Discovery and SAR of diarylsulfide cyclopropylamide LFA-1/ICAM-1 interaction antagonists

Article abstract of DOI:10.1016/S0960-894X(01)00105-6

Diarylsulfide cyclopropylamides were synthesized and evaluated as LFA-1/ICAM-1 interaction antagonists. A substituent pattern was identified which maximized potency and minimized protein binding as exemplified by antagonist 30 (IC₅₀ = 5 nM).

Full text of DOI:10.1016/S0960-894X(01)00105-6

Bioorganic & Medicinal Chemistry Letters 11 (2001) 973–976
Discovery and SAR of Diarylsulfide Cyclopropylamide
LFA-1/ICAM-1 Interaction Antagonists
James T. Link,* Bryan Sorensen, Gang Liu, Zhonghua Pei, Edward B. Reilly,
Sandra Leitza and Greg Okasinski
Metabolic Disease Research, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064, USA
Received 28 December 2000; accepted 5 February 2001
Abstract—Diarylsulfide cyclopropylamides were synthesized and evaluated as LFA-1/ICAM-1 interaction antagonists. A sub-
stituent pattern was identified which maximized potency and minimized protein binding as exemplified by antagonist 30 (IC50=5
nM). # 2001 Elsevier Science Ltd. All rights reserved.
Cell adhesion is the process by which leukocytes are
recruited to a site of injury.1ꢀ3 The process is mediated
by adhesion molecules on circulating leukocytes and on
vascular endothelial cells. The interaction between leu-
kocyte function-associated antigen-1 (LFA-1) on leu-
kocytes and intercellular adhesion molecule (ICAM-1)
on endothelial cells is critical to the adherence of leu-
kocytes prior to extravasation from the vasculature into
the surrounding tissue. Inhibition of the LFA-1/ICAM-
1 interaction would presumably suppress this early step
of the inflammatory response. An inhibitor could prove
useful for the treatment or prophylaxis of inflammatory
diseases, autoimmune diseases, tumor metastasis,
allograft rejection, and reperfusion injury.
including the diarylsulfide trans-cyclopropylamides 2.
Of the potential replacements surveyed, the cyclopro-
pylamides were the most potent in vitro. In this paper,
we present some of the trans-cyclopropylamide SARs
and related observations which allowed us to advance
our program.
The diarylsulfide cyclopropylamides were prepared as
outlined in Scheme 1. Benzenethiols, such as 2-bromo-
benzenethiol 3, were added to 4-halo- or 4-trifloxy-
benzaldehydes, like 5,12 under basic conditions to
provide diaryl sulfide aldehydes 6. Conversion of the
aldehydes to the cinnamic esters 7 was accomplished by
treatment with (ethoxycarbonylmethyl)triphenyl-phos-
phonium chloride. Cyclopropane formation utilizing
trimethylsulfoxonium iodide yielded the trans-cyclopro-
pyl esters 8. Hydrolysis (8–9) and amide formation
protocols, illustrated with amines like 1-(3-aminopro-
Early LFA-1/ICAM-1 interaction antagonists were
mAb based due to the difficulty of identifying small
molecule protein–protein interaction antagonists.4ꢀ6
Recently, four different classes of small molecule
antagonists have been identified,7ꢀ10 including trans-
cinnamide diarylsulfides 1 from our laboratories (Fig.
1).11 Initially, we were concerned about the potential
metabolic sensitivity of the diarylsulfide cinnamide
antagonists and incubated one analogue with rat and
human liver microsomes. This study indicated the cin-
namide diarylsulfide was susceptable to cinnamide iso-
merization followed by degradation. Although it
ultimately proved unneccessary to modify the cinnamide,
a number of cinnamide replacements were surveyed
*Corresponding author. Fax: +1-847-938-1674; e-mail: james.link@
abbott.com
Figure 1.
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00105-6

