Second-Generation Lymphocyte Function-Associated Antigen-1 Inhibitors:  1H-Imidazo[1,2-α]imidazol-2-one Derivatives

A novel class of lymphocyte function-associated antigen-1 (LFA-1) inhibitors is described. Discovered during the process to improve the physicochemical and metabolic properties of BIRT377 (1, Figure 1), a previously reported hydantoin-based LFA-1 inhibitor, these compounds are characterized by an imidazole-based 5,5-bicyclic scaffold, the 1,3,3-trisubstituted 1H-imidazo [1,2-alpha]imidazol-2-one (i.e. structure 3). The structure-activity relationship (SAR) shows that electron-withdrawing groups at C-5 on the imidazole ring benefit potency and that oxygen-containing functional groups attached to a C-5-sulfonyl or sulfonamide group further improve potency. This latter gain in potency is attributed to the interaction(s) of the functionalized sulfonyl/sulfonamide groups with the protein, likely polar-polar in nature, as suggested by SAR data. X-ray studies revealed that these bicyclic inhibitors bind to the I-domain of LFA-1 in a pattern similar to that of compound 1.