Synthesis and biological activity of N-substituted aminocarbonyl-1,3- dioxolanes as VLA-4 antagonists

Article abstract of DOI:10.1016/j.bmcl.2010.07.069

A novel set of compounds with a 1,3-dioxolane ring which acts as a proline bioisostere have been successfully designed as VLA-4 receptor antagonists. Compounds (18e), (28j), and (35g) were shown to have high receptor affinities.

Full text of DOI:10.1016/j.bmcl.2010.07.069

Bioorganic & Medicinal Chemistry Letters 20 (2010) 5514–5520
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and biological activity of N-substituted
aminocarbonyl-1,3-dioxolanes as VLA-4 antagonists
a
a
a
a
b
Abdul Rehman a, , Ajay Soni , Keshav Naik , Sreeji Nair , Venkata P. Palle , Sunanda Dastidar ,
*
Abhijit Ray b, M. S. Alam c, Mohammad Salman a, Ian A. Cliffe a, Viswajanani Sattigeri a
a Department of Medicinal Chemistry, New Drug Discovery Research, Ranbaxy Research Laboratories, Plot 20, Sector 18, Gurgaon 122015, Haryana, India
b Department of Pharmacology, New Drug Discovery Research, Ranbaxy Research Laboratories, Plot 20, Sector 18, Gurgaon 122015, Haryana, India
c Department of Chemistry, Jamia Hamdard, New Delhi 110062, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel set of compounds with a 1,3-dioxolane ring which acts as a proline bioisostere have been success-
fully designed as VLA-4 receptor antagonists. Compounds (18e), (28j), and (35g) were shown to have high
receptor affinities.
Received 12 May 2010
Revised 10 July 2010
Accepted 16 July 2010
Available online 23 July 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
1,3-Dioxolane
Bioisosters
VLA-4 antagonist
Very late antigen-4 (VLA-4,
a
4b1) is a member of the b1 sub-
ophysiological processes, and so the inhibition of VLA-4 is expected
to be of therapeutic benefit in the treatment of a variety of inflam-
matory diseases.3,4
VLA-4 binds to a motif containing the sequence EILDVPST with-
in VCAM-1, and peptidomimetic inhibitors of the critical leucine—
aspartic acid—valine (LDV) sequence have been reported.5 Non-
peptidomimetic inhibitors have also been developed ( Fig. 1) in
family of integrins and is expressed on all circulating leukocytes
except platelets.1,2 VLA-4 mediates both cell–cell and cell–matrix
interactions by binding to cell surface ligands such as vascular cell
adhesion molecule-1 (VCAM-1) and cell–matrix proteins such as
fibronectin. These interactions are important for the activation,
migration, and proliferation of leukocytes during normal and path-
H
H
H
H
N
H
N
N
N
N
N
S
N
S
N
S
OH
OH
OH
O
O
O
O
O
N
O
O
O
O
O
O
Cl
O
O
O
N
H
Cl
(1) American Home Product/Elan
Cl
(2) American Home Product/Elan
(3) Merck
H
N
H
H
OMe
O
S
N
Cl
N
O
N
S
OH
O
N
O
O
OH
O
Cl
OH
Cl
O
O
O
O
MeO
O
Cl
Cl
(4) GSK & Tanabe,TR-14035
(5) Merck
Figure 1. Potent VLA-4 inhibitors.
(6) CT-5219
* Corresponding author. Tel.: +91 09999100317; fax: +91 124 2343545.
E-mail address: ab_rehman@rediffmail.com (A. Rehman).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.07.069

