title: Novel cyclic azo-bridged analogs of gonadotropin-releasing hormone.
abstract: Five linear analogs of GnRH containing a p-aminophenylalanine (Pap) residue in their sequence and their six corresponding azo-bridged cyclic derivatives were synthesized. The precyclic peptides were prepared on solid-support, while azo-cyclization was performed in solution by diazotization of the p-aminophenylalanine residue followed by intramolecular coupling of the formed diazo salt with either tyrosine or histidine side chains present in the sequence. All peptides were examined for their binding ability to the GnRH receptor expressed on rat pituitary membranes and for their LH-release activity from dispersed rat pituitary cells. Linear analogs 1 i.e [Pap(5)] GnRH and 3, i.e. [Tyr(3), Pap(5)] GnRH, were found to bind to the GnRH receptors only slightly less avidly than native GnRH. Their cyclization, however, led to a marked reduction in the binding capacity, i.e. from IC(50) of 10(-9) M to the 10(-7) M range, and in biopotency, i.e. LH-release. All other linear and cyclic peptides were found to bind selectively to the GnRH receptor only in the low microM range. Only peptide 1 was found comparable to native GnRH in respect to LH-release activity and thus may potentially be a good agonist of the parent peptide. Peptides 1-4, the most potent GnRH receptor binders, were examined for their conformational properties using CD. Cyclic-azo peptides 2 and 4 were further evaluated by NMR spectroscopy in solution combined with molecular modeling. The structural information obtained explains in part the GnRH-like biological activity observed.
authors.affiliation: Department of Organic Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Gil
authors.initials: G
authors.lastname: Fridkin
authors.forename: Shai
authors.initials: S
authors.lastname: Rahimipour
authors.forename: Nurit
authors.initials: N
authors.lastname: Ben-Aroya
authors.forename: Aviva
authors.initials: A
authors.lastname: Kapitkovsky
authors.forename: Susanna
authors.initials: S
authors.lastname: Di-Segni
authors.forename: Masha
authors.initials: M
authors.lastname: Rosenberg
authors.forename: Irina
authors.initials: I
authors.lastname: Kustanovich
authors.forename: Yitzhak
authors.initials: Y
authors.lastname: Koch
authors.forename: Chaim
authors.initials: C
authors.lastname: Gilon
authors.forename: Mati
authors.initials: M
authors.lastname: Fridkin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001391:Azo Compounds / Q000737:chemistry*; D003500:Cyclization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000737:chemistry* / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism; D008958:Models, Molecular; D010456:Peptides, Cyclic / Q000737:chemistry*; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar; D011966:Receptors, LHRH / Q000378:metabolism
chemical_list: D001391:Azo Compounds; D010456:Peptides, Cyclic; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone