NPY Y1 antagonists: structure-activity relationships of arginine derivatives and hybrid compounds with...

Previously, omega-guanidino- and omega-aminoalkanamides, structurally derived from arpromidine-like histamine H2 receptor agonists, were reported as novel neuropeptide Y Y1 antagonists. Regardless of the backbone, they resemble BIBP 3226, an argininamide with high NPY Y1 receptor affinity and selectivity, with respect to nature and arrangement of the 'terminal' diaryl, guanidine, and hydroxyphenyl groups. Hybrid compounds were synthesized combining the argininamide backbone of BIBP 3226 or partial structures derived from the C-terminal dipeptide of NPY with characteristic substructures of arpromidine- or amide-type NPY antagonists. Additionally, some analogs of BIBP 3226 with reduced flexibility were prepared. Structure-activity relationships indicate that, in contrast to alkanamides, homologs and/or isomers of BIBP 3226 with vicinal arrangement of the phenyl rings have decreased Y1 antagonistic activity (Ca2+-assay in HEL cells). Replacement of the hydroxybenzyl group by an imidazole ring further decreases activity. It is concluded that the binding sites of NPY antagonists with one and with two basic groups are not identical. Analogs with a rigid tetrahydro-2-benzazepine or an indan group in place of the benzyl moiety in BIBP 3226 are active, indicating the role of the OH group and supporting the model proposed for the interaction of BIBP 3226 with the Y1 receptor.