Synthesis of novel apio carbocyclic nucleoside analogues as selective a(3) adenosine receptor agonists

On the basis of the biological activity of neplanocin A and apio-dideoxyadenosine (apio-ddA), novel apio-neplanocin A analogues 5a-d, combining the properties of two nucleosides, were stereoselectively synthesized. The apio moiety of the target nucleosides 5a-d was stereoselectively introduced by treating lactol 10 with 37% formaldehyde in the presence of potassium carbonate. The carbasugar moiety of neplanocin A was successively built by exposing diene 12 on a Grubbs catalyst in methylene chloride. The final nucleosides 5a-d were synthesized from the condensation of the glycosyl donor 14 with nucleic bases under the standard Mitsunobu conditions. Similarly, apio-aristeromycin 6 and (N)-apio-methanocarbaadenosine 7 were derived from the common intermediate 13 using catalytic hydrogenation and Simmons-Smith cyclopropanation as key steps. All of the final nucleosides 5a-d, 6, and 7 did not show significant inhibitory activity against S-adenosylhomocysteine hydrolase (SAH) up to 100 muM, maybe due to the absence of the secondary hydroxyl group at the C3'-position, which should be oxidized by cofactor-bound NAD(+). However, apio-neplanocin A (5a) showed potent and highly selective binding affinity (K(i) = 628 +/- 69 nM) at the A(3) adenosine receptor without any binding affinity at the A(1) and A(2A) adenosine receptors. In conclusion, we have first developed novel carbocyclic nucleosides with unnatural apio-carbasugars using stereoselective hydroxymethylation and RCM reaction and also discovered a new template of human A(3) adenosine receptor agonist, which play a great role in developing new A(3) adenosine receptor agonist as well as in identifying the binding site of the receptor.     

A new synthetic route to (North)-methanocarba nucleosides designed as A3 adenosine receptor agonists

Activation of the A3 adenosine receptor (AR) is associated with cerebroprotective, cardioprotective, and anticancer effects. Among potent and selective A3 AR agonists are novel methanocarba adenosine analogues in which the conformation of a pseudo-ribose moiety is locked in the North (N) hemisphere of the pseudorotational cycle. 5'-Uronamide (N)-methanocarba nucleosides, such as MRS1898 and MRS2346, are examples of full agonists of the human A3 AR. An improved convergent approach from easily accessible 2,3-O-isopropylidene-d-erythrose (2b), and the combination of a strategic intramolecular cyclopropanation step plus the acid-catalyzed isomerization of an isopropylidene group, provided a suitable pseudosugar precursor (23) for the synthesis of MRS1898, MRS2346, and related analogues. This new synthetic route uses readily available building blocks and opens the way for the preparation of a variety of targets on a reasonable scale.     

A neoceptor approach to unraveling microscopic interactions between the human A2A adenosine receptor and its agonists

Strategically mutated neoceptors, e.g., with anionic residues in TMs 3 and 7 intended for pairing with positively charged amine-modified nucleosides, were derived from the antiinflammatory A(2A) adenosine receptor (AR). Adenosine derivatives functionalized at the 5', 2, and N(6) positions were synthesized. The T88D mutation selectively enhanced the binding of the chain-length-optimized 5'-(2-aminoethyl)uronamide but not 5'-(2-hydroxyethyl)uronamide, suggesting a critical role of the positively charged amine. Combination of this modification with the N(6)-(2-methylbenzyl) group enhanced affinity at the Q89D- and N181D- but not the T88D-A(2A)AR. Amino groups placed near the 2- or N(6)-position only slightly affected the binding to mutant receptors. The 5'-hydrazide MRS3412 was 670- and 161-fold enhanced, in binding and functionally, respectively, at the Q89D-A(2A)AR compared to the wild-type. Thus, we identified and modeled pairs of A(2A)AR-derived neoceptor-neoligand, which are pharmacologically orthogonal with respect to the native species.     

Three-dimensional pharmacophore modeling of liver-X receptor agonists

High cholesterol levels contribute to hyperlipidemia. Liver X receptors (LXRs) are the drug targets. LXRs regulate the cholesterol absorption, biosynthesis, transportation, and metabolism. Novel agonists of LXR, especially LXRβ, are attractive solutions for treating hyperlipidemia. In order to discover novel LXRβ agonists, a three-dimensional pharmacophore model was built based upon known LXRβ agonists. The model was validated with a test set, a virtual screening experiment, and the FlexX docking approach. Results show that the model is capable of predicting a LXRβ agonist activity. Ligand-based virtual screening results can be refined by cross-linking by structure-based approaches. This is because two ligands that are mapped in the same way to the same pharmacophore model may have significantly different binding behaviors in the receptor's binding pocket. This paper reports our approach to identify reliable pharmacophore models through combining both ligand- and structure-based approaches.     

