Search tips
Search criteria

Results 1-19 (19)

Clipboard (0)
Year of Publication
more »
Document Types
1.  Synthesis and Anti-Renal Fibrosis Activity of Conformationally Locked Truncated 2-Hexynyl-N6-Substituted-(N)-Methanocarba-nucleosides as A3 Adenosine Receptor Antagonists and Partial Agonists 
Journal of Medicinal Chemistry  2014;57(4):1344-1354.
Truncated N6-substituted-(N)-methanocarba-adenosine derivatives with 2-hexynyl substitution were synthesized to examine parallels with corresponding 4′-thioadenosines. Hydrophobic N6 and/or C2 substituents were tolerated in A3AR binding, but only an unsubstituted 6-amino group with a C2-hexynyl group promoted high hA2AAR affinity. A small hydrophobic alkyl (4b and 4c) or N6-cycloalkyl group (4d) showed excellent binding affinity at the hA3AR and was better than an unsubstituted free amino group (4a). A3AR affinities of 3-halobenzylamine derivatives 4f–4i did not differ significantly, with Ki values of 7.8–16.0 nM. N6-Methyl derivative 4b (Ki = 4.9 nM) was a highly selective, low efficacy partial A3AR agonist. All compounds were screened for renoprotective effects in human TGF-β1-stimulated mProx tubular cells, a kidney fibrosis model. Most compounds strongly inhibited TGF-β1-induced collagen I upregulation, and their A3AR binding affinities were proportional to antifibrotic effects; 4b was most potent (IC50 = 0.83 μM), indicating its potential as a good therapeutic candidate for treating renal fibrosis.
PMCID: PMC3954500  PMID: 24456490
2.  Rational Design of Sulfonated A3 Adenosine Receptor-Selective Nucleosides as Pharmacological Tools to Study Chronic Neuropathic Pain 
Journal of medicinal chemistry  2013;56(14):10.1021/jm4007966.
(N)-Methanocarba (bicyclo[3.1.0]hexane)-adenosine derivatives were probed for sites of charged sulfonate substitution, which precludes diffusion across biological membranes, e.g. blood brain barrier. Molecular modeling predicted that sulfonate groups on C2-phenylethynyl substituents would provide high affinity at both mouse (m) and human (h) A3 adenosine receptors (ARs), while a N6-p-sulfo-phenylethyl substituent would determine higher hA3AR vs. mA3AR affinity. These modeling predictions, based on steric fitting of the binding cavity and crucial interactions with key residues, were confirmed by binding/efficacy studies of synthesized sulfonates. N6-3-Chlorobenzyl-2-(3-sulfophenylethynyl) derivative 7 (MRS5841) bound selectively to h/m A3ARs (Ki hA3AR 1.9 nM) as agonist, while corresponding p-sulfo isomer 6 (MRS5701) displayed mixed A1/A3AR agonism. Both nucleosides administered i.p. reduced mouse chronic neuropathic pain that was ascribed to either A3 or A1/A3ARs using A3AR genetic deletion. Thus, rational design methods based on A3AR homology models successfully predicted sites for sulfonate incorporation, for delineating adenosine’s CNS vs. peripheral actions.
PMCID: PMC3858399  PMID: 23789857
Molecular modeling; G protein-coupled receptor; neuropathic pain; purines; radioligand binding; adenosine receptor
3.  Structural Sweet Spot for A1 Adenosine Receptor Activation by Truncated (N)- Methanocarba Nucleosides: Receptor Docking and Potent Anticonvulsant Activity 
Journal of medicinal chemistry  2012;55(18):8075-8090.
