Divalent cannabinoid-1 receptor ligands: A linker attachment point survey of SR141716A for development of high-affinity CB1R molecular probes

The cannabinoid-1 receptor (CB1R) inverse agonist SR141716A has proven useful for study of the endocannabinoid system, including development of divalent CB1R ligands possessing a second functional motif attached via a linker unit. These have predominantly employed the C3 position of the central pyrazole ring for linker attachment. Despite this precedent, a novel series of C3-linked CB1R-D2R divalent ligands exhibited extremely high affinity at the D2R, but only poor affinity for the CB1R. A systematic linker attachment point survey of the SR141716A pharmacophore was therefore undertaken, establishing the C5 position as the optimal site for linker conjugation. This linker attachment survey enabled the identification of a novel divalent ligand as a lead compound to inform ongoing development of high-affinity CB1R molecular probes.     

Molecular Determinants of Phosphatidylinositol 4,5-Bisphosphate (PI(4,5)P2) Binding to Transient Receptor Potential V1 (TRPV1) Channels

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) has been recognized as an important activator of certain transient receptor potential (TRP) channels. More specifically, TRPV1 is a pain receptor activated by a wide range of stimuli. However, whether or not PI(4,5)P₂ is a TRPV1 agonist remains open to debate. Utilizing a combined approach of mutagenesis and molecular modeling, we identified a PI(4,5)P₂ binding site located between the TRP box and the S4-S5 linker. At this site, PI(4,5)P₂ interacts with the amino acid residues Arg-575 and Arg-579 in the S4-S5 linker and with Lys-694 in the TRP box. We confirmed that PI(4,5)P₂ behaves as a channel agonist and found that Arg-575, Arg-579, and Lys-694 mutations to alanine reduce PI(4,5)P₂ binding affinity. Additionally, in silico mutations R575A, R579A, and K694A showed that the reduction in binding affinity results from the delocalization of PI(4,5)P₂ in the binding pocket. Molecular dynamics simulations indicate that PI(4,5)P₂ binding induces conformational rearrangements of the structure formed by S6 and the TRP domain, which cause an opening of the lower TRPV1 channel gate.     

7-Azaindolequinuclidinones (7-AIQD): A novel class of cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptor ligands

A series of N-benzyl-7-azaindolequinuclidinone (7-AIQD) analogs have been synthesized and evaluated for affinity toward CB1 and CB2 cannabinoid receptors and identified as a novel class of cannabinoid receptor ligands. Structure–activity relationship (SAR) studies indicate that 7-AIQD analogs are dual CB1/CB2 receptor ligands exhibiting high potency with somewhat greater selectivity towards CB2 receptors compared to the previously reported indolequinuclidinone (IQD) analogs. Initial binding assays showed that 7-AIQD analogs 8b, 8d, 8f, 8g and 9b (1 μM) produced more that 50% displacement of the CB1/CB2 non-selective agonist CP-55,940 (0.1 nM). Furthermore, Ki values determined from full competition binding curves showed that analogs 8a, 8b and 8g exhibit high affinity (110, 115 and 23.7 nM, respectively) and moderate selectivity (26.3, 6.1 and 9.2-fold, respectively) for CB2 relative to CB1 receptors. Functional studies examining modulation of G-protein activity demonstrated that 8a acts as a neutral antagonist at CB1 and CB2 receptors, while 8b exhibits inverse agonist activity at these receptors. Analogs 8f and 8g exhibit different intrinsic activities, depending on the receptor examined. Molecular docking and binding free energy calculations for the most active compounds (8a, 8b, 8f, and 8g) were performed to better understand the CB2 receptor-selective mechanism at the atomic level. Compound 8g exhibited the highest predicted binding affinity at both CB1 and CB2 receptors, and all four compounds were shown to have higher predicted binding affinities with the CB2 receptor compared to their corresponding binding affinities with the CB1 receptor. Further structural optimization of 7-AIQD analogs may lead to the identification of potential clinical agents.     

