p38 kinase inhibitors for the treatment of arthritis and osteoporosis: Thienyl, furyl, and pyrrolyl ureas

Article abstract of DOI:10.1016/S0960-894X(00)00574-6

Inhibitors of the MAP kinase p38 are potentially useful for the treatment for osteoporosis, arthritis, and other inflammatory diseases. A series of thienyl, furyl, and pyrrolyl ureas has been identified as potent p38 inhibitors, displaying in vitro activity in the nanomolar range. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00574-6

Bioorganic & Medicinal Chemistry Letters 11 (2001) 9±12
p38 Kinase Inhibitors for the Treatment of Arthritis and
Osteoporosis: Thienyl, Furyl, and Pyrrolyl Ureas
Aniko M. Redman,a Je€rey S. Johnson,a Robert Dally,a Steve Swartz,a
Hanno Wild,a Holger Paulsen,a Yolanda Caringal,a David Gunn,a Joel Renick,a
Martin Osterhout,a Jill Kingery-Wood,a Roger A. Smith,a Wendy Lee,a
Jacques Dumas,a Scott M. Wilhelm,b Timothy J. Housley,b Ajay Bhargava,b
Gerald E. Ranges,b Alka Shrikhande,b Deborah Young,b Michael Bombarab
and William J. Scotta,*
aDepartment of Chemistry Research, Bayer Research Center, Pharmaceutical Division, 400 Morgan Lane,
West Haven, CT 06516, USA
bDepartment of Cancer and Osteoporosis Research, Bayer Research Center, Pharmaceutical Division,
400 Morgan Lane, West Haven, CT 06516, USA
Received 15 August 2000; accepted 2 October 2000
AbstractÐInhibitors of the MAP kinase p38 are potentially useful for the treatment for osteoporosis, arthritis, and other in¯am-
matory diseases. A series of thienyl, furyl, and pyrrolyl ureas has been identi®ed as potent p38 inhibitors, displaying in vitro activity
in the nanomolar range. # 2000 Elsevier Science Ltd. All rights reserved.
Members of the MAP kinase family are implicated in the
activation of a wide variety of transcription factors and
proteins involved in the control of cytokine production. A
pair of novel protein kinase homologues (p38) involved in
the regulation of cytokine synthesis have been described.1
Small molecule inhibitors of p38, such as SB 203580 12,3
(Fig. 1), can potentially lead to the treatment of osteo-
porosis and in¯ammatory disorders.
(Maybridge GK 00687) was identi®ed as a reversible
p38 inhibitor (Fig. 1). It was rapidly shown that the
corresponding furans and pyrroles were also active.
This paper describes our e€ort to optimize substitutions
on both rings of the lead urea.4
Chemistry
Ureas were synthesized by the reaction of the hetero-
cyclic amines with phosgene (or a phosgene equivalent),
followed by treatment with anilines (Scheme 1). Alter-
natively, heterocyclic amines were reacted with iso-
cyanates.
Figure 1. p38 Kinase inhibitors.
Following high throughput screening of the Bayer com-
pound library, the commercially available thienyl urea 2
Scheme 1. Synthesis of thienyl, furyl, and pyrrole ureas.
In the case of pyrroles, the ring nitrogen did not need
protection during this reaction sequence. Methyl 3-amino-
*Corresponding author. Tel.: +1-203-812-2935; fax: +1-203-812-
3655; e-mail: william.scott.b@bayer.com, aniko.redman.b@bayer.com
0960-894X/01/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00574-6

10
A. M. Redman et al. / Bioorg. Med. Chem. Lett. 11 (2001) 9±12
5-tert-butyl-2-thiophene carboxylate was obtained by the
condensation of methyl thioglycolate with (Z)-3-chloro-
4,4-dimethyl-2-pentenenitrile5 according to a published
procedure.6 Other substituted 4-alkylthiophenes could
be prepared by the synthesis of cyanoalkynes, such as
nitrile 5 and their subsequent treatment with methyl
thioglycolate (Scheme 2).7
Scheme 5. Synthesis of 3-aminopyrroles.
