The SAR of 4-substituted (6,6-bicyclic) piperidine cathepsin S inhibitors

Article abstract of DOI:10.1016/j.bmcl.2006.01.038

A series of competitive, reversible cathepsin S (CatS) inhibitors was investigated. An earlier disclosure detailed the discovery of the 4-(2-keto-1-benzimidazolinyl)-piperidin-1-yl moiety as an effective replacement for the 4-arylpiperazin-1-yl group foun

Full text of DOI:10.1016/j.bmcl.2006.01.038

Bioorganic & Medicinal Chemistry Letters 16 (2006) 2209–2212
The SAR of 4-substituted (6,6-bicyclic) piperidine cathepsin
S inhibitors
Cheryl A. Grice,* Kevin Tays, Haripada Khatuya, Darin J. Gustin, Christopher R. Butler,
Jianmei Wei, Clark A. Sehon, Siquan Sun, Yin Gu, Wen Jiang, Robin L. Thurmond,
Lars Karlsson and James P. Edwards
Johnson and Johnson Pharmaceutical Research and Development, L.L.C., 3210 Merryfield Row, San Diego, CA 92121, USA
Received 1 December 2005; revised 9 January 2006; accepted 10 January 2006
Available online 3 February 2006
Abstract—A series of competitive, reversible cathepsin S (CatS) inhibitors was investigated. An earlier disclosure detailed the dis-
covery of the 4-(2-keto-1-benzimidazolinyl)-piperidin-1-yl moiety as an effective replacement for the 4-arylpiperazin-1-yl group
found in our screening hit. Continued investigation into replacements for the 4-aryl piperazine resulted in the identification of poten-
tially useful CatS inhibitors with enzymatic and cellular activity similar to that of JNJ 10329670 as disclosed in a previous
publication.
Ó 2006 Elsevier Ltd. All rights reserved.
Cathepsin S (CatS), a cysteine protease found in the
lysosome of hematopoietic cells, is integrally involved
in antigen presentation of major histocompatibility
complex class II (MHC-II) molecules. These molecules
bind antigens and transport them to the cell surface
for display to various cells of the immune system. The
invariant chain (Ii), a component of MHC-II complex,
prevents premature binding of non-antigenic peptides
by acting as a chaperone. CatS mediates the cleavage
of the Ii p10 fragment, prior to cell surface antigen pre-
sentation to CD4+ T cells.1–3 Inhibition of CatS would
block the necessary degradation of the Ii, preventing
antigen presentation, resulting in immunosuppression
with specificity for CD4+ T cells. In CatS ꢀ/ꢀ mice,
the flow of MHC-II molecules to the cell surface is sig-
nificantly reduced.3 It is anticipated that selective inhibi-
tion of CatS would be therapeutically useful in diseases
that are characterized by hyperimmune responses.
led to the identification of compounds II and III (JNJ
10329670).4,5 Compounds in the latter series have im-
proved selectivity profiles, cellular activity, and pharma-
cokinetics, with suitable physicochemical properties for
further development. Both series share several common
structural motifs; the aryl substituted pyrazole group, a
saturated linker three carbons in length, and a 1,4-
substituted basic nitrogen containing ring. Increasing
the lipophilicity of the tetrahydropyrazolopyridine aryl,
substituent was previously noted to improve enzymatic
CatS activity.5,6
In this report, we wish to detail our continued investiga-
tion into replacements for the aryl piperazine portion of
compound II. The analogs included here maintain the
structural commonality detailed above for both series
II and III. The headgroup replacements of interest are
shown in Figure 1.
