title: Acyclic and cyclopropyl analogues of adenosine bisphosphate antagonists of the P2Y1 receptor: structure-activity relationships and receptor docking.
abstract: The activation of P2Y1 receptors in platelets contributes to platelet aggregation, and selective antagonists are sought as potential antithrombotic agents. We reported (Kim et al. J. Med. Chem. 2000, 43, 746-755) that acyclic analogues of adenine nucleotides, containing two phosphate groups on a symmetrically branched aliphatic chain, attached at the 9-position of adenine, are moderately potent P2Y1 receptor antagonists. In this study we have varied the chain structure, to include asymmetric substitution, olefinic, and cyclopropyl groups. These antagonists inhibited the stimulation of phospholipase C in turkey erythrocyte membranes induced by 30 nM 2-MeS-ADP in the micromolar range. In the series of symmetrically branched aliphatic groups substituted with two phosphate groups, the optimal antagonist potency occurred with the 2-methylpropyl group. A 2-chloro-N(6)-methyladenine derivative, 2-[2-(2-chloro-6-methylaminopurin-9-yl)methyl]propane-1,3-bisoxy(diammoniumphosphate) (7), was a full antagonist at the P2Y1 receptor with an IC(50) value of 0.48 microM. Esterification of one of the phosphate groups or substitution with O-acetyl greatly reduced the antagonist potency at the P2Y1 receptor. Removal of a methylene group of 7 or inclusion of an olefinic or cyclopropyl group also reduced potency. A pair of enantiomeric glycerol derivatives demonstrated a 5-fold stereoselectivity for the S-isomer. Stereoisomerically defined analogues of 7 containing a cyclopropyl group in place of the branched carbon were less potent than 7 as antagonists, with IC(50) values of 2-3 microM. No agonist activity was observed for these analogues. A new rhodopsin-based molecular model of the P2Y1 receptor indicated that the optimal docked orientation of the two monophosphate moieties relative to the adenine N(6) (compared to a rigid, bicyclic analogue) was consistent with the dependence of antagonist potency on chain length. The 3'-phosphate was predicted to occupy a restricted space, deeper in the binding cleft than the 5'-phosphate location. In summary, modification of the flexible spacer chain linking bisphosphate groups to the adenine moiety provided many moderately potent antagonists.
authors.affiliation: Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810, USA.
authors.forename: H S
authors.initials: HS
authors.lastname: Kim
authors.forename: D
authors.initials: D
authors.lastname: Barak
authors.forename: T K
authors.initials: TK
authors.lastname: Harden
authors.forename: J L
authors.initials: JL
authors.lastname: Boyer
authors.forename: K A
authors.initials: KA
authors.lastname: Jacobson
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000737:chemistry; D058472:Receptors, Purinergic P2Y1; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014421:Turkey; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D007295:Inositol Phosphates; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D000244:Adenosine Diphosphate; D010738:Type C Phospholipases