Synthesis, Purification, and Selective ß2-AR Agonist and Bronchodilatory Effects of Catecholic Tetrahydroisoquinolines from Portulaca oleracea.

A green, biomimetic, phosphate-mediated Pictet-Spengler reaction was used in the synthesis of three catecholic tetrahydroisoquinolines, 1, 2, and 12, present in the medicinal plant Portulaca oleracea, as well as their analogues 3-11, 13, and 14, with dopamine hydrochloride and aldehydes as the substrates. AB-8 macroporous resin column chromatography was applied for purification of the products from the one-step high-efficacy synthesis. It eliminated the difficulties in the isolation of catecholic tetrahydroisoquinolines from the aqueous reaction system and unreacted dopamine hydrochloride. Activity screening in CHO-K1/Gα15 cell models consistently expressing α1B-, ß1-, or ß2-adrenergic receptors indicated that 12 and 2, compounds that are present in P. oleracea, possessed the most potent ß2-adrenergic receptor agonist activity and 2 was a selective ß2-adrenergic receptor agonist at the concentration of 100 µM. Both 12 and 2 exhibited dose-dependent bronchodilator effects on the histamine-induced contraction of isolated guinea-pig tracheal smooth muscle, with EC50 values of 0.8 and 2.8 µM, respectively. These findings explain the scientific rationale of P. oleracea use as an antiasthmatic herb in folk medicine and provide the basis for the discovery of novel antiasthma drugs.

Design, synthesis and biological evaluation of 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one derivatives as potent ß2-adrenoceptor agonists.

A series of novel ß2-adrenoceptor agonists with a 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one moiety was designed, synthesized and evaluated for biological activity in human embryonic kidney 293 cells and isolated guinea pig trachea. Compounds 9g and (R)-18c exhibited the most excellent ß2-adrenoceptor agonistic effects and high ß2/ß1-selectivity with EC50 values of 36 pM for 9g and 21 pM for (R)-18c. They produced potent airway smooth muscle relaxant effects with fast onset of action and long duration of action in an in vitro guinea pig trachea model of bronchodilation. These results support further development of the two compounds into drug candidates.

Resorcinol-, catechol- and saligenin-based bronchodilating ß2-agonists as inhibitors of human cholinesterase activity.

We investigated the influence of bronchodilating ß2-agonists on the activity of human acetylcholinesterase (AChE) and usual, atypical and fluoride-resistant butyrylcholinesterase (BChE). We determined the inhibition potency of racemate and enantiomers of fenoterol as a resorcinol derivative, isoetharine and epinephrine as catechol derivatives and salbutamol and salmeterol as saligenin derivatives. All of the tested compounds reversibly inhibited cholinesterases with Ki constants ranging from 9.4 µM to 6.4 mM and had the highest inhibition potency towards usual BChE, but generally none of the cholinesterases displayed any stereoselectivity. Kinetic and docking results revealed that the inhibition potency of the studied compounds could be related to the size of the hydroxyaminoethyl chain on the benzene ring. The additional π-π interaction of salmeterol's benzene ring and Trp286 and hydrogen bond with His447 probably enhanced inhibition by salmeterol which was singled out as the most potent inhibitor of all the cholinesterases.

Molecular hybridization yields triazole bronchodilators for the treatment of COPD.

A 1,2,4-triazole motif was employed as a bioisostere for the ester commonly used in muscarinic antagonists, and subsequent integrative conjugation to a ß2 agonist quinolinone furnished a new class of bifunctional MABAs for the treatment of COPD. Medicinal chemistry optimization using the principles of 'inhalation by design' furnished a clinical candidate with desirable pharmacological, pharmacokinetic and biopharmaceutical properties.

Multivalent design of long-acting ß(2)-adrenoceptor agonists incorporating biarylamines.

A series of potent ß2-adrenoceptor agonists incorporating a biarylamine secondary binding group was identified. The previously reported milveterol (5), identified by a multivalent approach and containing a typical ß2-agonist primary binding group linked via a phenethylamine linker to a hydrophilic secondary binding group, served as an initiation point. A more hydrophobic set of secondary binding groups was explored, prepared rapidly from a common intermediate by Buchwald-Hartwig amination. TD-5471 (25), a potent and selective full agonist of the human ß2-adrenoceptor, was identified as the most promising agent. It is potent, with slow onset in an in vitro guinea pig trachea model and shows a dose-dependent and long duration of action in an in vivo guinea pig model of bronchoprotection. TD-5471 is structurally differentiated from milveterol and its long duration of action is consistent with a correlation with hydrophobicity observed in other long-acting ß2-agonist discovery programs.

