A series of thiazole derivatives bearing thiazolidin-4-one as non-competitive ADAMTS-5 (aggrecanase-2) inhibitors

Article abstract of DOI:10.1016/j.bmcl.2013.01.121

A series of thiazole bearing thiazolidin-4-one was discovered via high-throughput screening as non-competitive inhibitors of ADAMTS-5. Compound 31 appeared to give the best ADAMTS-5 inhibition and good selectivity over other metalloproteases.

Full text of DOI:10.1016/j.bmcl.2013.01.121

Accepted Manuscript
A series of thiazole derivatives bearing thiazolidin-4-one as non-competitive
ADAMTS-5 (Aggrecanase-2) inhibitors
Masakazu Atobe, Naomi Maekawara, Noriko Ishiguro, Shinya Sogame,
Yoshihito Suenaga, Masashi Kawanishi, Hiroko Suzuki, Norimasa Jinno, Eiichi
Tanaka, Shiro Miyoshi
PII:
S0960-894X(13)00154-6
DOI:
http://dx.doi.org/10.1016/j.bmcl.2013.01.121
BMCL 20109
Reference:
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date:
Revised Date:
Accepted Date:
27 November 2012
24 January 2013
28 January 2013
Please cite this article as: Atobe, M., Maekawara, N., Ishiguro, N., Sogame, S., Suenaga, Y., Kawanishi, M., Suzuki,
H., Jinno, N., Tanaka, E., Miyoshi, S., A series of thiazole derivatives bearing thiazolidin-4-one as non-competitive
ADAMTS-5 (Aggrecanase-2) inhibitors, Bioorganic & Medicinal Chemistry Letters (2013), doi: http://dx.doi.org/
10.1016/j.bmcl.2013.01.121
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A series of thiazole derivatives bearing
thiazolidin-4-one as non-competitive
ADAMTS-5(Aggrecanase-2) inhibitors
Leave this area blank for abstract info.
Masakazu Atobe,* Naomi Maekawara, Noriko Ishiguro, Shinya Sogame, Yoshihito Suenaga, Masashi
Kawanishi, Hiroko Suzuki, Norimasa Jinno, Eiichi Tanaka, and Shiro Miyoshi.

Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com
A series of thiazole derivatives bearing thiazolidin-4-one as non-competitive
ADAMTS-5 (Aggrecanase-2) inhibitors
Masakazu Atobe, Naomi Maekawara, Noriko Ishiguro, Shinya Sogame, Yoshihito Suenaga, Masashi
Kawanishi, Hiroko Suzuki, Norimasa Jinno, Eiichi Tanaka and Shiro Miyoshi.
Pharmaceutical Research Center, Asahi Kasei Pharma Corporation, 632-1 Mifuku, Izunokuni-shi, Shizuoka 410-2321, Japan
ARTICLE INFO
ABSTRACT
A series of thiazole bearing thiazolidin-4-one was discovered via high-throughput screening as
non-competitive inhibitors of ADAMTS-5. Compound 31 appeared to give the best ADAMTS-5
inhibition and good selectivity over other metalloproteases.
Article history:
Received
Revised
Accepted
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
ADAMTS-5
thiazole
thiazolidin-4-one
non-competitive inhibitor
osteoarthritis
bidentate zinc chelators such as hydroxamic acid6, reverse
hydroxamamate7, carboxylic acid8 and other structures9. However,
in the development of new therapeutic agents targeting
ADAMTS-5, there remains considerable room for new structural
classes not coordinating the active site zinc atom.
On screening our in-house compound library, a thiazole
bearing thiazolidin-4-one 1 was identified as having potent
inhibitory activity against ADAMTS-5 (Fig. 1).
Osteoarthritis (OA) is
a
degenerative joint disease
characterized by loss of joint cartilage and bone thickening,
possibly leading to bony outgrowths1. The prevalence of OA
globally is 11.3%, or approximately 85 million people, and this is
expected to increase from 85 million in 2009 to 122 million in
2017. A significant increase in OA incidence has occurred in
recent years2.
The pathogenesis of OA is poorly understood, but a major
feature is the loss of two most important components of cartilage
extracellular matrix (ECM); Type II collagen and aggrecan.
Aggrecan loss resulting from decreased synthesis by
chondrocytes and activation of enzymes that degrade cartilage is
recognized as one of the earliest processes in the course of OA;
thus aggrecan appears to have an additional role in collagen
protection from degradation3. Therefore, inhibition of
aggrecanases has evolved as a potential drug target for treatment
of OA. Recent evidence that ADAMTS-5 knockout mice are
protected from cartilage destruction in OA model shows that
ADAMTS-5 may have a major role in OA4. Furthermore, AGG-
523, a specific aggrecanase inhibitor developed by Pfizer,
reduced the release of aggrecanase-generated aggrecan fragments
into rat joints in a rat model of meniscal tear-induced joint
instability5. Thus, ADAMTS-5 inhibitors may protect cartilage
from OA progression. The vast majority of reported ADAMTS-5
Compound 1 was then tested for its ability to inhibit
ADAMTS-4, -13, MMP-2, -3, 14 and TACE10. As listed in Table
1, 1 showed excellent ADAMTS-5 selectivity over other Zn
metalloproteases.
i—nh—ibit—ors can be viewed as zinc chelating compounds via
 Corresponding author. Tel.: +81-558-76-8493; fax: +81-558-76-5755; e-mail: atobe.mb@om.asahi-kasei.co.jp

