Structure and activity relationships of tartrate-based TACE inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.06.104

The syntheses and structure-activity relationships of the tartrate-based TACE inhibitors are discussed. The optimization of both the prime and non-prime sites led to compounds with picomolar activity. Several analogs demonstrated good rat pharmacokinetics

Full text of DOI:10.1016/j.bmcl.2010.06.104

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4812–4815
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Structure and activity relationships of tartrate-based TACE inhibitors
a
a
b
a
b
Dansu Li a, , Janeta Popovici-Muller , David B. Belanger , John Caldwell , Chaoyang Dai , Maria David ,
Vinay M. Girijavallabhan b, Brian J. Lavey b, Joe F. Lee b, Zhidan Liu b, Rob Mazzola b, Razia Rizvi b,
Kristin E. Rosner a, Bandarpalle Shankar b, Jim Spitler b, Pauline C. Ting b, Henry Vaccaro b, Wensheng Yu b,
Guowei Zhou b, Zhaoning Zhu b, Xiaoda Niu c, Jing Sun c, Zhuyan Guo b, Peter Orth b, Shiying Chen c,
Joseph A. Kozlowski b, Daniel J. Lundell c, Vincent Madison b, Brian McKittrick b, John J. Piwinski a,
Neng-Yang Shih a, Gerald W. Shipps Jr. a, M. Arshad Siddiqui a, Corey O. Strickland b
*
a Department of Medicinal Chemistry, Merck Research Laboratories, Cambridge, 320 Bent Street, Cambridge, MA 02141, United States
b Department of Medicinal Chemistry, Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, NJ 07033, United States
c Department of Inflammation, Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, NJ 07033, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The syntheses and structure–activity relationships of the tartrate-based TACE inhibitors are discussed.
The optimization of both the prime and non-prime sites led to compounds with picomolar activity. Sev-
eral analogs demonstrated good rat pharmacokinetics.
Received 29 April 2010
Revised 15 June 2010
Accepted 21 June 2010
Available online 25 June 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
TACE inhibitor
Rheumatoid arthritis
Tartrates
Tumor necrosis factor-
a
(TNF-
a
) is a proinflammatory cytokine
tion of the prime and non-prime sites. Our goal was to improve
potency as well as to achieve acceptable bioavailability.
that plays a central role in several autoimmune disorders such as
rheumatoid arthritis (RA), Crohn’s disease, and psoriasis.1 The cur-
Our initial efforts focused on the design of the optimal group in
the S30 region, a binding site on the protein which has been found
to confer both selectivity and potency in other reported series.5 It
was discovered that switching the 2,4-disubstituted thiophene
ring (compound 2) to a 2,5-analog afforded similar activity (com-
pound 3). We decided to focus on compound 3 to further explore
the S30 region with modifications of the phenyl ring and the results
are depicted in Table 1. Addition of an ortho-chloro substituent
(3a) improved the potency, while either meta- or para-chloro sub-
stituents (3b and 3c) were not beneficial. Changing to an ortho-
methoxy group further improved the potency to 3 nM (3d). Het-
erocycles were also tolerated, since both the thiophene (3e) and
the imidazole (3f) analogs maintained similar activities as com-
pound 3. While the naphthalene compound 3g lost most of the
activity, the fused benzimidazoles (3h and 3i) had similar poten-
cies compared to 3d. The crystal structure of 3i is shown in Figure
2.6 Its binding mode is similar to what was reported4 earlier. As ex-
pected, the methylene linker directs the benzimidazole group to-
ward the S30 region.
rent success of anti-TNF-
a
biologics such as EnbrelÒ, RemicadeÒ,
and HumiraÒ in the treatment of RA has increased interest in dis-
covering an orally active small molecule inhibitor to modulate the
level of TNF-
One target of interest is TACE (TNF-
metalloprotease that releases the soluble 17-kDa form of TNF-
from membrane-bound pro-TNF- . A TACE inhibitor would have
the potential to treat RA by reducing the level of soluble TNF-a 2
a.
a
converting enzyme), the
a
a
.
