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.     

Dimethyltyrosine, the Viagra of Opioids

Introduction Theintroductionof2′,6′dimethyl L tyrosine(Dmt)[1]attheN terminusofTyr Tic(1,2,3,4tetra hydroisoquinoline3carboxylicacid)containingδopi oidantagonists[2—8]enhancesreceptoraffinityand invitrobioactivitytoseveralordersofmagnitude[1]and itsap…     

Investigation of ractopamine‐imprinted polymer for dispersive solid‐phase extraction of trace β‐agonists in pig tissues

Ractopamine, as an alternative β‐agonist to clenbuterol, is more and more used as leanness‐enhancing agent in the swine industry. This work presents a new molecularly imprinted polymer (MIP) using ractopamine as template for dispersive solid‐phase extraction of trace ractopamine and the structural related β‐agonists in animal tissues. The binding properties and selectivity of MIP were investigated. High selectivity in polar environment was found, since the extraction capacity of ractopamine with the MIP was 4.5‐fold as much as that with the non‐imprinted polymer in acetonitrile. Cross‐selectivity investigation indicates that the MIP preferentially binds the template and then the structural analogues according to their molecular similarity. Thermodynamic and kinetic investigation was performed to interpret the specific adsorption and molecular recognition of the MIP for ractopamine. Standard free energy, standard enthalpy, and standard entropy were determined. Related information suggested that adsorption of ractopamine onto MIP was an exothermic, spontaneous process. The MIP can be applied as dispersive solid‐phase extraction material for enrichment of ractopamine, isoxsuprine, fenoterol and clenbuterol in complex samples before HPLC analysis. The method revealed detection limits of 0.20–0.90 μg/L, recoveries of 83.8–115.2 and 85.2–110.2% for the spiked pig muscle and pig liver, respectively, with the RSD from 2.5 to 8.8%.     

Design,synthesis and evaluation of potent G-protein coupled receptor 40 agonists

GPR40 has emerged as an attractive drug target for the treatment of type 2 diabetes due to its role in the enhancement of insulin secretion with glucose dependency. With the aim to improve the metabolic and safety profiles, a series of novel phenylpropionic acid derivatives were synthesized. Extensive structural optimization led to identification of compounds 22g and 23e as potent GPR40 agonists with moderate liver microsomal stability. All the discovery supported further exploration surrounding this scaffold.     

Screening of synthetic and plant-derived compounds for (anti)estrogenic and (anti)androgenic activities

Recently we constructed yeast cells that either express the human estrogen receptor α or the human androgen receptor in combination with a consensus ERE or ARE repeat in the promoter region of a green fluorescent protein (yEGFP) read-out system. These bioassays were proven to be highly specific for their cognate agonistic compounds. In this study the value of these yeast bioassays was assessed for analysis of compounds with antagonistic properties. Several pure antagonists, selective estrogen receptor modulators (SERMs) and plant-derived compounds were tested. The pure antiestrogens ICI 182,780 and RU 58668 were also classified as pure ER antagonists in the yeast estrogen bioassay and the pure antiandrogen flutamide was also a pure AR antagonist in the yeast androgen bioassay. The plant-derived compounds flavone and guggulsterone displayed both antiestrogenic and antiandrogenic activities, while 3,3′-diindolylmethane (DIM) and equol combined an estrogenic mode of action with an antiandrogenic activity. Indol-3-carbinol (I3C) only showed an antiandrogenic activity. Coumestrol, genistein, naringenin and 8-prenylnaringenin were estrogenic and acted additively, while the plant sterols failed to show any effect. Although hormonally inactive, in vitro and in vivo metabolism of the aforementioned plant sterols may still lead to the formation of active metabolites in other test systems.     

