Synthesis and Structure-Activity Relationships of Novel Arylpiperazines as Potent and Selective Agonists of the Melanocortin Subtype-4 Receptor

Article abstract of DOI:10.1021/jm0304109

The melanocortin receptors have been implicated as potential targets for a number of important therapeutic indications, including inflammation, sexual dysfunction, and obesity. We identified compound 1, an arylpiperazine attached to the dipeptide H-D-Tic-D-p-Cl-Phe-OH, as a novel melanocortin subtype-4 receptor (MC4R) agonist through iterative directed screening of nonpeptidyl G-protein-coupled receptor biased libraries. Structure-activity relationship (SAR) studies demonstrated that substitutions at the ortho position of the aryl ring improved binding and functional potency. For example, the o-isopropyl-substituted compound 29 (K_i = 720 nM) possessed 9-fold better binding affinity compared to the unsubstituted aryl ring (K_i = 6600 nM). Sulfonamide 39 (K_i = 220 nM) fills this space with a polar substituent, resulting in a further 2-fold improvement in binding affinity. The most potent compounds such as the diethylamine 44 (K_i = 60 nM) contain a basic group at this position. Basic heterocycles such as the imidazole 50 (K_i = 110 nM) were similarly effective. We also demonstrated good oral bioavailability for sulfonamide 39.

Full text of DOI:10.1021/jm0304109

744
J . Med. Chem. 2004, 47, 744-755
Syn th esis a n d Str u ctu r e-Activity Rela tion sh ip s of Novel Ar ylp ip er a zin es a s
P oten t a n d Selective Agon ists of th e Mela n ocor tin Su btyp e-4 Recep tor
Timothy I. Richardson,* Paul L. Ornstein, Karin Briner, Matthew J . Fisher, Ryan T. Backer, C. Kelly Biggers,
Michael P. Clay, Paul J . Emmerson, Larry W. Hertel, Hansen M. Hsiung, Saba Husain, Steven D. Kahl,
J onathan A. Lee, Terry D. Lindstrom, Michael J . Martinelli, J ohn P. Mayer, J effery T. Mullaney,
Thomas P. O’Brien, J oseph M. Pawlak, Kevin D. Revell, J ikesh Shah, J ohn M. Zgombick,† R. J ason Herr,‡
Alex Melekhov,‡ Peter B. Sampson,‡ and Chi-Hsin R. King‡
Lilly Research Laboratories, A Division of Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana 46285, and
Albany Molecular Research, Inc., P.O. Box 15098, Albany, New York 12212
Received August 26, 2003
The melanocortin receptors have been implicated as potential targets for a number of important
therapeutic indications, including inflammation, sexual dysfunction, and obesity. We identified
compound 1, an arylpiperazine attached to the dipeptide H-D-Tic-D-p-Cl-Phe-OH, as a novel
melanocortin subtype-4 receptor (MC4R) agonist through iterative directed screening of
nonpeptidyl G-protein-coupled receptor biased libraries. Structure-activity relationship (SAR)
studies demonstrated that substitutions at the ortho position of the aryl ring improved binding
and functional potency. For example, the o-isopropyl-substituted compound 29 (Ki ) 720 nM)
possessed 9-fold better binding affinity compared to the unsubstituted aryl ring (Ki ) 6600
nM). Sulfonamide 39 (Ki ) 220 nM) fills this space with a polar substituent, resulting in a
further 2-fold improvement in binding affinity. The most potent compounds such as the
diethylamine 44 (Ki ) 60 nM) contain a basic group at this position. Basic heterocycles such
as the imidazole 50 (Ki ) 110 nM) were similarly effective. We also demonstrated good oral
bioavailability for sulfonamide 39.
In tr od u ction
The melanocortin receptors form a family of G-
protein-coupled receptors (GPCRs) that are activated by
the melanocortin peptides: adrenocorticotropin (ACTH)
and R-, â-, and γ-melanocyte-stimulating hormones
(MSH). These peptide hormones are derived from post-
translational processing of a precursor protein, pro-
opiomelanocortin (POMC), which also gives rise to
â-lipotropin and â-endorphin. They have a wide range
of physiological effects on mammalian reproductive,
immune, and central nervous systems.1
F igu r e 1.
Five members of the melanocortin receptor family
have been cloned and characterized.2 MC1R is expressed
in melanocytes and plays a key role in pigmentation and
coat color. MC2R is expressed in the adrenal cortex and
adipose tissues and, in response to ACTH, controls
production of mineralcorticoid and glucocorticoid. MC3R
is expressed in the brain, heart, gut, and placenta. Its
physiological function is not well-defined, but based on
a knock-out model, it is believed to be involved in
nutrient partitioning.3 MC4R is expressed in the hypo-
thalamus and plays a critical role in regulating metabo-
lism, feeding, and reproductive behavior. MC5R is
expressed in the lung, gut, spleen, and skin and is
involved in exocrine gland secretion. The involvement
of the melanocortin receptors in a wide range of mam-
malian physiology has driven several research groups
to identify selective, non-peptide agonists as possible
drug treatments for melanocortin-mediated diseases.4
We identified arylpiperazine 1 through iterative
directed screening of nonpeptidyl GPCR-biased librar-
ies.5 It is a full agonist at the human MC4 receptor
(Ki ) 900 ( 170 nM, EC50 ) 120 ( 1 nM; 98% relative
efficacy, n g 2). A key feature of this compound is the
[(aminosulfonyl)phenyl]piperazine, which was a con-
served element of these libraries. As a result, we had
limited structure-activity relationship (SAR) data in
this area of the lead compound. Efforts to develop the
SAR around the arylpiperazine are described below.