Discovery of TD-4306, a long-acting ß2-agonist for the treatment of asthma and COPD.

A multivalent approach focused on amine-based secondary binding groups was applied to the discovery of long-acting inhaled ß2-agonists. Addition of amine moieties to the neutral secondary binding group of an existing ß2-agonist series was found to provide improved in vivo efficacy, but also led to the formation of biologically active aldehyde metabolites which were viewed as a risk for the development of these compounds. Structural simplification of the scaffold and blocking the site of metabolism to prevent aldehyde formation afforded a potent series of dibasic ß2-agonists with improved duration of action relative to their monobasic analogs. Additional optimization led to the discovery of 29 (TD-4306), a potent and selective ß2-agonist with potential for once-daily dosing.

The in vitro pharmacology of GS-5759, a novel bifunctional phosphodiesterase 4 inhibitor and long acting ß2-adrenoceptor agonist.

Inhaled long-acting ß(2)-adrenoceptor agonists (LABA) that act as bronchodilators and the oral anti-inflammatory phosphodiesterase 4 (PDE4) inhibitor roflumilast are both approved therapies for chronic obstructive pulmonary disease (COPD). Here we describe the activity of a novel, inhaled, bifunctional, small molecule (R)-6-[(3-{[4-(5-{[2-hydroxy-2-(8-hydroxy-2-oxo-1,2-dihydroquinolin-5-yl)ethyl]amino}pent-1-yn-1-yl)phenyl]carbamoyl}phenyl)sulfonyl]-4-[(3-methoxyphenyl)amino]-8-methylquinoline-3-carboxamide (GS-5759), which has specific ß(2) agonist and PDE4 inhibitory activity. GS-5759 demonstrated potent and full agonist activity at ß(2) adrenoceptors (EC(50) = 8 ± 4 nM) and is a potent inhibitor of the PDE4 enzyme (IC(50) = 5 ± 3 nM). In cell assays, GS-5759 inhibited lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) production in human peripheral mononuclear cells (PBMC) with an IC(50) = 0.3 nM [confidence interval (CI) 0.1-0.6] and in human neutrophils formyl-methionyl-leucyl-phenylalanine (fMLP)-induced super oxide anion production with an IC(50) = 3 nM (CI 0.8-8). The addition of the ß(2) antagonist ICI 118551 shifted the IC(50) in these cell assays to 4 and 38 nM, respectively, demonstrating the contribution of both ß(2) agonist and PDE4 inhibitory activity to GS-5759. GS-5759 was also a potent inhibitor of profibrotic and proinflammatory mediator release from human lung fibroblasts. GS-5759 relaxed guinea pig airway smooth muscle strips precontracted with carbachol in a concentration-dependent manner with an EC(50) = 0.5 µM (CI 0.2-2) and had slow dissociation kinetics with an Off T(1/2) > 720 minutes at an EC(80) concentration of 3 µM. GS-5759 is a novel bifunctional molecule with both potent ß(2) agonist and PDE4 inhibitor activity that could provide inhaled bronchodilator and anti-inflammatory therapy for COPD.

Discovery of a rapidly metabolized, long-acting ß(2) adrenergic receptor agonist with a short onset time incorporating a sulfone group suitable for once-daily dosing.

A series of novel, potent, and selective human ß2 adrenoceptor agonists incorporating a sulfone moiety on the terminal right-hand-side phenyl ring of (R)-salmeterol is presented. Sulfone 10b had salmeterol-like potency and selectivity profile, long duration of action on guinea pig trachea, and longer than salmeterol duration of action in vivo, suitable for once-daily dosing. It had lower than salmeterol oral absorption in rat, lower bioavailability in rat and dog, and a high turnover in human hepatocytes. It was metabolized in human hepatocytes by hydroxylation, oxidation, cleavage, and conjugation; most of the metabolites would be expected to have reduced or no ß2 activity. The 4-biphenylsulfonic acid was identified as a crystalline, non-hygroscopic salt of 10b, suitable for inhaled delivery. Furthermore, it was free of any genetic toxicity issues and was considered as a backup to vilanterol.

