A series of 2-(3-aryl-1-oxo-2-propenyl)-3-methylquinoxaline-1,4-dioxides 1a-l and 2-acetyl-3-methylquinoxaline-1,4-dioxide 2 were evaluated against Mycobacterium tuberculosis H(37)Rv. With the exception of the 4-nitro analog 1k, significant antitubercular potencies were observed in series 1 and 2 which have IC(50) values in the range of 1-23 microM. Negative correlations were noted between the IC(50) values of 1a-j, l towards M. tuberculosis and both the sigma and pi constants of the substituents in the benzylidene aryl ring. In particular, 1h emerged as a lead compound having IC(50) and IC(90) figures of 1.03 microM and 1.53 microM, respectively. This molecule affected respiration in rat liver mitochondria which is likely one way that 1h and the bioactive analogs exert their antitubercular properties. The quinoxaline 2, which lacks an alpha,beta-unsaturated group, has no effect on mitochondrial respiration using concentrations which inhibit the growth of M. tuberculosis.
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