Resu lts
Ch em istr y. The final compounds for biological test-
ing were prepared as described in Scheme 1. The
commercially available amino acids D-p-chlorophenyl-
alanine methyl ester (D-p-Cl-Phe-OMe) and D-N-Boc-
1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Boc-D-
Tic-OH) were coupled using EDC-DMAP to give dipep-
tide 2. The methyl ester was then cleaved with sodium
hydroxide to give Boc-D-Tic-D-p-Cl-Phe-OH (3). The
arylpiperazines 4 were coupled to dipeptide 3 with
* Corresponding author. Phone: 317-433-2372. Fax: 317-276-7600.
E-mail: timrich@lilly.com.
† Deceased.
‡ Albany Molecular Research, Inc.
10.1021/jm0304109 CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/06/2004

Novel Arylpiperazines as Melanocortin Agonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3 745
Sch em e 1. Preparation of Boc-D-Tic-D-p-Cl-Phe-OH and
Sch em e 3. Derivatives of
Coupling to Arylpiperazinesa
N-(2-Cyanophenyl)piperazinea
a
Reagents: (a) EDC, DMAP, CH2Cl2; (b) NaOH, MeOH; (c)
i
HATU, HOAt, Pr2NEt, CH2Cl2; (d) TFA, DMS, CH2Cl2.
Sch em e 2. Pd Coupling of Aryl Bromides to
Piperazinea
a
Reagents: Pd2(dba)3, BINAP, NaOtBu, toluene.
HATU-HOAt followed by TFA deprotection, purifica-
tion, and HCl salt formation to give the final compounds
for assay. The arylpiperazines 4a -d were commercially
available. Those arylpiperazines that were not com-
mercially available were prepared as described in
Schemes 2-5.
Many arylpiperazines were prepared by direct N-
arylation of piperazine with readily available aryl
bromides 5 (Scheme 2). The conditions of Buchwald,6
palladium catalysis with BINAP as the ligand and
sodium tert-butoxide as the base, provided the desired
arylpiperazines 6a -f in excellent yields.
Commercially available N-(2-cyanophenyl)piperazine
(7) proved itself a versatile intermediate (Scheme 3).
After protecting the piperazine of 7 with Boc2O, the
cyano group was reduced with sodium borohydride in
the presence of TFA to give benzylamine 8. Reaction of
8 with methanesulfonyl chloride gave 9, while reductive
amination with formaldehyde gave 10. The cyano group
of 7 was hydrolyzed to the acid followed by protection
of the piperazine with Boc2O in a one-pot procedure to
give benzoic acid 11. Benzoic acid 11 was reduced to
alcohol 12 with borane. Alcohol 12 was reacted with
imidazole under Mitsunobu conditions to give compound
13. Alternatively, alcohol 12 was activated as the
mesylate and reacted with 2-methylimidazole to give
compound 14. Finally, the cyano group of N-(2-cy-
anophenyl)piperazine (7) was easily reduced with DIBAL
followed protection of the piperazine with Boc2O in a
one-pot procedure to give benzaldehyde 15. Benzalde-
hyde 15 was further elaborated via reductive amination
with various secondary amines to give arylpiperazines
16a -d . Lithiated heterocycles such as 2-lithio-1-meth-
ylimidazole (17) were added to benzaldehyde 15 to give
secondary alcohols such as 18. Radical deoxygenation
of 18 provided the C2-linked imidazole 19.
a
Reagents: (a) Boc2O, K2CO3, THF, H2O; (b) NaBH4, TFA,
THF; (c) MsCl, Et3N, CH2Cl2; (d) HCHO, NaCNBH3, CH3CN; (e)
KOH, EtOH; then Boc2O, NaHCO3; (f) BH3‚THF, THF; (g) imi-
dazole, PPh3, DEAD, THF; (h) MsCl, DMAP, Et3N, CH2Cl2; then
2-methylimidazole, THF; (i) DIBAL, dioxane; then Rochelle salt,
H2O; then NaHCO3, Boc2O; (j) R2NH, Ti(OiPr)4; then NaBH4,
EtOH; (k) nBuLi, 1-methylimidzole, THF; then 15, THF; (l) NaH,
CS2, MeI; (m) Bu3SnH, AIBN, toluene, 80 °C.
(Scheme 4). The piperazine was protected with Boc2O
and the aryl nitro group was then reduced via hydro-
genation to give aniline 21. Aniline 21 was reacted with
methanesulfonyl chloride to give sulfonamide 22. Hy-
drogenation of the aryl nitro group of 20 in the presence
of formaldehyde gave dimethylaniline 23.
Finally, several arylpiperazines were prepared from
commercially available N-(2-hydroxyphenyl)piperazine
24 (Scheme 5). The piperazine nitrogen was protected
with Boc2O. The phenol was alkylated with benzyl
bromide to give 25a and with 2-(dimethylamino)ethyl
Several desired arylpiperazines were derived from
commercially available N-(2-nitrophenyl)piperazine (20)

746 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3
Sch em e 4. Derivatives of N-(2-Nitrophenyl)piperazinea
Richardson et al.