A1 adenosine receptor (AR) agonists display antiischemic and antiepileptic neuroprotective activity, but peripheral cardiovascular side effects impeded their development. SAR study of N6-cycloalkylmethyl 4′-truncated (N)-methanocarba-adenosines identified 10 (MRS5474, N6-dicyclopropylmethyl, Ki 47.9 nM) as a moderately A1AR-selective full agonist. Two stereochemically defined N6-methynyl group substituents displayed narrow SAR; larger than cyclobutyl greatly reduced AR affinity, and larger or smaller than cyclopropyl reduced A1AR selectivity. Nucleoside docking to A1AR homology model characterized distinct hydrophobic cyclopropyl subpockets, the larger “A” forming contacts with Thr270 (7.35), Tyr271 (7.36), Ile274 (7.39) and carbon chains of glutamates (EL2), and smaller subpocket “B” between TM6 and TM7. 10 suppressed minimal clonic seizures (6 Hz mouse model) without typical rotarod impairment of A1AR agonists. Truncated nucleosides, an appealing preclinical approach, have more drug-like physicochemical properties than other A1AR agonists. Thus, we identified highly restricted regions for substitution around N6 suitable for an A1AR agonist with anticonvulsant activity.
PMCID: PMC3463139  PMID: 22921089
G protein-coupled receptor; purines; molecular modeling; seizures; in vivo
4.  Structure-Guided Design of A3 Adenosine Receptor-Selective Nucleosides: Combination of 2-Arylethynyl and Bicyclo[3.1.0]hexane Substitutions 
Journal of Medicinal Chemistry  2012;55(10):4847-4860.
(N)-Methanocarba adenosine 5′-methyluronamides containing known A3 AR (adenosine receptor)-enhancing modifications, i.e. 2-(arylethynyl)adenine and N6-methyl or N6-(3-substituted-benzyl), were nanomolar full agonists of human (h) A3AR and highly selective (Ki ~0.6 nM, N6-methyl 2-(halophenylethynyl) analogues 13, 14). Combined 2-arylethynyl-N6-3-chlorobenzyl substitutions preserved A3AR affinity/selectivity in the (N)-methanocarba series (e.g. 3,4-difluoro full agonist MRS5698 31, Ki 3 nM, human and mouse A3) better than for ribosides. Polyaromatic 2-ethynyl N6-3-chlorobenzyl analogues, such as potent linearly extended 2-p-biphenylethynyl MRS5679 34 (Ki hA3 3.1 nM; A1, A2A: inactive) and fluorescent 1-pyrene adduct MRS5704 35 (Ki hA3 68.3 nM) were conformationally rigid; receptor docking identified a large, mainly hydrophobic binding region. The vicinity of receptor-bound C2 groups was probed by homology modeling based on recent X-ray structure of an agonist-bound A2AAR, with a predicted helical rearrangement requiring an agonist-specific outward displacement of TM2 resembling opsin. Thus, X-ray structure of related A2AAR is useful in guiding design of new A3AR agonists.
PMCID: PMC3371665  PMID: 22559880
G protein-coupled receptor; purines; molecular modeling; structure activity relationship; radioligand binding; adenylate cyclase
5.  Structure-Activity Relationships of Truncated D- and L-4′-Thioadenosine Derivatives as Species-Independent A3 Adenosine Receptor Antagonists1 
Journal of medicinal chemistry  2008;51(20):6609-6613.
Novel D- and L-4′-thioadenosine derivatives lacking the 4′-hydroxymethyl moiety were synthesized, starting from D-mannose and D-gulonic γ-lactone, respectively, as potent and selective species-independent A3 adenosine receptor (AR) antagonists. Among the novel 4′-truncated 2-H nucleosides tested, a N6-(3-chlorobenzyl) derivative 7c was the most potent at the human A3 AR (Ki = 1.5 nM), but a N6-(3-bromobenzyl) derivative 7d showed the optimal species-independent binding affinity.
PMCID: PMC3616494  PMID: 18811138
6.  Synthesis and Biological Evaluation of a New Series of 1,2,4-triazolo[1,5-a]-1,3,5-triazines as Human A2A Adenosine Receptor Antagonists with Improved Water Solubility 
Journal of medicinal chemistry  2011;54(3):877-889.
