Discovery of N-benzyl-N′-(4-pipyridinyl)urea CCR5 antagonists as anti-HIV-1 agents (I): Optimization of the amine portion

Article abstract of DOI:10.1016/j.bmcl.2010.10.033

Several series of carbamate, urea and carboxamide-based CCR5 antagonists have been discovered via optimizations at the amine portion of lead compound 2. All compounds were evaluated for their antiviral activities. Lead urea 29 showed good pharmacokinetic properties, justifying further development of this series.

Full text of DOI:10.1016/j.bmcl.2010.10.033

Bioorganic & Medicinal Chemistry Letters 20 (2010) 7397–7400
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of N-benzyl-N0-(4-pipyridinyl)urea CCR5 antagonists as anti-HIV-1
agents (I): Optimization of the amine portion
Maosheng Duan a, , Jennifer Peckham b, Mark Edelstein a, Robert Ferris a, Wieslaw M. Kazmierski a,
⇑
Andrew Spaltenstein a, Pat Wheelan a, Zhiping Xiong a
a Infectious Diseases Center for Excellence in Drug Discovery, GlaxoSmithKline, Five Moore Drive, Research Triangle Park, NC 27709, United States
b Metabolic Pathways Center for Excellence in Drug Discovery, GlaxoSmithKline, Five Moore Drive, Research Triangle Park, NC 27709, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Several series of carbamate, urea and carboxamide-based CCR5 antagonists have been discovered via
optimizations at the amine portion of lead compound 2. All compounds were evaluated for their antiviral
activities. Lead urea 29 showed good pharmacokinetic properties, justifying further development of this
series.
Received 16 August 2010
Revised 5 October 2010
Accepted 6 October 2010
Available online 12 October 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Key words:
CCR5, HIV
Carbamates
Ureas
Optimization
The Chemokine Receptor R5 (CCR5) plays a critical role as viral
entry co-receptor in the early stage of HIV-1 infection. Preventing
its interaction with viral envelope protein gp120 ultimately blocks
viral entry thus shutting down viral replication.1 Maraviroc is the
first marketed CCR5 inhibitor used as part of highly active antiret-
roviral therapy (HAART) in anti HIV-1 therapy.2
We previously reported several series of 4,4-disubstituted
piperindine and cyclohexylamine based CCR5 antagonists,3 exem-
plified by compound 1 (Fig. 1). The structure–activity relationship
(SAR) in these series revealed that the central piperidine and a phe-
nyl substituted quaternary carbon were critical for antiviral activ-
ity, and two-carbon linker between the piperidine and tropane was
optimal length. These observations led us to continue the explora-
tions of novel CCR5 antagonists by retaining the 4,4-disubstituted
piperidine as a central scaffold and diversifying both the amine and
the acyl termini.
amides. Herein, we wish to describe the syntheses of this set of
analogues and report their structure–activity relationship.
The synthesis was initiated by preparing key intermediate 11.
2-Chloro-5-{[(1,1-dimethylethyl) amino]sulfonyl}-4-fluorobenzoic
acid 6, was first obtained in two steps from the commercially
available 2-chloro-4-fluorobenzoic acid 4 (Scheme 1). Aldehyde
7, prepared as previously described,5 was converted into alcohol
8 with NaBH4. Removal of Boc, followed by HATU coupling with
6, resulted in alcohol 10, setting the stage for the Swern oxidation
towards intermediate 11.
With intermediate 11 in hand, we next derivatized the carba-
mate moiety. Reductive amination of Boc protected piperidinone
with allyl amine yielded 13, which was then reacted with the
in situ generated benzyl chloroformates 15, affording intermedi-
ates 16. Subsequent removal of Boc followed by reductive amina-
tion with the aldehyde 11 furnished the carbamate series 17a–f
(Scheme 2).
Our efforts began with the synthesis of a small library varying
amine substituents while keeping the acyl moiety unchanged
(Fig. 2). Carbamate 3 was quickly identified as our initial hit,4
and showed attractive potency in both HOS and PBL antiviral
assays.
Preparation of the urea series was achieved by using the syn-
thetic sequence in Scheme 3. Thus, isocyanates 19 were generated
by treating amines 18 with slight excess of phosgene in presence of
pyridine. Next, reaction with 13 yielded intermediate 20. Upon Boc
removal from 20, the urea series 21a–l was synthesized by reduc-
tive alkylation with aldehyde 11.
With this result in hand, we decided to further optimize the
amine portion by expanding the carbamates to urea and carbox-
The synthesis of the final amide series began with coupling
amine 13 under HATU condition with phenyl acetic acid 22. After
Boc deprotection of amide 23, the resulting piperidine 24 was
reductively alkylated with 11, yielding the carboxamide series
25a–e (Scheme 4).
⇑
Corresponding author. Fax: +1 919 483 6053.
E-mail addresses: maosheng.a.duan@gsk.com, duanmaosheng@hotmail.com (M.
Duan).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.10.033

