Design, synthesis, and SAR of heterocycle-containing antagonists of the human CCR5 receptor for the treatment of HIV-1 infection

Article abstract of DOI:10.1016/S0960-894X(01)00655-2

Replacement of the large hydantoin-indole moiety from our previous work with a variety of smaller heterocyclic analogues gave rise to potent CCR5 antagonists having binding affinity comparable to the hydantoin analogues. The synthesis, SAR, and biological profiles of this class of antagonists are described.

Full text of DOI:10.1016/S0960-894X(01)00655-2

Bioorganic & Medicinal Chemistry Letters 11 (2001) 3103–3106
Design, Synthesis, and SAR of Heterocycle-Containing
Antagonists of the Human CCR5 Receptor 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—Replacement of the large hydantoin-indole moiety from our previous work with a variety of smaller heterocyclic analo-
gues gave rise to potent CCR5 antagonists having binding affinity comparable to the hydantoin analogues. The synthesis, SAR, and
biological profiles of this class of antagonists are described. # 2001 Elsevier Science Ltd. All rights reserved.
The use of highly active anti-retroviral therapy
(HAART) for the clinical control of HIV-1 infection
has been highly successful atreducing disease progres-
sion as well as death rate. However, one can no longer
assume that HAART will be consistently beneficial due
to an alarming emergence of resistance (>30%) and the
significant side effects associated with these treatments.1
Thus, new, complementary, and better therapies are
needed to help many patients whose treatment options
are running out. The investigation of a new class of
AIDS drug has been spurred by a series of recent
reports on chemokines and chemokine receptors.2,3
Recently, we reported the SAR of our early CCR5
benchmark compound (I), which was discovered by
an extensive screening effort followed by SAR studies
(Fig. 1).4 Incorporation of a hydantoin-indole moiety
together with a N-CBZ-group on the piperidine moiety
led to potent CCR5 antagonists (IIa,b) as described
previously (Table 1).5 Even though this series of
hydantoin-indole analogues (IIa,b) showed high CCR5
binding affinity, their relatively high molecular weight
was a major drawback of that series. Thus, we turned our
attention to relatively small-size heterocycles (e.g., B in IIc)
as replacements of the large hydantoin-indole moiety.
Since the discovery of the importance of the N-CBZ
group for both CCR5 binding and antiviral activity, this
subunit has been employed throughout our SAR stud-
ies.4,5 A general synthesis of several heterocyclic deriva-
tives is shown in Schemes 1 and 2.
*Corresponding author. Fax: +1-732-594-5350; e-mail: dooseop_kim@
merck.com
Figure 1. Replacementof ht e N-methylsulfonamide of I with hetero-
cycles.
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00655-2

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D. Kim et al. / Bioorg. Med. Chem. Lett. 11 (2001) 3103–3106
Allylation of phenylacetic acid 1 followed by reduction
with LAH gave the primary alcohol 3, which was cou-
pled to a variety of heterocycles to give 4. Cleavage of
the olefin with ozone or catalytic OsO4, followed by
NaIO4, gave the desired aldehyde 5, which was used to
reductively alkylate a variety of piperidines to give 6. In
the presence of the a-methyl group at the benzylic posi-
tion, route 1 employing an SN2 substitution of the tri-
flate from alcohol 3 with heterocycles could not be used
due to steric hindrance. Instead, neo-pentyl type amine 8
was used in a benzimidazole synthesis. Allylation of the
a-methylbenzyl cyanide 7 followed by reduction afforded
the primary amine 8, which was reacted with o-fluoro-
nitrobenzene to give the nitro compound 9. Reduction of
the nitro group followed by cyclization using orthoesters
gave the benzimidazoles 11. The synthesis of benzothia-
zepine 18 and isoindolone 21 is summarized in Scheme 2.
Allylation of 12 followed by DIBAL reduction afforded
aldehyde 13. Reduction of the aldehyde 13 was followed
by TBDMS protection to give 14. Cleavage of the olefin
followed by reductive amination gave the compound 16.
Deprotection of the TBDMS group followed by Swern
oxidation gave the aldehyde 17. Cyclization of 17 with 2-
aminobenzenesulfonamide gave a diastereomeric mix-
ture 18, which was separated by flash chromatography.
Isoindolone 21 was prepared following a procedure
similar to that described in the literature.6 The olefinic
compounds (11 and 21) were cleaved and the resulting
aldehydes were coupled to a variety of piperidines to
give the desired compounds in Tables 2 and 3.
Scheme 1. Reagents: (a) LiHMDS, THF, À78 ꢀC, then allyl bromide;
À78 ꢀC to rt; (b) LAH, THF; (c) (CF3SO2)2O, 2,6-lutidine, CH2Cl2;
(d) catOsO 4, 4-methylmorpholine N-oxide, t-BuOH, H2O, acetone; (e)
NaIO4, THF; (f) NaBH(OAc)3, DIPEA, THF, molecular sieves, THF,
rt; (g) 1-Fluoro-2-nitrobenzene, K2CO3, DMF, rt, 18 h; (h) SnCl2,
concd HCl, THF; (i) CR(OMe)3, concd HCl.
Table 1. CCR5 antagonist activity of heterocycle analogues
Entry
R
CCR5a
IC50 (nM)b
Entry
R
CCR5a
IC50 (nM)b
22
23
15
27
26
27
23
15
24
25
111
335
28
29
30
15
16
28
Scheme 2. Reagents: (a) LiHMDS, THF, À78 ꢀC, then allyl bromide;
À78 ꢀC to rt; (b) DIBAL, CH2Cl2; (c) LiBH4; (d) TBDMSCl; (e)
OsO4, NMMO, t-BuOH, H2O, acetone; (f) NaIO4, THF; (g) Na-
BH(OAc)3, DIPEA, THF, molecular sieves, THF, rt; (h) Bu4NF,
THF; (i) (COCl)2, DMSO, DIPEA, CH2Cl2; (j) NMP, 100 ꢀC, 18 h; (k)
ethylamine, Bu2SnCl2, Na2SO4, molecular sieves, CH2Cl2; (l) n-BuLi,
aSee ref 4a 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
I (Fig. 1).
ꢀ
.
THF, BF3 OEt, then 150 C.

