The bioassay-guided fractionation of the EtOH extract of the leaves of Galenia africana led to the isolation of three known flavonoids, (2S)-5,7,2′-trihydroxyflavanone (1), (E)-3,2′,4′- trihydroxychalcone (2), and (E)-2′,4′-dihydroxychalcone (3), and the new (E)-3,2′,4′-trihydroxy-3′-methoxychalcone (4). Compounds 1 and 3 exhibited moderate antituberculosis activity. During synergistic studies, a combination of compound 4 and an existing antituberculosis drug, isoniazid, reduced their original MICs 4-fold, resulting in a fractional inhibitory concentration of 0.50. The most pronounced effect was demonstrated by compound 1 and isoniazid reducing their MICs 16-fold and resulting in an FIC of 0.12. Both EtOH extract and isolated compounds failed to exhibit any NADPH oxidase activity at 800.0 μM concentrations, indicating that mycothiol disulfide reductase is not the target for their antituberculosis activity.
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