Synthesis and structure-activity relationships of long-acting beta2 adrenergic receptor agonists incorporating arylsulfonamide groups

Indium Promotes Direct Sulfonamidation of Unactivated Alcohols

An improved protocol has been developed for the direct sulfonamidation of unactivated alkyl alcohols using In(OTf)3 as a Lewis acid catalyst. Although the established methods using Lewis or Brønsted acids have been well-studied for the direct functionalization of alcohols, their substrate scope mainly focuses on the π-activated alcohols. In this reaction, unactivated aliphatic alcohols were evaluated and afforded the desired sulfonamide products with good to excellent yields.

Discovery and Identification of Novel 5-Hydroxy-4H-benzo[1,4]oxazin-3-one Derivatives as Potent β2-Adrenoceptor Agonists through Structure-Based Design, Synthesis, and Biological Evaluation

Although β2-agonists are crucial for treatment of chronic respiratory diseases, optimizing β2-agonistic activity and selectivity remains essential for achieving favorable therapeutic outcomes. A structure-based molecular design workflow was employed to discover a novel class of β2 agonists featuring a 5-hydroxy-4H-benzo[1,4]oxazin-3-one scaffold, which potently stimulated β2 adrenoceptors (β2-ARs). Screening for the β2-agonistic activity and selectivity led to the identification of compound A19 (EC50 = 3.7 pM), which functioned as a partial β2-agonist in HEK-293 cells containing endogenous β2-ARs. Compound A19 exhibited significant relaxant effects, rapid onset time (Ot50 = 2.14 min), and long duration of action (>12 h) on isolated guinea pig tracheal strips, as well as advantageous pharmacokinetic characteristics in vivo, rendering A19 suitable for inhalation administration. Moreover, A19 suppressed the upregulation of inflammatory cytokines and leukocytes and improved lung function in a rat model of COPD, thereby indicating that A19 is a potential β2 agonist candidate for further study.

Photochemical Synthesis of the Bioactive Fragment of Salbutamol and Derivatives in a Self‐Optimizing Flow Chemistry Platform

The implementation of self‐optimizing flow reactors has been mostly limited to model reactions or known synthesis routes. In this work, a self‐optimizing flow photochemistry platform is used to develop an original synthesis of the bioactive fragment of Salbutamol and derivatives. The key photochemical steps for the construction of the aryl vicinyl amino alcohol moiety consist of a C−C bond forming reaction followed by an unprecedented, high yielding (>80 %), benzylic oxidative cyclization.

Development of Inhaled GABAA Receptor Modulators to Improve Airway Function in Bronchoconstrictive Disorders

We report the modification of MIDD0301, an imidazodiazepine GABA_A receptor (GABA_AR) ligand, using two alkyl substituents. We developed PI310 with a 6-(4-phenylbutoxy)hexyl chain as used in the long-acting β2-agonist salmeterol and PI320 with a poly(ethylene glycol) chain as used to improve the brain:plasma ratio of naloxegol, a naloxone analogue. Both imidazodiazepines showed affinity toward the GABA_AR binding site of clonazepam, with IC₅₀ values of 576 and 242 nM, respectively. Molecular docking analysis, using the available α₁β₃γ₂ GABA_AR structural data, suggests binding of the diazepine core between the α1+/γ2- interface, whereas alkyl substituents are located outside the binding site and thus interact with the protein surface and solvent molecules. The physicochemical properties of these compounds are very different. The solubility of PI310 is low in water. PEGylation of PI320 significantly improves aqueous solubility and cell permeability. Neither compound is toxic in HEK293 cells following exposure at >300 μM for 18 h. Ex vivo studies using guinea pig tracheal rings showed that PI310 was unable to relax the constricted airway smooth muscle. In contrast, PI320 induced muscle relaxation at organ bath concentrations as low as 5 μM, with rapid onset (15 min) at 25 μM. PI320 also reduced airway hyper-responsiveness in vivo in a mouse model of steroid-resistant lung inflammation induced by intratracheal challenge with INFγ and lipopolysaccharide (LPS). At nebulized doses of 7.2 mg/kg, PI320 and albuterol were equally effective in reducing airway hyper-responsiveness. Ten minutes after nebulization, the lung concentration of PI320 was 50-fold that of PI310, indicating superior availability of PI320 when nebulized as an aqueous solution. Overall, PI320 is a promising inhaled drug candidate to quickly relax airway smooth muscle in bronchoconstrictive disorders, such as asthma. Future studies will evaluate the pharmacokinetic/pharmacodynamic properties of PI320 when administered orally.

Recent Advances in β2-Agonists for Treatment of Chronic Respiratory Diseases and Heart Failure

β₂-Adrenoceptor (β₂-AR) agonists are widely used as bronchodilators. The emerge of ultralong acting β₂-agonists is an important breakthrough in pulmonary medicine. In this review, we will provide mechanistic insights into the application of β₂-agonists in asthma, chronic obstructive pulmonary disease (COPD), and heart failure (HF). Recent studies in β-AR signal transduction have revealed opposing functions of the β₁-AR and the β₂-AR on cardiomyocyte survival. Thus, β₂-agonists and β-blockers in combination may represent a novel strategy for HF management. Allosteric modulation and biased agonism at the β₂-AR also provide a theoretical basis for developing drugs with novel mechanisms of action and pharmacological profiles. Overlap of COPD and HF presents a substantial clinical challenge but also a unique opportunity for evaluation of the cardiovascular safety of β₂-agonists. Further basic and clinical research along these lines can help us develop better drugs and innovative strategies for the management of these difficult-to-treat diseases.

Design, synthesis and biological evaluation of 8-(2-amino-1-hydroxyethyl)-6-hydroxy-1,4-benzoxazine-3(4H)-one derivatives as potent β2-adrenoceptor agonists

A series of β₂-adrenoceptor agonists with an 8-(2-amino-1-hydroxyethyl)-6-hydroxy-1,4-benzoxazine-3(4H)-one moiety is presented. The stimulatory effects of the compounds on human β₂-adrenoceptor and β₁-adrenoceptor were characterized by a cell-based assay. Their smooth muscle relaxant activities were tested on isolated guinea pig trachea. Most of the compounds were found to be potent and selective agonists of the β₂-adrenoceptor. One of the compounds, (R)-18c, possessed a strong β₂-adrenoceptor agonistic effect with an EC₅₀ value of 24 pM. It produced a full and potent airway smooth muscle relaxant effect same as olodaterol. Its onset of action was 3.5 min and its duration of action was more than 12 h in an in vitro guinea pig trachea model of bronchodilation. These results suggest that (R)-18c is a potential candidate for long-acting β₂-AR agonists.

Design, synthesis and biological evaluation of 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one derivatives as potent β2-adrenoceptor agonists

A series of novel β₂-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 β₂-adrenoceptor agonistic effects and high β₂/β₁-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.

Discovery of TD-4306, a long-acting β2-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 β2-agonists. Addition of amine moieties to the neutral secondary binding group of an existing β2-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 β2-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 β2-agonist with potential for once-daily dosing.

Recent structural advances of β1 and β2 adrenoceptors yield keys for ligand recognition and drug design

Because they represent attractive drug targets, adrenoceptors have been widely studied. Recent progress in structural data of β-adrenoceptors allows us to understand and predict key interactions in ligand recognition and receptor activation. Nevertheless, an important aspect of this process has only begun to be explored: the stabilization of a conformational state of these receptors upon contact with a ligand and the capacity of a ligand to influence receptor conformation through allosteric modulation, biased signaling, and selectivity. The aim of the present Perspective is to identify the well-defined orthosteric binding site and possible allosteric sites and to analyze the importance of the ligand-receptor interaction in the stabilization of certain receptor conformations. For this purpose, we have reviewed recent advances made through the use of X-ray data from ligand-β-adrenoceptor (including ADRB1 and ADRB2) crystal structures. Most importantly, implications in the medicinal chemistry field are explored in relation to drug design.

Sports doping: emerging designer and therapeutic β2-agonists

Beta2-adrenergic agonists, or β2-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 β2-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 β2-agonists molecules either by modifying the molecule of known β2-agonists or by introducing moieties producing indole-, adamantyl- or phenyl urea derivatives. New emerging β2-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.

Hybrids consisting of the pharmacophores of salmeterol and roflumilast or phthalazinone: dual β₂-adrenoceptor agonists-PDE4 inhibitors for the treatment of COPD

A novel class of dual pharmacology bronchodilators targeting both β(2)-adrenoceptor and PDE4 was designed and synthesised by combining the pharmacophores of salmeterol and roflumilast or phthalazinone. All the compounds exhibited better β(2)-adrenoceptor agonist activities (pEC(50)=8.47-9.20) than the reference compound salmeterol (pEC(50)=8.3) and good inhibitory activity on PDE4B2 (IC(50)=0.235-1.093 μM).

Slow receptor dissociation is not a key factor in the duration of action of inhaled long-acting β2-adrenoceptor agonists

BACKGROUND AND PURPOSE

β(2) -Adrenoceptor agonists are important bronchodilators used for the treatment of chronic obstructive pulmonary disease and asthma. Clinical data on β(2) -adrenoceptor agonists show a range of onset and duration of action. We have investigated whether the receptor binding kinetics of β(2) -adrenoceptor agonists can explain their observed onset of action and duration of effect in the clinic.

EXPERIMENTAL APPROACH

[(3) H]-DHA was used to label β(2) -adrenoceptors expressed in CHO-cell membranes (K(d) of 0.084 nM). Competition kinetic experiments were performed in the presence of unlabelled β(2) agonists at 37°C in HBSS containing GTP. To determine the kinetic parameters, three concentrations (10, 3 and 1 ×K(i) ) of the unlabelled compound were employed against a fixed concentration of [(3) H]-DHA (0.6 nM).

KEY RESULTS

The clinically used β(2) -adrenoceptor agonists exhibited a range of association and dissociation rates. The kinetic K(d) and the competition K(i) values of the eight β(2) -adrenoceptor agonists examined were strongly correlated, suggesting that the method had produced accurate k(off) and k(on) rates. The kinetic on-rate was highly correlated with equilibrium binding affinity.

CONCLUSIONS AND IMPLICATIONS

Although the β(2) -adrenoceptor agonists displayed a range of kinetic rate parameters, simulations at relevant drug concentrations suggest that receptor kinetics do not play an important role in determining onset of action in the clinic. In addition, it is unlikely that receptor kinetics exert an important influence on the duration of action of these agonists, as indacaterol (once daily dosing) had a shorter residency time at the receptor than salmeterol (twice daily dosing).

Comparison of the bronchodilating effects of inhaled β₂-agonists after methacholine challenge in a human lung reperfusion model

The aim of the present investigation was to compare the onset of action and intrinsic activity of the long-acting β(2)-agonist GW597901 with the fast- and short-acting salbutamol as model compounds using an isolated human lung reperfusion model. Twelve resected human lung lobes were challenged with methacholine (MCh) and subsequently nebulised with either GW597901 or salbutamol. Prostaglandin E(2) (PGE(2)) concentrations in the perfusion fluid were compared with the dose of MCh that was required to induce a bronchoconstriction. After successful MCh provocation, nebulisation of GW597901 and salbutamol fully reversed any observed bronchoconstriction. The bronchodilating effect was more pronounced for GW597901. Salbutamol revealed an immediate onset of action while the effect of GW597901 was observed with an approximate delay of 6 min. Higher doses of MCh were required for a successful bronchial challenge in the presence of elevated PGE(2) levels (r=0.8171, p ≤ 0.05). For the first time, an isolated perfused human lung model has been established for comparing the onset of action and potency of a short- and long-acting β(2)-agonist. We therefore conclude that it is an alternative for determination of drug effect characteristics and suitable for supplementing or predicting clinical data.

Third-generation long-acting β₂-adrenoceptor agonists: medicinal chemistry strategies employed in the identification of once-daily inhaled β₂-adrenoceptor agonists

Inhaled long-acting β(2)-adrenoceptor agonists (LABAs) are highly effective bronchodilators in the treatment of asthma and chronic obstructive pulmonary disease. There is significant interest in the development of third-generation compounds that improve upon the marketed twice-daily LABAs salmeterol and formoterol. A principal advantage sought from the next generation is duration of action that supports once-daily dosing, although improved efficacy, faster onset, and increased therapeutic index are also frequently cited as objectives. Recent publications detailing medicinal chemistry programs directed at the discovery of third-generation LABAs illustrate a wide variety of strategies that have been successfully employed towards these goals. Some recent scientific advances in the understanding of inhaled bronchodilators are discussed and the reported medicinal chemistry strategies are reviewed in the context of these advances.

Dual β2-adrenoceptor agonists-PDE4 inhibitors for the treatment of asthma and COPD

We designed and synthesized a novel class of dual pharmacology bronchodilators targeting both β(2)-adrenoceptor and PDE4 by applying a multivalent approach. The most potent dual pharmacology molecule, compound 29, possessed good inhibitory activity on PDE4B2 (IC(50)=0.278 μM, which was more potent than phthalazinone, IC(50)=0.520 μM) and possessed excellent relaxant effects on tracheal rings precontracted by histamine (pEC(50)=9.3).