Identifying conformational changes of the β2 adrenoceptor that enable accurate prediction of ligand/receptor interactions and screening for GPCR modulators

The new β₂ Adrenoceptor (β₂AR) crystal structures provide a high-resolution snapshot of receptor interactions with two particular partial inverse agonists, (−)-carazolol and timolol. However, both experimental and computational studies of GPCR structure are significantly complicated by the existence of multiple conformational states coupled to ligand type and receptor activity. Agonists and antagonists induce or stabilize distinct changes in receptor structure that mediate a range of pharmacological activities. In this work, we (1) established that the existing β₂AR crystallographic conformers can be extended to describe ligand/receptor interactions for additional antagonist types, (2) generated agonist-bound receptor conformations, and (3) validated these models for agonist and antagonist virtual ligand screening (VLS). Using a ligand directed refinement protocol, we derived a single agonist-bound receptor conformation that selectively retrieved a diverse set of full and partial β₂AR agonists in VLS trials. Additionally, the impact of extracellular loop two conformation on VLS was assessed by docking studies with rhodopsin-based β₂AR homology models, and loop-deleted receptor models. A general strategy for constructing and selecting agonist-bound receptor pocket conformations is presented, which may prove broadly useful in creating agonist and antagonist bound models for other GPCRs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Activation of β2-Adrenergic Receptor Induced by Three Catecholamine Agonists: a Docking and Molecular Dynamics Study

We studied the activation of β₂-adrenergic receptor(β₂AR) by norepinephrine, epinephrine and isoproterenol using docking and molecular dynamics(MD) simulation. The simulation was done on the assumption that β₂AR was surrounded with explicit water and infinite lipid bilayer membrane at body temperature. So the result should be close to that under the physiological conditions. We calculated the structure of binding sites in β₂AR for the three activators. We also simulated the change of the conformation of β₂AR in the transmembrane regions(TMs), in the molecular switches, and in the conserved DRY(Aspartic acid, Arginine and Tyrosine) motif. This study provides detailed information concerning the structure of β₂AR during activation process.     

Conformational studies on (+)-anatoxin-a and derivatives

Summary Anatoxin-a (AnTX) is a highly potent agonist acting at the nicotinic acetylcholine receptor (nAChR) and represents a valuable tool in the study of this receptor. Molecular mechanics, semi-empirical and ab initio molecular orbital energy minimization procedures were conducted to investigate the conformation of AnTX. For each minimization procedure, the s-trans enone isomer of protonated AnTX was the energetically favoured conformer due to intramolecular electrostatic interactions. Our studies are discussed in the light of previous experimental observations and conformational studies, in addition to their importance in the development of future pharmacophore models for nAChR agonist binding.     

Improved asymmetric synthesis of dopamine D1 full agonist, dihydrexidine, employing chiral ligand-controlled asymmetric conjugate addition of aryllithium to a nitroalkene

Asymmetric conjugate addition of 2-trityloxymethylpheyllithium to a nitroalkene was mediated by a chiral ligand to give the key intermediate for dopamine D1 full agonist dihydrexidine 1. The shortcut of both Curtius rearrangement and Pictet-Spengler type cyclization, which were the drawback of the previously reported synthesis involving asymmetric conjugate addition of phenyllithium to an enoate, was realized by the newly developed asymmetric reaction. Short and efficient synthetic way gave optically pure dihydrexidine in 45% overall yield via eight steps. Improved synthesis of the best chiral ligand 13 was realized under the Buchwald conditions.     

Design of Drug Efficacy Guided by Free Energy Simulations of the β2-Adrenoceptor

G-protein-coupled receptors (GPCRs) play important roles in physiological processes and are modulated by drugs that either activate or block signaling. Rational design of the pharmacological efficacy profiles of GPCR ligands could enable the development of more efficient drugs, but is challenging even if high-resolution receptor structures are available. We performed molecular dynamics simulations of the β₂ adrenergic receptor in active and inactive conformations to assess if binding free energy calculations can predict differences in ligand efficacy for closely related compounds. Previously identified ligands were successfully classified into groups with comparable efficacy profiles based on the calculated shift in ligand affinity upon activation. A series of ligands were then predicted and synthesized, leading to the discovery of partial agonists with nanomolar potencies and novel scaffolds. Our results demonstrate that free energy simulations enable design of ligand efficacy and the same approach can be applied to other GPCR drug targets.