Discovery and SAR study of 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-ones as soluble and highly potent PDE7 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2014.11.090

The discovery and SAR study of a new series of soluble and highly potent phosphodiesterase (PDE) 7 inhibitors are described herein. We explored a new lead compound with improved solubility, which led to the discovery of a 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-one series. The introduction of 3-piperidines at the 7-position resulted in the significant enhancement of PDE7 activity. In particular, compound 32 also showed strong PDE7 inhibitory activity; good selectivity against PDE3, 4, and 5; and good aqueous solubility.

Full text of DOI:10.1016/j.bmcl.2014.11.090

Bioorganic & Medicinal Chemistry Letters xxx (2014) xxx–xxx
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery and SAR study of 2-(4-pyridylamino)thieno[3,2-d]
pyrimidin-4(3H)-ones as soluble and highly potent PDE7 inhibitors
⇑
Yusuke Endo , Kentaro Kawai, Takeshi Asano, Seiji Amano, Yoshihito Asanuma, Keisuke Sawada,
⇑
Keiji Ogura, Naoya Nagata, Noriko Ueo, Nobuaki Takahashi, Yo Sonoda, Noriyuki Kamei
Drug Research Center, Kaken Pharmaceutical Co. Ltd, 14, Shinomiya Minamigawara-cho, Yamashina, Kyoto 607-8042, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The discovery and SAR study of a new series of soluble and highly potent phosphodiesterase (PDE) 7
inhibitors are described herein. We explored a new lead compound with improved solubility, which
led to the discovery of a 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-one series. The introduction
of 3-piperidines at the 7-position resulted in the significant enhancement of PDE7 activity. In particular,
compound 32 also showed strong PDE7 inhibitory activity; good selectivity against PDE3, 4, and 5; and
good aqueous solubility.
Received 18 November 2014
Revised 28 November 2014
Accepted 29 November 2014
Available online xxxx
Keywords:
Ó 2014 Elsevier Ltd. All rights reserved.
Phosphodiesterase
Thienopyrimidinone
T-cell
Aqueous solubility
Phosphodiesterases (PDEs) hydrolyze the second messenger
activated lymphocytes. However, compound 3 and its derivatives
had poor solubility in the aqueous neutral solution compared to
compound 2. We considered that the introduction of substituents
at the 7-position drastically decreased aqueous solubility.
Therefore, we needed to discover another lead compound with a
7-substituent that had good physicochemical properties as well
as good biological activity and enzyme selectivity.
In this Letter, we describe how we investigated the modifications
of a previous series and obtained an alternative lead compound
with improved aqueous solubility and potency.
We thought that the modification of substituents at the 2- and
7-positions would lead to increase both of solubility and potency.
Therefore, our first approach was the modification of substituents
at the 2-position of thieno[3,2-d]pyrimidin-4(3H)-one. In our
previous study, the bulky cyclopentyl group of 2-(cyclopentylami-
no)thieno[3,2-d]pyrimidin-4(3H)-ones was considered to fit the
hydrophobic binding subpocket to increase PDE7 activity. We
assumed that an aromatic amino group was suitable for the 2-posi-
tion and prepared analogues with an aromatic amino group at the
2-position (7–17) as shown in Scheme 1.
0
0
molecules 3 ,5 -cyclic adenosine monophosphate (cAMP) and
0
0
3
,5 -cyclic guanosine monophosphate (cGMP) to affect cellular sig-
naling. Among the 11 PDEs, the inhibitors of PDE3, PDE4, and PDE5
have been developed for clinical use; therefore, the PDE family is
recognized as a druggable target.1 PDE7 selectively catalyzes
the degradation of cAMP to AMP, and the inhibition of PDE7 results
in increased levels of cAMP. In addition, PDE7 is upregulated in
–3
4
5
activated T-cells and in B-lymphocytes. The PDE7 inhibitors will
have broad application as treatment for T-cell related diseases,
autoimmune diseases,5 CNS disorders,6 and airway diseases.
Considering the clinical utility, discovery of selective PDE7
inhibitors is desired for avoiding side effects caused by inhibiting
other PDE enzymes.