Ta ble 1. Initial Functional Group Exploration: Binding
Affinity and Agonist Potency at HMC4a
compd
R
Kib (nM)
EC50c (nM)
R-MSH
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
26.6 ( 3.0
6600 ( 400
1700 ( 360
1300 ( 180
720 ( 63
2.56 ( 0.48
360 ( 160
1300 ( 33
145 ( 1
110 ( 6
490 ( 120
71 ( 4
H
Me
Et
iPr
OH
1900 ( 400
1100 ( 25
570 ( 180
460 ( 110
640 ( 30
OMe
OEt
OiPr
OPh
OBn
NO2
NH2
NMe2
NHSO2Me
CH2OH
(S)-CH(OH)CH3
(R)-CH(OH)CH3
CH2NHSO2Me
CH2NMe2
40 ( 7
93 ( 45
400 ( 50
150 ( 51
210 ( 26
200 ( 32
44 ( 6
640 ( 90
2400 ( 300
1700 ( 200
1100 ( 250
220 ( 35
a
Reagents: (a) Boc2O, Et3N, CH2Cl2; (b) H2, Pd/C, EtOH; (c)
16 ( 3
i
MsCl, Et3N, CH2Cl2; (d) HCHO, Pd/C, PrOH.
630 ( 230
350 ( 88
150 ( 3
34.0 ( 0.8
44 ( 14
48 ( 7
Sch em e 5. Derivatives of
340 ( 30
N-(2-Hydroxyphenyl)piperazinea
210 ( 33
60 ( 8
7.00 ( 0.02
98 ( 24
OCH2CH2NMe2
230 ( 17
a
b
Receptors expressed in HEK293 cells. Ki values (n ) 2 or 4)
( SEM determined by radioligand binding assay using 125I-NDP-
R-MSH. c EC50 values (n ) 2 or 3) ( SEM determined by
concentration of compound at 50% maximum cAMP release.
Ta ble 2. Benzyl Amine SAR: Binding Affinity and Agonist
Potency at HMC4a
a
Reagents: (a) Boc2O, Et3N, CH2Cl2; (b) BnBr, K2CO3, DMF;
(c) ClCH2CH2NMe2, K2CO3, KI, 18-crown-6, DMF; (d) ROH, PPh3,
DEAD, THF.
chloride to give 25b. Alternatively, the phenol was
alkylated under Mitsunobu conditions to give imidazole
25c.
P h a r m a cology. Our initial efforts to optimize the
arylpiperazine portion of lead compound 1 were guided
by several primary assays. Affinities were determined
by competitive inhibition of 125I-NDP-R-MSH binding in
HEK293 cells stably transfected with human MC1,
MC3, MC4, or MC5 receptors. Agonist potencies were
determined by measuring cAMP release in HEK293
cells stably transfected with human MC4 or MC3
receptors. The agonist relative efficacies as determined
by the percentage of cAMP release relative to NDP-R-
MSH were >80% for all compounds. Full concentra-
tion-response curves are provided in Figure 2 for select
compounds. Further details of these assays are given
in the Experimental Section.
Various substitutions in the ortho position of the
arylpiperazine were explored (Table 1). It was observed
that increasing the size of the ortho substituent resulted
in an increase in binding affinity and functional potency.
For example, the isopropyl-substituted compound 29
possesses 9-fold better binding affinity than the unsub-
stituted compound 26. In a similar manner, O-linked
alkyl substitutions such as isopropoxide (33) have better
binding affinity compared to phenol 30. In general,
aromatic groups such as phenyl (34) and benzyl (35)
provided little benefit over the alkyl groups. The nitro
(36), aniline (37), and dimethylaniline (38) compounds
all possess binding affinities similar to the lead (1);
however, sulfonamide 39, the reversed sulfonamide of
1, has 4-fold better binding affinity and 8-fold better
functional potency. Extending the hydroxy functional
group out by one carbon atom to give benzyl alcohol 40
resulted in a 3-fold increase in binding affinity relative
a
b
Receptors expressed in HEK293 cells. Ki values (n ) 2 or 4)
( SEM determined by radioligand binding assay using 125I-NDP-
R-MSH. c EC50 values (n ) 2) ( SEM determined by concentration
of compound at 50% maximum cAMP release.
to phenol 30. The secondary alcohols 41 and 42 have
5-fold better binding affinity compared to 30. Benzyl-
methanesulfonamide 43 is equipotent compared to
sulfonamide 39. However, N,N-dimethylbenzylamine 44
has 18-fold better binding affinity and 6-fold better
functional potency than dimethylaniline 38. N,N-Di-

Novel Arylpiperazines as Melanocortin Agonists
Ta ble 3. Binding Affinity at hMC1, hMC3, hMC4, and hMC5 and Agonist Potency at hMC4 and MC5 for Key Compoundsa
Kib (µM) EC50c (µM)
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3 747
compd
MC1R
MC3R
MC4R
MC5R
MC3R
MC4R
39
44
50
12 ( 3
>20
4.0 ( 0.7
8.8 ( 1.1
7.0 ( 1.7
3.6 ( 0.1
0.220 ( 0.035
0.060 ( 0.008
0.110 ( 0.023
1.2 ( 0.2
1.4 ( 0.6
0.7 ( 0.1
2.0 ( 0.6
1.8 ( 0.7
1.6 ( 0.6
0.016 ( 0.003
0.00700 ( 0.00002
0.014 ( 0.007
a
b
Receptors expressed in HEK293 cells. Ki values (n ) 2 or 4) ( SEM determined by radioligand binding assay using 125I-NDP-R-
MSH. c EC50 values (n ) 2) ( SEM determined by concentration of compound at 50% maximum cAMP release.
