Enhanced selectivity profile of pyrazole-urea based DFG-out p38α inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.06.073

By targeting an extended region of the conventional 'DFG-out' pocket of p38α, while minimizing interactions with the specificity pocket and eliminating interactions with the adenine binding site, we are able to design and synthesize a number of pyrazole-u

Full text of DOI:10.1016/j.bmcl.2010.06.073

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4885–4891
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Enhanced selectivity profile of pyrazole-urea based DFG-out p38
a
inhibitors
a
a
b
b
a
Hu Liu a, , Cyrille Kuhn , Frederic Feru , Suzanne L. Jacques , Gayatri D. Deshmukh , Ping Ye ,
*
Glen R. Rennie a, Theresa Johnson a, Steven Kazmirski c, Simon Low c, Rocco Coli b, Yuan-hua Ding c,
Alan C. Cheng a, Haile Tecle a, Jessie M. English b, Robert Stanton a, Joe C. Wu b,
*
a Department of Chemistry, Cambridge South Laboratories, Pfizer Inc., 620 Memorial Drive, Cambridge, MA 02139, USA
b Department of Biochemistry, Cambridge South Laboratories, Pfizer Inc., 620 Memorial Drive, Cambridge, MA 02139, USA
c Department of Structural Biology, Cambridge South Laboratories, Pfizer Inc., 620 Memorial Drive, Cambridge, MA 02139, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
By targeting an extended region of the conventional ‘DFG-out’ pocket of p38a, while minimizing interac-
tions with the specificity pocket and eliminating interactions with the adenine binding site, we are able to
Received 11 April 2010
Revised 11 June 2010
Accepted 14 June 2010
Available online 17 June 2010
design and synthesize a number of pyrazole-urea based DFG-out p38
and excellent selectivity.
a inhibitors with good potencies,
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Kinase inhibitor
p38
Pyrazole-urea
DFG-out
Mitogen-activated protein kinases (MAPKs) are important com-
ponents of signal transduction pathways that mediate cell prolifer-
ation, differentiation, and death.1 p38 is a critical member of this
family and is important in enabling the production of pro-inflam-
matory cytokines such as TNF and IL-1.2 Injectable biologic thera-
pies that bind and inactivate TNF are effective treatments for
rheumatoid arthritis and psoriasis.3 Consequently, inhibition of
p38 with a small molecule kinase inhibitor could provide an effec-
tive oral therapy for the chronic treatment of these autoimmune
diseases. This belief is further evidenced by the fact that several
industry, largely due to the clinical and subsequent commercial
success of DFG-out inhibitors such as imatinib8 for cABL kinase
(Novartis), and sorafenib9 for Raf kinase (Bayer, Scheme 1). Among
p38 inhibitors,
doramapimod (BIRB796, Scheme 1).10 BIRB796 is a NCKI that binds
to p38
in the DFG-out mode,11 and was discontinued from further
a notable example is Boehringer Ingelheim’s
a
development in phase II. While the reason for BIRB796’s failure in
the clinic is not apparent from the literature, we suspect lack of
selectivity might be culpable. We believe that p38 inhibitors with
further enhanced margins of selectivity against other kinases
would have improved safety margins and greater clinical tolerance
for chronic treatment of autoimmune diseases.
p38a
kinase inhibitors have reached clinical trials.4
Although ATP mimetics are still the mainstream platform for
developing kinase inhibitors, wherein small molecules target the
ATP pocket,5 this approach has led to many recurring concerns/
problems: (1) achieving selectivity among the >500 kinases in
the genome; (2) selectivity for other proteins which use ATP as a
substrate; (3) poor inhibitor pharmacokinetics (PK) properties,
including solubility, and bioavailability. These problems have led
to an increased interest in identifying novel protein kinase inhibi-
tors whose potency is derived at least in part from interactions
outside of the ATP binding pocket, referred to here as a nonclassical
approach and ‘nonclassical kinase inhibitors’ (NCKIs).6 Among the
NCKIs, inhibitors that bind to the DFG-out conformations of
kinases7 have gained increasing attention from the pharmaceutical
The rationale for the current study arises from the observation
that most of the known ‘DFG-out’ inhibitors, including Imatinib,
Sorafenib and BIRB796, bind to their respective targets not only
in the ‘DFG-out’ pocket made available by the movement of the
phenylalanine residue in the conserved DFG segment of the kinase
activation loop, but also within the ATP pocket and the adjacent ki-
nase specificity pocket. The additional binding of these inhibitors
with hinge residues in the adenine binding pocket is often required
to achieve desired potencies. Although the ‘DFG-out’ inhibitors are
known for improved selectivity profiles,6 many of them do cross
inhibit other kinases, especially when tested at high inhibitor con-
centration, such as 10 l
M (Fig. 1).12
We speculated that inhibitors that bind primarily within the
DFG-out pocket and minimally interact with the kinase specificity
pocket, but lack direct interactions with the adenine binding site,
might possess greater selectivity and improved safety margin. To-
* Corresponding authors. Tel.: +1 617 551 3302; fax: +1 617 551 3084 (H.L.); tel.:
+1 617 995 2951 (J.C.W).
E-mail addresses: hu.liu@pfizer.com (H. Liu), joewu@aileronrx.com (J.C. Wu).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.06.073

4886
H. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4885–4891
N
H
N
H
N
N
N
N
O
Imatinib
(c-ABL inhibitor)
N
H
N
N
H
N
O
O
N
N
H
O
N
H
O
N
H
N
Cl
O
F3C
N
BIRB796
(p38 inhbitor)
Sorafenib
(RAF inhibitor)
O
α
Scheme 1. Representative NCKIs that bind to the DFG-out conformations of kinases.
Figure 1. Selectivity profiles of imatinib, sorafenib and BIRB796 against a panel of 40 kinases at 10 lM.
Scheme 3. Diazotization of 3-aminobenzonitrile (1), followed by
tin (II) chloride promoted reduction, and neutralization gave the
free 3-hydrazinylbenzonitrile (3) in a 57% overall yield for three
steps. Refluxing the nitrile 3 and 4,4-dimethyl-3-oxopentanenitrile
in toluene resulted in the closure of the pyrazole ring to provide
pyrazolyl-benzonitrile 4 in 50% yield. Treatment of 4 with the
appropriate isocyanate afforded ureas 5a/5b in acceptable yields.
LAH reduction of the nitrile moieties in 5a/5b gave the amino-
methyl derivatives 6a/6b in good yields. Pyrazolyl-phenylurea 6a
was further converted to its methylated derivative via reductive
amination conditions in low yield (18%).
O
N
H
N
N
H
N
Anchor
Linker
Hook
Scheme 2. Design of novel pyrazolyl-urea based p38
a
inhibitors.
ward that end, we designed novel pyrazolyl-urea based p38a inhib-
With pyrazolyl-phenylureas 6 and 7 in hand, we then turned
our attention towards the synthesis of their amide derivatives 8
and 9 using standard coupling conditions (Table 1). Compounds
itors that contain a simple pyrazolyl-urea as the anchor, and addi-
tional linker and ‘hook’ moieties, wherein the ‘hook’ moiety
contains a suitable combination of H-bond acceptors and donors
(Scheme 2). While the simple pyrazolyl-urea anchor is expected to
minimize interactions with the adenine binding site, the combined
linker and ‘hook’ groups are expected to achieve desired potencies,
improve selectivity, and serve as a handle for physical property
modifications.
