Bioassay-guided isolation and structure elucidation of anti-mycobacterium tuberculosis compounds from Galatella grimmii (Regel & Schmalh.) Sennikov

Background: Galatella is a genus in the family Asteraceae, represented by 35-45 species. Considering the high effectiveness of the ethyl acetate (EtOAc) fraction of G. grimmii against Mycobacterium tuberculosis (MIC = 0.5 µg/mL), a bioassay-directed fractionation of this extract was carried out.

Methods: The methanolic extract of the aerial parts of G. grimmii was obtained using maceration, then it was suspended in water and partitioned with petroleum ether, dichloromethane (CH₂Cl₂), EtOAc, and n-butanol (n-BuOH), successively. The most potent fraction (EtOAc), was selected for further isolation by Sephadex LH-20 and semi-preparative HPLC to obtain active compounds.

Results: Fractionation of the EtOAc solvent fraction resulted in the characterization of five compounds, among them, compounds 1 and 2 showed the highest anti-mycobacterial effects with MICs of 0.062 and 1.00 µg/mL against H37Rv M. tuberculosis, respectively, which were higher than those of rifampin (MIC of 1.25 µg/mL) and isoniazid (MIC of 0.31 µg/mL), as positive controls. Also, compound 1 ​​inhibited all tested strains of drug-resistant Mycobacterium (MDR and XDR). Notably, the isolated compounds have been reported for the first time from G. grimmii.

Conclusion: Due to the potent anti-mycobacterial effect of isolated compounds from G. grimmii, this study could pave the way for developing a novel class of natural anti-tuberculosis compounds.