Synthesis and SAR of thieno[3,2-b]pyridinyl urea derivatives as urotensin-II receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2014.09.089

The preparation and SAR profile of thieno[3,2-b]pyridinyl urea derivatives as novel and potent urotensin-II receptor antagonists are described. An activity optimization study, probing the effects of substituents on thieno[3,2-b]pyridinyl core and benzyl group of the piperidinyl moiety, led to the identification of p-fluorobenzyl substituted thieno[3,2-b]pyridinyl urea 6n as a highly potent UT antagonist with an IC₅₀ value of 13 nM. Although 6n displays good metabolic stability and low hERG binding activity, it has an unacceptable oral bioavailability.

Full text of DOI:10.1016/j.bmcl.2014.09.089

Accepted Manuscript
Synthesis and SAR of thieno[3,2-b]pyridinyl urea derivatives as urotensin-II
receptor antagonists
Chae Jo Lim, Seung Ae Oh, Byung Ho Lee, Kwang-Seok Oh, Kyu Yang Yi
PII:
S0960-894X(14)01045-2
DOI:
http://dx.doi.org/10.1016/j.bmcl.2014.09.089
BMCL 22055
Reference:
Bioorganic & Medicinal Chemistry Letters
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Received Date:
Revised Date:
Accepted Date:
19 August 2014
25 September 2014
30 September 2014
Please cite this article as: Lim, C.J., Oh, S.A., Lee, B.H., Oh, K-S., Yi, K.Y., Synthesis and SAR of thieno[3,2-
b]pyridinyl urea derivatives as urotensin-II receptor antagonists, Bioorganic & Medicinal Chemistry Letters (2014),
doi: http://dx.doi.org/10.1016/j.bmcl.2014.09.089
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Synthesis and SAR of thieno[3,2-b]pyridinyl
urea derivatives as urotensin-II receptor
antagonists
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Chae Jo Lim, Seung Ae Oh, Byung Ho Lee, Kwang-Seok Oh, Kyu Yang Yi
6n IC50 = 13 nM
The synthesis and SAR of thieno[3,2-b]pyridinyl urea derivatives as urotensin-II receptor antagonists are described.

Bioorganic & Medicinal Chemistry Letters
journal homepage: www.els evier.com
Synthesis and SAR of thieno[3,2-b]pyridinyl urea derivatives as urotensin-II
receptor antagonists
Chae Jo Lima,b, Seung Ae Oha,b, Byung Ho Leea, Kwang-Seok Oha,b, Kyu Yang Yia,b,∗
a Division of Drug Discovery Research, Korea Research Institute of Chemical Technology, Yuseong-gu, Daejeon 305-343, Republic of Korea
b Department of Medicinal and Pharmaceutical Chemistry, University of Science and Technology, Yuseong-gu, Daejeon 305-350, Republic of Korea
ARTICLE INFO
ABSTRACT
Article history:
Received
The preparation and SAR profile of thieno[3,2-b]pyridinyl urea derivatives as novel and potent
urotensin-II receptor antagonists are described. An activity optimization study, probing the
effects of substituents on thieno[3,2-b]pyridinyl core and benzyl group of the piperidinyl moiety,
led to the identification of p-fluorobenzyl substituted thieno[3,2-b]pyridinyl urea 6n as a highly
potent UT antagonist with an IC50 value of 13 nM. Although 6n displays good metabolic stability
and low hERG binding activity, it has an unacceptable oral bioavailability.
Revised
Accepted
Available online
Keywords:
Urotensin-II receptor
Antagonists
Thieno[3,2-b]pyridinyl urea
Cardiovasculr disease
2012 Elsevier Ltd. All rights reserved.
Urotensin-II (U-II) is a cysteine-linked cyclic peptide that is
expressed in a variety of tissues, including blood vessels, heart,
liver, kidney, skeletal muscle, and lung.1 U-II is known to be the
most potent vasoconstrictor, displaying a 10 times greater
potency than that of endothelin.2 U-II is an endogenous ligand of
the G protein-coupled receptor known as a GPR14 or the
urotensin-II receptor (UT).3 Activation of UT by binding of U-II
promotes complex signal transduction pathways that control a
wide range of physiological effects including vasoconstriction,
vasodilatation, cell proliferation and hypertrophy.4 Particularly
interesting are UT’s roles in cardiovascular functions that also
include modulation of cardiac contractility, cardiomyocyte
hypertrophy and fibrosis. These effects suggest that U-II and its
receptors are involved in the pathogenesis of cardiovascular
disease.5 Furthermore, several studies have demonstrated that
elevated plasma levels of U-II and increased levels of UT
expression are associated with numerous cardiorenal and
metabolic diseases, including hypertension,6 heart failure,7
atherosclerosis,8 diabetes, 9 and renal failure.10 Therefore, UT has
emerged as one of the most promising therapeutic targets for
treating heart failure as well as a broad range of other
cardiovascular maladies. Since the discovery at Actelion that
Palosuran11,12 (Fig. 1) is a small molecule UT antagonist for
cardiovascular indications, which reached phase II clinical stage
for diabetic nephropathy in 2004 but ceased due to lack of
efficacy,
a variety of pharmacophore derivatives of UT
antagonists have been developed.13 In particular, urea based UT
antagonists have been described by several research groups.14
As part of a continuing program aimed at the development of
novel and potent UT antagonists,15 we carried out a structure
activity relationship (SAR) study of newly prepared 5-membered
heteroaryl fused pyridinyl urea derivatives (see for example
Table 1) that have the basic backbone structure of Palosuran. An
initial effort focused on substances containing a modified
pyridine core and explored the effects of 5-membered heteroaryl
rings to the pyridine core (1-7 in Table 1). The results show that
the pyrrolo[2,3-b]pyridinyl derivative 1 exhibits moderate UT
OH
O
N
HN
N
N
H
UT hIC50 = 3.6 nM
Figure 1. Structure of Palosuran
———
∗ Corresponding author. Tel.: +82 42 860 7143; fax: +82 42 860 7149; E-mail address: kyyi@krict.re.kr (K.Y. Yi)

