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

Article abstract of DOI:10.1016/j.bmcl.2012.01.013

We designed and synthesized a novel class of dual pharmacology bronchodilators targeting both b2-adrenoceptor and PDE4 by applying a multivalent approach. The most potent dual pharmacology molecule, compound 29, possessed good inhibitory activity on PDE4B2 (IC₅₀ = 0.278 μM, which was more potent than phthalazinone, IC₅₀ = 0.520 lM) and possessed excellent relaxant effects on tracheal rings precontracted by histamine (pEC₅₀ = 9.3).

Full text of DOI:10.1016/j.bmcl.2012.01.013

Bioorganic & Medicinal Chemistry Letters 22 (2012) 1523–1526
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Dual b2-adrenoceptor agonists-PDE4 inhibitors for the treatment of asthma
and COPD
Wen-Jun Shan a, Ling Huang a, Qi Zhou a, Huai-Lei Jiang a, Zong-Hua Luo a, Ke-fang Lai b, , Xing-Shu Li a,
⇑
⇑
a Institute of Drug Synthesis and Pharmaceutical Process, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
b State Key Laboratory of Respiratory Diseases, Guangzhou Medical College, Guangzhou 510120, China
a r t i c l e i n f o
a b s t r a c t
Article history:
We designed and synthesized a novel class of dual pharmacology bronchodilators targeting both b2-adre-
Received 5 October 2011
Revised 26 December 2011
Accepted 6 January 2012
Available online 14 January 2012
noceptor and PDE4 by applying a multivalent approach. The most potent dual pharmacology molecule,
compound 29, possessed good inhibitory activity on PDE4B2 (IC50 = 0.278 lM, which was more potent
than phthalazinone, IC50 = 0.520
l
M) and possessed excellent relaxant effects on tracheal rings precon-
tracted by histamine (pEC50 = 9.3).
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Asthma and COPD
Bronchodilator
b2-Adrenoceptor agonist
PDE4 inhibitor
Asthma and chronic obstructive pulmonary disease (COPD) are
both prevalent and chronic respiratory diseases that affect millions
of people worldwide.1 Although the etiology of asthma and COPD
are not completely understood, smooth muscle dysfunction and
chronic inflammation are known to play important roles in the
pathophysiology of these diseases. Thus, both anti-inflammatory
and bronchodilator medicines are used extensively in this context.
The b2-adrenoceptor agonists (b2-agonists) are the most effective
bronchodilators, offering proven benefits in reducing the burden of
asthma and COPD.2,3 Activation of the b2-adrenoceptor results in the
activation of adenylyl cyclase (AC) via a stimulatory G-protein (Gs)
and an increase in the cAMP concentration,4 which is a key regulator
of numerous signalling cascades.5 The currentlyused b2-agonists are
illustrated in Figure 1. Among them, salbutamol (Fig. 1, 1) is a typi-
cally short-acting agonist with a rapid onset of action. Salmeterol
(Fig. 1, 2) and formoterol (Fig. 1, 3) are the two most prescribed rep-
resentatives of inhaled long-acting b2-agonists. Recently, indacater-
ol (Fig. 1, 4) has been approved in the USA and Europe as a once-daily
b2-agonist for the treatment of COPD.6
including asthma and COPD.11 The PDE4 family consist of four iso-
forms: PDE4A, 4B, 4C and 4D. Knockout studies have revealed that
PDE4B could suppress TNF-a production.12 In this regard, PDE4B
inhibitors are expected to be useful anti-inflammatory agents.
There are a number of PDE4 inhibitors, including rolipram (Fig. 2,
5), rofiumilast (Fig. 2, 6), cilomilast (Fig. 2, 7) and AWD12-
281(Fig. 2, 8), that have been investigated in clinical trials.13 More
recently, rofiumilast has been approved by the FDA for the treat-
ment of COPD. This approval has stimulated the development of
PDE4 inhibitors greatly.
The multifaceted condition of some diseases has encouraged ac-
tive research in the development of multifunctional drugs. These
drugs possess two or more complementary biological activities
and they may represent an important advance in the treatment
of the diseases.14–16 Inspired by the development of multifunc-
tional drugs, we wished to design a new kind of inhibitor for the
treatment of both asthma and COPD, which could target the b2-
adrenoceptor and PDE4. In this Letter, we describe the preliminary
study toward the synthesis and evaluation of novel hybrids that
possess dual activity as b2-agonists and PDE4B inhibitors.
The synthetic route of dual b2-agonists and PDE4 inhibitors (28–
31) is shown in Schemes 1–4. First, epoxide 13, the synthetic inter-
mediate containing the pharmacophore of the b2-adrenoceptor
agonist, was synthesized from the commercially available 4-hydro-
xy-3-nitro-acetophenone by several steps according to procedures
reported previously.17 Then, intermediates 20–23, which possess
the pharmacophore of the PDE4 inhibitor, were synthesized via
the route outlined in Scheme 2. The reaction of 1,2-dimethoxyben-
zene with 1,2-cyclohexanedicarboxylic anhydride provided com-
pound 14. Compound 14 was then reacted with hydrazine to
The phosphodiesterase (PDE) enzymes, important regulators of
intracellular cyclic nucleotide signalling,7,5 catalyze the hydrolysis
of cAMP and cGMP to the corresponding nucleoside 50-monophos-
phates. PDE4, one of the eleven PDE enzyme families,8,9 is particu-
larly abundant in inflammatory-, immune- and airway smooth
muscle cells.10 PDE4 inhibitors have been evaluated as promising
therapies for the treatment of inflammatory pulmonary disorders,
⇑
Corresponding authors. Tel./fax: +86 20 3994 3050.
E-mail address: lixs@mail.sysu.edu.cn (X.-S. Li).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.01.013

