Previously unknown N-aminosaccharin was prepared in good yield via the one-step direct amination of saccharin sodium salt with hydroxylamine-O-mesitylenesulfonic acid (MSH) and its reactivity investigated. N-aminosaccharin and its derivatives were tested against hCA isoforms and the parent compound was identified to be a selective, low micromolar inhibitor (K_i= 8.8 μM) of hCA I. These findings provide a ligand-efficient starting point for the design of potent hCA I inhibitors – a promising drug target for retinal/cerebral edema treatment.