Pyridazine-derived γ-secretase modulators

Article abstract of DOI:10.1016/j.bmcl.2011.04.143

SAR of a novel series of pyridazine-derived γ-secretase modulators is described. Compound 25 was found to be a potent modulator in vitro, which on further profiling, was found to decrease Aβ42 and Aβ40, and maintain the levels of total Aβ. Furthermore, 25

Full text of DOI:10.1016/j.bmcl.2011.04.143

Bioorganic & Medicinal Chemistry Letters 21 (2011) 4016–4019
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Pyridazine-derived c-secretase modulators
⇑
Zehong Wan , Adrian Hall, Yun Jin, Jia-Ning Xiang, Eric Yang, Andrew Eatherton, Beverley Smith,
Guang Yang, Haihua Yu, Ju Wang, Liang Ye, Lit-Fui Lau, Ting Yang, William Mitchell, Wei Cai,
Xiaomin Zhang, Yingxia Sang, Yonghui Wang, Zhaolong Tong, Ziqiang Cheng, Ishrut Hussain,
John D. Elliott, Yasuji Matsuoka
Research and Development, GlaxoSmithKline Pharmaceuticals, 898 Halei Road, Zhangjiang Hi-tech Park, Pudong, Shanghai 201023, China
a r t i c l e i n f o
a b s t r a c t
Article history:
SAR of a novel series of pyridazine-derived c-secretase modulators is described. Compound 25 was found
Received 27 January 2011
Revised 8 April 2011
Accepted 29 April 2011
Available online 13 May 2011
to be a potent modulator in vitro, which on further profiling, was found to decrease Ab42 and Ab40, and
maintain the levels of total Ab. Furthermore, 25 demonstrated excellent pharmacokinetic parameters as
well as good CNS penetration in the rat.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
SAR
c
-secretase
Modulator
AD
GSI
GSM
Pyridazine
Amyloid-beta
Alzheimer’s disease (AD) is a chronic and relentlessly progres-
O
O
sive neurologic disorder, affecting over 30 million people world-
wide, and is characterized by specific patterns of neuronal loss
leading to significant cognitive and other functional impairments.1
The deposition of fibril Tau and Ab within the CNS are the defining
neuropathological hallmarks of AD. The latter are thought to be
causative of the disease and consist of amyloid-beta (Ab) peptides
of 40–42 amino acids (Ab40 and Ab42 respectively).2 These pep-
tides are produced from amyloid precursor protein (APP) by the
F
N
N
N
S
N
N
N
N
H
N
N
N
1
N
Cmpd A
Cmpd B
N
H
O
F
sequential action of b-secretase and
effort has been invested to identify inhibitors of either enzyme to
reduce Ab production.3
-secretase inhibitors (GSIs) have been
c-secretase, thus a significant
O
c
shown to successfully reduce brain Ab dose-dependently in pre-
clinical models.4 Several GSIs have been progressed to clinical
development with LY-450139 as the most advanced. However, its
Phase III clinical trial was recently halted due to lack of cognitive
improvement in AD patients and higher risk of developing skin
cancer upon treatment (Eli Lilly News Release, 2010).
N
Figure 1. Analogs with phenyl-imidazole fragment.
verse outcomes are not completely understood. However, it is
known that many other substrates are cleaved by
c-secretase in
Consistent with the unexpected outcomes of LY-450139, some
addition to APP.7 Toxicity may arise through inhibition of the pro-
cessing of these other substrates. For example, inhibition of cleavage
preclinical studies showed that inhibition of c-secretase may impair
learning and memory5 and induce skin cancer.6 Causes of these ad-
of Notch, which is a known c-secretase substrate and a transmem-
brane receptor involved in the regulation of cell differentiation,
leads to abnormalities in the gastrointestinal tract and the immune
system.8 To avoid adverse reactions mediated by inhibition of Notch
⇑
Corresponding author.
E-mail address: zehong.2.wan@gsk.com (Z. Wan).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.04.143

