Antagonists of the human CCR5 receptor as anti-HIV-1 agents. Part 4: Synthesis and structure-activity relationships for 1-[N-(methyl)-N-(phenylsulfonyl)amino]-2-(phenyl)-4-(4-(N-(alkyl)-N- (benzyloxycarbonyl)amino)piperidin-1-yl)butanes

Article abstract of DOI:10.1016/S0960-894X(01)00492-9

(2S)-2-(3-Chlorophenyl)-1-[N-(methyl)-N-(phenylsulfonyl)amino]-4-[spiro (2,3-dihydrobenzthiophene-3,4′-piperidin-1′-yl)]butane S-oxide (1b) has been identified as a potent CCR5 antagonist having an IC₅₀ = 10 nM. Herein, structure-activity relationship studies of non-spiro piperidines are described, which led to the discovery of 4-(N-(alkyl)-N-(benzyloxycarbonyl)amino)piperidine derivatives (3-5) as potent CCR5 antagonists.

Full text of DOI:10.1016/S0960-894X(01)00492-9

Bioorganic & Medicinal Chemistry Letters 11 (2001) 2475–2479
Antagonists of the Human CCR5 Receptor as Anti-HIV-1 Agents.
Part 4: Synthesis and Structure–Activity Relationships for 1-[N-
(Methyl)-N-(phenylsulfonyl)amino]-2-(phenyl)-4-(4-(N-(alkyl)-N-
(benzyloxycarbonyl)amino)piperidin-1-yl)butanes
Paul E. Finke,a,* Bryan Oates,a Sander G. Mills,a Malcolm MacCoss,a Lorraine Malkowitz,b
Martin S. Springer,b Sandra L. Gould,b Julie A. DeMartino,b Anthony Carella,c
Gwen Carver,c Karen Holmes,c Renee Danzeisen,c Daria Hazuda,c Joseph Kessler,c
Janet Lineberger,c Michael Miller,c William A. Schleifc and Emilio A. Eminic
aDepartment of Medicinal Chemistry, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
bDepartment of Immunology Research, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
cDepartment of Antiviral Research, Merck Research Laboratories, PO Box 4, West Point, PA 19486, USA
Received 9 April 2001; accepted 2 July 2001
Abstract—(2S)-2-(3-Chlorophenyl)-1-[N-(methyl)-N-(phenylsulfonyl)amino]-4-[spiro(2,3-dihydrobenzthiophene-3,40-piperidin-10-
yl)]butane S-oxide (1b) has been identified as a potent CCR5 antagonist having an IC50=10 nM. Herein, structure–activity rela-
tionship studies of non-spiro piperidines are described, which led to the discovery of 4-(N-(alkyl)-N-(benzyloxy-
carbonyl)amino)piperidine derivatives (3–5) as potent CCR5 antagonists. # 2001 Elsevier Science Ltd. All rights reserved.
The chemokine receptor CCR5, a member of the seven-
transmembrane G-protein coupled family of receptors,1
has been identified as a primary co-receptor with CD4
by which macrophage tropic HIV-1 virus strains infect
their host cells.2 These CCR5 utilizing HIV-1 strains,
now called R5 variants, have been associated with the
initial and early phases of HIV-1 infection, although
they are generally present throughout the course of the
disease AIDS. Given the importance of CCR5 for the
establishment, and possible maintenance, of HIV-1
infection in vivo,3 numerous efforts have been initiated
in an effort to identify suitable CCR5 antagonists for
use as potential therapeutic agents for the treatment of
HIV-1 infection.4ꢀ7
the 2-phenyl substitution afforded 1b (IC50=10 nM)9
and then optimization of the spiropiperidine led to the
spiro(indan-1-one-2,40-piperidin-10-yl) derivative 2 with
In our previous manuscripts in this series,8ꢀ10 the
discovery of (2S)-2-(3,4-dichlorophenyl)-1-[(N-methyl-
N-phenylsulfonyl)amino]-4-[spiro(2,3-dihydrobenzthio-
phene-3,40-piperidin-10-yl)]butane S-oxide (1a), having
an IC50=35 nM for inhibition of [125I]-MIP-1a binding
to CCR5, was described.8 Subsequent investigation of
*Corresponding author. Fax: +1-732-594-5790; e-mail: paul_finke@
merck.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00492-9

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P. E. Finke et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2475–2479
a CCR5 binding affinity of 5 nM.10 Based on two pos-
sible models of the spiro portion of 2,10 further struc-
ture–activity relationship(SAR) studies as herein
described led to the discovery of a new class of non-
spiro piperidine CCR5 antagonists (3–5) containing the 4-
(N-(alkyl)-N-(alkoxycarbonyl)amino)piperidine moiety.