Our focus was to identify an orally active and highly selective TACE
inhibitor.3
Recently, we disclosed a novel series of tartrate diamide TACE
inhibitors4 such as 1 (Fig. 1). A unique tridentate zinc binding mode
was revealed with the tartrate scaffold. Non-prime site amine
exploration identified 2-arylpyrrolidines as preferred moieties.
Addition of a benzyl group (compound 2) provided a substantial
potency gain compared to 1 by extending into the S30 region. Here-
in, we report our structure–activity relationship (SAR) investiga-
Synthesis of benzyl-linked aromatic thiophenes is exemplified
in Scheme 1 for compound 3a. Negishi7 coupling of commercially
available 4 with 2-chlorobenzylzinc chloride, followed by depro-
* Corresponding author. Tel.: +1 617 499 3533.
E-mail address: dansu.li@spcorp.com (D. Li).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.06.104

D. Li et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4812–4815
4813
Cl
Cl
Cl
O
OH
OH
O
OH
O
H
N
H
N
H
N
S
S
N
S
N
N
OH O
OH O
OH O
44% inhibition
Ki = 45 nM
Ki = 20 nM
at 500 nM
3
1
2
Figure 1.
Table 1
TACE Ki of thienyl-benzyl linked tartrate diamide analogs
Cl
R
O
OH
H
N
S
N
OH O
Compound
R
TACE Ki (nM)
3
20
Cl
3a
9.3
3b
3c
48
37
Cl
Cl
Figure 2. X-ray structure of compound 3i (stick) bound to TACE catalytic domain
(PDB code: 3LGP). The S10/S30 loop residues were removed in order to show the
inhibitor binding.
O
3d
3e
3f
3
S
N
11
37
Though several S30 motifs with improved potency were identi-
fied (3d, 3h, and 3i), it was decided to re-examine the SAR for
the non-prime amide around compound 3h. Heterocyclic analogs
of 2-phenylpyrrolidines4 were investigated and the results are
shown in Table 2. Of the pyridine compounds (12a–c), the 4-pyri-
dine (12b) was the less favored. While thiophene 12d was equipo-
tent to 3h, thiazole analog (12e) afforded a slightly less active
compound. The introduction of aminothiazole (12f) restored the
potency. Interestingly, isoindoline analogs 12g and 12h provided
compounds with excellent enzymatic activity. Although our efforts
to find an optimal group in the S30 region had greatly improved the
potency (compound 3 vs 12h), most of the compounds from this
series exhibited poor rat pharmacokinetics (PK) profiles.
In order to maintain good potency and gain oral bioavailability,
our efforts were redirected to further explore the SAR of the prime
site amide. A series of analogs was prepared to investigate whether
the thiophene moiety could be replaced with a six-membered ring
(Table 3). Compared to compound 3 (Fig. 1), the phenyl analog 13a
was less potent. To address whether this potency loss was due to a
different projection in the S30 pocket, biphenyl compounds 13b
and 13c were synthesized and had similar activities as compound
3. Next replacement of the benzene ring with a heterocycle was ex-
plored. Pyridine analog 13d showed significantly better biochemi-
N
3g
3h
3i
50% at 500 nMa
N
4
2
N
F3C
N
N
a
The data are reported as % inhibition.
tection gave amine 5, which reacted with acid 68 to afford com-
pound 3a after final acetonide deprotection.
The general synthesis of the amines for the nitrogen-linked
compounds (3f, 3h, and 3i) is described in Scheme 2. Protection
of 2-thiophenemethanamine (7) gave phthalimide 8, which was
converted to thienyl chloride 9 upon treatment with paraformalde-
hyde/HCl followed by zinc chloride.9 Alkylation with 2-methyl-
benzimidazole gave compound 10. Deprotection with hydrazine
hydrate yielded amine 11, from which 3h was prepared following
the procedures shown in Scheme 1.
Cl
O O
Cl
N
OH
O
O
HN
O
O
O
OH
H
N
6
c,
d
a, b
H2N
Cl
S
N
Br
S
S
4
OH O
Cl
3a
5
Scheme 1. Reagents and conditions: (a) 2-chlorobenzylzinc chloride, (t-Bu3P)2Pd, 95%; (b) 4 M HCl/dioxane, 90%; (c) acid 6, DIEA, DMF, HATU, 64%; (d) 90:10 TFA/water, rt,
87%.

