N-aryl 2,6-dimethoxybiphenylalanine analogues as VLA-4 antagonists

Article abstract of DOI:10.1016/S0960-894X(02)00009-4

A series of N-arylated phenylalanine derivatives has been synthesized and has been shown to be potent inhibitors of the integrin VLA-4. N-phenyl and N-heteroaryl derivatives with hydrogen bond acceptors in the meta position demonstrated low nanomolar acti

Full text of DOI:10.1016/S0960-894X(02)00009-4

Bioorganic & Medicinal Chemistry Letters 12 (2002) 729–731
N-Aryl 2,6-Dimethoxybiphenylalanine Analogues as
VLA-4 Antagonists
a,
a
b
George A. Doherty, * Theodore Kamenecka, Ermenegilda McCauley,
b
b
a
a
Gail Van Riper, Richard A. Mumford, Sharon Tong and William K. Hagmann
aDepartment of Medicinal Chemistry, Merck Research Laboratories, Rahway, NJ 07065, USA
bDepartment of Immunology & Rheumatology Research, Merck Research Laboratories, Rahway, NJ 07065, USA
Received 8 October 2001; accepted 12 December 2001
Abstract—A series of N-arylated phenylalanine derivatives has been synthesized and has been shown to be potent inhibitors ofthe
integrin VLA-4. N-phenyl and N-heteroaryl derivatives with hydrogen bond acceptors in the meta position demonstrated low
nanomolar activity against VLA-4. # 2002 Elsevier Science Ltd. All rights reserved.
VLA-4 (a b ; CD49d/CD29; ‘very late antigen-4’) is a
4
1
key cell surface integrin present on leukocytes and pla-
telets, which binds vascular cell adhesion molecule-1
(
VCAM-1) on endothelial cell surfaces and leads to
leukocyte infiltration into extravascular tissue. Anti-
bodies against VLA-4 have been shown to block leuko-
cyte infiltration and prevent tissue damage in
1
,2
inflammatory disease models ofasthma,
3
multiple
sclerosis, rheumatoid arthritis (RA), and inflamma-
,4
5
The phenylalanine derivative 2 was readily prepared in
multigram quantities. The nitrogen of( l)-tyrosine-tert-
butyl ester was initially protected as a tert-butyl carba-
mate then the phenol hydroxyl converted to the corre-
sponding triflate. The triflate underwent standard
Suzuki coupling with 2,6-dimethoxyphenylboronic acid,
followed by deprotection of the a tert-butyl carbamate
6
tory bowl disease (IBD). Orally active small molecule
inhibitors ofVLA-4 might ther eof re serve as us euf l
agents in the treatment ofthese diseases.
Initial efforts in our laboratories led to the discovery of
the acylated phenylalanine derivative 1 as a low nano-
molar inhibitor ofVLA-4. The amide bond is very
7
8
group in the presence ofthe tert-butyl ester to give rise
to the aminoester 2 (Scheme 1).
important, but it was unclear ifthe amide carbonyl was
serving as a hydrogen bond acceptor, ifthe amide
nitrogen N–H was serving as a hydrogen bond donor,
or both. In an effort to test the hypothesis that the
amide bond hydrogen was providing a key binding
interaction with VLA-4 and also to move away from
peptide-like inhibitors ofVLA-4, we investigated a ser-
ies of N-arylated derivatives ofamino acid 2. These
arylated derivatives provide a N–H bond whose hydro-
gen bonding potential could be modified by substitution
on the aryl group or by different heteroaryl groups.
Using this amino acid as the building block, a series of
N-arylated derivatives was synthesized. Coupling
between the amino ester and a series ofaryl halides
ꢀ
Scheme 1. (a) Boc
2,6-dimethoxyphenylboronic acid, Pd(PPh
(d) H SO , tBuOAc.
2
O; (b) Triflic anhydride, pyridine, CH
2
Cl
2
, 0 C; (c)
;
*
5
Corresponding author. Tel.: +1-732-594-3686; fax +1-732-594-
966; e-mail: george_doherty@merck.com
)
4
, K CO
2
, EtOH, PhCH
3
3
3
2
4
0
960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00009-4

