Synthesis and evaluation of histamine H3 receptor ligand based on lactam scaffold as agents for treating neuropathic pain

Article abstract of DOI:10.1016/j.bmcl.2019.04.015

The synthesis and H₃ receptor ligand of a new series of lactam derivatives are reported. The new compounds were evaluated in vitro in H₃ and H₁ receptor-binding assays. The structure-activity relationship led us to the pro

Full text of DOI:10.1016/j.bmcl.2019.04.015

Accepted Manuscript
Synthesis and evaluation of histamine H receptor ligand based on lactam scaf-
3
fold as agents for treating neuropathic pain
Fei Dou, Xudong Cao, Peng Jing, Chunyan Wu, Yuxin Zhang, Yin Chen, Guisen
Zhang
PII:
S0960-894X(19)30224-0
https://doi.org/10.1016/j.bmcl.2019.04.015
BMCL 26382
DOI:
Reference:
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date:
Accepted Date:
28 January 2019
7 April 2019
Please cite this article as: Dou, F., Cao, X., Jing, P., Wu, C., Zhang, Y., Chen, Y., Zhang, G., Synthesis and evaluation
of histamine H receptor ligand based on lactam scaffold as agents for treating neuropathic pain, Bioorganic &
3
Medicinal Chemistry Letters (2019), doi: https://doi.org/10.1016/j.bmcl.2019.04.015
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Synthesis and evaluation of histamine H receptor ligand based on lactam
3
scaffold as agents for treating neuropathic pain
a,c 1
b,1
c,
c
d
Fei Dou , Xudong Cao , Peng Jing Chunyan Wu , Yuxin Zhang , Yin
a,c
b,
Chen * and Guisen Zhang *
a
Jiangsu Marine Resources Development Research Institute, Lianyungang 222005,
China
b
Systems Biology Theme, Department of Biomedical Engineering, College of Life
Science and Technology, Huazhong University of Science and Technology, Wuhan
4
30074
c
Jiangsu Nhwa Pharmaceutical Co., Ltd. 69 Democratic South Road, Xuzhou, Jiangsu,
2
21116
d
College of life science, Nanjing Agricultural University, Nanjin, 210095
1
*
These authors contributed equally to this work
Corresponding authors.
E-mail addresses: chenyin0914001@126.com (Y. Chen), gszhang@hust.edu.cn (G.
Zhang)
1

Abstract
The synthesis and H receptor ligand of a new series of lactam derivatives are
3
reported. The new compounds were evaluated in vitro in H and H receptor-binding
3
1
assays. The structure-activity relationship led us to the promising derivative
-methyl-7-(3-morpholinopropoxy)-3,4-dihydroisoquinolin-1(2H)-one (11). The
2
compound with highest affinity and greatest selectivity were further profiled, In
addition, compound 11 exerted dose-dependent anti-nociceptive effects in the
formalin test. These characteristics suggested that the potent and selective compound
11 could be a potent candidate for pain treatment.
Keywords: Synthesis；H receptors；anti-nociceptive
3
2

Pain, as a fundamental and central life experience, limits our exposure to
potentially damaging or life-threatening events[1,2]. Current analgesic medications
include opioids, non-steroidal anti-inflammatory drugs (NSAIDs) and analgesic
adjuvants[3,4]. Opioids induce a wide variety of well-known side effects, including
tolerance and physical dependence. Meanwhile, NSAIDs cause adverse
gastrointestinal reactions and renal toxicity and inhibit platelet aggregation [3].
Antidepressants, anticonvulsants, and anesthetics, have demonstrated some efficacy in
the treatment of neuropathic pain, earning the nickname “analgesic adjuvants”.
However, they have limited independent efficacy in treating pain[4]. The so-called
“analgesic adjuvants”, e.g., antidepressants, anticonvulsants and anesthetics [5], show
some efficacy in the treatment of neuropathic pain [6]. However, these analgesic
adjuvants have also shown limited effectiveness for neuropathic pain [7]. Therefore,
there is a continuing unmet medical need for analgesics with new mechanisms of
action to improve the efficacy of existing therapies and reduce unwanted effects.
The histamine H receptor is largely expressed in the anterior part of the cortex, in
3
the hippocampus, striatum, and to a lesser extent in the hypothalamus and spinal cord.
H receptor have invoked more complexity in vivo H R biology and interesting
3
3
therapeutic applications, such as Alzheimer’s disease, attention deficit hyperactivity
disorder, schizophrenia, sleep disorder.[8] Moreover, the H receptors are expressed in
3
the tissues known to be involved in nociception (specific thalamic areas, dorsal root
ganglia, spinal cord, and skin tissues) and therefore, might offer treatment
opportunities for different modalities of pain.[9]
Our interest has been focused on the development of novel ligands with high
affinity towards the H receptor and selectivity over the H subtype. Pitolisant is an
3
1
inverse agonist of the histamine H receptor that is being developed by Bioproject[10].
3
Oral pitolisant is approved in the European for the treatment of narcolepsy with or
without cataplexy in adults. Bavisant (JNJ-31001074) is a highly selective, orally
active antagonist of the human H3 receptor with a novel mechanism of action,
involving wakefulness and cognition, with potential as a treatment for ADHD.[11] S
3

