Design, synthesis and biological activity evaluation of desloratadine analogues as H1 receptor antagonists

Article abstract of DOI:10.1016/j.bmc.2013.05.004

A series of N-substituted desloratadine analogues were designed and synthesized. They were tested for H₁ antihistamine activity by inhibiting histamine-induced contraction of isolated ileum muscles of guinea-pigs in vitro and inhibiting histamine-induced asthmatic reaction in guinea-pigs in vivo. All the evaluated compounds exhibited significant antihistamine activity compared with desloratadine. Five active compounds induced no sedative effects on mouse and four of them exhibited lower anticholinergic side effects than desloratadine. Among these analogues, compound 10, (1S,4S)-4-chlorocyclohexyl desloratadine displayed the highest activity and best safety profile. And it was believed to be a potential candidate as the 3rd generation antihistamine.

Full text of DOI:10.1016/j.bmc.2013.05.004

Bioorganic & Medicinal Chemistry 21 (2013) 4178–4185
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Design, synthesis and biological activity evaluation of desloratadine
analogues as H1 receptor antagonists
b
Yan Lin a,b, Yue Wang c, Li-Feng Sima b, Dong-Hua Wang d, Xiao-Hui Cao b, Li-Gong Chen b, , Bo Chen
⇑
a Institute of Chemical Industry of Forest Products, CAF, Nanjing 210042, PR China
b School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China
c Department of Chemical Engineering, Ren’ai College of Tianjin University, Tianjin 301636, PR China
d School of Pharmaceutical Science and Technology, Tianjin University, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of N-substituted desloratadine analogues were designed and synthesized. They were tested for
H1 antihistamine activity by inhibiting histamine-induced contraction of isolated ileum muscles of gui-
nea-pigs in vitro and inhibiting histamine-induced asthmatic reaction in guinea-pigs in vivo. All the eval-
uated compounds exhibited significant antihistamine activity compared with desloratadine. Five active
compounds induced no sedative effects on mouse and four of them exhibited lower anticholinergic side
effects than desloratadine. Among these analogues, compound 10, (1S,4S)-4-chlorocyclohexyl deslorata-
dine displayed the highest activity and best safety profile. And it was believed to be a potential candidate
as the 3rd generation antihistamine.
Received 20 March 2013
Revised 26 April 2013
Accepted 6 May 2013
Available online 15 May 2013
Keywords:
Antihistamine activity
Biological activity
Biological isostere
Desloratadine analogues
H1 receptor antagonist
Side effect
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
ilar affinity to histamine H1 receptor and muscarinic (M) receptor,
and it may inevitably cause dry mouth, dizziness, fatigue and other
Histamine is one of the most important chemical mediators.
And through its interactions with H1 receptors existing in tissues,
histamine is involved in many allergic disorders, such as allergic
rhinitis, asthma and urticaria.1–4 H1 receptor antagonists, that is,
antihistamines, are used as the first-line treatment for these aller-
gic diseases.5–7 The first-generation H1 antihistamines are effec-
tive, but their applications are considerably limited due to the
sedative and anticholinergic effects.8,9 This led to the development
of the second- and third-generation antihistamines.10–14 And the
third-generation are usually used to describe some new antihista-
mines that are selective isomers or active metabolites of older sec-
ond-generation antihistamine.15 These two generations were
devoid of the side effects of the first generation and exhibit distin-
guished antihistamine activity. Among them, desloratdine (a) is
one of the remarkable representatives. Desloratadine is the active
metabolite of loratadine (b), while it is at least 10 times more po-
tent than loratadine.10,16 For its widely use in clinic, desloratadine
demonstrates the advantages over other H1 antihistamines in that
it has high H1 antihistamine activity, wide therapeutic range and
low potential for drug interactions.10,17,18 On the other hand, it
was reported that low concentration of desloratadine showed sim-
symptoms and may also induce sedation effect on patients with
compromised blood–brain barrier.19 Therefore, researchers are
paying much attention to investigate novel histamine antagonists
based on the structure of desloratadine.12,20,21
It was reported that the environment of the tertiary amine
nitrogen atom in the antihistamine molecule is closely related with
the antihistamine activity.22,23 In our previous work, the structure–
activity relationship study showed that the introduction of
hydroxyalkyl group to the tertiary amine nitrogen atom in desl-
oratadine could effectively enhance the H1 antihistamine activity
of the compounds and the oxygen atom in the molecules may play
important part in the high activity.24,25 N-(3-hydroxypropyl) desl-
oratadine (1) was the most active compound in the tests. Then we
considered if other heteroatom groups can play the similar effect
on the antihistamine activity. In this paper, we summarized our
work on a new series of desloratadine derivatives, in which N-(3-
hydroxypropyl) desloratadine (1) as lead compound, heteroatom
and semi-rigid cyclohexyl groups were introduced to the mole-
cules, respectively. Eleven desloratadine derivatives 1–11 (Fig. 1)
were designed, synthesized and evaluated for their antihistamine
activities. The results showed that all of them exhibited significant
antihistamine activity compared with desloratadine. Then five ac-
tive compounds 1–4 and 10 were evaluated for the sedation effect
and anticholinergic side effect. It turned out that most of them
⇑
Corresponding author. Tel./fax: +86 022 27406314.
E-mail address: lgchen@tju.edu.cn (L.-G. Chen).