methylbenzylamine 44 compares favorably with the
endogenous ligand R-MSH, having only 2-fold less
binding affinity and functional potency. Ethanolamine
45 has 2-fold less binding affinity compared to 44 but
is equipotent to sulfonamide 39.
fied by attaching a large number of dipeptides.5 Iterative
directed screening of these libraries against the MC4
receptor provided our lead compound 1, in which the
arylpiperazine nitrogen is attached to the dipeptide
D-Tic-D-p-Cl-Phe. The same consensus dipeptide for
MC4R has been reported by several other groups.4b,8
In the work described here, modification of the
arylpiperazine portion resulted in further optimization
of the lead series. A wide variety of functional groups
at the position ortho to the piperazine were tolerated
by the MC4 receptor. Binding was clearly improved as
this space was filled; for example, in going from the
unsubstituted compound 26 to the isopropyl-substituted
compound 29, we obtained a ligand with 9-fold better
binding affinity. Sulfonamide 39, which fills this space
with a polar substituent, provides a further 2-fold
improvement in binding affinity. Our most potent
compounds filled this space with basic groups such as
the dialkylamines 44, 46, and 47. We found that we
could also fill this space with basic heterocycles such
as the imidazole 50.
Structure-activity relationships around N,N-dimeth-
ylbenzylamine 44 were also explored (Table 2). Increas-
ing the size of the alkyl groups resulted in a 2-fold
increase in binding affinity: compare the dimethyl-
amine (44) to the diethyl and dipropylamines (46 and
47). The cyclic amines pyrrolidine and piperidine (48
and 49) had affinities similar to the diethyl and dipro-
pylamine (46 and 47). The tertiary amine was also
replaced with basic heterocycles. The binding affinity
of imidazole 50 was 5-fold less than that of 44, but it
maintained good functional potency. The N-linked and
C-linked imidazoles 51 and 52 were similar to 50. When
the imidazole was extended out from the aryl ring by
adding an oxygen linker, the resulting compound 53 was
3-fold less potent with 3-fold lower binding affinity than
52.
Overall the compounds demonstrated good to excel-
lent selectivity for MC4R over the other subtypes (Table
3). Sulfonamide 39 was >30-fold selective for MC4 over
MC1 and MC3 based on affinity. The selectivity over
MC5 was 5-fold. N,N-Dimethylbenzylamine 44 was
5-fold more selective than 39 at these receptors. The
heterocyclic replacement for the benzylamine, imidazole
50, was more similar in selectivity to sulfonamide 39.
Concentration-response curves for these compounds as
well as the lead, arylpiperazine 1, are presented in
Figure 2a,b.
In summary, we have described the synthesis and
structure-activity relationships of a novel series of
arylpiperazines that are potent and selective agonists
at the human MC4 receptor. Our efforts to optimize the
arylpiperazine portion of the lead series successfully
improved the binding affinity and functional potency at
MC4. We have also demonstrated good oral bioavail-
ability for sulfonamide 39. Further improvement of this
lead series and its potential use as a mediator of
melanocortin physiology will be reported in due course.
Sulfonamide 39 was chosen for bioavailability studies.
It was dosed at 5 mg/kg iv (n ) 3) and 30 mg/kg po (n
) 3) in Fischer 344 rats in 10% acacia via gavage. Its
oral bioavailability in rats was 30% with a volume of
distribution of 4.5 ( 0.3 L/kg, while its clearance was
43 ( 1 mL/min/kg with a Tmax of 3 ( 2 h and a T1/2 of
1.7 ( 0.2 h.
Exp er im en ta l Section
Gen er a l. All reagents and solvents were used without
further purification or drying. All reagents were purchased
from Sigma-Aldrich, unless otherwise specified. Amino acids
were purchased from Bachem, Novabiochem, or Midwest
BioTech. Commercial grade anhydrous solvents were pur-
chased from EMD chemicals or Mallinckrodt. All reactions
were performed under an atmosphere of nitrogen, unless
otherwise specified. Thin-layer chromatography (TLC) was
conducted on precoated silica gel plates (Analtech or EM
Science) and visualized with either short-wave UV light, 10%
phosphomolybdic acid, or ceric ammonium molybdate. Flash
column chromatography was carried out using prepacked silica
gel columns from Biotage or Isco. Ion exchange chromatogra-
phy was carried out using SCX BondElut columns from Varian.