8 and 9 were evaluated in p38
a method to kinetically determine the binding of a compound to
active or inactive p38 . In the active p38 cascade assay, com-
pounds are first preincubated with active p38 before activity is
determined by the addition of MK2 and its substrate. In the case
of the unactive p38 cascade assay, compounds are preincubated
with unactive p38 , followed by activation by MKK6 and then
dilution into a MK2 and substrate mixture.
a
cascade assays,13 which provide
a
a
a
a
a
The synthesis of pyrazolyl-ureas 6 and 7, with aminomethyl
moieties suitable for further synthetic elaborations, is shown in

H. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4885–4891
4887
t-Bu
NH2
NH2 HCl
HN
NH2
HN
CN
N
O
iii
NH2
N
ii
i
CN
N
N
1
2
3
N
4
t-Bu
t-Bu
O
O
t-Bu
Ar
Ar
O
N
N
N
H
Ph
N
N
H
N
H
H
N
N
N
H
N
N
H
N
iv
v
N
vi
NH2
6a: Ar = Ph
6b: Ar =
5a: Ar = Ph
5b: Ar =
NH
7
Scheme 3. Synthesis of pyrazolyl-3-phenylurea intermediates 6 and 7. Reagents and conditions: (i) (a) NaNO2, HCl; (b) SnCl2, HCl, 78%; (ii) NaHCO3, 73%; (iii) toluene, reflux,
50%; (iv) Ar–N@C@O, CH2Cl2, reflux, 50–60%; (v) LiAlH4, THF, rt, 96–64%; (vi) (a) formaldehyde, toluene, 80 °C; (b) NaBH4, rt, THF, 18%.
Table 1
Synthesis and evaluation 8/9 in p38a cascade assay
t-Bu
t-Bu
O
O
Ph
Ph
R2
N
H
N
N
H
N
H
N
R2-CO2H
N
N
H
N
R1
NH
R1
N
HATU, i-Pr2NEt
6a: R1 = H
7: R1 = Me
8: R1 = H
9: R1 = Me
O
Entry
Compound
R1
R2
IC50 against unactive p38
a
(l
M)a
IC50 against active p38a (l
M)a
1
2
3
4
5
6
7
6a
8a
8b
8c
8d
8e
8f
H
H
H
H
H
H
H
2.85
>16.7
2.3
–CH2NH2
–CH2NH–C(O)–O–Me
–CH2NH–C(O)–H
–CH2NH–C(O)–CH3
–CH2NH–C(O)–Ph
–CH2NH–C(O)-3-pyridyl
0.176
0.176
0.068
0.006
0.169
0.051
0.287
0.332
0.034
0.441
0.205
O
N
N
8
8g
H
0.038
0.243
O
H
9
10
8h
8i
H
H
–CH2NH–C(O)-2-furanyl
(rac)–CH(Me)–NH–C(O)–CH3
0.018
0.168
0.088
0.48
O
11
8j
H
0.715
4.55
N
H
12
13
8k
9a
H
Me
–CH2NH–S(O)2–CH3
–CH2NH–C(O)–CH3
0.108
0.211
0.649
1.6
a
Average of three experiments with SD <15%.
As shown in Table 1, all the pyrazolyl-phenylurea derivatives
tested in Table 1 show better potencies in the unactive p38 cas-
cade assay, than in the active p38 cascade assay. This observation
is in agreement with the assumption that the pyrazolyl-phenylure-
as 6a, 8 and 9, which are ‘DFG-out’ type inhibitors for p38
14 have
better binding affinities towards unactive p38 versus its active
form. For example, compound 6a (Table 1, entry 1), which repre-
sents the pyrazolyl-phenylurea anchor, has an IC50 of 2.85
against unactive p38a, and an IC50 >16.7 lM against active p38a.