0968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.05.004

Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
4179
a
R= H
R=
( Desloratadine)
b
7
R= COOEt
R=
(Loratadine)
1
2
3
R=
R=
Cl
8
R=
R=
N
9
4
R=
R=
N
R
10 R=
11 R=
5
6
R=
2
Figure 1. Structures of desloratadine, loratadine and 11 designed compounds.
exhibited almost no sedative side effects and much lower anticho-
linergic effects than desloratadine.
chlorination of compound 1 with SOCl2 in good yield.26,27 Because
alcohol 1 is quite stable, it should be converted to compound 12 by
esterification of methyl sulfonylchloride in the presence of trieth-
ylamine and then it can be easily substituted by other groups.28
By this method, the fluoride 4 was obtained by fluorination of com-
pound c with tetrabutylammoniumfluoride in acetonitrile.29–31
The Gabriel reaction of compound 12 led to compounds 5 and 6
sequentially.32–34 Compound 7 was obtained by the treatment of
compound 12 with dimethylamine in methanol. On the other hand,
with the same synthetic method of compound 3, the chlorination
2. Chemistry
In this paper, compounds 1, 2, 8 and 9 were synthesized accord-
ing to the procedure described in our previous work.24,25 With
compounds 1 and 9 in hand, substitution of the hydroxyl group
with suitable reagents yields the designed target compounds
(Scheme 1 and Scheme 2). Compound 3 was synthesized by the
Cl
Cl
Cl
N
N
N
c
b
N
1
N
4
N
O
O S
O
OH
Cl
F
12
f
a
d
Cl
Cl
N
N
N
N
N
5
O
N
N
3
N
7
Cl
e
O
Cl
N
N
6
NH2
Scheme 1. Synthesis of desloratadine derivatives 3–7. Reagents and conditions: (a) SOCl2, CH2Cl2, 40 °C, 6 h; (b) MsCl, Et3N, CH2Cl2, 50 °C, 0.5 h; (c) TBAF, CH3CN, 3 h; (d)
phthalimide potassium, DMF, 4 h; (e) H2NNH2ꢀH2O, CH3OH, 80 °C, 7 h; (f) HN(CH3)2ꢀH2O, CH3OH, 6 h.

4180
Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
Cl
Cl
Cl
N
SOCl2, CH2Cl2
+
o
40
, 6 h
C
N
N
N
N
N
Cl
OH
9
11
10
Scheme 2. Synthesis of compounds 10 and 11.
of compound 9 with the hydroxyl group on six member ring affor-
ded the desired compound 10, accompanied with certain amounts
of elimination product 11 (Scheme 2).26,27,35
As shown in Figure 2, after the synthesized compounds addi-
tion, the average muscle tensions reduced sharply in 5 min in these
groups (P <0.05). And it can be seen that all the tested compounds
can antagonize the spasm induced by histamine. Compared with
the negative control group, it is easy to see the great advantages
of compounds 1, 2, 3, 4, 10 and desloratadine group (P <0.05).
Among these compounds, compound 10 exhibited the most potent
antihistamine activity and much better than desloratadine (the
antispasmodic percentage: 61.13% vs 49.12%).
Meanwhile, alcohol 1 was found to show great antihistamine
activity and this was consistent with the results in our previous
work. It is interesting to notice that another alcohol 9 with the hy-
droxyl group linked to the six-member ring showed the least anti-
histamine activity in the series. Besides, simple substitution
pattern without heteroatom was also investigated. Compound 2
showed good activity while compound 8 was not so active. Addi-
tionally, other heteroatom groups were investigated. The results
revealed that halogen containing compounds 3, 4 and 10, with dis-
tinct decrease of muscle tension, were proved to be promising H1-
antagonists. They were much more active than the other com-
pounds in the test (except compound 1). With the comparisons
of compounds 1 and 9, compounds 2 and 8, compounds 3 and
10, it can be seen that the linker group played complicated role
in the interaction with histamine receptor. Moreover, the effects
of different nitrogen containing groups were considered. Com-
pounds 5, 6 and 7 exhibited certain antagonistic activity, but they
were not as active as their counterparts.
3. Results and discussion
Alcohol 1, as the lead compound, was reported previously in our
work, which exhibited more potent antihistamine activity than
loratadine.24,25 In order to explore the effect of hydroxyl group in
the molecule, we designed and synthesized compounds 2–4 and
6 based on biological isostere principle. The amino derivatives 5
and 7 were also synthesized. Meanwhile, replacement of carbon
chain in compound 1 by the cyclohexyl group resulted in com-
pound 8. For comparison, derivatives 9, 10 and 11 were synthe-
sized as well. In order to determine the structure-activity
relationships, the eleven synthesized compounds and deslorata-
dine were evaluated for the effects on isolated ileum smooth mus-
cle tension in guinea pigs in vitro and asthma-relieving effects on
the histamine-induced asthmatic reaction in guinea pigs in vivo.
Besides, five of them and desloratadine were evaluated for the
sedation and anticholinergic activity.
Firstly, the eleven synthesized compounds (1–11) were chosen
to be assessed for their ability to inhibit histamine-induced con-
traction of guinea pigs ileum.24,25 This test is a reliable measure
of H1-antagonist activity. Desloratadine was used as the standard
in this test. Smooth muscle tensions at three different times were
recorded and the antispasmodic percentages were figured out to
preliminarily judge the antihistamine activity of these compounds
in vitro. All the results were listed in Table 1. And in order to show
the trends visually, the results were described in Figure 2.
For the uncertainty relationship between the bioactivity in vitro
and in vivo, these compounds were also investigated for the asth-
ma-relieving effects on the histamine-induced asthmatic guinea-
Table 1
The effects of compounds on the inhibition of histamine-induced smooth muscle spasmsa (x s, n = 8)
ꢀ
Test groups
Smooth muscle tension (g)
Before drug
Antispasmodic percentage (%)
After histamine
After drug
Negative control group
Desloratadine
Compound 1
Compound 2
Compound 3
Compound 4
Compound 5
Compound 6
Compound 7
Compound 8
Compound 9
Compound 10
Compound 11
1.86 0.08
1.85 0.18
1.80 0.11
1.84 0.19
1.86 0.09
1.83 0.17
1.79 0.16
1.87 0.21
1.81 0.14
1.87 0.11
1.86 0.11
1.80 0.09
1.88 0.12
3.39 0.87
3.32 0.51
3.77 1.50
3.27 0.89
3.33 0.71
3.51 0.49
3.69 1.85
3.25 1.31
3.95 1.23
3.75 1.43
3.35 1.17
3.66 1.22
3.44 0.94
3.37 1.05c
1.67 0.30b,d
1.73 0.39b,d
1.80 0.31b,d
1.81 0.40b,d
1.74 0.50b,d
2.71 1.45
2.36 0.89
2.66 0.65
2.57 0.90
1.27 5.65c
49.12 9.55b
45.17 28.58b
42.51 14.82b
43.04 18.14b
48.73 19.89b
26.56 11.34b
25.96 10.93b
30.36 12.41b
29.39 12.88b
13.03 8.56b
61.13 13.52b,c
28.31 16.22b
2.93 1.13
1.29 0.15b,c,d
2.38 1.30b,d
a
b
c
The concentration of desloratadine and the 11 compounds was 0.2 mg/mL.
