Synthesis and bioactivity of pyrazole and triazole derivatives as potential PDE4 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2016.06.002

A series of pyrazole and triazole derivatives containing 5-phenyl-2-furan functionality were designed and synthesized as phosphodiesterase type 4 (PDE4) inhibitors. The bioassay results showed that title compounds exhibited considerable inhibitory activit

Full text of DOI:10.1016/j.bmcl.2016.06.002

Accepted Manuscript
Synthesis and Bioactivity of Pyrazole and Triazole Derivatives as Potential
PDE4 Inhibitors
Ya-Sheng Li, Hao Tian, Dong-Sheng Zhao, De-Kun Hu, Xing-Yu Liu, Hong-
Wei Jin, Gao-Peng Song, Zi-Ning Cui
PII:
S0960-894X(16)30606-0
DOI:
http://dx.doi.org/10.1016/j.bmcl.2016.06.002
BMCL 23955
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
29 January 2016
18 May 2016
2 June 2016
Please cite this article as: Li, Y-S., Tian, H., Zhao, D-S., Hu, D-K., Liu, X-Y., Jin, H-W., Song, G-P., Cui, Z-N.,
Synthesis and Bioactivity of Pyrazole and Triazole Derivatives as Potential PDE4 Inhibitors, Bioorganic &
Medicinal Chemistry Letters (2016), doi: http://dx.doi.org/10.1016/j.bmcl.2016.06.002
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Synthesis and Bioactivity of Pyrazole and Triazole Derivatives
as Potential PDE4 Inhibitors
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Ya-Sheng Lia,#, Hao Tiana,#, Dong-Sheng Zhaob,#, De-Kun Hua, Xing-Yu Liua,
Hong-Wei Jinc, Gao-Peng Songd,*, Zi-Ning Cuia, *
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a State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources,
Integrative Microbiology Research Centre, Guangdong Province Key Laboratory of
Microbial Signals and Disease Control, South China Agricultural University, Guangzhou,
510642, China
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b Department of pharmacy, Quanzhou Medical College, Quanzhou 362100, China
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State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical
Sciences, Peking University, Beijing 100191, China
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College of Materials and Energy, South China Agricultural University, Guangzhou
510642, China
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To whom Correspondence should be addressed. Telephone/Fax: +86-20-85288229.
E-mail: ziningcui@scau.edu.cn (Z. C.), vinsin1021@126.com (G. S.)
#These authors contributed equally to this paper.
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Abstract: A series of pyrazole and triazole derivatives containing 5-phenyl-2-furan
functionality were designed and synthesized as phosphodiesterase type 4 (PDE4)
inhibitors. The bioassay results showed that title compounds exhibited considerable
inhibitory activity against PDE4B and blockade of LPS-induced TNFα release.
Meanwhile, the activity of compounds containing 1,2,4-triazole (series II) was higher
than that of pyrazole-attached derivatives (series I). The primary structure–activity
relationship study and docking results showed that the 1,2,4-triazole moiety of compound
IIk played a key role to form integral hydrogen bonds and π-π stacking interaction with
PDE4B protein while the rest part of the molecule extended into the catalytic domain to
block the access of cAMP and formed the foundation for inhibition of PDE4. Compound
IIk would be great promise as a hit compound for further study based on the preliminary
structure-activity relationship and molecular modeling studies.
Key words: synthesis; 5-phenyl-2-furan; pyrazole and triazole derivatives; PDE4
inhibitor; molecular simulation
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Phosphodiesterases (PDEs) play a key role in catalyzing the hydrolysis of the
secondary signal messengers, cyclic adenosine monophosphate (cAMP) and cyclic
guanosine monophosphate (cGMP), which are able to regulate the function of airway
smooth muscle, inflammatory cells, and immune cells.1-3 The PDE4, as one of the
11-membered PDEs, specifically targets the second messenger cAMP and is expressed
predominantly in inflammatory and immune cells including eosinophils, lymphocytes,
macrophages, and neutrophils.4,5 When PDE4 is inhibited, the resultant elevation of
intracellular cAMP levels leads to an activation of specific protein phosphorylation
cascades, which elicit a variety of functional responses in the inflammatory cells such as
suppression of TNFα production.6-8 Therefore, the development of PDE4 inhibitors as
anti-inflammatory drugs for the treatment of asthma and chronic obstructive pulmonary
disease (COPD) has made a long standing research effort.9-14
PDE4 inhibitors have been extensively studied as anti-inflammatory drugs since the
discovery of rolipram (Fig.1) and piclamilast (Fig.1) in the 1990s. A detailed
structure-activity relationship (SAR) study revealed that the 4-(3,4-dialkoxyphenyl)
moiety of catechol (Fig.1) was important for PDE4 inhibition where two alkoxy groups
occupied each different lipophilic pocket and the catechol ether oxygens constructed
H-bond to the purine-selective glutamine residue, which is surrounded by the P-clamp.15,16
Further structural modification suggested that the 8-methoxyquinoline-5- carboxamides
(such as SCH 365351) showed excellent PDE4 inhibitory activity. Modeling studies on
the 8-methoxyquinoline-5-carboxamide related compounds demonstrated that the
quinoline moiety binds to the adenosine recognition site, while the amide portion served
as a linker to anchor a group containing a polar atom which provided favorable
interactions with the metal ion binding site of PDE4.17-19 Five-membered heterocyclic
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oxazole moiety was explored as possible linker to replace the amide portion, whcih was
found to be a highly versatile linker and the derivatives exhibited significantly potent
PDE4 inhibitory activity.20-22 In this study, the oxazole was replaced by furan ring, and
pyrazole and triazole were introduced to form a new combination as PDE4-inhibitor
pharmacophores (Fig.1).