Further elongation from the pyrazolyl-phenylurea anchor, such
as in compound 8a (Table 1, entry 2), results in a dramatically im-
a
a
proved potency against both unactive and active p38
methyl carbamate moiety (8b, Table 1, entry 3) at the end of the
chain does not improve the potencies further (IC50’s of 0.176
and 0.287 M against unactive and active p38 , respectively),
the NH-Ac-glycine derivative 8d (Table 1,entry 5) demonstrates
a. Although a
a,
a
lM
l
a
lM

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H. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4885–4891
Table 2
Evaluation of 8l–8s in p38
a cascade assay
t-Bu
t-Bu
O
O
Ph
Ph
R2
N
N
N
N
H
N
H
R2-CO2H
N
N
H
H
N
HATU, i-Pr2NEt
H
NH2
N
6a
O
8
Entry
1
Compound
R2
IC50 against unactive p38
a
(l
M)a
IC50 against active p38a (l
M)a
8d
–CH2NH–C(O)–CH3
0.006
0.034
O
2
3
8l
0.068
0.185
0.296
N
O
8m
8n
0.599
0.063
N
O
O
N
4
0.016
N
N
5
6
8o
8p
0.231
0.132
0.536
0.677
N
N
N
N
7
8
8q
8r
0.0488
0.0279
0.135
0.201
N
N
N
N
9
8s
0.0782
0.331
a
Average of three experiments with SD <15%.
excellent potencies against both unactive and active p38
a
(IC50’s of
in Table 2. The presence of a H-bond acceptor in the ‘hook’ region is
required for potency, yet the presence of a H-bond donor is much
less essential (Table 2, entry 1 vs entries 2 and 4). For example,
compound 8n (Table 2, entry 4), wherein a pyridone moiety serves
as the hydrogen bonding group in the ‘hook’ area, has an IC50 of
0.006 and 0.034 M, respectively). Further examination
l
M
l
around the NH-Ac-glycine side chain (Table 1, entries 6–11) re-
vealed the following: (a) the acetyl amide ‘hook’ moiety could be
replaced with other type of amides, such as small heteroaryl
amides (e.g., Table 1, entries 8 and 9); (b) the
a-position of the
0.016
l
M against unactive p38
a, and an IC50 of 0.063 lM against
NH-Ac-glycine side chain has limited tolerance for lipophilic sub-
stitutions (e.g., Table 1, entries 10 and 11). It is also important to
notice that changing the acetamide to methyl sulfonamide results
in loss of potency (Table 1, entries 12 vs 5). Similarly, blocking the
NH group immediately off the anchor with a methyl group (Table
1, entries 13 vs 5) also significantly diminishes potencies.
active p38
a
. The spatial disposition of the H-bond acceptor is also
crucial for potency. Indeed, pyrazole type hydrogen bonding
groups (Table 2, entries 7–9) are more preferred over imidazole
type hydrogen bonding groups (Table 2, entries 5 and 6).
Selectivity data for the NH-Ac derived pyrazolyl-phenylurea 8d
against a panel of 40 kinases at 10 lM is shown in Figure 2, and
More detailed structure–activity relationship (SAR) studies
around compound 8d were carried out and the results summarized
remarkable selectivity is observed. This result supports the key
rationale for the design of these pyrazolyl-phenylureas, which is
Figure 2. Selectivity profile of 8d against a panel of 40 kinases at 10 lM.

H. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4885–4891
4889
Table 3
Evaluation of 8d, 8n and 8r in in vitro ADME and safety assays
Entry Compound Solubility
(turbidimetric, pH
6.5, phosphate
PAMPA
(Papp) (cm/ microsomal
s)
Human
Dofetilide
binding (%
inhibition at
DDI-CYP
inhibition
(%
clearance (CLh)
(mL/min/kg)
buffer) (
l
M)a
10
lm)
inhibition
at 3
lm)
1
2
3
8d
8n
8r
>200
7.38 Â 10À6 13.3
12.9 Â 10À6 17.9
4.80 Â 10À6 18.6
À11%
9%
1A2
2C9
2D6
3A4
1A2
2C9
2D6 21%
3A4 30%
1A2
2C9
5%
0%
2%
0%
4%
6%
50–150
100–200
3%
4%
5%
2D6 18%
3A4 26%
a
Data are shown as the range of maximum kinetic solubility and minimum kinetic solubility.
that greater selectivity is possible from compounds that bind
mainly within the DFG-out pocket, with no direct interaction with
the adenine binding site, and minimized interactions with the ki-
nase specificity pocket; and this potential is further realized by
the right choices of linker and ‘hook’ moieties.
