Structure-Based Design,Synthesis And Screening Of Novel Inhibitors Of β-Ketoacylacyl Carrier Protein Synthase Ⅲ (FabH) As Antibacterial Agents

Tuberculosis is the leading global cause of morbidity and mortality owing to an infectious bacterial agent, Mycobacterium tuberculosis. An estimated incidence rate of infecting 8 million and killing of 3 million people annually continue to make infection by Mycobacterium tuberculosis a serious worldwide health problem. The situation has recently been exacerbated by the human immunodeficiency virus(HIV) pandemic and the increased prevalence of multi-drug resistant(MDR) strains of Mycobacterium tuberculosis. In 1993, tuberculosis was declared a global emergency by the World Health Organization (WHO). Effective treatment of tuberculosis infections requires the identification of both new drugs and drug targets.As fatty acid biosynthesis in pathogenic microorganisms is essential for cell viability, the enzymes involved in the FAS pathway has recently attracted considerable interest as a genomics-driven target for antibacterial drug discovery. β-Ketoacyl-acyl carrier protein synthase III (KAS III, FabH) is the initiator of the fatty acid chain elongation cycle and plays an essential and regulatory role for the entire biosynthetic pathway. The pivotal role of this enzyme, combined with its unique structure features and ubiquitous occurrence in bacteria, has made it an excellent molecular target for the development of novel antibacterial agents. Structure-based design, synthesis and SAR of the novel inhibitors of β-ketoacyl-acyl carrier protein synthase III were reported in this paper.Combinatorial chemistry and library design have been reconciled by applying medicinal chemistry concepts to virtual library design. Based on crystal structure information and substrate specificity of mtFabH, and with the SAR revealed in literature, a novel virtual library (57917 compounds) of mtFabH inhibitors was created for further virtual screening by DOCK program. Forty-four compounds were selected for synthesized with some new synthetic schemes, including seventeen 5-oxo-tetra-hydro-furan-3-carboxylic acids, twenty-six 5-oxo-2, 5-dihydro-1H-pyrrole-3- carboxy-lic acids, forty-three compounds have not been found in literature.With benzaldehyde as starting materials, a new synthetic scheme was developed for the synthesis of 5-oxo-tetra- hydro-furan-3-carboxylic acids through substitution, Stobbe condensation, dehydration, esterification, Aldol condensation and hydrolyza-tion reaction. Also a facile scheme was designed for synthesis of 5-oxo-2, 5-dihydro-1H- pyrrole-S-carboxylic acids, and it worked well.The antibacterial activity was evaluated with mycobacterium phlei. Most of the prepared compounds showed remarkably anti-mycobacterium phlei activity at a dose of lmM. The activities of compounds TB040710,TB040715, TB040723 and TB041116 are comparable to TB040212, the positive control. Therefore, they are regarded as valuable compounds for further study to develop new antibacterial drugs. In addition, compounds TB040710 and TB040715 showed modest antibacterial activity with an MIC for Staphylococcus aureaus ATCC29213 of 16mg/L and 8.0mg/L, respectively. In the HLF cytotoxicity test by MTT method, 5-oxo-tetra- hydro-furan-3-carboxylic acids have lower effect than the positive control. Compound TB040413 and TB040521 were not active against FAS I protein used to generate NADP for this assay.Some SAR could be found from the results of pharmacological tests above. For 5-oxo-tetrahydro-furan-3-carboxylic acids, the saturated aliphatic side-chain, benzene ring contained electron-withdrawing groups and syn-isomer at a position of the γ-lactone ring make great contribution to the antibacterial activities; while methyl, methoxyl might decrease the activities. Most of 5-oxo-2, 5-dibydro-1H-pyrrole-3-carboxylic acids have less antibacterial activity than 5-oxo-tetrahydro-furan-3-carboxylic acids. It has been found that 2, 6-dichlorobenzyl group played a key role in this kind of compounds. Analogues lacking this moiety demonstrated greatly reduced activity against mycobacterium phlei. These would be very helpful for new designs of the compounds of the kind.In conclusion, most of the synthesized compounds have definite anti-myco-bacterium phlei activity and they are promising for developing new potent antibacterial agents.