7
Several groups have reported potent PDE7 inhibitors.8–12
We recently reported the identification of a novel series of
2
-(cyclopentylamino)thieno[3,2-d]pyrimidin-4(3H)-one
tives (Fig. 1). We obtained a hit compound 1, and the preliminary
deriva-
1
3
modifications resulted in the discovery of the fragment-sized
compound 2 with highly improved ligand efficiency.1
4,15
Computa-
tional modeling and a structure–activity relationship (SAR) study
led to 7-substituted derivatives as selective PDE7 inhibitors,
including the initial lead compound 3, which showed single
nanomolar potency for PDE7 with 170-fold selectivity over PDE4
and <100 nM inhibitory activity of IL-2 production from mouse
Methyl 3-aminothiophene-2-carboxylate (4) was treated with
ethyl isothiocyanate to generate the fused ring product 5. The
methylation of 5 with iodomethane followed by the oxidation of
the sulfur generated sulfone 6. The methanesulfonyl moiety of 6
was substituted with various amines to produce 7–17.
Investigation of substituents at the 2-position of the thienopyri-
midinone started by replacing the cyclopentylamino group with a
phenylamino group (Table 1). The activity of phenyl analogue 7
⇑
Corresponding authors.
http://dx.doi.org/10.1016/j.bmcl.2014.11.090
960-894X/Ó 2014 Elsevier Ltd. All rights reserved.
0
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2
Y. Endo et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
O
5
S
3
N2
4
6
N
N
N
N
H
7
1
1
PDE7A, IC50 = 160 nM
O
O
N
S
N
S
N
N
N
NH
NH
2
3
PDE7A, IC = 150 nM
Solubility , 12.1 µg/mL
PDE7A, IC = 2.0 nM
Solubility , 0.09 µg/mL
50
5
0
a
a
Figure 1. 2-(Cyclopentylamino)thieno[3,2-d]pyrimidin-4(3H)-one series. aMeasured by the weight dissolved in phosphate buffer (pH 6.8).
dropped slightly, but the aqueous solubility improved compared to
compound 2. This finding encouraged us to further examine the
SAR study at the 2-position. Next, compounds 8–10 were prepared
to verify the effect of substituents on the aromatic ring. The intro-
duction of methyl group at the ortho position (8) was well tolerated
with regard to PDE7 activity, whereas meta- and para-substituted
analogues (9 and 10) showed significantly decreased potency.
Because compound 8 additionally displayed good aqueous solubil-
ity, the ortho position was found to be suitable for incorporating
the substituents. While the introduction of a larger ethyl (11)
and an electron-withdrawing cyano (12) group resulted in low
potency, fluoro and chloro derivatives (13 and 14) showed higher
potency than 7. Additionally, 13 showed improved solubility.
These results revealed that only small substituents at the ortho
position would be tolerated for PDE7 activity and that the fluoro
group would be the most effective substituent with regard to both
PDE7 activity and aqueous solubility.
improved PDE7 activity than expected while maintaining aqueous
solubility. The fluoro group, as a substituent on the pyridine, was
also suitable for potency, as was the benzene group. Thus, screen-
ing at the 2-position revealed that the 3-fluoro-4-pyridylamino
group contributed to the improved activity and solubility. With
respect to the PDE4 activity, compounds (8, 13, 14, and 17) with
substituents at the ortho position showed slightly increased PDE7
selectivity.
In our previous study,13 aromatic rings at the 7-position were
suitable for improving potency; however, the incorporation led
to markedly decreased aqueous solubility. Therefore, we needed
to explore favorable substituents at the 7-position of thienopyri-
midinone. The introduction of various substituents at the 7-posi-
tion into 17 was carried out to examine whether the PDE7
activity and aqueous solubility were compatible. Compounds 19,
21–22, and 24 were synthesized as shown in Scheme 2. Iodination
of sulfone 6 with NIS followed by substitution of methanesulfonyl
group with 4-amino-3-fluoropyridine generated the iodide 18.
Cyanide 19 was obtained by the displacement of iodine. Compound
18 was functionalized by Heck reaction with ethylene glycol
monovinyl ether followed by ketonization to generate compound
20. The reduction and Grignard reaction of 20 gave the alcohols
21 and 22, respectively. The alcohol 24 was obtained via Heck
reaction of 18 and hydrogenation followed by reduction with LAH.