A. Rehman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5514–5520
5515
O
O
O
O
O
HO
HO
O
O
O
O
(i)
O
O
O
O
(ii)
O
OH
O
(10)
O
(11)
(9)
(iii)
X
O
OH
O
(iv)
O
O
O
O
+
O
O
O
HN
Ph
R1
H2N
O
HN
Ph
(14a) X = NO2, R1 = Me
(14b) X = OH, R1 = Bn
(13)
(12)
(v)
NH2
X
O
O
(vi)
O
(vii)
O
N
H
O
O
R1
O
N
O
H
O
O
O
O
HN
Ph
HN
Ph
(15a) X = NO2, R1 = Me
(15b) X = OH, R1 = Bn
(16)
O
H
R2
H
N
R2
N
O
O
O
OH
O
O
O
N
(iv)
O
O
N
H
O
H
O
O
O
HN
Ph
HN
Ph
(18a-18g)
(17a-17g)
O
R3
O
(vi)
(viii)
O
Ph
O
O
N
(15b)
H
O
O
Ph
HN
O
R3
O
OH
O
O
N
H
O
O
(19a-16c)
HN
Ph
(20a-20c)
Scheme 1. Reagents: (i) dimethoxymethane, BF3ÁEtO, isopropyl acetate, 100%; (ii) KOH, EtOH, 56%; (iii) 2-phenylaniline, EDC, NMM, HOBt, DMF, 67%; (iv) LiOHÁH2O,
THF:MeOH:H2O, 50–95%; (v) EDC, NMM, HOBt, DMF, 73%; (vi) 10% Pd/C, MeOH, 87%; (vii) R2-COOH, EDC, NMM, HOBt, DMF, 45–75%; (viii) R3-CH2Br, K2CO3, acetone, 51–80%.
which an N-acylphenylalanine core appears to be critical for activ-
ity. Unlike the LDV-based mimics which in general are very selec-
tive for VLA-4, N-acylphenylalanine derivatives are dual inhibitors
of VLA-4/VCAM and a4b7/MAdCAM (mucosal adhesion cell adhe-
sion molecule) interactions. Elan has reported the SAR of com-
pound (1) (CT-757) and shown that its oral bioavailability in rats

5516
A. Rehman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5514–5520
R2
tained an N-(2-phenyl)phenylaminocarboxy group attached to
X
the proline ring. We now report the results of further work where-
in 1,3-dioxolane ring (8) was evaluated as bioisoster of proline in
standard N-acylphenylalanine derivatives (7).
HN
O
N
OH
COOH
O
O
N
O
O
O
(+)-Diethyl-L-tartrate (9) was reacted with dimethoxymethane
N
in the presence of borane trifluoride to form the 1,3-dioxolane
derivative (10). Selective hydrolysis of a single ethyl ester group
was performed under basic conditions and the resulting mono acid
(11) was coupled with 2-phenylaniline using EDC and HOBt. The
ester group of the amide (12) (Scheme 1) was hydrolyzed and
O
HN
R1
R
(7)
(8)
the acid (13) was coupled with 4-nitro or 4-hydroxyphenyl-L-ala-
Figure 2. Proline-based and 1,3-dioxolane-based VLA-4 inhibitors.
nine methyl ester (14a or 14b) to give compounds ( 15a and
15b). The nitro group of (15a) was reduced by catalytic hydrogena-
tion and the aniline (16) coupled with various acids to give amides
(17a–17g). Finally, the esters were hydrolyzed under basic condi-
tions to produce the desired acids (18a–18g). To prepare ether
derivatives, the phenolic group (15b) was alkylated with a range
of benzyl bromides in the presence of potassium carbonate to
furnish the desired esters (19a–19c) which were hydrolyzed under
basic conditions to the acids (20a–20c).
In order to provide structure diversity in the acyl portion we
prepared a number of amide derivatives by one of two different
methods. In the first method (Scheme 2), the amino group of tyro-
sine (21) was Boc protected and the phenolic group of the product
(22) alkylated using 2,6-dichlorobenzyl bromide and potassium
carbonate to furnish ether (23). Deprotection of the Boc group un-
der acidic conditions gave amine (24). Intermediate (11) was re-
acted with various amines to produce amides (25a–25n). Basic
hydrolysis of the ester groups gave acids (26a–26n) which were
was poor (10–15%) with most of the drug being eliminated rapidly
in the bile.6 Two potent analogs of compound (1) are the piperidine
(2, IC50 = 40 nM) and pyridine (3, IC50 = 0.08 nM) which had less pro-
tein binding and lower bioavailability.7,8 The biphenylalanine (4)
(TR-14035) and the tyrosine analog (5) have also shown potent
VLA-4 antagonistic activity9 and Celltech has reported that the thia-
proline (6, CT-5219) is a very potent VLA-4 antagonist (IC50
=
35 nM). This latter compound exhibited poor bioavailability in rats
and sheep and showed rapid elimination, particularly in rats.10,11
Literature suggests that derivatization of the phenylalanine por-
tion of N-acylphenylalanine inhibitors has been a major focus of at-
tempts to obtain optimal potency and selectivity for a4b1. Earlier,
we reported substituted proline ureas of general formula (7) as
VLA-4 inhibitors (Fig. 2) in which the ureido group acted as a bio-
isostere of the sulfonamide group in compounds (1–3).12 It was
found that the compounds with highest binding affinities con-
Cl
OH
OH
O
(ii)
(i)
Cl
O
BocNH
O
O
H2N
BocNH
O
O
O
(23)
(22)
(21)
(iii)
Cl
O
O
O
(iv)
(v)
O
O
O
O
O
O
O
OH
O
O
O
+
O
O
Cl
O
NHR
NHR
H2N
OH
(11)
O
(25a-25n)
(26a-26n)
(24)
(vi)
Cl
Cl
O
O
(v)
Cl
Cl
O
O
OH
O
O
O
O
O
N
H
O
N
H
O
O
O
NHR
NHR
(27a-27n)
(28a-28n)
Scheme 2. Reagents: (i) Boc anhydride, Et3N, DCM, 100%; (ii) 2,6-dichlorobenzylbromide, K2CO3, acetone, 74%; (iii) TFA, DCM, 100%; (iv) RNH2, EDC, NMM, HOBt, DMF, 70–
80%; (v) LiOH, THF, MeOH, H2O, 70–80%, (vi) EDC, NMM, HOBt, DMF, 50–75%.

