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(R)-2-(4-(4-Chlorophenoxy)piperidin-1-yl)-4-((tetrahydro-2H-pyran-4-yl)amino)-6,7-dihydrothieno[3,2-d]pyrimidine 5-Oxide

¹H NMR (400 MHz, CDCl₃) δ 1.49 (dq, J = 4.2, 11.8 Hz, 1H), 1.62 (dq, J = 4.2, 11.8 Hz, 1H), 1.74–1.89 (m, 3H), 1.90–2.02 (m, 3H), 2.96–3.07 (m, 2H), 3.29 (dt, J = 13.6, 8.4 Hz, 1H), 3.44 (ddd, J = 19.2, 11.2, 2.0 Hz, 2H), 3.62 (dt, J = 17.2, 7.8 Hz, 1H), 3.76 (m, 2H), 3.96 (dd, J = 15.6, 12.8 Hz, J = 2H), 4.09–3.99 (m, 3H), 4.51 (m, 1H), 6.21 (br d, J = 6.0 Hz, 1H), 6.86 (d, J = 8.8 Hz, 2H), 7.24 (d, J = 8.8 Hz, 2H);

¹³C NMR (100 MHz, CDCl₃) δ 30.4, 32.5, 32.7, 41.0, 47.2, 49.6, 66.9, 66.9, 72.9, 107.8, 117.5, 125.9, 129.5, 155.8, 158.9, 163.0, 174.6.

The use of phosphodiesterase type 4 (PDE4) inhibitors  for the treatment of COPD (chronic obstructive pulmonary disease) by reducing inflammation and improving lung function is well documented. Given the potential therapeutic benefit offered by these compounds, a number of PDE4-selective inhibitors containing a dihydrothieno[3,2-d]pyrimidine core were identified as preclinical candidates in Boehringer Ingelheim Pharmaceuticals discovery laboratories

While the pathogenesis of chronic obstructive pulmonary disease (COPD) is incompletely understood, chronic inflammation is a major factor. In fact, the inflammatory response is abnormal, with CD8⁺ T-cells, CD68⁺ macrophages, and neutrophils predominating in the conducting airways, lung parenchyma, and pulmonary vasculature. Elevated levels of the second messenger cAMP can inhibit some inflammatory processes. Theophylline has long been used in treating asthma; it causes bronchodilation by inhibiting cyclic nucleotide phosphodiesterase (PDE), which inactivates cAMP. By inhibiting PDE, theophylline increases cAMP, inhibiting inflammation and relaxing airway smooth muscle. Rather than one PDE, there are now known to be more than 50, with differing activities, substrate preferences, and tissue distributions. Thus, the possibility exists of selectively inhibiting only the enzyme(s) in the tissue(s) of interest. PDE 4 is the primary cAMP-hydrolyzing enzyme in inflammatory and immune cells (macrophages, eosinophils, neutrophils). Inhibiting PDE 4 in these cells leads to increased cAMP levels, down-regulating the inflammatory response. Because PDE 4 is also expressed in airway smooth muscle and, in vitro, PDE 4 inhibitors relax lung smooth muscle, selective PDE 4 inhibitors are being developed for treating COPD. Clinical studies have been conducted with PDE 4 inhibitors;

Chronic obstructive pulmonary disease (COPD) is a serious and increasing global public health problem; physiologically, it is characterized by progressive, irreversible airflow obstruction and pathologically, by an abnormal airway inflammatory response to noxious particles or gases (MacNee 2005a). The COPD patient suffers a reduction in forced expiratory volume in 1 second (FEV₁), a reduction in the ratio of FEV₁ to forced vital capacity (FVC), compared with reference values, absolute reductions in expiratory airflow, and little improvement after treatment with an inhaled bronchodilator. Airflow limitation in COPD patients results from mucosal inflammation and edema, bronchoconstriction, increased secretions in the airways, and loss of elastic recoil. Patients with COPD can experience ‘exacerbations,’ involving rapid and prolonged worsening of symptoms (Seneff et al 1995; Connors et al 1996; Dewan et al 2000; Rodriguez-Roisin 2006; Mohan et al 2006). Many are idiopathic, though they often involve bacteria; airway inflammation in exacerbations can be caused or triggered by bacterial antigens (Murphy et al 2000; Blanchard 2002; Murphy 2006;Veeramachaneni and Sethi 2006). Increased IL-6, IL-1β, TNF-α, GRO-α, MCP-1, and IL-8 levels are found in COPD patient sputum; their levels increase further during exacerbations. COPD has many causes and significant differences in prognosis exist, depending on the cause (Barnes 1998; Madison and Irwin 1998).

COPD is already the fourth leading cause of death worldwide, according to the World Health Organization (WHO); the WHO estimates that by the year 2020, COPD will be the third-leading cause of death and the fifth-leading cause of disability worldwide (Murray and Lopez 1997). COPD is the fastest-growing cause of death in developed nations and is responsible for over 2.7 million deaths per year worldwide. In the US, there are currently estimated to be 16 million people with COPD. There are estimated to be up to 20 million sufferers in Japan, which has the world’s highest per capita cigarette consumption and a further 8–12 million in Europe. In 2000, COPD accounted for over 20 million outpatient visits, 3.4 million emergency room visits, 6 million hospitalizations, and 116,500 deaths in the US (National Center for Health Statistics 2002). Factors associated with COPD, including immobility, often lead to secondary health consequences (Polkey and Moxham 2006).

