The discovery and optimization of a series of 2-aminobenzoxazole derivatives as ChemR23 inhibitors.

A structural class of 2-aminobenzoxazole derivatives possessing biphenyltetrazole was discovered to be potent human ChemR23 inhibitors. We initially tried to improve the potency of compound 1, which was found through in-house screening using the human plasmacytoid dendritic cell (pDC)-like cell line CAL-1. The introduction of a chiral methyl moiety at a benzylic position in a center of compound 1 showed a large impact on the inhibitory activity against calcium signaling of ChemR23 induced by the natural ligand chemerin. As a result of further investigations at the benzylic position, (R)-isomer 6b was found to show a 30-fold increased potency over desmethyl compound 1. In addition, an extensive structure-activity relationship study on the benzoxazole moiety successfully led to a further increase in the potency. The antagonistic effect of the compounds was based on the induction of ChemR23 internalization. In addition, we observed that compound 31, which contained an amide moiety on benzoxazole, inhibited chemotaxis of CAL-1 cells induced by chemerin in vitro. These results suggest that our ChemR23 inhibitors are attractive compounds for the treatment of pDC-related autoimmune diseases, such as systemic lupus erythematosus and psoriasis.