Synthetic Study toward Total Synthesis of (±)-Germine: Synthesis of (±)-4-Methylenegermine.

The total synthesis of 4-methylenegermine is described.

3,4-Diarylpiperidines as potent renin inhibitors.

The discovery and SAR of a series of potent renin inhibitors possessing a novel 3,4-diarylpiperidine scaffold are described herein. The resulting compound 38 exhibit low nanomolar plasma renin IC(50), had a clean CYP 3A4 profile and displayed micromolar affinity for the hERG channel. Furthermore, it was found to be efficacious in the double transgenic rat hypertension model and show good to moderate oral bioavailability in two animal species.

Impact of passive permeability and gut efflux transport on the oral bioavailability of novel series of piperidine-based renin inhibitors in rodents.

An oral bioavailability issue encountered during the course of lead optimization in the renin program is described herein. The low F(po) of pyridone analogs was shown to be caused by a combination of poor passive permeability and gut efflux transport. Substitution of pyridone ring for a more lipophilic moiety (logD>1.7) had minimal effect on rMdr1a transport but led to increased passive permeability (P(app)>10 × 10(-6) cm/s), which contributed to overwhelm gut transporters and increase rat F(po). LogD and in vitro passive permeability determination were found to be key in guiding SAR and improve oral exposure of renin inhibitors.

Renin inhibitors for the treatment of hypertension: design and optimization of a novel series of tertiary alcohol-bearing piperidines.

The design and optimization of a novel series of renin inhibitor is described herein. Strategically, by committing the necessary resources to the development of synthetic sequences and scaffolds that were most amenable for late stage structural diversification, even as the focus of the SAR campaign moved from one end of the molecule to another, highly potent renin inhibitors could be rapidly identified and profiled.

Renin inhibitors for the treatment of hypertension: design and optimization of a novel series of pyridone-substituted piperidines.

An SAR campaign aimed at decreasing the overall lipophilicity of renin inhibitors such as 1 is described herein. It was found that replacement of the northern appendage in 1 with an N-methyl pyridone and subsequent re-optimization of the benzyl amide handle afforded compounds with in vitro and in vivo profiles suitable for further profiling. An unexpected CV toxicity in dogs observed with compound 20 led to the employment of a time and resource sparing rodent model for in vivo screening of key compounds. This culminated in the identification of compound 31 as an optimized renin inhibitor.

The discovery and synthesis of potent zwitterionic inhibitors of renin.

The incorporation of a carboxylic acid within in a series of 3-amido-4-aryl substituted piperidines (represented by general structure 32) led to the discovery of potent, zwitterionic, renin inhibitors with improved off-target profiles (CYP3A4 time-dependent inhibition and hERG affinity) relative to analogous non-zwitterionic inhibitors of the past (i.e., 3). Strategies to address the oral absorption of these zwitterions are also discussed within.

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.

Addressing time-dependent CYP 3A4 inhibition observed in a novel series of substituted amino propanamide renin inhibitors, a case study.

Time-dependent inhibitors of CYPs have the potential to perpetrate drug-drug interactions in the clinical setting. After finding that several leading compounds in a novel series of substituted amino propanamide renin inhibitors inactivated CYP3A4 in an NADPH-dependent and time-dependent manner, a search to identify the cause of this liability was initiated. Extensive SAR revealed that the amide bridge present in compound 1 as a possible culprit. Through the installation of a metabolic soft spot distal to this moiety, potent renin inhibitors with improved CYP profile were identified.

The discovery and synthesis of highly potent subtype selective phosphodiesterase 4D inhibitors.

The SAR study of a series of 6-aryloxymethyl-8-aryl substituted quinolines is described. Optimization of the series led to the discovery of compound 26b, a highly potent (IC50=0.6 nM) and selective PDE4D inhibitor with a 75-fold selectivity over the A, B, and C subtypes and over 18,000-fold selectivity against other PDE family members. Rat pharmacokinetics and tissue distribution are also summarized.

Identification of a new biaryl scaffold generating potent renin inhibitors.

The discovery and SAR of a series of potent renin inhibitors possessing a novel biaryl scaffold are described herein. Molecular modeling revealed that the cyclopropylamide spacer present in 1 can be replaced by a simple, substituted aromatic ring such as a toluene in 2. The resulting compounds exhibit subnanomolar renin IC(50) and good oral bioavailability in rats.

Design and optimization of a substituted amino propanamide series of renin inhibitors for the treatment of hypertension.

The discovery and SAR of a new series of substituted amino propanamide renin inhibitors are herein described. This work has led to the preparation of compounds with in vitro and in vivo profiles suitable for further development. Specifically, challenges pertaining to oral bioavailability, covalent binding and time-dependent CYP 3A4 inhibition were overcome thereby culminating in the identification of compound 50 as an optimized renin inhibitor with good efficacy in the hypertensive double-transgenic rat model.

