Synthesis of fluorescein aromatic esters in the presence of P2O5/SiO2 as catalyst and their hydrolysis studies in the presence of lipase

A series of fluorescein aryl esters were synthesized by the esterification of fluorescein with carboxylic acids in the presence of P2O5/SiO2 and their hydrolytic properties were investigated. The rate of hydrolysis in the presence or absence of lipase, due to the increase of fluorescein concentration, was measured by monitoring of fluorescence of the solution and correlated with enzyme activity. In addition, the substitute effect on the aromatic ring of fluorescein esters was studied. In contrast to fluorescein diacetate or dibutyrate, fluorescein dibenzoate and fluorescein bis(4-methylbenzoate) were found to be better substrates for the fluorometric assay of lipase with the higher rate of hydrolysis and better Km value, respectively. As little as 9.3 ng mL−1 of lipase can be detected with fluorescein bis(4-methylbenzoate).