Benzothiazole based inhibitors of p38α MAP kinase

Article abstract of DOI:10.1016/j.bmcl.2008.02.011

Rational design, synthesis, and SAR studies of a novel class of benzothiazole based inhibitors of p38α MAP kinase are described. The issue of metabolic instability associated with vicinal phenyl, benzo[d]thiazol-6-yl oxazoles/imidazoles was addressed by t

Full text of DOI:10.1016/j.bmcl.2008.02.011

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 1874–1879
Benzothiazole based inhibitors of p38a MAP kinase
Chunjian Liu,* James Lin, Sidney Pitt, Rosemary F. Zhang, John S. Sack, Susan E. Kiefer,
Kevin Kish, Arthur M. Doweyko, Hongjian Zhang, Punit H. Marathe, James Trzaskos,
Murray Mckinnon, John H. Dodd, Joel C. Barrish,
Gary L. Schieven and Katerina Leftheris
Bristol-Myers Squibb Research and Development, PO Box 4000, Princeton, NJ 08543-4000, USA
Received 7 December 2007; revised 4 February 2008; accepted 7 February 2008
Available online 10 February 2008
Abstract—Rational design, synthesis, and SAR studies of a novel class of benzothiazole based inhibitors of p38a MAP kinase are
described. The issue of metabolic instability associated with vicinal phenyl, benzo[d]thiazol-6-yl oxazoles/imidazoles was addressed
by the replacement of the central oxazole or imidazole ring with an aminopyrazole system. The proposed binding mode of this new
class of p38a inhibitors was confirmed by X-ray crystallographic studies of a representative inhibitor (6a) bound to the p38a enzyme.
Ó 2008 Elsevier Ltd. All rights reserved.
The p38a mitogen-activated protein (MAP) kinase is an
important mediator of inflammatory cytokines includ-
ing tumor necrosis factor alpha (TNF-a) and interleu-
kin-1b (IL-1b).1 It has been demonstrated by
numerous preclinical studies2 that inhibition of p38a
MAP kinase could effectively inhibit TNF-a production
both in vitro and in vivo. Excessive production of TNF-
a and IL-1b is believed to underlie many inflammatory
diseases including rheumatoid arthritis (RA), Crohn’s
disease, inflammatory bowel disease, and psoriasis.3
The blockage of TNF-a function by biological agents,
such as etanercept (EnbrelÒ), a soluble TNF-a receptor,
and infliximab (RemicadeÒ), a TNF-a antibody, has
clinically proven to be effective in the treatment of RA
and Crohn’s disease.4 Therefore, it is expected that
low molecular weight p38a MAP kinase inhibitors
may become orally active therapeutic agents for the
treatment of inflammatory conditions.
the central imidazole ring to other five membered bio-
isosteres. More recently, however, scientists at Roche
hydrophobic
interaction
hydrophobic
interaction
F
F
Met 109
N
Met 109
N
Lys 53
N
HN
Lys 53
N
HN
SOMe
SB-203580 (SmithKline Beecham)
1 (Roche Palo Alto)
N
F
HN
S
N
NH
A large number of classes of p38a inhibitors have been
identified.5 One is the vicinal aryl, pyridin-4-yl hetero-
arenes, derived from SB-2035806 that was identified at
SmithKline Beecham (Fig. 1). Modifications to SB-
203580, until recently, have been limited to changes of
H2N
2
F
N
N
N
O
N
N
N
Keywords: Inhibitors of p38a MAP kinase; Benzothiazoles; Vicinal
phenyl, benzo[d]thiazol-6-yl oxazoles; Vicinal phenyl, benzo[d]thiazol-
6-yl imidazoles; Vicinal phenyl, benzo[d]thiazol-6-yl pyrazoles; X-ray
co-crystal structure; TNFa inhibition in hPBMC.
