Pyridone derivatives as potent, orally bioavailable VLA-4 integrin antagonists

Article abstract of DOI:10.1016/j.bmcl.2006.08.044

A series of pyridone-N-benzyl-propanoic acids have been optimised to afford potent orally bioavailable VLA-4 antagonists.

Full text of DOI:10.1016/j.bmcl.2006.08.044

Bioorganic & Medicinal Chemistry Letters 16 (2006) 5538–5541
Pyridone derivatives as potent, orally bioavailable
VLA-4 integrin antagonists
Jason Witherington,a,* Emma L. Blaney,a Vincent Bordas,a Richard L. Elliott,a
Alessandra Gaiba,a Neil Garton,a Philip M. Green,b Antoinette Naylor,a
David G. Smith,a David J. Spalding,a Andrew K. Taklea and Robert W. Warda
aDepartment of DMPK and Medicinal Chemistry, Neurology and GI Centre of Excellence for Drug Discovery,
GlaxoSmithKline Research Limited, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
bDepartment of Assay Development and Compound Profiling, Medicines Research Centre,
GlaxoSmithKline, Stevenage SG1 2NY, UK
Received 14 June 2006; revised 31 July 2006; accepted 8 August 2006
Available online 22 August 2006
Abstract—A series of pyridone-N-benzyl-propanoic acids have been optimised to afford potent orally bioavailable VLA-4
antagonists.
Ó 2006 Elsevier Ltd. All rights reserved.
VLA-4 (Very Late Antigen-4, a4b1, or CD49d/CD29) is
a member of the superfamily of transmembrane glyco-
protein integrins made up of a- and b-heterodimers ex-
pressed on all leukocytes except neutrophils and
platelets.1–3 VLA-4 binds to an alternatively spliced seg-
ment of fibronectin (CS-1) on extracellular matrix and
to vascular cell adhesion molecule-1 (VCAM-1) on
endothelium. VCAM-1 is expressed on vascular endo-
thelial cells in response to proinflammatory cytokines
and the VCAM-1/VLA-4 binding interaction has been
shown to be critical for lymphocyte migration to extra-
vascular tissues.4 Antibodies against VLA-4 have been
shown to block leukocyte infiltration and prevent tissue
damage in inflammatory disease models of asthma,5
rheumatoid arthritis,6 multiple sclerosis (MS),7 and
inflammatory bowel disease.8 Recently, humanised
monoclonal anti-a4 antibody (Tysabri) has demonstrat-
ed efficacy for MS and Crohn’s disease in phase III clin-
ical trials.9 Orally active small molecule inhibitors of
VLA-4 might therefore serve as useful agents in the
treatment of these diseases (Scheme 1).
sequent SAR optimisation and in vivo properties of
these compounds. Previously it had been reported that
the presence of an ortho methyl group in the terminal
aromatic ring of the urea gave optimal inhibitory poten-
cy.11 Indeed, we had found incorporation of this substi-
tuent did afford a very potent inhibitor (2),10 although
the corresponding unsubstituted analogue (1) also dis-
played excellent potency. Interestingly, although initial-
ly it appears that increasing the size of the substituent
leads to a decrease in potency (cf 2 with 3 and 5), incor-
poration of the ortho acetamido group (6) is well toler-
ated and may suggest that this group is able to
participate in a hydrogen bonding interaction with the
protein. Incorporation of a second methyl group at
any of the other positions in the terminal ring other than
the 6-position (10) is clearly disfavoured (7, 8, and 9),
suggesting a tight binding pocket (Tables 1–4).
A feature of many urea containing VLA-4 antagonists is
the presence of a methyl group beta to the carboxylate
moiety.12 Intrigued by this observation we decided to
explore the SAR around this part of the molecule.
Incorporation of the methyl group into the side chain
of our inhibitors did afford a modest increase in potency
in the R-enantiomer (cf 11 and 13). Unfortunately,
incorporation of the potency enhancing B-ring substitu-
ent10 and a b-methyl moiety did not afford an additive
increase in potency in the more potent R-enantiomer
(cf 13 and 15) but did afford a modest increase in the
Recently, we disclosed a novel series of pyridone con-
taining VLA-4 antagonists.10 Herein we report the sub-
Keywords: VLA-4; Integrin; Pyridone; Bioavailability.
*
Corresponding author. Tel.: +44 01279 627832; e-mail: Jason_
Witherington@GSK.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.08.044

