Carborane-Containing Hydroxyamidine Scaffolds as Novel Inhibitors of Indoleamine 2,3-Dioxygenase 1 (IDO1)

Two new carborane-containing hydroxyamidines were prepared as potential inhibitors of the indoleamine 2,3-dioxygenase 1 (IDO1) enzyme. One compound (3) displayed low micromolar (1.90 μM) inhibition of IDO1, with the related compound (4) displaying >5-fold lower inhibitory activity, i.e. subtle differences in structure between the two carborane compounds led to dramatic changes in inhibitor binding. In silico docking experiments unravel a possible molecular mechanism that is consistent with the observed difference in IDO1 binding for 3 and 4 and also for the phenyl bioisosteres 1 and 2.