Derivatives of 2-[(alkylsulfonyl) oxy]-1H-isoindole-1, 3 (2H)-diones (N-(sulfonyloxy) phthalimides) with ring substituents in the 6-position were found to exhibit enhanced inhibitory potency and selectivity for HLE. The most potent inhibitor of HLE in this series was 6-amino-2-[(methylsulfonyl) oxy]-1H-isoindole-1, 3 (2H)-dione10 with ak obs [I] of 110,000 M− 1 s− 1.