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.