2-Carbamoyl pyrroles were prepared from ester 18
by saponi®cation and EDCI coupling, followed by
reduction of the nitro group (Scheme 6). N-Alkyl-3-
aminopyrrole was generated by treatment of nitro-
pyrrole 18 with an alkylating agent followed by hydro-
genation.
Scheme 2. Synthesis of 4-alkylthiophenes from cyanoalkynes.
4-Nitro- and 4-aminothienyl ureas 9 and 10 were
obtained from methyl 3-amino-2-thiophenecarboxylate
(7) via a protection, nitration, and deprotection proto-
col. The nitro group was reduced after urea formation
(Scheme 3).
Scheme 6. Synthesis of pyrrole amides.
Results and Discussion
Simple changes in the 5-position of the thiophene ring
had a profound e€ect on potency (Table 1).14
Scheme 3. Synthesis of 4-nitro and 4-aminothienyl ureas.
Among various alkyl substitutents, tert-butyl was opti-
mal (entry 22). Sterically more demanding groups were
not well tolerated (entries 24 and 25), while smaller alkyl
groups also resulted in loss of activity (entry 21). Sur-
prisingly, urea 10 with an amino group in the 4-position
was again a potent inhibitor. Nitrophenyl urea 9 dis-
played no activity.
Variation of the ester moiety was studied by Ti(IV)
mediated transesteri®cation,8 or by BOC-protection of
the amine, saponi®cation, ester formation and amine
deprotection. Amide analogues, such as thiophene 13,
were obtained from the corresponding esters using a Cbz-
protection of the amine, amidation and deprotection
protocol, or more simply by Weinreb amidation9
(Scheme 4).
Table 1. Thiophene alkyl substituents
Entry
R
% Inhibition
(5 mM)
p38 a2
IC50 (nM)
21
22
23
24
25
26
27
9
iPr
C(CH3)3
2-Methylpropyl
3-Methylbutyl
1-Hydroxy-1-methylethyl
Phenyl
37
94
0
8
34
0
17
0
90
413
Scheme 4. Amidation of esters.
2-Phenylethyl
NO2
NH2
Furyl amines, such as 12, were synthesized according
to a previously published procedure.10,11 3-Amino-
pyrroles were synthesized by Friedel±Crafts alkylation
of methyl pyrrole-3-carboxylate (15),12 followed by
electrophilic nitration and reduction of the nitro group
(Scheme 5).13
10
441
The e€ect of various ester substitutions is summarized
in Table 2. Within the simple alkyl ester series, ana-

A. M. Redman et al. / Bioorg. Med. Chem. Lett. 11 (2001) 9±12
Table 4. Substitution of the phenyl moiety
11
logues with bulkier alkyl groups were, in general,
weaker inhibitors (entries 28±30).
Table 2. Thiophene ester substituents
Entry
X
Y
Ar
% Inhibition E. coli p38 a2
(0.5 mM)
IC50 (nM)
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
O
O
O
OMe
OMe
NHMe
OMe
NMHe
OMe
OMe
NHMe 4-Fluorophenyl
OMe
OMe
OMe 4-Hydroxyphenyl
OMe 4-Acetamidophenyl
OMe 4-Methoxyphenyl
OMe
OMe 4-Carboxyphenyl
OMe 4-Acetylphenyl
OMe 2,3-Dichlorophenyl
OMe 4-Fluorophenyl
Phenyl
68
40
70
10
63
6
35
80
76
40
44
23
8
16
4
21
79
67
97
290
660
119
4-Ethylphenyl
4-Ethylphenyl
4-Isopropyl
4-Isopropyl
4-Phenylphenyl
4-Fluorophenyl
Entry
Y
p38 a2
IC50 (nM)
22
28
29
30
31
32
33
34
OMe
OEt
OPr
413
3020
482
741
57
56
464
5310
270
830
88
220
750
610
OiPr
O(CH2)2OH
O(CH2)3OH
O(CH2)2OCH3
OCH2CO2CH3
4-Chlorophenyl
4-Aminophenyl
4-Nitrophenyl
Esters with free hydroxyl groups, such as ureas 31 and
32, showed a signi®cant increase in potency. Other polar
substituents (entries 33 and 34) led to a signi®cant
decrease in activity.
