Amino-substituted heterocycles as isosteres of trans-cinnamides: Design and synthesis of heterocyclic biaryl sulfides as potent antagonists of LFA-1/ICAM-1 binding

Article abstract of DOI:10.1016/j.bmcl.2004.10.008

2-Amino-4-phenyl pyridine and, to a lesser extent, 4-amino-6-phenyl pyrimidine, were established as isosteres of trans-cinnamide moiety. Applying this isosterism to previously reported p-arylthio cinnamides resulted in the identification of 4-amino-6-(p-arylthio)phenyl-pyrimidines and 2-amino-4-(p-arylthio)phenyl-pyridines as potent antagonists of LFA-1/ICAM-1 binding.

Full text of DOI:10.1016/j.bmcl.2004.10.008

Bioorganic & Medicinal Chemistry Letters 15 (2005) 195–201
Amino-substituted heterocycles as isosteres of
trans-cinnamides: design and synthesis of heterocyclic biaryl
sulfides as potent antagonists of LFA-1/ICAM-1 binding
Gary T. Wang,* Sheldon Wang, Robert Gentles, Thomas Sowin, Sandra Leitza,
Edward B. Reilly and Thomas W. von Geldern
Global Pharmaceutical Research & Development, Abbott Laboratories, Abbott Park Rd., Abbott Park, Il 60064, USA
Received 17 September 2004; revised 4 October 2004; accepted 4 October 2004
Abstract—2-Amino-4-phenyl pyridine and, to a lesser extent, 4-amino-6-phenyl pyrimidine, were established as isosteres of trans-
cinnamide moiety. Applying this isosterism to previously reported p-arylthio cinnamides resulted in the identification of 4-
amino-6-(p-arylthio)phenyl-pyrimidines and 2-amino-4-(p-arylthio)phenyl-pyridines as potent antagonists of LFA-1/ICAM-1
binding.
Ó 2004 Elsevier Ltd. All rights reserved.
Adhesion-mediated leukocyte emigration is a mecha-
nism of host defense following inflammation, injury or
infection.1,2 During this process, circulating leukocytes
are attracted to the injury or infection site and cross
the vascular endothelium wall to enter the surrounding
tissues, where the leukocytes neutralize the pathogens
and carry out regulated tissue destruction. However,
over activation of this process leads to untoward tissue
damage, as found in many inflammatory diseases and
reperfusion injury such as ischemia following stroke,
myocardial infarction and trauma. At the molecular
level, the recruitment of leukocytes is primarily mediated
by the interaction between leukocyte-function-associ-
ated antigen-1 (LFA-1, also known as CD11a/CD18
or avb2 integrin) on leukocytes and intercellular adhe-
sion molecule-1 (ICAM-1, also known as CD54) on
endothelial cells.1,2 Thus, inhibition of LFA-1/ICAM-1
binding represents a potential therapeutic target for
these conditions.3
high throughput screening lead, extensive medicinal
chemistry effort led to the identification of several sub-
series of compounds with potent LFA-1/ICAM-1 antag-
onist activity, good solubility and pharmacokinetic
properties.4–7 During the course of the project, the met-
abolic stability of the trans-cinnamide moiety became a
concern, since incubating one analog of p-arylthio trans-
cinnamides with rat and human liver microsomes
resulted in cinnamide isomerization and subsequent deg-
radation. Thus, we undertook an effort to identify
replacements of the trans-cinnamide moiety, even
though it was ultimately proven that the cinnamide
was sufficiently stable. Toward this end, diarylsulfide
trans-cyclopropylamides 3 (Fig. 1) have been reported
by Link et al.8 This class of compounds, in which the
olefin bond of the cinnamide was replaced with a cyclo-
propyl ring, have been shown to have LFA-1/ICAM-1
antagonist activity comparable with the analogous cinn-
amides 1. Alternatively, we envisioned that properly
substituted heterocycles depicted by 4 (Fig. 1), such as
4-amino-6-(p-arylthio)phenyl-pyrimidine or 2-amino-4-
(p-arylthio)phenyl-pyridine, could serve as isosteres of
1. Based on both electronic and steric considerations,
these moieties could potentially replace both the olefin
bond and the carbonyl of the trans-cinnamide moiety.
We report our findings in this paper.
Our laboratories have reported several series of p-aryl-
thio trans-cinnamides, represented by structure 1 and
exemplified by compound 2 (Fig. 1), as potent antago-
nists of LFA-1/ICAM-1 interaction.3 Starting from a
Keywords: trans-Cinnamide isostere; Cell adhesion; LFA-1/ICAM-1
binding.
*
Our attention was first focused on 4-amino-6-(p-aryl-
thio)phenyl-pyrimidines 10 which were synthesized
Corresponding author. Tel.: +1 8479372489; fax: +1 8479355165;
e-mail: gary.t.wang@abbott.com
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.10.008

