Twenty-one known specialised metabolites were isolated from the flowers of Vernonanthura nudiflora (Less.) H. Rob., the structures of the compounds were established based on 1 D and 2 D NMR spectroscopic experiments. Others 28 compounds were putatively identified using the dereplication technique by UHPLC-HRMS/MS. Twenty-three of the compounds are being reported for the first time in this species. The mixture of sesquiterpene lactones piptocarphins A and B (17 + 18), and the flavone velutin (14) were tested against several microorganisms and showed promising activity against Mycobacterium tuberculosis with MIC of 15.6 μg/mL and 31.2 μg/mL, respectively. Furthermore, 17 + 18 showed greater cytotoxicity against VERO cells (IC50 = 7.0 ± 1.73) compared to compound 14 (IC50 85.0 ± 10.6 µg/mL). These findings reveal the feasibility of using the UHPLC-ESI-HRMS/MS-based dereplication strategy in complex fractions to identify specialised metabolites, moreover to V. nudiflora flowers being a source of compounds with antimycobacterial potential.
Keywords: Mycobacterium tuberculosis; Sesquiterpene lactones; UHPLC-HRMS/MS; antimicrobial activity; piptocarphins; velutin.