Selective Toll-like receptor 7 agonists with novel chromeno[3,4-d]imidazol-4(1H)-one and 2-(trifluoromethyl)quinoline/ quinazoline-4-amine scaffolds.

Toll-like receptors (TLRs) are promising targets for treatment of viral infections, autoimmune diseases, and cancers. Here, two new series of selective small-molecule TLR7 agonists with novel scaffolds and good selectivity over TLR8 are described, some with potencies in the low micromolar range. 8-Hydroxy-1-isobutylchromeno[3,4-d]imidazol-4(1H)-one (26) from the first series was designed and synthesized on the basis of previously described TLR7 antagonist 2, and is shown to be a selective TLR7 agonist (EC, 1.8 μM). The second series was based on 2-(trifluoromethyl)quinolin-4-amine and 2-(trifluoromethyl)quinazolin-4-amine scaffolds, which were defined according to our in-house ligand-based virtual screening protocol. Further synthesis of a focused library of analogs, biological evaluation, and docking studies provided systematic exploration of the structure-activity relationships, which indicate that a secondary or tertiary amine with smaller flexible alkyl substituents up to three carbon atoms in length, or bulkier rigid aliphatic rings is required at position 4 on 2-(trifluoromethyl)quinoline/quinazoline scaffold for potent TLR7 agonist activity. The influence of selected TLR7 agonists on cytokine production is also reported showing that N-cyclopropyl-2-(trifluoromethyl)quinazolin-4-amine (46) is able to induce increased levels of IL-6 and IL-8. These data demonstrate successful in-silico definition of novel TLR7 versus TLR8-selective compounds as promising chemical probes for further development of potent small-molecule immunomodulators.