Discovery of 5-(N-hydroxycarbamimidoyl) benzofuran derivatives as novel indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors

Human indoleamine 2,3-dioxygenase 1 (hIDO1) and tryptophan dioxygenase (hTDO) are rate-limiting enzymes in the kynurenine pathway (KP) of L-tryptophan (L-Trp) metabolism and are becoming key drug targets in the combination therapy of checkpoint inhibitors in immunoncology. To discover a selective and potent IDO1 inhibitor, a structure-activity relationship (SAR) study of N-hydroxybenzofuran-5-carboximidamide as a novel scaffold was investigated in a systematic manner. Among the synthesized compounds, the N-3-bromophenyl derivative 19 showed the most potent inhibition, with an IC50 value of 0.44 mu M for the enzyme and 1.1 mu M in HeLa cells. The molecular modeling of 19 with the X-ray crystal structure of IDO1 indicated that dipole-ionic interactions with heme iron, halogen bonding with Cys129 and the two hydrophobic interactions were important for the high potency of 19.

Automated summary

Through a structure-activity relationship study, the N-3-bromophenyl derivative 19 was identified as the most potent inhibitor of IDO1, with an IC50 value of 0.44 μM. Molecular modeling revealed that interactions with heme iron, halogen bonding with Cys129, and hydrophobic interactions were crucial for the high potency of compound 19.