Antimicrobial sesquiterpene lactones from Artemisia sieberi

Two new sesquiterpene lactones 3R, 8R-dihydroxygermacr-4(15),9(10)-dien-6S,7S,11RH,12,6-olide (1) and 1R, 8S-dihydroxy-11R,13-dihydrobalchanin(2), together with two known compounds 11-epiartapshin (3) and 3′-hydroxygenkwanin (4), were isolated from Artemisia sieberi. Their structures were elucidated by 1D, 2D NMR, MS, and X-ray diffraction. Compound 4 inhibited Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus with Minimal inhibitory concentration values of 50 and 25 μg/disk, respectively. All the isolated compounds exhibited moderate antifungal activities.