Discovery of human CCR5 antagonists containing hydantoins for the treatment of HIV-1 infection

Article abstract of DOI:10.1016/S0960-894X(01)00654-0

A series of hydantoin derivatives has been discovered as highly potent nonpeptide antagonists for the human CCR5 receptor. The synthesis, SAR, and biological profiles of this class of antagonists are described.

Full text of DOI:10.1016/S0960-894X(01)00654-0

Bioorganic & Medicinal Chemistry Letters 11 (2001) 3099–3102
Discovery of Human CCR5 Antagonists Containing Hydantoins
for the Treatment of HIV-1 Infection
Dooseop Kim,a,* Liping Wang,a Charles G. Caldwell,a Ping Chen,a Paul E. Finke,a
Bryan Oates,a Malcolm MacCoss,a Sander G. Mills,a Lorraine Malkowitz,b
Sandra L. Gould,b Julie A. DeMartino,b Martin S. Springer,b Daria Hazuda,c
Michael Miller,c Joseph Kessler,c Renee Danzeisen,c Gwen Carver,c Anthony Carella,c
c
Karen Holmes,c JanetLineberger, William A. Schleif c and Emilio A. Eminic
aDepartment of Medicinal Chemistry, Merck Research Laboratories, RY 121-240, POBox 2000, Rahway, NJ 07065, USA
bDepartment of Immunology Research, Merck Research Laboratories, POBox 2000, Rahway, NJ 07065, USA
cDepartment of Antiviral Research, Merck Research Laboratories, West Point, PA 19486, USA
Received 19 June 2001; accepted 11 September 2001
Abstract—A series of hydantoin derivatives has been discovered as highly potent nonpeptide antagonists for the human CCR5
receptor. The synthesis, SAR, and biological profiles of this class of antagonists are described. # 2001 Elsevier Science Ltd. All
rights reserved.
The design and synthesis of small-molecule antagonists
of chemokine receptors have become a major focus of
effort since the discovery that chemokine receptors act
as co-receptors in association with CD4 for HIV entry
into cells.1,2 Chemokines are a family of chemotactic
cytokines, which are characterized by a distinctive pat-
tern of conserved cysteine residues.2 They range in size
from ꢀ70 to 120 amino acids and are involved in the
recruitment and activation of a variety of cell types.
Chemokines are divided into four groups (CXC, CC, C,
and CX3C), depending on the number and spacing of
the conserved cysteine residues. CCR5 is one of the
receptors for the CC chemokines (b-chemokines), MIP-
1a, MIP-1b, and RANTES, in which two cysteine resi-
dues are adjacent. CCR5, a cell-surface 7-transmem-
brane G-protein coupled receptor, has been identified as
a co-receptor for entry of M-tropic HIV viral strains
into host cells.1 Recenthuman geneitc evidence sup-
ports CCR5 as a therapeutic target. Individuals homo-
zygous for a 32-base pair deletion in the gene for CCR5
lack this receptor on their cell surfaces and are highly
resistant to HIV-1 infection,3 while infected hetero-
zygous individuals show significantly delayed progres-
sion to AIDS.4 This led to our efforts to identify potent
CCR5 antagonists for use as therapeutic agents for the
treatment of HIV-1. An extensive screening of the
Merck sample collection for compounds with affinity for
the CCR5 receptor identified a series of active lead com-
pounds (e.g., I) that has already been reported (Fig. 1).5a
Modification of the early sulfonamide lead I, containing
a 1-amino-2-aryl-4-(piperidin-1-yl)butane core struc-
ture, resulted in the identification of a variety of potent
CCR5 antagonists with low nanomolar binding affinity
for CCR5. Recent reports have highlighted the SAR at
the indicated four areas of the lead as shown in Figure 2.5
The main focus of this paper is an investigation of the
SAR for the replacement of the sulfonamide group with
a hydantoin pharmacophore. Hydantoins have been
*Corresponding author. Fax:+1-732-594-5350; e-mail: dooseop_kim@
merck.com
Figure 1. CCR5 antagonist lead compounds.
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00654-0