Iso-lactam and reduced amide analogues of the peptidomimetic dopamine receptor modulator 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide

An analogue of the highly potent gamma-lactam Pro-Leu-Gly-NH(2) peptidomimetic, 3(R)-[(2(S)-pyrrolidinylcarbonyl) amino]-2-oxo-1-pyrrolidineacetamide (2), 4(R)-[[2(S)-pyrrolidinylcarbonyl]amino]-2-oxo-1-pyrrolidineacetamide (3), in which the lactam carbonyl moiety has been placed in a different position with respect to the 3-amino group was synthesized. Also, a series of analogues of 2, compounds 4-6, were synthesized in which each of the amide bonds of 2 were systematically replaced with a reduced amide bond surrogate. The analogues were tested for their ability to enhance the binding of [3H]N-propylnorapomorphine to dopamine receptors in a functional in vitro assay utilizing bovine striatal membranes. Peptidomimetic 3 was shown to be more potent than 2, while 4 and 5 were significantly less effective than 2. Peptidomimetic 6 had a pharmacological profile similar to that of 2.     

Allosteric modulator ORG27569 induces CB1 cannabinoid receptor high affinity agonist binding state, receptor internalization, and Gi protein-independent ERK1/2 kinase activation

The cannabinoid receptor 1 (CB1), a member of the class A G protein-coupled receptor family, is expressed in brain tissue where agonist stimulation primarily activates the pertussis toxin-sensitive inhibitory G protein (G(i)). Ligands such as CP55940 ((1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3- hydroxypropyl)cyclohexan-1-ol) and Δ(9)-tetrahydrocannabinol are orthosteric agonists for the receptor, bind the conventional binding pocket, and trigger G(i)-mediated effects including inhibition of adenylate cyclase. ORG27569 (5-chloro-3-ethyl-1H-indole-2-carboxylic acid [2-(4-piperidin-1-yl-phenyl)ethyl]amide) has been identified as an allosteric modulator that displays positive cooperativity for CP55940 binding to CB1 yet acts as an antagonist of G protein coupling. To examine this apparent conundrum, we used the wild-type CB1 and two mutants, T210A and T210I (D'Antona, A. M., Ahn, K. H., and Kendall, D. A. (2006) Biochemistry 45, 5606-5617), which collectively cover a spectrum of receptor states from inactive to partially active to more fully constitutively active. Using these receptors, we demonstrated that ORG27569 induces a CB1 receptor state that is characterized by enhanced agonist affinity and decreased inverse agonist affinity consistent with an active conformation. Also consistent with this conformation, the impact of ORG27569 binding was most dramatic on the inactive T210A receptor and less pronounced on the already active T210I receptor. Although ORG27569 antagonized CP55940-induced guanosine 5'-3-O-(thio)triphosphate binding, which is indicative of G protein coupling inhibition in a concentration-dependent manner, the ORG27569-induced conformational change of the CB1 receptor led to cellular internalization and downstream activation of ERK signaling, providing the first case of allosteric ligand-biased signaling via CB1. ORG27569-induced ERK phosphorylation persisted even after pertussis toxin treatment to abrogate G(i) and occurs in HEK293 and neuronal cells.     

Amino Acid Derivatives as Bitter Taste Receptor (T2R) Blockers

In humans, the 25 bitter taste receptors (T2Rs) are activated by hundreds of structurally diverse bitter compounds. However, only five antagonists or bitter blockers are known. In this study, using molecular modeling guided site-directed mutagenesis, we elucidated the ligand-binding pocket of T2R4. We found seven amino acids located in the extracellular side of transmembrane 3 (TM3), TM4, extracellular loop 2 (ECL2), and ECL3 to be involved in T2R4 binding to its agonist quinine. ECL2 residues Asn-173 and Thr-174 are essential for quinine binding. Guided by a molecular model of T2R4, a number of amino acid derivatives were screened for their ability to bind to T2R4. These predictions were tested by calcium imaging assays that led to identification of γ-aminobutryic acid (GABA) and Nα,Nα-bis(carboxymethyl)-l-lysine (BCML) as competitive inhibitors of quinine-activated T2R4 with an IC₅₀ of 3.2 ± 0.3 μm and 59 ± 18 nm, respectively. Interestingly, pharmacological characterization using a constitutively active mutant of T2R4 reveals that GABA acts as an antagonist, whereas BCML acts as an inverse agonist on T2R4. Site-directed mutagenesis confirms that the two novel bitter blockers share the same orthosteric site as the agonist quinine. The signature residues Ala-90 and Lys-270 play important roles in interacting with BCML and GABA, respectively. This is the first report to characterize a T2R endogenous antagonist and an inverse agonist. The novel bitter blockers will facilitate physiological studies focused on understanding the roles of T2Rs in extraoral tissues.     