New mu-opioid receptor agonists with piperazine moiety

New mu-opioid receptor (MOR) agonists containing piperazine and homopiperazine moieties in the structures were synthesized and their affinities to and agonist potencies on MOR were evaluated. Among the synthesized compounds, 4-[4-(2-methoxyphenyl)piperazin-1-yl]-N,N-dimethyl-2,2-diphenylbutanamide (20 Aa) showed the highest affinity to the human MOR expressed in Chinese hamster ovary (CHO)-K1 cells, and the highest agonist potency on the MOR in isolated guinea-pig ileum preparation.     

Eigenvalue analysis of peroxisome proliferator-activated receptor gamma agonists

Eigenvalue analysis (EVA) was conducted on a series of potent agonists of peroxisome proliferator-activated receptor gamma (PPARgamma). Predictive EVA quantitative structure-activity relationship (QSAR) models were established using the SYBYL package, which had conventional r2 and cross-validated coefficient (q2) values up to 0.920 and 0.587 for the AM1 method and 0.863 and 0.586 for the PM3 method, respectively. These models were validated by a test set containing 18 compounds. The capability to predict by these two models for PPARgamma agonists, with the best predictive r2pred value of 0.614 for AM1 and 0.822 for PM3 methods, set a successful example for applying a similar approach in building QSAR models for PPARalpha and -delta that could potentially offer a new opportunity in the design of novel PPAR modulators.     

Tritiation of two potent catecholamine beta-adrenergic receptor agonists

The tritiation of the beta-adrenergic catecholamines isoproterenol and hydroxybenzylisoproterenol is described.     

Beta-adrenergic receptors: regulatory role of agonists.

Direct radioligand binding studies have been used to probe the molecular mechanisms whereby agonist catecholamines regulate the function of beta-adrenergic receptors in a model system, the frog erythrocyte. The unique characteristics of agonist as opposed to antagonist action are first, the ability to stimulate the adenylate cyclase through the receptor and second, the ability to desensitize the system by alterations induced in beta-adrenergic receptors. These properties of agonist are not shared by antagonist despite the high affinity and specificity of antagonist binding to the beta-adrenergic receptors. Agonist and antagonist receptor complexes may be distinguished in a variety of ways including differences in their sensitivity to regulatory guanine nucleotides and also by gel chromatography on AcA 34 Ultragel. The agonist receptor complex appears to elute from the columns with an apparently increased size. A "dynamic receptor affinity model" of beta-adrenergic receptor action is proposed which features several distinct conformational states of the receptor. Agonists have much higher affinity for the physiologically active or coupled state of the receptor, whereas antagonists have equal affinity for both. In addition, a third "desensitized" state of the receptor is also postulated to exist.     

New mu-opioid receptor agonists with phenoxyacetic acid moiety

New muq-opioid receptor (MOR) agonists containing 4-hydroxypiperidine, piperidine and piperazine moieties were synthesized and evaluated to find a peripheral opioid analgesic. Among the synthesized compounds, 12-[1-[3-(N,N-dimethylcarbamoyl)-3,3-diphenylpropyl]-4-hydroxypiperidin-4-yl]phenoxy]acetic acid (8: SS620) having phenoxyacetic acid and 4-hydroxypiperidine moieties showed the highest agonist potency on the MOR in an isolated guinea-pig ileum preparation, and it also had selectivity to the human MOR expressed in Chinese hamster ovary (CHO)-K1 cells compared with the same types of delta- and kappa-opioid receptors (DOR and KOR). In addition, compound 8 showed a 10 times more potent MOR agonist activity than loperamide. Furthermore, compound 8 showed a peripheral analgesic activity in vivo screening on rat.     

Structural comparison of NK2 receptor agonists and antagonists

Summary The conformational space of two NK₂ receptor agonists and a new potent antagonist has been sampled by the simulated annealing technique. Low-energy conformers were obtained, which were compared with respect to their key residues, namely phenylalanine, leucine and methionine. The hypothesis is that they share part of the binding site on the receptor.     

Exploring the molecular basis of selectivity in A1 adenosine receptors agonists: a case study

Adenosine is a naturally occurring purine nucleoside that has a wide variety of well-documented regulatory functions and physiological roles. Selective activation of the adenosine A₁ receptor has drawn attention in drug discovery for the therapeutic effects on neural and cardiovascular disorders. We have developed a model of the human A₁ adenosine receptor using bovine rhodopsin as a template. A flexible docking approach has been subsequently carried out for evaluating the molecular interactions of twenty-one selective A₁ agonists with the receptor model. The results of these studies are consistent with mutational and biochemical data. In particular, they highlight a wide hydrogen-bonding network between the nucleoside portion of the ligands and the A₁ receptor as well as key amino acids for hydrophobic interactions with the different N⁶-groups of the agonists. The models presented here provide a detailed molecular map for the selective stimulation of the adenosine A₁ receptor subtype and a steady basis for the rational design of new A₁ selective ligands.     