Some of the representative compounds from Tables 1 and 2 (8d,
8n and 8r) were further tested for their in vitro ADME and safety
profiles, and the results are summarized in Table 3. Compound
8d demonstrates an acceptable combination of solubility and per-
meability, as determined in the partial artificial membrane perme-
Table 4
Synthesis and evaluation of 11/12 in p38a cascade assay
t-Bu
O
t-Bu
R3
R4
R5
O
R6
O
Ar
Ar
N
H
N
N
H
N
N
H
N
H
N
N
O
O
10
H
N
R2
NH2
DMF
O
11: Ar = Ph
12: Ar =
6a: Ar = Ph
6b: Ar =
Entry
Compound
Ar
R2
IC50 against unactive p38
a
(
l
M)a
IC50 against active p38a (l
M)a
1
2
11a
11b
Ph
Ph
–CH2CH2–C(O)OH
–CH2C(Me)2–C(O)OH
0.037
0.039
0.393
3.68
3
11c
Ph
0.030
1.1
OH
(rac)-
O
4
11d
Ph
0.057
3.36
OH
(rac)-
O
5
6
11e
12
Ph
0.014
0.005
0.737
0.006
OH
(rac)-
O
–CH2CH2–C(O)OH
a
Average of three experiments with SD <15%.

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H. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4885–4891
Figure 3. Selectivity profiles of 11a, 11b, 11c and 11e against a panel of 40 kinases at 10 lM.
Figure 4. Selectivity profile of 12 against a panel of 35 kinases at 10 lM.
Table 5
Evaluation of 11a, 11b, 11c and 11e in in vitro ADME and safety assays
Entry Compound Solubility PAMPA Human
Dofetilide
binding (%
inhibition at
DDI-CYP
inhibition
(%
(turbidimetric, pH (Papp) (cm/ microsomal
6.5, phosphate
buffer) (
M)a
s)
clearance (CLh)
(mL/min/kg)
l
10
lm)
inhibition
at 3
lm)
1
2
3
4
11a
11b
11c
11e
100–200
5.57 Â 10À6 <5.00
10.9 Â 10À6 7.23
4.94 Â 10À6 <5.28
9.48 Â 10À6 10.5
À2%
À5%
À4%
À7%
1A2
2C9
2D6
3A4
1A2 17%
2C9
2D6
0%
0%
0%
0%
>200
3%
0%
3A4 10%
>200
1A2
2C9
2D6
3A4
0%
0%
0%
0%
100–200
1A2 10%
2C9
2D6
3A4
8%
6%
4%
a
Data are shown as the range of maximum kinetic solubility and minimum kinetic solubility.
ation assay (PAMPA) (Table 3, entry 1). Furthermore, 8d does not
notably inhibit a cocktail of CYP P450 enzymes that consists of
CYP1A2, 2C9, 2D6, 3A4, and does not interfere with dofetilide bind-
ing. However, all three evaluated compounds showed poor stabil-
ity in human liver microsome assays, which we believe is at least
partially caused by their high distribution coefficients at physiolog-
ical pH (Log D).
As mentioned earlier, the combination of the linker and ‘hook’
moieties could also serve as a handle for physical property modifi-
cations. Toward that end, reacting the aminomethyl-pyrazolyl-ur-

H. Liu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4885–4891
4891
eas 6 with cyclic anhydrides 10 (wherein R3 and R5 optionally
forms a ring) in DMF provided pyrazolyl-phenylureas 11/12 with
a carboxylic acid moiety as the ‘hook’ group. These compounds
More thorough SAR studies on the ‘hook’ and linker regions,
accompanied by fine tuning of the pyrazole-urea anchor are de-
sired, as they will provide more insightful understanding of the
pocket that interacts with the linker and ‘hook’ moiety, facilitate
the development of a SBDD (structure-based drug design) plat-
form, and hence delineate a path forward for applying this strategy
to inhibitors for other kinases. These results will be published in
the due course.