180
210
32
1200
44
42
60
27
43
6
44
12
28
947
400
663
387
253
OMe 2,3-Dichlorophenyl
OMe 3,4- Dichlorophenyl
NH OMe
NH OMe
NH OMe
NH OMe
NH OMe
Phenyl
Replacement of the thiophene ring by furan or pyrrole
heterocycles resulted in increased potency, except in the
case of N-methylcarbamoyl pyrroles (Table 3).
4-Fluorophenyl
2-Chlorophenyl
3-Chlorophenyl
4-Chlorophenyl
89
85
95
92
99
95
NH OMe 2,3-Dichlorophenyl
NH NHMe 2,3-Dichlorophenyl
Table 3. Ester versus amide on various heterocycles
NH OMe
NH NHMe
NMe OMe
NMe OMe
NMe OMe
1-Naphthyl
1-Naphthyl
Phenyl
4- Methylphenyl
4-Fluorophenyl
96
32
42
50
67
NMe OMe 2,3-Dichlorophenyl
NMe OMe 1-Naphthyl
Entry
X
Y
E. coli p38 a2
IC50 (nM)
stituents led to decreased potency (entries 41, 43, and
45). Placing halogens in both the ortho and meta posi-
tions led to the best inhibitors (entries 56, 58, 65, and
71). Hydrogen bonding amino and hydroxyl sub-
stituents, as in ureas 49 and 50, caused some loss of
activity. Acylation of the amine moiety or alkylation of
the phenol led to inactive analogues (entries 51 and 52,
respectively), as did the introduction of electron with-
drawing groups other than halogen (entries 53±55). The
overall trend pointed to halogens and small alkyl groups
on the phenyl ring to provide optimal lipophilicity.
Among the heterocycles, pyrroles consistently showed
higher potency.
22
35
36
37
38
39
S
S
O
O
NH
NH
OMe
NHMe
OMe
NHMe
OMe
NHMe
248
34
73
32
33
67
During further optimization it was found that replacing
esters with amides greatly improved the activity of
thiophene ureas (Table 3, entry 35 vs 22). This e€ect was
less signi®cant in the case of furan and pyrrole ureas
(entry 37 vs 36 and entry 39 vs 38). This discrepancy
may be due to the thiophene being the most lipophilic of
the three heterocycles. The e€ect of phenyl substitution
was ®rst investigated in the thiophene series, followed by
a more focused optimization of furan and pyrrole ureas
(Table 4).
A few ureas with signi®cant activity against p38 kinase
were selected to measure inhibition of IL-6 production
in SW1353 cells treated with both cytokines IL-1 and
TNF-a.15 SB 203580 (1) was used as a reference com-
pound. The observed cellular activity of our analogues
does not directly correlate with the p38 IC50 values. How-
ever, data presented in Table 5 suggest that functional
activity is driven by the combination of primary target
potency and appropriate lipophilicity (clogP<4.5).
In the ester series small alkyl groups and halogens were
tolerated in the para position (Table 3, entry 22, Table
4, entry 48). Increasing the size of the para-alkyl sub-

12
A. M. Redman et al. / Bioorg. Med. Chem. Lett. 11 (2001) 9±12
Table 5. Inhibition of IL-6 production in SW1353 cells
J. C.; Smietana, J. M.; Sorenson, M. E.; Gallagher, T. F.;
Sheldrake, P. L.; Bradbeer, J.; Badger, A. M.; Laydon, J. T.;
Lee, J. C.; Hillegrass, L. M.; Griswold, D. E.; Breton, J. J.;
Chabot-Fletcher, M. C.; Adams, J. L. J. Med. Chem. 1996, 39,
3929.
3. Wilson, K.; McCa€rey, P.; Hsiao, K.; Pazhanisamy, S.;
Galullo, V.; Bemis, G.; Fitzgibbon, J.; Caron, P.; Murcko, M.;
Su, M. Chem. Biol. 1997, 4, 423.
4. For additional examples of urea-based p38 kinase inhibi-
tors, see: (a) Dumas, J.; Sibley, R.; Riedl, B.; Monahan, M.
