We report the initial results of the synthesis and biochemical evaluation of a series of aminosulfonate based compounds of phenol and the determination of the pKa of the parent phenol in an attempt to investigate the role of this physicochemical factor in the irreversible inhibition of the enzyme estrone sulfatase (ES). The results of the study show that there is a strong correlation between the observed pKa and inhibitory activity. We postulate that the stability of the phenoxide ion, as indicated by the acid dissociation constant, is an important factor in the irreversible inhibition of this enzyme.