Design and synthesis of an aminopiperidine series of γ-secretase modulators

Article abstract of DOI:10.1016/j.bmcl.2013.10.063

The design, synthesis, and SAR of cyclic diamines as novel γ secretase modulators (GSMs) are presented in this Letter. Starting from information in the literature and in-house cyclic diamines library, we have found a 3(S)-aminopiperidine as a potent structure for lowering Aβ42 production both in vitro and in vivo.

Full text of DOI:10.1016/j.bmcl.2013.10.063

Bioorganic & Medicinal Chemistry Letters 24 (2014) 378–381
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of an aminopiperidine series of
modulators
c-secretase
Tomonori Kobayashi a, Seiji Iwama b, Akira Fusano b, Yoshihiro Kato b, Atsushi Ikeda b,
Yasuhiro Teranishi b, Akemi Nishihara b, Masanori Tobe b,
⇑
a Dainippon Sumitomo Pharma Co., Ltd, Kasugade Naka 3-1-98, Konohana-ku, Osaka 554-0022, Japan
b Dainippon Sumitomo Pharma Co., Ltd, Enoki 33-94, Suita, Osaka 564-0053, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The design, synthesis, and SAR of cyclic diamines as novel
in this Letter. Starting from information in the literature and in-house cyclic diamines library, we have
found a 3(S)-aminopiperidine as a potent structure for lowering Ab42 production both in vitro and
in vivo.
c secretase modulators (GSMs) are presented
Received 3 October 2013
Revised 22 October 2013
Accepted 29 October 2013
Available online 6 November 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Alzheimer’s disease
c
c
-Secretase modulator
-Secretase inhibitor
Amyloid b peptide
Piperidine
A widely pursued strategy for the treatment of Alzheimer’s dis-
ease is based on inhibition of the production of neurotoxic amyloid
b (Ab) peptides, especially Ab42.1 Ab peptides are generated by ini-
tial cleavage of the amyloid precursor protein (APP) by b-secretase
to form a C-terminal fragment (CTF), which is subsequently cleaved
other GSMs have subsequently been reported, revealing that the
imidazolyl methoxy phenyl structure is a key pharmacophore for
GSM activity.6 Using a scaffold hopping strategy, we designed
and prepared a focused library of compounds with the imidazolyl
methoxy phenyl carboxamide moiety (Fig. 1). The olefinic double
bond in Eisai’s compound was replaced with amides, which are
well-known to provide more polarity and to avoid the potential
for Michael addition. Structural rigidity of the lactam was provided
with cyclic diamines that are often seen in another class of GSMs.7
We, thus, combined our cyclic diamine library with the imidazolyl
methoxy phenyl carboxylic acids to obtain about 200 compounds.
Using rat-fetus primary neuronal cell-based assay with Ab42 ELISA,
we measured in vitro Ab42 lowering activity of the prepared com-
pounds (Table 1).8 At the screening stage, the substituent of the
nitrogen atom on the right hand side of the cyclic amines was fixed
by a 3-trifluoromethylbenzyl group. The secondary amide deriva-
tives 1–5 displayed weak activity, whereas compounds 6-10 with
primary amide groups showed strong activity. Especially, the
3(S)-aminopiperidine 10 exhibited the most potent activity. The
(S) enantiomer 10 was more potent than the (R) enantiomer 9. Sub-
stitution of the amide nitrogen in 3-aminopiperidine with a methyl
(11), ethyl (12) or isopropyl (13) group resulted in complete loss of
activity, indicating that the hydrogen atom is indispensable for
GSM activity.
by
c
-secretase to produce Ab peptides having 37–42 amino acids in
length.2
c-Secretase inhibitors (GSIs) have been shown to reduce
corticospinal fluid Ab42 in humans; however, significant off-target
liabilities have emerged during clinical development. In addition to
APP,
c-secretase has multiple substrates including the Notch recep-
tor. Notch cleavage by
c
-secretase is critical for regulating neuronal
development and cell differentiation. Recently, a phase III clinical
trial with the GSI semagacestat was halted due to adverse events,
including increased incidence in skin tumors and worsening of cog-
nition.3 On the other hand,
c
-secretase modulators (GSMs) selec-
tively inhibit the production of Ab42 without blocking the overall
function of
-secretase on CTF and other substrates, such as Notch.4
c
Therefore this class of molecules should not cause Notch-related
side effects and could offer a better safety profile than GSIs. Herein,
we discuss the synthesis and structure–activity relationship (SAR)
of a series of novel aminopiperidine derived GSMs with good
in vitro and in vivo suppression of Ab42 production.
Eisai Co., Ltd has previously reported a GSM containing a cyclic
cinnamide motif (Fig. 1).5 Based on this structure, a number of
Next, we explored the right hand side moiety of the 3-aminopi-
peridine derivatives (Table 2). We first investigated the effect of
substitution of the benzyl groups. The use of methyl groups
⇑
Corresponding author. Tel.: +81 6 6337 5927; fax: +81 6 6337 6010.
E-mail address: masanori-tobe@ds-pharma.co.jp (M. Tobe).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.10.063

