Indoleamine‐2,3‐dioxygenase‐1 (IDO1) is a critical immunoregulatory enzyme responsible for the metabolism of tryptophan during inflammation and disease. Based on a 2,5‐dimethylfuran framework, examples of indoleamine‐2,3‐dioxygenase 1 (IDO1) inhibitors containing a diverse set of boron‐based functional groups (closo‐1,2‐ and 1,7‐carborane, boronic acids and esters, and benzoxaboroles) are reported. The novel boron derivatives display low micrometer affinity for the human recombinant enzyme, with IC50 values ranging from 8 to 60 μM. Superior results are observed for the closo‐carborane compounds which demonstrate a significant improvement in potency over their phenyl analogues, with inhibition of the IDO1 enzyme increased by up to ≈80%.