sodium hydride in DMF. Final Boc removal was per-
formed with HCl in methanol or with TFA. Alter-
natively, the N-alkyl moiety could be installed first by
reductive amination of the corresponding alkylamine
with Boc-piperidone (18). Acylation of 19 (R2=Et, n-
Pr, allyl) could then be done with a variety of chloro-
formates, acid chlorides, isocyanates, and methane-
sulfonyl chloride to afford other carbamate (6c), urea
(6d), amide (6f), and sulfonamide (6g) substituted
piperidines. A second alkylation of the distal urea N–H
with methyl iodide prior to the Boc removal afforded
the dialkyl ureas 6e.
The synthesis of these modified piperidine derivatives
was based on our previously described routes9ꢀ12
(Scheme 1) and initially utilized the unsubstituted, racemic
3-phenyl-4-(N-methyl-N-phenylsulfonylamino)butanal
(7a). In addition, selected compounds were also pre-
pared in the chiral (S) and/or the (S)-3-chlorophenyl
series (4 and 5) from 7b and/or 7c, respectively. The
reductive amination of appropriately substituted piper-
idines 6a–g (Scheme 2) using sodium triacetoxyborohy-
dride in dichloroethane (DCE) afforded the coupled
products 3–5, 8, and 9–11 (see Tables 1 and 2 for
structures) in 50–90% yields.
These compounds were then evaluated in a [125I]-MIP-
1a based binding assay of CCR5 stably expressed in
Chinese hamster ovary (CHO) cells 8,13 (Tables 1 and 2).
The initial investigation of non-spiro derivatives was
done in the racemic, des-chloro series 3. As previously
reported,10 the best spiropiperidine was the ketone 2
(IC50=5 nM) in which the carbonyl oxygen was beta to
the C-4 piperidine position. Not surprisingly, the 4-
amides, such as 8, were not active in the CCR5 binding
The preparations of the piperidines that were utilized in
Scheme 1 were carried out in several ways depending on
the substitution pattern (Scheme 2). Some initial 4-car-
boxamide substituted piperidines 6a (e.g., R0=R00=Et)
were prepared from piperidine-4-carboxylic acid (12a)
by reaction of the N-Cbz protected acid chloride with
various amines followed by hydrogenation to remove
the Cbz. Placing the carbonyl beta to the piperidine as
in 2 was first accomplished by Curtius rearrangement of
the acyl azide of 12b to give the isocyanate 13. Reaction
with methanol or t-butanol afforded the carbamate
derivatives 14 (R1=Me or t-Bu). N-Alkylation and/or
Cbz removal then afforded the N-alkyl or N-H carbam-
ate derivatives 6c. The cyclic carbamate derivative 6b
was also obtained by reacting the intermediate isocyan-
ate 13 with 2-chloroethanol followed by internal alkyl-
ation of the nitrogen using NaH in DMF. Two more
direct routes were also developed depending on the
