Structures of compounds used to evaluate esterase activity profiles. A) α-naphthyl acetate is a non-specific esterase substrate and is used to visualize general esterase activity. B) S-ANAA and C) R-ANAA are chiral esters previously used by Yamazaki et al. to demonstrate stereoselective preferences between cancer and normal cells. D) N-acetyl-L-alanyl-p-nitroanilide releases p-nitroanaline upon hydrolysis and is routinely used to monitor OPH activity.