Structure-activity relationships of suramin and pyridoxal-5'-phosphate derivatives as P2 receptor antagonists

Extracellular adenine and uracil 5'-nucleotides are important signalling molecules that exert a great variety of effects in numerous tissues and cell types through the activation of P2 receptors. In the past eight years, an extended series of P2 receptors (P2X(17), ionotropic subunits; P2Y(1,2,4,6,11,12), metabotropic receptors) has been cloned from vertebrate tissues. In this rapidly expanding field, one of the main current challenges is to relate the cloned P2 receptor subtypes to the diverse physiological responses mediated by the pharmacological phenotypes of native P2 receptors. Unfortunately, subtype-selective P2 ligands, especially potent and selective antagonists, have been only slowly forthcoming, and this acts as a considerable impediment to progress. However, a number of new P2 receptor antagonists have recently been described which to some degree are more potent and more selective than earlier antagonists like suramin or pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). This work moves us closer to the ideal goal of classifying the recombinant and native P2 receptor subtypes on the basis of antagonist profiles. This review begins with a brief account of the current status of P2 receptors and their ligands. It then focuses on structure-activity relationships of PPADS and suramin analogues and will finish with a brief discussion of some related therapeutic possibilities.     

Structure-activity relationships of pyrazole derivatives as cannabinoid receptor antagonists

As a potent, specific antagonist for the brain cannabinoid receptor (CB1), the biarylpyrazole N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A; 1) was the lead compound for initiating studies designed to examine the structure-activity relationships of related compounds and to search for more selective and potent cannabimimetic ligands. A series of pyrazole derivatives was designed and synthesized to aid in the characterization of the cannabinoid receptor binding sites and also to serve as potentially useful pharmacological probes. Therapeutically, such compounds may have the ability to antagonize harmful side effects of cannabinoids and cannabimimetic agents. Structural requirements for potent and selective brain cannabinoid CB1 receptor antagonistic activity included (a) a para-substituted phenyl ring at the 5-position, (b) a carboxamido group at the 3-position, and (c) a 2,4-dichlorophenyl substituent at the 1-position of the pyrazole ring. The most potent compound of this series contained a p-iodophenyl group at the 5-position, a piperidinyl carboxamide at the 3-position, and a 2,4-dichlorophenyl group at the 1-position of the pyrazole ring. The iodinated nature of this compound offers additional utility as a gamma-enriching SPECT (single photon emission computed tomography) ligand that may be useful in characterizing brain CB1 receptor binding in vivo.     

Structure-activity relationships of dimethindene derivatives as new M2-selective muscarinic receptor antagonists

A series of 2,3-disubstituted indenes, which are analogues of the widely used histamine H(1) receptor antagonist dimethindene, have been synthesized and studied as muscarinic and histamine receptor antagonists. The affinities of these compounds for the five human muscarinic receptor subtypes (M(1)-M(5)) and for human histamine H(1) receptors were determined in radioligand binding studies using membranes from transfected Chinese hamster ovary (CHO) cells and [(3)H]N-methylscopolamine ([(3)H]NMS). The results demonstrate that the diisopropyl analogue 19 has a similar high affinity as (S)-dimethindene at M(2) receptors ((S)-dimethindene: pK(i) = 7.52; (-)-19: pK(i) = 7.37) with an improved selectivity pattern ((S)-dimethindene: M(2)/M(1) = 6-fold, M(2)/M(3) = 5-fold, M(2)/M(4) = 10-fold, M(2)/M(5) = 25-fold; (-)-19: M(2)/M(1) = 36-fold, M(2)/M(3) = 96-fold, M(2)/M(4) = 42-fold, M(2)/M(5) = 275-fold). In addition, compound (-)-19 showed 35-fold lower affinity at histamine H(1) receptors (pK(i) = 5.61) than (S)-dimethindene (pK(i) = 7.16). Another interesting compound is the fluoroethyl derivative 20 (pK(i)/M(2) = 7.49), which also exhibits a higher M(2) selectivity (M(2)/M(1) = 19-fold; M(2)/M(3) = 22-fold; M(2)/M(4) = 13-fold; M(2)/M(5) = 62-fold) than (S)-dimethindene. Unfortunately, compound 20 also shows a high affinity for histamine H(1) receptors (pK(i) = 8.14). The compound with the highest affinity for M(2) receptors (pK(i) = 7.91), the dimethylaminomethylene analogue 31, displayed only a small preference for M(2) receptors. In conclusion, compound (-)-19 might be useful to test the hypothesis that blockade of muscarinic M(2) receptors in the brain is a viable mechanism by which to produce improved cognition. This second-generation dimethindene analogue might also be the starting point for the development of M(2)-selective muscarinic antagonists useful for quantifying M(2) receptors in the central nervous system with positron emission tomography imaging.     