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J. T. Link et al. / Bioorg. Med. Chem. Lett. 11 (2001) 973–976
pyl)-2-pyrrolidinone, yielded diarylsulfide cyclopropyl
cinnamides 10. Further modification using Buchwald/
Hartwig aryl halide amine coupling protocols led to
piperidine substituted analogues like 11.13 Resolution of
intermediates by preparative HPLC on chiral columns
was accomplished at either the cyclopropyl ester or
amide stages depending upon the ease of the individual
separation. Parallel synthesis allowed for rapid optimi-
zation of both the amide and piperidine regions of these
analogues.
Like the cinnamides 1,11 diarylsulfide cyclopropamides
2 are most potent when R1 is in the ortho or meta posi-
tion (relative to the arylthio group) and R2 and R3 are
small and electron withdrawing (Fig. 1). One potent
series is obtained when R1 is isopropyl and R2 and R3
are C1 (Table 1). Variation of the amide portion of the
molecule revealed that a number of different groups (R4
and R5) are tolerated. The preferred substitutent at this
position is 1-(3-aminopropyl)-2-pyrrolidinone as illu-
strated by 12a, which gave an IC50 of 7 nM in an LFA-1/
ICAM-1 binding assay.14 Each trans-cyclopropylamide
enantiomer of the diaryl sulfide core was evaluated
independently. One cyclopropane antipode was con-
sistantly more potent than the other (column 3 vs
column 6). The more potent antipode was evaluated
more thoroughly and an IC70 and IC80 were determined.
Scheme 1. (a) Tf2O, pyr, 0 ꢁC!rt, 1 h; (b) i-Pr2NEt, CH3CN, 25 min,
74%; (c) EtO2CCH2PPh3Cl, NaH, THF, 2 h, 85%; (d) Me3SOI, NaH,
DMSO, 12 h, 65%; (e) NaOH, THF, EtOH, H2O, 98%; (f) 1-(3-ami-
nopropyl)-2-pyrrolidinone, EDAC, HOBt, DMF, rt, 95%; (g) ethyl
nipecotate, Pd2(dba)3, (ꢂ)-BINAP, NaOt-Bu, tol, 80 ꢁC, 12 h, 84%;
(h) NaOH, THF, EtOH, H2O, 97%.
Table 1. Diarylsulfide cyclopropylamide SAR 12–18
Compound
R
No serum
IC50 (nM)a,b
No serum
IC70 (nM)a,b
No serum
IC80 (nM)a,b
Enantiomer no serum
IC50 (nM)a,c
12a,b
13a,b
14a,b
15a,b
16a,bd
17a,bd
18a,b
7
12
8
40
50
26
16
55
13
24
63
95
54
9
6
33
34
26
33
17
21
7
13
6
110
25
54
9
aValues are means of two experiments.
btrans-Cyclopropylamide antipode a.
ctrans-Cyclopropylamide antipode b.
d1:1 mixture of diastereomers.

J. T. Link et al. / Bioorg. Med. Chem. Lett. 11 (2001) 973–976
975
In order to ensure the agents had appropriate water
solubility for in vivo utility it was necessary that they
contain an acid. A number of amino acids were sur-
veyed (13–18) and both straight chain and cyclic amino
acids were tolerated.
Examination of the potency of 12–18 in the presence of
plasma protein yielded much higher IC50’s. For example,
cyclopropylamide 16a (which was the least affected
member of this set of compounds) gave an IC50 with no
serum of 13 nM and an IC50 in the presence of 50%
FBS of 1.48 mM. In the JY-8/ICAM-1 cellular adhesion
assay with 50% serum, the analogues 12–18 were inac-
tive at concentrations of 4 mM. In response to this pro-
tein binding problem we sought to alter the polarity of
each region of the antagonist.
A cell based adhesion assay, which measured the ability
of the antagonists to block the adherence of LFA-1
expressing JY-8 cells to immobilized ICAM-1, was used
to confirm functional activity in vitro.14 Among the
compounds in Table 1, b-amino acid 14a was the most
potent antagonist in this assay giving an IC50 value of
150 nM (n=2).
One region where we found substituent polarity could
be varied was in the R1 position. Racemic trans-cyclo-
Table 2. Diarylsulfide cyclopropylamide SAR 19–26
Compound
R
No serum IC50, nMa
Compound
R
No serum IC50, nMa
19
32
23
115
20
40
24
620
21
22
15
25b
26b
100
50
200
aValues are means of two experiments.
bMixture of diastereomers.
Table 3. Diarylsulfide cyclopropylamide SAR 16a and 27–30
No serum
50% FBS
IC70 (nM)
Compound
IC50 (nM)a
IC70 (nM)a
IC80 (nM)a
IC50 (nM)
IC80 (nM)
16a
27b
28b
29c
30c
13
15
10
31
5
55
26
21
97
10
110
40
26
142
19
1480
33
29
640
27
3520
120
116
2100
89
8820
210
199
3200
133
aValues are means of two experiments.
bMixture of two trans-cyclopropylamide diastereomers differing in the configuration of the 3-carboxypiperidine stereocenter of the antagonists.
cSingle diastereomer derived from 28.

