Anthraquinones from the Roots of Kniphofia insignis and Evaluation of Their Antimicrobial Activities

Abstract

Sequential extraction using a cold maceration method and column chromatographic separation of the roots Kniphofia insignis headed to the isolation of three anthraquinones: one monomeric anthraquinone (1) and two dimeric anthraquinones (2 and 3). It was further purified by Sephadex LH-20 and recrystallized. The structures of these compounds were established based on the spectroscopic analyses including NMR (1H-NMR and 13C-NMR and infrared) and comparison with reported literatures. In an in vitro antimicrobial assay of the crude extracts, the isolated compounds were made against four bacterial strains (S. aureus ATCC 25923, B. subtilis ATCC 6633, E. coli ATCC 35218, and P. aeruginosa ATCC 27853) and Fusarium spp. fungal strain. In the crude extracts of chloroform, substantial antimicrobial activity was seen with the highest activity against B. subtilis (16 mm) and E. coli (22 mm). Meanwhile, compound 1 has a better zone of inhibition with 14 mm against P. aeruginosa, whereas compound 2 showed better activity (13 mm) against Fusarium spp. fungal strain.