Synthesis, in vitro and in vivo evaluation of fluorine-18 labelled FE-GW405833 as a PET tracer for type 2 cannabinoid receptor imaging

The type 2 cannabinoid receptor (CB?R) is part of the endocannabinoid system and is expressed in tissues related to the immune system. As the CB?R has a very low brain expression in non-pathological conditions, but is upregulated in activated microglia, it is an interesting target for visualization of neuroinflammation using positron emission tomography with a suitable radiolabeled CB?R ligand. In this study, we radiolabelled a fluoroethyl derivative of GW405833, a well known CB?R partial agonist, with fluorine-18 (half-life 109.8 min) by alkylation of the phenol precursor with 1-bromo-2-[1?F]fluoroethane. In vitro studies showed that FE-GW405833 behaved as a selective high affinity (27 nM) inverse agonist for hCB?R. [1?F]FE-GW405833 showed moderate initial brain uptake in mice and rats, but a slow washout from brain and plasma due to retention of a radiometabolite. Specific binding of the tracer to human CB?R was demonstrated in vivo in a rat model with local CB?R overexpression in the brain. Optimized derivatives of GW405833 that are less susceptible to metabolism will need to be developed in order to provide a useful tracer for CB?R quantification with PET.     

4-Hydroxy-1-[3-(5-(1,2,4-triazol-4-yl)-1H-indol-3-yl)propyl]piperidines: selective h5-HT1D agonists for the treatment of migraine

A series of 4-hydroxy-1-[3-(5-(1,2,4-triazol-4-yl)-1H-indol-3-yl)propyl] piperidines was investigated as potential selective h5-HT1D agonists for the treatment of migraine. The 4-[(N-benzyl-N-methyl)amino]methyl analog 12a was found to be a full agonist at the h5-HT1D receptor with good binding selectivity over the h5-HT1B receptor.     

Synthesis and evaluation of arylpiperazines derivatives of 3,5-dioxo-(2H,4H)-1,2,4-triazine as 5-HT1AR ligands

5-HT_1AR agonist or partial agonists are established drug candidates for psychiatric and neurological disorders. We have reported the synthesis and evaluation of a series of high affinity 5-HT_1AR partial agonist PET imaging agents with greater selectivity over α-1AR. The characteristic of these molecules are 3,5-dioxo-(2H,4H)-1,2,4-triazine skeleton tethered to an arylpiperazine unit through an alkyl side chain. The most potent 5-HT_1AR agonistic properties were found to be associated with the molecules bearing C-4 alkyl group as the linker. Therefore development of 3,5-dioxo-(2H,4H)-1,2,4-triazine bearing arylpiperazine derivatives may provide high affinity selective 5-HT_1AR ligands. Herein we describe the synthesis and evaluation of the binding properties of a series of arylpiperazine analogues of 3,5-dioxo-(2H,4H)-1,2,4-triazine.     

1-Alkyl-2-aryl-4-(1-naphthoyl)pyrroles: new high affinity ligands for the cannabinoid CB1 and CB2 receptors

Two series of 1-alkyl-2-aryl-4-(1-naphthoyl)pyrroles were synthesized and their affinities for the cannabinoid CB(1) and CB(2) receptors were determined. In the 2-phenyl series (5) the N-alkyl group was varied from n-propyl to n-heptyl. A second series of 23 1-pentyl-2-aryl-4-(1-naphthoyl)-pyrroles (6) was also prepared. Several compounds in both series have CB(1) receptor affinities in the 6-30nM range. The high affinities of these pyrrole derivatives relative to JWH-030 (1, R=C(5)H(11)) support the hypothesis that these pyrroles interact with the CB(1) receptor primarily by aromatic stacking.     

Inhibition of striatal dopamine release by CB1 receptor activation requires nonsynaptic communication involving GABA, H2O2, and KATP channels