1H NMR spectra were collected on Varian 400 MHz or Bruker
300 MHz instruments and are recorded in parts per million
(ppm) δ values, relative to CHCl3 (δ 7.27), CHD2OD (δ 3.30),
or DMSO (δ 2.53) as the internal standard. Mass spectra were
obtained on a Micromass QTOF-II, a Finnigen LCQ Duo Ion
Trap or a PESciex API 150EX mass spectrometer, using
electrospray ionization (ES) or atmospheric pressure chemical
ionization (APCI). Abbreviations: Boc, tert-butoxycarbonyl;
Boc2O, di-tert-butyl dicarbonate; BINAP, 2,2′-bis(diphenylphos-
phino)-1,1′-binaphthyl; DMAP, 4-(dimethylamino)pyridine;
DMS, dimethyl sulfide; EDC, 1-(3-(dimethylamino)propyl)-3-
Discu ssion
One successful strategy for the development of non-
peptidyl ligands for GPCR targets is the “privileged
structure” approach.7 Historically this approach has
been largely empirical but it is now apparent that ligand
binding chemical space is conserved across a range of
evolutionarily related GPCRs. As a result, modification
of a common scaffold that has proved itself successful
at one receptor provides ligands that are selective for
another. This approach appears to be most fruitful using
conformationally rigid scaffolds such as benzodiaz-
epines, biaryls, and spiropiperidines. In this example,
we generated a series of libraries that were biased
toward GPCR targets using the arylpiperazine as a
conserved “privileged structure” scaffold that was modi-

748 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3
Richardson et al.
F igu r e 2. (a) Comparison of novel arylpiperazine compounds 1, 39, 44, and 50 in MC1, MC3, MC4, and MC5 receptor binding
profiles. The compounds shown have between 5- and >300-fold higher affinity for the MC4 receptor. Error bars indicate SEM for
n ) 2 or 4 independent determinations. (b) Agonist potencies for compounds 1, 39, 44, and 50 were determined by measuring
cAMP released from cells stably transfected with the MC3 or MC4 receptor. The compounds shown exhibit higher relative efficacies
and agonist potencies for the MC4 receptor compared to the MC3 receptor. Percent maximum stimulation is relative to the cAMP
release in the presence of NDP-RMSH. Error bars indicate SEM for n ) 2 independent determinations.
ethylcarbodiimide hydrochloride; HOAt, 1-hydroxy-7-azaben-
zotriazole; HATU, O-(7-azobenzotriazol-1-yl)-1,1,3,3-tetrame-
thyluronium hexafluorophosphate; HEK, human embryonic
kidney; Pd2(dba)3, tris(dibenzylideneacetone)dipalladium(0);
TFA, trifluoroacetic acid; Tic, 1,2,3,4-tetrahydroisoquinoline-
3-carboxylic acid.
dissolved in water (200 mL). Ethyl acetate (200 mL) was added
followed by addition of a saturated sodium bicarbonate solu-
tion. The mixture was stirred for about 5 min, and then the
organic layer was separated, washed with water (200 mL), and
dried over magnesium sulfate. Concentration of the mixture
under reduced pressure produced a white solid (32.2 g). To
the solid was added methylene chloride (200 mL), D-Boc-Tic-
OH (35.8 g, 129 mmol), and 4-(dimethylamino)pyridine (75
Boc-D-Tic-D-p-Cl-P h e-OH (3). Step 1. The HCl salt of H-D-
p-Cl-Phe-OMe (Midwest Biotech, 35.8 g, 129 mmol) was

Novel Arylpiperazines as Melanocortin Agonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3 749
mg). The mixture was cooled to 0 °C and EDC (24.7 g, 129
mmol) was added in two portions. After stirring for about 20
min, the ice bath was removed and the solution was allowed
to warm to room temperature. The solution was stirred for
about 4 h and then diluted with water (400 mL). The organic
layer was washed with water (3×), dried over magnesium
sulfate, and concentrated under reduced pressure to give a
clear oil (70 g). Silica gel column chromatography (35% ethyl
acetate/heptane) afforded about 55.6 g (85%) of the intermedi-
ate Boc-D-Tic-p-Cl-D-Phe-OMe (2). 1H NMR (DMSO) (two
rotomers observed): δ 8.26 (d, 1H), 8.19 (d, 0.5 H), 7.24 (d,
2H), 7.00-7.19 (m, 8H), 4.68 (m, 0.5H), 4.20-4.60 (m, 4.5H),
3.58 (s, 3H), 3.51 (s, 1.5H), 2.77-3.10 (m, 6H), 1.42 (s, 3H),
1.21 (s, 9H). LRMS (ES): 473.0 (M + 1), 471.1 (M - 1).
Step 2. The compound of step 1 (54.3 g, 114 mmol) was
dissolved in methanol (170 mL). The solution was cooled to 0
°C with an ice bath and 1 N NaOH (290 mL) was added
dropwise. After vigorous stirring for about 20 min, the mixture
was warmed to about 25 °C. The solution was concentrated
under reduced pressure to give a yellow oil. The oil was
dissolved in water (200 mL) and the pH was adjusted to about
1. Ethyl acetate (200 mL) was added, and the organic layer
was separated and dried over magnesium sulfate. The organic
solution was filtered and concentrated to produce about 46.3
g of the title compound. 1H NMR (DMSO) (two rotomers
observed): δ 7.98 (d, 1H), 7.82 (d, 0.5 H), 6.90-7.41 (m, 16H),
4.20-4.70 (m, 8.5H), 2.60-3.20 (m, 8.5H), 1.32-1.41 (m, 19H).
LRMS (ES): 459.1 (M + 1), 457.1 (M - 1).
N-(2-Eth ylp h en yl)p ip er a zin e (6a ). 2-Ethylbromobenzene
(390 mg, 2.11 mmol), piperazine (280 mg, 3.25 mmol), Pd2-
(dba)3 (58 mg, 0.063 mmol), BINAP (60 mg, 0.096 mmol),
sodium t-butoxide (285 mg, 2.97 mmol), and anhydrous toluene
(4 mL) were combined in a 15 mL round-bottomed flask. The
flask was evacuated and flushed with nitrogen (3×). The
mixture was lowered into an oil bath and heated to 100 °C.