alkoxy and N-alkyl substitution. Starting with commer-
cial 4-bromopiperidine (15), the amine 16 was prepared
via reduction of the azide obtained by displacement of
the bromide in DMF after first Boc protection of the
piperidine nitrogen. Acylation with various chloro-
formates afforded the N-H carbamates 17 which were
then N-alkylated with an appropriate alkyl halide and
Scheme 2. Reagents: (a) Cbz-Cl, NaOH, water/acetone; (b) oxalyl
chloride, DMF (cat), DCM, rt; (c) R0R00NH, DCM, rt; (d) 10% Pd/C,
H2 (40 psi), MeOH; (e) NaN3, acetone/water, 0 ꢁC; (f) toluene, 80 ꢁC;
(g) 2-chloroethanol, DIPEA, rt; (h) NaH, DMF, rt; (i) MeOH,
DIPEA or t-BuOH, CuCl2, rt; (j) R2X, NaH, DMF, rt; (k) (Boc)2O,
DIPEA, DCM; (l) NaN3, DMF, rt; (m) R1OCOCl, DIPEA, DCM, rt;
(n) HCl, MeOH, rt or TFA, rt; (o) R2NH2, HOAc, NaBH(OAc)3,
DCE, rt; (p) R1NCO, DIPEA, DMAP (cat), DCM, rt; (q) R1COCl,
DIPEA, rt; (r) MeSO2Cl, DIPEA, DCM, rt; (s) MeI, NaH, DMF, rt.
Scheme 1. Reagents: (a) HOAc or DIPEA (if 6 was an HCl salt),
NaBH(OAc)3, DCE.

P. E. Finke et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2475–2479
2477
assay (IC50>10,000 nM for several primary and sec-
ondary amides). However, the carbamates with their
carbonyl now beta to the piperidine as in 2 showed
interesting activity without the spiro structure. The N-
ethyl Boc derivative 3d was found to have an IC50=30
nM, being equipotent to the corresponding racemic des-
chloro analogue 1c.9 Since the N–H derivatives 3b–c
were only 1000 nM, the N-alkyl appeared to also play a
critical role in the observed activity of 3d. The N-
methyl-N-(methoxycarbonyl)amino compound 3e was
found to be the minimal carbamate structure and was
comparable to the simple 4-phenylpiperidine derivative
(IC50=150 vs 120 nM).9 Interestingly, 3a, the cyclic
version of 3e, was essentially inactive (37% I@1000
nM), suggesting that the preferred orientation of the
carbonyl is precluded with this cyclic constraint. Thus,
configurations A and B of the carbamate moiety (Fig. 1)
are not likely to be the active species, leaving config-
urations C and D, with C placing the carbonyl in the
same position as the carbonyl of 2 (see structure 2) in a
proposed model.10 The preferred orientation of the car-
bamate (either C or D) was the subject of further
investigation and will be reported elsewhere.
The developing SAR for these carbamates (Table 1) in
fact did indicate two distinct binding motifs. Increasing
the size of the N-alkyl in the methoxycarbonyl series
(3e–k) gave increasing activity, the optimum size being
about that of the cyclohexylmethyl groupof 3j; how-
ever, the benzyl derivative 3k was significantly poorer.
