Synthesis and mycobacterial evaluation of 5-substituted-6-acetyl-2-amino-7-methyl-5,8-dihydropyrido-[2,3-d]pyrimidin-4(3H)-one derivatives.

5-Substituted-6-acetyl-2-amino-7-methyl-5,8-dihydropyrido[2,3-d]pyrimidin-4(3H)-one derivatives were synthesized and evaluated against Mycobacterium tuberculosis H37Rv, Mycobacterium aurum, Escherichia coli, and Staphylococcus aureus as well as a human monocyte-derived macrophage (THP-1), and murine macrophage (RAW 264.7) cell lines to assess their antibacterial and cytotoxic potential, respectively. The compounds showed activity in the range of 1.95-125 µg/ml against M. tuberculosis but showed no activity against M. aurum, E. coli, and S. aureus, indicating selectivity towards slow-growing mycobacterial pathogens. The compounds exhibited very low to no cytotoxicity up to 500 µg/ml concentration against eukaryotic cell lines. The most potent molecule, 2l, showed a minimum inhibitory concentration of 1.95 µg/ml against M. tuberculosis H37Rv and a selectivity index of >250 against both the eukaryotic cell lines. Furthermore, 2l showed moderate inhibition of whole-cell mycobacterial drug-efflux pumps when compared to verapamil, a known potent inhibitor of efflux pumps. Thus, derivative 2l was identified as an antituberculosis hit molecule, which could be used to yield more potent lead molecules.