O
O
O
Cl
Cl
O
O
O
NH
N
HN
rolipram
piclamilast
F3C
N
F3C
N
converted amide
linker into
oxazole ring
O
R
Cl
Cl
O
R1
O
N
O
N
N
HN
R2
O
SCH 365351
converted oxazole into furan ring
imide was cycled into pyrazole and triazole
N
Structures of PDE4 inhibitors
X
R1
N
O
O
X=C, N
Titile compounds in present work
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Figure 1. The designed strategy for the title compounds.
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The synthetic route of title compounds I and II was shown in Scheme 1. The key
intermediate 2 was synthesized from substituted aniline by Meerwein arylation reaction
according to the reported procedure.23,24 A mixture of 5-substituted phenyl-2-
furancarboxylic acid 2 and thionyl chloride was refluxed in anhydrous toluene for 3 h to
afford the 5-phenyl-2-furancarbonyl chloride, which was added into pyrazole or 1, 2,
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4-triazole in anhydrous dichloromethane to react and obtain the title compounds I and II
as solid (see the supplementary data for the details).
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R1= Ia: 4-Cl; Ib: 2-NO2; Ic: 2-Cl; Id: 3-Cl; Ie: 3-F; If: 4-F; Ig: 2.4-di-F; Ih: 2.6-di-F; Ii:
H; Ij: 4-CH3; Ik: 4-OCH3; Il: 3-NO2; Im: 2-F; IIa: 4-Cl; IIb: 2-NO2; IIc: 2-Cl; IId:
3-Cl; IIe: 3-F; IIf: 4-F; IIg: 2.4-di-F; IIh: 2.6-di-F; IIi: H; IIj: 4-CH3; IIk: 4-OCH3
Scheme 1: The synthetic route of the title compounds I and II. Reagents and
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conditions: (a) NaNO2, hydrochloric acid, 0-5 C, 3 h; (b) furoic acid, CuCl2 (cat.),
acetone-H2O, r.t., 5 h; (40-65%, two steps) (c) SOCl2, anhydrous toluene, reflux, 3 h; (d)
pyrazole or 1,2,4-triazole, anhydrous dichloromethane, reflux, 4 h (75-91%, two steps).
In vitro data for the inhibition of PDE4B and blockade of LPS-induced TNFα release
were listed in Table 1. Rolipram was chosen as the positive control. Generally, the
activity of title compounds containing 1,2,4-triazole (series II) was better than that of
compounds containing pyrazole (series I), except compounds e and h. Among the title
compounds, the IC50 value of IIk was 1.2 0.1 µM and 9.8 0.7 µM respectively against
PDE4B and TNFα, which showed comparable or better activity than rolipram (1.5 0.1
µM and 12.5 1.1 µM) (Table 1). Compound Ik displayed comparable IC50 values
(2.8 0.3 µM agaisnt PDE4B and 22.7 2.4 µM against TNFα) to that of rolipram. In
addition, compounds Ia and IIa, Ig and IIg also showed favorable activity. A primary
structure–activity relationship study showed that the position of the substituted group
played a key role in the bioactivity. Activity with respect to substitution at the benzene
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ring follows the trend: 4->2,4->3->2,6->2-. The compounds Ii and IIi without any
substituted group showed the poorest activity.
Table 1 Impact on enzymatic potency (PDE4B) and inhibition of TNFα release from
human blood mononuclear cells stimulated with lipopolysaccharide a
Compd.
X
R1
PDE4B
TNFα
Compd.
X
R1
PDE4B
IC50(µM)
3.9 0.5
56.8 2.7
47.8 1.9
20.7 1.2
27.9 1.9
8.7 0.6
4.8 0.3
36.7 2.1
65.7 3.1
5.6 0.3
1.2 0.1
1.5 0.1
TNFα
IC50(µM)
5.6 0.3
IC50(µM)
36.7 3.1
256.1 9.8
172.4 7.9
78.1 3.4
80.4 3.2
53.8 2.8
24.1 1.3
120.4 6.2
217.6 8.6
89.5 5.8
22.7 2.4
57.2 3.7
168.9 8.7
IC50(µM)
28.4 1.6
194.5 8.1
159.7 7.4
64.1 3.1
81.5 3.2
21.4 1.5
15.7 0.9
152.4 8.1
189.7 9.5
28.9 2.1
9.8 0.7
C
C
C
C
C
C
C
C
C
C
C
C
C
4-Cl
N
N
N
N
N
N
N
N
N
N
N
4-Cl
Ia
Ib
Ic
Id
Ie
If
IIa
2-NO2
2-Cl
75.8 3.1
68.1 2.9
29.4 1.8
20.1 1.6
10.2 0.9
6.4 0.7
2-NO2
2-Cl
IIb
IIc
3-Cl
3-Cl
IId
IIe
3-F
3-F
4-F
4-F
IIf
2.4-di-F
2.6-di-F
H
2.4-di-F
2.6-di-F
H
Ig
Ih
Ii
IIg
21.7 2.5
78.1 3.2
18.7 1.8
2.8 0.3
IIh
IIi
4-CH3
4-OCH3
3-NO2
2-F
4-CH3
4-OCH3
Ij
IIj
Ik
Il
IIk
rolipram
16.8 1.7
65.1 2.8
12.5 1.1
Im
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a Results are the average of at least three assays.