Recently, we reported on our efforts to identify novel
noncovalent inhibitors of CatS.4,5 Our initial lead com-
pound I, as previously disclosed, was identified through
virtual screening of a subset of the J&J PRD library
using DOCK.4 Subsequent development of the SAR
Amines 1 and 2 were prepared according to Scheme 1
starting with readily available intermediates, 13a and
13b.7 Reductive amination8 of the anilines with tert-bu-
tyl-4-oxo-1-piperidinecarboxylate followed by reduction
of the double bond using H2 in the presence of Pd/C or
PtO2 afforded the desired amines 14a and 14b. Subse-
quent hydrolysis, cyclization, and deprotection using
standard conditions resulted in the preparation of the
desired amines.9
Keywords: Cathepsin S; Cysteine protease inhibitor.
*
Corresponding author. Tel.: +1 858 784 3054; fax: +1 858 450
2089; e-mail: cgrice@prdus.jnj.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.01.038

2210
C. A. Grice et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2209–2212
H3C
Cl
CN
Linker
I
N
O
CF3
N
N
N
N
N
OR
N
N
N
Cl
N
N
N
N
OCH3
N
Aryl Piperazine
Headgroup
N
NH2
O
N
O
SO2CH3
Pyrazole
Tailgroup
II: R = CONH2
III: JNJ 10329670
I
O
N
Cl
R
O
N
NH
O
O
X
OH
NH
O
S
X
O
N
O
OEt
N
O
a
b,c,d
NH
O
N
H
N
H
N
H
N
N
H
N
Boc
15
Boc
16
1: X = CH2, R = H
2: X = CH2, R = Cl
3: X = O, R = H
6: X = N
7: X = CH
8
11
Scheme 2. Preparation of compound 11. Reagents and conditions: (a)
NaH, ethyl bromoacetate, DMF, 0 °C, 33%; (b) LiOH, H2O, THF, rt,
93%; (c) HATU, DMF, rt, 33%; (d) 1:1 TFA/CH2Cl2, rt, 45 min, 49%.
4: X = NH, R = H
5: X = NH, R = Cl
O
N
N
The targeted CatS inhibitors were prepared using one of
two methods as depicted by Schemes 3 and 4. Both pro-
cedures require the preparation of pyrazole 17, as de-
scribed previously.4 The first method results in the
N
N
N
O
N
H
N
H
N
H
N
H
R3
R3
N
Amines
N
9
10
11
12
HN
N
1-12
O
a
Figure 1. Aryl piperazine replacements.
b
N
N
R4
R4
17
18
O
R
R3
N
N
R
OEt
c,d,e
Amine
O
OH
R
NH
a,b
N
O
OEt
N
NH2
R4
N
N
H
BOC
Scheme 3. Preparation of compounds 20–23, 28, 31, 32, 34, and 37–57.
Reagents and conditions: (a) epichlorohydrin (4–6 equiv), Cs2CO3
(2 equiv), DMF, rt; (b) amine, EtOH, reflux.
13a: R = H
13b: R = Cl
14a: R = H
14b: R = Cl
1: R = H
2: R = Cl
Scheme 1. Synthesis of compounds 1 and 2. Reagents and conditions:
(a) Boc-piperidone, NaBH(OAc)3, CH2Cl2, AcOH, rt, R = H, 71%,
R = Cl, 66%; (b) R = H: H2, 10% Pd/C, EtOAc, rt, 95%; R = Cl: PtO2,
H2, EtOAc, rt, 46%; (c) 1.0 M NaOH, 4:1 MeOH/H2O, rt, R = H,
93%, R = Cl, 74%; (d) EDCI, CH2Cl2, rt, R = H, 95%, R = Cl, 52%;
(e) 1:1 TFA/CH2Cl2, rt, R = H, 95%, R = Cl, 93%.
O
R3
R3
N
Amines
1-12
N
HN
H
N
a
b
N
N
R4
R4
17
19
Piperidines 3–8 and piperazine 12 were prepared accord-
ing to literature procedures.10–12 Amines 9 and 10 were
prepared via reductive amination using readily available
starting materials.8 Amine 11 was prepared according to
Scheme 2. The hydroxyl group of compound 15, pre-
pared according to a literature procedure,13 was alkyl-
ated with ethyl bromoacetate to yield ester 16.
