Aloesin (1) and 7-O-methyl-6'-O-coumaroylaloesin (2) were isolated from the leaf latex of Aloe monticola Reynolds, and their structures determined on the basis of NMR and mass spectroscopic analyses. The antimicrobial activities of the isolated chromones were evaluated against 21 bacterial and 4 fungal strains. Both compounds displayed antibacterial and antifungal effects against most bacterial and fungal strains tested, but their action was more prominent against Salmonella typhi, Shigella dysentery and Staphylococcus aureus (MIC = 10 μg/ml). Acute toxicity tests on mice revealed that neither the latex nor the isolated compounds possess toxicity up to a dose of 2000 mg/kg, signifying an oral LD50 greater than 2000 mg/kg. The results indicate that A. monticola possesses genuine in vitro antimicrobial effect attributed in full or in part to the presence of the isolated chromones in the latex.
Keywords: 7-O-methyl-6′-O-coumaroylaloesin; Aloe monticola; aloesin; antimicrobial; chromones.