T. Kobayashi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 378–381
379
Imidazolyl phenyl group
Cyclic amine
O
O
O
N
O
R3
N
N
N
R1
R2
F
N
N
N
Eisai compound
Amide-cyclic amine scaffold library
Figure 1.
Table 1
Diamine
O
O
N
CF3
N
Compound
Diamine
Ab42 inhibitiona (%)
H
N
N
1
2
39
17
H
N
N
N
3
4
5
18
51
19
N
N
N
N
N
N
6
31
N
H
N
N
7
8
78
40
N
H
N
H
9
72
82
N
N
N
N
H
10
N
H
11
<1
N
Me
(continued on next page)

380
T. Kobayashi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 378–381
Table 1 (continued)
N
N
Et
12
13
<1
<1
N
N
iPr
a
Ab42 inhibition was assayed at 2.5 lM. Each value is the average of two determinations.
O
R
O
N
N
H
c
N
N
C3
14 (RS, R = H)
21 (R, R = 4-CH3)
15 ( , R = 2-CH )
22 ( , R = 4-CF )
RS
R
16 (RS, R = 3-CH33)
23 (R, R = 4-Br)3
24 ( , R = 4-CH )
S
17 ( , R = 4-CH )
RS
18 (RS, R = 4-OC3H3) 25 (S, R = 4-CF33)
19 (RS, R = 4-Br)
26 (S, R = 4-Br)
O
O
O
R
O
O
N
N
O
N
N
a
d
OH
N
H
R
N
H
(S)
O
N
N
N
N
C3
C3 stereo
C3 stereo
33
27 (R = 4-CH3)
b
28 (R = 4-CF3
)
34: RS
37: RS
35:
38:
R
R
29 (R = 4-Br)
36: S
39: S
(R = Boc)
(R = H)
O
H
N
e
R
O
N
N
N
H
O
(RS)
N
30 (R = H)
31 (R = 4-CH3
)
32 (R = 4-Br)
Scheme 1. Reagents and conditions: (a) 3-Amino NBoc piperidine, WSCD, HOBT, DMF, rt,; (b) HCl, 1,4-dioxane, rt,; (c) The corresponding benzylbromide, K2CO3, DMF, rt.; (d)
the corresponding benzoic acid, WSCD, HOAt, DMF, rt.; (e) the corresponding isocyanate, THF, rt.
(o-, m-, and p-), giving compounds 15–17, increased GSM activity
compared to the use of no substituent (compound 14), with substi-
tution at the p-position providing the best activity. A hydrophilic
methoxy group at the p-position (18) did not affect the activity,
whereas the use of a hydrophobic trifluoromethyl group (19) or a
bromo group (20) resulted in strong activity. This trend was also
seen in other Eisai-type GSMs.6b We prepared the enantiomerically
pure 3(R) and 3(S) derivatives (21–23 and 24–26, respectively).
3(S) derivatives displayed stronger activity (>90% inhibition at
has strong influence on GSM activity in some cases.6b–e In our 3-
aminopiperidine scaffold, 3(S) enantiomers might provide more
favorable interaction to the active site than their enantiomers.
Next, we investigated linker moiety that connects the piperidine
nitrogen to the phenyl or benzyl group. The amide 27–29 and urea
30–32 derivatives showed decreased activity than the correspond-
ing derivatives with a methylene linker. Based on these findings,
we considered that the basicity of the nitrogen atom at the piper-
idine and the hydrophobic interaction at this region are important
for high GSM activity. Then, we carried out metabolic stability tests
in human liver microsome with highly active compounds (24–26).
As a result, only 26 had acceptable pharmacokinetic properties for
2.5
information about interaction of Eisai-type GSMs with
it is reported that stereochemistry in the right hand side moiety
lM) than their enantiomers. Although there is little structural
c-secretase,