Corresponding author. Tel.: +1 609 252 3682; fax: +1 609 252
7410; e-mail: chunjian.liu@bms.com
N
NH
O
4
(Pfizer)
3
(Pfizer)
*
Figure 1. Novel p38a inhibitor 2 versus some of the known p38a
inhibitors.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.02.011

C. Liu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1874–1879
1875
Palo Alto demonstrated with 12f that the central five
membered ring could also be replaced with bicyclic het-
eroaryl rings. X-ray co-crystal structures of both SB-
203580 and 1 with the p38a enzyme indicate that the
binding modes for these two inhibitors are essentially
the same. That is, as shown in Figure 1, the key interac-
tions include: (1) a hydrogen-bonding interaction be-
tween the terminal pyridine nitrogen and the main
chain NH of Met109 of p38a, (2) a hydrogen-bonding
interaction between an imidazole nitrogen in SB-
203580 or between the 4-azaindole nitrogen of 1 and
Lys53 of p38a, and (3) a hydrophobic interaction of
the phenyl with a hydrophobic pocket of p38a. In the
modification of SB-203580 into 1, the imidazole nitro-
gen is extended outward by a distance of one bond. With
a similar consideration, we wondered if the pyridine ring
in the vicinal aryl, pyridin-4-yl heteroarene series could
be replaced with a bicyclic heteroaryl system wherein a
hydrogen-bonding acceptor (for Met109) is present,
but extended outward by a distance of one bond com-
pared to the original pyridine nitrogen. Our investiga-
tion has resulted in the discovery of a novel class of
benzothiazole based inhibitors of p38a MAP kinase.
Among them, compound 2 represents a series that is
not only highly potent against p38a and effective in
inhibiting TNFa production in cells, but also possesses
appropriate metabolic and pharmacokinetic profiles
for further investigation. It should be mentioned that
in the course of our studies, structurally similar p38a
inhibitors such as 3 and 4 were disclosed by scientists
at Pfizer.7 Inhibitor 3 was reported to be metabolically
unstable, while 4 was disclosed only with enzymatic
activity and appeared to represent a series of moderately
potent p38a inhibitors.
5 (Scheme 1), 6 (Scheme 2), and 7 (Scheme 3). It was ex-
pected that the benzothiazole nitrogen would form a
hydrogen bond with the NH of Met109 of p38a. Based
on our previous experience,2d 2-Isopropylamino was
also installed with the expectation that the amino NH
would make a secondary hydrogen bond to the carbonyl
oxygen of Met109, and that the isopropyl would provide
a hydrophobic interaction close to the binding site. The
synthesis of 5 started with the treatment of 1-(4-amino-
phenyl)ethanone (8) with potassium thiocyanate and
bromine in glacial acetic acid at room temperature
(RT) to provide 2-aminobenzothiazole 9. Reaction of
9 with tert-butyl nitrite and copper (II) bromide at RT
supplied 2-bromobenzothiazole 10. Mixing 10 with iso-
propyl amine in 1,4-dioxane at 100 °C resulted in the
formation of 11. The target 5 was then obtained by heat-
ing 11 with N,N-dimethylformamide dimethyl acetal
(DMFDMA), followed by phenyl hydrazine.
N
S
N
S
a, b
H2N
H2N
CO2Et
CHO
13
14
N
S
d
c
H2N
N
O
15
N
S
N
e
Br
HN
S
N
N
We envisioned that the bicyclic benzothiazole system
might be a replacement for the original pyridine ring
in SB-203580, prompting us to synthesize compounds
O
O
16
6
Scheme 2. Reagents and conditions: (a) LiAlH4, THF, 0 °C, 46%
yield; (b) MnO2, THF, RT, 87% yield; (c) (1-phenyl-1-tosyl)methyl
isocyanide, K2CO3, EtOH, reflux, 52% yield; (d) CuBr2, t-BuONO,
MeCN, rt, 23% yield; (e) i-PrNH2, THF, 50 °C, 43% yield.