The structure activity relationship (SAR) of 1,2,4-triazolo[1,5-a]-1,3,5-triazine derivatives related to ZM241385 as antagonists of the A2A adenosine receptor (AR) was explored through the synthesis of analogues substituted at the 5 position. The A2A AR X-ray structure was used to propose a structural basis for the activity and selectivity of the analogues and to direct the synthetic design strategy to provide access to solvent-exposed regions. Thus, we have identified a point of substitution for the attachment of solubilizing groups to enhance both aqueous solubility and physicochemical properties, maintaining potent interactions with the A2A AR and, in some cases, receptor subtype selectivity. Among the most potent and selective novel compounds were a long-chain ether-containing amine congener 20 (Ki 11.5 nM) and its urethane-protected derivative 14 (Ki 17.8 nM). Compounds 20 and 31 (Ki 11.5 and 16.9 nM, respectively) were readily water soluble up to 10 mM. The analogues were docked in the crystallographic structure of the hA2A AR and in a homology model of the hA3 AR, and the per residue electrostatic and hydrophobic contributions to the binding were assessed and stabilizing factors were proposed.
PMCID: PMC3578427  PMID: 21214204
G protein-coupled receptor; purines; molecular modeling; structure activity relationship; radioligand binding; adenylyl cyclase
7.  Evaluation of Molecular Modeling of Agonist Binding in Light of the Crystallographic Structure of an Agonist-Bound A2A Adenosine Receptor 
Journal of Medicinal Chemistry  2011;55(1):538-552.
Molecular modeling of agonist binding to the human A2A adenosine receptor (AR) was assessed and extended in light of crystallographic structures. Heterocyclic adenine nitrogens of co-crystallized agonist overlayed corresponding positions of the heterocyclic base of a bound triazolotriazine antagonist, and ribose moiety was coordinated in a hydrophilic region, as previously predicted based on modeling using the inactive receptor. Automatic agonist docking of 20 known potent nucleoside agonists to agonist-bound A2AAR crystallographic structures predicted new stabilizing protein interactions, to provide a structural basis for previous empirical structure activity relationships consistent with previous mutagenesis results. We predicted binding of novel C2 terminal amino acid conjugates of A2AAR agonist CGS21680 and used these models to interpret effects on binding affinity of newly-synthesized agonists. D-Amino acid conjugates were generally more potent than L- stereoisomers, and free terminal carboxylates more potent than corresponding methyl esters. Amino acid moieties were coordinated close to extracellular loops 2 and 3. Thus, molecular modeling is useful in probing ligand recognition and rational design of GPCR–targeting compounds with specific pharmacological profiles.
PMCID: PMC3261785  PMID: 22104008
G protein-coupled receptor; nucleosides; purines; radioligand binding; docking; X-ray crystallography
8.  Structure-Activity Relationships of Truncated C2- or C8-Substituted Adenosine Derivatives as Dual Acting A2A and A3 Adenosine Receptor Ligands 
Journal of Medicinal Chemistry  2011;55(1):342-356.
Truncated N6-substituted-4′-oxo- and 4′-thioadenosine derivatives with C2 or C8 substitution were studied as dual acting A2A and A3 adenosine receptor (AR) ligands. The lithiation-mediated stannyl transfer and palladium-catalyzed cross coupling reactions were utilized for functionalization of the C2 position of 6-chloropurine nucleosides. An unsubstituted 6-amino group and a hydrophobic C2 substituent were required for high affinity at the hA2AAR, but hydrophobic C8 substitution abolished binding at the hA2AAR. However, most of synthesized compounds displayed medium to high binding affinity at the hA3AR, regardless of C2 or C8 substitution, and low efficacy in a functional cAMP assay. Several compounds tended to be full hA2AAR agonists. C2 substitution probed geometrically through hA2AAR-docking, was important for binding in order of hexynyl > hexenyl > hexanyl. Compound 4g was the most potent ligand acting dually as hA2AAR agonist and hA3AR antagonist, which might be useful for treatment of asthma or other inflammatory diseases.
