Influence of compound substructures on potency and selectivity on human COX-1 and COX-2. Rows in the heatmap are indexed by the isoenzyme type whereas columns correspond to compound substructures. Substructures are depicted in red within arbitrary molecules presenting it. The color represents the average influence (pIC50 units) of each substructure on bioactivity. Red corresponds to an average increase in bioactivity, whereas blue indicates a deleterious effect. Well-known chemical moieties, e.g. pyrrole rings (c), were singled out as selectivity determinants. For instance, substructure d is present in sulfonamides such as diflumidone, and substructure b in selective 1,2-diarylpyrroles COX-2 inhibitors.