Identification of potent and selective TACE inhibitors via the S1 pocket

Article abstract of DOI:10.1016/j.bmcl.2006.10.004

By focusing on the P1 portion of the piperidine β-sulfone ligands we identified a motif that induces selectivity and resulted in a series of TACE inhibitors that demonstrated excellent in vitro potency against isolated TACE enzyme and excellent selectivity over MMPs 1, 2, 9, 13, and 14.

Full text of DOI:10.1016/j.bmcl.2006.10.004

Bioorganic & Medicinal Chemistry Letters 17 (2007) 34–39
Identification of potent and selective TACE inhibitors
via the S1 pocket
Jeffrey S. Condon,a Diane Joseph-McCarthy,a Jeremy I. Levin,c Henry-Georges Lombart,a
Frank E. Lovering,a,* Linhong Sun,b Weiheng Wang,a Weixin Xua and Yuhua Zhangb
aChemical and Screening Sciences, Wyeth Research, 200 Cambridge Park Drive, Cambridge, MA 02140, USA
bInflammation, Wyeth Research, 200 Cambridge Park Drive, Cambridge, MA 02140, USA
cChemical and Screening Sciences, Wyeth Research, 401 N. Middletown Road, Pearl River, NY 10965, USA
Received 22 August 2006; revised 2 October 2006; accepted 3 October 2006
Available online 5 October 2006
Abstract—By focusing on the P1 portion of the piperidine b-sulfone ligands we identified a motif that induces selectivity and resulted
in a series of TACE inhibitors that demonstrated excellent in vitro potency against isolated TACE enzyme and excellent selectivity
over MMPs 1, 2, 9, 13, and 14.
Ó 2006 Elsevier Ltd. All rights reserved.
TNF-a converting enzyme (TACE) is the protease
responsible for the release of soluble tumor necrosis
factor-a (TNF-a) from its parent membrane bound
pro-TNF-a.1–4 TNF-a is an important cytokine that
mediates the immuno-inflammatory responses of other
pro-inflammatory cytokines. These cytokines have been
linked to the pathogenesis of rheumatoid arthritis (RA)
and are involved in promoting inflammation as well as
bone and cartilage destruction. That TNF-a is an ideal
target for pharmaceutical intervention in the treatment
of RA has been demonstrated by the success of TNF-
a monoclonal antibodies (Remicade) and TNF-soluble
receptors (Enbrel).5,6 Herein we report on our progress
toward potent and selective small-molecule inhibitors
of TACE with the goal of inhibiting the production of
soluble TNF-a.
However, reports of selectivity-inducing inhibitor
modifications in areas other than the P10 group have
been less frequent.
We have recently disclosed a 4,40-piperidine b-sulfone
hydroxamate inhibitor (E) that shows good selectivity
for TACE over MMPs 1, 2, 9, 13, and 14 due to its ste-
rically bulky isopropyl sulfonamide P1 group.18 We now
report the extension of that work to the design and syn-
thesis of several additional highly selective TACE inhib-
itors through the systematic variation of P1 substituents
at the piperidine nitrogen. It is noteworthy that neither
the b-piperidine sulfone hydroxamate scaffold, nor the
P10 butyne is responsible for this selectivity as illustrated
by the broad spectrum inhibitory activity of compounds
C and D.8,19 As past efforts from our labs9,18 indicate,
gaining selectivity against MMP-2 and MMP-13 is more
challenging than MMPs 1, 9, and 14, and we have fo-
cused our screening paradigm on those more challenging
MMPs.20
Studies from our labs7–10 (C, Fig. 1) and others11 illus-
trate the difficulty of gaining selectivity for TACE over
various MMPs. Historically the design of selective
TACE inhibitors has focused on the S10 pocket for
increasing selectivity over the MMPs.11,12 As a result
of these efforts highly TACE-specific inhibitors have
been disclosed that take advantage of protein–inhibitor
interactions in this region (A and B, Fig. 1).13–17
Initial efforts focused on the exploration of alkyl sulfon-
amide variants of E that were prepared as outlined in
Scheme 1.21 While all of the compounds in Table 1 are
active against TACE, only a few followed the pattern
of selectivity established by compound E. Of the alkyl
sulfonamides, 1–9, only cyclopropyl sulfonamide (7)
proved to be >100-fold selective for TACE over
MMP-2 and -13. We were surprised to discover that
compound 6, a morpholine-substituted analog of E,
Keywords: Inflammation; TACE; Rheumatoid arthritis.
*
Corresponding author. Tel.: +1 617 665 5612; fax: +1 617 665
5685; e-mail: flovering@wyeth.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.10.004