H2N
N
S
a
b
H2N
O
O
9
N
S
N
S
8
a
H2N
Br
N
S
N
S
CO2Et
CO2Et
c
HN
Br
13
17
O
O
N
N
b, c
d
11
10
HN
Br
S
S
CHO
CHO
N
e
d
HN
18
19
N
S
O
N
S
12
e
HN
N
N
S
HN
HN
N
7
N
Scheme 3. Reagents and conditions: (a) CuBr2, t-BuONO, MeCN,
RT, 84% yield; (b) Dibal-H, toluene, THF, À78 °C to RT, 90% yield;
(c) MnO2, THF, RT, 83% yield; (d) i. i-PrNH2, 1,4-dioxane, pressure
tube, 150 °C; ii. 1 N HCl, 1,4-dioxane, 65 °C, 81% yield; (e) i. aq
NH4OH, RT; ii. (1-phenyl-1-tosyl)methyl isocyanide, piperazine, 19%
yield.
5
Scheme 1. Reagents and conditions: (a) KSCN, Br2, AcOH, rt; (b)
CuBr2, t-BuONO, MeCN, RT, 31% yield over two steps; (c) i-PrNH2,
1,4-dioxane, 100 °C; (d) DMFDMA, 100 °C; (e) PhNHNH2HCl,
Na2CO3, AcOH, MeOH/H2O, reflux, 50% yield over three steps.

1876
C. Liu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1874–1879
Table 2. In vitro activity of 5a–i versus 5, 6a versus 6, and 7a versus 7
For the preparation of 6 (Scheme 2), benzothiazole-6-
caboxylate 13 was reduced with LiAlH4 at 0 °C, and
the resultant alcohol was then oxidized with manganese
(IV) oxide at RT to aldehyde 14. Treatment of 14 with
(1-phenyl-1-tosyl)methyl isocyanide in the presence of
K2CO3 in refluxing ethanol afforded oxazole 15. Con-
version of 15 to 6 was realized in the same way as 2-ami-
R1
N
S
HN
N
N
5a-i
nobenzothiazole
isopropylaminobenzothiazole 11 (Scheme 1).
9
was
converted
to
2-
R1
R1
N
S
N
S
HN
HN
To synthesize 7 (Scheme 3), 2-aminobenzothiazole 13
was converted to 2-bromobenzothiazole 17 with tert-bu-
tyl nitrite and copper (II) bromide at RT. Reduction of
the ester functionality of 17 with diisobutylaluminum
hydride (Dibal-H) at À78 °C and a subsequent oxida-
tion with manganese (IV) oxide at RT gave rise to
benzothiazole-6-carbaldehyde 18. When 18 was treated
with excess isopropyl amine in 1,4-dioxane at 150 °C
in a pressure tube, the desired substitution reaction at
the 2-position occurred smoothly. Meanwhile, the alde-
hyde formed the corresponding imine with isopropyl
amine. The imine could readily be hydrolyzed back to
aldehyde 19 with 1 N hydrochloride acid at 65 °C.
Reacting 19 sequentially with aqueous ammonium
hydroxide and (1-phenyl-1-tosyl)methyl isocyanide
furnished imidazole 7.
N
N
HN
7, 7a
O
6, 6a
a
b
Compound
R1
p38a IC50
(nM)
hPBMC TNFa IC50
(nM)
5
H
21
> 1000
33
213
171
5a
5b
5c
5d
5e
5f
5g
5h
5i
p-Me
m-Me
o-Me
p-Cl
m-Cl
o-Cl
p-F
m-F
o-F
H
146
> 1000
72
232
175
48
> 250
171
249
96
33
20
Compounds 5, 6, and 7 were then assayed against the
p38a enzyme.2d To our encouragement, all three com-
pounds proved to be potent p38a inhibitors. Inhibitors
5 and 6 both displayed an IC50 value of 21 nM, and
the potency (IC50) of 7 was determined to be 7.1 nM
(Table 1). Moreover, all three compounds were active
at inhibiting LPS-induced TNF-a production in human
peripheral blood mononuclear cells (hPBMC)2d with
IC50 values of 213 nM, 96 nM, and 107 nM,
respectively.