Hydrolysis of the ester to the acid, followed by cycliza-
tion and deprotection, gave piperidine 11.
R3
N
N
Amine
N
R4
Scheme 4. Preparation of compounds 24–27, 29, 30, 33, 35, and 36.
Reagents and conditions: (a) 3-bromopropanol, Cs2CO3, DMF, rt; (b)
amine, NaBH(OAc)3, AcOH, CH2Cl2.

C. A. Grice et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2209–2212
2211
Table 2. Effect of aryl substitution on CatS activity
formation of a secondary alcohol in the linker region as
depicted by structure II above. These analogs were pre-
pared according to Scheme 3. The pyrazole 17 was con-
verted to racemic epoxide intermediate 18 using
epichlorohydrin. Epoxide ring opening was accom-
plished using the amines shown in Figure 1 in refluxing
EtOH to afford the desired compounds in 50–90% yield.
N2
N1
N
R3
A4
N
C3
O
N
R5
N
A3
A2
SO2Me
O
5'
N
X
8'
6'
R2
7'
The second method, Scheme 4, provides access to the
unsubstituted linker analogs as depicted by structure
III above.5 Common intermediate 17, was regioselec-
tively alkylated with 3-bromopropanol. The alcohol
was oxidized to the corresponding aldehyde using
Dess–Martin periodinane. The amines from Figure 1
were coupled to the aldehyde under reductive amination
conditions to afford the desired deshydroxy analogs in
40–80% yield.
b
Entry
X
R2
R3
R5 CatS
Ii
IC50 (nM) IC50 (lM)
a1a
a
23
27
28
29
30
31
32
33
34
35
36
37
C
C
C
C
C
N
C
C
C
C
C
N
H
H
A4-CF3 OH 16
A4-CF3 23
0.41
0.95
1.3
—
60%
72%
H
60-Cl A4-CF3 OH 16
60-Cl A4-CF3
50-Me A4-CF3
H
H
130
145
2.0
1.3
1.8
1.6
4.4
2.6
1.6
0.9
H
H
H
A4-CF3 OH 80
A4-Br
OH 32
60
OH 48
A4-Br
H
Variation of R4 (SO2Me, Ac, Boc, and H), as shown in
Table 1, indicates a preference for methyl sulfonamide.
A notable loss of in vitro enzymatic activity is seen with
R4 = Boc and H. Substitution of H for OH at R5 has a
minimal effect on in vitro enzymatic activity or invariant
chain degradation, with comparable analogs being equi-
potent (22 vs 26 and 23 vs 27). Both Tables 1 and 2 list
the affinity for the alpha-1 (a1a) adrenergic receptor as
percent inhibition at 1 lM for select compounds. Several
analogs described below, offer insight into substitutions
that can be incorporated to decrease alpha-1 cross-reac-
tivity. As previously reported in the literature, substitu-
tion at R2 with a chloro substituent is expected to reduce
potentially unwanted cross reactivity with the a1a recep-
tor.5 The data obtained for entries 38 and 42 support
this trend.
60-Cl A4-Br
60-Cl A4-Br
50-Me A4-Br
H
H
130
170
H
A4-Br
OH 68
a Average of 4–6 determinations.
b a1a % inhibition values at 1 lM were determined by Cerep, SA.
The data in Table 3 indicate that structural changes to
Y, R2, and R3 failed to confer improved cellular activity
but were well tolerated in terms of enzyme inhibition.
Additional molecules incorporating modifications to the
left-hand side utilizing amines 8, 9, 10, 11, and 12 are
included in Table 4. Substitution at the anilinic position
(tetrahydroquinoline, 48) versus the homolog (tetrahy-
droisoquinoline, 49) is preferred for CatS enzymatic
inhibition. However, the potency of 48 is an order of
magnitude lower than 41, suggesting that the presence
of a second basic nitrogen in this position is unfavor-
able. Analogs 50 and 51 also substituted in the anilinic
As shown in Table 2, modifications of the C3-aryl moi-
ety of the pyrazole confirmed both 4-trifluoromethyl
and 4-bromo substituents as optimal for in vitro enzy-
matic activity. Comparison of compounds containing
R5 = OH and R5 = H, again, demonstrates that this
change has no effect on in vitro enzymatic activity.