7398
M. Duan et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7397–7400
O
O
O
O
S
F
acyl portion
N
N
F
H
R'
N
F
Cl
N
N
R"
H
N
N
H
amine portion
1
Figure 1. The piperidine based CCR5 antagonist and the central core template.
O
O
O
S
F
N
N
F
O
O
O
H
S
Cl
N
O
N
N
F
H
N
O
F
Cl
N
R"
NO2
amine portion
2
3
HOS IC50 8.6 nM
PBL IC50 24 nM
Figure 2. The initial library design and the hit.
O
O
O
O
O
O
O
S
F
S
F
b
a
Cl
OH
OH
N
OH
H
Cl
F
Cl
Cl
5
4
6
HCl
HN
Boc
Boc
N
N
F
e
d
c
O
OH
OH
F
F
9
7
8
O
O
S
O
O
O
O
S
N
N
F
N
N
H
H
f
O
F
Cl
Cl
OH
F
F
10
11
Scheme 1. Reagents and conditions: (a) HSO3Cl, 150 °C, 6 h, 85%; (b) t-BuNH2, NaHCO3, dioxane/H2O, 70%; (c) NaBH4, MeOH, rt, 86%; (d) 4 M HCl, rt, quant.; (e) 6, HATU, Et3N,
DMF, rt, 65%; (f) Swern oxidation, 22%.
All compounds were tested for antiviral activity in both Human
OsteoSarcoma (HOS) (n = 2) and peripheral blood lymphocytes
(PBL) cells (n P 4) against the Ba-L strain of HIV-1.6 Compound in-
duced cellular toxicity was also investigated using CellTiter-Glo re-
agent (Promega). None of the compounds induced cell killing up to
substitutes at the para position with similar properties (hydrogen
bonding acceptor and electron withdrawing) were synthesized.
All except cyano-bearing 17e turned out to be less potent in the
HOS assay than the initial lead 3. The cyano group (17e) improved
the potency by ꢀtwofolds. (Table 1).
1
lM (data not shown) indicating that the observed potency is the
As bioisosteres of the carbamates, both phenyl and benzyl urea
analogues were synthesized to further optimize the amine portion.
As the data show in Table 2, the benzyl urea demonstrated better
antiviral profiles than its phenyl counterparts though this was
not true for the F substituent (21d vs 21c). CF3 substituted 21b is
9 times more potent than 21a in HOS cell assay, however, the rel-
ative potency of 21b in the PBL assay is lower. Again, cyanobenzyl
result of an antiviral effect and not toxicity (Tables 1–4).
We initially hypothesized from the p-nitro group in hit 3 that a
hydrogen bonding acceptor may be required for antiviral activity.
In addition, the strong electron-withdrawing nature of the nitro
substituent could potentially improve metabolic stability of the
benzyl moiety. Thus, a series of benzyl carbamates (17a–f) carrying