Considering the inhibitory activity of title compounds, it was of interest to explore the
binding to the PDE4 structure. The bioassay results demonstrated that compounds
containing para-methoxy group (Ik and IIk) showed the best activity among all the title
compounds. Therefore docking simulation of compound Ik and IIk at PDE4B (PDB ID:
1XMY) was conducted using Surflex-Dock in Sybyl 8.0 (see the supplementary data for
the method),16,25 and the docking contour maps were shown in Fig. 3. The docking
orientation demonstrated that the five-membered heterocyclic moiety as the pivotal
pharmacophore formed integral hydrogen bonds with the conserved glutamine residue
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(Gln443) (Fig. 3) and the heterocyclic ring was evidently positioned between the
phenylalanine (Phe446) and isoleucine (Ile410) (Fig. 3C and 3E), which formed the
cavity accommodating the hydrophobic moiety of compounds Ik and IIk. Compared with
the pyrazole derivative Ik, the 1,2,4-triazole moiety of IIk formed obvious π-π stacking
interaction with benzene ring (3.26 Å, Fig. 3E and 3F) in the phenylalanine (Phe446),
which could enhance the binding affinity with the enzyme. That could be the reason why
the activity of most title compounds containing 1,2,4-triazole (series II) was better than
that of compounds containing pyrazole. The remainder of the molecule was displayed to
extend into the catalytic domain in close to both the Zn2+ and Mg2+ cations (Fig. 3D and
3F), which played important roles in the catalytic mechanism of cAMP hydrolysis. The
para-methoxy group formed coordinate bond with the Zn2+ (2.23 Å, Ik, Fig. 3C and 3D)
and Mg2+ (1.92 Å, IIk, Fig. 3E and 3F) cations. Such orientation and interactions would
block the access of cAMP to the catalytic domain and formed the foundation for
inhibition of PDE4.
In summary, the design and synthesis of pyrazole and triazole derivatives containing
5-phenyl-2-furan moiety were reported in this letter. Their bioactivity against
phosphodiesterase type 4 and TNFα were evaluated. Compound IIk showed the best
inhibitory activity against PDE4B and blockade of LPS-induced TNFα release among all
the title compounds. The bioactivity showed that compounds containing 1,2,4-triazole
(series II) was better than that of compounds containing pyrazole (series I). The primary
structure–activity relationship study and docking results suggested that IIk interacted
well with PDE4B protein where the 1,2,4-triazole played a key role in formation of
integral hydrogen bond and π-π stacking interaction while the rest part of the molecule
extended into the catalytic domain to block the access of cAMP, which formed the
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foundation for inhibition of PDE4. The formation of hydrogen bonds, π-π stacking
interactions and the hydrophobic interactions in the ligand-receptor complex were vital
for the binding affinity. Such efforts were helpful to develop additional small molecules
with enhanced activity as novel and effective PDE4 inhibitors.
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C
E
B
D
F
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Figure 3. Model of PDE4 and docking of compounds Ik and IIk. (A, B) The entire
PDE4B structure (N-terminal domain, a catalytic domain and a C-terminal domain)
bound to IIk. (C, D) The catalytic domain bound to Ik. (E, F) The catalytic domain
bound to IIk.
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152 Acknowledgements
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We acknowledge the financial supports from the Special Fund for the Research and
Construction of Public Service Ability (2014A020210019 and 2016A020217014), the
National Key Project for Basic Research (973 Program, 2015CB150600), the Pearl River
S&T Nova Program of Guangzhou (201506010029), the National Natural Science
Foundation of China (21202047 and 31570122), the Specialty and Innovation Project
from the Department of Education in Guangdong Province (2014KTSCX031).
160 References and notes
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Graphical Abstract
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Synthesis and Bioactivity of Pyrazole and Triazole Derivatives as
Potential PDE4 Inhibitors
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Ya-Sheng Lia,#, Hao Tiana,#, Dong-Sheng Zhaob,#, De-Kun Hua, Xing-Yu Liua,
Hong-Wei Jinc, Gao-Peng Songd,*, Zi-Ning Cuia, *
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N
X
R1
N
O
O
X=C, N
1
IIk
(X = N, R = 4-OCH3)
IC50 = 1.2 M (PDE4B)
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