Isochlorogenic Acid Glucosides from the Arabian Medicinal Plant Artemisia sieberi and Their Antimicrobial Activities.

A phytochemical investigation of the stems of the Arabian plant Artemisia sieberi afforded three new isochlorogenic acid derivatives, namely isochlorogenic acid A-3'- O - β -glucopyranoside ( 1 ), isochlorogenic acid A-3'- O - β -glucopyranoside methyl ester ( 2 ), and isochlorogenic acid C-3'- O - β -glucopyranoside ( 3 ), obtained along with thirteen known secondary metabolites belonging to distinct structural classes. The structures of the new metabolites were elucidated by modern spectroscopic techniues based on high-resolution mass spectrometry (HR-ESIMS) and 1D/2D nuclear magnetic resonance (NMR). All isolated compounds were tested for their potential antimicrobial activity against four different bacterial strains ( Bacillus subtilis , Staphylococcus aureus , Escherichia coli , and Pseudomonas aeruginosa ), in addition to a fungal strain ( Candida tropicalis ), The results were expressed as the diameter of the clear zone (in millimetres) around each well. Compounds 1 and 3 (isochlorogenic acid A-3'- O - β -glucopyranoside and isochlorogenic acid C-3'- O - β -glucopyranoside, respectively) displayed remarkable antifungal effect and potent antibacterial activities against B. subtilis and S. aureus , respectively. 3 α ,4 α -10 β -trihydroxy-8 α -acetyloxyguaian-12,6 α -olide ( 6 ) and angelicoidenol 2- O - β -d-glucopyranoside ( 9 ) emerged as interesting dual antibacterial (selective on P. aeruginosa )/antifungal agents.