Structure-activity relationships and optimization of 3,5-dichloropyridine derivatives as novel P2X(7) receptor antagonists

Screening of a library of chemical compounds showed that the dichloropyridine-based analogue 9 was a novel P2X(7) receptor antagonist. To optimize its activity, we assessed the structure-activity relationships (SAR) of 9, focusing on the hydrazide linker, the dichloropyridine skeleton, and the hydrophobic acyl (R(2)) group. We found that the hydrazide linker and the 3,5-disubstituted chlorides in the pyridine skeleton were critical for P2X(7) antagonistic activity and that the presence of hydrophobic polycycloalkyl groups at the R(2) position optimized antagonistic activity. In the EtBr uptake assay in hP2X(7)-expressing HEK293 cells, the optimized antagonists, 51 and 52, had IC(50) values of 4.9 and 13 nM, respectively. The antagonistic effects of 51 and 52 were paralleled by their ability to inhibit the release of the pro-inflammatory cytokine, IL-1β, by LPS/IFN-γ/BzATP stimulation of THP-1 cells (IC(50) = 1.3 and 9.2 nM, respectively). In addition, 52 strongly inhibited iNOS/COX-2 expression and NO production in THP-1 cells, further indicating that this compound blocks inflammatory signaling and suggesting that the dichloropyridine analogues may be useful in developing P2X(7) receptor targeted anti-inflammatory agents.     

Acyclic and cyclopropyl analogues of adenosine bisphosphate antagonists of the P2Y1 receptor: structure-activity relationships and receptor docking.

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.     

Synthesis and structure-activity relationships of uracil nucleotide derivatives and analogues as agonists at human P2Y2, P2Y4, and P2Y6 receptors

A series of UTP, UDP, and UMP derivatives and analogues were synthesized and evaluated at the human pyrimidinergic P2Y receptor subtypes P2Y2, P2Y4, and P2Y6 stably expressed in 1321N1 astrocytoma cells. Substituents at N3 of UTP were poorly tolerated by P2Y2 and P2Y4 receptors. In contrast, a large phenacyl substituent at N3 of UDP was well tolerated by the P2Y6 receptor, yielding a potent and selective P2Y6 receptor agonist (3-phenacyl-UDP, EC50=70 nM, >500-fold selective). The most potent and selective P2Y2 receptor agonist of the present series was 2-thio-UTP (EC50=50 nM, >or=30-fold selective vs P2Y4 and P2Y6). All modifications at the uracil base of UTP led to a decrease in potency at the P2Y4 receptor. A beta,gamma-dichloromethylene modification in the triphosphate chain of 5-bromo-UTP was tolerated by all three receptor subtypes, thus opening up a new strategy to obtain ectonucleotide diphosphohydrolase- and phosphatase-resistant P2Y2, P2Y4, and P2Y6 receptor agonists.     

Structure-activity relationships of pyridoxal phosphate derivatives as potent and selective antagonists of P2X1 receptors.

Novel analogues of the P2 receptor antagonist pyridoxal-5'-phosphate 6-azophenyl-2',5'-disulfonate (2) were synthesized and studied as antagonists in functional assays at recombinant rat P2X1, P2X2, and P2X3 receptors expressed in Xenopus oocytes (ion flux stimulation) and at turkey erythrocyte P2Y1 receptors (phospholipase C activation). Selected compounds were also evaluated as antagonists of ion flux and the opening of a large pore at the recombinant human P2X7 receptor. Modifications were made in the 4-aldehyde and 5'-phosphate groups of the pyridoxal moiety: i.e. a CH2OH group at the 4-position in pyridoxine was either condensed as a cyclic phosphate or phosphorylated separately to form a bisphosphate, which reduced potency at P2 receptors. 5-Methylphosphonate substitution, anticipated to increase stability to hydrolysis, preserved P2 receptor potency. At the 6-position, halo, carboxylate, sulfonate, and phosphonate variations made on the phenylazo ring modulated potency at P2 receptors. The p-carboxyphenylazo analogue, 4, of phosphate 2 displayed an IC50 value of 9 nM at recombinant P2X1 receptors and was 1300-, 16-, and > 10,000-fold selective for P2X1 versus P2X2, P2X3, and P2Y1 subtypes, respectively. The corresponding 5-methylphosphonate was equipotent at P2X1 receptors. The 5-methylphosphonate analogue containing a 6-[3,5-bis(methylphosphonate)]phenylazo moiety, 9, had IC50 values of 11 and 25 nM at recombinant P2X1 and P2X3 receptors, respectively. The analogue containing a phenylazo 4-phosphonate group, 11, was also very potent at both P2X1 and P2X3 receptors. However, the corresponding 2,5-disulfonate analogue, 10, was 28-fold selective for P2X1 versus P2X3 receptors. None of the analogues were more potent at P2X7 and P2Y1 receptors than 2, which acted in the micromolar range at these two subtypes.     