J. S. Condon et al. / Bioorg. Med. Chem. Lett. 17 (2007) 34–39
35
Figure 1. Recently published MMP/TACE inhibitors.
O2
S
HOHNOC
O
Method A
N
S
R
O2
S
CO2Et
O
O
EtO2C
O
1 - 4
N
H
N
O2
S
HOHNOC
O
Boc
Methods B, C,
D, E, F
N
R
Scheme 1. Reagents and conditions: (1) di-tert-butyl dicarbonate, THF; (2) a—LDA, THF; b—CH2I2; (3) a—4-mercaptophenol, K2CO3, DMF; b—
m-CPBA, CH2Cl2; (4) 1-bromo-2-butyne, Cs2CO3, DMF. Method A: (i) NaOH, THF, MeOH; (ii) BOP, t-Bu–ONH2, DMF, Cs2CO3; (iii) TFA,
CH2Cl2; (iv) RSO2Cl, CH2Cl2, NaHCO3 (satd aq); (v) TFA, 45 °C. Method B: (i) TFA, CH2Cl2; (ii) tert-butylsulfinyl chloride, NaHCO3 (satd aq),
CH2Cl2; (iii) m-CPBA, CH2Cl2; (iv) NaOH, THF, MeOH; (v) BOP, H2NOH, DMF, Et3N. Method C: (i) TFA, CH2Cl2; (ii) 2-chloro-1-ethane-
sulfonyl chloride, Et3N, THF; (iii) morpholine, n-BuOH, 90 °C; (iv) NaOH, THF, MeOH; (v) BOP, H2NOH, DMF, Et3N. Method D: (i) TFA,
CH2Cl2; (ii) 1-chloropropane-2-sulfonyl chloride, Et3N, THF; (iii) morpholine, n-BuOH, 100 °C; (iv) NaOH, THF, MeOH; (v) BOP, H2NOH,
DMF, Et3N. Method E: (i) NaOH, THF, MeOH; (ii) BOP, t-Bu–ONH2, DMF, Et3N; (iii) TFA, CH2Cl2; (iv) ArBr or ArCl, i-Pr2EtN, DMA,
microwave, 140 °C; (v) TFA, 45 °C. Method F: (i) NaOH, THF, MeOH; (ii) BOP, t-Bu–ONH2, DMF, Et3N; (iii) TFA, CH2Cl2; (iv) SO2Cl2,
CH2Cl2, ꢀ90 °C, amine, i-Pr2EtN; (v) TFA, 45 °C.

36
J. S. Condon et al. / Bioorg. Med. Chem. Lett. 17 (2007) 34–39
Table 1.
O
O
S
O
HO
N
O
H
N
R
Compound
Method
R
TACEa
MMP-2a
MMP-13a
E
—
B
SO2CHMe2
SO2–tert-butyl
1.5
<1
355
73
230
238
295
136
72
1
2
3
A
A
A
C
D
A
A
A
E
SO2CH2–4-pyridine
SO2CHEt2
SO2CH2–cyc-C6H11
2.0
1.2
<1
82
58
4
11
37
5
SO2CH2CH2–N-morpholine
SO2CH(Me)CH2–N-morpholine
SO2–cyc-C3H5
2.2
1.4
1.6
1.3
2.8
1.33
5.6
43
6
37
130
1159
155
24.4
205
2040
7
161
54
8
SO2–cyc-C5H9
SO2–cyc-C6H11
9
4
10
11
2-Pyridine
4-Pyridine
62.6
2058
E
O
N
12
E
E
1.1
<1
40
56
N
N
13
176
166
a IC50 (nM).
Table 2.
showed poor selectivity. Contrary to expectations, the
MMP selectivity of the alicyclic sulfonamides 7–9 dimin-
ishes as the cycloalkyl ring size expands.
O
O
S
O
HO
N
H
O
Selective inhibitors were also accessed through heteroa-
ryl piperidine N-arylation (compounds 10–13, Table 1).
Although the 4-pyridyl derivative 11 is somewhat less
active against TACE than the corresponding 2-pyridyl
analog 10, it achieves >300-fold selectivity over both
MMP-2 and MMP-13. The benzoxazole 12 is not excep-
tionally selective over the MMPs, but the addition of a
flanking methyl group in benzimidazole 13 boosts selec-
tivity to >100-fold while retaining potency against
TACE.
N
O S O
R
Compounda
R
TACEb
MMP-2b
664
MMP-13b
2277
N
O
14
2.2
N
N
15
16
17
18
19
<1
99.5
19
385
147
—
Heterocyclic sulfonamides were also investigated (com-
pounds 14–19, Table 2). The best of these proved to
be the 3,5-dimethyl isoxazole (14) that demonstrated
>300-fold selectivity against MMPs 2 and 13. A similarly
sterically encumbered analog, the dimethyl pyrazole 15,
is at least 100-fold selective for TACE. Contrast this to
compounds 18 and 19, each having a single substituent b
to the sulfonamide. Both have greater potency against
MMP-2 and MMP-13 than 14, but their exceptional
potency against TACE precludes accurate assessment
of their selectivity. When there are no substituents b to
the sulfonamide (compounds 16 and 17), selectivity is
greatly reduced.
N
3.0
7
N
Cl
S
33
Cl
S
<1
22
23
Cl
N
<1
32
38
S
a Compounds prepared via Method A.
b IC50 (nM).
The X-ray structure of compound 14 bound to TACE
(PDB entry 2I4722) illustrates how the dimethyl isoxaz-
ole ring is accommodated by TACE. Modeling23 of 14
to an X-ray structure of MMP-13 (1ZTQ22,24) (Fig. 2),
we observe the isoxazole ring popping out of the S1
pocket, leaving it largely solvent exposed. This is due
to the somewhat larger and more hydrophobic MMP-
13 Tyr 151 residue replacing Lys 315 of TACE. As such,
Tyr 151 cannot readily adopt a conformation that