J. Witherington et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5538–5541
5539
EtO2C
H
N
Ph
EtO2C
a
b
O
OH
+
31a (S,S)
CO2H
EtO2C
H
N
30
Ph
O
OH
(R,S)
31b
HO
HO
H
N
c
Ph
CO2Me
O
OH
32 (R,S)
33
H
N
H
N
d-f
O
H
H
ii.
MeO
N
N
O
N
O
MeO
34
15
O
N
H
CO2H
Scheme 1. Reagents and conditions: (a) i—(COCl)2, 0 °C; ii—(2S)-2-amino-2-phenylethanol, Et3N, DCM, 0–25 °C (94%); (b) LiBH4, MeOH, THF
(90%); (c) i—3 N H2SO4, dioxane, reflux (94%); ii—concd H2SO4, MeOH, reflux (69%); (d) MsCl, Et3N, DCM (100%); (e) 34, Cs2CO3, DMF, 25 °C
(87%); (f) 0.5 N aq LiOH, THF, 25 °C (89%).
Table 2. The b-methyl SAR
Table 1. A-ring SAR
H
H
N
H
N
H
N
N
O
O
A
B
O
O
R1
N
CO2H
MeO
N
R
C
D
CO2H
R2
Compound
R
H
pKi a4b114
Compound
R1
R2
pKi a4b1
1
2
8.8
9.3
6.5
8.2
8.3
8.2
7.6
7.6
8.1
8.7
2
11
12
13
14
15
MeO
H
H
9.3
8.6
8.6
9.0
9.0
9.1
2-Me
2-iPr
H
3
H
(S)-Me
(R)-Me
(S)-Me
(R)-Me
4
2-OMe
2-Br
H
5
MeO
MeO
6
2-NHAc
2,3 DiMe
2,4 DiMe
2,5 DiMe
2,6 DiMe
7
8
9
10
the meta position with several groups being well tolerat-
ed in the R series but poorly tolerated in the S series (cf
21 with 28 and 22 with 29).
S-enantiomer (cf 12 and 14) although this modification
did not display a potency enhancement relative to the
baseline compound 2.
Having identified several potent inhibitors we sought to
determine whether they were orally bioavailable in the
rat. Initial evaluation of 2 and 11 suggested that like
many other urea containing VLA-4 antagonists, oral
absorption was likely to be an issue.13 Gratifyingly,
incorporation of the b-methyl substituent afforded a
modest improvement in oral absorption (cf 13 with 11)
and further profiling of this compound revealed the
compound to have low clearance and modest but vari-
able bioavailability. The profile was further improved
by incorporation of the B-ring methoxy group (13 with
Since we had observed a modest increase in potency by
incorporation of an ortho methoxy group into the
B-ring of the unbranched propionic acid series we decid-
ed to revaluate the SAR in the substituted series. Unfor-
tunately, incorporation of a variety of ortho substituents
in either enantiomeric form failed to improve the poten-
cy over the baseline compounds 12 and 13. Interestingly,
however, the enantiomers displayed divergent SAR at