A. Rehman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5514–5520
5517
Cl
Cl
O
O
(ii)
(i)
(23)
Cl
Cl
O
OH
BocNH
BocNH
O
O
(30)
(29)
(iii)
Cl
Cl
O
O
(iv)
Cl
O
Cl
O
O
O
N
O
H
O
H2N
O
O
O
(i)
(31)
(32)
Cl
O
Cl
O
Cl
(v)
O
Cl
O
O
O
O
N
O
O
H
O
N
O
H
O
O
O
N
R2
R1
OH
(34a-34n)
(vi)
(33)
Cl
O
Cl
O
OH
O
N
H
O
O
O
N
R2
R1
(35a-35n)
Scheme 3. Reagents and conditions: (i) LiOH, THF, MeOH, H2O, 90%; (ii) t-BuOH, DMAP, rt, 30%; (iii) H2SO4, t-BuOAc, 78%; (iv) (11) EDC, NMM, HOBt, 68%; (v) R1R2NH, EDC,
NMM, HOBt, DMF, 60–80% (34a–34e) or R1R2NH, ethylchloroformate, NMM, THF, 70–85% (34f–34n); (vi) TFA, DCM, 80–90%.
coupled with (24) to afford amides (27a–27n). Final hydrolysis
gave the target compounds (28a–28n).
of compounds (18a–18g) that 2,6-di-substitution of the phenyl-
carboxamido group gave a compound with higher binding affinity
than the unsubstituted or mono-ortho-substituted compound
(compare 18e with 18g and 18f). The high binding affinity of the
2,6-dichloro derivative 18e may arise from either an electron-
withdrawing or steric effect. However, an examination of the re-
sults with the pyridylcarboxamido analogs (18a–18d) indicates
that these compounds do not have particularly high binding affin-
ities, thereby implying that the high binding affinity of compound
18e arises from favorable steric and/or hydrophobic interactions at
the receptor. A similar trend is observed in the series of derivatives
in which an ether group is placed at the para-position of the phen-
ylalanine group (20a–20c). The 2,6-dichlorophenylmethylether
(20c) has a far higher receptor binding affinity than the 2-chloro-
phenylmethyl ether (20b) or the 2,6-difluorophenylmethylether
(20a), suggesting once again that steric as opposed to electrostatic
forces are at work.
In the second method (Scheme 3), the intermediate (23) was
hydrolyzed under basic conditions to afford the acid (29) which
was protected as a t-butyl ester (30). Selective Boc deprotection
gave amine (31) which was coupled with intermediate (11) to fur-
nish the amide (32). The methyl ester group was hydrolyzed to af-
ford the acid (33) which was coupled with a diverse set of amines
to afford amides (34a–34n). Hydrolysis under acidic conditions
then yielded the final compounds (35a–35n).
A diverse set of compounds incorporating a 1,3-dioxolane ring
in place of the proline ring normally found in many VLA-4 antago-
nists were synthesized and evaluated as potential VLA-4 antago-
nists by measuring their ability to inhibit binding of VLA-4 to
VCAM-1 in a U-937 (human T-cell line) cell adhesion assay.13
In the first part of the work, an exploration was undertaken of
the effect on binding to the VCAM-1 receptor of compounds con-
taining various substituents at the para-position of the phenyl ring
of the phenylalanine group (Table 1). It was observed in the series
In the second part of the work, the favored 2,6-dichlorophe-
nylmethyl substituent was retained at the para-position of the