J. S. Condon et al. / Bioorg. Med. Chem. Lett. 17 (2007) 34–39
37
Sulfamides 21–24 derived from cyclic amines were also
approximately 100-fold selective over MMP-13, but
were less selective over MMP-2. Compounds 25 and
26, with the additional functionality flanking the
sulfamide nitrogen, both attained the desired level of
selectivity over MMP-13, and the pyrrolidinol deriva-
tive 26 was also more than 100-fold selective over
MMP-2. Unfortunately, analogs of 26 prepared from
2,5-disubstituted
inaccessible.
pyrrolidines
proved
to
be
Despite the fact that there was now ready access to
TACE-selective piperidine sulfone hydroxamates
through variations of the P1 moiety, preparing inhib-
itors with substantial potency in human whole blood
(HWB) was a complicating issue. Of compounds 1–
26, only sulfamides 21 and 26 had IC50s of better than
2 lM in human whole blood. Previously, we reported
that the 4-picolyl derivative F and 4-pyridyl amide G
had promising activity in the HWB assay,18 with
IC50s of 2.7 and 1.3 lM, respectively, though they
lacked selectivity over MMP-2 and -13. We therefore
sought to synthesize 3,5-disubstituted pyridyl analogs
of F and G in an effort to enhance their selectivity
profiles while retaining HWB activity. Compounds
27 and 28 were prepared according to Methods G
and H (Scheme 2), respectively (see Table 4). We were
gratified to find that each of these now possessed
>100-fold selectivity against MMP-2 and -13, demon-
strating that the effect of the P1 group on selectivity
applies to alkyl and amide linkages as well. Further-
more, we were gratified to see that compound 28
did retain its 1.3 lM IC50 in the HWB assay,
validating this approach.
Figure 2. Superposition of the X-ray structure of compound 14 bound
to TACE (carbons shown in green) and a model of compound 14
bound to MMP-13 (carbons in purple). The ligands and residue
differences between TACE and MMP-13 in the S1 pocket are shown in
thick stick representation; zinc is shown in a space-filling model in
white.
allows the isoxazole ring to effectively bind in the MMP-
13 S1 pocket. Further steric clashes of compound 14
bound to MMP-13 can also be seen between an isoxaz-
ole methyl and Leu 159 (Thr 347 in TACE); this also
destabilizes the 14–MMP-13 interactions.
Having identified b,b0-disubstitution of the substituent
borne by the P1 sulfonamide of the piperidine ring as
a motif that supplied selectivity, we next prepared a
series of sulfamide derivatives 20–26 (Table 3) accord-
ing to Method F of Scheme 1. Thus, compound 20
was conceived as a direct mimetic of isopropyl sulfon-
amide E and had selectivity comparable to E over
MMP-13, but was only 30-fold selective over MMP-2.
In summary, we have disclosed an approach for increas-
ing the selectivity of 4,40-piperidine b-sulfone hydroxa-
mate inhibitors for TACE over MMP-2 and MMP-13
by manipulating the P1 substituent. The incorporation
of steric bulk adjacent to the attachment point of the
P1 group to the piperidine nitrogen, as exemplified best
Table 3.
O
O
S
O
HO
N
H
O
N
O S O
R
Compounda
R
TACEb
MMP-2b
MMP-13b
20
21
22
23
24
NMe2
N-Morpholine
N-Piperidine
1.8
1.0
1.2
1.0
1.5
61.3
51
229
195
144
117
104
51
31
N-Pyrrolidine
1-(4-N-Acetyl)piperazine
20
N
25
26
1.5
1.4
58
190
354
OMe
N
172
OH
a Compounds 21–26 prepared via Method F.
b IC50 (nM).

38
J. S. Condon et al. / Bioorg. Med. Chem. Lett. 17 (2007) 34–39
O2
S
O2
S
HOHNOC
O
t-Bu-OHNOC
O
Methods G and H
N
R
N
H
Scheme 2. Reagents and conditions: Method G: (i) 2,6-dichlorobenzaldehyde, NaBH(OAc)3, CH2Cl2; (ii) TFA, 45 °C. Method H: (i) 2,6-
dichlorobenzoic acid, BOP, Et3N, DMF; (ii) TFA, 45 °C.
Table 4. Hybridization of selectivity-inducing motifs
O
O
S
O
HO
N
O
H
N
R
Compound
R
TACEa
MMP-1a
MMP-2a
MMP-9a
MMP-13a
MMP-14a
F
CH2–4-Pyridine
C(O)–4-Pyridine
2.1
2.6
7,250
3,010
77
46
—
114
784
583
G
191
21.5
N
O
14
2.2
1.6
1.7
37,300
2,680
664
555
183
5500
920
—
2277
259
24,000
14,800
Cl
27b
28c
N
Cl
Cl
O
449
N
Cl
a IC50 (nM).
b Method G.
c Method H.
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