6
21
6.4
6a
7
o-F
H
40
7.1
3.3
107
35
7a
o-F
a n = 4, variation in individual values, <20%.
b n = 3, variation in individual values, <25%.
greater than 1000 nM against p38a. This is a drop of
greater than 50-fold in p38a activity compared to 5.
Methyl substitutions at the m-position and o-position
also led to losses in p38a activity, though to a lesser ex-
tent as demonstrated by analogues 5b (p38a
IC50 = 33 nM) and 5c (p38a IC50 = 146 nM). A very
similar SAR was observed with chloro substitutions
(5d–f). It was further found that even p-F (5g, p38a
IC50 = 48 nM) and m-F (5h, p38a IC50 = 33 nM) seemed
to decrease the p38 activity slightly. The only substituent
that did not appear detrimental to p38a binding affinity
was o-F, as 5i was at least as potent as 5. To assess fur-
ther the SAR of o-F, thiazole analogue 6a and imidazole
7a were synthesized (Table 2). Analogue 6a inhibited
p38a and TNFa production in hPBMC with IC50 values
of 6.4 nM and 40 nM, respectively, versus 21 nM and
96 nM, respectively, for 6. Similarly, 7a was more potent
than 7 in both enzymatic (IC50 of 3.3 nM versus 7.1 nM)
and cellular assays (IC50 of 35 nM vs 107 nM). This
SAR was also confirmed with analogues where the iso-
propylamino was replaced with other alkylamino groups
(data not shown). Thus, it could be concluded that the o-
F substitution on the phenyl of 5, 6, 7, and their ana-
logues was at least tolerated and most likely preferred.
With 5, 6, and 7 in hand, our lead optimization started
with the exploration of substituents on the phenyl ring.
This SAR study was efficiently conducted with ana-
logues of pyrazole 5 since, according to Scheme 1, these
analogues could be prepared by parallel synthesis at the
very last step with a variety of commercially available
substituted phenyl hydrazines. Compounds with p38a
IC50 values below 100 nM were routinely tested for
the inhibition of LPS-induced TNFa production in
hPBMC. Selected results are summarized in Table 2.
For traditional vicinal phenyl, pyridin-4-yl heteroarene
p38 inhibitors, a p- or m-substituent on the phenyl was
usually preferred.6,8 However, this was not the case after
replacement of the pyridine-4-yl with benzo[d]thiazol-6-
yl. When a methyl group was present at the p-position,
the corresponding analogue 5a displayed an IC50 of
Table 1. In vitro activity of 5, 6, and 7
Compound
5
6
7
a
p38a IC50 (nM)
21
213
21
96
7.1
107
b
hPBMC TNFa IC50 (nM)
Based on the enzymatic and cellular data from 5i, 6a,
and 7a, we were then more focused on the series repre-
sented by 6a and 7a. Our next SAR study was to exam-
a n = 4, variation in individual values, <20%.
b n = 3, variation in individual values, <25%.

C. Liu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1874–1879
1877
ine whether the isopropylamino group on 6a and 7a was
optimal. This was accomplished primarily with ana-
logues of oxazole 6a, and the results are given in Table
3. As expected, removal of the isopropylamino group
from 6a resulted in a drop in p38a potency, as 6b
(p38a IC50 = 47 nM) was shown to be 8-fold less active
than 6a. Adding the NH2 group to 6b improved the p38
IC50 to 16 nM, but 6c was still less potent than 6a. The
cellular activities (TNFa IC50s) of 6b and 6c were deter-
mined to be greater than 250 nM and 247 nM, respec-
tively. Replacement of the isopropylamino group with
ethylamino (6d) also increased the p38a IC50 from
6.4 nM to 12 nM and TNFa IC50 from 40 nM to
167 nM. However, (R)-2-butylamino and (S)-2-butyla-
mino were found to be appropriate replacements for
the isopropylamino, as both 6e (p38a IC50 = 6.5 nM,
TNFa IC50 = 27 nM) and 6f (p38a IC50 = 10 nM, TNFa
IC50 = 30 nM) showed very comparable enzymatic and
cellular potency to 6a. The use of (R)-2-butylamino
and (S)-2-butylamino in place of isopropylamino in
imidazole 7a led to 7b and 7c, the most potent benzothi-
azole based p38a inhibitors identified. Compounds 7b
and 7c inhibited p38a with IC50 values of 1.6 nM and
2.7 nM, respectively. Both compounds were also very
effective in inhibiting TNFa production in cells, display-
ing hPBMC TNFa IC50 of 13 nM and 20 nM, respec-
tively. In summary, isopropylamino, (R)-2-butylamino,
and (S)-2-butylamino were the most preferred groups
identified for R2.