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W.-J. Shan et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1523–1526
Figure 1. Structure of salbutamol (1), salmeterol (2), formoterol (3), indacaterol (4).
Figure 2. Structure of rolipram (5), roflumilast (6), cilomilast (7) and AWD12-281 (8).
Scheme 1. Reagents and conditions: (a) (chloromethyl)benzene, K2CO3; (b) bromine, acetic acid; (c) NaBH4, THF; (d) Pt/C, Me2S, H2; formaldehyde, acetic anhydride; (e)
K2CO3, THF/MeOH.
Scheme 2. Reagents and condition: (a) 1,2-cyclohexanedicarboxylic anhydride, AlCl3, CH2Cl2; (b) H2NNH2, EtOH, reflux; (c) Br(CH2)nBr, NaH, DMF; (d) benzylamine.
afford 4-(3,4-dimethoxyphenyl)-4a,5,8,8a-tetrahydro-2H-phthala-
zin-1-one (15), a known PDE4 inhibitor synthesized by Van der
Mey et. al.18,19 N-Alkyl phthalazinones 16–19 were obtained by
treating compound 15 with NaH and dibromoalkanes in DMF. The
reaction of 16–19 with benzylamine provided compounds 20–23,
respectively. Finally, the target compounds were synthesized by
the coupling of epoxide 13 with compounds 20–23, followed by
the deprotection via hydrogenation in the presence of Pd/C. In order
to investigate the relationship between the chiral center of the syn-
thesized compounds and the activity of the b2-adrenoceptor, each

W.-J. Shan et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1523–1526
1525
Scheme 3. Reagents and condition: (a) 20–23, 120 °C, neat; (b) 10% Pd/C, H2.
Scheme 4. Synthetic route of (R)-29 or (S)-29. Reagents and condition: (a) Ru-(R, R)-TsDPEN or Ru-(S, S)-TsDPEN, HCOONa, H2O.
enantiomer of 29, (R)-29 and (S)-29 (Scheme 4) was synthesized by
the reaction of a chiral epoxide (prepared from the alcohol 11) and
intermediate 21.
compound isoprenaline. Among the four target compounds (28–
31), compound 29, connected by a 4-carbon linker between the
PDE4 inhibitor and the b2-adrenoceptor agonist moiety, exhibited
the most potent b2-adrenoceptor agonist activity (Table 1), with
the pEC50 value (related to pKd) of 9.3. This value is higher than
that of isoprenaline (7.5). (R)-29 and (S)-29 were also examined
as b2-adrenoceptor agonists by an in vitro evaluation, and the re-
sults showed that (R)-29 had about a fivefold potency increase over
its racemic form, and about three orders of magnitude higher po-
tency than its enantiomer, (S)-29.
When isolated guinea pig tracheal rings were precontracted
with histamine, the dose–response curve of (R)-29 was shifted to
the right when using the well-known b2-AR selective inverse ago-
nist, ICI-11855122 (1 ꢀ 10ꢁ9–1 ꢀ 10ꢁ7 M), showing competitive
To study the in vitro b2-adrenoceptor agonist and PDE4 inhibi-
tory activities, in vitro assays were carried out. First, the effect on
the tracheal rings of guinea pigs were assessed with a protocol de-
scribed previously.20 The results detailed in Figure 3 indicated that
all the compounds examined produced a relaxant effect on the pre-
contracted tracheal rings by histamine. All the compounds induced
a concentration-dependent relaxation, and the maximum response
(Emax) to each was similar to that evoked by the reference
Table 1
EC50 for b2-adrenergic agonist compounds in the function ex vivo guinea pig trachea
bioassaya
b
Compound
n
pEC50
Emax (%)
Isoprenaline
28
29
30
31
(R)-29
(S)-29
Salmeterol
(R, R)-3.Tartrate
—
2
4
5
6
4
4
—
—
7.5
7.7
9.3
7.7
7.3
100
103
105
100
105
103
105
—
10.0
6.9
8.3c
9.9
100
a
Effect of isoproterenol and new b2-adrenoceptor agonists on isolated guinea pig
teacheal rings precontracted by histamine at 30 lM. The maximum relaxant effect
by isoproterenol was considered 100%.
Figure 3. Effect of agonists and isoproterenol on isolated guinea pig tracheal rings
b
pEC50 values are the mean of three experiments.
Ref. 21
precontracted by histamine at 30
lM. The maximum relaxant effect by isoprote-
c
renol was considered 100%. Each point represents the mean effect (n = 3).

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W.-J. Shan et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1523–1526
Table 2
Acknowledgment
Inhibition of cAMP hydrolysis by recombinant human PDE4B2 in the presence of 15
and new compoundsa
We thank the Natural Science Foundation of China (20972198)
and State Key Laboratory of Respiratory Diseases (2007DA-
80154F1110) for financial support of this study.
Compounds
n
PDE4B2 inhibition IC50 (lM)
(R)-Rolipram
15
28
29
(R)-29
(S)-29
30
—
—
2
4
4
4
5
6
—
—
0.500 0.028
0.520 0.042
0.280 0.021
0.278 0.013
0.265 0.009
0.284 0.016
0.257 0.020
0.251 0.015
0.120 (0.095b)
0.001 (0.0008c)
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2012.01.013.
31
Cilomilast
Rofiumilast
References and notes
a
b
c
Data are of average of three determinations SEM.
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