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D. Kim et al. / Bioorg. Med. Chem. Lett. 11 (2001) 3099–3102
reported to be attractive scaffolds in drug design.6 It
features two hydrogen bond acceptors and one donor in
the heterocycle, which may be useful in the search for
important pharmacophores. In addition to these binding
features, hydantoins have three sites of diversity amenable
to rapid analogue synthesis. These advantages along with
the interesting observation that the activity of amide
structure IV (IC50=640 nM) was considerably improved
over the benzoyl analogue III led us to incorporate the
hydantoin into the benchmark CCR5 antagonist (II).5b
These compounds were then evaluated for CCR5 bind-
ing affinity utilizing a 125I-MIP-1a binding assay.8
Selected compounds were assayed in a PBMC-based
viral replication assay as previously described.9
Sulfur-containing spiro-amines were not compatible
with the hydantoin moiety as shown in Table 1 (8–10),
whereas carbonyl spiropiperidine analogues restored
activity (11 and 12). The d-phenyl glycine analogue [12,
(R)-configuration, IC50=606 nM] was somewhatmore
potent than the l-phenyl analogue [13, (S)-configuration,
52% @ 1 mM). Thus, the (R)-configuration at this center
was held constant throughout our subsequent investigation.
Despite a decrease in potency for our initial compounds
relative to the lead, the moderate activity of the d-phenyl-
alanine analogue 11 (IC50=200 nM) suggested that it
might be possible to improve CCR5 potency for this
hydantoin pharmacophore with other modifications in
the core structure as they were developed in the sulfon-
amide series.5e
A general synthesis of hydantoin derivatives of interest
is described in Scheme 1.7 Allylation of 3-chlorobenzyl
cyanide 1 followed by reduction with LAH/AlCl3 gave
the primary amine 3, which was coupled to various N-
Boc amino acids such as d-phenyl alanine, d-phenyl
glycine, l-phenyl glycine, d-tryptophan, and so on to
give 4. Boc-deprotection with TFA followed by cyclization
wit h CDI afforded t he desired hydant o5in. Cleavage of
the olefin with ozone or catalytic OsO4 followed by
NaIO4, gave the desired aldehyde 6, which was used to
reductively alkylate a variety of piperidines to give 7.
The diastereomeric mixture 7 was separated by pre-
parative TLC to sort out the more active isomers.
Indeed, when the indanone spiropiperidine was replaced
with the 4-phenylpiperidine (see Table 2), compound 15
showed similar activity to that of compound 11
(IC50=250 vs 200 nM). Removal of the aryl substituent
(R2) resulted in a sharp decrease in the activity (14). The
hydantoin N–H (R3=H, Table 2) is essential for good
activity, when R2 is Ph or indole (15, 18, and 19). In
other cases, the hydantoin N–H alone does not seem to
Table 1. CCR5 antagonist activity of spiropiperidines
Entry
X
R1
CCR5a
IC50 (nM)b
Figure 2. SAR of known CCR5 antagonists.
8
S
SO
24% @ 1.7 mM
39% @ 1.7 mM
55% @ 1 mM
200
9
10
11
12
13
N–SO2Me
CO
CO
606
CO
52% @ 1 mM
Scheme 1. Reagents: (a) LDA, THF, À78 ꢁC, then allyl bromide,
À78 ꢁC t o rt ; (b) LAH, AlC,lTHF, 0–80ꢁC; (c) N-Boc-amino acid,
aSee ref 5a for the procedure.
3
bThe IC50 results are an average of three independent titrations having
calculated standard errors below 15%. The assay-to-assay variation was
generally Æ2-fold based on the results of the standard compound II.
HOBT, EDC, CH2Cl2; (d) TFA, rt; (e) CDI, THF, Hunig’s base, reflux; (f)
catOsO 4, 4-methylmorpholine N-oxide, t-BuOH, H2O, acetone; (g)
NaIO4, THF; (h) NaBH(OAc)3, DIPEA, THF, molecular sieves, rt .