D. Kim et al. / Bioorg. Med. Chem. Lett. 11 (2001) 3103–3106
3105
These compounds were then evaluated for CCR5 bind-
ing affinity utilizing a 125I-MIP-1a binding assay.7 The
IC90s of selected compounds were evaluated in a 48 h
single-cycle HIV (BAL) infection assay utilizing HeLa
Magi cells expressing both CXCR4 and CCR5 as pre-
viously described.8
tion on the N-CBZ, which showed potency enhance-
4d,4e,5
mentin some cases.
Indazole analogues (22 and 23) were found to possess
activity comparable to that of the hydantoin analogue
IIa (IC50=7 nM), whereas the tetrazole analogues (24
and 25) showed sharply decreased activity. In both
cases, the major isomers were more active than the
minor isomers (22 and 24). Mostof ht e imidazole ana-
logues (26–29) were as active as the indazoles. It was
notable that simple triazole analogue 30 also showed
good CCR5 binding affinity.
Tables 1–3 show the results for a series of compounds
incorporating a variety of heterocycles in combination
with the benzylic methyl group and the 4-NO2 substitu-
Table 2. CCR5 antagonist activity and antiviral activity of benzimi-
dazole analogues
The benzimidazole was chosen for further exploration
(Table 2) with additional substitution at the benzylic
position (R2, Table 2) and on the imidazole ring. Incor-
poration of the 4-NO2 group (R1, in Table 2) on the
CBZ moiety increased the binding affinity by 5- to 11-
fold (32, 34, and 36), whereas introduction of either an
a-methyl (R2) or ethyl (R3) resulted in a substantial loss
of binding affinity (33–35, Table 2). While introduction
of the benzylic methyl (R2=Me) was expected to give a
substantial increase in CCR5 binding as seen in both the
sulfonamide and hydantoin series (Fig. 1),4e,5 in this
situation the methyl resulted in a loss of binding affinity
for both 35 and 36 compared to 31 and 32. Presumably
the closer proximity of the rigid benzimidazole to the
methyl prevents its correct orientation in 35 and 36,
while the methyl beneficially orientates the more flexible
sulfonamide moiety of I and the hydantoin of IIa,b. The
viral spread assay results (Table 2) for selected compounds
containing the heterocyclic moieties indicated that the nitro
group in the N-CBZ increased the antiviral potency
from >3000 nM to 1000 nM (31 vs 32). Unfortunately, the
previous beneficial effectof ht e benzylic meht yl (R 2=Me,
Table 2) was notachieved for htese benzimidazole
Entry
R1
R2
R3
CCR5a
IC50 (nM)b
Viral Spread (nM)
c
HeLa (IC90)
31
32
33
34
35
36
H
NO2
H
NO2
H
H
H
H
H
CH3
CH3
H
H
Et246
Et48
H
25
4
>3000
1000
d
ND
3000
112
10
NDd
1000
NO2
H
aSee ref 4a 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
I (Fig. 1).
cSee ref 8 for the procedure.
dNotdetermined.
Table 3. CCR5 antagonist activity of heterocycle analogues
Entry
R1
H
R2
CCR5
IC50 (nM)b
Entry
R1
R2
CCR5
IC50 (nM)b
a
a
37c
55
39c
NO2
10
38d
H
18
40d
NO2
18
aSee ref 4a 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 I (Fig. 1).
cHigher Rf isomer.
dLower Rf isomer.