T. Kobayashi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 378–381
381
Table 2
novel structure for a new class of GSMs. Compound 26 displayed
good in vitro and in vivo Ab42 lowering activity. Although there
are many Eisai-type GSMs reported, our 3(S)-aminopiperidine scaf-
fold provides a facile synthetic program (simple amide condensa-
tion and N-substitution) suitable for optimization study. Further
optimization of this compound will be reported in due course.
O
O
N
N
N
H
R
C3
N
References and notes
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3. Schor, N. F. Ann. Neurol. 2011, 69, 237.
Compound
C3 stereo
R
Ab42 inhibitiona (%)
4. Oehlrich, D.; Berthelot, D. J. C.; Gijsen, H. J. M. J. Med. Chem. 2011, 54, 669.
5. Portelius, E.; Van Broeck, B.; Andreasson, U.; Gustavsson, M. K.; Mercken, M.;
Zetterberg, H.; Borghys, H.; Blennow, K. J. Alzheimers Dis. 2010, 21, 1005.
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14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
RS
RS
RS
RS
RS
RS
RS
R
R
R
S
S
S
S
S
S
RS
RS
RS
Benzyl
37
62
54
82
45
90
93
36
57
55
90
92
97
55
34
64
25
28
47
2-CH3 benzyl
3-CH3 benzyl
4-CH3 benzyl
4-OCH3 benzyl
4-CF3 benzyl
4-Br benzyl
4-CH3 benzyl
4-CF3 benzyl
4-Br benzyl
4-CH3 benzyl
4- CF3 benzyl
4-Br benzyl
4-CH3 benzoyl
4-CF3 benzoyl
4-Br benzoyl
–CONH- benzyl
–CONH- 4-CH3 benzyl
–CONH-4-Br benzyl
a
Ab42 inhibition was assayed at 2.5
determinations.
lM. Each value is the average of two
7. (a) Rivkin, A.; Ahearn, S. P.; Chichetti, S. M.; Kim, Y. R.; Li, C.; Rosenau, A.; Kattar,
S. D.; Jung, J.; Shah, S.; Hughes, B. L.; Crispino, J. L.; Middleton, R. E.; Szewczak,
A. A.; Munoz, B.; Shearman, M. S. Bioorg. Med. Chem. Lett. 2010, 20, 1269; (b)
Rivkin, A.; Ahearn, S. P.; Chichetti, S. M.; Hamblett, C. L.; Garcia, Y.; Martinez,
M.; Hubbs, J. L.; Reutershan, M. H.; Daniels, M. H.; Siliphaivanh, P.; Otte, K. M.;
Li, C.; Rosenau, A.; Surdi, L. M.; Jung, J.; Hughes, B. L.; Crispino, J. L.; Nikov, G. N.;
Middleton, R. E.; Moxham, C. M.; Szewczak, A. A.; Shah, S.; Moy, L. Y.; Kenific, C.
M.; Tanga, F.; Cruz, J. C.; Andrade, P.; Angagaw, M. H.; Shomer, N. H.; Miller, T.;
Munoz, B.; Shearman, M. S. Bioorg. Med. Chem. Lett. 2010, 20, 2279.
8. In vitro assay protocol for Ab42 inhibition: Rat fetus primary neurons were
treated with compounds at specified concentration for 1–3 days. The medium
