A novel daucosterol derivative and antibacterial activity of compounds from Arctotis arctotoides

Arctotis arctotoides is a perennial herb used medicinally for the treatment of various ailments in the Eastern Cape, South Africa. Different extracts of the plant were investigated for their antimicrobial constituents. This led to the isolation and identification of a new daucosterol derivative 3-O-[β-D-(6′-nonadeanoate) glucopyranosyl]-β-sitosterol and seven known compounds namely: serratagenic acid, stigmasterol, daucosterol, zaluzanin D, dehydrocostuslactone, nepetin, and pedalitin. The structures of the compounds were elucidated on the basis of spectral analysis, including homo and hetero nuclear correlation NMR experiments (COSY, NOESY, HMQC, HMBC) and mass spectra as well as by comparison with available data in the literature. The compounds exhibited antibacterial activity except stigmasterol, daucosterol and dehydrocostuslactone. Nepetin was the most active against Bacillus subtilis and Staphylococcus aureus with the minimum inhibitory concentrations of 4 μg mL-1 and 31 μg mL-1, respectively, while others exhibited moderate activity.