o
Scheme 1. Reagents and conditions: (a) 5N NaOH, EtOH, 90 C; (b) diphenylphosphoryl azide (DPPA), Et3N, DMF; (c) toluene,
reflux; (d) 16, Et3N, dichloromethane; (e) R4-benzylmagnesium chloride, THF; (f) conc HCl, 1,4-dioxane; (g) tert-butyl (2-
bromoethyl)carbamate, K2CO3, NaI, DMF, 80 oC. (h) conc HCl, 1,4-dioxane.
Table 1. UT binding affinities of 5-membered heteroaryl
fused pyridinyl urea derivatives
binding activity, whereas the pyrrolo[3,2-b] analog 2 has a 3.8-
fold lower binding affinity compared to 1. Futhermore, the
related
1-methyl-1H-pyrazolo[3,4-b]
(3),
3-methyl-3H-
imidazo[4,5-b] (4) and furo[3,2-b] (5) fused pyridinyl analogs
display largely decreased UT binding activities. Among the
substances tested, thieno[3,2-b]pyridinyl analog 6 has the most
highly potent UT binding activity (IC50 = 36 nM) which is 4.4-
fold greater than that of 1. In contrast, movement of the
thiophene group from the [3,2-b] pyridine position in 6 to the
[2,3-b] position in 7 results in a large loss in binding activity.
Based on the preliminary results, the thieno[3,2-b]pyridinyl urea
system was selected as the structural scaffold for the design,
synthesis and SAR evaluation of novel UT antagonists.15a
The general synthetic route employed for the preparation of
thieno[3,2-b]pyridinyl ureas 6 is outlined in Scheme 1. Nitriles 8,
serving as key intermediates in the pathways, were prepared
starting with commercially available thieno[3,2-b]pyridine-7-ol
using previously reported methods.16 Treatment of the substituted
thieno[3,2-b]pyridinyl carbonitriles 8 with 5N NaOH formed the
corresponding carboxylic acids 9, which upon reaction with
diphenylphosphoryl azide/triethylamine gave the corresponding
acyl azides 10. In parallel sequences, 4-benzyl substituted
piperidin-4-ols 13 were prepared by reaction of 1-boc-4-
piperidone 12 with various benzyl Grignard reagents. Removal of
the N-boc groups in 13 using conc HCl produced the
corresponding piperidines 14, which underwent alkylation with
tert-butyl (2-bromoethyl)carbamate/ potassium carbonate to form
the
tert-butyl
[2-(4-benzyl-4-hydroxypiperidin-1-
yl)ethyl]carbamates 15. Subsequent N-boc removal with conc
HCl generated the 1-(2-aminoethyl)-4-benzyl piperidin-4-ols 16.
Completion of the routes to the target ureas 6 was accomplished
by reaction of the thieno[3,2-b]pyridinyl isocyanates 11,
generated in situ by Curtius rearrangement of 10, with amines 16.
The binding affinities of the thieno[3,2-b]pyridinyl ureas to
membranes of HEK293 cells expressing human UT receptor
were determined by using a competitive binding assay with Eu-
labeled U-II and a time-resolved fluorometric (TRF) assay.17,18
a UT binding affinities were determined by using a competitive binding with
Eu-U-II and a TRF assay.
b Values are means of at least two measurements.

