title: Ribose-modified nucleosides as ligands for adenosine receptors: synthesis, conformational analysis, and biological evaluation of 1'-C-methyl adenosine analogues.
abstract: 1'-C-Methyl analogues of adenosine and selective adenosine A(1) receptor agonists, such as N-[(1R)-1-methyl-2-phenylethyl]adenosine ((R)-PIA) and N(6)-cyclopentyladenosine, were synthesized to further investigate the subdomain that binds the ribose moiety. Binding affinities of these new compounds at A(1) and A(2A) receptors in rat brain membranes and at A(3) in rat testis membranes were determined and compared. It was found that the 1'-C-methyl modification in adenosine resulted in a decrease of affinity, particularly at A(1) and A(2A) receptors. When this modification was combined with N(6) substitutions with groups that induce high potency and selectivity at A(1) receptors, the high affinity was in part restored and the selectivity was increased. The most potent compound proved to be the 1'-C-methyl analogue of (R)-PIA with a K(i) of 23 nM for the displacement of [(3)H]CHA binding from rat brain A(1) receptors and a > 435-fold selectivity over A(2A) receptors. In functional assays, these compounds inhibited forskolin-stimulated adenylate cyclase with IC(50) values ranging from 0.065 to 3.4 microM, acting as full agonists. Conformational analysis based on vicinal protonminus signproton J-coupling constants and molecular mechanics calculations using the MM2 force field proved that the methyl group on C1' in adenosine has a pronounced impact on the furanose conformation by driving its conformational equilibrium toward the north, gamma+, syn form.
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Camerino, 62032 Camerino, Italy.
authors.forename: Loredana
authors.initials: L
authors.lastname: Cappellacci
authors.forename: Grazia
authors.initials: G
authors.lastname: Barboni
authors.forename: Micaela
authors.initials: M
authors.lastname: Palmieri
authors.forename: Michela
authors.initials: M
authors.lastname: Pasqualini
authors.forename: Mario
authors.initials: M
authors.lastname: Grifantini
authors.forename: Barbara
authors.initials: B
authors.lastname: Costa
authors.forename: Claudia
authors.initials: C
authors.lastname: Martini
authors.forename: Palmarisa
authors.initials: P
authors.lastname: Franchetti
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives*; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001667:Binding, Competitive; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009690:Nucleic Acid Conformation; D058906:Purinergic P1 Receptor Agonists; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D004791:Enzyme Inhibitors; D008024:Ligands; D058906:Purinergic P1 Receptor Agonists; D000241:Adenosine