730
G. A. Doherty et al. / Bioorg. Med. Chem. Lett. 12 (2002) 729–731
9
utilizing conditions described by Buchwald and Hart-
1
The simplest N-phenyl substituted analogue 4 showed a
significant loss ofpotency compared with the acylated
derivative 1 or the benzoylated derivative 3. Since ani-
line is a much poorer hydrogen bond donor than acet-
0
wig, followed by deprotection of the tert-butyl ester,
provided swift access to the desired arylated derivatives
Scheme 2). Under these conditions, the amino acid was
(
1
1
racemized as determined by the synthesis ofthe ( S)-(À)-
amide, it was felt that the basicity of the aryl amine
needed to be reduced to make it a better hydrogen bond
donor relative to the amide. With this in mind, a num-
ber ofaryl amines substituted with electron with-
drawing groups were synthesized. Trifluoromethyl,
nitro, cyano and chloro substitution did little to increase
the potency ofthis series ( 5–11). Interestingly, a sig-
nificant increase in potency was seen with sulfonyl and
carboxamide substitutions (12–15). This increase in
potency was attributed to a possible binding interaction
between these hydrogen bonding substituents and VLA-
1
25
1
binding to VLA-4 on Jurkat cells by these compounds is
-phenylethyl ester of 15. Inhibition of
I-VCAM-Ig
7
shown in Table 1.
4
and not from an increased contribution from the ani-
ꢀ
Scheme 2. (a) ArX, NaOtBu, (rac)-BINAP, Pd
b) CF CO H, CH Cl
2
dba
3
, PhCH
3
, 75 C;
line N–H interaction. A sulfonamide in the para posi-
tion (15) showed a 3-fold increase in potency as
compared with the corresponding carboxamide (12).
Moving the sulfonamide from the para position (15) to
the meta position (16) provided a further increase in
potency. Thus, the introduction ofa meta sulfonamide
(
3
2
2
2
.
Table 1. Inhibition ofVLA-4/VCAM binding a by N-aryl phenylala-
nine derivatives
Compd
R
IC50
Compd
R
IC50
(nM)
(
nM)
Scheme 3. (a) Propanethiol, NaH, THF; (b) MCPBA, CH
NEt ; (d) CF CO H, CH Cl
2 2
Cl ; (c) 2,
1b
CH CO
3
12
10
4360
3
3
2
2
2
.
Table 2. Inihibition ofVLA-4/VCAM binding a by N-heteroaryl
phenylalanine derivatives
3b
PhCO
1.2
4
5
8870
11
6490
320
45% at 4 mM 12
46% at 4 mM 13
Compd
R
IC50 (nM) Compd
R
IC50 (nM)
3190
6
7
8
97
240
91
1
7
8
610
820
21
22
5250
3550
14
15
1
23
1
9
0
170
23
0.39
9
4470
16
12
2
4180
a
VCAM-Ig7.
l-phenylalanine derivative.
b
aVCAM-Ig7.