After heating for about 2 h, the mixture was cooled, diluted
with ethyl acetate (100 mL), filtered through Celite, and
concentrated to a crude oil (432 mg). Purification by silica gel
flash chromatography using a 99:1 to 85:15 gradient of
dichloromethane:0.5 M ammonia/methanol gave the final
product (225 mg, 1.18 mmol, 56%) as an oil. 1H NMR (400
MHz, CDCl3): δ 7.21 (dd, J ) 1.5, 7.3 Hz, 1H), 7.15 (dd, J )
1.8, 8.2 Hz, 1H), 7.21 (m, 2H), 2.98-3.02 (m, 4H), 2.82-2.86
(m, 4H), 2.69 (q, J ) 7.6, 2H), 1.23 (t, J ) 7.6, 3H). LRMS
(ES+): 191.2 (M + 1).
N-(2-Isop r op ylp h en yl)p ip er a zin e (6b). The title com-
pound was prepared from piperazine and 1-bromo-2-isoprop-
ylbenzene in a manner similar to that described for 6a . 1H
NMR (400 MHz, CDCl3): δ 7.27 (d, 1H, J ) 8.6), 7.19-7.08
(m, 3H), 3.53 (septet, 1H, J ) 7.0), 3.00-3.05 (m, 4H), 2.80-
2.87 (m, 4H), 1.84 (bs, 1H), 1.22 (d, 6H, J ) 7.0). LRMS
(ES+): 205.4 (M + 1).
yldimethylsilyl chloride (165 mg, 1.1 mmol), and imidazole (203
mg, 3.0 mmol) flushed with nitrogen was added 5 mL of
dimethylformamide. After stirring overnight, the mixture was
quenched with saturated sodium bicarbonate; diluted with
ethyl acetate; washed with NaH2PO4, saturated aqueous
sodium bicarbonate, water, and brine; dried (Na2SO4); filtered;
and concentrated. Purification by flash chromatography (10 g
of SiO2, linear gradient from 0 to 10% ethyl acetate/hexanes,
30 mL/min, over 30 min) gave 260 mg (0.82 mmol, 82%) of
(S)-[1-(2-bromophenyl)ethoxy]-tert-butyldimethylsilane as a
colorless oil. GC/MS (EI): 315 (M). The title compound was
prepared from piperazine and (S)-[1-(2-bromophenyl)ethoxy]-
tert-butyldimethylsilane in a manner similar the that de-
scribed for 6a .
1H NMR (400 MHz, CDCl3): δ 7.65 (dd, 1H, J
) 1.5 Hz), 7.31 (dt, 1H, J ) 1.5, 7.3 Hz), 7.26-7.20 (m, 2H),
5.51 (q, 1H, J ) 6.3 Hz), 3.17-3.08 (m, 4H), 2.96-2.90 (m,
4H), 2.20 (bs, 1H), 1.51 (d, 3H, J ) 6.3 Hz), 0.97 (s, 9H), 0.12
(s, 3H), 0.00 (s, 3H). LRMS (ES+): 321.5 (M + 1).
(R)-N-{2-[1-(ter t-Bu tyld im eth ylsila n yloxy)eth yl]p h en -
yl}p ip er a zin e (6f). The title compound was prepared from
(R)-(-)-2-bromo-R-methylbenzyl alcohol in a manner similar
1
to that described for 6e. H NMR (400 MHz, CDCl3): δ 7.65
(dd, 1H, J ) 1.5 Hz), 7.32 (dt, 1H, J ) 1.5, 7.3 Hz), 7.26-7.20
(m, 2H), 5.51 (q, 1H, J ) 6.3 Hz), 3.16-3.07 (m, 4H), 2.95-
2.89 (m, 4H), 2.09 (bs, 1H), 1.51 (d, 3H, J ) 5.9 Hz), 0.97 (s,
9H), 0.11 (s, 3H), 0.00 (s, 3H). LRMS (ES+): 321.5 (M + 1).
1-Boc-4-(2-(a m in om eth yl)p h en yl)p ip er a zin e (8). To a
solution of N-(2-cyanophenyl)piperazine 7 (2.4 g, 12.78 mmol)
in THF and H2O (25 mL, 1:1) was added K2CO3 (3.9 g, 28.12
mmol). The solution was allowed to stir for about 10 min at
room temperature. Boc2O (3.1 g, 14.06 mmol) was then added
and the reaction was allowed to stir for 1 h. The reaction
mixture was diluted with EtOAc (100 mL) and washed with
saturated NaHCO3 (100 mL) and brine (100 mL). The organic
phase was concentrated to give 3.2 g of 1-Boc-4-(2-cyanophen-
yl)piperazine (88%). To a solution of sodium borohydride (2.1
g, 56.03 mmol) in THF (25 mL) at 0 °C was added TFA (4.3
mL, 56.03 mmol) dropwise. 1-Boc-4-(2-cyanophenyl)piperazine
(3.2 g, 11.21 mmol) was then added slowly at room tempera-
ture. The reaction was allowed to stir for about 12 h at room
temperature. The reaction was quenched with H2O, diluted
5-fold with EtOAc, and washed with brine. The organic phase
was concentrated to give 1.0 g (30%) of the title compound. 1H
NMR (400 MHz, CDCl3): δ 7.34 (dd, 1H, J ) 7.5, 1.6 Hz), 7.25
(dt, 1H, J ) 7.6, 1.6 Hz), 7.14-7.08 (m, 2H), 3.94 (s, 2H), 3.60-
3.54 (m, 4H), 2.89-2.84 (m, 4H), 2.44 (bs, 2H), 1.48 (s, 9H).
