Isolation and chemical characterization of secondary metabolites from Gazania rigens and their antimicrobial and cytotoxic activities

Phytochemical study of Gazania rigens whole plant led to isolation and structural characterisation of six known compounds including lupeol (1), lupenone (2), β-sitosterol 3-O-β-glucopyranoside (3), dunalianoside D (4), 3,5-di-O-caffeoylquinic acid (5), and tachioside (6). Compounds (1–4, and 6) were isolated for the first time. The structures of the isolated compounds were elucidated using different spectroscopic analyses such as 1H,13C, and DEPT NMR analyses, besides HR-ESI-MS analysis. The isolated compounds and fractions were screened for in vitro antimicrobial activity against various bacterial and fungal strains. Only lupeol (1) exhibited a moderate antibacterial activity against K. pneumoniae with IC50 value of 19.05 µg/mL. The cytotoxic potential of the total ethanol extract and its derived fractions of G. rigens was evaluated against the MDA-MB-468 TNBC cell line using MTT assay. The petroleum ether, EtOAc and n-BuOH fractions exhibited a moderate inhibitory action with IC50 values of 22.42 ± 0.63, 25.55 ± 1.53, and 28.07 ± 0.63, respectively.