A series of sulfonamides was obtained by reacting substituted-2-(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxamido)benzoic acids with aromatic sulfonamides incorporating primary amino moieties. The new compounds were investigated as inhibitor of four carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the human (h) hCA I and II, and the α- and β-class CAs from the pathogenic bacterium Vibrio cholerae, VchCAα and VhcCAβ. hCA I was effectively inhibited by the new sulfonamides, with inhibition constants in the range of 4.9-96.0nM. hCA II also showed high affinity for these compounds (KIs of 2.1-22.3nM), whereas the two bacterial enzymes were less effectively inhibited, with KIs of 281-3192nM for VchCAα, and 5.40-9.26µM for VhcCAβ. As the physiological function hCA I is poorly understood, and it was recently shown to be involved in the pathogenesis of cerebral malaria and amyotrophic lateral sclerosis, selective and effective inhibitors may be useful as tools or drugs for better understanding this abundant isoform.