PMCID: PMC3266722  PMID: 22142423
lithiation-mediated stannyl transfer; structure-activity relationship; adenosine receptors; truncated adenosine; palladium-catalyzed cross coupling; dual-acting ligands
9.  ‘Reversine’ and its 2-Substituted Adenine Derivatives as Potent and Selective A3 Adenosine Receptor Antagonists 
Journal of medicinal chemistry  2005;48(15):4910-4918.
The dedifferentiation agent ‘reversine’ (2-(4-morpholinoanilino)-N6-cyclohexyladenine 2) was found to be a moderately potent antagonist for the human A3 adenosine receptor (AR) with a Ki value 0.66 μM. This result prompted an exploration of the structure-activity relationship of related derivatives, synthesized via sequential substitution of 6-chloro-2-fluoropurine with selected nucleophiles. Optimization of substituents at these two positions identified 2-phenylamino-N6-(cyclohexyl)adenine 12, 2-phenylamino-N6-(cycloheptyl)adenine 19, and 2-phenylamino-N6-(endo-norbornyl)adenine 21 as potent A3 AR ligands with Ki values of 51, 42 and 37 nM, respectively, with 30 – 200-fold selectivity in comparison to A1 and A2A ARs. The most selective A3 AR antagonist (>200-fold) was 2-phenyloxy-N6-(cyclohexyl)adenine 22. 9-Methylation of 12, but not 19, was well tolerated in A3 AR binding. Extension of the 2-phenylamino group to 2-benzyl- and 2-(2-phenylethylamino) reduced affinity. In the series of 2-phenylamino, 2-phenyloxy, and 2-phenylthio substitutions, the order of affinity at the A3 AR was oxy ≥ amino > thio. Selected derivatives, including reversine (KB value of 466 nM in Schild analysis), competitively antagonized the functional effects of a selective A3 AR agonist, i.e. inhibition of forskolin-stimulated cAMP production in stably transfected Chinese hamster ovary (CHO) cells. These results are in agreement with other studies suggesting the presence of a lipophilic pocket in the AR binding site that is filled by moderately sized cycloalkyl rings at the N6 position of both adenine and adenosine derivatives. Thus, the compound series reported herein comprise an important new series of selective A3 AR antagonists. We were unable to reproduce the dedifferentiation effect of reversine, previously reported, or to demonstrate any connection between A3 AR antagonist effects and dedifferentiation.
PMCID: PMC3474371  PMID: 16033270
10.  Orthogonal activation of the reengineered A3 adenosine receptor (neoceptor) using tailored nucleoside agonists 
Journal of medicinal chemistry  2006;49(9):2689-2702.
An alternative approach to overcome the inherent lack of specificity of conventional agonist therapy can be the reengineering of the GPCRs and their agonists. A reengineered receptor (neoceptor) could be selectively activated by a modified agonist, but not by the endogenous agonist. Assisted by rhodopsin-based molecular modeling, we pinpointed mutations of the A3 adenosine receptor (AR) for selective affinity enhancement following complementary modifications of adenosine. Ribose modifications examined included, at 3′: amino, aminomethyl, azido, guanidino, ureido; and at 5′: uronamido, azidodeoxy. N6-variations included: 3-iodobenzyl, 5-chloro-2-methyloxybenzyl, and methyl. An N6-3-iodobenzyl-3′-ureido adenosine derivative 10 activated phospholipase C in COS-7 cells (EC50=0.18 μM) or phospholipase D in chick primary cardiomyocytes mediated by a mutant (H272E), but not the wild-type, A3AR. The affinity enhancements for 10 and the corresponding 3′-acetamidomethyl analogue 6 were >100-fold and >20-fold, respectively. 10 concentration-dependently protected cardiomyocytes transfected with the neoceptor against hypoxia. Unlike 10, adenosine activated the wild-type A3AR (EC50 of 1.0 μM), but had no effect on the H272E mutant A3AR (100 μM). Compound 10 was inactive at human A1, A2A, and A2BARs. The orthogonal pair comprising an engineered receptor and a modified agonist should be useful for elucidating signaling pathways and could be therapeutically applied to diseases following organ-targeted delivery of the neoceptor gene.
