Antimicrobial guaianolide sesquiterpenoids from leaves of the Saudi Arabian plant Anvillea garcinii.

Anvillea garcinii is a medicinal plant used in the Arab region for intestinal diseases, lungs and liver diseases, digestive problems, and as an anti-diabetic. Repeated chromatographic purifications of A. garcinii leaves led to the isolation of two undescribed guaiane sesquiterpene lactones (1-2), along with four known germacranolides (3-6). The structures of the new compounds were established using spectroscopic (1D, 2D NMR) and spectrometric methods (ESIMS). Compounds 1 and 2 were shown to possess hydroxyl substituents at position 9, a structural feature rarely reported in guaianolide-type sesquiterpenes. The antimicrobial activity of 1-6 was screened against five different gram-positive/negative bacteria and the fungi Candida albicans and C. parapsilosis. Compounds 1 and 2 displayed remarkable antifungal effect against C. albicans and C. parapsilosis and potent antibacterial activities against Staphylococcus aureus.