5540
J. Witherington et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5538–5541
Table 3. B-ring SAR in the b-methyl series
we have systematically identified the key pharmaco-
phoric features responsible for high inhibitory potency.
In common with the literature the SAR around the
A-ring suggests an ortho methyl group is optimal as is
the presence of an ortho methoxy moiety in the B-ring.
Unfortunately incorporation of both these potency
enhancing substituents into the more potent b-methyl
propionic acid series does not lead to an additive in-
crease in potency. In vivo profiling of two of the more
potent inhibitors suggests oral bioavailability is achiev-
able with this series.
H
H
N
N
O
O
N
CO2H
R
Compound
R
R/S
pKi a4b1
16
17
18
19
20
21
22
23
24
25
26
27
28
29
2-Cl
R
R
R
R
R
R
R
S
S
S
S
S
S
S
9.0
8.4
8.7
8.2
9.0
9.1
8.6
8.7
7.7
8.3
7.3
8.6
7.6
7.7
2-OCF3
2-OEt
2-Et
2-Me
3-Cl
3-Me
2-Cl
References and notes
2-OCF3
2-OEt
2-Et
1. Hemler, M. E.; Elices, M. J.; Parker, C.; Takada, Y.
Immunol. Rev. 1990, 114, 45.
2. Springer, T. A. Cell 1994, 76, 301.
3. Elices, M. J. Curr. Opin. Anti-Inflam. Immunomod. Invest.
Drugs 1999, 1, 14.
4. (a) Gearing, A. J. H.; Newman, W. Immunol. Today 1993,
14, 506; (b) Hemler, M. E. Annu. Rev. Immunol. 1990, 8,
365.
2-Me
3-Cl
3-Me
5. Abraham, W. M.; Sielczak, M. W.; Ahmed, A.; Cortes,
A.; Lauredo, I. T.; Kim, J.; Pepinsky, B.; Benjamin, C. D.;
Leone, D. R.; Lobb, R. R. J. Clin. Invest. 1994, 93, 776.
6. Seiffge, D. J. Rheumatol. 1996, 23, 2086.
7. (a) Tubridy, N.; Behan, P. O.; Caplildeo, R.; Chaudhuri,
A.; Forbes, R.; Hawkins, C. P.; Hughes, R. A. C.; Palace,
J.; Sharrack, B.; Swingler, R.; Young, C.; Mosley, I. F.;
MacManus, D. G.; Donoghue, S.; Miller, D. H. Neurology
1999, 53, 466; (b) Keszthelyi, E.; Karlik, S.; Hyduk, S.;
Rice, A.; Gordon, G.; Yednock, T.; Horner, H. Neurology
1996, 47, 1053.
15) possibly due to the formation of an intra-molecular
hydrogen bond with the acidic urea functionality. Com-
pound 15 displayed the most encouraging PK profile
(%Fpo = 49, 84, 166, 185) and although the group size
was small (n = 4) the exposure and clearance appeared
highly variable suggesting events such as recycling and
transporter mediated absorption and/or elimination
may be contributing to the high, but variable,
bioavailability.
8. Podolsky, D. K.; Lobb, R.; King, N.; Benjamin, C. D.;
Pepinsky, B.; Sehgal, P.; deBaumont, M. J. Clin. Invest.
1993, 92, 972.
The single enantiomers of the pyridone analogue 15
were obtained15 by treatment of the known acid16 30
with oxalyl chloride followed by coupling with commer-
cially available (2S)-2-amino-2-phenylethanol to afford
the diastereomers 31a and 31b which were readily sepa-
rable using conventional column chromatography.
Reduction of 31b with lithium borohydride afforded
the corresponding alcohol 32 which was hydrolysed to
the corresponding acid then converted to the methyl es-
ter 33. Treatment of 33 with methane sulfonyl chloride
afforded the corresponding mesylate which was then
reacted with the known pyridone10 34 to afford the inter-
mediate ester which was then hydrolysed with lithium
hydroxide to afford the desired analogue 15 in good
overall yield.
9. (a) Polman, C. H.; O’Connor, P. W.; Havrdova, E.;
Hutchinson, M.; Kappos, L.; Miller, D. H.; Phillips, J.
T.; Lublin, F. D.; Giovannoni, G.; Wajgt, A.; Toal, M.;
Lynn, F.; Panzara, M. A.; Sandrock, A. W. N. Engl. J.
Med. 2006, 354, 899; (b) Sandborn, W. J.; Colombel, J.
F.; Enns, R.; Feagan, B. G.; Hanauer, S. B.; Lawrance,
I. C.; Panaccione, R.; Sanders, M.; Schreiber, S.;
Targan, S.; van Deventer, S.; Goldblum, R.; Despain,
D.; Hogge, G. S.; Rutgeerts, P. N. Engl. J. Med. 2005,
353, 1912.
10. Witherington, J.; Bordas, V.; Gaiba, A.; Green, P. M.;
Naylor, A.; Parr, N.; Smith, D. G.; Takle, A. K.; Ward, R.
W. Bioorg. Med. Chem. Lett. 2006, 16, 2256.
11. Lin, K.-C.; Ateeq, H. S.; Hsiung, S. H.; Chong, L. T.;
Zimmerman, C. N.; Castro, A.; Lee, W.-C.; Hammond, C.
E.; Kalkunte, S.; Chen, L.-L.; Pepinsky, R. B.; Leone, D.
R.; Sprague, A. G.; Abraham, W. M.; Gill, A.; Lobb, R.
R.; Adams, S. P. J. Med. Chem. 1999, 42, 920.
In summary, having previously successfully employed a
pyridone nucleus as a bioisostere for an amide moiety,
Table 4. Rat pharmacokinetic profiles of selected VLA-4 antagonists
Compound
DNAUCa (min kg/L)
Fb,c (%)
Cl (iv) (mL/min/kg)
t1/2 (h)
VSS (L/kg)
2
11
13
15
6
3
0.5
3
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
14
154 82
4
22 15
121 72
16
9
7
12
1.3 0.7
1.4 0.8
0.6 0.1
0.6 0.4
a Dose normalised area under the curve (0–8 h).
b Male Sprague–Dawley rats (n = 3–4, SD).
c Dose: iv infusion at 1 mg/kg; po at 3 mg/kg (n = 3–4, SD).

