title: Synthesis, biological evaluation, and molecular modeling of ribose-modified adenosine analogues as adenosine receptor agonists.
abstract: A number of 3'-C-methyl analogues of selective adenosine receptor agonists such as CPA, CHA, CCPA, 2'-Me-CCPA, NECA, and IB-MECA was synthesized to further investigate the subdomain of the receptor that binds the ribose moiety of the ligands. Affinity data at A(1), A(2A), and A(3) receptors in bovine brain membranes showed that the 3'-C-modification in adenosine resulted in a decrease of the affinity at all three receptor subtypes. When this modification was combined with N(6)-substitution with groups that induce high potency and selectivity at A(1) receptor, the affinity and selectivity were increased. However, all 3'-C-methyl derivatives proved to be very less active than the corresponding 2'-C-methyl analogues. The most active compound was found to be 3'-Me-CPA which displayed a K(i) value of 0.35 microM at A(1) receptor and a selectivity for A(1) vs A(2A) and A(3) receptors higher than 28-fold. 2'-Me-CCPA was confirmed to be the most selective, high affinity agonist so far known also at human A(1) receptor with a K(i) value of 3.3 nM and 2903- and 341-fold selective vs human A(2A) and A(3) receptors, respectively. In functional assay, 3'-Me-CPA, 3'-Me-CCPA, and 2-Cl-3'-Me-IB-MECA inhibited forskolin-stimulated adenylyl cyclase activity with IC(50) values ranging from 0.3 to 4.9 microM, acting as full agonists. A rhodopsin-based model of the bovine A(1)AR was built to rationalize the higher affinity and selectivity of 2'-C-methyl derivatives of N(6)-substituted-adenosine compared to that of 3'-C-methyl analogues. In the docking exploration, it was found that 2'-Me-CCPA was able to form a number of interactions with several polar residues in the transmembrane helices TM-3, TM-6, and TM-7 of bA(1)AR which were not preserved in the molecular dynamics simulation of 3'-Me-CCPA/bA(1)AR complex.
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Camerino, 62032 Camerino, Italy.
authors.forename: Loredana
authors.initials: L
authors.lastname: Cappellacci
authors.forename: Palmarisa
authors.initials: P
authors.lastname: Franchetti
authors.forename: Michela
authors.initials: M
authors.lastname: Pasqualini
authors.forename: Riccardo
authors.initials: R
authors.lastname: Petrelli
authors.forename: Patrizia
authors.initials: P
authors.lastname: Vita
authors.forename: Antonio
authors.initials: A
authors.lastname: Lavecchia
authors.forename: Ettore
authors.initials: E
authors.lastname: Novellino
authors.forename: Barbara
authors.initials: B
authors.lastname: Costa
authors.forename: Claudia
authors.initials: C
authors.lastname: Martini
authors.forename: Karl-Norbert
authors.initials: KN
authors.lastname: Klotz
authors.forename: Mario
authors.initials: M
authors.lastname: Grifantini
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D002417:Cattle; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D066298:In Vitro Techniques; D008958:Models, Molecular; D058906:Purinergic P1 Receptor Agonists; D011869:Radioligand Assay; D051381:Rats; D018047:Receptors, Purinergic P1 / Q000737:chemistry; D012266:Ribose / Q000737:chemistry*
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1; D012266:Ribose; D000241:Adenosine