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D. Kim et al. / Bioorg. Med. Chem. Lett. 11 (2001) 3103–3106
derivatives. The viral spread assay results also indicated
that the high potency in the CCR5 binding assay did
not translate into high potency in the viral spread assay
as in the previous case.5 The origin of this discordant
results is still under investigation.
4. (a) Dorn, C., Jr; Finke, P. E.; Oates, B.; Budhu, R. J.;
Mills, S. G.; MacCoss, 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, 259.
(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.; Malkowitz, L.; Springer, M. S.;
Gould, S. L.; DeMartino, J. A.; Carella, A.; Carver, G.;
Holmes, K.; Schleif, W. A.; Danzeisen, R.; Hazuda, D.; Kess-
ler, 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.; 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. Abstracts of Papers, 219th the National Meeting
of the American Chemical Society, San Francisco, CA, 2000;
Abstract MEDI 120 (manuscript in preparation for submis-
sion to Bioorg. Med. Chem. Lett.).
Results on conformationally more restricted analogues,
in which heterocycles were directly attached to the a-
position, are shown in Table 3. High binding affinity
was maintained in both benzothiazepine 38 and iso-
indolone 39.
Compounds 31–36, 38, and 39 were all found to be
selective CCR5 antagonists versus other chemokine
receptors, such as CCR1, CCR2, CCR3, CCR4, and
CXCR4 (IC50 >1000 nM). Preliminary pharmacoki-
netic properties for the best benzimidazole compound
32 were determined in the rat and showed an improved
14% oral bioavailability and lower clearance rate of
49 mL/min/kg, compared to IIb (Fig. 1, 1% oral bio-
availability and 84 mL/min/kg clearance),9 one of the
potent hydantoin analogues.
Replacement of the large hydantoin-indole moiety from
our previous work was accomplished with the synthesis
of a variety of smaller heterocyclic analogues. These
heterocyclic derivatives were found to have binding
affinity comparable to our hydantoin analogues IIa,b,
with compound 32 being the most potent compound,
having a 4-NO2 in the N-CBZ group. Increasing anti-
viral activity in our series suggests that efficient inhibi-
tion of HIV-1 replication may be possible by further
modification of potent heterocycle-based CCR5
antagonists with better understanding of the origin of
the discordant results.
5. Kim, D.; Wang, L.; Caldwell, C. G.; Chen, P.; Finke, P. E.;
Oates, B.; MacCoss, M.; Mills, S. G.; Malkowitz, L.;
Gould, S. L.; DeMartino, J. A.; Springer, M. S.; Hazuda,
D.; Miller, M.; Kessler, J.; Danzeisen, R.; Carver, G.;
Carella, A.; Holmes, K.; Lineberger, J.; Schleif, W. A.;
Emini, E. A. Bioorg. Med. Chem. Lett. 2001, 11, 3099.
6. Campbell, J. B.; Dedinas, R. F.; Trumbower-Walsh, S. A.
J. Org. Chem. 1996, 61, 6205.
7. For a description of the binding assay, see ref 4a, footnote 25.
8. Hazuda, D. J.; Felock, P.; Witmer, M.; Wolfe, A.; Still-
mock, K.; Grobler, J. A.; Espeseth, A.; Gabryelski, L.; Schleif,
W.; Blau, C.; Miller, M. D. Science 2000, 287, 646.
9. Average data generated after 2 mg/kg po and 0.5 mg/kg
iv doses in n=3 animals/dose. The vehicle for iv and oral
doses was PEG400/ethanol/water (20:20:60, v/v/v) and 20%
hydroxypropyl b-cyclodextrin, respectively.
References and Notes
1. Pomeranntz, R. J. JAMA 1999, 282, 1177.
2. Cocci, F.; DeVico, A. L.; Garzino-Demo, A.; Arya, S. K.;
Gallo, R. C.; Lusso, P. Science 1995, 270, 1881.
3. For a review of HIV-entry mechanisms and current entry
inhibitors, see: Blair, W. S.; Lin, P.-F.; Meanwell, N. A.;
Wallace, O. B. Drug Discov. Today 2000, 5, 183.