G. A. Doherty et al. / Bioorg. Med. Chem. Lett. 12 (2002) 729–731
731
Table 3. Sprague–Dawley rat pharmacokinetic parameters
not lead to a significant improvement in pharmacoki-
netics.
To date, most small molecule inhibitors ofVLA-4 have
been acylated amino acids, and many retain significant
1
5
peptide character. We have demonstrated that N-aryl
phenylalanine derivatives with significantly less peptide
character can serve as potent inhibitors ofVLA-4.
Compd
R
F%
24
Clp
mL/min/kg)
t
(h)
1/2
Vdss
(L/kg)
(
Acknowledgements
The authors are grateful to Zhen Wang, Junying Wang,
and Song Zheng for formulation and mass spectral
analysis ofpharmacokinetic samples and to Marcie
Donnelly for dosing of animals for pharmacokinetic
evaluation.
1
6
3
73
17
0.9
0.55
0.28
2
6
0.8
References and Notes
1
. Lin, K.-C.; Ateeq, H. S.; Hsiung, S. H.; Chong, L. T.;
Zimmerman, C. N.; Castro, A.; Lee, W.-C.; Hammond, C. E.;
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Adams, S. P. J. Med. Chem. 1999, 42, 920.
substituent provided an increase in potency of ꢁ800-fold
from the parent aniline derivative (4).
2
4
. Lin, K.-C.; Castro, A. C. Curr. Opin. Chem. Biol. 1998, 2,
53.
A series ofheteroaryl amines was examined next since
arylamines were not functioning as very effective amide
bond mimetics. The pyridyl substituted derivatives (17–
3. Tubridy, N.; Behan, P. O.; Capildeo, R.; Chaudhuri, A.;
Forbes, R.; Hawkins, C. P.; Hughes, R. A. C.; Palace, J.;
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Manus, D. G.; Donoghue, S.; Miller, D. H. Neurology 1999,
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2
2, Table 2) were made using a procedure similar to that
2
1
used to make the phenyl series and a slight modifica-
tion ofthis procedure was used to make the substituted
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imidine 23 was synthesized for comparison as illustrated
4. Keszthelyi, E.; Karlik, S.; Hyduk, S.; Rice, A.; Gordon, G.;
Yednock, T.; Horner, H. Neurology 1996, 47, 1053.
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3
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. Podolsky, D. K.; Lobb, R.; King, N.; Benjamin, C. D.;
1
4
in Scheme 3.
Pepinsky, B.; Sehgal, P.; deBaumont, M. J. Clin. Invest. 1993,
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9
The pyridyl derivatives (17–22) proved to be sig-
nificantly more potent than the corresponding phenyl
derivative (4). This increase in potency was seen in all
three positional isomers, which suggested it was due to
the aminopyridine hydrogen atom more effectively
mimicking the amide N–H. The 4-pyridyl isomer (19)
was more potent than the 2- or 3-pyridyl isomers (17–
7. Hagmann, W. K.; Durette, P. L.; Lanza, T.; Kevin, N. J.;
de Laszlo, S. E.; Kopka, I. E.; Young, D.; Magriotis, P. A.; Li,
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1
8) indicating an interaction between the pyridyl nitro-
8
. Lin, L. S.; Lanza, T.; de Laszlo, S. E.; Truong, Q.; Kame-
necka, T.; Hagmann, W. K. Tetrahedron Lett. 2000, 41, 7013.
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gen and VLA-4 could be occurring. Substitution with a
carboxamide (22) again led to a further increase in
potency. The meta substituted pyrimidine derivative 23
proved to be the first subnanomolar VLA-4 inhibitor in
this series.
9
10. Hartwig, J. F. Angew. Chem., Int. Ed. Eng. 1998, 37, 2046.
ꢀ
ꢀ
a
4.60 (25 )
11. Acetamide pKa1 À1.40 (25 ) versus aniline pK
see Dictionary of Organic Compounds; 6th Ed.; Chapman &
Hall: London, 1996; Vol. 1.
1
1
2. Wagaw, S.; Buchwald, S. L. J. Org. Chem. 1996, 61, 7240.
3. Cesium carbonate was used as base instead ofsodium tert-
The pharmacokinetic profiles ofthe meta-sulfonamide
substituted aniline 16 and the pyrimidine derivative 23
were measured in rats (Table 3). Both compounds
showed low bioavailability and high clearance (Table 3).
These pharmacokinetic profiles are very similar to our
sulfonylated proline series, which contain an amide
bond. Thus, replacement ofthe amide bond ofour
VLA-4 inhibitors with an aryl or heteroaryl amine did
butoxide.
4. Similar N-arylated compounds have been reported: Head,
1
J. C.; Porter, J. R.; Warrellow, G. J.; Archibald, S. C.;
Hutchinson, B. W. WO 0018759, 2000.
7
15. Adams, S. P.; Lobb, R. R. In Annual Reports in Medicinal
Chemistry; Doherty, A. M., Ed.; Academic: New York, 1999;
Vol. 34, Chapter 18.