Structure activity relationship studies of alkynyl 6-nitroquinoxalines as potential anti-tuberculosis agents

In this study, a series of quinoxaline derivatives were designed and evaluated for activity against Mycobacterium tuberculosis (H₃₇Rv strain). Several compounds displayed promising antimycobacterial activity, with multiple derivatives showing minimum inhibitory concentration (MIC₉₀) values in the low micromolar (<10 μM) range. Among these, compounds 4d and 3b were the most active in the series, with MIC values of 0.97 μM and 0.94 μM, respectively. Structure activity relationship (SAR) analysis revealed that the 6-nitroquinoxaline core is essential for activity, while the alkynyl linker plays a critical role in maintaining antimycobacterial potency. The presence and positioning of a hydroxyl group on the alkynyl side chain influenced activity, with tertiary alcohol derivatives generally providing improved potency. Among the synthesized compounds, compound 4 h exhibited a comparatively favorable in vitro selectivity index but was limited by low aqueous solubility. These findings highlight key structural characteristics within this scaffold and offer valuable insight for the further optimization of quinoxaline-based anti-tuberculosis agents.