5518
A. Rehman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5514–5520
Table 1
Activity of 1,3-dioxolanes as VLA-4 antagonists
R
O
OH
O
O
N
H
O
O
HN
Ph
Compd
R
IC50
8.3
(l
M)
n
Figure 3a. Structural overlay of CT-5219 (green) with 18e.
O
18a
1
N
N
O
O
18b
18c
2.7 0.46
2
1
N
H
N
N
H
9.5
N
O
O
Cl
N
H
18d
6.3
1
N
Cl
Cl
Figure 3b. Structural overlay of CT-5219 (green) with 28j.
N
H
18e
18f
0.1
9.0
1
1
Cl
O
N
H
O
N
H
18g
6.3
1
O
F
O
20a
20b
20c
7.9
1
2
3
Figure 3c. Structural overlay of CT-5219 (green) with 35g.
F
Cl
8.7 3.74
0.5 0.25
not appear to be playing a major role in this case because the
3,5-dichloropyrid-4-yl derivative (35k) had a similar binding affin-
ity to the phenyl analog (35j). Compounds containing electron-rich
aromatic systems such as thiazol-2-yl (35g), benzthiazol-2-yl
(28k), thien-2-ylmethyl (28l), and indol-3-ylethyl (28m) all had
sub-micromolar affinity which was reduced when the aromatic
systems were substituted (35l and 35m, 28n). It appears, therefore,
that a range of substituents are tolerated on the nitrogen atom of
the aminocarbonyl-1,3-dioxolane, indicating perhaps that this part
of the molecule plays a limited role in the binding of the ligands to
the VCAM-1 receptor. When tested for metabolic stability in hu-
O
O
Cl
Cl
phenylalanine group and attention turned to substitution of the
1,3-dioxolane ring in a study of a range of N-substituted aminocar-
bonyl-1,3-dioxolanes (Table 2). Very little of a structure–activity
trend was seen in the N-alkyl amides (28a–28j, 35n) with all com-
man liver microsomes (HLM) at 8 lM concentration for 1 h, com-
pounds having IC50 values in the range of 1–7
tion of the N-cyclopropyl amide (28j) which had an IC50 value of
0.3 M. In the set of N-aryl amides, ortho-substitution consistently
gave compounds (35a and 35b, 35d, 35f) having higher binding
affinities than unsubstituted (35e) or para-substituted (35c) deriv-
atives. An additional beneficial effect on activity was not observed
in compounds containing a second ortho-substituent (compare the
ortho-substituted compounds, 35b and 35a, with the 2,6-disubsti-
tuted compounds, 35j and 35i, respectively). Electronic effects do
l
M with the excep-
pounds (28j) and (35g) were found to be stable 72% and 52%,
respectively.
l
In conclusion, we have successfully demonstrated that the pro-
line ring of the N-acylphenylalanine class of VLA-4 antagonists can
be replaced by a range of N-substituted aminocarbonyl-1,3-dioxol-
anes. Three compounds with high affinity for the VLA-4 receptor,
each having a 2,6-dichlorophenyl substituent attached by means
of an amide or ether linkage to the para position of the phenylala-
nine group, were the N-(2-phenyl)phenyl amide (18e), N-cyclopro-

