Four Natural Compounds Separated from Folium Isatidis: Crystal Structures and Antibacterial Activity.

Four natural compounds were obtained by concentrating, separating and purifying from the Folium isatidis. These natural compounds have been characterized by elemental analysis, IR spectrum, NMR and single-crystal X-ray diffraction analysis. The results show that these natural compounds are 4(3H)-quinazolinone (I), 2,4(1H,3H)-quinazolinedione (II), methyl 3,4-dihydro-4-oxoquinazoline-2-carboxylate (III) and ethyl 3,4-dihydro-4-oxoquinazoline-2-carboxylate (IV). The antibacterial activity experiment showed that I and II had better activity against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Salmonella than III, IV and other multiple components, because III and IV have long branches and steric hindrance effect. Compounds I and II have planar structure, which can more easily combine with these bacteria and kill them. The above results have good guiding significance for studying the antibacterial activity for single components or mixtures from natural origin.