196
G. T. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 195–201
R2
CF3
O
S
R3
S
R4
N
N
R1
N
R5
O
O
1
2
IC50=60 nM (LFA-1/ICAM-1 binding)
R2
R2
S
R3
S
R3
R4
N
R4
N
R1
R1
R5
R5
X
c
O
3
4
Figure 1.
CF3
CF3
CF3
S
S
F
a
b
O
O
O
O
O
5
6
7
CF3
CF3
CF3
S
S
S
e
d
R1
N
Cl
OH
R2
N
N
N
N
N
N
8
9
10a-x
Scheme 1. (a) o-iso-Propyl thiophenol, Cs2CO3, DMF, rt 16h, 90–100%. (b) NaH, CO(OEt)2, THF, rt 2h, 76%. (c) HC(NH)NH2, 20% HOAc,
DMF, 120°C, 3 days, 14%. (d) POCl3, 60°C, 1h, 51%. (e) R1R2NH, DMF, 80°C, 16h, 70–80%.
according to Scheme 1. Reaction of 2-iso-propyl thio-
phenol with 1-fluoro-2-trifluoromethyl-4-acetyl benzene
5 under basic conditions gave the diaryl sulfide 6, which
was converted to the b-ketoester 7 by treating with
diethyl carbonate under basic conditions. Condensation
of 7 with formamidine gave the hydroxyl-pyrimidine 8
in low yield. The key common intermediate, chloropyr-
imidine 9, was then obtained by treating 8 with phos-
phoryl chloride. Displacement of the chloride of 9 with
a selected set of amines was carried out in a parallel syn-
thesis mode to rapidly prepare a set of analogs 10a–x.9
SAR of the cinnamide series,4,6 substitution on the ami-
no nitrogen of 10 with acidic residues, such as in 10m,
10n, 10o and 10p, gave more potent inhibitors.
We then turned our attention to 2-amino-4-(p-aryl-
thio)phenyl-pyridines. Three different series of pyridine
derivatives were synthesized, with the B ring substitution
fixed as trifluoromethyl ortho to the sulfur, and the A
ring being o-iso-propylphenyl (16a–ab), o-methoxyphen-
yl (17a–p) and 3,4-ethylenedioxyphenyl (18a–p). These
compounds were synthesized as illustrated in Scheme
2. The pyridyl biaryl 12 was prepared via the Suzuki
coupling of pyridine-4-boronic acid with 1-fluoro-2-tri-
fluoromethyl-4-bromo benzene. Oxidation of 12 with
hydrogen peroxide catalyzed by methyltrioxorhenium
(VII) gave the N-oxide 13, which was reacted with
appropriate thiophenols to give the diaryl sulfide pyr-
idine oxides 14a–c. Treating 14a–c with phosphoryl
chloride gave 2-chloropyridines 15a–c. Displacement
of the chloride of 15a–c with a set of selected amines
gave the desired compounds 16a–ab, 17a–p and 18a–p.
The LFA-1/ICAM-1 antagonist activity of 10a–x is
summarized in Table 1.10 The decision to fix the A-ring
substitution as o-iso-propyl and B-ring substitution as
o-trifluoromethyl (ortho to the sulfur) was based on the
SAR results of the cinnamide series, as was the selection
of the amines.4,6 Where a direct comparison is available,
the data (Table 1) indicated that the pyrimidine ring of
10 is a reasonable isostere of the trans-cinnamide moiety
of 1, even though the potency is typically reduced by 2-
to 4-fold. Thus, compound 10a showed an IC50 of
200nM, comparing to 60nM for the corresponding
trans-cinnamide analog, compound 10e exhibited an
IC50 of 320nM, comparing to 80nM for the correspond-
ing trans-cinnamide analog, and compound 10w showed
an IC50 of 680nM, comparing with 480nM for the cor-
responding trans-cinnamide analog. Consistent with the
The LFA-1/ICAM-1 antagonist IC50Õs of the represent-
ative pyridine derivatives were shown in Tables 2 and 3.
In the o-iso-propyl phenylthio series (16), comparison of
16t and 16x with the corresponding trans-cinnamide
analogs (Table 2) revealed that the pyridine derivatives
were essentially equipotent with the analogous trans-

