Synthesis of 2-arylbenzothiazole derivatives and their application in bacterial detection

A series of 2-arylbenzothiazole derivatives have been prepared as fluorogenic enzyme substrates in order to detect aminopeptidase, esterase, phosphatase and β-galactosidase activity in clinically important Gram-negative and Gram-positive bacteria. Substrates were incorporated into an agar-based culture medium and this allowed growth of intensely fluorescent bacterial colonies based on hydrolysis by specific enzymes. Substrate 20 targeted L-alanine aminopeptidase activity and was hydrolysed exclusively by a range of Gram-negative bacteria and inhibited the growth of a range of Gram-positive bacteria. Substrate 19a targeted β-alanyl aminopeptidase activity and generated fluorescent colonies of selected Gram-negative species including Pseudomonas aeruginosa. Substrate 21b targeted C8-esterase activity and resulted in strongly fluorescent colonies of selected species known to harbour such enzyme activity (e.g., Salmonella and Pseudomonas). Most Gram-negative species produced colonies with an intense blue fluorescence due to hydrolysis of phosphatase substrates 24a-c and substrate 24c was also hydrolysed by strains of Staphylococcus aureus. Compounds 26b and 26c targeted β-galactosidase activity and generated strongly fluorescent colonies with coliform bacteria that produced this enzyme (e.g., Escherichia coli).