K.; Lee, W.; Lowinger, T. B.; Redman, A. M.; Johnson, J. S.;
Kingery-Wood, J.; Scott, W. J.; Smith, R. A.; Bobko, M.;
Schoenleber, R.; Ranges, G. E.; Housley, T. J.; Bhargava, A.;
Wilhelm, S. M.; Shrikhande, A. Bioorg. Med. Chem. Lett.
2000, 10, 2047. (b) Dumas, J.; Hatoum-Mokdad, H.; Sibley,
R.; Riedl, B.; Monahan, M. K.; Lowinger, T. B.; Brennan, C.
R.; Natero, R.; Turner, T.; Scott, W. J.; Redman, A. M.;
Johnson, J. S.; Schoenleber, R.; Wilhelm, S. M.; Housley, T.
J.; Ranges, G. E.; Bhargava, A.; Shrikhande, A. Bioorg. Med.
Chem. Lett. 2000, 10, 2051.
5. Hackler, R. E.; Burow, K. W.; Kaster, S. V., Jr.; Wickiser,
D. I. J. Heterocycl. Chem. 1989, 26, 1575.
6. Hartmann, H.; Liebscher, J. Synthesis 1984, 3, 275.
7. A modi®cation of the Klein method was used: Ren, W.;
Rao, K. V. B.; Klein, R. S. J. Heterocycl. Chem. 1986, 23,
1757.
8. Seebach, D.; Hungerbuhler, E.; Naef, R.; Schnurrenberger,
P.; Weidmann, B.; Zuger, M. Synthesis 1982, 138.
9. Basha, A.; Lipton, M.; Weinreb, S. M. Tetrahedron Lett.
1977, 48, 4171.
10. Gewald, K.; Bellmann, P.; Jansch, H.-J. Liebigs Ann.
Chem. 1984, 1702. Tronchet, J. M. J.; Martin, O. R. Helv.
Chim. Acta 1976, 59, 945. Shiotani, S.; Morita, H.; Ishida, T.;
In, Y. J. Heterocycl. Chem. 1988, 25, 1205.
Entry
E. coli p38 a2
IC50 (nM)
Inhibition of IL-6
production IC50 (nM)
ClogP
(daylight)
1
20
248
34
73
33
67
42
6
50
905
1350
335
1140
15
464
79
16
3.6
5.6
4.9
5.0
4.6
3.4
4.3
4.9
3.8
5.3
4.1
22
35
36
38
39
61
65
66
67
68
44
12
28
309
35
In conclusion, a thienyl urea series has been identi®ed as
potent p38 inhibitors.16 On exploring di€erent substitu-
tion e€ects, a steep structure±activity correlation was
established for the C-5 position of the thiophene ring
and for the aryl side of the urea. In addition, furans and
pyrroles showed analogous trends. Optimization of the
lead thienyl urea 2 led to a 50-fold increase in in vitro
activity (compound 65). The best analogues of this new
class show potency in a cellular functional assay of
cytokine release.
Acknowledgements
We would like to thank Mr. Anthony Paiva for obtain-
ing mass spectra and Dr. Robert Schoenleber for helpful
discussions.
11. Redman, A. M.; Dumas, J.; Scott, W. J. Org. Lett. 2000,
2, 2061.
12. For the synthesis of ester 16, see: Anderson, J. H.; Huang,
C. W. Can. J. Chem. 1970, 48, 1550.
References and Notes
13. For an analogous electrophilic nitration of a furano-
pyrrole, see: Hendrickson, J. B.; De Vries, J. G. J. Org. Chem.
1985, 50, 1688.
14. Initial in vitro studies were conducted with bacculovirus-
derived p38. Later studies were conducted with E. coli-derived
enzyme.4,15
15. For experimental details on measuring IL-6 production in
SW1353 cells, see ref 4.
16. Ranges, G.; Scott, W.; Bombara, M.; Rauner, D.; Redman,
A.; Smith, R.; Paulsen, H.; Chen, J.; Gunn, D.; Renick, J. PCT
Int. Appl. WO 98/52558; Chem. Abstr. 1998, 130, 32886.
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