The data suggest a modest preference with respect to cel-
lular potency for the C3 4-trifluoromethyl substitution
as measured by the invariant chain degradation assay.
Table 3. Effect of varying the headgroup on cathepsin S activity
R3
N
O
N
N
OH
Y
N
N
Table 1. Effect of N-substitution on cathepsin S activity
SO2Me
8'
6'
R2
N
CF3
O
N
N
7'
R2
R5
N
b
Entry
Y
R3
CatS
a
IC50 (nM)
Ii IC50 (lM) a1a
O
N
R4
38
39
40
41
42
43
44
45
46
47
CH2 70-Cl CF3
CH2 70-Cl Br
13
18
23
33
18
33
48
65
88
133
0.98
0.75
1.8
<10%
—
—
Entry R4
R5
OH 1925
CatS IC50 (nM) Ii IC50 (lM) a1a
a
b
CH2
CH2
H
CF3
Br
H
2.0
1.9
—
20
21
22
23
24
25
26
27
H
—
—
—
—
—
NH 70-Cl CF3
NH 70-Cl Br
40%
—
Boc
Ac
OH
OH
826
120
28
1.5
1.1
0.41
—
NH
NH
O
H
H
H
H
CF3
Br
1.4c
1.1c
1.4c
—
—
—
MeSO2 OH
60%
—
H
H
H
H
H
1800
900
100
23
CF3
Br
—
—
Boc
Ac
—
—
—
O
0.81
0.95
MeSO2
72%
a Average of 4–6 determinations.
b a1a % inhibition values at 1 lM were determined by Cerep, SA.
a Average of 4–6 determinations.
b a1a % inhibition values at 1 lM were determined by Cerep, SA.
c Single determination.

2212
C. A. Grice et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2209–2212
Table 4. Effect of varying the headgroup on cathepsin S activity
3. Shi, G.-P.; Villadangos, J. A.; Dranoff, G.; Small, C.; Gu,
L.; Haley, K. J.; Riese, R.; Ploegh, H. L.; Chapman, H. A.
Immunity 1999, 10, 197; Nakagawa, T. Y.; Brissette, W.
H.; Lira, P. D.; Griffiths, R. J.; Petrushova, N.; Stock, J.;
McNeish, J. D.; Eastman, S. E.; Howard, E. D.; Clarke, S.
R. M.; Rosloniec, E. F.; Elliott, E. A.; Rudensky, A. Y.
Immunity 1999, 10, 207.
R3
N
Amine
N
OH
N
SO2Me
Entry Amines (Fig. 1) R3
CatS IC50 (nM) Ii IC50 (lM)
a
4. Thurmond, R. L.; Beavers, M. P.; Cai, H.; Meduna, S. P.;
Gustin, D. L.; Sun, S.; Almond, H. J.; Karlsson, L.;
Edwards, J. P. J. Med. Chem. 2004, 47, 4799; Kuntz, I. D.;
Blaney, J. M.; Oatley, S. J.; Langridge, R.; Ferrin, T. E. J.
Mol. Biol. 1982, 161, 269, The DOCK software suite of
programs is available from the University of California,
San Francisco, CA. DOCK 4.0 was used for this study.
5. Gustin, D. J.; Sehon, C. A.; Wei, J.; Cai, H.; Meduna, S.
P.; Khatuya, H.; Sun, S.; Gu, Y.; Jiang, W.; Thurmond,
R. L.; Karlsson, L.; Edwards, J. P. Bioorg. Med. Chem.
Lett. 2005, 15, 1687.
48
49
50
51
52
53
9
10
8
Br
Br
322
1775
30
—
—
CF3
Br
1.3
2.7b
0.93b
—
8
75
163
11
12
CF3
CF3 1700
a Average of four determinations.
b Single determination.