Design, synthesis and evaluation of dual pharmacology ß2-adrenoceptor agonists and PDE4 inhibitors.

A novel series of formoterol-phthalazinone hybrids were synthesised and evaluated as dual pharmacology ß2-adrenoceptor agonists and PDE4 inhibitors. Most of the hybrids displayed high ß2-adrenoceptor agonist and moderate PDE4 inhibitory activities. The most potent compound, (R,R)-11c, exhibited agonist (EC50=1.05nM, pEC50=9.0) and potent PDE4B2 inhibitory activities (IC50=0.092µM).

Sports doping: emerging designer and therapeutic ß2-agonists.

Beta2-adrenergic agonists, or ß2-agonists, are considered essential bronchodilator drugs in the treatment of bronchial asthma, both as symptom-relievers and, in combination with inhaled corticosteroids, as disease-controllers. The use of ß2-agonists is prohibited in sports by the World Anti-Doping Agency (WADA) due to claimed anabolic effects, and also, is prohibited as growth promoters in cattle fattening in the European Union. This paper reviews the last seven-year (2006-2012) literature concerning the development of novel ß2-agonists molecules either by modifying the molecule of known ß2-agonists or by introducing moieties producing indole-, adamantyl- or phenyl urea derivatives. New emerging ß2-agonists molecules for future therapeutic use are also presented, intending to emphasize their potential use for doping purposes or as growth promoters in the near future.

An investigation into the structure-activity relationships associated with the systematic modification of the ß(2)-adrenoceptor agonist indacaterol.

The synthesis of a series of indacaterol analogues in which each of the three structural regions of indacaterol are modified in a systematic manner is described. Evaluation of the affinity of these analogues for the ß(2)-adrenoceptor identified the 3,4-dihydroquinolinone and 5-n-butylindanyl analogues to demonstrate the most similar profiles to indacaterol. An α-methyl aminoindane analogue was discovered to be 25-fold more potent than indacaterol, and functional studies revealed an atypical ß(2)-adrenoceptor activation profile for this compound consistent with that of a slowly dissociating 'super agonist'.

Cell-based and in-silico studies on the high intrinsic activity of two boron-containing salbutamol derivatives at the human ß2-adrenoceptor.

Salbutamol is a well-known ß(2) adrenoceptor (ß(2)AR) partial agonist. We synthesized two boron-containing salbutamol derivatives (BCSDs) with greater potency and efficacy, compared to salbutamol, for inducing ß(2)AR-mediated smooth-muscle relaxation in guinea-pig tracheal rings. However, the mechanism involved in this pharmacological effect remains unclear. In order to gain insight, we carried out binding and functional assays for BCSDs in HEK-293T cells transfected with the human ß(2)AR (hß(2)AR). The transfected hß(2)AR showed similar affinity for BCSDs and salbutamol, but adenosine 3',5'-cyclic phosphate (cAMP) accumulation induced by both BCSDs was similar to that elicited by isoproterenol and greater than that induced by salbutamol. The boron-containing precursors (boric and phenylboronic acids, 100 µM) had no significant effect on salbutamol binding or salbutamol-induced cAMP accumulation. These experimental results are in agreement with theoretical docking simulations on lipid bilayer membrane-embedded hß(2)AR structures. These receptors showed slightly higher affinity for BCSDs than for salbutamol. An essential change between putative active and inactive conformational states depended on the interaction of the tested ligands with the fifth, sixth and seventh transmembrane domains. Overall, these data suggest that BCSDs induce and stabilize conformational states of the hß(2)AR that are highly capable of stimulating cAMP production.

A multivalent approach to the discovery of long-acting ß(2)-adrenoceptor agonists for the treatment of asthma and COPD.

A multivalent approach was applied to the design of long-acting inhaled ß(2)-adrenoceptor agonists. A series of dimeric arylethanolamines based on the short acting ß(2)-adrenoceptor agonist albuterol were prepared, varying the nature and length of the linker between the basic nitrogens. None of the C(2)-symmetric dimers demonstrated increased potency, however dimer 5j, derived from 4-phenethylamine, was found to have increased binding potency in vitro relative to the parent monomer. Optimization of this structure led to the identification of 22 (milveterol) which demonstrates high potency in vitro and long duration of action in a guinea pig model of bronchoprotection.

The discovery of long-acting saligenin ß2 adrenergic receptor agonists incorporating a urea group.

