Development of Spin-Labeled Probes for Adenosine Receptors

• Published in: Journal of medicinal chemistry 2005-03, Vol.48 (6), p.2108-2114
• Main Authors: Ilaš, Janez, Pečar, Slavko, Hockemeyer, Jörg, Euler, Harald, Kirfel, Armin, Müller, Christa E
• Format: Article
• Language: English
• Subjects: Adenosine A1 Receptor Antagonists; Adenosine A2 Receptor Antagonists; Animals; Binding, Competitive; Biological and medical sciences; Brain - drug effects; Brain - metabolism; Cell Line; Cricetinae; Cricetulus; Crystallography, X-Ray; Cyclic N-Oxides - chemical synthesis; Cyclic N-Oxides - chemistry; Cyclic N-Oxides - pharmacology; Cyclopentanes - chemical synthesis; Cyclopentanes - chemistry; Cyclopentanes - pharmacology; Humans; In Vitro Techniques; Ligands; Medical sciences; Molecular Structure; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Peptidergic system (neuropeptide, opioid peptide, opiates...). Adenosinergic and purinergic systems; Pharmacology. Drug treatments; Purinergic P1 Receptor Antagonists; Radioligand Assay; Rats; Receptor, Adenosine A1 - metabolism; Receptor, Adenosine A2B - metabolism; Receptors, Purinergic P1 - metabolism; Spin Labels - chemical synthesis; Structure-Activity Relationship; Xanthines - chemical synthesis; Xanthines - chemistry; Xanthines - pharmacology
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm049513x

Functionalized xanthine derivatives bearing a nitroxide moiety at the 3- or 8-position were synthesized as electron paramagnetic resonance (EPR) probes. The 8-cyclopentyl-1-propylxanthine derivative 4, spin-labeled at N3 by substitution with a nitroxide-bearing dihydropyrrole moiety, was a potent and selective A1 adenosine receptor antagonist (K i for A1 5.5 nM, 1600-fold selectivity vs A2A, >200-fold vs A2B, and 310-fold vs A3 adenosine receptors). 8-(1-Oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)-1,3-dipropylxanthine 10 (K i for A1 8.2 nM) was similarly potent and selective, while 8-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-1,3-dipropylxanthine 11 (K i for A1 160 nM) exhibited significantly lower affinity for A1 adenosine receptors. 8-[4-(((1-Oxyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-2-oxoethoxy)phenyl]-1-propylxanthine 14, a 3-unsubstituted xanthine derivative, was found to be a potent A2B adenosine receptor antagonist (K i for A2B 48 nM) but also exhibited high affinity for A1 receptors (K i for A1 15.7 nM). An X-ray structure of compound 10 was obtained, confirming the proposed structure. The novel spin-labeled A1-selective or A1/A2B-nonselective adenosine receptor antagonists may become useful probes for biophysicochemical investigations of adenosine receptors in their membrane environment.