3
8093 is an inverse agonist/antagonist of H receptor, which has displayed
3
antiallodynic and antihyperalgesic effect in chronic pain especially in a context of
neuropathic pain after chronic administration.[12] In this paper, on the basis of S
3
8093, by way of replacement of octahydrocyclopenta[c]pyrrole moiety with
introduction of a basicamine center and followed by the rigidization of
amidic group to form lactam derivatives 9-23 (Fig. 2). Evaluating their
pharmacological efficacy and in competitive receptor binding assays to determine
their relative affinity for H and H receptors. Among the derivatives prepared,
3
1
compound 11 exhibited high affinity for the H receptor and low affinity for the H
3
1
receptor. Further, compound 11 inhibited formalin-induced pain in mice.
First of all, we synthesized all the lactam derivatives 9-23 and 27as described in
Scheme 1. 2-(4-methoxy-phenyl)-ethylamine (1) in chloroform was reacted with
chloro ethyl formate and triethylamine to afford the product 3 . [13] Phosphorus
pentoxide was added to methanesulfonic acid in portions and heated at 130°C for 2 h.
Intermediate 3 was added and to afford the title compound 4. Compound 4 in DMF
was reacted with methyl iodide under the sodium hydride to give brown solid 5.
Under a nitrogen atmosphere, intermediate 5 was dissolved in HBr and refluxed 4 h to
afford the compound 6. Intermediate 6 reacted with 1,3-dibromopropane or
1
,4-dibromobutane to give compounds 7a-c, and then reaction with the piperidine or
pyrrodine afforded the final compounds 9-22.Intermediate 6 reacted with
epichlorohydrin and potassium carbonate to afford the product 8, and then reaction
with the morpholine to afford the compound 23.
Intermediate 4 in DMF was reacted with Iodoethane under the sodium hydride to
give compound 24. Compound 24 was dissolved in HBr and refluxed 4 h to afford the
compound 25. Intermediate 25 reacted with 1,3-dibromopropane o to give
intermediate 26, and then reaction with the morpholine to give compound 27.
In this work, our initial design focus was to investigate the effect of different amine
moieties for H and H receptors (Table 1, compounds 9-20). As shown in Table 1,
1
3
compound 9 (piperidine) and 10 (4-methylpiperidine) showed moderate affinities for
the H receptor, and weakly Histamine1/3 selectivity (8.2 and 8.7-fold). It should be
3
4

noted that the morpholine derivative 11 displayed high affinities for the H receptors
3
(
(
(
K = 6.5 nM). Moreover, compound 11 showed good Histamine 1/3 selectivity
i
158-fold) than S38093 (118-fold). Compounds 12 (2-methylpyrrolidin) and 13
pyrrolidine) exhibited moderate affinities for the H receptor, and weakly
3
Histamine1/3 selectivity. The amine moieties 1-ethylpiperazine, 1-methylpiperazine
and diethylamine (compounds 14 -16) showed low affinities for H receptors. When
3
amine moieties were piperidin-4-one, 2-methylpiperidine, 3-hydroxypyrrolidine and
4
-hydroxypiperidine compounds 17-20 exhibited affinities for the H receptor.
3
We determined the effect of the length of the linker between the phenyl group and
morpholine the ring. As shown in Table 1, chain lengths of two (21，K = 1208 nM) or
i
four (22，K = 856 nM) carbon atoms resulted in significantly reduced H receptor
i
3
binding. Introducing OH to the carbon chain of compound 23 (K > 2000 nM) resulted
i
in inactivation of H receptor. The length of the alkyl chain appeared to have a direct
3
impact on affinity for the H receptor. Taken together, the data indicate that the
3
three-carbon chain length (compound 11) was the most active. Compound 27 (K =
i
2
52 nM) is structurally identical to compound 11 except that the methyl is replaced
with an ethyl group. This replacement resulted in reduced the affinity for H receptor.
3
Together, the data indicated that compound 11 had high affinities for H receptor,
3
with good selectivity (compared to H receptor). The compound were considered
1
promising and were subjected to in vivo activity testing.
The above results led to the conclusion that compound 11 exhibited good
affinities for dopamine H receptor and with a low affinity for the H receptor. We
3
1
then assayed the acute toxicity of the compounds by determining their LD .
5
0
Compound 11 showed good safety profiles even at the highest dose tested (LD >
5
0
1
000 mg/kg).
The classical model of acute and chronic pain, the formalin test, was performed to
evaluate the antinociceptive effects. Intraplantar (ipl) injection of formalin elicits a
biphasic pain response: early (phase I) and delayed (phase II), characterized by paw
licking, biting, and other behaviors. Phase I pain is predominantly caused by direct
activation of C-fibers, whereas phase II pain appears to be dependent on a
5