Compared to the negative control group: P < 0.05.
Compared to the desloratadine group: P < 0.05.
d
Compared to the effects before drug: P < 0.05.

Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
4181
Figure 2. The effects of compounds on the inhibition of histamine-induced smooth muscle spasms. Groups 12 and 13 in this figure represent desloratadine and the negative
control group, respectively.
pigs in vivo.24,25 Desloratadine was also chosen as the standard.
The guinea-pigs were pretreated with intragastric administration
of desloratdine or the eleven synthesized compounds, and then
they were sprayed with histamine hydrochloric solution to induce
experimental asthma model of the guinea-pigs. The asthmogenic
latent periods were determined in order to determine the antihis-
tamine activity of the target compounds. The obtained results were
summarized in Table 2.
As shown in Table 2, all tested compounds and desloratadine
group can significantly prolong the asthmogenic latent periods of
histamine-induced asthmatic guinea-pigs with the prolongation
over 100 s. More importantly, most of the tested compounds
exhibited similar or more potent activity than desloratadine, even
though their dosages were only 1% of desloratadine group in the
test (0.01 mg/kg vs 1.00 mg/kg). Besides, the results showed that
compounds 3, 4, 10 and 11 exhibited excellent antihistamine activ-
ity, while alcohol 1 and amino derivative 6 were not so active com-
pared with them. It can be seen that the antihistamine activity was
improved by substituent groups with varying lipophilic character-
istic. In the series of amino derivatives 5, 6 and 7, the most hydro-
philic compound 6 showed the least antihistamine activity. Even
so, compound 6 was still more active than desloratadine. Addition-
ally, the introduction of halogen atom to the molecule contributed
to enhancing the in vivo activity effectively. The antihistamine
activities of compounds 3, 4 and 10 were found to be much better
than that of the other analogues. Noticeably, compound 10 was the
most active one in this test. And this accorded with the results
in vitro.
According to the antihistaminic activity results, it can be seen
that there is some consistency between the in vitro results and
in vivo results. In the in vitro test, compounds 1–4 and 10 can sig-
nificantly antagonize the spasm induced by histamine, thus they
exhibited better antihistamine activity than their counterparts.
And in the in vivo test, it is obvious that compounds 1–4 and 10
can prolong the asthmogenic latent periods of histamine-induced
asthmatic guinea-pigs and showed excellent activity. On the other
hand, there are some discrepancy between the in vitro results and
in vivo results. It is because that the organism environment is com-
plex, sometimes inferior in vitro results can also lead to positive ef-
fects in organism. As seen the results in Table 1 and Table 2, apart
from compounds 1–4 and 10, compounds 5, 8, 9 and 11 also exhib-
ited good in vivo antihistamine activity, though the in vitro results
of them were not much outstanding. Although the mechanism was
unknown, it can be seen that it is of great necessity to analysis both
in vitro results and in vivo results.
The next area of exploration in this paper was the side effects of
the selected active compounds 1–4 and 10. These antihistaminic
compounds were chosen to be tested for the sedative effects.
Firstly, the effects of five compounds on the ordinary behaviors
of mouse were determined. After the administration of saline, desl-
oratadine, or the synthesized compounds, each animal in the test
groups acted normal in the following seven days. All mice in the
test showed no sleep abnormalities and did not have other abnor-
mal performances, such as excitement, irritability, convulsion, sal-
ivation, muscle tremors. The mental state and body activity of the
mice in the synthesized-compound groups were similar with those
in the saline control group and desloratadine group. This indicated
that the five tested compounds almost caused no side effect on the
ordinary behavior and cannot induce sedation action of mouse
when it was administrated alone. Previous studies showed that
Table 2
a
ꢀ
The effects of synthesized compounds on the inhibition of histamine (x s, n = 10)
Test groups
The incubation period
The incubation period
before drug (s)
after drug (s)
Negative control
group
Desloratadine
group
99.10 46.69
117.50 44.29
127.10 40.46c
278.20 56.93b,d
Compound 1
Compound 2
Compound 3
Compound 4
Compound 5
Compound 6
Compound 7
Compound 8
Compound 9
Compound 10
Compound 11
102.30 41.56
119.30 44.65
108.30 46.25
89.90 26.86
97.00 34.56
97.70 37.58
93.90 50.19
108.20 42.91
92.80 41.84
98.00 47.00
98.20 48.18
221.90 89.30b,d
255.10 44.40b,d
256.90 74.34b,d
269.40 49.29b,d
247.90 113.43b,d
182.80 74.48b,d
212.80 67.11b,d
250.30 83.75b,d
222.00 100.15b,d
325.20 41.16b,d
262.70 79.56b,c,d
a
The desloratadine group (1.00 mg/kg) and eleven compounds groups (0.01 mg/
kg) were pretreated with intragastric administration in 2 mL/kg bw.
b
Compared to the negative control group: P < 0.05.
Compared to the desloratadine group: P < 0.05.
