A Novel Class of Highly Potent and Selective A1 Adenosine Antagonists:  Structure−Affinity Profile of a Series of 1,8-Naphthyridine Derivatives

• Published in: Journal of medicinal chemistry Vol. 43; no. 15; pp. 2814 - 2823
• Main Authors: Ferrarini, Pier Luigi, Mori, Claudio, Manera, Clementina, Martinelli, Adriano, Mori, Filippo, Saccomanni, Giuseppe, Barili, Pier Luigi, Betti, Laura, Giannaccini, Gino, Trincavelli, Letizia, Lucacchini, Antonio
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 27-07-2000
• Subjects: Adenylyl Cyclases - metabolism; Animals; Biological and medical sciences; Catecholaminergic system; Cattle; Cerebral Cortex - enzymology; Corpus Striatum - metabolism; In Vitro Techniques; Magnetic Resonance Spectroscopy; Male; Medical sciences; Naphthyridines - chemical synthesis; Naphthyridines - chemistry; Naphthyridines - pharmacology; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Pharmacology. Drug treatments; Purinergic P1 Receptor Antagonists; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2A; Receptor, Adenosine A3; Structure-Activity Relationship; Bovine; Nitrogen heterocycle; Central nervous system; Benzene derivatives; A1 Adenosine receptor; Selectivity; In vitro; Vertebrata; Mammalia; Structure activity relation; Chlorine Organic compounds; Animal; Bicyclic compound; Affinity; Artiodactyla; Antagonist; Chemical synthesis; Ungulata; Brain (vertebrata)
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm990321p

A series of 1,8-naphthyridine derivatives (12 − 36), bearing a phenyl group in position 2 and various substituents in positions 4 and 7, were synthesized in an attempt to obtain potent, selective antagonists for the A1 adenosine receptor subtype. The compounds were tested to evaluate their affinity for A1 compared with A2A and A3 adenosine receptor subtypes. In binding studies in bovine brain cortical membranes, most of the compounds showed an affinity for A1 receptors in the low nanomolar range and two in the subnanomolar range with an interesting degree of A1 versus A2A and A3 selectivity. Comparison of the 4-substituted derivatives indicated that 4-OH substitution, with a 4-quinoid structure, causes an increase in the A1 and A2A affinity and generally also in A1 selectivity. The kind of substitution in position 7 can greatly modulate the affinity:  the most interesting substituents in this position seemed to be electron-withdrawing groups; in particular the 7-chloronaphthyridine 25d showed a remarkable selectivity (A2A/A1 ratio of 670, A3/A1 ratio of 14 000) associated with a higher A1 affinity (K i = 0.15 nM). NMR studies on these compounds 12 − 36 indicated that the 4-OH-substituted ones prefer the tautomer in which the oxygen in position 4 is in the quinoid form and the nitrogen in position 1 is protonated. Theoretical calculations are in agreement with the NMR data.