Table 2. Effects of substituents of thieno[3,2-b]pyridinyl urea
derivatives on UT binding affinity
compared to 6. Repositioning the methyl substituent from the
ortho (6i) to the meta (6j) and para-(6k) positions leads to a large
decrease in UT binding. Additionally, the bromine containing
analogs 6l and 6m have high binding affinities and display
similar trends. In comparison with p-methyl analog 6k, the p-
fluoro analog 6n was found to have the most potent UT binding
activity (IC50 = 13 nM) among all substances tested.
OH
O
R4
N
HN
N
N
H
S
R1
The properties of the p-fluorobenzyl substituted thieno[3,2-
b]pyridinyl urea 6n were further evaluated. This substance was
observed to have good metabolic stability in human and rat liver
microsomes (52% and 100% for 30 min, respectively). In
addition, 6n does not inhibit cytochrome P450 enzymes 3A4
(>10% at 10 µM) and it has a low hERG binding activity
determined utilizing a patch clamp assay (IC50 = 5 µM).
Furthermore, the results of a iv/po pharmacokinetic study (10
mg/kg) show that 6n displays an acceptable clearance (Cl = 16
mL/min/kg) and half-life (t1/2 = 5.1 h). However, 6n exhibits low
oral bioavailability (F = 5%), probably resulting from poor
permeability (2.7 x 10-8cm/s, PAMPA).
R3
R2
6
UT
R1
R2
R3
R4
Compound
a,b
IC50 (nM)
36
78
6
H
H
H
H
H
H
H
6a
Me
47.3%c
3,220
1,230
6b
6c
6d
6e
6f
Ph
H
H
Br
H
H
H
H
H
H
In summary, the results of the initial SAR studies have led to
the identification of novel thieno[3,2-b]pyridinyl urea derivatives
as UT antagonists. A systematic binding optimization study, in
which substituents on the thieno[3,2-b]pyridine core and the
benzyl group of the piperidine moiety, resulted in the
identification of the p-fluorobenzyl substituted thieno[3,2-
b]pyridine urea 6n as a highly potent UT antagonist. This
substance also displays good metabolic stability, low CYP450
3A4 enzyme and acceptable hERG activity. Further
investigations of thieno[3,2-b]pyridinyl urea derivatives,
concentrating on the improvement of PK profile, are now in
progress.
H
Me
25.6%c
26
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Me
Et
Ph
H
H
H
6g
6h
6i
60
H
25.4%c
20
H
2-Me
3-Me
4-Me
2-Br
3-Br
4-F
6j
140
190
20
H
6k
6l
H
Acknowledgments
H
This research was financially supported by a grant from the
Ministry of Science, ICT & Future Planning (2011-0019397) and
the R&D program of MOTIE/KEIT (10038744), Korea.
6m
6n
42
H
13
H
a UT binding affinities were determined by using a competitive binding with
Eu-U-II and a TRF assay.
Supplementary Data
b Values are means of at least two measurements.
c Values are means of inhibition at 10 µM.
Supplementary data associated with this article can be found,
in the online version, at doi:
The SAR investigation began by exploring the effects on binding
affinities of substituents (R1, R2 and R3) on the thieno[3,2-
b]pyridine structure. As the results in Table 2 show, 6a with a
methyl group at the 2-position exhibits a 2-fold reduced UT
binding affinity compared to that of the unsubstituted analog 6.
Additionally, introduction of a bulky phenyl group (6b) at this
position results in a large decrease in binding affinity. 3-Bromo
(6c) and 3-methyl (6d) substituted analogs also do not display
improved binding activities. While the urea derivative containing
chlorine (6e) at the 7-position displays low UT binding,
introduction of a methyl group (6f) results in a highly potent UT
binding activity (IC50 = 26 nM). As the size of alkyl group
increases from methyl (6f) to ethyl (6g) and phenyl (6h), a
decrease in UT binding activity occurs. A further exploration was
conducted to evaluate the effects of substituents R4 on the benzyl
group of piperidinyl moiety. The o-methyl (6i) analog was found
to have a 1.8-fold more potent UT binding affinity (IC50 = 20 nM)
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