6. For the pharmacological characterization of a CatS
inhibitor from this series, see: Thurmond, R. L.; Sun, S.;
Sehon, C. A.; Baker, S. M.; Cai, H.; Gu, Y.; Jiang, W.;
Riley, J. P.; Williams, K. N.; Edwards, J. P.; Karlsson, L.
J. Pharmcol. Exp. Ther. 2004, 308, 268.
position are equipotent to analogs 42 and 43, further
supporting this hypothesis. Ring expansion of the oxa-
zine ring, as illustrated by compound 52, resulted in a
10-fold loss in enzymatic activity over compound 23.
Interestingly, these compounds show similar potency
in the cellular assay. Maintaining the benzylic substitu-
tion but increasing the aromaticity of the pendant group
with concomitant incorporation of a piperazine ring
resulted in a significant drop in enzymatic activity as
illustrated by compound 53.
7. Bunce, R. A.; Schilling, C. L., III Tetrahedron 1997, 53,
9477.
8. Abdel-Magid, A. F.; Carson, K. G.; Harris, B. D.; Marya-
noff, C. A.; Shah, R. D. J. Org. Chem. 1996, 61, 3849.
9. An alternative preparation of 1 was reported previously.
Ogawa, H.; Yamamura, Y.; Miyamoto, H.; Kondo, K.;
Yamashita, H.; Nakaya, K.; Chihara, T.; Mori, T.;
Tominaga, M.; Yabuuchi, Y. J. Med. Chem. 1993, 36,
2011.
10. Compounds 3, 6, and 7 were prepared using slight reagent
modifications of the procedures described in the patent
application. Bock, M. G.; Evans, B. E.; Willams, P. D.;
Anderson, P. S.; Freidinger, R. M.; Pettibone, D. J. PCT
Int. Appl. WO 9502405.
In conclusion, replacement of the N-arylpiperazine in
our original series of inhibitors with 4-(6,6-bicyclic) pip-
eridines resulted in the identification of several potent,
noncovalent CatS inhibitors. The incorporation of sub-
stituents on the remote aryl ring of the bicyclic head-
groups provided improved selectivity over the a1a
adrenergic receptor while maintaining CatS activity.
Several of these analogs have been selected for further
evaluation.
11. Preparation of compounds 4 and 5. Takai, H.; Obase, H.;
Nakamizo, N.; Teranishi, M.; Kubo, K.; Shuto, K.;
Kasuya, Y.; Shigenobl, K.; Hashikami, M.; Karashima,
N. Chem. Pharm. Bull. 1985, 33, 1116.
12. Preparation of compound 8. Takai, H.; Obase, H.;
Nakamizo, N.; Teranishi, M.; Kubo, K.; Shuto, K.;
Hashimoto, T. Chem. Pharm. Bull. 1985, 33, 1104.
13. Bell, I. M.; Erb, J. M.; Freidinger, R. M.; Gallicchio, S.
N.; Guare, J. P.; Guidotti, M. T.; Halpin, R. A.; Hobbs,
D. W.; Homnick, C. F.; Kuo, M. S.; Lis, E. V.; Mathre, D.
J.; Michelson, S. R.; Pawluczyk, J. M.; Pettibone, D. J.;
Reiss, D. R.; Vickers, S.; Williams, P. D.; Woyden, C. J.
J. Med. Chem. 1998, 41, 2146.
References and notes
1. Villandangos, J. A.; Bryant, R. A. R.; Deussing, J.;
Driessen, C.; Lennon-Dumenil, A.-M.; Riese, R. J.; Roth,
W.; Saftig, P.; Shi, G.-P.; Chapman, H. A.; Peters, C.;
Ploegh, H. L. Immunol. Rev. 1999, 172, 109.
2. Nakagawa, T. Y.; Rudensky, A. Y. Immunol. Rev. 1999,
172, 121.