Replacing the phenyl moiety with a more polar pyridyl group
was carried out to improve the solubility (15 and 16). These
compounds showed considerably improved aqueous solubility;
however, both compounds displayed decreased activity. Although
4
-pyridine 16 was 2-fold less active compared to 7, we tried to
introduce the substituent to the pyridyl ring. Compound 17 with
the fluoro group at the pyridine 3-position showed more
O
O
O
a
b, c
S
S
S
N
N
O
N
H
S
N
S
NH2
4
O
2
5
6
O
d
S
N
R1
N
N
H
7
-17
1
Scheme 1. Reagents and conditions: (a) ethyl isothiocyanate, pyridine, reflux; (b) NaH, MeI, DMF, 0 °C; (c) mCPBA, DCM, rt; (d) R -NH2, LiHMDS, DMSO, rt or THF, 60 °C.
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Y. Endo et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
3
Table 1
Table 2
PDE7 and PDE4 inhibitory activities and aqueous solubility data for the 2-position
In vitro activities and aqueous solubility data for the 7-position
O
O
S
N
S
N
R1
N
2
N
H
N
NH
N
R2
F
Compounds
R1
IC50 (nM)
Solubilityc
g/mL)
PDE7Aa
PDE4Ba
(l
Compounds R2
IC50 (nM)
Solubilityd
g/mL)
2
7
150
4900
12.1
19.5
(l
PDE7Aa PDE4Ba IL-2b
∗
∗
∗
∗
1
9
1
25
670
610
NDc
3.5
290
88
7400
4300
NC
HO
∗
∗
2
8.7
1700 5.4
8
9
10.1
65.5
84.0
1.9
2
2
2
4
2.1
3.9
56
260
480
17.9
HO
HO
>1000
>1000
>1000
NDb
NDb
NDb
∗
180
31.3
0.9
∗
∗
∗
1
1
0
1
2
7
1.1
310
NDc
N
MeO C
2
∗
∗
NC
3
0
1
0.68
1.2
280
180
160
130
48.9
22.7
1
1
2
3
2300
61
NDb
0.4
N
MeO C
2
∗
∗
F
2700
26.1
HO
3
∗
N
Cl
O
1
4
41
3000
6.3
∗
∗
∗
3
2
0.32
20
<100 28.1
NC
N
1
5
6
>1000
630
NDb
41.6
111
N
N
O
a
b
c
IC50 values are the mean of at least two experiments.
IC50 values are the mean of at least four experiments.
ND: not determined.
1
30,000
∗
d
F
Measured by the weight dissolved in phosphate buffer (pH 6.8).
N
1
7
60
5300
120
∗
Next, we hypothesized that a saturated ring system could be
a
b
c
IC50 values are the mean of at least two experiments.
ND: not determined.
Measured by the weight dissolved in phosphate buffer (pH 6.8).
suitable for acquiring the desired solubility due to the disruption
16
of molecular planarity and/or symmetry. Compounds with piper-
idines were designed and synthesized. Compounds 27 and 30–32
were synthesized as shown in Scheme 3. The coupling of iodide
18 with commercially available 25 followed by hydrogenation
and deprotection of Boc group generated the piperidine 26. Meth-
oxy carbonylation of 26 afforded the carbamate 27. Coupling of 18
with the boronate pinacol ester 28 was followed by reduction
and simultaneous deprotection to give the piperidine 29. The con-
densation of 29 with methyl chloroformate or carboxylic acid
afforded the carbamate 30 and amide 31–32, respectively.
The in vitro activities and aqueous solubility of compounds 27
and 30–32 are also summarized in Table 2. The piperidine
The inhibitory activities against PDE7, PDE4, and IL-2 produc-
tion from mouse activated lymphocytes and the aqueous solubility
of compounds 19, 21–22, 24 are summarized in Table 2. Compound
9 with a cyano group as a small unit showed better potency and
unexpectedly lower solubility than the 7-unsubstituted 17. Then,
we turned our attention to the introduction of substituents with
a hydroxyl group as a hydrophilic substituent at the 7-position to
improve aqueous solubility. The attempts generated potent and
soluble compounds 22 and 24.
1
7
1
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4
Y. Endo et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
O
N
S
N
NH
N
HO
F
e
O
S
N
21
N
NH
N
O
F
O
S
N
f
2
0
N
NH
N
HO
F
d
2
2
O
O
S
S
N
N
a, b
c
6
N
NH
N
NH
I
NC
F
F
N
N
18
19
g, h
O
O
N
S
N
S
N
i
N
NH
N
NH
N
F
F
O
O
HO
HO
2
4
23
Scheme 2. Reagents and conditions: (a) NIS, AcOH, CH
Pd(OAc) , DPPP, TEA, iPrOH, 100 °C; 6 mol/L HCl aq, rt; (e) NaBH
4.0 atm), 10% Pd/C, THF, rt; (i) LAH, THF, rt.