Diisothiocyanate derivatives as potent, insurmountable antagonists of P2Y6 nucleotide receptors

The physiological role of the P2Y(6) nucleotide receptor may involve cardiovascular, immune and digestive functions based on the receptor tissue distribution, and selective antagonists for this receptor are lacking. We have synthesized a series of symmetric aryl diisothiocyanate derivatives and examined their ability to inhibit phospholipase C (PLC) activity induced by activation of five subtypes of recombinant P2Y receptors. Several derivatives were more potent at inhibiting action of UDP at both human and rat P2Y(6) receptors expressed in 1321N1 human astrocytes than activation of human P2Y(1), P2Y(2), P2Y(4) and P2Y(11) receptors. The inhibition by diisothiocyanate derivatives of 1,2-diphenylethane (MRS2567) and 1,4-di-(phenylthioureido) butane (MRS2578) was concentration-dependent and insurmountable, with IC(50) values of 126+/-15 nM and 37+/-16 nM (human) and 101+/-27 nM and 98+/-11 nM (rat), respectively. A derivative of 1,4-phenylendiisothiocyanate (MRS2575) inhibited only human but not rat P2Y(6) receptor activity. MRS2567 and MRS2578 at 10microM did not affect the UTP (100nM)-induced responses of cells expressing P2Y(2) and P2Y(4) receptors, nor did they affect the 2-methylthio-ADP (30nM)-induced responses at the P2Y(1) receptor or the ATP (10microM)-induced responses at the P2Y(11) receptor. Other antagonists displayed mixed selectivities. The selective antagonists MRS2567, MRS2575 and MRS2578 (1microM) completely blocked the protection by UDP of cells undergoing TNFalpha-induced apoptosis. Thus, we have identified potent, insurmountable antagonists of P2Y(6) receptors that are selective within the family of PLC-coupled P2Y receptors.     

Structurally related nucleotides as selective agonists and antagonists at P2Y1 receptors

The P2Y1 receptor responds to adenine nucleotides and is present in platelets, heart, smooth muscles prostate, ovary, and brain. A selective antagonist may be useful as an antithrombotic agent. We have analyzed the binding site of this G protein-coupled receptor using ligand design, site-directed mutagenesis, and homology modeling based on rhodopsin. We have designed and synthesized a series of deoxyadenosine 3',5'-bisphosphate derivatives that act as antagonists, or, in some cases with small structural changes, as agonists or partial agonists. The 2-position accommodates Cl or thioethers, whereas the N6-position is limited to Me or Et. 2'-Substitution with OH or OMe increases agonist efficacy over 2'-H. Using molecular modeling of the binding site, the oxygen atoms of the ribose moiety were predicted to be non-essential, i.e. no specific H-bonds with the receptor protein appear in the model. We have, therefore, substituted this moiety with carbocylics, smaller and larger rings, conformationally constrained rings, and acyclics, with retention of affinity for the receptor. With simplified pharmacophores we are exploring the steric and electronic requirements of the receptor binding site, and the structural basis of receptor activation.     

