Design, Synthesis, and Evaluation of the Antitubercular Activity of 5-Phenyl Substituted-5, 6-dihydropyrido[2, 3-<i>d</i>]pyrimidine-4, 7(<i>3H</i>, <i>8H</i>)-dione Compounds

Tuberculosis (TB) remains a major public health challenge, with research on new anti-TB drugs crucial for global TB elimination efforts. Here, we report a novel class of anti-TB agents. Especially, compounds <b>5b</b> and <b>5j</b> exhibited the highest activity [minimum inhibitory concentration (MIC) H37Rv: 0.16 and 0.12 μg/mL]. Chiral resolution was performed on compounds <b>5b</b> and <b>5j</b>; the isomers were evaluated for their activity and safety, confirming that the <i>R</i>-isomer <b>5bb</b> and <b>5jb</b> displayed significant anti-TB activity (MIC H37Rv: 0.03-0.06 μg/mL; MDR-<i>Mtb</i>: 0.125-0.06 μg/mL) and low hERG toxicity. Further evaluations on <b>5bb</b> and <b>5jb</b> demonstrated good metabolic stability, favorable kinetic parameters and oral bioavailability (F: 56.7 and 63.8%, respectively). The results of <i>in vivo</i> activity assessment indicate that <b>5bb</b> and <b>5jb</b> exhibit protective and therapeutic effects on zebrafish larvae and adult zebrafish infected with <i>Mycobacterium marinum</i>. Based on these results, compounds <b>5bb</b> and <b>5jb</b> are considered promising candidates for further in-depth studies.