Formylchromone inhibits a human protein tyrosine phosphatase PTP1B with a IC50 value of 73 μM. The chemical reactivity of formylchromone was adjusted by substitution at various positions of the formylchromone skeleton. In an initial assessment of the structure–activity relationship, the most potent inhibitor showed an IC50 of 4.3 μM against PTP1B and strong or medium selectivity against other human PTPases, LAR and TC-PTP. This compound, ...