Based on studies in MMP-211, -312 and -1413 knockout mice,
inhibition of MMP-2, -3 and -14 appears to facilitate
proteoglycan degradation. In addition, investigation of
ADAMTS-4 knockout mice confirmed that ADAMTS-4 is not
responsible for aggrecan degradation in murine osteoarthritis14.
ADAMTS-13 cleaves the Tyr1605-Met1606 bond of a von
Willebrand factor subunit and plays a key role in the
pathogenesis of thrombotic thrombocytopenic purpura15.
Furthermore, TACE-deficient mice die shortly after birth16.
Therefore, we reasoned that a selective ADAMTS-5 inhibitor
would constitute an ideal OA therapeutic agent.
Next, we speculated that mode of ADAMTS-5 inhibition
elicited by compound 1 differs from that of known competitive
inhibitors. Indeed, Lineweaver-Burk plot analysis showed that 1
is a non-competitive inhibitor (Fig. 2). Therefore, we focused on
investigating the structure-activity relationships (SAR) to
results suggested that thiazolidin-4-one forms strong interactions
with ADAMTS-5.
In the SAR exploration of the phenyl group at the 4-position of
the thiazole ring (Table 3), replacement of the hydroxyl group
decreased ADAMTS-5 inhibition. Optimal R2 substituents are
seen in 10 (4-Cl-phenyl IC50: 6.4 M), 11 (4-Me-phenyl IC50:
0.72 M) and 12 (4-MeO-phenyl IC50: 1.0 M). Biphenyl moiety
13 appears to give increased ADAMTS-5 inhibition (IC50: 0.43
M). We prepared compounds bearing 2-thiophene 14 and 5-
bromo-2-thiophene 15 and found that these compounds had
decreased ADAMTS-5 activity. However, a compound bearing
3-bromo-2-thiophene 16 showed improved ADAMTS-5 activity
(IC50: 0.47 M); ortho substitution was favored over para. The
best compounds were in this series; 2-pyridine 17 and 4-bromo
pyridine 18 appeared to provide more potent inhibition with IC50
values of 0.4 M or 0.84 M.
optimize this lead compound.
3.0000
2.5000
(3 M)
2.0000
1.5000
(1.5 M)
1.0000
(0 M)
0.5000
0.0000
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
-0.5000
-1.0000
1/[s] (1/mM)
Figure 2: Lineweaver-Burk plot analysis the inhibition of ADAMTS-5 by 1
Our initial investigation focused on replacement of
thiazolidin-4-one (Table 2). When R1 = H (2), 3-pyridyl (3), R1 =
(4), 3,5-dimethyl-4-isoxazolyl (5) or 2-methyl-5-thiazolyl (6), no
ADAMTS-5 inhibition was seen. The corresponding 3-methyl 2-
benzimidazolyl analog (7) and 4-methyl 2-thiazolyl analog (8)
showed moderate ADAMTS-5 inhibition (2.8 or 2.9 M). These
SAR of the carboxymethyl groups at the 5-position on the
thiazole was investigated (Table 4). When R3 = H (19),
ADAMTS-5 inhibition was decreased. When R3 = Me (20), R3 =
Et (21), R3 = iPr (22) and R3 = n-Pr (23), ADAMTS-5 inhibition
was retained. N,N-dimethylamide group (24) showed decreased
ADAMTS-5 activity. We prepared demethyl carboxyl group (25),