Risk factors for the development of COPD include cigarette smoking, and occupational exposure to dust and chemicals (Senior and Anthonisen 1998; Anthonisen et al 2002; Fabbri and Hurd 2003; Zaher et al 2004). Smoking is the most common cause of COPD and the underlying inflammation typically persists in ex-smokers. Oxidative stress from cigarette smoke is also an issue in COPD (Domej et al 2006). Despite this, relatively few smokers ever develop COPD (Siafakas and Tzortzaki 2002).

While many details of the pathogenesis of COPD remain unclear, chronic inflammation is now recognized as a major factor, predominantly in small airways and lung parenchyma, characterized by increased numbers of macrophages, neutrophils, and T-cells (Barnes 2000; Stockley 2002). As recently as 1995, the American Thoracic Society issued a statement defining COPD without mentioning the underlying inflammation (American Thoracic Society 1995). Since then, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines have made it clear that chronic inflammation throughout the airways, parenchyma, and pulmonary vasculature plays a central role (Pauwels et al 2001; GOLD 2003). The comparatively recent realization of the role of airway inflammation in COPD has altered thinking with regard to potential therapies (Rogers and Giembycz 1998; Vignola 2004).

Most pharmacological therapies available for COPD, including bronchodilator and anti-inflammatory agents, were first developed for treating asthma. The mainstays of COPD treatment are inhaled corticosteroids (McEvoy and Niewoehner 1998; Borron and deBoisblanc 1998; Pauwels 2002; Gartlehner et al 2006;D’Souza 2006), supplemental oxygen (Petty 1998; Austin and Wood-Baker 2006), inhaled bronchodilators (Costello 1998; Doherty and Briggs 2004), and antibiotics (Taylor 1998), especially in severely affected patients (Anthonisen et al 1987; Saint et al 1995; Adams et al 2001; Miravitlles et al 2002; Donnelly and Rogers 2003; Sin et al 2003; Rabe 2006), though the use of antibiotics remains controversial (Ram et al 2006). Long-acting β₂-agonists (LABAs) improve the mucociliary component of COPD. Combination therapy with LABAs and anticholinergic bronchodilators resulted in modest benefits and improved health-related quality of life (Buhl and Farmer 2005; Appleton et al 2006). Treatment with mucolytics reduced exacerbations and the number of days of disability (Poole and Black 2006). The combined use of inhaled corticosteroids and LABAs has been demonstrated to produce sustained improvements in FEV₁ and positive effects on quality of life, number of hospitalizations, distance walked, and exacerbations (Mahler et al 2002;Szafranski et al 2003; Sin et al 2004; Miller-Larsson and Selroos 2006; van Schayck and Reid 2006). However, all of these treatments are essentially palliative and do not impact COPD progression (Hay 2000;Gamble et al 2003; Antoniu 2006a).

A further complication in drug development and therapy is that it can be difficult to determine the efficacy of therapy, because COPD has a long preclinical stage, is progressive, and patients generally do not present for treatment until their lung function is already seriously impaired. Moreover, because COPD involves irreversible loss of elasticity, destruction of the alveolar wall, and peribronchial fibrosis, there is often little room for clinical improvement.

Smoking cessation remains the most effective intervention for COPD. Indeed, to date, it is the only intervention shown to stop the decline in lung function, but it does not resolve the underlying inflammation, which persists even in ex-smokers. Smoking cessation is typically best achieved by a multifactor approach, including the use of bupropion, a nicotine replacement product, and behavior modification (Richmond and Zwar 2003).

In COPD, there is an abnormal inflammatory response, characterized by a predominance of CD8⁺ T-cells, CD68⁺ macrophages, and neutrophils in the conducting airways, lung parenchyma, and pulmonary vasculature (Soto and Hanania 2005; O’Donnell et al 2006; Wright and Churg 2006). Inflammatory mediators involved in COPD include lipids, inflammatory peptides, reactive oxygen and nitrogen species, chemokines, cytokines, and growth factors. COPD pathology also includes airway remodeling and mucociliary dysfunction (mucus hypersecretion and decreased mucus transport). Corticosteroids reduce the number of mast cells, but CD8⁺ and CD68⁺ cells, and neutrophils, are little affected (Jeffery 2005). Inflammation in COPD is not suppressed by corticosteroids, consistent with it being neutrophil-, not eosinophil-mediated. Corticosteroids also do not inhibit the increased concentrations of IL-8 and TNF-α (both neutrophil chemoattractants) found in induced sputum from COPD patients. Neutrophil-derived proteases, including neutrophil elastase and matrix metalloproteinases (MMPs), are involved in the inflammatory process and are responsible for the destruction of elastin fibers in the lung parenchyma (Mercer et al 2005; Gueders et al 2006). MMPs play important roles in the proteolytic degradation of extracellular matrix (ECM), in physiological and pathological processes (Corbel, Belleguic et al 2002). PDE 4 inhibitors can reduce MMP activity and the production of MMPs in human lung fibroblasts stimulated with pro-inflammatory cytokines (Lagente et al 2005). In COPD, abnormal remodeling results in increased deposition of ECM and collagen in lungs, because of an imbalance of MMPs and TIMPs (Jeffery 2001). Fibroblast/myofibroblast proliferation and activation also occur, increasing production of ECM-degrading enzymes (Crouch 1990; Segura-Valdez et al 2000). Additionally, over-expression of cytokines and growth factors stimulates lung fibroblasts to synthesize increased amounts of collagen and MMPs, including MMP-1 (collagenase-1) and MMP-2 and MMP-9 (gelatinases A and B) (Sasaki et al 2000; Zhu et al 2001).