4814
D. Li et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4812–4815
Table 3
O
TACE Ki of analogs with different prime site rings
O
a
b
H2N
N
R1
N
Cl
S
S
d
O
S
O
7
8
9
O
OH
R2
N
OH O
N
O
N
c
H2N
N
N
N
S
R1
R2
TACE Ki (nM)
S
O
Compound
10
11
Cla
70
H
13a
N
Scheme 2. Reagents and conditions: (a) monomethyl phthalate, EDC, HOBt, Et3N,
DCM, 67%; (b) paraformaldehyde, HCl, 0.5 M ZnCl2/THF, dioxane, 60 °C 78%; (c) 2-
13b
13c
H
H
22
17
methylbenzimidazole, NaI, Cs2CO3, DMF, 47%; (d) hydrazine hydrate, EtOH, DCM,
78%.
D,
H
N
H
N
Table 2
CN
TACE Ki of thienyl-benzimidazole tartrate diamide analogs
R2
13d
Cla
6
N
H
N
N
OH H
N
O
R1
N
S
OH O
13e
13f
13g
Cla
Cla
H
307
4
H
N
N
N
Compound
R1
R2
TACE Ki (nM)
H
N
CN
CN
CN
Cl
3h
CH3
CH3
CH3
CH3
4
12
N
N
H
N
N
N
12aa
12ba
12ca
12
36
8
H
N
13h
13i
H
H
2
N
N
N
H
N
315
CN
N
a
Racemic 3-Cl-phenylpyrrolidine.
N
N
S
of heterocycles (Table 4). The pyridine (14a and 14b) or thiophene
(14d and 14e) analogs afforded similar activity. As previously ob-
served, an increase in potency was obtained for compound 14c
(Ki = 5 nM) and 14f (Ki = 2 nM) with an ortho-substitution. The
isoxazole (14g) and thiadiazole (14h) analogs were more active
than the thiazoles (14i and 14j). The benzimidazole 14k and the
imidazole 14l analogs incurred a potency loss, however, switching
to the pyrazole 14m resulted in restoration of the activity to 4 nM.
In summary, the prime site amide modification led to compound
14m, which showed improved enzymatic potency and oral rat
PK10 (AUC = 4400 nM h at 10 mpk).
In an effort to block the potential metabolic oxidation of the
benzylic moiety, a methyl substituent was introduced as shown
in compound 15 (Ki = 0.86 nM). Only the R-orientation of the ben-
zylic methyl group shown in Figure 3 for 15 was tolerated as mod-
eling suggested that this methyl group may make favorable
hydrophobic interactions with the side chain of Val402. Both com-
pound 14m and 15 exhibit good selectivity against a panel of
metalloproteases (Table 5). Compound 15 also showed 20% bio-
availability in rat (Table 6).
12da
12ea
CH3
CH3
4
9
N
N
S
N
H2N
N
S
N
12f
CH3
2
12g
12h
N
CH3
CF3
0.5
0.2
N
a
Racemic 2-arylpyrrolidines.
cal potency than its regioisomer 13e. Changing the biaryl connec-
tion to an N-arylpiperidine afforded improved Ki (13f vs 13c), while
constraining the piperidine into a bicycle gave a slightly less active
compound 13g. Compound 13h with a (S)-methyl piperidine group
maintained good enzymatic potency whereas the (R)-methyl ana-
log 13i showed significantly reduced potency. Of the inhibitors
examined in Table 3, the biphenyl compound 13b showed moder-
ate rat PK,10 with a 6 h AUC of 1500 nM h after a 10 mpk oral dose
and it was consequently selected for further SAR profiling.
The synthesis of the prime site amine of 15 was accomplished
as shown in Scheme 3. Protection of (R)-1-phenylethanamine
(16) as the trifluoroacetamide, followed by iodination11 afforded
the corresponding intermediate 17, which underwent copper cata-
lyzed cross-coupling with pyrazole. Deprotection with lithium
hydroxide gave (R)-1-(4-(1H-pyrazol-1-yl)phenyl)-ethanamine
(19),8 which was then converted to the desired product 15 via
standard transformations.