LRMS (ES+) 292.1 (M + 1).
1-Boc-4-[2-((m eth ylsu lfon yl)a m in o)m eth yl)p h en yl]p ip -
er a zin e (9). 1-Boc-4-(2-(aminomethyl)phenyl)piperazine 8
(2.09 g, 7.18 mmol) was dissolved in methylene chloride (50
mL), cooled to 0 °C, and treated with triethylamine (1.5 mL,
10.8 mmol) followed by methanesulfonyl chloride (0.67 mL,
8.61 mmol). The resulting mixture was stirred for about 3 h
at room temperature; diluted with ether (200 mL); washed
with water (50 mL), saturated aqueous sodium bicarbonate
(50 mL), and brine (50 mL); and then dried over anhydrous
magnesium sulfate. Concentration under reduced pressure
followed by silica gel chromatography (30% ethyl acetate in
hexanes) afforded the title compound (2.07 g, 78%) as a clear
N-(2-Isop r op oxyp h en yl)p ip er a zin e (6c). The title com-
pound was prepared from piperazine and 1-bromo-2-isopro-
1
poxybenzene in a manner similar to that described for 6a . H
NMR (400 MHz, CDCl3): δ 6.96-6.84 (m, 4H), 4.60 (septet,
1H, J ) 5.9 Hz), 3.05 (m, 8H), 2.01 (bs, 1H), 1.35 (d, 6H, J )
5.9 Hz). LRMS (ES+): 221.4 (M + 1).
N-(2-P h en oxyph en yl)piper azin e (6d). A mixture of phen-
ylboronic acid (5.12 g, 42 mmol), 2-bromophenol (3.55 g, 21
mmol), Cu(OAc)2 (7.63 g, 42 mmol), pyridine (8 mL, 103 mmol),
and 4 Å molecular sieves (2.1 g) in CH2Cl2 was stirred at room
temperature overnight. The mixture was diluted with CH2-
Cl2, filtered through Celite, washed with 1 M NaOH and brine,
and dried. Removal of solvent gave 1-bromo-2-phenoxybenzene
as crystals (1.40 g, 27%). LRMS (ES): 248 (M + 1). The title
compound was prepared from piperazine and 1-bromo-2-
phenoxybenzene in a manner similar to that described for 6a .
1H NMR (400 MHz, CDCl3): δ 7.31-7.24 (m, 3H), 7.14-7.08
(m, 1H), 7.06-6.98 (m, 2H), 6.97-6.90 (m, 3H), 3.07-3.01 (m,
4H), 2.86-2.80 (m, 4H). LRMS (ES+): 255.1 (M + 1).
1
oil. H NMR (300 MHz, CDCl3): δ 7.25-7.40 (m, 2H), 7.00-
7.15 (m, 2H), 4.40 (s, 1H), 3.55-3.65 (m, 4H), 2.80-2.95 (m,
4H), 2.75 (s, 3H), 1.60 (s, 9H). LRMS (APCI): 370 (M + H).
1-Boc-4-[2-((d im e t h yla m in o)m e t h yl)p h e n yl]p ip e r a -
zin e (10). 1-Boc-4-((2-aminomethyl)phenyl)piperazine 8 (2.0
g, 6.86 mmol) was dissolved in CH3CN (15 mL) and cooled to
about 0 °C. Aqueous formaldehyde (7.56 mL of a 37 wt %
aqueous solution) was added to the cold solution followed by
the addition of sodium cyanoborohydride (2.15 g, 34.32 mmol).
The reaction mixture was allowed to stir at 0 °C for about 5
min and then allowed to warm to room temperature. The
mixture was then concentrated to dryness. The resulting
residue was taken up in EtOAc (100 mL) and washed with
saturated NaHCO3 solution (100 mL) and brine (100 mL). The
organic phase was concentrated to dryness to afford about 2.2
(S)-N-{2-[1-((ter t-Bu tyldim eth ylsilan yl)oxy)eth yl]ph en -
yl}p ip er a zin e (6e). To a 25 mL flask containing (S)-(-)-2-
bromo-R-methylbenzyl alcohol (200 mg, 1.0 mmol), tert-but-

750 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3
Richardson et al.
1
g of the title compound. 1H NMR (300 MHz, CDCl3): δ 7.55
(d, J ) 7.3 Hz, 1H), 7.20-7.25 (m, 1H), 7.00-7.10 (m, 2H),
3.65 (s, 2H), 3.55 (t, J ) 4.4 Hz, 4H), 2.90 (t, J ) 4.6 Hz, 4H),
2.25 (s, 6H), 1.50 (s, 9H). LRMS (ES+): 320.2 (M + 1).
mmol, 54%). H NMR (400 MHz, CDCl3): δ 7.30 (dt, 1H, J )
1.4, 8.0 Hz), 7.17 (dd, 1H, J ) 8.0, 0.9 Hz), 7.08 (dt, 1H, J )
1.2, 7.6 Hz), 6.95 (d, 1H, J ) 1.4 Hz), 6.82 (d, 1H, J ) 1.4 Hz),
6.79 (d, 1H, J ) 7.6), 5.13 (s, 2H), 3.57 (m, 4H), 2.81 (m, 4H),
2.33 (s, 3H), 1.51 (s, 9H). LRMS (ES+): 357.2 (M + H).