Compared to the effects before drug: P < 0.05.
c
d

4182
Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
Table 3
a
ꢀ
Five compounds on the hypnotic effects of pentobarbital sodium (x s, n = 10)
Groups
Dosage (mg/kg)
Loss of righting reflex latency (min)
Recovery of righting reflex (min)
Pentobarbital sodium alone
100
1.94 0.25
90 12
Pentobarbital sodium and desloratadine
100 + 1
2.23 0.44⁄⁄NN
1.54 0.11⁄⁄NN
1.46 0.19⁄⁄NN
1.47 0.25
93 14
Pentobarbital sodium and low doses of compound 1
Pentobarbital sodium and high doses of compound 1
Pentobarbital sodium and low doses of compound 2
Pentobarbital sodium and high doses of compound 2
Pentobarbital sodium and low doses of compound 3
Pentobarbital sodium and high doses of compound 3
Pentobarbital sodium and low doses of compound 4
Pentobarbital sodium and high doses of compound 4
Pentobarbital sodium and low doses of compound 10
Pentobarbital sodium and high doses of compound 10
100 + 50
100 + 200
100 + 50
100 + 200
100 + 50
100 + 200
100 + 50
100 + 200
100 + 50
100 + 200
76 2⁄⁄NN
100 7⁄
76 2⁄⁄NN
1.61 0.32⁄NN
1.48 0.26⁄⁄NN
1.58 0.24⁄⁄NN
1.47 0.27⁄⁄NN
1.45 0.27⁄⁄NN
1.61 0.18⁄⁄NN
1.62 0.19⁄⁄NN
99
8
97 16
120 13⁄⁄NN
98 20
123 13⁄⁄NN
82 5N
103 4⁄⁄N
a
Compared to the group use pentobarbital sodium alone: ⁄P <0.05, ⁄⁄P <0.01; Compared to the group use pentobarbital sodium and desloratadine: NP <0.05, NNP <0.01.
the sedative effect of H1 antagonist is exhibited due to their blood
brain barrier penetration for which lipophilicity of compounds
plays an important role in the hydrophobic interactions at the
receptor site. While in our test hydrophilic compounds 1 and 10
exhibited no significant difference compared with other lipophilic
compounds. This may showed the great importance of deslorata-
dine structure.
Then we tested the effects of the five active compounds (1–4
and 10) on the hypnotic effect caused by pentobarbital sodium,
which can preliminarily judge the interaction between the synthe-
sized compounds and pentobarbital sodium. After the administra-
tion of the tested compounds, the mice were injected with
pentobarbital sodium. The loss of righting reflex latency and the
recovering period were recorded. The results were described in Ta-
ble 3. As seen in Table 3, desloratadine had basically no effect on
the hypnotic effect caused by pentobarbital sodium because the
loss of righting reflex latency and its recovering period in this
group showed no significant differences compared with the pento-
barbital sodium group. While compared with these two groups, the
loss of righting reflex latency was shortened by the synthesized
five compounds both in high dose and low dose groups (P <0.05).
It meant that the synergistic effect was observed when these five
compounds were separately administrated with pentobarbital so-
dium. On the other hand, compounds 1, 2 and 10 in the low dose
group gave rise to the significant short periods of the righting re-
flex recovery. Though the mechanism was unknown, it seemed
that low dose of these three compounds can alleviate the hypnotic
effects caused by pentobarbital sodium to some extent. And it
should be noticed that even the low dose of the tested five com-
pounds was much more than the dose of desloratadine, which
meant that these compounds were not totally inferior to deslorat-
adine on the hypnotic effects caused by pentobarbital sodium.
In addition, five active compounds 1–4 and 10 were evaluated
for the inhibition of acetylcholine-induced smooth muscle tension
in guinea pigs to judge the anticholinergic side effects of these
compounds. Atropine was used as positive control group, deslorat-
adine and the five compounds were tested and the test method
was similar to the former one for antihistamine selectivity
in vitro. The results were showed in Table 4. It can be seen that
the addition of acetylcholine caused strong contraction of smooth
muscles and sharp increase of the muscle tension. Atropine, a kind
of anticholinergic drug, can relieve muscle spasm effectively. The
results in Table 4 showed that even a few of atropine (0.1 lg/mL)
can dramatically decrease the smooth muscle tension and its anti-
spasmodic percentage was up to 74.90%. Besides, desloratadine
and selected five compounds can significantly inhibit the acetyl-
choline-induced smooth muscle contraction and displayed varying
antispasmodic percentages. It indicated that desloratadine and the
Table 4
The effects of compounds on the inhibition of acetylcholine-induced smooth muscle spasmsa (x s, n = 8).
