title: Nucleosides and nucleotides. 200. Reinvestigation of 5'-N-ethylcarboxamidoadenosine derivatives: structure-activity relationships for P(3) purinoceptor-like proteins.
abstract: The non-P(1) and non-P(2) muscle relaxant effect of ATP in rabbit thoracic aorta has recently been attributed to a putative P(3) purinoceptor, which is activated by either adenosine or ATP. Since the physiological roles of this putative P(3) purinoceptor and of a new [(3)H]-5'-N-ethylcarboxamidoadenosine (NECA)-binding protein from rat brain membranes called P(3) purinoceptor-like protein (P(3)LP), due to its ligand specificity, have not been fully elucidated, we needed a specific ligand to obtain further information about the receptor. We examined the structure-activity relationship (SAR) of various 5'-N-substituted-carboxamidoadenosine derivatives toward P(3)LP and discovered a hydrophobic binding region near the 5'-N-substituted-carboxamide group. From the linear alkyl N-substituted derivatives, the N-n-pentyl derivative 10 was found to be the most potent ligand with a K(i) value of 12 nM. In the series of the N-cycloalkyl derivatives, the N-cyclohexyl derivative 27 was the strongest ligand with a K(i) value of 18 nM. On the other hand, the N-substituents having branched alkyl side chains and bulky cycloalkyl groups did not show any potent affinities for P(3)LP. Therefore, the hydrophobic pocket accommodates approximately a 10-carbon-atom-long linear alkyl side chain, while a considerably stronger hydrophobic binding region of about a 5-carbon-atom-long depth exists near the nitrogen atom of the amide group. This pocket also allows substitution with bulky hydrophobic groups since the 5'-N-cycloalkyl derivatives have high affinities. We also examined the receptor selectivity for the selected nucleosides 10 and 27 with 1 [9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine, HAK2701] and NECA versus P(1) purinoceptor subtypes, such as adenosine A(1), A(2A), A(2B), and A(3) receptors, and found that 27 is the most selective ligand for P(3)LP.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-12, Nishi-6, Kita-ku, Sapporo 060-0812, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Umino
authors.forename: K
authors.initials: K
authors.lastname: Yoshioka
authors.forename: Y
authors.initials: Y
authors.lastname: Saitoh
authors.forename: N
authors.initials: N
authors.lastname: Minakawa
authors.forename: H
authors.initials: H
authors.lastname: Nakata
authors.forename: A
authors.initials: A
authors.lastname: Matsuda
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D066298:In Vitro Techniques; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D011869:Radioligand Assay; D051381:Rats; D011983:Receptors, Purinergic / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: C421916:1-(adenin-9-yl)-1-deoxy-N-cyclohexylribofuranuronamide; D008024:Ligands; D011983:Receptors, Purinergic; D000241:Adenosine