PMCID: PMC3471142  PMID: 16640329
11.  (N)-Methanocarba 2,N6-Disubstituted Adenine Nucleosides as Highly Potent and Selective A3 Adenosine Receptor Agonists 
Journal of medicinal chemistry  2005;48(6):1745-1758.
A series of ring-constrained (N)-methanocarba-5′-uronamide 2,N6-disubstituted adenine nucleosides have been synthesized via Mitsunobu condensation of the nucleobase precursor with a pseudosugar ring containing a 5′-ester functionality. Following appropriate functionalization of the adenine ring, the ester group was converted to the 5′-N-methylamide. The compounds, mainly 2-chloro substituted derivatives, were tested in both binding and functional assays at human adenosine receptors (ARs), and many were found to be highly potent and selective A3AR agonists. Selected compounds were compared in binding to the rat A3AR to assess their viability for testing in rat disease models. The N6-(3-chlorobenzyl) and N6-(3-bromobenzyl) analogues displayed Ki values at the human A3AR of 0.29 and 0.38 nM, respectively. Other subnanomolar affinities were observed for the following N6 derivatives: 2,5-dichlorobenzyl, 5-iodo-2-methoxybenzyl, trans-2-phenyl-1-cyclopropyl, and 2,2-diphenylethyl. Selectivity for the human A3AR in comparison to the A1AR was (fold): the N6-(2,2-diphenylethyl) analogue 34 (1900), the N6-(2,5-dimethoxybenzyl) analogue 26 (1200), the N6-(2,5-dichlorobenzyl) and N6-(2-phenyl-1-cyclopropyl) analogues 20 and 33 (1000), and the N6-(3-substituted benzyl) analogues 17, 18, 28, and 29 (700–900). Typically, even greater selectivity ratios were obtained in comparison with the A2A and A2BARs. The (N)-methanocarba-5′-uronamide analogues were full agonists at the A3AR, as indicated by the inhibition of forskolin-stimluated adenylate cyclase at a concentration of 10 µM. The N6-(2,2-diphenylethyl) derivative was an A3AR agonist in the (N)-methanocarba-5′-uronamide series, although it was an antagonist in the ribose series. Thus, many of the previously known groups that enhance A3AR affinity in the 9-riboside series, including those that reducing intrinsic efficacy, may be adapted to the (N)-methanocarba nucleoside series of full agonists.
PMCID: PMC3463111  PMID: 15771421
12.  Architecture of P2Y Nucleotide Receptors: Structural Comparison Based on Sequence Analysis, Mutagenesis, and Homology Modeling† 
Journal of medicinal chemistry  2004;47(22):5393-5404.