ꢀ
Groups
Final concentration (
lg/mL)
Smooth muscle tension (g)
After acetycholine
Antispasmodic percentage (%)
Before drug
After drug
Negative control group
Acetylcholine
Atropine
5.24 0.31
4.92 0.88
4.78 1.11
4.74 0.78
4.59 0.75
5.02 0.98
4.47 1.29
4.87 0.73
4.82 0.89
5.54 0.67
5.09 0.94
4.56 0.64
4.78 1.14
4.54 0.92
4.57 0.92
4.68 0.69
4.79 1.16
5.63 0.91
4.72 1.11
5.24 0.31
14.53 3.05
14.84 5.78
19.46 7.14
18.81 5.54
19.66 11.00
14.72 4.77
16.13 4.13
17.01 5.38
17.71 3.77
20.37 9.85
14.90 5.11
18.67 9.67
11.20 2.32
18.80 7.09
20.90 6.17
15.68 6.58
16.42 1.72
12.78 2.85
5.17 0.36
12.25 4.00⁄⁄
3.47 1.20⁄⁄
4.19 2.38⁄⁄
6.04 3.24⁄⁄
6.72 1.56⁄⁄
7.43 1.99⁄⁄
3.58 1.35⁄⁄
4.38 2.53
1.31 3.66
0.2
0.1
1.0
2.0
1.4
1.0
1.0
0.6
0.2
1.4
1.0
0.6
1.0
0.6
0.2
2.0
1.4
1.0
17.64 16.83
74.90 8.90ꢀꢀ
Desloratadine
75.11 15.99ꢀꢀ
67.06 18.34ꢀꢀ
58.27 16.95ꢀꢀd
45.87 19.31ꢀꢀddNN
77.06 9.40ꢀꢀ
High doses of compound 1
Middle doses of compound 1
Low doses of compound 1
High doses of compound 2
Middle doses of compound 2
Low doses of compound 2
High doses of compound 3
Middle doses of compound 3
Low doses of compound 3
High doses of compound 4
Middle doses of compound 4
Low doses of compound 4
High doses of compound 10
Middle doses of compound 10
Low doses of compound 10
73.09 15.85ꢀꢀ
56.14 13.24ꢀꢀddN
69.51 12.33ꢀꢀ
56.45 23.89ꢀꢀ
47.21 26.13ꢀdN
61.41 15.82ꢀꢀ
62.47 12.20ꢀꢀdN
54.35 13.72ꢀꢀddNN
70.61 9.50ꢀꢀ
7.51 2.07⁄⁄
5.68 2.27⁄⁄
6.94 5.24⁄⁄
8.56 3.18⁄⁄
4.13 1.74⁄⁄
6.58 2.24⁄⁄
9.11 2.25⁄⁄
4.40 1.91⁄⁄
5.59 2.25⁄⁄
7.07 2.89⁄⁄
61.39 23.70ꢀꢀ
44.89 19.63ꢀꢀdNN
a
Compared to after acetycholine: ⁄P <0.05, ⁄⁄P <0.01; compared to acetycholine group:ꢀP <0.05, ꢀꢀP <0.01; compared to atropine group:dP <0.05, ddP <0.01; compared to
desloratadine group: NP <0.05, NNP <0.01.

Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
4183
five synthesized compounds antagonized cholinergic responses to
varying degrees in these models. While it also can be seen that
antispasmodic percentages of compounds 1, 3, 4 and 10 were
much lower than that of desloratadine, and so were their anticho-
linergic side effects. Especially, both compounds 1 and 10 had
showed much lower inhibitory effects on acetylcholine-induced
smooth muscle contraction than their counterparts in the assay.
Considering their good antihistaminic activity, they can be poten-
tial for the new antihistamines.
2.52–2.46 (m, 1H), 2.43–2.36 (m, 6H), 2.05–2.00 (m, 2H), 1.88–
1.83 (m, 2H), 1.35–0.97 (m, 4H); 13C NMR (CDCl3, 125 MHz), d:
157.93, 146.83, 139.72, 139.63, 138.01, 137.44, 133.67, 132.83,
132.50, 131.16, 129.29, 126.21, 122.30, 70.72, 62.85, 51.09, 51.00,
34.98, 34.97, 32.09, 31.64, 31.38, 27.13, 26.66, 26.58. HR-MS
(ESI), calcd C25H29ClN2O: [M+H]+ m/z: 409.2041, found: 409.2053.
5.1. Synthesis of compounds 326,27
Thionyl chloride (38.4 mmol) was added to the solution of com-
pound 1 (4.8 mmol) in 50 mL CH2Cl2 at 0–5 °C. Then the mixture
was heated to reflux for 6 h. Dichloromethane and the excess thio-
nyl chloride were removed under vacuum. The residue was dis-
solved by the solution of ethanol and water (ethanol/water = 2:1,
V/V) 40 mL. And then the mixture was adjusted to pH = 10 with
10% wt. NaOH aqueous solution, followed by extraction with
CH2Cl2. The organic phase was dried by anhydrous magnesium sul-
fate. After filtration and concentration, the residue was purified by
silica gel column (petroleum ether/ethyl acetate/metha-
nol = 3:1:0.2, V/V/V) to afford 3 in the yield of 63.8%. 1H NMR
(CDCl3, 500 MHz), d: 8.40 (d, J = 5.0 Hz, 1H), 7.42 (d, J = 6.5 Hz,
1H), 7.12 (t, J = 9.8 Hz, 3H), 7.09 (t, J = 6.0 Hz, 1H), 3.58 (t,
J = 6.8 Hz, 2H), 3.33–3.46 (m, 2H), 2.72–2.86 (m, 4H), 2.30–2.53
(m, 6H), 2.09–2.15 (m, 2H), 1.91–1.96 (m, 2H); 13C NMR (CDCl3,
125 MHz), d: 157.83, 146.84, 139.75, 139.09, 138.05, 137.47,
133.63, 132.87, 132.85, 131.06, 129.18, 126.22, 122.31, 55.54,
55.20, 55.14, 43.57, 32.05, 31.66, 31.96, 30.32. HR-MS (ESI), calcd
4. Conclusion
A series of desloratadine derivatives were designed and synthe-
sized. All the compounds can effectively inhibit histamine-induced
contraction of guinea pigs ileum and exhibit promising antihista-
minic activity against histamine-induced asthmatic guinea-pigs.
They showed similar activity even at 1% dosages of desloratadine
group in vivo. The tested five compounds induced no sedative ef-
fects on mice. And when administrated together with pentobarbi-
tal sodium, they showed synergistic effects to some extent. Four of
the five compounds exhibited lower anticholinergic side effects
than desloratadine. Among these analogues, compound 10,
(1S,4S)-4-chlorocyclohexyl desloratadine, was the most active
antagonist. It showed far more potent antihistaminic activity than
desloratadine both in vitro and in vivo and much lower side effects
than desloratadine. Therefore, it could serve as a drug candidate for
further study.
C
22H24Cl2N2: [M+HꢁHCl]+ m/z: 351.1623, found: 351.1633.