Adenosine 5'-O-(1-boranotriphosphate) derivatives as novel P2Y(1) receptor agonists

P2-receptors (P2-Rs) represent important targets for novel drug development. Most ATP analogues proposed as potential drug candidates have shortcomings such as limited receptor-selectivity and limited stability that justify the search for new P2-R agonists. Therefore, a novel series of nucleotides based on the adenosine 5'-O-(1-boranotriphosphate) (ATP-alpha-B) scaffold was developed and tested as P2Y(1)-R agonists. An efficient four-step one-pot synthesis of several ATP-alpha-B analogues from the corresponding nucleosides was developed, as well as a facile method for the separation of the diastereoisomers (A and B isomers) of the chiral products. The potency of the new analogues as P2Y(1)-R agonists was evaluated by the agonist-induced Ca2+ release of HEK 293 cells stably transfected with rat-brain P2Y(1)-R. ATP-alpha-B A isomer was equipotent with ATP (EC50 = 2 x 10(-7) M). However, 2-MeS- and 2-Cl- substitutions on ATP-alpha-B (A isomer) increased the potency of the agonist up to 100-fold, with EC50 values of 4.5 x 10(-9) and 3.6 x 10(-9) M, compared to that of the ATP-alpha-B (A isomer). Diastereoisomers A of all ATP-alpha-B analogues were more potent in inducing Ca2+ release than the corresponding B counterparts, with a 20-fold difference for 2-MeS-ATP-alpha-B analogues. The chemical stability of the new P2Y(1)-R agonists was evaluated by 31P NMR under physiological and gastric-juice pH values at 37 degrees C, with rates of hydrolysis of 2-MeS-ATP-alpha-B of 1.38 x 10(-7) s-1 (t1/2 of 1395 h) and 3.24 x 10(-5) s-1 (t1/2 = 5.9 h), respectively. The enzymatic stability of the new analogues toward spleen NTPDase was evaluated. Most of the new analogues were poor substrates for the NTPDase, with ATP-alpha-B (A isomer) hydrolysis being 5% of the hydrolysis rate of ATP. Diastereoisomers A and B exhibited different stability, with A isomers being significantly more stable, up to 9-fold. Furthermore, A isomers that are potent P2Y(1)-R agonists barely interact with NTPDase, thus exhibiting protein selectivity. Therefore, on the basis of our findings, the new, highly water-soluble, P2Y(1)-R agonists may be considered as potentially promising drug candidates.     

Structure-activity relationship of uridine 5'-diphosphoglucose analogues as agonists of the human P2Y14 receptor

UDP-glucose (UDPG) and derivatives are naturally occurring agonists of the Gi protein-coupled P2Y14 receptor, which occurs in the immune system. We synthesized and characterized pharmacologically novel analogues of UDPG modified on the nucleobase, ribose, and glucose moieties, as the basis for designing novel ligands in conjunction with modeling. The recombinant human P2Y14 receptor expressed in COS-7 cells was coupled to phospholipase C through an engineered Galpha-q/i protein. Most modifications of the uracil or ribose moieties abolished activity; this is among the least permissive P2Y receptors. However, a 2-thiouracil modification in 15 (EC50 49 +/- 2 nM) enhanced the potency of UDPG (but not UDP-glucuronic acid) by 7-fold. 4-Thio analogue 13 was equipotent to UDPG, but S-alkylation was detrimental. Compound 15 was docked in a rhodposin-based receptor homology model, which correctly predicted potent agonism of UDP-fructose, UDP-mannose, and UDP-inositol. The hexose moiety of UDPG interacts with multiple H-bonding and charged residues and provides a fertile region for agonist modification.     

Structure-activity relationships in the development of excitatory amino acid receptor agonists and competitive antagonists

Development of new selective ligands for excitatory amino acid receptors has been fundamental in supporting this rapidly developing field. Some of the most important ligands have come from the laboratories of Jeff Watkins, Povl Krogsgaard-Larsen and Tage Honoré, who collaborate in this double-length review to describe the chemical features and SARs of agonists and antagonists, particularly those features associated with subtype selectivity.     

Structure-activity relationships of new agonists and antagonists of different metabotropic glutamate receptor subtypes.