Z. Wan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4016–4019
4017
processing, research focus has been shifted to developing
tase modulators (GSMs). Heterogeneous proteolysis of APP by
-secretase leads to the productionof Ab peptides in various lengths,
ranging from 37 to 43 amino acid residues. While GSIs inhibit pro-
duction of all Ab peptide species, GSMs shift the cleavage site to-
wards production of shorter non-amyloidogenic peptides.9
c
-secre-
to its potent inhibition of Notch processing (Table 1). A chemistry
program was then initiated to optimize this template. Our initial
objective was to identify GSMs with selectivity greater than 100
fold over Notch processing favoring inhibition of Ab42 production.
Greater attention was paid to Ab42 due to the less clear patholog-
ical role of Ab40.
c
Because GSMs selectively inhibit
c
-secretase activity, Notch pro-
Synthesis. Pyridazine derivative 6 was prepared from aniline 2
(Scheme 1). Bromination with NBS, diazotization, and displace-
ment with KI afforded 3, which was coupled with 4-methyl-imid-
azole to provide 4. Formation of the boronic acid, Suzuki coupling
with 3,6-dichloro-pyridazine, followed by Buchwald reaction with
(S)-1-(4-fluorophenyl)-ethanamine then furnished compound 6.
This synthetic route was utilized to prepare compounds 12–25
(Table 1) by using appropriate dichloro-pyridazines and amines.
Compound 11 was synthesized from 1-[4-iodo-3-(methyl-
oxy)phenyl]ethanone 7 (Scheme 2). Coupling with 4-methyl-imid-
cessing is spared and its signaling function is largely intact. There-
fore, GSMs are believed to be a better tolerated Ab-lowering
approach than GSIs.
Our research program was aimed at discovering novel, potent
and brain penetrant GSMs for AD.10 A pyridazine amide analog
(1, Fig. 1) was identified through cross-screening of our internal
compound collection. This compound also contains phenyl-
imidazole fragment, a common component of known GSMs (e.g.,
A and B).11 However, compound 1 behaved more alike a GSI due
Table 1
In vitro SAR for pyridazine derivatives
N
N
N
linker
N
NH
R3
MeO
R1
R2
R3
Compd
R1
R2
Linker
Ab42apIC50
Ab40apIC50
Notcha,bpIC50
O
1
H
H
H
H
4-F
4-F
5.6
6.5
4.7
6.2
6.0
12
CH2
<4.7
13
14
6
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
4-F
7.0
6.2
7.2
7.1
7.2
7.3
6.8
7.3
6.1
6.0
6.7
6.8
6.9
7.1
6.8
6.9
agonist
<4.7
<4.7
<4.7
<4.7
5.0
4-F
4-F
15
16
17
18
19
H
3-F
2-F
4-OCH3
4-CF3
<4.7
<4.7
20
21
H
H
H
H
4-F
H
7.3
6.8
6.9
6.5
5
O
<4.7
HO
22
H
H
4-F
7.4
6.8
4.7
23
24
25
26
27
11
28
CH3
CH3
H
CH3
4-F
4-F
4-F
4-F
4-F
4-F
4-F
6.5
6.7
7.2
6.9
7.2
7.3
7.0
5.9
6.3
6.7
5.8
6.8
7.0
5.6
<4.7
H
4.8
CH3
5.0
H
CN
4.8
H
CH2CH3
CH(CH3)2
CF3
agonist
agonist
agonist
H
H
a
Ab42, Ab40 and Notch were assayed in the same way as reported previously.10
When screened at 10 l
M, greater than 30% increase of luciferase activity signal was displayed by agonists in the Notch reporter assay.10
b