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J. T. Link et al. / Bioorg. Med. Chem. Lett. 11 (2001) 973–976
propylamides 19–26 were synthesized in parallel. Pyrroli-
dinyl and piperidinyl analogues (19 and 20, respectively)
had reasonable potency, which was improved upon by
morpholine analogue 21, which gave an IC50 value of 15
nM in an LFA/ICAM assay (Table 2). Placement of
more polar substituents chosen to potentially improve
water solubility at various positions around the ring
resulted in less potent analogues (22–25). However, the
racemic mixture of diastereomers 26 gave an IC50 quite
close to that of the unsubstituted piperidine 20 indicat-
ing an acid could be placed at this position.
pylamides could be made. Further optimization identi-
fied analogues with improved protein binding profiles as
exemplified by antagonist A-324920 (30) (IC50=5 nM).
Acknowledgements
The authors are deeply indebted to Mike Fitzgerald for
HPLC resolution of several diarylsulfide cyclopropanes.
Dean Hickman is thanked for performing liver micro-
some experiments and Kennan Marsh and Bach-Nga
Nguyen are thanked for pharmacokinetic studies.
Moving to a more potent series and varying R1 sub-
stituents a group of potent antagonists with reduced
protein binding affinity was identified. Palladium-medi-
ated coupling of ethyl nipecotate and hydrolysis of each
enantiomer of trans-cyclopropylamide 10 gave 27 and
28, respectively, each as a 1:1 mixture of diastereomers.
Both diastereomeric mixtures 27 and 28 show good
activity in the presence of serum in the LFA-1/ICAM-1
binding assay and represent a significant improvement
over the profile observed for 16a (Table 3). Diaster-
eomeric mixture 28 was separated into its components
29 and A-324920 (30). Carboxypiperidine A-324920 (30)
represented an advance for our program identifying a
substituent pattern which delivered potency while mini-
mizing protein binding. In the absence of serum, A-
324920 (30) gave an IC50 of 5 nM in the LFA-1/ICAM-1
binding assay while in the presence of 50% FBS an IC50
of 27 nM was obtained. The 5-fold reduction in potency
was a vast improvement over previous analogues like
16a, which showed a greater than two orders of magni-
tude reduction. In the JY-8/ICAM-1 cellular adhesion
assay A-324920 (30) gave an IC70 of 9 nM in the
absence of serum. In the presence of 50% serum an IC50
of 50 nM and an IC70 of 200 nM were measured.
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The pharmacokinetics of 28 in rats at 5 mpk po was
measured. Although the bioavailability (F=27%), half
life (t1/2=1.2 h), and maximum observed concentration
in the bloodstream (Cmax=0.35 mg/mL) were not opti-
mal, the results suggested that further refinement of
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Lead modification of trans-cinnamide 1 led to the iden-
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indicated that potent LFA-1/ICAM-1 trans-cyclopro-
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