Synthesis, structure–activity relationships andstereochemical investigations of new tricyclic pyridazinone derivatives as potential STAT3 inhibitors

Through a cell-based biological screening, the benzocinnolinone derivative 2c was identified as a promising STAT3 inhibitor. Since SAR studies on a series of compounds structurally related to 2c (1c, 2a–p, 3c, 4c, 6) showed that the latter had the most significant inhibitory activity, we investigated in depth its essential structural features. In particular, enantiomeric separation was performed, and the absolute configuration of the stereoisomers was assigned by theoretical and crystallographic studies.The biological evaluation highlighted that (S)-(-)-2c is twice as potent as (R)-(+)-2c.