result, the rest of the SAR study was focused on
improving the metabolic stability of this class of
p38a inhibitors. Since substitution on the phenyl ring
in 5, 6, and 7 at different positions and replacement of
the isopropyl with a variety of other alkyl or complete
removal of the isopropylamino did not address the is-
sue, we turned our attention to the central five mem-
bered ring. Considering that the 3-position of pyrazole
5 and the 2-position of oxazole 6 and imidazole 7
could be sites for metabolic oxidation, our interest
was particularly drawn toward substituting the carbon
at those positions in the five membered rings with a
nitrogen atom. We also wanted to make the targets
reasonably more hydrophilic, which should also favor
improving metabolic stability and other properties,
such as solubility. Thus, aminopyrazole 8 and its
analogues were synthesized according to Scheme 4.
(Benzo[d]thiazol-6-yl)acetonitrile 23 was synthesized
from commercially available 2-(4-aminophenyl)aceto-
nitrile (20) in the same way as 1-(benzo[d]thiazol-6-
yl)ethanone (11) from 1-(4-aminophenyl)ethanone (8)
(Scheme 1). Treatment of 23 with lithium bis(trimeth-
ylsilyl)amide, followed by methyl 2-flurobenzoate, pro-
vided oxopropanenitrile 24. Heating 24 with hydrazine
afforded 8.
Table 4 lists the in vitro activities of aminopyrazole 8
and its analogues, 2 and 8a–c. Analogue 8 inhibited
p38a with an IC50 of 3.7 nM and TNFa production in
hPBMC with an IC50 of 51 nM. Similarly, 2 and 8a dis-
played p38a IC50 values of 3.2 nM and 5.5 nM, respec-
tively. The cellular activities (TNFa IC50 values) of 2
and 8a were 39 nM and 77 nM, respectively. More
importantly, the metabolic stability of these compounds
was significantly improved compared to their oxazole
and imidazole counterparts. The metabolic rates in
microsomes for 2, for example, were 0.006 nmol/
min mg-protein in humans, 0.052 nmol/min mg-protein
in rats, and 0.056 nmol/min mg-protein in mice. Com-
pounds 8b and 8c demonstrated that N-alkylation of
the pyrazole at the position next to the amino group in-
curred a loss in p38a activity, as the N-methylation (8b)
Thus far, the vicinal phenyl, benzo[d]thiazol-6-yl oxaz-
oles/imidazoles were identified as a novel class of
highly potent p38 inhibitors. However, profiling these
compounds indicated that they might be metabolically
unstable, especially in mice. For example, the meta-
bolic rates in microsomes2d for 7a were 0.109 nmol/
min mg-protein in humans, 0.081 nmol/min mg-protein
in rats, and 0.255 nmol/min mg-protein in mice. As a
Table 3. In vitro activity of 6a–h and 7a–c
N
S
N
S
R2
R2
F
F
H2N
N
S
a
b
H2N
N
N
CN
CN
HN
O
6a-f
7a-c
20
21
N
N
S
d
c
HN
Br
CN
CN
S
Compound R2
p38a IC50
(nM)
hPBMC TNFa IC50
(nM)
a
b
23
22
6a
6b
6c
6d
6e
6f
i-PrNH
H
6.4
47
16
12
40
N
S
N
S
f
F
>250
247
167
27
HN
F
HN
NH2
EtNH
O
N
NH
NC
H2N
24
(R)-2-BuNH 6.5
(S)-2-BuNH 10
8
30
35
7a
7b
7c
i-PrNH
3.3
Scheme 4. Reagents and conditions: (a) KSCN, Br2, AcOH, rt, 86%
yield; (b) CuBr2, t-BuONO, MeCN, RT, 83% yield; (c) i-PrNH2, 1,4-
dioxane, pressure tube, 130 °C, 72% yield; (d) lithium bis(trimethyl-
silyl)amide, methyl 2-fluorobenzoate, À78 °C to RT; (f) anhydrous
NH2NH2, AcOH/EtOH, 90 °C, 6 h, 17% yield over two steps.