Based on the observed potency gain with the benzimidazole
group in the S30 pocket (compound 3h), it was decided to investi-
gate replacement of the distal phenyl group in 13b with a variety

D. Li et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4812–4815
4815
Table 4
Table 6
TACE Ki of prime site biaryl tartrate diamide analogs
Rat pharmacokinetic parameters for 15
R1
PK parameters
R2
iv
O
OH
H
N
Dose (mg/kg)
Cl (mL/min/kg)
AUC (nM h)
3
35
3100
N
OH O
R1
H
R2
TACE Ki (nM)
po
Compound
14a
Dose (mg/kg)
t1/2 (h)
AUC (nM h)
F (%)
10
N
0.6
2100
20
36
15
14b
H
N
CN
14c
H
5
O
N
S
a
b
N
H
17
H2N
F3C
14d
14e
H
H
28
13
I
16
S
CN
S
O
H2N
N
F3C
14f
H
2
c
H
N
N
N
N
18
19
14g
14h
14i
14j
H
8
3
N
O
Scheme 3. Reagents: (a) TFAA, PhI(O2CCF3)2, I2, DCM, 55%; (b) CuI, Cs2CO3,
1,10-phenanthroline, DMA, 74%; (c) LiOH, MeOH, 84%.
Cla
Cla
Cla
S
N
N
N
S
S
18
74
References and notes
N
N
1. (a) Bradley, J. R. J. Pathol. 2008, 214, 149; (b) Palladino, M. A.; Bahjat, F. R.;
Theodorakis, E. A.; Moldawer, L. L. Nat. Rev. Drug Disc. 2003, 2, 736; (c) Newton,
R. C.; Decicco, C. P. J. Med. Chem. 1999, 42, 2295; (d) Newton, R. C.; Solomon, K.
A.; Covington, M. B.; Decicco, C. P.; Haley, P. J.; Friedman, S. M.; Vaddi, K. Ann.
Rheum. Dis. 2001, 60, 25.
2. (a) Black, R. A.; Rauch, C. T.; Kozlosky, C. J.; Peschon, J. J.; Slack, J. L.; Wolfson, M.
R.; Castner, B. J.; Stocking, K. L.; Reddy, P.; Srinivasan, S.; Melson, N.; Bioiani, N.;
Schooley, K. A.; Gerhart, M.; Davis, R.; Fitzner, J. N.; Johnson, R. S.; Paxton, R. J.;
March, C. J.; Cerretti, D. P. Nature 1997, 385, 729; (b) Moss, M. L.; Jin, S.-L.; Milla,
M. E.; Bickett, D. M.; Burkhart, W.; Carter, H. L.; Chem, W. J.; Clay, W. C.;
Didsbury, J. R.; Hassler, D.; Hoffman, C. R.; Kost, T. A.; Lambert, M. H.;
Leesnitzer, M. A.; McCauley, P.; McGeehan, F.; Mitchell, J.; Moyer, M.; Pahel, G.;
Rocque, W.; Overton, L. K.; Schoenen, R.; Seaton, T.; Su, J. L.; Becherer, J. D.
Nature 1997, 385, 733.
3. For recent reviews of TACE inhibitors see: (a) DasGupta, S.; Murumkar, P. R.;
Giridhar, R.; Yadav, M. R. Bioorg. Med. Chem. 2009, 17, 444; (b) Skotnicki, J. S.;
Levin, J. I. Ann. Rep. Med. Chem. 2003, 38, 153; (c) Moss, M. L.; Sklair-Tavron, L.;
Nudelman, R. Nat. Clin. Pract. Rheumatol. 2008, 4, 300.
4. Rosner, K. E.; Guo, Z.; Orth, P.; Shipps, G. W., Jr.; Belanger, D. B.; Chan, T. Y.;
Curran, P. J.; Dai, C.; Deng, Y.; Girijavallabhan, V. M.; Hong, L.; Lavey, B. J.; Lee, J.