D. Kim et al. / Bioorg. Med. Chem. Lett. 11 (2001) 3099–3102
3101
be sufficient to provide good activity (20, 21, and 23). It
was notable that incorporation of d-tryptophan side
chain onto the hydantoin gave rise to a separable
diastereomeric mixture of indole analogues, 18 and 19.
Because the (S)-stereochemistry at the benzylic position
was already established in other active CCR5 antago-
nists,5 the stereochemistry at the benzylic position in the
more potent diastereomer 18 was assumed to be (S).
From the decreased activity of 20 and 21, itbecame
apparent that the indole N–H is another essential phar-
macophore. Deletion of the 3-chloro- moiety (R1, Table 2)
resulted in a substantial loss of binding activity (22).
Replacement of the indole moiety with a smaller imida-
zole was also unsatisfactory (23).
Table 2. CCR5 antagonist activity of phenylpiperidines
Two further important modifications to the original
structure have been highlighted recently: (1) addition of
a methyl group at the benzylic position5e and (2) the
incorporation of a 4-CBZ carbamate moiety in place of
the 4-phenyl in the piperidine.5d These two groups were
then combined in the indole-substituted hydantoin
structure 18 (Table 3). This combination produced
remarkably potent compounds with low nanomolar
IC50 values (2–5 nM). Potency enhancement resulting
from a benzylic methyl group was not observed for the
phenyl piperidine series (24 vs 25), whereas either a
meta-chloro on the central phenyl or a methyl group at
the benzylic position alone increased the binding affinity
slightly in the carbamate series (28, 29, 32, and 33).
However, an additive effect of these two was not
observed. Compounds 30 and 34 that combined these
two substitutions showed a sharp decrease in the binding
affinity over the des-chloro and/or des-methyl examples.
Entry
R1
R2
R3
CCR5a IC50 (nM)b
14
15
16
Cl
Cl
Cl
Cl
Cl
Cl
H
Ph
Ph
Ph
H
H
Me
Bn
H
43% @ 10 mM
250
52% @ 1 mM
40% @ 1 mM
25
17
18c
19d
Indol-3-yl
Indol-3-yl
H
80
20
21
Cl
H
H
67% @ 1 mM
43% @ 1 mM
Cl
22
23
H
H
Indol-3-yl
H
H
71% @ 1 mM
25% @ 1 mM
The increase in antiviral activity was ca. 2-fold over the
compound 27, when the modifications were made (28,
29, and 32). The viral spread assay results for selected
carbamate compounds containing the indole moiety
indicate that the high potency in the CCR5 binding assay
did not translate into high potency in the viral spread
assay. While initial studies suggest that optimization of
aSee ref 5a for the procedure.
bThe IC50 results are an average of three independent titrations having
calculated standard errors below 15%. The assay-to-assay variation
was generally Æ2-fold based on the results of the standard compound II.
cHigher Rf isomer.
dLower Rf isomer.
Table 3. CCR5 antagonist activity and antiviral activity of indole series
Entry
R1
R2
R3
CCR5a IC50 (nM)b
Antiviral activity IC95 (nM)
24
25
26
27
28d
29
30
31
32
33
34
H
H
Cl
H
Cl
H
Cl
H
H
Me
Me
H
Ph
Ph
Ph
71% @ 1 mM
80% @ 1 mM
100
NDc
ND
ND
CBZ-N-(Et)
CBZ-N-(Et)
CBZ-N-(Et)
CBZ-N-(Et)
CBZ-N-(Allyl)
CBZ-N-(Allyl)
CBZ-N-(Allyl)
CBZ-N-(Allyl)
13
2 (22)e
4
77
7
3
5
32
25,000
12,500
12,500
ND
>3,000
12,500
>3000
ND
H
Me
Me
H
H
Me
Me
Cl
H
Cl
aSee ref 5a for the procedure.
bThe IC50 results are an average of three independent titrations having calculated standard errors below 15%. The assay-to-assay variation was
generally Æ2-fold based on the results of the standard compound II.
cND, notdetermined.
dHigher Rf diastereomer.
eIC50 of lower Rf diastereomer. The rest of the above examples are diastereomeric mixtures.