With larger alkoxy groups, the activity rapidly dimin-
ished (3l–m). Conversely, keeping the N-alkyl constant
with an ethyl moiety and increasing the size of the
alkoxy groupagain led to enhanced activity as seen with
the series 3f,n–r, the best now being the benzyloxy
compound 3r. The optimum size of the N-alkyl group
(3r–v) was determined to be between ethyl, n-propyl, or
allyl (IC50=2 nM). While moderate sized groups
afforded the expected intermediate binding activity
(data not shown), the incompatibility of two large
groups in the same molecule is highlighted with com-
pound 3m. A tentative hypothesis is that the latter ben-
zyloxy compounds adopt conformation C in which the
smaller N-alkyl group is adjacent to the piperidine,
Table 1. Structures and CCR5 binding activities for compounds 3–5
Compd
R1
R2
CCR5a
PBMCb
IC50 (nM)c IC95 (mM)d
3a
3b
3c
3d
3e
–CH2CH2–
>1000
1000
1000
30
150
40
20
15
10
6
nde
nd
nd
nd
nd
nd
nd
nd
nd
25
nd
nd
nd
nd
nd
nd
nd
13
Me
t-Bu
t-Bu
Me
Me
Me
Me
Me
Me
Me
Et
Bn
Et
t-Bu
H
H
Et
Me
3f
Et
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
n-Pr
n-Bu
n-C6H13
c-C6H11–CH2
Bn
c-C6H11–CH2
c-C6H11–CH2
Et
100
35
800
40
25
15
10
2
Table 2. Structures and CCR5 binding activities for compounds 9
and 10
Et
Et
Et
Et
c-C6H11–CH2
Ph
Bn
5r
3s
Bn
Bn
Et
Me
2
5
13
25
3t
5t
3u
3v
4v
3w
3x
3y
3z
3aa
4aa
3bb
5bb
5cc
4dd
5dd
Bn
Bn
Bn
Bn
n-Pr
n-Pr
n-Bu
Allyl
Allyl
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
2
4
5
2
1.5
4
3
3
6
1.5
1.5
2
2
0.8
2
25
nd
>13
0.8
0.8
nd
nd
nd
nd
nd
0.1–0.4f
0.2
0.2
3
nd
0.4
Compd
X
R1
R2
CCR5a
IC50 (nM)b
Bn
3s
9a
9b
9c
9d
9e
9f
9g
O
N–H
N–H
N–H
N–H
N–H
N–Me
N–H
N–H
N–H
—
Bn
Me
Me
Bn
Bn
Ph
Bn
n-Pr
H
Et
H
2
1000
120
100
2.5
4
20
6
75
0.75
120
100
3
4
20
2-Me–C6H4–CH2
3-Me–C6H4–CH2
4-Me–C6H4–CH2
4-CF3–C6H4–CH2
4-NO2–C6H4–CH2
4-NO2–C6H4–CH2
4-NO2–C6H4–CH2
4-NO2–C6H4–CH2
3-NH2COC6H4–CH2
4-NH2COC6H4–CH2
4-NH2COC6H4–CH2
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
Allyl
Et
n-Pr
n-Pr
n-Pr
n-Pr
Allyl
n-Pr
Allyl
Allyl
n-Pr
n-Pr
n-Pr
(R)-a-Me–Bn
(S)-a-Me–Bn
4-NO2–Bn
Me
9h
9i (S)
10a
10b
10c
10d
10e
10f
3
—
—
—
—
Ph
Bn
aSee refs 8 and 13 for a description of the binding assay.
bSee ref 14 for a description of the PBMC antiviral assay.
PhOCH2
PhCH2CH2
4-NO2–Bn
cThe IC50 values are an average of three independent titrations having
calculated standard errors usually less than 15%. The assay-to-assay
variation was generally less than ꢂ2-fold based on the results for the
standard compound 1b.
—
2
aSee ref 8 for a description of the binding assay.
bThe IC50 values are an average of three independent titrations having
calculated standard errors usually less than 15%. The assay-to-assay
variation was generally less than ꢂ2-fold based on the results for the
standard compound 1b.
dUsually, the result of a single experiment. For derivatives j, r–t, and v,
1b was used as a standard and was 13–25 mM in these assays.
eNo data.
fThe range of three determinations.

2478
P. E. Finke et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2475–2479
4-nitro substitution was also explored with 9i and 10f,
which also afforded potent binding. The sulfonamide 11
(Scheme 1) was less active than 3f (IC50=300 vs 40 nM).