1. We investigated the agonist and antagonist activities of 22 new phenylglycine and phenylalanine derivatives for metabotropic glutamate receptors (mGluRs) by examining their effects on the signal transduction of mGluR1, mGluR2 and mGluR6 subtypes expressed in Chinese hamster ovary cells. This analysis revealed several structural characteristics that govern receptor subtype specificity of the agonist and antagonist activities of phenylglycine derivatives. 2. Hydroxyphenylglycine derivatives possessed either an agonist activity on mGluR1/mGluR6 or an antagonist activity on mGluR1. 3. Carboxyphenylglycine derivatives showed an agonist activity on mGluR2 but an antagonist activity on mGluR1. 4. alpha-Methylation or alpha-ethylation of the carboxyphenylglycine derivatives converts the agonist property for mGluR2 to an antagonist property, thus producing antagonists at both mGluR1 and mGluR2. 5. Structurally-corresponding phenylalanine derivatives showed little or no agonist or antagonist activity on any subtypes of the receptors. 6. This investigation demonstrates that the nature and positions of side chains and ring substituents incorporated into the phenylglycine structure are critical in determining the agonist and antagonist activities of members of this group of compounds on different subtypes of the mGluR family. 7. We also tested two alpha-methyl derivatives of mGluR agonists. (2S, 1'S, 2'S)-2-(2-Carboxycyclopropyl)glycine (L-CCG-I) is a potent agonist for mGluR2 but alpha-methylation of this compound changes its activity to that of an mGluR2-selective antagonist. In contrast, alpha-methylation of L-2-amino-4-phosphonobutyrate (L-AP4) results in retention of an agonist activity on mGluR6. Thus, alpha-methylation produces different effects, depending on the chemical structures of lead compounds and/or on the subtype of mGluR tested.     

Structure-activity relationships of vanilloid receptor agonists for arteriolar TRPV1

BACKGROUND AND PURPOSE

The transient receptor potential vanilloid 1 (TRPV1) plays a role in the activation of sensory neurons by various painful stimuli and is a therapeutic target. However, functional TRPV1 that affect microvascular diameter are also expressed in peripheral arteries and we attempted to characterize this receptor.

EXPERIMENTAL APPROACH

Sensory TRPV1 activation was measured in rats by use of an eye wiping assay. Arteriolar TRPV1-mediated smooth muscle specific responses (arteriolar diameter, changes in intracellular Ca²⁺) were determined in isolated, pressurized skeletal muscle arterioles obtained from the rat and wild-type or TRPV1^−/− mice and in canine isolated smooth muscle cells. The vascular pharmacology of the TRPV1 agonists (potency, efficacy, kinetics of action and receptor desensitization) was determined in rat isolated skeletal muscle arteries.

KEY RESULTS

Capsaicin evoked a constrictor response in isolated arteries similar to that mediated by noradrenaline, this was absent in arteries from TRPV1 knockout mice and competitively inhibited by TRPV1 antagonist AMG9810. Capsaicin increased intracellular Ca²⁺ in the arteriolar wall and in isolated smooth muscle cells. The TRPV1 agonists evoked similar vascular constrictions (MSK-195 and JYL-79) or were without effect (resiniferatoxin and JYL-273), although all increased the number of responses (sensory activation) in the eye wiping assay. Maximal doses of all agonists induced complete desensitization (tachyphylaxis) of arteriolar TRPV1 (with the exception of capsaicin). Responses to the partial agonist JYL-1511 suggested 10% TRPV1 activation is sufficient to evoke vascular tachyphylaxis without sensory activation.

CONCLUSIONS AND IMPLICATIONS

Arteriolar TRPV1 have different pharmacological properties from those located on sensory neurons in the rat.     

Structure-activity relationships of a series of pyrrolo[3,2-d]pyrimidine derivatives and related compounds as neuropeptide Y5 receptor antagonists

Neuropeptide Y (NPY) has been shown to play an important role in the regulation of food intake and energy balance. Pharmacological data suggests that the Y5 receptor subtype contributes to the effects of NPY on appetite, and therefore a Y5 antagonist might be a useful therapeutic agent for the treatment of obesity. In attempts to identify potential Y5 antagonists, a series of pyrrolo[3, 2-d]pyrimidine derivatives was prepared and evaluated for their ability to bind to Y5 receptors in vitro. We report here the synthesis and initial structure-activity relationship investigations for this class of compounds. The target compounds were prepared by a variety of synthetic routes designed to modify both the substitution and the heterocyclic core of the pyrrolo[3,2-d]pyrimidine lead 1. In addition to identifying several potent Y5 antagonists for evaluation as potential antiobesity agents, a pharmacophore model for the human Y5 receptor is presented.     

Structure-activity relationships of xanthocillin derivatives as thrombopoietin receptor agonist

Xanthocillin derivatives, which show thrombopoietin receptor agonist activity, were synthesized through our developed method. Bioassay data suggest the importance of alkene geometry, the presence of substituents at the benzene ring that support hydrophobic character, and the moderate size of the molecule. One of the two isonitrile group of the natural product appears to be dispensable.     