G. T. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 195–201
Table 1. Structure–activity relationships of 4-amino-6-(p-arylthiophenyl)-pyrimidines
197
CF3
S
R1
N
10a-x
R2
A ring
B ring
N
N
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
O
O
O
10a
200 (60nM)c
10m
120b
120b
108b
OH
N
N
N
N
10b
10c
470
420
10n
10o
OH
N
N
N
O
O
N
O
NH
N
N
N
O
N
N
N
N
10d
1270
10p
51b
N
N
N
N
O
N
H
O
N
320 (80nM)c
10q
10r
10s
10t
10u
10v
10w
620
N
10e
10f
10g
10h
10i
N
490
230b
230b
300
O
N
N
N
OH
OH
N
N
740
N
O
N
680
O
N
220b
550
H
N
760
N
N
N
H
N
O
OH
10j
228b
O
N
H
N
N
HO
N
10k
340
680 (480)c
NH2
NH2
O
O
10L
230
10x
158
N
OH
N
a The IC50 reported is the result of single determination unless noted.
b Average of two determinations.
c Number in parenthesis is the IC50 of the corresponding trans-cinnamide analog.
cinnamides. Further analysis of the data showed that the
pyridine derivatives 16 (Table 2) were typically ꢀ3-times
more potent than the the analogous pyrimidine deriva-
tives 10 (Table 1), as indicated by the comparison of
16g with 10j, 16j with 10m, 16k with 10m, 16m with
10o, 16n with 10L and 16z with 10u. The data (Table
2) also indicated a strong preference for polar and acidic
substituents on the amino nitrogen. Thus, compounds
with hydrophobic substituents at this position (16b–f,
16o–r) were essentially inactive, while several com-
pounds with acidic substituents (16j, 16k, 16L, 16m
and 16y) showed IC50 < 50nM, consistent with the pre-
vious reports on the trans-cinnamides.4,5 The data for
the o-methoxyphenylthio series (17) and 3,4-ethylenedi-
oxyphenylthio series (18) in Table 3 similarly indicated
that 2-aminopyridine derivatives were good mimics of