The more potent compounds were also tested in a
PBMC cell-based assay using the R5 HIV-1 viral isolate
YU-2.14 Since considerable variation in results was
obtained in this assay with only moderately potent
inhibitors, 1b was usually included as a standard during
this assay period.9 Disappointingly, the enhanced CCR5
binding seen for 3j, 3s–t, and amide 10c did not trans-
late into improved antiviral efficacy compared to 1b
(IC95=13–25 mM vs 25 mM, respectively), although the
ureas 9d and 9e did offer some improvement (IC95=3
and 6 mM). Interestingly, while the CCR5 binding assay
results were essentially the same, the allyl derivatives 3v
and 4v finally showed significantly better antiviral
activity compared to 3t (IC95=both 800 nM vs 25 mM).
Introduction of the polar 4-nitro and carboxamide
groups of 4aa and 5dd also afforded enhanced antiviral
activity in the PBMC assay (IC95=100–400 nM). The
combination of both the allyl and 4-nitro moieties in the
carbamates 3bb and 5bb (IC95=200 nM), urea 9i
(IC95=250 nM), and especially amide 10f (IC95=50
nM) afforded the best efficacy in the PBMC assay with
IC95’s now in the lower nanomolar range.
Figure 1. Four possible conformations of carbamate derivatives.
while the former series adopts conformation D in which
the larger alkyl group is away from the piperidine and
the smaller methoxy occupies the more restricted posi-
tion. The better activity of the benzyloxy series then
implies a superior interaction of the carbonyl of con-
former C with the receptor. The extended conformation
of the benzyl in conformation C was also in agreement
with the good binding, but poor antiviral activity14 (see
below), previously seen with a 4-(3-phenylpropyl)piper-
idine compound (IC50=5 nM, PBMC assay,
IC95=50,000 nM).10
Previously, the chiral, 3-chlorophenyl derivative 1b had
shown 3- to 4-fold improvement over the racemic
unsubstituted compound 1c in both the binding
(IC50=10 vs 35 nM) and antiviral assays. Unfortu-
nately, for unknown reasons, neither the expected affin-
ity enhancement nor any improvement in antiviral
efficacy were realized for the chiral, 3-chlorophenyl
analogues 5r and 5t with these non-spiro carbamate
derivatives.
Thus, with the synthesis of the initial carbamates, the
spiro structure of 1 and 2 was found not to be required
for potent CCR5 binding activity. Optimization of the
two alkyl portions implicated two distinct binding
motifs of which the N-alkyl-N-benzyloxycarbonyl-
amino derivatives were the more potent. Further use of
the N-allyl, substitution on the benzyl, and investigation
of other linking functionality led to significantly
enhanced antiviral activity of the N-allyl-4-nitrobenzyl
compounds with IC95’s of 50–200 nM in the PBMC
assay. Further investigations of these findings in com-
bination with other core structures will be reported in
the near future.
Substitution on the benzyl was also investigated. The
isomeric 2-, 3-, and 4-methyl derivatives 3w–y showed
very little effect on binding, although the larger tri-
fluoromethyl groupof 3z appeared to be detrimental, as
well as 4-phenyl and 1- or 2-naphthyl (data not shown).
However, the polar 4-nitro and 3- and 4-carboxamide
moieties of 3aa, 4aa, 3bb, and 4dd showed equal or more
potent binding which was also maintained in 5bb–dd.
Although not evident from the binding data (IC50=1–2
nM), the 4-nitro and 4-carboxamide groups provided
much improved antiviral activity (see below).
References and Notes
1. For a review of the chemokines and their receptors, see:
Baggiolini, M.; Dewald, B.; Moser, B. Annu. Rev. Immunol.
1997, 15, 675.
2. For a review of the co-receptor search, see: Fauci, A. S.
Nature 1996, 384, 529.
3. Liu, R.; Paxton, W. A.; Choe, S.; Ceradini, D.; Martin,
S. R.; Horuk, R.; MacDonald, M. E.; Stuhlmann, H.; Koup,
R. A.; Landau, N. R. Cell 1996, 86, 367.
4. (a) Blair, W. S.; Lin, P.-F.; Meanwell, N. A.; Wallace, O. B.
Drug Discovery Today 2000, 5, 183. (b) ; Horuk, R.; Ng, H. P.;
Med. Res. Rev. 2000, 2, 155.