4018
Z. Wan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4016–4019
Table 3
I
CuI, Cs2CO3
Rat CNS penetration data of .25a
NH2
8-hydroxyquinoline
OMe
NBS, 85%
OMe
H
N
Blood Conc. (
l
M)
Brain Conc. (
l
M)
Br:Bl
NaNO2, KI
TsOH, 62%
58%
15.998 1.709
9.085 3.257
0.56 0.16
N
Br
2
3
a
Compound was dosed orally in (30 mg/kg) 1% (w/v) methylcellulose aq. Values
MeO
are the mean from three rats. Samples were taken 6 h post-dose.
MeO
N
BuLi, (iPrO)3B
57%
N
N
N
N
N
Br
Cl
F
N N
Cl
Cl
4
azole followed by ring formation with ethyl 3-methyl-2-oxobut
anoate and hydrazine provided 9. Chlorination with POCl3 and
Buchwald coupling with (S)-1-(4-fluorophenyl)-ethanamine then
furnished 11. This synthetic sequence was applied to prepare pyrid-
azine derivatives 26–28 (Table 1) by choosing appropriate a-keto-
esters for the ring formation.
Results and discussion. Compound 1 displays comparable po-
tency to inhibit both Ab42 production and Notch processing and
is thus more alike a GSI, although about 10-fold less potent to in-
hibit Ab40 production. Replacement of the carbonyl group with a
simple CH2 not only improved potency against Ab42/40, but also
demonstrated more than 60-fold selectivity at Notch (12). Di-sub-
stitution of the carbon linker (13) further improved its potency at
Ab42, but to our surprise, this compound enhanced Notch process-
5
Pd(dppf)2Cl2, Na2CO3
DME, reflux, 78%
F
MeO
H2N
N
N
N
N
NH
Pd(OAc)2, Cs2CO3
BINAP, TEA, Tol,
reflux, 60%
6
Scheme 1. Synthetic Strategy for Analogs 6 & 12–25
O
MeO
I
O
CuI, Cs2CO3
MeO
N
O
8-hydroxyquinoline
O
N
O
H
ing at a high concentration (10 lM). It is very interesting to note
DMSO, 110oC
N
H2N-NH2
LiHMDS, THF, 60%
that this enhancement was reduced through mono-substitution
(14 and 6) with the S-enantiomer 6 being 10 fold more potent than
the R-enantiomer 14. Different substituents on the phenyl ring
(15–19), ranging from strong electron donating group (OCH3) to
strong electron withdrawing group (CF3), did not significantly alter
potency. A few other chiral linkers were well tolerated (20–22).
Having identified several chiral benzyl amines which provided
good levels of in vitro potency, we selected (S)-1-(4-fluoro-
phenyl)-ethanamino group due to convenient access and fixed this
while we varied the substitution of the pyridazine ring. Di-substi-
tution with methyl group (23) resulted in loss of potency. Mono-
substitution of R2 = CH3 gave rise to compound 25 with potency
similar to 6 but with a CYP inhibition profile much improved (data
not shown). Nitrile was also tolerated at this position (26). Substi-
tution with larger groups (27, 11 and 28) resulted in enhanced
Notch processing as noticed previously, although still potent at
inhibiting Ab42.
N
7
50%
8
MeO
N
MeO
N
N
N
N
N
N
POCl3
N
OH
Cl
81%
9
10
F
MeO
N
H2N
N
N
F
N
NH
Pd(OAc)2, Cs2CO3
BINAP, TEA, Tol,
reflux, 60%
11
Scheme 2. Synthetic Strategy for Analogs 11 & 26–28
Following in vitro potency assessment, compounds with a pIC50
value P 6 were assessed in terms of in vitro metabolic stability in
rat and human liver microsomes and for inhibition of five human
CYP isoforms (CYP1A2, 2C9, 2C19, 2D6, and 3A4). Selected ana-
logues were profiled to assess their potential as time-dependent
CYP inhibitors. Based on these data, compound 25 emerged as
the most interesting compound for studying mechanism of action
(Fig. 2). SHSY5Y-APPswe cells were thus pre-incubated with 25
for 24 h. Medium was harvested and subject to analysis of Ab42,
Ab40, total Ab and cell viability (determined via WST-1). Total Ab
in this assay system includes all Ab generated by
as Ab36, 37, 38 and 40. Levels of Ab42 and Ab40 were decreased in
a concentration-dependent manner after treatment (0.01–3 M),
c-secretase, such
l
while total Ab levels were maintained indicating the rise in shorter
Ab species compensating for the decrease in Ab42 and Ab40. This is
in contrast to the profile of inhibitors such as LY-450139 which de-
creases levels of all Ab species and thus the total Ab. Cytotoxicity
was exhibited when 25 was tested at higher concentrations.
The in vivo pharmacokinetic profile of 25 is listed in Table 2.
Compound 25 demonstrated low clearance and excellent oral bio-
availability in the rat.
Figure 2. Effect of 25 on Ab levels and cell viability in SHSY5Y-APPswe cells.
Table 2
Rat PK (iv  po) of 25a
CLb (mL/min/kg)
Vdss (L/kg)
t
(h)
Fpo (%)
98
½
5.1
1.4
3.1
Compound 25 (Table 3) also demonstrated good brain penetra-
tion and showed that a 30 mg/kg oral dose could deliver brain
a
Crystalline HCl salts were dosed to SD rats at 1 mg/kg (iv) and 2 mg/kg (po) with
vehicle of 1% (w/v) methylcellulose (po) and DMSO solution with 10% HP-b-CD
(w/v) (iv)
concentrations of 9.1
l
M which is significantly higher than the
M at Ab40) values indicat-
in vitro IC50 (0.06 M at Ab42 and 0.2
l
l

Z. Wan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4016–4019
4019
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