(R)-2-BuNH 1.6
(S)-2-BuNH 2.7
13
20
a n = 4, variation in individual values, <20%.
b n = 3, variation in individual values, <25%.

1878
C. Liu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1874–1879
Table 4. In vitro activity of 8, 2, and 8a–c
N
F
HN
R3
S
N
N
H2N
R4
8, 2, 8a-c
a
b
Compound R3
R4 p38a IC50 hPBMC TNFa IC50
(nM)
(nM)
8
i-Pr
(R)-2-Bu
(S)-2-Bu
H
H
H
3.7
3.2
5.5
51
39
2
8a
8b
8c
77
118
> 250
(R)-2-Bu Me 11
(R)-2-Bu Et 17
Figure 2. The X-ray co-structure of 6a with p38a.
a n = 4, variation in individual values, <20%.
b n = 3, variation in individual values, <25%.
˚
Lys53 NH (2.87 A). In addition to these H-bonding
and N-ethylation (8c) increased the p38a IC50 from
3.2 nM (2) to 11 nM and 17 nM, respectively. The cellu-
lar activities (TNFa IC50 values) of 8b and 8c were
determined to be 118 nM and greater than 250 nM,
respectively.
interactions, the 2-fluorophenyl group occupies the
hydrophobic selectivity pocket. The pendant isopropyl
group interacts with the second hydrophobic site char-
acteristically found at the outer rim of the hinge region.
The relatively lipophilic P-Loop is closed upon the li-
gand, forming a tight hydrophobic interaction between
the sulfur of the benzothiazole ring system and Tyr35
(shown by van der Waals spheres).
A pharmacokinetic study of 2 in rats was undertaken,9
and the results showed that 2 had a half life (t1/2) of
1.7 h and a clearance of 1.4 L/h kg after intravenous
dosing at 2 mg/kg. The oral AUC and bioavailability
of 2 were 2266 nM h and 24% after administration of
a solution dosed (5 mg/kg) in PEG400.
In summary, a novel class of benzothiazole based inhib-
itors of p38a MAP kinase was proposed, synthesized,
and evaluated. Vicinal phenyl, benzo[d]thiazol-6-yl
oxazoles/imidazoles were found to be highly potent
p38a inhibitors in vitro, but were metabolically unsta-
ble. The issue of metabolic instability was addressed
by the replacement of the oxazole or imidazole ring with
an aminopyrazole system. The proposed binding mode
of this new class of p38a inhibitors was confirmed by
X-ray co-crystal structure of 6a with the p38a enzyme.
