The crystal structure of the iodo analog of -(bromoacetyl)amino-4-chlo
ro-3-methoxyisocoumarin, an inhibitor of human neutrophil elastase (HN
E), C12H9ClINO4, has been determined. The isocoumarin ring system is h
ighly planar, with the carbonyl group of the amide function being copl
anar with the isocoumarin ring.