5. Experimental sections
5.2. Synthesis of compound 1228
Almost chemicals were purchased from Guangfu Technology
Development Co., Ltd, Tianjin (China). And all chemicals used in
this study were of analytical grade or purified according to stan-
dard procedures. 1H and 13C NMR spectra were recorded on INOVA
500 Hz spectrometer in CDCl3 with TMS as an internal standard.
The 19F NMR spectrum was recorded on INOVA 400 Hz spectrom-
eter in CDCl3 with CFCl3 as external standards. HR-MS was re-
corded on MicroOTOF-Q II.
The target compounds 1, 2, 8 and 9 were synthesized according
to our previous papers.24,25 Compound 1 was obtained from 3-ami-
no-1-propanol. Similarly, compounds 2, 8 and 9 were obtained
from propylamine, cyclohexylamine and t-4-aminocyclohexanol,
respectively.
Compound 1 (5.4 mmol) and 40 mL CH2Cl2 were added to a
two-necked flask, followed by the addition of triethylamine
(7.6 mmol). Then methylsulfonyl chloride (28.2 mmol) was added
slowly to the stirring mixture with the temperature controlled at
0–5 °C. After that, the mixture was warmed to room temperature
and kept stirring for 0.5 h. The mixture was washed by 10% wt.
K2CO3 aqueous solution and brine successively. Then it was dried
over anhydrous MgSO4, followed by filtration and concentration.
The residue was used for further reactions directly.
5.3. Synthesis of compound 429–31
Compound 2: 45.7%; 1H NMR (CDCl3, 500 MHz) d: 8.40 (s, 1H),
7.43 (d, J = 8.0 Hz, 1H), 7.14 (m, 3H), 7.08 (dd, J1 = 4.5 Hz,
J2 = 7.5 Hz, 1H), 3.44–3.33 (m, 2H), 2.86–2.73 (m, 4H), 2.56–2.50
(m, 1H), 2.45 (t, J = 5.3 Hz, 1H), 2.43–2.37 (m, 2H), 2.33–2.26 (m,
2H), 2.13–2.05 (m, 2H), 1.54–1.46 (m, 2H), 0.88 (t, J = 7.5 Hz, 3H);
13C NMR (CDCl3, 125 MHz) d: 157.90, 146.81, 139.72, 139.45,
138.07, 137.38, 133.58, 132.79, 132.60, 131.08, 129.14, 126.17,
122.23, 60.77, 55.17, 55.13, 32.05, 31.63, 31.24, 30.98,20.43, 12.26;
HR-MS (ESI), calcd C22H25ClN2: [M+H]+ m/z: 353.1779, found:
353.1787.
The mixture of compound 12 (4.7 mmol) and tetrabutylammo-
niumfluoride (7.1 mmol) was refluxed in 40 mL acetonitrile for 3 h.
After acetonitrile was removed under vacuum, the residue was dis-
solved in 40 mL CH2Cl2 and washed by brine. The organic phase
was dried by anhydrous magnisium sulfate, followed by filtration
and concentration. The residue was purified by silica gel column
(petroleum ether/ethyl acetate/methanol = 3:1:0.1, V/V/V) to give
4 in the total yield of 28.8%. 1H NMR (CDCl3, 500 MHz), d: 8.40 (t,
J = 2.3 Hz, 1H), 7.42 (dd, J1 = 1.5 Hz, J2 = 6.0 Hz, 1H), 7.15 (s, 1H),
7.13 (d, J = 1.5 Hz, 2H), 7.07–7.11 (m, 1H), 4.55 (t, J = 6.3 Hz, 1H),
4.46 (t, J = 6.3 Hz, 1H), 3.35–3.45 (m, 2H), 2.73–2.87 (m, 4H),
2.49–2.55 (m, 2H), 2.33–2.47 (m, 4H), 2.11–2.13 (m, 2H), 1.84–
1.89 (m, 2H); 13C NMR (CDCl3, 125 MHz), d: 157.83, 146.88,
139.76, 139.11, 138.05, 137.50, 133.64, 132.88, 132.87, 131.08,
129.19, 126.25, 122.33, 83.54, 82.23, 55.17, 55.13, 54.45, 54.40,
32.06, 31.67, 31.19, 30.94, 28.43, 28.27. 19F NMR (CDCl3), d: -
219.86. HR-MS (ESI), calcd C22H24ClFN2: [M+H]+ m/z: 371.1690,
found: 371.1688.
Compound 8: 32.0%; 1H NMR (CDCl3, 500 MHz), d: 8.40 (t,
J = 2.3 Hz, 1H), 7.43 (d, J = 8.0 Hz, 1H), 7.13 (t, J = 4.0 Hz, 3H),
7.09–7.07 (m, 1H), 3.44–3.34 (m, 2H), 2.86–2.78 (m, 4H), 2.53–
2.48 (m, 1H), 2.42–2.32 (m, 6H), 1.85 (s, 2H), 1.77 (s, 2H), 1.61
(d, J = 7.0 Hz, 1H), 1.26–1.20 (m, 4H), 1.10–1.06 (m, 1H); 13C NMR
(CDCl3, 125 MHz), d: 158.07, 146.85, 140.02, 139.72, 138.11,
137.34, 133.63, 132.76, 132.34, 131.21, 129.16, 126.17, 122.22,
63.85, 50.83, 50.72, 32.12, 31.78, 31.65, 31.53, 29.18, 29.06,
27.13, 26.59, 26.28. HR-MS (ESI), calcd C25H29ClN2: [M+H]+ m/z:
393.2092, found: 393.2096.
5.4. Synthesis of compound 532–34
Compound 9: 48.2%; 1H NMR (CDCl3, 500 MHz), d: 8.39 (s, 1H),
7.43 (d, J = 7.5 Hz, 1H), 7.17 (s, 1H),7.14–7.10 (m, 2H), 7.09–7.07
(m, 1H), 3.54 (m, 1H), 3.43–3.33 (m, 2H), 2.86–2.76 (m, 4H),
The mixture of KOH (3.9 g) in 50 mL methanol was added to
phthalimide (68.0 mmol) in 50 mL dry ethanol. After stirring for

4184
Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
3 h, the mixture was filtrated and the residue phthalimide potas-
sium was dried to give the yield of 92.3%.