were evaluated in the p38
Compound 11a, which has a flexible oxobutanoic acid side
chain, has an IC50 of 0.037 M against unactive p38 , and an IC50
of 0.393 M against active p38 (Table 4, entry 1). Substitutions
at the -carbon of the acid moiety are also well tolerated (11b,
a cascade assays (Table 4).
l
a
l
a
a
Table 4, entry 2). More conformational restrained analogues, such
as 11c and 11d (Table 4, entries 3 and 4), retained their inhibitory
activity. On the other hand, cyclohex-3-enecarboxylic acid deriva-
tive 11e, which has an unsaturated carbocycle (Table 4, entry 5),
has slightly improved potency. Furthermore, it is interesting to no-
tice that switching from a phenyl urea to a naphthyl urea resulted
Acknowledgment
The authors thank Dr. Richard Nugent for helpful suggestions
and discussions.
in 12, which has an IC50 of 0.005
l
M against unactive p38
a, and an
References and notes
IC50 of 0.006 M against active p38
is caused by an increased lipophilic occupancy in the specific bind-
ing area.
Some of the representative compounds from Table 4 were fur-
ther tested for their selectivity against other kinases at 10 lM. As
expected, remarkable selectivity is again observed for phenyl-pyr-
azole-urea acids 11a, 11b, 11c and 11e against a panel of 40 ki-
nases (Fig. 3).
It is also interesting to notice that the naphthyl derivative 12,
which is highly potent against both unactive and active p38
(Table 4, entry 6), showed a similar selectivity profile at 10
against a slightly different panel of 35 kinases (Fig. 4).
Pyrazole-urea acids 11a, 11b, 11c and 11e were also tested in
in vitro ADME and safety assays, and the results are summarized
in Table 5. As expected, these acids show good solubility and im-
proved stability in human liver microsome assays, when compared
with neutral inhibitors, such as 8d (Table 3, entry 1). On the other
hand, these acids demonstrate a range of permeability, as deter-
mined in the PAMPA model, with introduction of lipophilic groups
(11e, Table 5, entry 4) or steric hindrance around the acid moiety
(11b, Table 5, entry 2) restoring the permeability to an excellent le-
vel. Furthermore, all compounds show clean profiles in the CYP
P450 enzymes inhibition assays, and in the dofetilide binding
assay.
In conclusion, we demonstrated that by simultaneously target-
ing the conventional ‘DFG-out’ pocket, and an extended region of
p38a, we synthesized several pyrazole-urea based p38a inhibitors,
which demonstrated good potencies and superior selectivity. These
pyrazolyl-ureas differ from the well known ‘DFG-out’ type inhibi-
tors, such as Imatinib, Sorafenib and BIRB796, in that they have
no direct interactions with the adenine binding site, yet have se-
lected linker and ‘hook’ moieties attached to the pyrazole-urea an-
chor, which allows them to achieve desired potencies, selectivity,
and physical properties.
l
a
(Table 4, entry 6). This likely
1. (a) Rincon, M. Curr. Opin. Immunol. 2001, 13, 339; (b) Kuida, K.; Boucher, D. M. J.
Biol. Chem. 2004, 135, 653.
2. (a) Johnson, G. L.; Lapadat, R. Science 2002, 298, 1911; (b) Schett, G.; Zwerina, J.;
Firestein, G. Ann. Rheum. Dis. 2008, 67, 909; (c) Gaestel, M.; Mengel, A.; Bothe,
U.; Asadullah, K. Curr. Med. Chem. 2007, 14, 2214.
3. (a) Sizova, L. Br. J. Clin. Pharmacol. 2008, 66, 173; (b) Lutt, J. R.; Deodhar, A. Drugs
2008, 68, 591.