Understanding diseases via receptor regulation

In this issue of Chemistry & Biology, Guy and coworkers demonstrate that they can selectively recruit individual nuclear receptors by using small molecules (proteomimetics) in combination with specific agonists. This may ultimately lead to a link between the receptor's signaling pathway and its role in individual diseases.     

Screening for 2-quinolinone-derived selective androgen receptor agonists in doping control analysis

Selective androgen receptor modulators (SARMs) represent a class of emerging drugs with high potential for misuse in sports, and therefore members of this group are banned as anabolic agents by the World Anti-Doping Agency. Preventive approaches to restrict their use include early implementation of target analytes into doping control screening assays and evaluation of the mass spectrometric behavior of these drugs to allow their unequivocal identification as well as the characterization of structurally related compounds and metabolic products. Four model SARMs with the 6-alkylamino-2-quinolinone structure, including the advanced drug candidate LGD-2226, were synthesized. Fragmentation pathways after positive electrospray ionization and collision-induced dissociation were studied using an LTQ Orbitrap mass analyzer, and diagnostic product ions and common dissociation pathways were employed to establish a screening procedure targeting intact quinolinone-based SARMs as well as putative metabolic products such as dealkylated analogues. Therefore, features of a triple quadrupole mass analyzer such as multiple reaction monitoring and precursor ion scanning were utilized. Sample preparation based on commonly employed liquid-liquid extraction and subsequent liquid chromatographic/tandem mass spectrometric measurement allowed for detection limits of 0.01-0.2 ng/mL, and intra- and interday precisions between 3.2 and 8.5% and between 6.3 and 16.6%, respectively. Recoveries varied from 81 to 98%, and tests for ion suppression or enhancement effects were negative for all analytes.     

High specific activity tritium labelling of some sigma-1 receptor agonists

The high specific activity tritiation of (+)-SKF-10,047 (1) and N,N-dimethyltryptamine (4) is described. [N-allyl-³H] (+)-SKF-10,047 (3) was prepared by Lindlar catalyst tritiation of (+)-N-propargylnormetazocine (2) and [N-methyl-³H] N,N-dimethyltryptamine (6) was synthesized by the alkylation of N-methyltryptamine (5) with [³H] methyl iodide. Both sigma-1 synthetic agonist 3 and endogenous agonist 6 have been useful in studying this receptor.     

Considerations on the recognition of the D1 receptor by agonists

Summary A model of the mechanism for recognition of the D1 receptor has been developed. Conformational analysis for 10 agonists from diverse chemical families was carried out as a first step toward the characterization of the bioactive form. First, maximum structural overlap of the features common to all ligands allowed a simple identification of the candidate bioactive form for each ligand. At a second level of characterization, steric and electronic properties were computed for all accessible structures to analyze those properties that may modulate receptor recognition.     

Neuronal nicotinic receptor agonists: a multi-approach development of the pharmacophore

Based on the results obtained with different automated computational approaches as applied to the study of eleven high-affinity agonists of the neuronal nicotine acetylcholine receptor (nAChR), belonging to different chemical classes, new relevant features were detected which complement the existing pharmacophores. Convergent results from DISCO (Distance Comparison), QXP (Quick Explore), Catalyst/HipHop, and MIPSIM (Molecular Interaction Potential Similarity) allowed us to identify and locate, in a well defined spatial arrangement, three geometrically independent key structural features: (i) a positively charged nitrogen atom for ionic or hydrogen bond interactions, (ii) a lone pair of the pyridine nitrogen or a specific lone pair of a carbonyl oxygen, as a hydrogen bond acceptor, and (iii) a centre of a hydrophobic area generally occupied by aliphatic cycles. The pharmacophore presented herein, along with predictive 2D and 3D QSAR models recently developed in our group, could represent valuable computational tools for the design of new nAChR agonists having therapeutical potential.     

腺嘌呤核苷的环磷酰化反应

腺嘌呤核苷3’,5’-环磷酸(c-AMP)的磷酸衍生物可能作为c-AMP在体内的模拟物或贮存形式,因此研究c-AMP磷酸衍生物的合成及其生物活性,有可能为发现新药开辟途径.作者曾报道c-AMP的磷酯和磷酰胺的合成,并发现这类衍生物对肿瘤细胞的DNA和RNA的合成有较强抑制作用.本文讨论了含有不同离去基团的三价磷试剂与2'-保护的核苷反应,可以直接环合生成各种核苷3’,5’-环亚磷酸衍生物,后者进一步与碘或硫反应可