198
G. T. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 195–201
CF3
CF3
CF3
X
CF3
F
F
S
F
a
b
c
Br
N
N
N
O-
O-
11
14a: X=o-iso-Pr
14b: X=o-OMe
12
13
14c: X=3,4-OCH2CH2O-
CF3
CF3
X
X
S
S
e
R1
N
d
Cl
R2
N
N
16a-x: X=o-iso-Pr
17a-p: X=o-OMe
15a: X=o-iso-Pr
15b: X=o-OMe
18a-p: X=3,4-OCH2CH2O-
15c: X=3,4-OCH2CH2O-
Scheme 2. (a) Pyridine-4-boronic acid, n-PrOH, H2O, Pd(OAc)2, Ph3P, reflux, 4h, 82%. (b) CH3ReO3, H2O2, CH2Cl2, rt, 16h, 94%. (c) Cs2CO3,
DMA, thiophenol, 100°C, 16h, 77–90%. (d) POCl3, 100°C, 10h, 60–82%. (e) R1R2NH, DMSO, 140°C, 16h, 60–85%.
Table 2. Structure–activity relationships of 2-amino-4-[30-trifluoromethyl-40-(o-iso-propylphenylthio)]-pyridines
CF3
S
R1
N
16a-ab
R2
A ring
N
B ring
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
N
N
16a
250
16o
58% inhi. @ 1lM
N
N
N
16b
16c
1000
16p
16q
54% inhi. @ 1lM
21% inhi. @ 1lM
N
N
34% inhi. @ 1lM
N
N
16d
16e
16f
16g
16h
40% inhi. @ 1lM
8% inhi. @ 1lM
22% inhi. @ 1lM
76
16r
16s
16t
16u
16v
0% inhi. @ 1lM
165
N
N
N
N
O
O
N
N
H
93 (60)b
N
N
N
N
N
OH
40% inhi. @ 1lM
82% inhi. @ 1lM
N
N
N
N
OH
160
N
N
N
OH
OH
16i
16j
16k
160
16w
16x
16y
93
N
N
CO2H
CO2H
42 (50)b
43 (30)b
264 (480)b
N
N
N
OH
N
26
CO2H

G. T. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 195–201
199
Table 2 (continued)
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
OH
HN
O
16L
16m
43
16z
62
90
N
CO2H
N
OH
N
N
O
NH
51
73
16aa
16ab
N
N
N
N
N
CO2H
N
O
16n
112
NH2
a The IC50Õs are the results of single determination.
b Number in parenthesis is the IC50 of the corresponding trans-cinnamide analog.
Table 3. Structure–activity relationships of 2-amino-4-(p-arylthio)phenyl-pyridines
CF3
X
S
R1
N
17a-p: X=o-OMe
18a-p: X=3,4-OCH2CH2O
R2
N
A ring
B ring
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
Compound
–NR1R2
IC50 (nM)a LFA-1/ICAM-1
OH
OH
17a
18a
77
126
17i
18i
111
132
N
N
N
O
17b
18b
331
510
17j
18j
140
140
NH2
OH
N
N
N
CO2H
CO2H
N
17c
18c
80
147
17k
18k
113
71 (50)b
CO2H
HN
17d
18d
88
112
17L
18L
122
76 (30)b
O
N
N
OH
N
N
17e
18e
214
192
17m
18m
900
747
CO2H
O
H
N
17f
18f
88
168
17n
18n
186
351
N
N
O
N
N
O
OH
17g
18g
128
300
17o
18o
121
131 (60)b
N
N
O
OH
17h
18h
80
390
17p
18p
168
365
N
N
N
a All the IC50Õs are the average of two determinations.
b Number in parenthesis is the IC50 of the corresponding trans-cinnamide analog.
the trans-cinnamides 1. However, the o-methoxy- and
the 3,4-ethylenedioxy-substitution on the A ring appears
to be less optimal than the o-iso-propyl.
A set of thiazole derivatives were synthesized according
to Scheme 3, involving the bromination of disulfide
methyl ketone 6 and condensation of the resulting a-
bromomethyl ketone with thioureas to give the desired
We also examined five-membered ring heterocycles as
the replacement of the trans-cinnamide moiety of 1.
2-amino-4-(p-arylthio)phenyl-thiazoles
LFA-1/ICAM-1 antagonist activity of representative
20a–d.
The

