Tetrahydroimidazo[1,2-a]pyrazine Derivatives: Synthesis and Evaluation As Gαq-Protein Ligands.

The 5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine derivative BIM-46174 and its dimeric form BIM-46187 (1) are heterocyclized dipeptides that belong to the very few cell-permeable compounds known to preferentially silence G alpha(q)proteins. To explore the chemical space of G alpha(q)inhibitors of the BIM chemotype, a combinatorial approach was conducted towards a library of BIM molecules. This library was evaluated in a second messenger-based fluorescence assay to analyze the activity of G alpha(q)proteins through the determination of intracellularmyo-inositol 1-phosphate. Structure-activity relationships were deduced and structural requirements for biological activity obtained, which were (i) a redox reactive thiol/disulfane substructure, (ii) anN-terminal basic amino group, (iii) a cyclohexylalanine moiety, and (iv) a bicyclic skeleton. Active compounds exhibited cellular toxicity, which was investigated in detail for the prototypical inhibitor1. This compound affects the structural cytoskeletal dynamics in a G alpha(q/11)-independent manner.