The main psychoactive component of marijuana, Delta9-tetrahydrocannabinol (THC), acts in the CNS via type 1 cannabinoid receptors (CB1Rs). The behavioral consequences of THC or synthetic CB1R agonists include suppression of motor activity. One explanation for movement suppression might be inhibition of striatal dopamine (DA) release by CB1Rs, which are densely localized in motor striatum; however, data from previous studies are inconclusive. Here we examined the effect of CB1R activation on locally evoked DA release monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry in striatal slices. Consistent with previous reports, DA release evoked by a single stimulus pulse was unaffected by WIN55,212-2, a cannabinoid receptor agonist. However, when DA release was evoked by a train of stimuli, WIN55,212-2 caused a significant decrease in evoked extracellular DA concentration ([DA]o), implicating the involvement of local striatal circuitry, with similar suppression seen in guinea pig, rat, and mouse striatum. Pulse-train evoked [DA]o was not altered by either AM251, an inverse CB1R agonist, or VCHSR1, a neutral antagonist, indicating the absence of DA release regulation by endogenous cannabinoids with the stimulation protocol used. However, both CB1R antagonists prevented and reversed suppression of evoked [DA]o by WIN55,212-2. The effect of WIN55,212-2 was also prevented by picrotoxin, a GABAA receptor antagonist, and by catalase, a metabolizing enzyme for hydrogen peroxide (H2O2). Furthermore, blockade of ATP-sensitive K+ (KATP) channels by tolbutamide or glybenclamide prevented the effect of WIN55,212-2 on DA release. Together, these data indicate that suppression of DA release by CB1R activation within striatum occurs via a novel nonsynaptic mechanism that involves GABA release inhibition, increased generation of the diffusible messenger H2O2, and activation of KATP channels to inhibit DA release. In addition, the findings suggest a possible physiological substrate for the motor effects of cannabinoid agonist administration.     

Interaction of the nicotinic agonist (R,S)-3-pyridyl-1-methyl-2-(3-pyridyl)-azetidine (MPA) with nicotinic acetylcholine receptor subtypes expressed in cell lines and rat cortex

The interaction of the nicotinic agonist (R,S)-3-pyridyl-1-methyl-2-(3-pyridyl)-azetidine (MPA) with different nicotinic acetylcholine receptor (nAChR) subtypes was studied in cell lines and rat cortex. MPA showed an affinity (Ki = 1.21 nM) which was higher than anatoxin-a > (−)-nicotine > (+)-[R]nornicotine > (−)-[S]nornicotine > and (+)-nicotine, but lower than cytisine (Ki = 0.46 nM) in competing for (−)-[³H]nicotine binding in M10 cells, which stably express the recombinant ₄β₂ nAChR subtype. A one-binding site model was observed in all competing experiments between (−)-[³H]nicotine binding and each of the agonists studied in M10 cells. MPA showed a 13-fold higher affinity for (−)-[³H]nicotine binding sites compared to the [³H]epibatidine binding sites in rat cortical membranes. In human neuroblastoma SH-SY5Y cells, which predominantly express the ₃ nAChR subunit mRNA, MPA displaced [³H]epibatidine binding from a single population of the binding sites with an affinity in the same nM range as that observed MPA in displacing [³H]epibatidine binding in rat cortical membranes. Chronic treatment of M10 cells with MPA significantly up-regulated the number of (−)-[³H]nicotine binding sites in a concentration dependent manner. Thus MPA appears to have higher affinity to 4-subunit containing receptor subtype than ₃-subunit containing receptor subtype of nAChRs. Furthermore MPA binds to ₄β₂ receptor subtype with higher affinity than (−)-nicotine and behaves, opposite to cytisine, as a full agonist in up-regulating the number of nAChRs. © 1998 Elsevier Science Ltd. All rights reserved.     

Generation of an agonistic binding site for blockers of the M(3) muscarinic acetylcholine receptor

GPCRs (G-protein-coupled receptors) exist in a spontaneous equilibrium between active and inactive conformations that are stabilized by agonists and inverse agonists respectively. Because ligand binding of agonists and inverse agonists often occurs in a competitive manner, one can assume an overlap between both binding sites. Only a few studies report mutations in GPCRs that convert receptor blockers into agonists by unknown mechanisms. Taking advantage of a genetically modified yeast strain, we screened libraries of mutant M(3)Rs {M(3) mAChRs [muscarinic ACh (acetylcholine) receptors)]} and identified 13 mutants which could be activated by atropine (EC50 0.3-10 microM), an inverse agonist on wild-type M(3)R. Many of the mutations sensitizing M(3)R to atropine activation were located at the junction of intracellular loop 3 and helix 6, a region known to be involved in G-protein coupling. In addition to atropine, the pharmacological switch was found for other M(3)R blockers such as scopolamine, pirenzepine and oxybutynine. However, atropine functions as an agonist on the mutant M(3)R only when expressed in yeast, but not in mammalian COS-7 cells, although high-affinity ligand binding was comparable in both expression systems. Interestingly, we found that atropine still blocks carbachol-induced activation of the M(3)R mutants in the yeast expression system by binding at the high-affinity-binding site (Ki approximately 10 nM). Our results indicate that blocker-to-agonist converting mutations enable atropine to function as both agonist and antagonist by interaction with two functionally distinct binding sites.     

