Synthesis of a Small Library of Nature-Inspired Xanthones and Study of Their Antimicrobial Activity.

A series of thirteen xanthones - was prepared based on substitutional (appendage) diversity reactions. The series was structurally characterized based on their spectral data and HRMS, and the structures of xanthone derivatives , , and were determined by single-crystal X-ray diffraction. This series, along with an in-house series of aminated xanthones - was tested for in-vitro antimicrobial activity against seven bacterial (including two multidrug-resistant) strains and five fungal strains. 1-(Dibromomethyl)-3,4-dimethoxy-9-xanthen-9-one () and 1-(dibromomethyl)-3,4,6-trimethoxy-9-xanthen-9-one () exhibited antibacterial activity against all tested strains. In addition, 3,4-dihydroxy-1-methyl-9-xanthen-9-one () revealed a potent inhibitory effect on the growth of dermatophyte clinical strains ( FF5, FF1 and FF9), with a MIC of 16 µg/mL for all the tested strains. Compounds and showed a potent inhibitory effect on two virulence factors: germ tube and biofilm formation.