A. Rehman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5514–5520
5519
Table 2
Activity of 1,3-dioxolanes as VLA-4 antagonists
Cl
O
Cl
O
CO2H
O
O
N
H
O
R
Compd
R
IC50
(l
M)
n
Compd
R
IC50
(lM)
n
N
H
N
H
28a
1.4 0.55
2
35a
0.6 0.25
2
F
CH3
N
N
H
H
28b
28c
28d
1.2 0.75
2.1 1.06
1.5 0.40
3
2
2
35b
35c
35d
0.7 0.25
2.8
3
1
3
Cl
N
H
Cl
N
H
N
N
H
H
0.6 0.2
O
N
H
28e
28f
1.1 0.45
4.4 3.4
3
2
35e
35f
1.5 0.7
0.9 0.5
2
3
N
H
nC7H15
N
H
N
H
CF3
S
N
CH3
N
CH3
N
28g
25h
1.5
6.6
1
1
35g
35h
0.2 0.1
1.5
3
1
H
H
N
S
N
H
N
N
F
N
H
N
H
28i
28j
28k
1.2 0.1
0.3 0.1
0.6 0.01
3
3
1
35i
35j
35k
0.5 0.1
0.7 0.3
0.4
2
3
1
F
Cl
N
H
N
H
Cl
Cl
S
N
N
H
N
H
N
Cl
t-butyl
N
H
S
N
28l
0.7 0.3
0.6 0.2
3
35l
1
1
N
H
N
N
Ph
t-butyl
N
H
28m
28n
3
2
35m
35n
2.6
3.4
1
1
N
N
H
N
H
p-Tolyl
O
N
H
N
3
0.3
O
O
pyl amide (28j), and N-(thiazol-2-yl) amide (35g). Interestingly,
overlay of the three compounds indicates that orientation of the
functional groups of these compounds were similar to CT-5219
in the energy minimized structure (Figs. 3a–c). Subsequent work
on the further optimization of this series of compounds will be dis-
closed in due course.

5520
A. Rehman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5514–5520
7. Sarantakis, D.; Baudy, R. B.; Bicksler, J. J.; Cannon, C.; Dressen, D. B.; Giberson, J.;
Acknowledgment
Grant, F.F.; Konradi, A. W.; Kreft, A.; Kubrak, D.; Leeson, P. D.; Lombardo, L. J.;
Mann, C. W.; Pleiss, M. A.; Sze, J.; Thorsett, E. J.; Vandevert, C.; Yang, C. Abstracts
of papers, 219th National Meeting of the American Chemical Society, San
Francisco, CA; American Chemical Society: Washington, DC, 2000; MEDI 136.
8. Lin, L. S.; Lanza, T.; Jewell, J. P.; Jones, C.; Kieckowski, G. R.; Treonze, K.; Si, Q.;
Manior, S.; Koo, G.; Tong, X.; Wang, J.; Schuelke, A.; Pivnichy, J.; Wang, R.; Raab,
C.; Vincent, S.; Davies, P.; Mumford, R. A.; MacCoss, M.; Hagmann, W. K. J. Med.
Chem. 2009, 52, 3449.
We thank the Analytical Chemistry Department of New Drug
Discovery Research, Ranbaxy for providing spectral data.
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