Second‐Generation CD73 Inhibitors Based on a 4,6‐Biaryl‐2‐thiopyridine Scaffold

Abstract Various series of 4,6‐biaryl‐2‐thiopyridine derivatives were synthesized and evaluated as potential ecto‐5′‐nucleotidase (CD73) inhibitors. Two synthetic routes were explored and the coupling of 4,6‐disubstituted 3‐cyano‐2‐chloro‐pyridines with selected thiols allowed us to explore the structural diversity. Somehow divergent results were obtained in biological assays on CD73 inhibition using either the purified recombinant protein or cell‐based assays, highlighting the difficulty to target protein‐protein interface on proteins existing as soluble and membrane‐bound forms. Among the 18 new derivatives obtained, three derivatives incorporating morpholino substituents on the 4,6‐biaryl‐2‐thiopyridine core were shown to be able to reverse the adenosine‐mediated immune suppression on human T cells. The higher blockade efficiency was observed for 2‐((3‐cyano‐4,6‐bis(4‐morpholinophenyl)pyridin‐2‐yl)thio)‐N‐(isoxazol‐3‐yl)acetamide (with total reversion at 100 μM ) and methyl 2‐((3‐cyano‐4,6‐bis(4‐morpholinophenyl)pyridin‐2‐yl)thio)acetate (with partial reversion at 10 μM). Thus, this series of compounds illustrates a new chemotype of CD73 allosteric inhibitors.