Human P2Y receptors encompass at least eight subtypes of Class A G protein-coupled receptors (GPCRs), responding to adenine and/or uracil nucleotides. Using a BLAST search against the Homo sapiens subset of the SWISS–PROT and TrEMBL databases, we identified 68 proteins showing high similarity to P2Y receptors. To address the problem of low sequence identity between rhodopsin and the P2Y receptors, we performed a multiple-sequence alignment of the retrieved proteins and the template bovine rhodopsin, combining manual identification of the transmembrane domains (TMs) with automatic techniques. The resulting phylogenetic tree delineated two distinct subgroups of P2Y receptors: Gq-coupled subtypes (e.g., P2Y1) and those coupled to Gi (e.g., P2Y12). On the basis of sequence comparison we mutated three Tyr residues of the putative P2Y1 binding pocket to Ala and Phe and characterized pharmacologically the mutant receptors expressed in COS-7 cells. The mutation of Y306 (7.35, site of a cationic residue in P2Y12) or Y203 in the second extracellular loop selectively decreased the affinity of the agonist 2-MeSADP, and the Y306F mutation also reduced antagonist (MRS2179) affinity by 5-fold. The Y273A (6.48) mutation precluded the receptor activation without a major effect on the ligand-binding affinities, but the Y273F mutant receptor still activated G proteins with full agonist affinity. Thus, we have identified new recognition elements to further define the P2Y1 binding site and related these to other P2Y receptor subtypes. Following sequence-based secondary-structure prediction, we constructed complete models of all the human P2Y receptors by homology to rhodopsin. Ligand docking on P2Y1 and P2Y12 receptor models was guided by mutagenesis results, to identify the residues implicated in the binding process. Different sets of cationic residues in the two subgroups appeared to coordinate phosphate-bearing ligands. Within the P2Y1 subgroup these residues are R3.29, K/R6.55, and R7.39. Within the P2Y12 subgroup, the only residue in common with P2Y1 is R6.55, and the role of R3.29 in TM3 seems to be fulfilled by a Lys residue in EL2, whereas the R7.39 in TM7 seems to be substituted by K7.35. Thus, we have identified common and distinguishing features of P2Y receptor structure and have proposed modes of ligand binding for the two representative subtypes that already have well-developed ligands.
PMCID: PMC3431558  PMID: 15481977
13.  Neoceptor Concept Based on Molecular Complementarity in GPCRs: A Mutant Adenosine A3 Receptor with Selectively Enhanced Affinity for Amine-Modified Nucleosides 
Journal of medicinal chemistry  2001;44(24):4125-4136.
Adenosine A3 receptors are of interest in the treatment of cardiac ischemia, inflammation, and neurodegenerative diseases. In an effort to create a unique receptor mutant that would be activated by tailor-made synthetic ligands, we mutated the human A3 receptor at the site of a critical His residue in TM7, previously proposed to be involved in ligand recognition through interaction with the ribose moiety. The H272E mutant receptor displayed reduced affinity for most of the uncharged A3 receptor agonists and antagonists examined. For example, the nonselective agonist 1a was 19-fold less potent at the mutant receptor than at the wild-type receptor. The introduction of an amino group on the ribose moiety of adenosine resulted in either equipotency or enhanced binding affinity at the H272E mutant relative to wild-type A3 receptors, depending on the position of the amino group. 3′-Amino-3′-deoxyadenosine proved to be 7-fold more potent at the H272E mutant receptor than at the wild-type receptor, while the corresponding 2′- and 5′-amino analogues did not display significantly enhanced affinities. An 3′-amino-N6-iodobenzyl analogue showed only a small enhancement at the mutant (Ki = 320 nM) vs wild-type receptors. The 3′-amino group was intended for a direct electrostatic interaction with the negatively charged ribose-binding region of the mutant receptor, yet molecular modeling did not support this notion. This design approach is an example of engineering the structure of mutant receptors to recognize synthetic ligands for which they are selectively matched on the basis of molecular complementarity between the mutant receptor and the ligand. We have termed such engineered receptors “neoceptors”, since the ligand recognition profile of such mutant receptors need not correspond to the profile of the parent, native receptor.
PMCID: PMC3413945  PMID: 11708915
14.  Structure-Activity Relationships of 2,N6,5′-Substituted Adenosine Derivatives with Potent Activity at the A2B Adenosine Receptor 
Journal of medicinal chemistry  2007;50(8):1810-1827.