F.; Li, D.; Liu, Z.; Popovici-Muller, J.; Ting, P. C.; Vaccaro, H.; Wang, L.; Wang, T.;
Yu, W.; Zhou, G.; Niu, X.; Sun, J.; Kozlowski, J. A.; Lundell, D. J.; Madison, V.;
McKittrick, B.; Piwinski, J. J.; Shih, N.-Y.; Siddiqui, M. A.; Strickland, C. O. Bioorg.
Med. Chem. Lett. 2010, 20, 1189.
5. (a) Levin, J. I.; Chen, J. M.; Cheung, K.; Cole, D.; Crago, C.; Santos, E. D.; Du, X.;
Khafizova, G.; MacEwan, G.; Niu, C.; Salaski, E. J.; Zask, A.; Cummons, T.; Sung,
A.; Xu, J.; Zhang, Y.; Xu, W.; Ayral-Kaloustian, S.; Jin, G.; Cowling, R.; Barone, D.;
Mohler, K. M.; Black, R. A.; Skotnicki, J. S. Bioorg. Med. Chem. Lett. 2003, 13,
2799; (b) Chen, X.-T.; Ghavimi, B.; Corbett, R. L.; Xue, C.-B.; Liu, R.-Q.;
Covington, M. B.; Qian, M.; Vaddi, K. G.; Christ, D. D.; Hartman, K. D.;
Ribadeneira, M. D.; Trzaskos, J. M.; Newton, R. C.; Decicco, C. P.; Duan, J. J.-W.
Bioorg. Med. Chem. Lett. 2007, 17, 1865.
6. RCSB protein data bank (PDB) deposition number: 3LGP.
7. Negishi, E; Handbook of Organopalladium Chemistry for Organic Synthesis
2002, 1, 229.
8. Guo, Z.; Orth, P.; Zhu, Z.; Mazzola, R. D.; Chan, T.-Y.; Vaccaro, H. A.; McKittrick,
B.; Kozlowski, J. A.; Lavey, B. J.; Zhou, G.; Paliwal, S.; Wong, S.-C; Shih, N.-Y;
Ting, P. C.; Rosner, K. E.; Shipps, G. W., Jr.; Siddiqui, M. A.; Belanger, D. B.; Dai,
C.; Li, D.; Girijavallabhan, V. M.; Popovici-Müller, J.; Yu, W.; Zhao, L. WO 2005/
121130 (US 2006/0252778).
14k
Cla
296
N
N
Cla
Cla
270
4
N
14l
N
N
14m
a
Racemic 3-Cl-phenylpyrrolidine
Cl
N
N
O
N
OH
H
N
OH O
15
Figure 3. Compound 15.
Table 5
Selectivity data for 14m and 15
Ki (
l
M)
14m
15
TACE
0.004
0.602
>100
1.9
19
47
11
3.5
0.12
0.00086
0.166
>100
43.6
—
ADAM10
MMP1
MMP2
MMP3
MMP7
MMP9
MMP13
MMP14
3.8
88.4
3.3
1.1
We explored the SAR of both the prime and non-prime site
9. Feigel, M.; Lugert, G.; Heichert, C. Liebigs Ann. Chem. 1987, 4, 367.
10. Description of the rat PK studies: Following an overnight fast, two male
Sprague–Dawley rats (Charles River, Co.) were dosed orally at a dose of 10 mg/
kg. Blood was collected into heparin-containing tubes serially from each
animal at 0.5, 1, 2, 3, 4, and 6 h post-dosing and centrifuged to generate
plasma. Samples at each time point collected from two rats were pooled for LC/
MS/MS analysis.
11. Tagat, J. R.; Steensma, R. W.; McCombie, S. W.; Nazareno, D. V.; Lin, S.-I.;
Neustadt, B. R.; Cox, K.; Xu, S.; Wojcik, L.; Murray, M. G.; Vantuno, N.; Baroudy,
B. M.; Strizki, J. M. J. Med. Chem. 2001, 44, 3343.
amides, which successfully led to potency improvements with
two series of TACE inhibitors. Moreover, compound 15 was shown
to be potent, selective over a panel of MMPs and orally available in
rats. These improvements demonstrate that the tartrate moiety is a
viable zinc-coordinating motif. Additional efforts towards further
improving potency and oral bioavailability of this series will be dis-
cussed in future publications.