2-methyl analog (26), carboxyethyl group (27) and carboxyl-
propyl group (28), and found that 27 showed the most potent
ADAMTS-5 activity.
Compound 31 was tested for its ability to inhibit ADAMTS-4
and -13, MMP-2, -3 and -14 and TACE. As shown in Table 6, 31
showed excellent ADAMTS-5 selectivity over other
metalloproteases. The in vitro ADME profile of 31 was also
determined. Compound 31 was found to be intrinsically stable in
plasma (human CLint: 2.7 ml/min/kg; rat CLint: 0 ml/min/kg).
31 displayed moderate apparent permeability as measured by flux
through MDCK cells in transwell culture (A/B Papp = 5.55 × 10-6
cm/s).
Ex vivo cartilage explant studies using compound 31 were then
performed17. As a positive control, the published multi-MMP
inhibitor 1-benzyl-4-((4-(4-chlorophenoxy) phenyl)-sulfonyl)-N-
hydroxypiperidine-4-carboxamide (33, Figure 4)18, which has an
IC50 of 0.42 M against ADAMTS-5 and 1.0 M against
ADAMTS-4, demonstrated highly potent activity in the surgical
OA rabbit model at 15 mg/kg. This compound was shown to
inhibit spontaneous aggrecan degradation in IL-1-stimulated
bovine cartilage (91% inhibition at 10 M), and compound 31
showed 66% inhibition at 10 M (IC50: 22 M). These data
support the hypothesis that protection of cartilage aggrecan leads
to preservation of aggrecanase activity (Fig. 3).
We then focused on optimization of 27 derivatives by a
combination of substituents at the 4-position of the thiazole ring
(Table 5). Optimal R4 substituents are seen in 29 (biphenyl IC50:
0.43 M), 30 (4-bromo-thiophene IC50: 0.72 M) and 32 (4-
bromo-pyridine IC50: 0.63 M). Finally, compounds bearing
pyridine (31) appeared to give the best ADAMTS-5 inhibition
(IC50: 0.23 M).
The synthesis of thiazole derivatives (5-18 and 21-32) is
shown in Scheme 1-6. Compounds 1-4, 19 and 20 were
commercially available. As shown in Scheme 1, reaction of 3-
bromo-4-oxo-4-phenylbutanoic acid derivatives 34a-j and
arylmethyl thioamide 35a-e in ethanol under reflux (Hanzsch
reaction) produced thiazoleacetate 36a-m, followed by
hydrolysis to give 5-8, 10-14 or 25-29.

reagent at -78oC resulted in the formation of -ketoester 45. C-
alkylation with the appropriate bromide and NaH and then
decarboxylation of 47 under acidic conditions gave ketone 48.
Bromination and Hanzsch reaction led to a thiazole ring,
followed by hydrolysis to give 18 or 32.
Compound 9 was prepared by condensation reaction between
2-mercaptosuccinic acid 37 and nitrile 38 (Scheme 2).
As shown in Scheme 5, Compound 21-23 was prepared by
Hanzsch reaction.
As shown in Scheme 3, commercially available carboxylic
acid 39a-f was esterified to give the ethyl ester 40a-f, which
underwent bromine-mediated bromination to provide 41a-f.
Hanzsch reaction with 35a and basic hydrolysis provided 15-17,
30 or 31.
Scheme 6 shows the synthesis of 24 via amidation of 1 under
peptide formation conditions.
In conclusion, we presented a series of thiazoles bearing
thiazolidin-4-one as non-competitive inhibitors of ADAMTS-5.
Compound 31 appeared to give the best ADAMTS-5 inhibition
and good selectivity over other metalloproteases. 31 was also
shown to inhibit the spontaneous aggrecan degradation in IL-1-
stimulated bovine cartilage. The continued development of
selective ADAMTS-5 inhibitors is currently underway and will
be reported in the near future.
Compounds 18 and 32 were synthesized according to Scheme
4. The reaction between 5-bromopicolinic acid (43) and
carbodiimidazole, and the subsequent reaction with lithium

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