSAR analysis based on some synthetic furanone compounds. Two QSAR techniques, CoMFA and CoMSIA, were used to perform QSAR analysis on a large number of synthetic furanones. Statistically significant QSAR models (q2= 0.639, r2= 0.992, F= 272.206, SEE= 0.052) were obtained. The CoMFA results suggested that on the 5-,3'-, and 4'-positions, only very small groups are preferred, and the O, N or Br atom with negative charges at 4-position will produce strong QS inhibitory potency, but the opposite result seen at 5-position. Moreover, the relationships between the different substructure moieties on the furanone core and their molecular field effects were comprehensively studied. The 3,5-position substitutes on the furanone ring were further investigated. Twelve compounds were designed and pre-estimated by the 3D-QSAR model.(3) Database search by Surflex-Sim based on halogenated furanones. Twenty-six compounds with Surflex-Sim similarity scores higher than 0.80 were regarded as good candidate compounds, in which the core structures show some deriversities, including lactam ring, pyrrolidin-2-one, pyrimidine, etc.(4) Thirty-five candidate compounds were synthesized and characterized by MS, NMR, UV and IR, and their biological activities were tested. The results are in good agreement with the prediction using the QSAR model based on chemical/physical properties of the molecules, which are valuable and applicable in aiding further development of QS inhibitory lead copounds.