(m, 4H), 2.53–2.48 (m, 1H), 2.45–2.31 (m, 6H), 2.07–2.04 (m,
2H), 1.87–1.72 (m, 4H), 1.66–1.60 (m, 2H); 13C NMR (CDCl3,
125 MHz), d: 157.92, 146.85, 139.74, 139.56, 138.04, 137.43,
133.65, 132.84, 132.63, 131.14, 129.18, 126.21, 122.29, 62.68,
59.35, 50.75, 50.65, 33.74, 33.72, 32.09, 31.66, 31.58, 31.32,
Phthalimide potassium (5.6 mmol) and tetrabutyl ammonium
bromide (0.2 g) were added to compound 12 in 35 mL DMF. The
mixture was stirred at 50 °C for 4 h. After cooled to room temper-
ature, the reaction mixture was dropped to 300 mL water and ad-
justed to pH = 10 by 10% wt. NaOH aqueous solution, followed by
extraction with ethyl acetate. The organic layer was combined
and dried by anhydrous MgSO4. After filtration and concentration,
the residue was purified by silica gel column (petroleum ether/
ethyl acetate/methanol = 3:1:0.3, V/V/V) to give 5 in the yield of
77.8%. 1H NMR (CDCl3, 500 MHz), d: 8.37 (dd, J1 = 1.8 Hz,
J2 = 3.0 Hz, 1H), 7.82 (q, J = 3.0 Hz, 1H), 7.70 (q, J = 3.0 Hz, 1H),
7.41 (dd, J1 = 1.7 Hz, J2 = 6.5 Hz, 1H), 7.05–7.12 (m, 4H), 3.74 (t,
J1 = 7.0 Hz, J2 = 3.5 Hz, 2H), 3.31–3.39 (m, 2H), 2.70–2.82 (m, 4H),
2.38 (t, J = 7.0 Hz, 2H), 2.33–2.36 (m, 1H), 2.22–2.27 (m, 3H),
1.99–2.06 (m, 2H), 1.84–1.88 (m, 2H); 13C NMR (CDCl3,
125 MHz), d: 168.66, 157.89, 146.83, 139.69, 139.34, 138.00,
137.40, 134.09, 133.61, 132.80, 132.61, 132.44, 131.08, 129.17,
126.19, 123.34, 122.28, 56.11, 55.14, 55.10, 36.87, 32.06, 31.61,
31.15, 30.91, 25.87. HR-MS (ESI), calcd C30H28ClN3O2: [M+H]+ m/
z: 498.1943, found: 498.1945.
22.92, 22.61. HR-MS (ESI), calcd
427.1702, found: 427.1710.
C
25H28Cl2N2: [M+H]+ m/z:
Compound 11: yield 53.1%. 1H NMR (CDCl3, 500 MHz), d: 8.39
(d, J = 3.5 Hz, 1H), 7.42 (d, J = 6.5 Hz, 1H), 7.15–7.10 (m, 3H),
7.08–7.06 (m, 1H), 5.64–5.59 (m, 2H), 3.44–3.33 (m, 2H), 2.86–
2.76 (m, 4H), 2.64–2.60 (m, 1H), 2.55–2.49 (m, 1H), 2.45–2.32
(m, 5H), 2.16–2.01 (m, 4H), 1.92–1.90 (m, 1H), 1.48–1.39 (m,
1H); 13C NMR (CDCl3, 125 MHz), d: 158.01, 146.88, 139.80,
139.73, 138.07, 137.40, 133.65, 132.82, 132.52, 131.20, 129.19,
127.09, 126.22, 126.05, 122.27, 60.21, 51.03, 50.58, 32.12, 31.68,
31.43, 27.61, 27.14, 26.36, 26.10. HR-MS (ESI), calcd C25H27ClN2:
[M+H]+ m/z: 391.1936, found: 391.1944.
6. Biological methods
6.1. Antihistamine active assay
5.5. Synthesis of compound 632–34
The effects on isolated ileum smooth muscle tension in guinea
pigs in vitro and asthma-relieving effects on the histamine induced
asthmatic reaction in guinea-pigs in vivo were examined according
to our previous work.24,25
(1) Effects on isolated ileum smooth muscle tension in guinea
pigs in vitro.
After the guinea-pigs were knocked out, the abdomens were
opened and 15 cm of the ileum sections were cut out. The pieces
were placed in a Petri dish containing Tyrode’s solution at 37 °C
and continuously bubbled with oxygen. For the contraction exper-
iments, the intestines were sliced (1 cm length) and put into Tyr-
ode’s solution that was continuously bubbled with oxygen at
37 °C. One end of the intestine was fixed to a ventilation hook
and the other end was fixed to a tension transducer which was
connected to a computer interface. The smooth muscle tension
data was recorded by a BL system.
80% Hydrazine hydrate solution (4.4 mmol) was added to the
solution of compound 5 (2.2 mmol) in 30 mL ethanol. The reaction
mixture was heated to reflux for 7 h. After filteration, the filtrate
was concentrated and purified by silica gel column (ethyl ace-
tate/methanol/ammonia water = 1:1:0.2, V/V/V) to afford 6 in the
yield of 43.4%. 1H NMR (CDCl3, 500 MHz), d: 8.31 (d, J = 4.5 Hz,
1H), 7.43 (d, J = 8.0 Hz, 1H), 7.10–7.14 (m, 3H), 7.08 (dd,
J1 = 3.0 Hz, J2 = 5.0 Hz, 1H), 5.30 (s, 2H), 3.33–3.43 (m, 2H), 2.79–
2.86 (m, 2H), 2.76 (t, J = 6.5 Hz, 4H), 2.48–2.54 (m, 1H), 2.31–2.42
(m, 5H), 2.07–2.14 (m, 2H), 1.62–1.68 (m, 2H); 13C NMR (CDCl3,
125 MHz), d: 159.80, 146.79, 139.72, 139.13, 138.00, 137.46,
133.61, 132.81, 132.75, 131.04, 129.15, 126.18, 122.30, 56.59,
55.18, 55.13, 40.91, 31.60, 31.16, 30.93, 30.04, 19.36. HR-MS
(ESI), calcd C22H26ClN3: [M+H]+ m/z: 368.1888, found: 368.1891.