was collected and quantified Ab42 with an enzymed-linked immunosorbent
assay (ELISA) kit (Human/Rat b amyloid (42) ELISA kit, High-sensitive, Wako,
Japan) by manufacturer’s instructions.
further pharmacological evaluation (data not shown). We deter-
mined the IC50 value of the most potent compound (26) as
250 nM, which is almost the same value as that of Eisai’s com-
pound (240 nM, in-house data). The synthesis of compound 26 is
shown in Scheme 1. The imidazolyl methoxy phenyl carboxylic
acid 33 was prepared according to the literature,9 and then com-
bined to the N-tert-butyloxycarbonyl (Boc)-protected 3(S)-amino
piperidine to give 36. Deprotection of the Boc group in 36 with a
hydrogen chloride gave the free amine 39, which was alkylated
with 4-bromobenzylbromide to provide compound 26.10 Com-
pound 26 showed acceptable ClogP and polar surface area (PSA)
values (3.93 and 59 Å2, respectively) for CNS drugs and exhibited
9. Koike, T.; Nakamura, M.; Tomata, Y.; Takai, T.; Hoashi, Y.; Kajita, Y.; Tsukamoto,
T.; Kamata, M. Patent: U.S. 2012/59030 A1, 2012.
10. Chemical properties of compound 26: 1H NMR (DMSO-d6, 400 MHz) d 8.25 (1H,
d, J = 7.8 Hz), 7.83 (1H, d, J = 1.4 Hz), 7.59 (1H, d, J = 1.8 Hz), 7.54–7.48 (3H, m),
7.44 (1H, d, J = 8.2 Hz), 7.27 (2H, d, J = 8.2 Hz), 7.18 (1H, t, J = 1.1 Hz), 4.02–3.88
(1H, m), 3.88 (3H, s), 3.57–3.39 (2H, m), 2.85 (1H, d, J = 7.3 Hz), 2.72 (1H, d,
J = 10.5 Hz), 2.14 (3H, s), 2.01–1.77 (3H, m), 1.74–1.63 (1H, m), 1.60–1.46 (1H,
m), 1.41–1.28 (1H, m). 13C NMR (CDCl3, 100 MHz) d 165.2, 152.3, 138.1, 136.8,
134.8, 131.4, 130.6, 129.0, 124.5, 121.2, 118.6, 116.2, 120.0, 77.2, 62.1, 57.6,
56.1, 53.7, 45.4, 28.6, 21.7, 13.6.; HRMS (ESI) m/z calcd for C24H28BrN4O2
483.1390; found 483.1394 (M+H); Anal. Calcd for C24H27BrN4O2Á0.25H2 O; C,
59.08; H, 5.68; N, 11.48; Br, 16.38. Found: C, 58.86; H, 5.55; N, 11.21; Br, 16.16.
good water solubility (8.0 lg/mL, pH 7.4) and membrane perme-
ability (50 Â 10À6 cm/s, pH 7.4) in an artificial membrane perme-
ability assay. Next, we evaluated the efficacy of compound 26 in
suppressing the production of Ab42 in vivo. Compound 26, given
orally at 100 mg/kg, reduced Ab42 production in the hippocampus
and plasma of wild-type mice by 55% and 66%, respectively.
In summary, cell-based screening of an in-house focused library
resulted in the discovery of the 3(S)-aminopiperidine scaffold as a