Synthesis and structure-activity relationships of (R)-1-alkyl-3-[2-(2-amino)phenethyl]-5-(2-fluorophenyl)-6-methyluracils as human GnRH receptor antagonists

The synthesis of a series of (R)-1-alkyl-3-[2-(2-amino)phenethyl]-5-(2-fluorophenyl)-6-methyluracils is discussed. SAR around N-1 of the uracil was explored, which led to the discovery that an electron-deficient 2,6-disubstituted benzyl group is required for optimal receptor binding. The best compound from the series had binding affinity of 0.7 nM (K(i) for the human GnRH receptor, which was 8-fold better than the 2,6-difluorobenzyl analog.     

First "hybrid" ligands of vanilloid TRPV1 and cannabinoid CB2 receptors and non-polyunsaturated fatty acid-derived CB2-selective ligands

12-Phenylacetyl-ricinoleoyl-vanillamide (phenylacetylrinvanil, PhAR, IDN5890), is an ultra-potent agonist of human vanilloid TRPV1 receptors also endowed with moderate affinity for human cannabinoid CB(2) receptors. To improve its CB(2) affinity and temper its potency at TRPV1, the modification of the polar headgroup and the lipophilic 12-acylgroup of PhAR was pursued. Replacement of the vanillyl headgroup of PhAR with various aromatic or alkyl amino groups decreased activity at TRPV1 receptors, although the dopamine, cyclopropylamine, 1'-(R)- and 1'-(S)-methyl-ethanolamine, and ethanolamine derivatives retained significant potency (EC(50) 31-126 nM). Within these compounds, the 12-phenylacetylricinoleyl cyclopropylamide and ethanolamide were the strongest ligands at CB(2) receptors, with K(i) of 22 and 44 nM, and 14- and >20-fold selectivity over cannabinoid CB(1) receptors, respectively. The propyl- and allyl-derivatives also exhibited high affinity at CB(2) receptors (K(i)=40 and 22 nM, with 40 and >80-fold selectivity over CB(1) receptors, respectively), but no activity at TRPV1 receptors. The cyclopropyl- and allyl-derivatives behaved as CB(2) inverse agonists in the GTP-gamma-S binding assay. Addition of para-methoxy, -tert-butyl or -chlorine groups to the 12-phenylacetyl moiety of PhAR produced compounds that retained full potency at TRPV1 receptors, but with improved selectivity over CB(2) or CB(1) receptors. Thus, the manipulation of PhAR led to the development of the first CB(2)/TRPV1 dual ligands and of an entirely new class of inverse agonists at CB(2) receptors. Both types of compounds might find application in the treatment of inflammation, and represent new molecular probes to investigate the endocannabinoid-endovanilloid signalling system.     

Bivalent ligand approach on N-{2-[(3-methoxyphenyl)methylamino]ethyl}acetamide: synthesis, binding affinity and intrinsic activity for MT(1) and MT(2) melatonin receptors

We report the synthesis, binding properties and intrinsic activity at MT(1) and MT(2) melatonin receptors of new dimeric melatonin receptor ligands in which two units of the monomeric agonist N-{2-[(3-methoxyphenyl)methylamino]ethyl}acetamide (1) are linked together through different anchor points. Dimerization of compound 1 through the methoxy substituent leads to a substantial improvement in selectivity for the MT(1) receptor, and to a partial agonist behavior. Compound 3a, with a trimethylene linker, was the most selective for the MT(1) subtype (112-fold selectivity) and compound 3d, characterized by a hexamethylene spacer, had the highest MT(1) binding affinity (pK(iMT1)=8.47) and 54-fold MT(1)-selectivity. Dimerization through the aniline nitrogen of 1 abolished MT(1) selectivity, leading to compounds with either a full agonist or an antagonist behavior depending on the nature of the linker.     

Synthesis and cannabinoid-1 receptor binding affinity of conformationally constrained analogs of taranabant

The design, synthesis, and binding activity of ring constrained analogs of the acyclic cannabinoid-1 receptor (CB1R) inverse agonist taranabant 1 are described. The initial inspiration for these taranabant derivatives was its conformation 1a, determined by ¹H NMR, X-ray, and molecular modeling. The constrained analogs were all much less potent than their acyclic parent structure. The results obtained are discussed in the context of a predicted binding of 1 to a homology model of CB1R.     