5. Shiraishi, M.; Aramaki, Y.; Seto, M.; Imoto, H.; Nishi-
kawa, Y.; Kanzaki, N.; Okamoto, M.; Sawada, H.; Nishi-
mura, O.; Baba, M.; Fujino, M. J. Med. Chem. 2000, 43, 2049.
6. Armour, D. R.; Price, D. A.; Stammen, B. L. C.; Wood, A.;
Perros, M.; Edwards, M. P. EPO Patent 1,013,276 A1, 2000
(Pfizer); Chem. Abstr. 2000, 133, 74,024x.
7. Baroudy, B. M.; Clader, J. W.; Josien, H. B.; McCombie,
S. W.; McKittrick, B. A.; Miller, M. W.; Neustadt, B. R.;
Palani, A.; Smith, E. M.; Steensma, R.; Tagat, J. R.; Vice, S.
Other acyl groups were also investigated with the prep-
aration of amides and ureas. The same SAR was seen
regarding the relative size of the two groups with the
best again being the benzyl related compounds as illus-
trated in the urea series 9a–e. While neither showed
improved activity over 9e, the results of the a-methyl
urea derivatives 9g and 9h showed that a stereochemical
preference exists for the (R) isomer, thus indicating a
preferred directionality for the benzyl moiety in the
binding site. A second alkylation on the terminal nitro-
gen (9f) was always detrimental by at least 10-fold.
Several amide derivatives were also quite potent as seen
with 10a–e; however, the benzamide 10b was a con-
siderably poorer inhibitor than 10c, indicating that the
binding site could not tolerate the extended confirma-
tion of the planar benzamide, in agreement with the
previously proposed binding model.10 The effect of the

P. E. Finke et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2475–2479
2479
F.; Laughlin, M. A.; Gilbert, E.; Labroli, M. A. WO 00/66558,
2000 (Schering); Chem. Abstr. 2000, 133, 350,248c.
11. (a) MacCoss, M.; Mills, S. G.; Shah, S. K.; Chiang, Y.-C.
P.; Dunn, P. T.; Koyama, H. US Patent 6,013,652, 2000;
Chem. Abstr. 2000, 132, 78470s. (b) Caldwell, C. G.; Finke, P.
E.; MacCoss, M.; Meurer, L. C.; Mills, S. G.; Oates, B. US
Patent 6,136,827, 2000; Chem. Abstr. 2000, 130, 168,242g (for
the equivalent WO Patent 99/04,794).
8. Dorn, C. P.; Finke, P. E.; Oates, B.; Budhu, R. J.; Mills,
S. G.; MacCoss, M.; Malkowitz, L.; Springer, M. S.; Daugh-
erty, 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.
9. 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.
12. Hale, J. J.; Finke, P. E.; MacCoss, M. Bioorg. Med. Chem.
Lett. 1993, 3, 319.
13. For a description of the binding assay, see ref 8, footnote
25. The CCR5 binding titrations were usually done in tripli-
cate with standard errors of <15%. Assay-to-assay varia-
bility was generally ꢂ2-fold or less based on the standard
compound 1b.
14. Condra, J. H.; Schleif, W. A.; Blahy, O. M.; Gabryelski,
L. J.; Graham, D. J.; Quintero, J. C.; Rhodes, A.; Robbins,
H. L.; Roth, E.; Shivaprakash, M.; Titus, D.; Yang, T.; Tep-
pler, H.; Squires, K. E.; Deutsch, P. J.; Emini, E. A. Nature
1995, 374, 569.
10. Finke, P. E.; Meurer, L. C.; Oates, B.; Shah, S. K.; Loe-
bach, J. L.; Mills, S. G.; MacCoss, M.; Castonguay, L.; Mal-
kowitz, L.; Springer, M. S.; Gould, S. L.; DeMartino, J. A.
Bioorg. Med. Chem. Lett 2001, 11, 2469.