Structure-Based Development of 3,4-Fused Tricyclic Benzofuran Derivatives as Polyketide Synthase 13 Inhibitors with Negligible hERG Inhibition

Polyketide synthase 13 (Pks13) is vital for synthesizing mycolic acid, which are essential for the survival of <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>). Compounds that target Pks13 hold significant promise for developing new chemical entities for multidrug-resistant TB. The early lead benzofuran-3-carboxamide TAM16, demonstrated robust in vivo efficacy in murine models of tuberculosis infection; however, its further advancement was halted due to the cardiotoxicity associated with hERG inhibition. We implemented a conformational restriction strategy to explore the chemical space of 3,4-fused tricyclic benzofurans and indoles employing a structure-based design approach. Representative compounds were identified as Pks13-TE inhibitors, showing resistance against mutant strains from coumestan-resistant <i>Mtb</i> colonies. Notably, <b>29</b> and <b>30</b> exhibited potent antitubercular activity against <i>Mtb</i> H37Rv strain (MIC = 0.0156-0.0313 μg/mL), with negligible hERG inhibition (IC₅₀ > 100 μM) suggesting that the 3,4-fused tricyclic benzofurans may present promising scaffold for developing Pks13-TE inhibitors without hERG liability.