ATP binding to a unique site in the type-1 S2- inositol 1,4,5-trisphosphate receptor defines susceptibility to phosphorylation by protein kinase A

The subtype- and splice variant-specific modulation of inositol 1,4,5-trisphosphate receptors (InsP3R) by interaction with cellular factors plays a fundamental role in defining the characteristics of Ca2+ release in individual cell types. In this study, we investigate the binding properties and functional consequences of the expression of a putative nucleotide binding fold (referred to as the ATPC site) unique to the S2- splice variant of the type-1 InsP3R (InsP3R-1), the predominant splice variant in peripheral tissue. A glutathione S-transferase fusion protein encompassing amino acids 1574-1765 of the S2- InsP3R-1 and including the glycine-rich motif Gly-Tyr-Gly-Glu-Lys-Gly bound ATP specifically as measured by fluorescent trinitrophenyl-ATP binding. This binding was completely abrogated by a point mutation (G1690A) in the nucleotide binding fold. The functional sensitivity of S2- InsP3R-1 constructs was evaluated in DT40-3KO-M3 cells, a null background for InsP3R, engineered to express muscarinic M3 receptors. The S2- InsP3R-1 containing the G1690A mutation was markedly less sensitive to agonist stimulation than wild type S2- InsP3R-1 or receptors containing a similar (Gly --> Ala) mutation in the established nucleotide binding sites in InsP3R-1 (the ATPA and ATPB sites). The ATP sensitivity of InsP3-induced Ca2+ release, however, was not altered by the G1690A mutation when measured in permeabilized DT40-3KO cells, suggesting a unique role for the ATPC site. Ca2+ release was dramatically potentiated following activation of cAMP-dependent protein kinase in DT40-3KO cells transiently expressing wild type S2- InsP3R or Gly --> Ala mutations in the ATPA and ATPB sites, but phosphorylation of the receptor and the potentiation of Ca2+ release were absent in cells expressing the G1690A mutation in S2- InsP3R. These data indicate that ATP binding specifically to the ATPC site in S2- InsP3R-1 controls the susceptibility of the receptor to protein kinase A-mediated phosphorylation, contributes to the functional sensitivity of the S2- InsP3R-1 and ultimately the sensitivity of cells to agonist stimulation.     

Synthesis of enantiomerically pure trans-(1R,2R)- and cis-(1S,2R)-1-amino-2-indanol by lipase and omega-transaminase

Syntheses of trans-(1R,2R) and cis-(1S,2R)-1-amino-2-indanol (AI) were accomplished by a series of enantioselective enzymatic reactions using lipase and transaminase (TA). Lipase catalysed enantioselective hydrolysis of 2-acetoxyindanone was employed to prepare (R)-2-hydroxy indanone (HI). trans-AI (5 mM) (de > 98%) was produced from 20 mM (R)-2- HI using omega-TA and 50 mM (S)-1-aminoindan as an amino donor in water-saturated ethyl acetate. For the production of cis-AI, the diastereomeric (2R)-AI was synthesized from (R)-2-HI using reductive amination, and the kinetic resolution was performed with omega-TA. The enantioselectivity of omega-TA for (2R)-AI was increased to 22.1 in the presence of 5% gamma-cyclodextrin. cis-AI (15.4 mM) (96% de) was obtained from 40 mM (2R)-AI using 30 mM pyruvate and omega-TA (25 mg) in 10 mL of 100 mM phosphate buffer (pH 7.0).     

Synthesis and antipicornavirus activity of (R)- and (S)-1-[5-(4'-chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazolidin-2-one

The new pyridyl imidazolidinone derivative, 1-[5-(4'-chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazolidin-2-one (+/-)-1a, was synthesized and found to have an excellent antiviral activity against EV71 (IC50 = 0.009 microM). Therefore, both the enantiomers, (S)-(+)-1a and (R)-(-)-1a, have been prepared starting from readily available monomethyl (R)-3-methylglutarate (7) as a useful chiral building block and their antiviral activity was evaluated in a plaque reduction assay. Interestingly, we observed that the enantiomer (S)-(+)-1a was 10-fold more active against enterovirus71 (EV71) (IC50 = 0.003 microM) than the corresponding enantiomer (R)-(-)-1a (IC50 = 0.033 microM). Similar results were found against all five strains (1743, 2086, 2231, 4643, and BrCr) of EV71 tested. This demonstrated that the absolute configuration of the chiral carbon atom at the 3-position of the alkyl linker considerably influenced the anti-EV71 activity of these pyridyl imidazolidinones.