Further profiling of 2 indicates that it is selective to p38a
over a number of other kinases. When tested at 10 lM, 2
showed negligible activity (20% inhibition or less)
against the following kinases: Atk1, Atk2, Atk3, Blk,
Bmx, Brk, Btk, CaMKIIa, CHK1, CHK2, CK2a1, c-
MET, Csk, EGFR, EphA3, EphB4, ERK1, ERK2,
FES, FGFR1, FGFR2, FGFR3, FGFR4, Fyn, GSK3a,
GSK3b, Hck, Hyl, IGF1R, IRAK4, Lck, Lyn A, Lyn B,
MAPKAP-K2, MAPKAP-K3, MAPKAP-K5, NEK2,
PDGFRb, PHKG2, PKA, PKCa, PKCb1, PKCb2,
PKCc, PKCd, RSK2, Src, Yes. However, 2 did show
activity against Abl1 (65% inhibition), Fgr (54% inhibi-
tion), and Flt3 (68% inhibition). JNK family members
were not included in the kinase panel at the time when
2 was studied. Interestingly, 2 was found to be 10-fold
more selective for p38a versus p38b. This noticeable
p38a selectivity over p38b is generally true for the ben-
zothiazole based inhibitors of p38a MAP kinase.
References and notes
1. (a) Schieven, G. L. Curr. Top. Med. Chem. 2005, 5, 921;
(b) Saklatvala, J. Curr. Opin. Pharm. 2004, 4, 372; (c)
Kumar, S.; Boehm, J.; Lee, J. C. Nat. Rev. Drug Discov.
2003, 2, 717; (d) Adams, J. L.; Badge, A. M.; Kumar, S.;
Lee, J. C. Prog. Med. Chem. 2001, 38, 1; (e) Lee, J. C.;
Laydon, J. T.; McDonnell, P. C.; Gallagher, T. F.; Kimar,
S.; Green, D.; McNulty, D.; Blumenthal, M. J.; Heys, J.
R.; Landvatter, S. W.; Strickler, J. E.; McLaughlin, M.
M.; Siemens, I. R.; Fisher, S. M.; Livi, G. P.; White, J. R.;
Adams, J. L.; Young, P. R. Nature 1994, 372, 739.
The anticipated binding mode of this class of p38a
inhibitors was confirmed by an X-ray crystallographic
study of 6a bound to the p38a enzyme.10 Figure 2 illus-
trates the X-ray structure of the complex of 6a with
p38a. The ligand engages two H-bonds with p38a at
the hinge region: between the benzothiazole nitrogen
and the Met109 NH (2.09 A), and the isopropylamine
˚
NH and the Met109 carbonyl oxygen (1.84 A). Another
H-bond occurs between the oxazole nitrogen and the
2. For example (a) Hynes, J., Jr.; Dyckman, A. J.; Lin, S.;
Wrobleski, S.; Wu, H.; Gillooly, K. M.; Kanner, S. B.;
Lonial, H.; Loo, D.; McIntyre, K. W.; Pitt, S.; Shen, D.
R.; Shuster, D. J.; Yang, X.; Zhang, R.; Behnia, K.;
Zhang, H.; Marathe, P. H.; Doweyko, A. M.; Tokarski, J.
S.; Sack, J. S.; Pokross, M.; Kiefer, S. E.; Newitt, J. A.;
Barrish, J. C.; Dodd, J. H.; Schieven, G. L.; Leftheris, K.
J. Med. Chem. 2008, 51, 4; (b) Goldberg, D. R.; Hao, M.;
Qian, K. C.; Swinamer, A. D.; Gao, D. A.; Xiong, Z.;
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9. Pharmacokinetic study of 2: Male Sprague–Dawley rats
(250–300 g) were fasted overnight prior to PO dosing and
fed 4 h post dose. Blood samples (0.3 mL) were collected
from the jugular vein into K2EDTA-containing tubes
and then centrifuged at 4 °C (1500–2000g) to obtain
plasma. Two groups of animals (N = 3 per group)
received the compound either as an intravenous infusion
(2 mg/kg over 10 min) via the jugular vein or by oral
gavage (5 mg/kg). Serial blood samples were obtained at
0.17 (for IV only), 0.25, 0.5, 0.75, 1, 2, 4, 6, and 8 h post
dose. Plasma samples, obtained by centrifugation at 4 °C
(1500–2000g), were stored at À20 °C until analysis by
LC/MS/MS.
10. PDB deposition number: 3C5U.