1,2-Benzisothiazol-3-one 1,1-Dioxide Inhibitors of Human Mast Cell Tryptase

A library of compounds were prepared by reacting 2-(bromomethyl)-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (5) with commercially available carboxylic acids in the presence of potassium carbonate or a tertiary amine base. From this library, (1,1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl N-[(phenylmethoxy)carbonyl]-β-alanate (7b) emerged as a potent inhibitor of human mast cell tryptase (IC50 = 0.85 μM). Extension of the side chain of 7b by two carbons gave (1,1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 5-[[(phenylmethoxy)carbonyl]amino]pentanoate (7d) which was an 8-fold more potent inhibitor (IC50 = 0.1 μM). Further modification of this series produced benzoic acid derivative (1,1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 4-[[(phenylmethoxy)carbonyl]amino]benzoate (7n) which is the most potent inhibitor identified in this series (IC50 = 0.064 μM). These compounds exhibit time-dependent inhibition consistent with mechanism-based inhibition. For 7b, the initial enzyme velocity is not a saturable function of the inhibitor concentration and the initial K i could not be determined (K i > 10 μM). The steady-state rate constant, K i*, was determined to be 396 nM. On the other hand, compounds 7d and 7n are time-dependent inhibitors with a saturable initial complex. From these studies, an initial rate constant, K i, for 7d and 7n was found to be 345 and 465 nM, respectively. The steady-state inhibition constants, K i*, for 7d and 7n were calculated to be 60 and 52 nM, respectively. Compound 7n is a 13-fold more potent inhibitor than 7b, and these kinetic studies indicate that the increase in inhibitory activity is due to an increase in initial affinity toward the enzyme and not an increase in chemical reactivity. These inhibitors generally show high selectivity for tryptase, being 40-fold weaker inhibitors of elastase, being 100-fold weaker against trypsin, and showing no inhibition against thrombin. These compounds are not inhibitors of thrombin, plasmin t-PA, urokinase, and factor Xa (IC50 > 33 μM). In the delayed-type hypersensitivity (DTH) mouse model, a model of skin inflammation, a 5% solution of 7d reduced edema by 69% compared to control animals.