Antistaphylococcal Activity of Novel Salicylanilide Derivatives

This study examined the antibacterial properties of nineteen benzoxazole, isoniazid, ethionamide and salicylanilide derivatives against Staphylococcus aureus (S. aureus). It was found that three salicylanilide-derived compounds demonstrated antistaphylococcal activity: 5-Chloro-2-hydroxy-N-(4-(trifluoromethyl)phenyl)benzamide (5-Cl-4'-CF3- SAL), 4-chloro-2-(3-chlorophenylcarbamyoyl)phenyl)-2-(benzyloxycarbonylamino)propanoate (AIM31) and 4-chloro-2- (4-(trifluoromethyl)phenylcarbamoyl)phenyl acetate (AIM33). Investigation of the chemical structures of these three compounds and comparison with a non-inhibitory salicylanilide compound (i.e. 5,3'-diCl-SAL) illustrated that different combinations of chemical groups at defined positions on the salicylanilide core structure had a marked influence on antistaphylococcal activity. The most effective compound was AIM33 which inhibited staphylococcal growth and displayed an initial MIC value of 3.12 μg ml-1 and subsequent investigation revealed that an MIC as low as of 0.5 μg ml-1 was achievable. In this case, the dual presence of a trifluoromethyl group and an acetylated phenolic hydroxyl to the salicylanilide core structure led to greatly enhanced activity.