2, N6, and/or 5′ substituted adenosine derivatives were synthesized via alkylation of 2-oxypurine nucleosides leading to 2-aralkylether derivatives. 2-(3-(Indolyl)ethyloxy)adenosine 17 was found to be a potent agonist of the human A2BAR in both binding and cAMP assays. Simplification, altered connectivity and mimicking of the indole ring of 17 failed to maintain A2BAR potency. Introduction of N6-ethyl or N6-guanidino substitution, shown to favor A2BAR potency, failed to enhance potency in the 2-(3-(indolyl)ethyloxy)adenosine series. Indole 5″- or 6″-halo substitution was favored at the A2BAR, but a 5′-N-ethylcarboxyamide did not further enhance potency. 2-(3″-(6″-Bromoindolyl)ethyloxy)adenosine 28 displayed an A2BAR EC50 value (nM) of 128, i.e. more potent than the parent 17 (299) and similar to 5′-N-ethylcarboxamidoadenosine (140). 28 was a full agonist at A2B and A2AARs and a low efficacy partial agonist at A1 and A3ARs. Thus, we have identified and optimized 2-(2-arylethyl)oxo moieties in AR agonists that enhance A2BAR potency and selectivity.
PMCID: PMC3405160  PMID: 17378544
G protein-coupled receptor; nucleosides; adenylate cyclase; purines; receptor binding; indole
15.  Functionalized Congeners of A3 Adenosine Receptor-Selective Nucleosides Containing a Bicyclo[3.1.0]hexane Ring System† 
Journal of medicinal chemistry  2009;52(23):7580-7592.
(N)-Methanocarba nucleosides containing bicyclo[3.1.0]hexane replacement of the ribose ring previously demonstrated selectivity as A3 adenosine receptor (AR) agonists (5′-uronamides) or antagonists (5′-truncated). Here, these two series were modified in parallel at the adenine C2 position. N6-3-Chlorobenzyl-5′-N-methyluronamides derivatives with functionalized 2-alkynyl chains of varying length terminating in a reactive carboxylate, ester, or amine group were full, potent human A3AR agonists. Flexibility of chain substitution allowed the conjugation with a fluorescent cyanine dye (Cy5) and biotin, resulting in binding Ki values of 17 and 36 nM, respectively. The distal end of the chain was predicted by homology modeling to bind at the A3AR extracellular regions. Corresponding l-nucleosides were nearly inactive in AR binding. In the 5′-truncated nucleoside series, 2-Cl analogues were more potent at A3AR than 2-H and 2-F, functional efficacy in adenylate cyclase inhibition varied, and introduction of a 2-alkynyl chain greatly reduced affinity. SAR parallels between the two series lost stringency at distal positions. The most potent and selective novel compounds were amine congener 15 (Ki = 2.1 nM) and truncated partial agonist 22 (Ki = 4.9 nM).
PMCID: PMC3109436  PMID: 19499950
16.  Novel 2- and 4- Substituted 1H-Imidazo[4,5-c]quinolin-4-amine Derivatives as Allosteric Modulators of the A3 Adenosine Receptor 
Journal of medicinal chemistry  2009;52(7):2098-2108.
4-Arylamino and 2- cycloalkyl (including amino substitution) modifications were made in a series of 1H-imidazo-[4,5-c]quinolin-4-amine derivatives as allosteric modulators of the human A3 adenosine receptor (AR). In addition to allosteric modulation of the maximum functional efficacy (in [35S]GTPγS G protein binding assay) of the A3AR agonist Cl-IB-MECA (15), some analogues also weakly inhibited equilibrium radioligand binding at ARs. 4-(3,5-Dichlorophenylamino) (6) or 2-(1-adamantyl) (20) substitution produced allosteric enhancement (twice the maximal agonist efficacy), with minimal inhibition of orthosteric AR binding. 2-(4-Tetrahydropyranyl) substitution abolished allosteric enhancement but preserved inhibition of orthosteric binding. Introduction of nitrogen in the six-membered ring at 2 position, to improve aqueous solubility and provide a derivatization site, greatly reduced the allosteric enhancement. 2-(4-(Benzoylamino)cyclohexyl) analogues 23 and 24 were weak negative A3AR modulators. Thus, consistent with previous findings, the allosteric and orthosteric inhibitory A3AR effects in imidazoquinolines are structurally separable, suggesting the possible design of additional derivatives with enhanced positive or negative allosteric A3AR activity and improved selectivity in comparison to inhibition of orthosteric binding.