Alkyl-bridged substituted 8-arylquinolines as highly potent PDE IV inhibitors.

Substituted 8-arylquinoline analogs bearing alkyl-linked side chain were identified as potent inhibitors of type 4 phophodiesterase. These compounds address the potential liabilities of the clinical candidate L-454560. The pharmacokinetic profile of the best analogs and the in vivo efficacy in an ovalbumin-induced bronchoconstriction assay in conscious guinea pigs are reported.

Design, synthesis, and biological evaluation of 8-biarylquinolines: a novel class of PDE4 inhibitors.

The structure-activity relationship of a novel series of 8-biarylquinolines acting as type 4 phosphodiesterase (PDE4) inhibitors is described herein. Prototypical compounds from this series are potent and non-selective inhibitors of the four distinct PDE4 (IC(50)<10 nM) isozymes (A-D). In a human whole blood in vitro assay, they inhibit (IC(50)<0.5 microM) the LPS-induced release of the cytokine TNF-alpha. Optimized inhibitors were evaluated in vivo for efficacy in an ovalbumin-induced bronchoconstriction model in conscious guinea pigs. Their propensity to produce an emetic response was evaluated by performing pharmacokinetic studies in squirrel monkeys. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of efficacy over emesis.

Interspecies in vitro metabolism of the phosphodiesterase-4 (PDE4) inhibitor L-454,560.

L-454,560 is a potent phosphodiesterase 4 (PDE4) inhibitor which was identified as a development candidate for the treatment of asthma and chronic obstructive pulmonary disease (COPD). As part of the discovery of this compound, interspecies in vitro metabolism data was generated using liver microsomes and hepatocytes in order to understand the metabolic fate of the compound. In microsomes, metabolism of the 3-methyl-1,2,4-oxadiazole ring was the predominant pathway observed, including ring cleavage. In rat hepatocytes, hydroxylation of the methyl group on the oxadiazole ring and double-bond isomerization were the most abundant metabolites observed. No major species differences were found in terms of microsomal metabolite profiles. The use of LC with UV and MS detection is highlighted, as well as information from tandem mass spectrometry and NMR.

Nitrogen-bridged substituted 8-arylquinolines as potent PDE IV inhibitors.

Potent inhibitors of the human PDE IV enzyme are described. Substituted 8-arylquinoline analogs bearing nitrogen-linked side chain were identified as potent inhibitors based on the SAR described herein. The pharmacokinetic profile of the best analog and the in vivo efficacy in an ovalbumin-induced bronchoconstriction assay in conscious guinea pigs are reported.

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.

Dynamic activation of cystic fibrosis transmembrane conductance regulator by type 3 and type 4D phosphodiesterase inhibitors.

The diseases of cystic fibrosis, chronic obstructive pulmonary disease (COPD), and chronic bronchitis are characterized by mucus-congested and inflamed airways. Anti-inflammatory agents that can simultaneously restore or enhance mucociliary clearance through cystic fibrosis transmembrane conductance regulator (CFTR) activation may represent new therapeutics in their treatment. Herein, we report the activation of CFTR-mediated chloride secretion by phosphodiesterase (PDE) 4 inhibitors in T84 monolayer using (125)I anion as tracer. In the absence of forskolin, the iodide secretion was insensitive to PDE4 inhibitor L-826,141 [4-[2-(3,4-bis-difluoromethoxyphenyl)-2-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenyl]-ethyl]-3-methylpyridine-1-oxide], roflumilast, or to PDE3 inhibitor trequinsin. However, these inhibitors potently augmented iodide secretion after forskolin stimulation, with efficacy coupled to the activation states of adenylyl cyclase. The iodide secretion from PDE3 or PDE4 inhibition was characterized at first by a prolonged efflux duration, followed by progressively elevated peak efflux rates at higher inhibitor concentrations. Paralleled with an increased phosphor-cAMP response element-binding protein formation, the CFTR activation dissociated from a global cAMP elevation and was blocked by H89 [N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide]. 2-(4-Fluorophenoxy)-N-[(1S)-1-(4-methoxyphenyl)ethyl]nicotinamide, a stereoselective PDE4D inhibitor, augmented iodide efflux more efficiently than its less potent (R)-isomer. The peak efflux from maximal PDE4 and PDE3 inhibition matched that from full adenylyl cyclase activation. These data suggest that PDE3 and PDE4 (mainly PDE4D) form the major cAMP diffusion barrier in T84 cells to ensure a compartmentalized CFTR signaling. Together with their potent anti-inflammatory properties, the potentially enhanced airway mucociliary clearance from CFTR activation may have contributed to the efficacy of PDE4 inhibitors in COPD and asthmatic patients. PDE4 inhibitors may represent new opportunities to combat cystic fibrosis and other respiratory diseases in future.