J. Witherington et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5538–5541
5541
12. Singh, J.; Vlihmen, H. V.; Liao, Y.; Lee, W.-C.; Corbenise,
M.; Harris, M.; Shu, I.-H.; Gill, A.; Cuervo, J. H.;
Abraham, W. M.; Adams, S. P. J. Med. Chem. 2002, 45,
2988.
13. Chiba, J.; Takayama, G.; Takashi, T.; Yokoyama, M.;
Nakayama, ; Baldwin, J. J.; McDonald, E.; Moriarty, K.
J.; Sarko, C. R.; Saionz, K. W.; Swanson, R.; Hussain, Z.;
Wong, A.; Machinaga, N. Bioorg. Med. Chem. 2006, 14,
2725.
14. The Jurkat J6 Scintillation Proximity Assay was used to
investigate the interaction of the integrin VLA-4 (Very
Late Antigen-4; a4b1; CD49d, CD29) expressed on the
Jurkat J6 cell membrane with test compounds. J6 cells (1
million cells/well) were allowed to coat wheat germ
agglutinin coated SPA beads (Amersham, 1 mg/well) in
assay buffer containing 50 mM Hepes, 100 mM NaCl and
1 mM MnCl2 (pH with 4 M NaOH to 7.5). Tritiated H
3
Standard Compound A (1–3 nM final assay concentra-
tion) and test compounds were dissolved in an appropriate
solvent and diluted in assay buffer. Data are presented as
mean pKi. Standard compound A is (2S)-3-[4-({[4-(ami-
nocarbonyl)-1-piperidinyl]carbonyl}oxy)phenyl]-2-[((2S)-
4-methyl-2-{[2-(2-methylphenoxy)acetyl]amino}penta-
noyl)amino] propanoic acid potassium salt which is
described in patent application WO 00/37444.
15. (a) Witherington, J; Elliot, R. L. JP 2005255675; (b)
Witherington, J; Elliot, R. L. WO 2004014859.
16. DeGraw, J. I.; Christie, P. H.; Tagawa, H.; Kisliuk, R. L.;
Gaumont, Y.; Schmid, F. A.; Sirotnak, F. M. J. Med.
Chem. 1986, 29, 1056.