Novel Selective IDO1 Inhibitors with Isoxazolo[5,4-d]pyrimidin-4(5H)-one Scaffold

Abstract

Indoleamine 2,3-dioxygenase 1 (IDO1) is a promising target in immunomodulation of several pathological conditions, especially cancers. Here we present the synthesis of a series of IDO1 inhibitors with the novel isoxazolo[5,4-d]pyrimidin-4(5H)-one scaffold. A focused library was prepared using a 6- or 7-step synthetic procedure to allow a systematic investigation of the structure-activity relationships of the described scaffold. Chemistry-driven modifications lead us to the discovery of our best-in-class inhibitors possessing p-trifluoromethyl (23), p-cyclohexyl (32), or p-methoxycarbonyl (20, 39) substituted aniline moieties with IC50 values in the low micromolar range. In addition to hIDO1, compounds were tested for their inhibition of indoleamine 2,3-dioxygenase 2 and tryptophan dioxygenase, and found to be selective for hIDO1. Our results thus demonstrate a successful study on IDO1-selective isoxazolo[5,4-d]pyrimidin-4(5H)-one inhibitors, defining promising chemical probes with a novel scaffold for further development of potent small-molecule immunomodulators.

ProBiS-Dock: A Hybrid Multitemplate Homology Flexible Docking Algorithm Enabled by Protein Binding Site Comparison

“…Of the 22 commercially available and visually inspected in silico hits tested (Table S6), compounds 3 and 11 , with IC 50 values of 41.5 and 30.8 μM (Table ), respectively, showed the most promising inhibitory activity against IDO1. Subsequently, a synthetic procedure was established for the preparation of compound 11 , in which an IC 50 value of 50 μM was determined for the synthesized hit, which we described recently . The inhibition by the other purchased compounds (Table S6) was lower than 50% at 100 μM.…”

Structural Optimization and Biological Evaluation of Isoxazolo[5,4-d]pyrimidines as Selective Toll-Like Receptor 7 Agonists

“…Hydroxylammonium chloride (1.1 equiv) was dissolved in the mixture of THF/EtOH/H 2 O (2:5:1, v/v), and then appropriate aldehyde (1.0 equiv) was added . After stirring at room temperature for 30 min, THF and EtOH were removed under reduced pressure.…”

“…Appropriate aldehyde oxime ( 8a – l ) (1.0 equiv) was dissolved in anhydrous DMF and cooled to 0 °C in an ice batch. NCS (1.0 equiv) was added portionwise to the reaction mixture, which was stirred for 16 h at room temperature . Then, the mixture of n -hexane/Et 2 O (2:1, v/v) and H 2 O was added and transferred to a separating funnel.…”

“…A solution of NaOEt in EtOH was prepared from sodium (1.5 equiv) and absolute EtOH (∼30 equiv). The freshly prepared NaOEt was added dropwise to a stirred solution of 2-cyanoacetamide (1.0 equiv) in absolute EtOH at 50 °C . After the addition of NaOEt, the resulting suspension was cooled to 0 °C.…”

Protein binding sites for drug design

“…It enables the search for new active ligands by leveraging existing knowledge in the PDB. The potential of the software for drug discovery has been confirmed in vitro by the discovery of new inhibitors of human indoleamine 2,3-dioxygenase 1, an enzyme that is an attractive target for cancer therapy (Dolšak et al 2021 ).…”