200
G. T. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 195–201
Table 4. Structure–activity relationships of 2-amino-4-(p-arylthio)-
phenyl-thiazoles
than the corresponding trans-cinnamides (Table 4).
The fact that five-membered ring heterocycles gave
much less active compounds is likely due to the fact
that five-membered ring heterocylces as in 20a–d or
21a–c do not mimic the geometry of trans-cinnamide
as closely as six-membered ring as in 10 or 16–18.
However, an electronic effect cannot be ruled out, since
the location of the N atom in the heterocycles of 20a–d
and 21a–c has been shifted. Properly substituted
pyrrole, imidazole or pyrazole would resolve this
ambiguity.
CF3
S
N
R1
N
X
R2
Compound
X
S
–NR1R2
IC50 (nM)a
LFA-1/ICAM-1
O
Compound 10n and 10p were tested in a cell-based adhe-
sion assay measuring the adherence of LFA-1 expressing
JY8 cells to immobilized ICAM-1, giving a EC50 of
90nM and 20nM, respectively.
20a
3000 (60)b
N
N
20b
20c
S
S
40 % inhi. @ 20lM
N
In summary, we have established 2-amino-4-phenyl
pyridine and, to a lesser extent, 4-amino-6-phenyl
pyrimidine as isosteres of trans-cinnamide moiety, lead-
ing to the identification of 4-amino-6-(p-arylthio)-
phenyl-pyrimidines and 2-amino-4-(p-arylthio)phenyl-
pyridines as potent antagonists of LFA-1/ICAM-1
binding.
O
12,000
N
O
N
H
N
H
O
20d
21a
21b
21c
S
10,500
2500 (60)b
15,000
3600
O
O
O
References and notes
N
N
1. Springer, T. A. Cell 1994, 76, 301.
2. Gahmberg, C. G. Curr. Opin. Cell Biol. 1997, 9, 643.
3. Liu, G. Exp. Opin. Therap. Patents 2001, 11, 1383.
4. Liu, G.; Link, J. T.; Pei, Z.; Reilly, E. B.; Leitza, S.;
Nguyen, B.; Marsh, K. C.; Okasinski, G. F.; von Geldern,
T. W.; Ormes, M.; Fowler, K.; Gallatin, M. J. Med. Chem.
2000, 43, 4025.
N
O
N
5. Liu, G.; Huth, J. R.; Olejniczak, E. T.; Mendoza, R.;
DeVries, P.; Leitza, S.; Reilly, E. B.; Okasinski, G. F.;
Fesik, S. W.; von Geldern, T. W. J. Med. Chem. 2001, 44,
1202.
a All the inhibition data are the average of two determinations.
b Number in parenthesis is the IC50 of the corresponding trans-cinna-
mide analog.
6. Pei, Z.; Xin, Z.; Liu, G.; Li, Y.; Reilly, E. B.; Lubbers, N.
L.; Huth, J. R.; Link, J. T.; von Geldern, T. W.; Cox, B.
F.; Leitza, S.; Gao, Y.; Marsh, K. C.; DeVries, P.;
Okasinski, G. F. J. Med. Chem. 2001, 44,
2913.
thiazole derivatives (Table 4) clearly indicated that the
2-amino-thiazole moiety is not a good isostere of the
trans-cinnamide of 1. A small set of oxazole derivatives
(21a–c) were also prepared and found much less potent
7. Winn, M.; Reilly, E. B.; Liu, G.; Huth, J. R.; Jae, H.-S.;
Freeman, J.; Pei, Z.; Xin, Z.; Lynch, J.; Kester, J.; von
CF3
S
CF3
S
b
a
6
N
R1
Br
N
O
19
20a-d
S
R2
c
CF3
S
N
R1
N
21a-c
O
R2
Scheme 3. (a) (n-Bu)4NBr3, MeOH, CH2Cl2, rt 16h, 100%. (b) H2NC(S)NR1R2, DMF, rt 16h, 40–90%. (c) H2NC(O)NR1R2, DMF, 100°C, 24h,
20–60%.

G. T. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 195–201
201
Geldern, T. W.; Leitza, S.; DeVries, P.; Dickinson, R.;
Mussatto, D.; Okasinski, G. F. J. Med. Chem. 2001, 44,
4393.
9. All the compounds used for biological testing were
purified by reverse-phase HPLC. The identity and purity
were established by H NMR and MS spectra and HPLC
1
8. Link, J. T.; Sorensen, B.; Liu, G.; Pei, Z.; Reilly, E. B.;
Leitza, S.; Okasinski, G. Bioorg. Med. Chem. Lett. 2001,
11, 973.
analysis.
10. The LFA-1/ICAM-1 binding assay and the JY-8 cell
adhesion assay were described in Ref. 4.