4. (a) Pettus, L. H.; Wurz, R. P. Curr. Top. Med. Chem. 2008, 8, 1452; (b) Peifer, C.;
Wagner, G.; Laufer, S. Curr. Top. Med. Chem. 2006, 6, 113; (c) Goldstein, D. M.;
Gabriel, T. Curr. Top. Med. Chem. 2005, 5, 1017.
5. Gill, A. L.; Verdonk, M.; Boyle, R. G.; Taylor, R. Curr. Top. Med. Chem. 2007, 7,
1408.
6. Liao, J. J.-L. J. Med. Chem. 2007, 50, 409.
7. (a) Okram, B.; Nagle, A.; Adrian, F. J.; Lee, C.; Ren, P.; Wang, X.; Sim, T.; Xie, Y.;
Wang, X.; Xia, G.; Spraggon, G.; Warmuth, M.; Liu, Y.; Gray, N. S. Chem. Biol.
2006, 13, 779; (b) Liu, Y.; Gray, N. S. Nat. Chem. Biol. 2006, 2, 358; (c) Sawa, M.
Mini-Rev. Med. Chem. 2008, 8, 1291.
a
lM
8. Mueller, B. A. Curr. Pharm. Design 2009, 15, 120.
9. Mendez-Sanchez, N.; Vasquez-Fernandez, F.; Zamora-Valdes, D.; Uribe, M. Ann.
Hepatol. 2008, 7, 46.
10. (a) Regan, J.; Breitfelder, S.; Cirillo, P.; Gilmore, T.; Graham, A. G.; Hickey, E. R.;
Klaus, B.; Madwed, J.; Moriak, M.; Moss, N.; Pargellis, C. A.; Pav, S.; Proto, A.;
Swinamer, A.; Tong, L.; Torcellini, C. J. Med. Chem. 2002, 45, 2994; (b) Regan, J.;
Capolino, A.; Cirillo, P. F.; Gilmore, T.; Graham, A. G.; Hickey, E.; Kroe, R. R.;
Madwed, J.; Moriak, M.; Nelson, R.; Pargellis, C. A.; Swinamer, A.; Torcellini, C.;
Tsang, M.; Moss, N. J. Med. Chem. 2003, 46, 4676; (c) Moss, N.; Breitfelder, S.;
Betageri, R.; Cirillo, P. F.; Fadra, T.; Hickey, E. R.; Kirrane, T.; Kroe, R. R.;
Madwed, J.; Nelson, R. M.; Pargellis, C. A.; Qian, K. C.; Regan, J.; Swinamer, A.;
Torcellini, C. Bioorg. Med. Chem. Lett. 2007, 17, 4242.
11. Pargellis, C.; Tong, L.; Churchill, L.; Cirillo, P. F.; Gilmore, T.; Graham, A. G.;
Grob, P. M.; Hickey, E. R.; Moss, N.; Pav, S.; Regan, J. Nat. Struct. Biol. 2002, 9,
268.
12. Card, A.; Caldwell, C.; Min, H.; Lokchander, B.; Xi, H.; Sciabola, S.; Kamath, A. V.;
Clugston, S. L.; Tschantz, W. R.; Wang, L.; Moshinsky, D. J. J. Biomol. Screen 2009,
141, 31.
13. Tecle, H.; Feru, F.; Liu, H.; Kuhn, C.; Rennie, G.; Morris, M.; Shao, J.; Chang, A. C.;
Gikunju, D.; Miret, J.; Coli, R.; Xi, S.; Clugston, S. L.; Low, S.; Kazmirski, S.; Ding,
Y.-H.; Cao, Q.; Johnson, T. L.; Deshmukh, G. D.; DiNitto, J. P.; Wu, J. C.; English, J.
M. Chem. Biol. Drug Des. 2009, 74, 547.
14. The p-38a co-crystals with this class of compounds are often partially resolved
for the ligands. Nevertheless, based on some of the partially resolved
structures, it is clear that these ureas bind to the ‘DFG-out’ conformation of
the protein.