Structure-activity relationships of truncated D- and l-4'-thioadenosine derivatives as species-independent A3 adenosine receptor antagonists

Novel D- and l-4'-thioadenosine derivatives lacking the 4'-hydroxymethyl moiety were synthesized, starting from d-mannose and d-gulonic gamma-lactone, respectively, as potent and selective species-independent A 3 adenosine receptor (AR) antagonists. Among the novel 4'-truncated 2-H nucleosides tested, a N(6)-(3-chlorobenzyl) derivative 7c was the most potent at the human A 3 AR (K i = 1.5 nM), but a N(6)-(3-bromobenzyl) derivative 7d showed the optimal species-independent binding affinity.     

P2Y receptor antagonists in thrombosis

The dual role of P2Y1 and P2Y12 receptors in platelet aggregation by ADP has been firmly established, based on the action of selective inhibitors, gene targeting in mice and human genetic evidence. Both of these receptor subtypes constitute targets for antithrombotic agents, and compounds with a dual action might also be of interest. However, the agents currently on the market (ticlopidine and clopidogrel), or known to be in development (cangrelor, AZD-6140 and prasugrel), all target the P2Y12 receptor. The thienopyridines (ticlopidine, clopidogrel and prasugrel) irreversibly inactivate the P2Y12 receptor via the covalent binding of an active metabolite generated in the liver, while the other compounds are competitive antagonists. Cangrelor, an ATP derivative, is suitable for intravenous perfusion, whereas AZD-6140 is in clinical development as an orally active agent.     

薯蓣皂苷元衍生物抗肿瘤的构效关系研究

为阐明薯蓣皂苷元衍生物的体外抗肿瘤活性的构效关系,基于Bcl-2蛋白小分子抑制剂的三维药效团模型的各药效点的特点,本研究利用autodock4.2将薯蓣皂苷元衍生物和Bcl-2进行了大量对接及分析,选择性的合成了31个化合物,采用MTT法测定了这些化合物对A375、A549、HepG-2和K562等4个肿瘤细胞株的体外抗肿瘤活性。初步的构效关系研究表明,薯蓣皂苷元失F环的26-位脂肪酸酯、芳香酸酯类衍生物几乎没有活性;薯蓣皂苷元三氮唑溴盐类衍生物均具有较好的体外抗肿瘤活性,且三氮唑上连有较大的疏水基团的衍生物的活性更好;薯蓣皂苷元及其失F环的杂环类、薯蓣皂苷元失F环氨基酸酯类衍生物能形成较强氢键、偶极作用的衍生物的活性更好。     

Structure-activity relationships of uridine 5'-diphosphate analogues at the human P2Y6 receptor

The structure-activity relationships and molecular modeling of the uracil nucleotide activated P2Y6 receptor have been studied. Uridine 5'-diphosphate (UDP) analogues bearing substitutions of the ribose moiety, the uracil ring, and the diphosphate group were synthesized and assayed for activity at the human P2Y6 receptor. The uracil ring was modified at the 4 position, with the synthesis of 4-substituted-thiouridine 5'-diphosphate analogues, as well as at positions 2, 3, and 5. The effect of modifications at the level of the phosphate chain was studied by preparing a cyclic 3',5'-diphosphate analogue, a 3'-diphosphate analogue, and several dinucleotide diphosphates. 5-Iodo-UDP 32 (EC50 = 0.15 microM) was equipotent to UDP, while substitutions of the 2'-hydroxyl (amino, azido) greatly reduce potency. The 2- and 4-thio analogues, 20 and 21, respectively, were also relatively potent in comparison to UDP. However, most other modifications greatly reduced potency. Molecular modeling indicates that the beta-phosphate of 5'-UDP and analogues is essential for the establishment of electrostatic interactions with two of the three conserved cationic residues of the receptor. Among 4-thioether derivatives, a 4-ethylthio analogue 23 displayed an EC50 of 0.28 microM, indicative of favorable interactions predicted for a small 4-alkylthio moiety with the aromatic ring of Y33 in TM1. The activity of analogue 19 in which the ribose was substituted with a 2-oxabicyclohexane ring in a rigid (S)-conformation (P = 126 degrees , 1'-exo) was consistent with molecular modeling. These results provide a better understanding of molecular recognition at the P2Y6 receptor and will be helpful in designing selective and potent P2Y6 receptor ligands.