Synthesis And Activity Studies Of Novel Dispiro Pyrrolidine Compounds As Potential Antimycobacterial Agents

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Date
2015-11
Authors
Ang, Chee Wei
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Publisher
Universiti Sains Malaysia
Abstract
A mini library of fifty two highly functionalized dispiro pyrrolidines were synthesized successfully using 1,3-dipolar cycloaddition. This reaction is proved to be highly regioselective, giving only one set of regioisomer as product. These compounds were characterized using various instrumental methods such as CHN, NMR, mass spectrometry and X-ray analysis. The antimycobacterial activity of the newly synthesized dispiro pyrrolidines were tested against Mycobacterium tuberculosis H37RV strains using BacTiter-Glo Microbial Cell Viability assay. Compound 3c, or 4´-(4-bromophenyl)-1´-methyldispiro[acenaphthylene-1,2´- pyrrolidine-3´,2˝-indane]-2,1˝(1H)-dione was found to be the most potent among all, with IC50 of 2.20 μM and MIC of 12.5 μM. Comparing with standard drugs, compound 3c was found to be more potent than cycloserine and pyrimethamine by 10.7-, 11.0-fold at IC50 and more than 8-fold at MIC. Compound 3c also exerted a comparable activity with ethambutol but less potent when compared to isoniazid. Cytotoxicity study was performed using Hs27 and primary colorectal fibroblasts to screen the tolerability of the active compounds in human cells. The lead compound 3c was proven to be non-toxic up to 250 μM and recorded a good selectivity index of >20. Molecular docking analysis was carried out to understand the important interactions of the active compounds with the target enzyme, enoyl-acyl carrier protein reductase (InhA). This class of compounds were found to dock at the substrate binding site, which can potentially compete with the fatty acyl substrate and inhibit the enzyme. Compound 3c especially, displayed the important dual hydrogen bonding network with catalytic residue Tyr 158 and the nucleotide cofactor, which is a conserved feature in most of the known inhibitors identified so far. To support the in silico study, direct protein-ligand binding assay was used based on the intrinsic tryptophan fluorescence of the protein. The binding of 3c to InhA resulted in a conformational change of the protein, causing concentration- and time-dependent fluorescence quenching. With the urgent need of new antitubercular agents, these findings have established dispiro pyrrolidines as a practical lead for TB drug discovery.
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Synthesis
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