M. Duan et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7397–7400
7399
Table 1
Boc
Boc
a
N
N
Antiviral potency of carbamate analogues 17a–f in HOS and PBL cell assays
O
N
O
O
O
H
Boc
S
F
13
12
O
N
N
N
F
c
O
N
N
O
Cl
O
OH
N
O
R
b
O
Cl
R
R
R
16
15
14
Compound #
R
HOS IC50 (nM)
PBL IC50 (nM)
O
O
N
O
17a
17b
15
22
40
S
N
d,e
NA
O
N
F
Cl
17c
17d
41
17
NA
4.5
N
O
F
R
17a-f
17e
17f
4.5
27
NA
NA
Scheme 2. Reagents and conditions: (a) NaBH(OAc)3, CH2Cl2, rt, quant.; (b)
phosgene, K2CO3, CH2Cl2, rt; (c) i-Pr2EtN, CH2Cl2, rt, 35–90%; (d) HCl, rt, quant.;
(e) 11, NaBH(OAc)3, i-Pr2EtN, CH2Cl2, rt, 30–60%.
NA: not available.
Boc
NH2
N
O
O
N
n
a
n
b
n=0,1
Table 2
N
N
n
n=0,1
R
R
H
Antiviral potency of urea analogues 21a–j in HOS and PBL cell assays
R
18
19
O
O
O
20
S
F
N
N
F
O
O
O
O
N
Cl
S
N
N
F
c,d
N
N
n
H
O
N
F
Cl
R
N
N
n
H
Compound #
R
n
HOS IC50 (nM)
64
PBL IC50 (nM)
NA
R
21a
0
21a-l
21b
21c
21d
1
0
1
6.9
34
42
Scheme 3. Reagents and conditions: (a) phosgene, pyridine, CH2Cl2, rt; (b) 13, i-
Pr2EtN, CH2Cl2, rt, 50–81%; (c) HCl, rt, quant.; (d) 11, NaBH(OAc)3, i-Pr2EtN, CH2Cl2,
rt, 52–69%.
NA
NA
46
21e
21f
0
1
20.5
3.9
25
HCl
HN
R
Boc
OH
R
a
O
N
O
b
3.7
O
N
R
N
21g
21h
0
1
11.5
26
35
22
23
24
146
O
O
O
S
N
N
F
c
R
21i
21j
1
0
3100
60
NA
NA
O
N
F
Cl
N
25a-e
NA: not available.
Scheme 4. Reagents and conditions: (a) 13, HATU, i-Pr2EtN, CH2Cl2, rt; (b) HCl,
CH2Cl2, rt; (c) 11, NaBH(OAc)3, i-Pr2EtN, CH2Cl2, rt, 52–69%.
the HOS assay, however, its antiviral potency in the PBL assay was
disappointing, presumably due to high c log P of 25a. To best mimic
the benzyl carbamate/urea, phenyl propanamides 26 and 27 were
synthesized via a similar approach (Fig. 3). Surprisingly, both amides
exhibited a dramatic loss of potency, which was not attributed to
replacing t-But with methyl substituent in the benzenesulfonamide
portion (see SAR in the follow-on communication).7
The described potency SAR identified the benzyl ureas as the
lead scaffold and cyano (CN) as the best para-phenyl substituent.
This observation led us to focus on the p-cyanobenzyl urea series
and to further probe SAR on the allyl portion of p-cyanobenzyl
urea 21f exhibited much better activity than cyanophenyl urea 21e
in both HOS and PBL assays. Methyl sulfone (21g) and methyl ester
(21h) behaved similarly as they did in the carbamate series. Sur-
prisingly, the amide caused significant loss of potency (21i). Ace-
tate 21j also failed to improve the antiviral activity.
Carboxamides exhibited similar antiviral activity as the phenyl
urea analogues except for 25a (Table 3). The trifluoromethyl(CF3)
substituent provided a substantial potency improvement of 25a in