It is now generally accepted that bronchial asthma is also a chronic inflammatory disease (Barnes et al 1988;Barnes 1995). The central role of inflammation of the airways in asthma’s pathogenesis is consistent with the efficacy of corticosteroids in controlling clinical symptoms. Eosinophils are important in initiating and continuing the inflammatory state (Holgate et al 1987; Bruijnzeel 1989; Underwood et al 1994; Teixeira et al 1997), while other inflammatory cells, including lymphocytes, also infiltrate the airways (Holgate et al 1987;Teixeira et al 1997). The familiar acute symptoms of asthma are the result of airway smooth muscle contraction. While recognition of the key role of inflammation has led to an emphasis on anti-inflammatory therapy in asthma, a significant minority of patients remains poorly controlled and some exhibit accelerated declines in lung function, consistent with airway remodeling (Martin and Reid 2006). Reversal or prevention of structural changes in remodeling may require additional therapy (Burgess et al 2006).

There is currently no cure for asthma; treatment depends primarily on inhaled glucocorticoids to reduce inflammation (Taylor 1998; Petty 1998), and inhaled bronchodilators to reduce symptoms (Torphy 1994;Costello 1998; Georgitis 1999; DeKorte 2003). Such treatments, however, do not address disease progression.

COPD and asthma are both characterized by airflow obstruction, but they are distinct in terms of risk factors and clinical presentation. While both involve chronic inflammation and cellular infiltration and activation, different cell types are implicated and there are differences in the inflammatory states (Giembycz 2000;Fabbri and Hurd 2003; Barnes 2006). In COPD, neutrophil infiltration into the airways and their activation appear to be key (Stockley 2002); in asthma, the inflammatory response involves airway infiltration by activated eosinophils and lymphocytes, and T-cell activation of the allergic response (Holgate et al 1987;Saetta et al 1998; Barnes 2006). While macrophages are present in both conditions, the major controller cells are CD8⁺ T-cells in COPD (O’Shaughnessy et al 1997; Saetta et al 1998) and CD4⁺ T-cells in asthma. IL-1, IL-8, and TNF-α are the key cytokines in COPD, while in asthma, IL-4, IL-5, and IL-13 are more important. There are differences in histopathological features of lung biopsies between COPD patients and asthmatics; COPD patients have many fewer eosinophils in lung tissue than asthmatics.

While the early phases of COPD and asthma are distinguishable, there are common features, including airway hyper-responsiveness and mucus hypersecretion. MUC5AC is a major mucin gene expressed in the airways; its expression is increased in COPD and asthmatic patients. At least in vitro, epidermal growth factor stimulates MUC5AC mRNA and protein expression; this can be reversed by PDE 4 inhibitors, which may contribute to their clinical efficacy in COPD and asthma (Mata et al 2005). Similar structural and fibrotic changes make COPD and asthma much less distinguishable in extreme cases; the chronic phases of both involve inflammatory responses, alveolar detachment, mucus hypersecretion, and subepithelial fibrosis. The two conditions have been linked epidemiologically; adults with asthma are up to 12 times more likely to develop COPD over time than those without (Guerra 2005).

PAPER

A practical, safe, and efficient process for the synthesis of PDE4 (phosphodiesterase type 4) inhibitors represented by 1 and 2 was developed and demonstrated on a multi-kilogram scale. Key aspects of the process include the regioselective synthesis of dihydrothieno[3,2-d]pyrimidine-2,4-diol 9 and the asymmetric sulfur oxidation of intermediate 11.

Development of a Practical Process for the Synthesis of PDE4 Inhibitors

REF

Pouzet, P.; Hoenke, C.; Martyres, D.; Nickolaus, P.; Jung, B.; Hamman, H. Dihydrothienopyrimidines for the treatment of inflammatory diseases. PatentWO 2006111549 A1, October 26, 2006.

Ohnacker, G.; Woitun, E. Novel dihydrothieno[3, 2-d]pyrimidines. U.S. Patent US 3,318,881, May 9, 1967.

/////PDE4 Inhibitors, Boehringer Ingelheim Pharmaceuticals, BI ?, PRECLINICAL, 1910076-27-5

• Supporting Info

Clc1ccc(cc1)OC2CCN(CC2)c4nc(NC3CCOCC3)c5c(n4)CCS5=O