New Indolyl Substrates for Chromogenic and Fluorogenic Detection of Esterase Activity in Solution

Three indolyl substrates for chromogenic detection of esterase activity have been synthesised. Hydrolysis of the non-coloured esters 1 catalysed by hog liver esterase, affords after oxidation the coloured water soluble indolinones 3 with absorption maxima at 478, 502 and 540 nm, respectively. The rate of hydrolysis was found to be slower compared to that of p-nitrophenyl acetate in all three cases. However, the chromophores obtained after hydrolysis and oxidation are advantageous in that they have their absorption maxima at longer wavelengths than p-nitrophenolate. Hydrolysis of 1a was also monitored using fluorescence spectroscopy since the obtained intermediate 2a is fluorescent.