combination of peripheral tissue inflammation and functional changes in the spinal
cord, involving both peripheral and central sensitization.
In the formalin test, pregabalin (40 mg/kg) and S38093 (1mg/kg) shown
antinociception in both phases. Compound 11 (1−10 mg/kg) produced dose-dependent
antinociception in the formalin test and was (slightly) more efficacious against
delayed-phase pain (Figure 3). The ED value was mg/kg for 1.3mg/kg and
5
0
2
.4mg/kg in the phase I and phase II pain, respectively.
In this study, a series of lactam derivatives were synthesized via an efficient
method, several of which were shown to be potent and selective H receptor ligands.
3
Compound 11 appears safe in preliminary tests and exerts clear dose-dependent
antiallodynic effects against formalin induced pain in mice. Moreover, compound 11
showed significant anti-nociceptive effects in phases I and II, identifying compound
11 as a candidate agent for the treatment of pain. Further studies of this compound are
currently underway in our laboratory.
Acknowledgement
Financial support for this research provided by the National Natural Science
Foundation of China for youth (Nos. 81602971 ).
Conflict of Interest
The authors declare that there is no financial/commercial conflict of interest.
References
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[
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7

Figure.1 Representative H receptor ligand
3
8

Figure. 2 Design of new lactam derivatives
9

a
Scheme 1
a
o
Reagents and conditions: (i) DCM, Triethylamine , 0 C-r.t.; (ii) P O , Sulphonethane,
2
5
o
1
60 C; (iii) CH I,NaH, DMF; (iv) HBr/H O; (v) Acetone, K CO , reflux; (vi) CH CN,
3 2 2 3 3
K CO , reflux; (vii) Acetone, K CO , reflux; (viii) CH OH, reflux.
2
3
2
3
3
10

a
Scheme 2
a
Reagents and conditions: (i) CH CH Br,NaH, DMF; (ii) HBr/H O; (iii) Acetone,
3
2
2
K CO , reflux; (iv) CH CN, K CO , reflux
2
3
3
2
3
11

Table.1. Binding Affinities for the H and H Receptors of Compounds 9-23 and 27.
1
3
Ki（nM）
Selectivity
(H /H )
Compound Structure
H3
H1
1
3
9
23
189
8.2
10
32
279
8.7
11
6.5
1027 158
1
1
2
3
26
39
68
2.6
169
4.3
-
1
1
1
1
4
5
6
7
1098
706
542
176
-
-
-
-
12

1
1
8
9
165
112
-
-
-
-
2
2
2
2
2
0
1
2
3
35
908
25.9
1208
856
-
-
-
-
-
>2000 -
7
252
3.6
-
-
S 38093
-
426
118
13

Fig. 3. Anti-nociceptive effect of pregabalin, S38093 and compound 11 in phase I (0-5
min) and phase II (15-45 min) of the formalin test in rats (10/group). Each column
and vertical line represents mean±SEM of the values obtained in at least ten animals.
#
##
Statistically significant differences: p<0.05; p<0.01 vs. vehicle; *p<0.05; **p<0.01
vs. vehicle+formalin (two-way ANOVA followed by Newman-Keuls test).
14

Graphical abstract
15

Highlights
1
2
3
. A a series of lactam derivatives were designed and synthesized.
. Compound 11 shown to be potent and selective H receptor ligands.
3
. Compound 11 exerted dose-dependent anti-nociceptive effects in the formalin test.
16