Hunting the emesis and efficacy targets of PDE4 inhibitors: identification of the photoaffinity probe 8-(3-azidophenyl)-6- [(4-iodo-1H-1-imidazolyl)methyl]quinoline (APIIMQ)

Regioselective Arylation of Quinoline N-Oxides (C8), Indolines (C7) and N-tert-Butylbenzamide with Arylboronic Acids

Herein, we disclose Ru(II)-catalyzed regioselective distal C(sp2)-H arylation of quinoline N-oxide with arylboronic acids to 8-arylquinolines. In the developed method, the Ru(II)-catalyst shows dual activity, that is, distal C-H activation of quinoline N-oxides followed by in situ deoxygenation of arylated quinoline N-oxide in the same pot. The current catalytic method features use of Ru metal as the catalyst and arylboronic acids as the arylating source under mild reaction conditions. Use of the Rh(III)-catalyst in place of Ru(II) under the same conditions afforded 8-arylquinoline N-oxides with excellent regioselectivity. Furthermore, the developed Ru(II) catalytic system is also extended for the C(sp2)-H arylation of indolines, N-tert-butylbenzamide, and 6-(5H)-phenanthridinone. Formation of the quinoline N-oxide coordinated ruthenium adduct is found to be the key reaction intermediate, which has been characterized by single crystal X-ray diffraction and NMR spectroscopy.

Synthesis of 8-heteroaryl nitroxoline analogues via one-pot sequential Pd-catalyzed coupling reactions

A series of 8-heteroaryl substituted quinolines were prepared, either by direct C–H arylation of five-membered heteroarenes, or Pd-catalyzed coupling of organoboron reagents with bromoquinolines.

Application of data mining and visualization techniques for the prediction of drug-induced nausea in man

The therapeutic value of many drugs can be limited by gastrointestinal (GI) adverse effects such as nausea and vomiting. Nausea is a subjective human sensation, hence little is known about preclinical biomarkers that may accurately and effectively predict its presence in man. The aim of this analysis was to use informatics and data-mining tools to identify plausible preclinical GI effects that may be associated with nausea and that could be of potential use in its prediction. A total of 86 marketed drugs were used in this analysis, and the main outcome was a confirmation that nausogenic and non-nausogenic drugs can be clearly separated based on their preclinical GI observations. Specifically, combinations of common preclinical GI effects (vomiting, diarrhea, and salivary hypersecretion) proved to be strong predictors. The model was subsequently validated with a subset of 20 blinded proprietary small molecules and successfully predicted clinical outcome in 90% of cases. This investigation demonstrated the feasibility of data-mining approaches to facilitate discovery of novel, plausible associations that can be used to understand drug-induced adverse effects.

Synthesis of 8-arylquinolines via one-pot Pd-catalyzed borylation of quinoline-8-yl halides and subsequent Suzuki-Miyaura coupling

A one-pot process has been developed for the synthesis of 8-arylquinolines via Pd-catalyzed borylation of quinoline-8-yl halides and subsequent Suzuki-Miyaura coupling with aryl halides using n-BuPAd(2) as ligand. Yields of up to 98% were obtained.

Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies

Phosphodiesterase (PDE) 4 inhibitors have been in development as a novel anti-inflammatory therapy for more than 20 years, with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, only one selective PDE4 inhibitor, roflumilast (Daxas (®)), has been approved for use in humans and available in Canada and the European Union in 2011 for the treatment of a specific population of patients with severe COPD. In many other cases, the development of PDE4 inhibitors of various structural classes has been discontinued due to lack of efficacy and/or dose-limiting adverse events. Indeed, for many of these compounds, it is likely that the maximum tolerated dose is either subtherapeutic or at the very bottom of the efficacy dose-response curve. Thus, a significant ongoing challenge that faces the pharmaceutical industry is to synthesize compounds with therapeutic ratios that are superior to roflumilast. Several strategies are being considered, but clinically effective compounds with an optimal pharmacophore have not, thus far, been reported. In this chapter, alternative means of harnessing the clinical efficacy of PDE4 inhibitors are described. These concepts are based on the assumption that additive or synergistic anti-inflammatory effects can be produced with inhibitors that target either two or more PDE families or with a PDE4 inhibitor in combination with other anti-inflammatory drugs such as a glucocorticoid.

Discovery of MK-0952, a selective PDE4 inhibitor for the treatment of long-term memory loss and mild cognitive impairment

The structure-activity relationship of a novel series of 8-biarylnaphthyridinones acting as type 4 phosphodiesterase (PDE4) inhibitors for the treatment of long-term memory loss and mild cognitive impairment is described herein. The manuscript describes a new paradigm for the development of PDE4 inhibitor targeting CNS indications. This effort led to the discovery of the clinical candidate MK-0952, an intrinsically potent inhibitor (IC(50)=0.6 nM) displaying limited whole blood activity (IC(50)=555 nM). Supporting in vivo results in two preclinical efficacy tests and one test assessing adverse effects are also reported. The comparative profiles of MK-0952 and two other Merck compounds are described to validate the proposed hypothesis.

Neuroanatomical and pharmacological assessment of Fos expression induced in the rat brain by the phosphodiesterase-4 inhibitor 6-(4-pyridylmethyl)-8-(3-nitrophenyl) quinoline

A major obstacle in the therapeutic development of phosphodiesterase-4 (PDE4) inhibitors is the production of adverse side effects such as nausea and vomiting. Immunohistochemical detection of Fos-like immunoreactivity (FLI) was used to address the neuroanatomical basis for the pharmacological actions of PDE4 inhibitors. The potent and selective PDE4 inhibitors 6-(4-pyridylmethyl)-8-(3-nitrophenyl) quinoline (PMNPQ) and rolipram elevated FLI in brain regions potentially relevant to the anti-depressant and emetic effects of PDE4 inhibition. PMNPQ and rolipram elevated FLI in the locus coeruleus, habenula, paraventricular nucleus of the thalamus, amygdala and nucleus accumbens, all structures with strong limbic connectivity implicated in arousal, memory and affective aspects of behaviour. Consistent with the emetic effects of PDE4 inhibitors such as PMNPQ and rolipram, these compounds elevated FLI in caudal brainstem nuclei such as the area postrema and nucleus of the solitary tract. Administration of the NK(1) antagonist RP 67580 prior to PMNPQ reversed increases in FLI produced by PMNPQ in these regions. RP 67580 did not, however, reduce PMNPQ-induced FLI in limbic structures. These findings suggest that PDE4 inhibitors produce emesis by increasing NK(1) receptor activation in the AP/NTS and implicate brain regions associated with reward and mood such as the amygdala, paraventricular nucleus of the thalamus, habenula and nucleus accumbens in the anti-depressant activity of such compounds.

Discovery of a substituted 8-arylquinoline series of PDE4 inhibitors: Structure–activity relationship, optimization, and identification of a highly potent, well tolerated, PDE4 inhibitor

The discovery and SAR of a new series of substituted 8-arylquinoline PDE4 inhibitors are herein described. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of emesis to efficacy in several animal models. Typical optimized compounds from this series are potent inhibitors of PDE4 (IC(50)<1nM) and also of LPS-induced TNF-alpha release in human whole blood (IC(50)<0.5microM). The same compounds are potent inhibitors of ovalbumin-induced bronchoconstriction in conscious guinea pigs (EC(50)<0.1mg/kg ip) but require a dose of about 10mg/kg po in the squirrel monkey to produce an emetic response. From this series of compounds, 23a (L-454,560) was identified as an optimized compound.

Phosphodiesterase-4 as a potential drug target

Phosphodiesterase-4 (PDE4) is the predominant enzyme in some specific cell types that is responsible for the degradation of the second messenger, cAMP. Consequently, PDE4 plays a crucial role in cell signalling and, as such, it has been the target of clinical drug development of various indications, ranging from anti-inflammation to memory enhancement. In this review, the fundamental biological role of PDE4 in intracellular signalling, its tissue distribution and regulation are described. The historical development of various chemical classes of PDE4 inhibitors and the challenges that face these inhibitors as therapeutics are also discussed. Finally, recent advances in the structural biology of PDE4 and their complexes with various inhibitors, as well as its potential impact on the rational design of potent and selective PDE4 inhibitors, are presented.

Predictive, non-GLP models of secondary pharmacodynamics: putting the best compounds forward

Secondary pharmacodynamic studies of new chemical entities (NCEs) play a critical role in support of efficient drug discovery. In an era in which speed and efficiency are the norm for pharmaceutical discovery, the need to identify NCEs with greater patient tolerability continues to increase. Early use of secondary pharmacodynamic models (in vivo and in vitro) provides the foundation for critical, early decisions regarding lead molecules. Scientifically robust, non-GLP (good laboratory practices) secondary pharmacodynamic studies can eliminate compounds or structural series with undesirable profiles early, and may prove useful in defining structure-activity relationships (SARs) with regards to off-target effects.

The next generation of PDE4 inhibitors

A number of highly potent PDE4 inhibitors are being developed for the treatment of asthma, chronic obstructive pulmonary disease, rheumatoid arthritis, multiple sclerosis and Crohn's disease. Cilomilast (Ariflo, SB 207499, SmithKline Beecham), the most advanced member of the class in Phase III clinical trials, was reported to have a limited therapeutic window. Other inhibitors with improved profiles in preclinical models are entering into (or are in) clinical trials. The recent developments in understanding PDE4 catalysis, inhibitor binding and their emetic response should facilitate the design of the next generation of PDE4 inhibitors.

Monitor: molecules and profiles

Monitor provides an insight into the latest developments in drug discovery through brief synopses of recent presentations and publications together with expert commentaries on the latest technologies. There are two sections: Molecules summarizes the chemistry and the pharmacological significance and biological relevance of new molecules reported in the literature and on the conference scene; Profiles offers commentary on promising lines of research, emerging molecular targets, novel technology, advances in synthetic and separation techniques and legislative issues.