Trimethyl Lock: A Stable Chromogenic Substrate for Esterases

p-Nitrophenyl acetate is the most commonly used substrate for detecting thecatalytic activity of esterases, including those that activate prodrugs in human cells. Thissubstrate is unstable in aqueous solution, limiting its utility. Here, a stable chromogenicsubstrate for esterases is produced by the structural isolation of an acetyl ester andp-nitroaniline group using a trimethyl lock moiety. Upon ester hydrolysis, unfavorablesteric interactions between the three methyl groups of this o-hydroxycinnamic acidderivative encourage rapid lactonization to form a hydrocoumarin and releasep-nitroaniline. This “prochromophore” could find use in a variety of assays.