The experiments were conducted containing the negative con-
trol group, desloratadine group and synthesized eleven compounds
groups (Table 1).The smooth muscle tension values were recorded
after the ileum peristalsis curve tended to stabilized. Then hista-
mine (0.05 mL) was added and the average tension values in each
group were recorded. When the maximum contraction was
achieved, the eleven synthesized compounds or the blank DMSO
(the negative control group) were added. After 3 min, the average
tension values were recorded. The parallel operation was repeated
for 8 times. The antispasmodic percentage was evaluated using the
following formula.
5.6. Synthesis of compound 7
30% Dimethylamine aqueous solution (3.1 mmol) was added to
the solution of compound 12 (4.7 mmol) in 40 mL methanol. The
mixture was heated to reflux for 6 h. After methanol was removed
under vacuum, the residue was dissolved by 40 mL CH2Cl2 and
washed by saturated salt water. Then the organic phase was com-
bined and dried by anhydrous MgSO4, followed by filtration and
concentration. The residue was purified by silica gel column
(petroleum ether/ethyl acetate/methanol = 3:1:0.1, V/V/V) to af-
ford 7 in the total yield of 67.0%. 1H NMR (CDCl3, 500 MHz), d:
8.39 (d, J = 5.0 Hz, 1H), 7.43 (d, J = 7.0 Hz, 1H), 7.17 (s, 1H), 7.08–
7.14 (m, 3H), 3.32–3.47 (m, 2H), 2.94–2.99 (m, 4H), 2.80–2.87
(m, 2H), 2.78 (s, 3H), 2.70–2.73 (m, 6H), 2.60–2.68 (m, 1H), 2.45–
2.64 (m, 4H), 2.08–2.14 (m, 2H); 13C NMR (CDCl3, 125 MHz), d:
156.82, 146.82, 139.85, 137.89, 137.58, 135.96, 134.53, 133.69,
133.24, 130.57, 129.24, 126.38, 122.64, 56.43, 54.80, 54.49, 43.78,
39.57, 31.83, 31.68, 29.81, 29.56, 21.80. HR-MS (ESI), calcd
Formula:
Tension after histamine ꢁ Tension after drug
Antispasmodic percentage ¼
Tension after histamine
ꢂ 100
(2) Asthma-relieving effects on the histamine induced asth-
matic reaction in guinea pigs in vivo.
The guinea pigs were placed in a plexiglass jar. After the hista-
mine hydrochloride solution (0.8 mg/mL) was sprayed by the
ultrasonic nebulizer on the guinea pigs, the convulsions and falls
time was recorded as the asthmogenic latent periods of the guinea
pigs. Guinea pigs whose latent periods exceeded 180 s were elim-
inated from the trial. The selected 130 guinea pigs were randomly
divided into 13 groups, 10 each group: the negative control group,
the desloratadine group (1 mg/kg) and the eleven compounds
groups (0.01 mg/kg). Sixty min after intragastric administration
C
24H30ClN3: [M+H]+ m/z: 396.2201, found: 396.2202.
5.7. Compound 10 and 11 were obtained by the same synthetic
method of compound 3
Compound 10: yield 40.7%. 1H NMR (CDCl3, 500 MHz), d: 8.39
(s, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.12 (dd, J1 = 8.0 Hz, J2 = 4.0 Hz,
3H), 7.08–7.06 (m, 1H), 4.38 (s, 1H), 3.44–3.33 (m, 2H), 2.85–2.76

Y. Lin et al. / Bioorg. Med. Chem. 21 (2013) 4178–4185
4185
Tension after acetylcholine ꢁ Tension after drug
at 2 mL/kg bw, the guinea pigs were put into the glass bell jar and
Antispasmodic percentage ¼
ꢂ 100
Tension after acetylcholine
sprayed with the histamine hydrochloride as pretreated. The asth-
ma latent period was then recorded. If there was no asthma phe-
nomenon for over 6 min, the latency was recorded as 6 min.
Acknowledgement
6.2. Sedative effects assay
The authors would like to acknowledge Professor Ren-bin
Huang of Guangxi Medical University for the biological activity
evaluations in this paper.
(1) The effects of five compounds on mouse ordinary behavior.
The selected 130 guinea pigs were randomly divided into 13
groups, 10 in each group: the negative control group (saline
10 mL/kg), the desloratadine group (1 mg/kg), the pentobarbital
sodium group (10 mg/kg), the selected five active compounds 1,
2, 3, 4 and 10 low dose groups (0.05 mg/kg) and their high dose
groups (0.2 mg/kg). The dosing capacity of each group was equally
10 mL/kg. After administration, the ordinary behavior concluding
mental state and body activities were observed and other abnor-
mal activities were checked.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2013.05.004.
References and notes
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group, and selected five compounds groups in three concentrations
(the final concentration of each group was given in Table 4).The
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stalsis curve tended to stabilized. Then acetycholine (0.2 lg/mL)
was added and the average tension values in each group were re-
corded. When the maximum contraction was achieved, the five
synthesized compounds or the blank water (the negative control
group) were added. After 3 min, the average tension values were
recorded. The parallel operation was repeated for 8 times. The anti-
spasmodic percentage was evaluated using the following formula.
Formula: