Discovery of substituted phenyl urea derivatives as novel long-acting β2-adrenoreceptor agonists

Article abstract of DOI:10.1016/j.bmcl.2010.12.096

The synthesis of diverse functionalized ureas in a semi-parallel fashion is described, as well as their β₁/β₂-adrenergic activities and the corresponding structure-activity relationship (SAR). We have focused on lipophilicity and duration of action, and we have discovered a strong correlation in this series of molecules. A quantitative structure-activity relationship (QSAR) analysis will be presented that quantifies this relationship.

Full text of DOI:10.1016/j.bmcl.2010.12.096

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1545–1548
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of substituted phenyl urea derivatives as novel long-acting
b2-adrenoreceptor agonists
Daniel Pérez a, , Maribel Crespo a, Laia Solé a, Maria Prat a, Carla Carcasona c, Elena Calama b, Raquel Otal b,
⇑
Amadeu Gavaldá c, Mireia Gómez-Angelats b, Montserrat Miralpeix b, Carles Puig a
a Department of Medicinal Chemistry, Almirall, 08960 Sant Just Desvern, Barcelona, Spain
b Respiratory Therapeutic Area Discovery, Almirall, 08980 Sant Feliu de Llobregat, Barcelona, Spain
c Systems Pharmacology, Almirall, 08980 Sant Feliu de Llobregat, Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of diverse functionalized ureas in a semi-parallel fashion is described, as well as their b1/b2-
adrenergic activities and the corresponding structure–activity relationship (SAR). We have focused on
lipophilicity and duration of action, and we have discovered a strong correlation in this series of mole-
cules. A quantitative structure–activity relationship (QSAR) analysis will be presented that quantifies this
relationship.
Received 28 October 2010
Revised 15 December 2010
Accepted 18 December 2010
Available online 6 January 2011
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
LABA
b2
Adrenoreceptor agonist
Asthma
COPD
Bronchodilator
Duration of action
The search for new ultra long-acting b2-adrenoreceptor agonists
(LABA’s), for the treatment of asthma and COPD, has become a very
active area ofdrugdiscoveryin recent years. Once-a-daycompounds
are entering the market (indacaterol1, 3) or in advanced clinical
phase (vilanterol2, 4) and will potentially become the therapy of
choice over salmeterol 1 or formoterol 2, the two currentlymarketed
(twice-daily) long acting b2-adrenoreceptor agonists (Fig. 1). Dura-
tion of action is one of the most challenging issues in the field, and
there are many publications3–6 related to this topic. Two distinct
hypotheses have been put forward to explain this issue: the exo-site
hypothesis7 and the diffusion microkinetic hypothesis.8
We focused our attention on the microkinetic theory, and the
effect of lipophilicity on duration of action was investigated in a
series of compounds developed in our LABA research program.
OH
H
N
HO
HO
O
1
OH
H
N
H
O
N
The exosite theory requires the presence of a specific binding
site for the drug, apart from the orthosteric site, which contributes
to retain the agonist for receptor activation. Such a mechanism
would result in longer receptor residence time.
HO
O
2
OH
H
N
On the other hand the microkinetic theory is based on the par-
tition of the drug into the membrane. Thus, in theory, lipophilic
compounds will remain longer in the cellular membrane resulting
in drugs with extended duration of action. The more soluble a mol-
ecule is in aqueous media, the more prone to be diffused away
from the tissue.
HO
HN
3
O
Cl
OH
H
N
O
HO
HO
O
Cl
4
⇑
Corresponding author. Tel.: +34 93 291 75 93.
E-mail address: daniel.perez@almirall.com (D. Pérez).
Figure 1. Structures of salmeterol l, formoterol 2, indacaterol 3, and vilanterol 4.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.12.096

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D. Pérez et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1545–1548
OH
Our aim was to find potent, selective and long-acting b2 ago-
O
H
N
NH
R
nists suitable for inhaled dry powder formulation. The starting
points were b2-adrenoreceptor agonists with the general formula
5 where Ar = saligenin or 8-hydroxycarbostyril moieties (Fig. 2).
As was the case for other compounds in the literature, the car-
bostyril moiety provided higher potency compared to saligenin
and additionally meta substitution of phenyl urea showed im-
proved potency over para substitution.
Ar
NH
5
OH
H
N
H
N
H
N
R
In general, the presence of an a-methyl adjacent to amine affor-
O
ded less selective compounds versus the b1 receptor and this fea-
ture was removed early from our strategy.
Thus 6 became our refined scaffold for further modifications
(Fig. 2).
HO
HN
6
O
Figure 2. Structures of general scaffold 5 and refined scaffold 6.
H
N
NO2
NO2
H2N
NO2
H
a
b
Cl
O
NO2
c
O
N
NH2
d
e
N
O
O
O
O
Cl
H3N
OH
HO
H
N
H
H
H
C
f
H
H
N
N
O
N
N
N
N
OH
R
h
i
O
R
+
O
O
g
O
NH
HO
HN
7
O
O
Scheme 1. Reagents and conditions: (a) KCN, MeOH/H2O, 95 °C, 4 h, 62%; (b) BH3ÁSMe2, THF, rt, 24 h, 43%; (c) (BOC)2O, THF, rt, 2 h, 85%; (d) Pd/C 10%, H2(30 psi), rt, 3 h,
MeOH, 44%; (e) triphosgene, Et3N, CH2Cl2, rt, 2.5 h, no isolation; (f) isocyanate split into aliquots, NH2-R (1.1 equiv), rt, on; (g) HCl concd, dioxane, rt, 2 h, 51–82% (yields over
three last steps); (h) Et3N, NaBH4, DMSO/MeOH, rt, 6 h, 43–77%; (i) Pd/C 10%, H2, MeOH, rt, 4 h, 25–87%.
Table 1
Biological data and calculated log P values for urea analogues
OH
H
H
H
N
N
N
R
O
HO
HN
O
Compound
number
R
c log Pa In vitro duration of action (% of trachea
b2 potency in G-P trachea b1 potency in rat left atria
In vivo potency
e
tone recovery in 1 h)b
(EC50; nM)c
(EC50; nM)d
(lg/ml)
(IC50 at
4 h)
(IC50 at
24 h)
3
∗
8
9
2.28
2.31
2.72
3.15
12
15
9
0.07
0.2
>10,000
900
0.2
0.3
2
∗
∗
>100
>>10
3
10
11
0.09
0.05
>10,000
>10,000
∗
2
1
O
12
0.83
52
0.13
—
—
—
∗
∗
NH2
13
14
2.22
2.36
23
16
0.2
0.2
550
—
—
—
—
O
∗
∗
6300
F
Cl
15
3.51
4
0.2
1600
ꢀ4
>>100
Cl

D. Pérez et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1545–1548
1547
∗
16
17
4.04
4.04
2
4
0.2
0.7
8890
5770
1
3
1.5
7
∗
18
19
3.94
4.62
8
0
3.2
1
296
—
—
—
—
∗
∗
O
ꢁ10,000
∗
20
3
3.99
3.88
5
0
0.9
1
—
—
5
—
Indacaterol
2310
12
a
b
c
Calculated log P using ACD/ChemSketch.
In vitro duration of action; expressed as the percentage of tone recovery reached after 1 h of washout of the test compound.
b2 adrenoreceptor agonist activity in isolated guinea-pig tracheal rings expressed as the concentration required to produce a 50% of relaxation (EC50) versus the 100%
relaxation (Emax) produced by 0.1 lM of isoprenaline.
d
b1 adrenoreceptor agonist activity in rat left atria expressed as the concentration required to induce a 50% of an ionotropic effect.10
Bronchocoprotective potency and duration of action was measured in guinea-pigs after 4 and 24 h of compounds’ administration by aerosol. Data are expressed as the
e
concentration of the compound required to produce a 50% inhibition of the bronchoconstriction induced by acetylcholine (iv).
phenpropyl analog 11 showing an exceptional one (2% recovery),
while maintaining high potency and selectivity.
60
50
40
30
20
10
0
The use of a more polar residue (compound 12) gave a faster
recovery of tracheal tone (52%), suggesting a relationship between
lipophilicity of the fragment ‘R’ and the corresponding in vitro
duration of action.
As a result, we chose to further investigate ‘R’ residues with
high log P. Given the distance between the secondary amine and
the residue ‘R’, we considered the pKa of the amine would be unaf-
fected by the nature of ‘R’. So, we used c log P instead of c log D to
assess lipophilicity.
As shown in Table 1, all compounds showed high potency in the
isolated guinea-pig trachea assay, most in the subnanomolar range,
as well as good selectivity versus the left atria assay (low b1 activ-
ity). The remarkably high tolerance of our scaffold to maintain high
potency and selectivity over a wide diversity of substituents ‘R’ is
noteworthy.
y = 95.505e-0.8368x
R2 = 0.7252
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
clogP
Figure 3. Correlation between % of tone recovery at 1 h versus c log P of the
Many of the ureas described also demonstrated good duration
of action values in the in vitro model and for some of them this
translated into long duration of action in vivo.
In an attempt to quantify the relationship between lipophilicity
and in vitro duration of action, we plotted both variables in a graph,
and an interesting correlation was found as shown in Figure 3.
(Compound 19 was excluded from the graph for mathematical
reasons, as curve was below the abscissa).
Therefore, we could establish a clear link between lipophilicity
and duration of action, and we can conclude that lipophilicity is
one of the main aspects that drive duration of action, both
in vitro and in vivo in our chemical series—a novel example of
how to achieve a desired pharmacological profile in a series of LA-
BA’s by modulation of physicochemical properties.
These findings support the microkinetic theory as the more
plausible explanation of the extended duration of action observed
in the series, since it is the lipophilicity of the ‘R’ substituent, and
not its individual chemical features that appears to be driving
duration of action.
compounds selected.
The synthesis of these compounds was achieved starting from
1-(chloromethyl)-3-nitrobenzene as described in Scheme 1. Final
compounds 6 were initially prepared in racemic form. The key
intermediate was the isocyanate 7, which was formed using tri-
phosgene in the presence of triethylamine. This intermediate was
not isolated and allowed us to incorporate a variety of different
amines following a parallel strategy.
The resulting crude isocyanate was split into aliquots and added
simultaneously the corresponding amines to form their ureas.
Once the urea was formed the amine was deprotected. The cou-
pling step with the quinolone moiety was done via reductive ami-
nation. The yield of this step was dependent upon the amine used.
Finally a deprotection of the hydroxyl via debenzylation gave
the desired compounds with good yields and purities.
In the case of the most interesting molecules we developed an
enantioselective synthesis9 to obtain the more active R-
enantiomers.
Following the above strategy several ureas were synthesized. To
assess in vitro duration of action, we measured the percent recov-
ery of tracheal tone at 1 h (the lower the recovery the longer the
duration of action). Compound 8 gave high b2 functional potency,
excellent b1/b2 selectivity and 12% recovery of tracheal tone at
1 h (Table 1). For more lipophilic residues (entries 9–11), a de-
crease in the % recovery of tracheal tone at 1 h was observed, with
Furthermore, three of our ureas (11, 16, 17) showed a sustained
in vivo duration of action in guinea-pig comparable to that of ref-
erence compound 3 (indacaterol).
Due to their excellent in vitro profile and in vivo duration of ac-
tion, we synthesized selected ureas in enantiomerically pure R-
form for further profiling, to fully assess their potential to produce
a long lasting and safer inhaled bronchodilator.
The results of these studies will be presented in due course.

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D. Pérez et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1545–1548
3. Brown, A. D.; Bunnage, M. E.; Glossop, P. A.; James, K.; Jones, R.; Lane, C. A. L.;
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We thank Andreu Ruiz, Juan Manuel Monleón and Oriol Llera
for their excellent technical assistance.
4. Brown, A. D.; Bunnage, M. E.; Glossop, P. A.; Holbrook, M.; Jones, R. D.; Lane, C.
A. L.; Lewthwaite, R. A.; Mantell, S.; Perros-Huguet, C.; Price, D. A.; Webster, R.
Bioorg. Med. Chem. Lett. 2007, 17, 6188.
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