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D. Kim et al. / Bioorg. Med. Chem. Lett. 11 (2001) 3099–3102
antiviral activity may be possible by further modification
around the hydantoin and tryptophan areas, the origin
of this discordant result is still under investigation.
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Compounds 27–29 and 31–34 were all found to be
selective CCR5 antagonists versus other chemokine
receptors, such as CCR1, CCR2, CCR3, CCR4, and
CXCR4 (IC50>1000 nM).
5. (a) Dorn, C., Jr.; Finke, P. E.; Oates, B.; Budhu, R. J.;
Mills, S. G.; MacCoss, M.; Malkowitz, L.; Springer, M. S.;
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(b) Finke, P. E.; Meurer, L. C.; Oates, B.; Mills, S. G.; Mac-
Coss, M.; Malkowitz, L.; Springer, M. S.; Daugherty, B. L.;
Gould, S. L.; DeMartino, J. A.; Siciliano, S. J.; Carella, A.;
Carver, G.; Holmes, K.; Danzeisen, R.; Hazuda, D.; Kessler,
J.; Lineberger, J.; Miller, M.; Schleif, W. A.; Emini, E. A.
Bioorg. Med. Chem. Lett. 2001, 11, 265. (c) Finke, P. E.;
Oates, B.; Meurer, L. C.; Mills, S. G.; MacCoss, M.; Mal-
kowitz, L.; Springer, M. S.; Gould, S. L.; DeMartino, J. A.;
Carella, A.; Carver, G.; Holmes, K.; Schleif, W. A.; Danzei-
sen, R.; Hazuda, D.; Kessler, J.; Lineberger, J.; Miller, M.;
Emini, E. A. Bioorg. Med. Chem. Lett. 2001, 11, 2469. (d)
Finke, P. E.; Oates, B.; Meurer, L. C.; Mills, S. G.; . MacCoss,
M.; Malkowitz, L.; Springer, M. S.; Gould, S. L.; DeMartino,
J. A.; Carella, A.; Carver, G.; Holmes, K.; Schleif, W. A.;
Danzeisen, R.; Hazuda, D.; Kessler, J.; Lineberger, J.; Miller,
M.; Emini, E. A. Bioorg. Med. Chem. Lett. 2001, 11, 2475. (e)
Caldwell, C. G.; Chen, P.; Donnelly, K. F.; Finke, P. E.;
Shankaran, K.; Meurer, L. C.; Oates, B.; MacCoss, M.; Mills,
S. G.; Malkowitz, L.; Springer, M. S.; Gould, S. L.; DeMar-
tino, J. A.; Carella, A.; Carver, G.; Holmes, K.; Schleif, W. A.;
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of the American Chemical Society, San Francisco, CA,;
American Chemical Society: Washington, DC, 2000; Abstract
MEDI 120 (manuscript in preparation for submission to
Bioorg. Med. Chem. Lett.).
In summary, starting with lead I as a design template, a
series of hydantoin-based CCR5 receptor antagonists was
synthesized and evaluated for their binding potency as
well as antiviral activity. Replacement of the sulfonamide
with a hydantoin moiety was possible. Aromatic amino
acid derivatives were found to be active in the binding
assay with the d-tryptophan derivative 28 being the
most potent compound. When coupled with carba-
mates, benzylic methyl, or 3-chloro, antiviral activity
increased in our series (Table 3). This suggests that efficient
inhibition of HIV-1 replication may be possible by further
modification of potent hydantoin-based CCR5 antago-
nists, blocking entry of M-tropic HIV viral strains into
the host cells effectively.
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