A series of novel, potent and selective human ß(2) adrenoceptor agonists incorporating a urea moiety on the terminal right-hand side phenyl ring of (R)-salmeterol is presented. Urea 9j had long duration of action in vitro on guinea pig trachea, and also in vivo similar to that of salmeterol. It had lower oral absorption and bioavailability than salmeterol in both rat and dog. It had a turnover ratio similar to salmeterol, with no evidence for formation of any aniline metabolites in human liver microsomes and hepatocytes. However no crystalline salts suitable for inhaled delivery were identified.

Efficient conversion of a nonselective norepinephrin reuptake inhibitor into a dual muscarinic antagonist-ß2-agonist for the treatment of chronic obstructive pulmonary disease.

Following interrogation of a wide-ligand profile database, a nonselective norepinephrin reuptake inhibitor was converted into a novel muscarinic antagonist using two medicinal chemistry transformations (M3/NRI selectivity of >1000). Conjugation to a ß(2) agonist motif furnished a molecule with balanced dual pharmacology, as demonstrated in a guinea pig trachea tissue model of bronchoconstriction. This approach provides new starting points for the treatment of chronic obstructive pulmonary disease and illustrates the potential for building selectivity into GPCR modulators that possess intrinsic promiscuity or reverse selectivity.

Design-driven LO: the discovery of new ultra long acting dibasic ß2-adrenoceptor agonists.

Starting with the molecular scaffold of the DA(2)/ß(2) dual agonist sibenadet (Viozan™), a number of molecular changes were incorporated, which were designed to increase the potency and selectivity of the target molecule, and improve its pharmacokinetics. Through this process a novel, high potency, full ß(2)-agonist with high selectivity and long duration capable of being dosed once daily has been discovered.

The discovery of long-acting saligenin ß2 adrenergic receptor agonists incorporating hydantoin or uracil rings.

A series of novel, potent and selective human ß(2) adrenoceptor agonists incorporating a hydantoin or a uracil ring on the right-hand side phenyl ring of (R)-salmeterol is presented. Hydantoin 12a had long duration of action in vitro on guinea pig trachea, and 12h in guinea pigs in vivo at its EC(90) 25 µM. It had lower oral absorption than salmeterol in rats, and lower bioavailability than salmeterol in vivo in both rats and dogs (2% and 5%, respectively). An improved method for measuring the absorbed fraction of analogues dosed to rats, which considers the glucuronidated fraction is presented. Compound 12a was metabolised in human liver microsomes and hepatocytes to the active hydantoic acid 12m.

Design driven HtL: The discovery and synthesis of new high efficacy ß2-agonists.

The design and synthesis of a new series of high efficacy ß(2)-agonists devoid of the key benzylic alcohol present in previously described highly efficacious ß(2)-agonists is reported. A hypothesis for the unprecedented level of efficacy is proposed based on considerations of ß(2)-adrenoceptor crystal structure, other biophysical data and modeling studies.

Discovery of muscarinic acetylcholine receptor antagonist and beta 2 adrenoceptor agonist (MABA) dual pharmacology molecules.

We sought to design dual pharmacology bronchodilators targeting both the M(3) muscarinic acetylcholine and beta-2 adrenergic (ß(2)) receptors by applying our multivalent approach to drug discovery. Herein, we describe our initial discovery and the SAR of the first such compounds with matched potencies at both receptors.

Design, synthesis and in vitro evaluation of (R)-4-(2-(tert-butylamino)-1-hydroxyethyl)-2-(hydroxymethyl)phenyl hydrogen phenylboronate: a novel salbutamol derivative with high intrinsic efficacy on the ß2 adrenoceptor.

We tested a set of boron containing arylethanolamine derivatives on the human and guinea pig ß(2) adrenoceptor (ß(2)AR) 3-D structures by docking methodology. The compound with the highest affinity based on docking analysis, (R)-4-(2-(tert-butylamino)-1-hydroxyethyl)-2-(hydroxymethyl)phenyl hydrogen phenylboronate (boronterol) was synthesized, characterized and tested in guinea pig tracheal rings at basal tone and with histamine-induced contractions. Boronterol was at least eightfold more potent than salbutamol as a smooth muscle relaxant drug (judged by the EC(50) values) and showed a similar maximal relaxant effect as isoproterenol. ICI118,551 showed competitive antagonism on the relaxing effect of boronterol. These results suggest the ß(2)AR agonist action of boronterol.