2
Cl
2
, 40 °C; (b) 4-amino-3-fluoropyridine, LiHMDS, THF, rt; (c) CuCN, DMF, 100 °C; (d) ethylene glycol monovinyl ether,
2
4
, MeOH, rt; (f) MeMgBr, THF, rt; (g) 2-hydroxyethyl acrylate, PdCl (PPh , TEA, CH CN, 80 °C; (h) H
2
3
)
2
3
2
(
derivatives (27 and 30) achieved significant enhancement of PDE7
inhibitory activity. The 4-piperidine 27 had poor solubility,
whereas the 3-piperidine 30 showed remarkably high solubility.
Therefore, the other 3-piperidine compounds (31 and 32) were
evaluated. Both of the compounds had strong potency along with
the desired solubility. Compounds 30 and 32 exhibited sub-nano-
molar PDE7 inhibitory activity and good inhibitory activity of IL-
particular, compound 32 showed a good profile of selectivity over
other PDE enzymes: 60-fold selectivity over PDE4, 50-fold selectiv-
ity over PDE3, and 9000-fold selectivity against PDE5.
In summary, we explored the substituents at the 2- and
7-position of thienopyrimidinone toward the discovery of an
alternative lead compound with improved solubility. A screen at
the 2-position led to the discovery of 2-(4-pyridylamino)thieno
[3,2-d]pyrimidin-4(3H)-ones. Compounds with 3-piperidines at
the 7-position showed good solubility, highly potent activity and
good PDE7 selectivity. Among them, compound 32 exhibited the
most potent PDE7 inhibitory activity reported to date.
2
production. The optically pure forms of 32 were obtained by chiral
HPLC separation and then studied. One enantiomer was more
potent for PDE7, PDE4 and IL-2 than the other enantiomer (PDE7
inhibitory activity: 0.22 nM vs 0.64 nM, PDE4 inhibitory activity:
1
4 nM vs 220 nM, IL-2 inhibitory activity: 30 nM vs 120 nM). The
PDE4 activity of piperidine analogues (30–32) varied depending
on the pendant groups of piperidine, which revealed that the piper-
idine substituent played a role in PDE7 selectivity against PDE4.
The inhibitory activity of compounds 30, 31, and 32 against
PDE3 and PDE5 are summarized in Supporting information Table 1.
These compounds had moderate to good PDE7 selectivity. In
Acknowledgments
We thank Masanao Shimano, Hiroshi Shin, Hirohide Ishige,
and Yuuta Onodera for their helpful discussions; Rie Suzuki for
analytical assistance; and Hironobu Ogura for his assistance with
the preparation of the manuscript.
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Y. Endo et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
5
O
N
O
S
S
N
N
a, b, c
d
NH
N
1
8
N
NH
N
F
F
N
N
H
e, f
MeO C
2
2
6
27
O
N
O
S
S
N
N
B(Pin)
B(Pin)
g or h
NH
N
N
NH
N
F
F
N
BocN
HN
N
Boc
R
28
25
2
9
30-32
Scheme 3. Reagents and conditions: (a) 25, Pd(OAc)
2
, PPh
3
, satd NaHCO
3
aq, DMF, EtOH, 90 °C; (b) H
SiH, TFA, toluene, rt; 4 mol/L NaOH aq, rt; (g) MeOCOCl, NMM, CH
2
, 10% Pd(OH)
2
, THF, EtOH, rt; (c) TFA, toluene, rt; (d) MeOCOCl, TEA,
Cl , rt; (h) R-CO H WSC, HOBt,
DMF, rt; (e) 28, Pd(OAc)
2
, PPh
3
, satd NaHCO
3
aq, DMF, EtOH, 85 °C; (f) Et
3
2
2
2
NMM, DMF, rt.
8.
Barnes, M. J.; Cooper, N.; Davenport, R. J.; Dyke, H. J.; Galleway, F. P.; Galvin, F.
C.; Gowers, L.; Haughan, A. F.; Lowe, C.; Meissner, J. W.; Montana, J. G.; Morgan,
T.; Picken, C. L.; Watson, R. J. Bioorg. Med. Chem. Lett. 2001, 11, 1081.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2014.
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