7400
M. Duan et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7397–7400
Table 3
O
O
O
Antiviral potency of amide analogues 25a–e in HOS and PBL cell assays
S
F
N
N
F
H
O
O
O
O
N
Cl
S
F
N
N
F
N
R
N
R
H
O
N
Cl
CN
N
28 R = n-Bu HOS IC50 = 2.6nM, PBL IC50 =11nM
29 R = m-Fluorophenyl HOS IC50 = 0.4 nM, PBL IC50 = 1.7nM
Compound #
R
HOS IC50 (nM)
PBL IC50 (nM)
Figure 4. n-Butyl and m-fluorophenyl derivatives 28 and 29 and their antiviral
activity.
25a
25b
3.3
52
53
NA
The pharmacokinetic profile of urea 29 was evaluated in Spra-
gue Dawley rats at 1 mg/kg using 5% mannitol with 0.05% acetic
acid as dose vehicle. Encouragingly, 29 showed acceptable clear-
ance and bioavailability (22%).
25c
25d
65
18
NA
87
In summary, starting from Lead 3, we synthesized and evalu-
ated carbamate, urea and carboxamide-based CCR5 antagonist
scaffolds. Compounds in these series were generally very potent
in both HOS and PBL antiviral assays. In particular, the p-cyanoben-
zyl urea motif enabled the most potent antiviral profiles across the
series. Moreover, replacement of allyl in 21f with m-fluorophenyl
29 dramatically enhanced its antiviral activity. Urea 29 was found
to possess satisfactory in vivo properties in the rat PK model, sug-
gesting that 29 is an interesting lead molecule for additional
medicinal chemistry explorations. Subsequent optimization of
the acyl portion will be reported in the follow-on communication.
25e
210
NA
NA: not available.
Table 4
Pharmacokinetics of 29 in rat at 1 mg/kg
Compound #
Cl (mL/min/kg)
18
t1/2 (h)
Vdss (L/kg)
11.6
%F
29
10.8
22
References and notes
O
O
O
S
F
1. Dragic, T.; Litwin, V.; Allaway, P. G.; Martin, R. S.; Huang, Y.; Nagashima, A. K.;
Cayanan, C.; Maddaon, J. P.; Koup, A. R.; Moore, P. J., et al Nature 1996, 381, 667.
2. Price, D. A.; Armour, D.; De Groot, M.; Leishman, D.; Napier, C.; Perros, M.;
Stamman, B. L.; Wood, A. Bioorg. Med. Chem. Lett. 2006, 16, 4633.
3. (a) Duan, M.; Aquino, C.; Ferris, R.; Kazmierski, M. W.; Kenakin, T.; Koble, C.;
Wheelan, P.; Watson, C.; Youngman, M. Bioorg. Med. Chem. Lett. 2009, 19, 1610;
(b) Duan, M.; Aquino, C.; Ferris, R.; Kazmierski, M. W.; Wheelan, P. Bioorg. Med.
Chem. Lett. 2009, 19, 4988.
4. Merck used the same carbamate motif in their CCR5 antagonists: Shankaran, K.;
Donnelly, K. L.; Shah, S. K.; Caldwell, C. G.; Chen, P.; Finke, P. E.; Oates, B.;
MacCoss, M.; Mills, S. G.; DeMartino, J. A.; Gould, S. L.; Malkowitz, L.; Siciliano, S.
J.; Springer, M. S.; Kwei, G.; Carella, A.; Carver, G.; Danzeisen, R.; Hazuda, D.;
Holmes, K.; Kessler, J.; Lineberger, J.; Miller, M. D.; Emini, E. A.; Schleif, W. A.
Bioorg. Med. Chem. Lett. 2004, 14, 3589.
N
N
H
O
N
Cl
N
F
R
26 R = OCF3 HOS IC50 = 420nM
27 R = CN HOS IC50 = 150nM
Figure 3. 3-Phenyl propanamide derivatives 26 and 27 and their HOS IC50
.
5. Kazmierski, W. M.; Aquino, C.; Chauder, B.; Deanda, F.; Ferris, R.; Jones-Hertzog,
D.; Kenakin, T.; Koble, C.; Watson, C.; Wheelan, P.; Yang, H.; Youngman, M. J.
Med. Chem. 2008, 51, 6538.
6. Muniz-Medina, V.; Jones, S.; Maglich, J.; Galardi, C.; Hollinggswirth, R.;
Kazmierski, W.; Ferris, R.; Edelstein, M.; Chiswell, K.; Kenakin, T. Mol.
Pharmacol. 2009, 75, 490.
urea. Compounds 28 and 29 were synthesized using the synthetic
sequence in Schemes 3 and 4. The n-butyl analog 28 exhibited a
similar potency to the allyl analogue 21f. However, we were ex-
cited to discover that the replacement of allyl with a m-fluoro-
phenyl moiety further improved the antiviral activity to subnano
molar level (Fig. 4).
7. Duan, M.; Peckhman, J.; Edelstein, M.; Ferris, R.; Kazmierski, K. M.; Wheelan, P.;
Xiong, Z. Bioorg. Med. Chem. Lett. 2010, xx, yyzz.