PMCID: PMC2765805  PMID: 19284749
nucleoside; G protein-coupled receptor; allosterism; adenosine receptor; radioligand binding; imidazoquinolines
17.  Semi-Rational Design of (N)-Methanocarba Nucleosides as Dual Acting A1 and A3Adenosine Receptor Agonists: Novel Prototypes for Cardioprotection 
Journal of medicinal chemistry  2005;48(26):8103-8107.
Ring-constrained adenosine analogues have been designed to act as dualagonists at tissue-protective A1 and A3 adenosine receptors (ARs). 9-Ribosides transformed into the ring-constrained (N)-methanocarba-2-chloro-5′-uronamides consistently lost affinity at A1/A2AARs and gained at A3AR. Among 9-riboside derivatives, only N6-cyclopentyl and 7-norbornyl moieties were extrapolated for mixed A1/A3 selectivity and rat/human A3AR equipotency. Consequently, 2 was balanced in affinity and potency at A1/A3ARs as envisioned and dramatically protected in an intact heart model of global ischemia and reperfusion.
PMCID: PMC2597460  PMID: 16366590
18.  Structure-Activity Relationships of new 1H-Imidazo[4,5-c]quinolin-4-amine Derivatives as Allosteric Enhancers of the A3 Adenosine Receptor 
Journal of medicinal chemistry  2006;49(11):3354-3361.
1H-imidazo[4,5-c]quinolin-4-amine derivatives have been synthesized as allosteric modulators of the human A3 adenosine receptor (AR). Structural modifications were made at the 4-amino and 2 positions. The compounds were tested in both binding and functional assays, and many were found to be allosteric enhancers of the action of A3AR agonists by several different criteria. First, a potentiation of the maximum efficacy of the agonist Cl-IB-MECA was observed for numerous derivatives. Also, a number of these compounds decreased the rate of dissociation of the agonist [125I]I-AB-MECA from the A3AR. Most prominently, compound 43 (LUF6000) was found to enhance agonist efficacy in a functional assay by 45% and decrease dissociation rate similarly without influencing agonist potency. The structural requirements for allosteric enhancement at the A3AR were distinct from the requirements to inhibit equilibrium binding. Thus, we have prepared allosteric enhancers of the human A3AR that have an improved allosteric effect in comparison to the inhibition of equilibrium binding at the orthosteric site.
PMCID: PMC2547348  PMID: 16722654
19.  Structure-Based Discovery of A2A Adenosine Receptor Ligands 
Journal of Medicinal Chemistry  2010;53(9):3748-3755.
The recent determination of X-ray structures of pharmacologically relevant GPCRs has made these targets accessible to structure-based ligand discovery. Here we explore whether novel chemotypes may be discovered for the A2A adenosine receptor, based on complementarity to its recently determined structure. The A2A adenosine receptor signals in the periphery and the CNS, with agonists explored as anti-inflammatory drugs and antagonists explored for neurodegenerative diseases. We used molecular docking to screen a 1.4 million compound database against the X-ray structure computationally and tested 20 high-ranking, previously unknown molecules experimentally. Of these 35% showed substantial activity with affinities between 200 nM and 9 μM. For the most potent of these new inhibitors, over 50-fold specificity was observed for the A2A versus the related A1 and A3 subtypes. These high hit rates and affinities at least partly reflect the bias of commercial libraries toward GPCR-like chemotypes, an issue that we attempt to investigate quantitatively. Despite this bias, many of the most potent new ligands were novel, dissimilar from known ligands, providing new lead structures for modulation of this medically important target.
PMCID: PMC2865168  PMID: 20405927

Results 1-19 (19)