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

A multivalent approach was applied to the design of long-acting inhaled β(2)-adrenoceptor agonists. A series of dimeric arylethanolamines based on the short acting β(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.

From libraries to candidate: the discovery of new ultra long-acting dibasic β₂-adrenoceptor agonists

Libraries of dibasic compounds designed around the molecular scaffold of the DA(2)/β(2) dual agonist sibenadet (Viozan™) have yielded a number of promising starting points that have been further optimised into novel potent and selective target molecules with required pharmacokinetic properties. From a shortlist, 31 was discovered as a novel, high potency, and highly efficacious β(2)-agonist with high selectivity and a duration of action commensurable with once daily dosing.

A perspective on synthetic and solid-form enablement of inhalation candidates

The administration of compounds by a dry-powder inhaler presents significant challenges to the development and discovery chemist, owing to the stringent requirements placed upon the physical characteristics of the active pharmaceutical ingredient and the high complexity of the molecules concerned. The current state of synthetic chemistry technology is such that commercial syntheses of these compounds are demanding but achievable. While synthetic chemistry will remain a major component of the development of inhaled therapies, the main challenge facing practitioners in this area is the early identification of a suitable solid form. Further advances in the prediction of solid-form properties would significantly enable this field and may allow triage of molecules to be carried out at the design stage of projects.

Inhalation by design: novel ultra-long-acting β(2)-adrenoreceptor agonists for inhaled once-daily treatment of asthma and chronic obstructive pulmonary disease that utilize a sulfonamide agonist headgroup

A novel series of potent and selective sulfonamide derived β(2)-adrenoreceptor agonists are described that exhibit potential as inhaled ultra-long-acting bronchodilators for the treatment of asthma and chronic obstructive pulmonary disease. Analogues from this series mediate very long-lasting smooth muscle relaxation in guinea pig tracheal strips. The sulfonamide agonist headgroup confers high levels of intrinsic crystallinity that could relate to the acidic sulfonamide motif supporting a zwitterionic form in the solid state. Optimization of pharmacokinetic properties was achieved through targeted introduction of a phenolic moiety to support rapid phase II clearance, thereby minimizing systemic exposure following inhalation and reducing systemically mediated adverse events. Compound 38 (PF-610355) is identified as a clinical candidate from this series, with in vivo duration of action studies confirming its potential for once-daily use in humans. Compound 38 is currently in advanced phase II clinical studies.

Efficacy is a contributing factor to the clinical onset of bronchodilation of inhaled beta(2)-adrenoceptor agonists

Inhaled beta(2) adrenoceptor (beta(2) AR) agonists are widely used as bronchodilator therapies for asthma and COPD. Different agonists have varying rates of onset of action, e.g. indacaterol and salbutamol are effective bronchodilators within 5 min whereas salmeterol takes 15 min to achieve significant bronchodilation over baseline (Brookman et al., Curr Med Res Opin 23:3113-3122, 2007). This has been attributed to differences in the lipophilicity of the agonists such that hydrophobic ligands take longer to diffuse into tissue and may even access the receptor via the membrane compartment (Anderson et al., Eur Respir J 7:569-578, 1994). While this holds true for salmeterol and salbutamol, the relatively high lipophilicity of indacaterol should result in a slower onset of action. Here we have explored the possibility that the efficacy of these ligands may also contribute to their onset of action. We have characterised efficacy and rate of cyclic adenosine monophosphate (cAMP) accumulation in primary human bronchial smooth muscle cells using a competition assay (AlphaScreen, Perkin Elmer) and in HEK 293-GloSensor cells endogenously expressing the beta(2) AR using a luminescence readout. For all agonists tested, cAMP was generated in a concentration-dependent manner. For both assay formats, the relative efficacies were unchanged, with isoprenaline > formoterol > indacaterol > salbutamol > salmeterol. The rate of cAMP generation varied for each agonist and correlated well with intrinsic efficacy in that the high-efficacy agonists promoted the most rapid rise in cAMP levels. We have demonstrated that the rate of cAMP accumulation is influenced by agonist efficacy and that this, in combination with lipophilicity, may explain why beta(2) AR agonists demonstrate differences in their onset of action.