Structure–activity studies on the nociceptin/orphanin FQ receptor antagonist 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4′-piperidin-1-yl]propyl} pyrrolidine-2-carboxamide Original Research Article

Twelve derivatives of the nociceptin/orphanin FQ (N/OFQ) receptor (NOP) antagonist 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4′-piperidin-1-yl]propyl} pyrrolidine-2-carboxamide (Comp 24) were synthesized and tested in binding experiments performed on CHOhNOP cell membranes. Among them, a novel interesting NOP receptor antagonist (compound 35) was identified by blending chemical moieties taken from different NOP receptor ligands. In vitro in various assays, Compound 35 consistently behaved as a pure, highly potent (pA2 in the range 8.0–9.9), competitive and NOP selective antagonist. However compound 35 was found inactive when challenged against N/OFQ in vivo in the mouse tail withdrawal assay. Thus, the usefulness of the novel NOP ligand compound 35 is limited to in vitro investigations.