1-Boc-4-(2-ca r boxyp h en yl)p ip er a zin e (11). To a solution
of N-(2-cyanophenyl)piperazine 7 (37.45 g, 200 mmol) in 500
mL of absolute ethanol was added 1000 mL of 25% aqueous
KOH. The solution was heated to reflux for about 72 h and
then cooled to about 0 °C. The solution was acidified with 890
mL of 5 M HCl, and then solid NaHCO3 was added to bring
the pH of the solution to about 8. NaHCO3 (12.7 g, 120 mmol)
and Boc2O (11.4 g, 52.2 mmol) were added, and the mixture
was stirred overnight, which was then acidified with 5 M HCl
to about pH 1. After addition of EtOAc and brine, the aqueous
solution was separated and extracted with EtOAc (2×). The
combined organic solutions were washed with water (2×) and
brine, dried (Na2SO4), filtered, and concentrated. The material
was purified by recrystallization from EtOAc/hexanes to afford
2-(N-Boc-p ip er a zin -1-yl)ben za ld eh yd e (15). To a solu-
tion of N-(2-cyanophenyl)piperazine 7 (375 mg, 2.0 mmol) in
15 mL of dioxane was added DIBAL-H (6 mL of a 1 M solution
in heptane, 6 mmol). After stirring at room temperature for
about 48 h, the solution was transferred via cannula into 20
mL of 0.5 M Rochelle salt. After stirring for about 2 h, NaHCO3
(636 mg, 6 mmol) and Boc2O (567 mg, 2.6 mmol) were added.
After stirring overnight, EtOAc and brine were added. After
separation, the aqueous solution was extracted with EtOAc
(3×). The combined organic layers were washed with water
and brine, dried (Na2SO4), filtered, and concentrated. Purifica-
tion by flash chromatography (35 g of SiO2, linear gradient
from 10 to 20% EtOAc/hexane over 30 min at 35 mL/min)
afforded about 436 mg (1.50 mmol, 75%) of the title compound
1
about 49.8 g (162 mmol, 81%) of the title compound. H NMR
1
as a yellow oil. H NMR (400 MHz, CDCl3): δ 10.34 (s, 1H),
(400 MHz, CDCl3): δ 16.5 (bs, 1H), 8.30 (dd, 1H, J ) 7.8, 1.7
Hz), 7.60 (dt, 1H, J ) 7.6, 1.6 Hz), 7.45-7.37 (m, 2H), 4.40-
4.80 (m, 4H), 3.06-2.98 (m, 4H), 1.49 (s, 9H). LRMS (ES-):
305.2 (M - 1).
7.82 (dd, 1H, J ) 7.7, 1.6 Hz), 7.54 (dt, 1H, J ) 7.7, 1.7 Hz),
7.18-7.08 (m, 2H), 3.65-3.60 (m, 4H), 3.06-3.01 (m, 4H), 1.48
(s, 9H). LRMS (ES+): 291.1 (M + 1).
1-Boc-4-(2-(p yr r olid in -1-ylm et h yl)p h en yl)p ip er a zin e
(16c). To a solution of 2-(N-Boc-piperazin-1-yl)benzaldehyde
15 (400 mg, 1.4 mmol) in pyrrolidine (0.33 mL, 4 mmol) was
added titanium isopropoxide (1.2 mL, 4 mmol), and the
mixture was stirred at room temperature under a nitrogen
atmosphere. After about 30 min, the mixture was diluted with
ethanol (4 mL). Sodium borohydride (106 mg, 2.8 mmol) was
added and the mixture was stirred for about 16 h. Water (2
mL) was added, and the resulting suspension was filtered. The
filter cake was washed with methanol (5 mL), and the filtrate
was concentrated to dryness. Purification by flash chromatog-
raphy (1:1 hexanes/ethyl acetate) gave the title compound (470
mg, 96%) as a colorless oil. 1H NMR (300 MHz, CDCl3): δ
7.40-7.44 (m, 1H), 7.19-7.26 (m, 1H), 7.01-7.08 (m, 2H), 3.68
(s, 2H), 3.55 (t, J ) 4.5 Hz, 4H), 2.92-2.95 (m, 4H), 2.53 (m,
4H), 1.75 (m, 4H), 1.49 (s, 9H). LRMS (APCI): 346 (M + H).
1-Boc-4-(2-(h yd r oxym eth yl)p h en yl)p ip er a zin e (12). To
a solution of 1-Boc-4-(2-carboxyphenyl)piperazine 11 (37.5 g,
123 mmol) in 1000 mL of THF at 0 °C was added BH3-THF
(369 mL of a 1 M solution in THF, 369 mmol). The cold bath
was removed and the solution stirred overnight. Another 50
mL of BH3-THF was added. After stirring for 9 h, the solution
was cooled to about 0 °C and then 220 mL of 2 M NaOH was
added followed by EtOAc and brine. After separation, the
aqueous solution was extracted with EtOAc (2×). The com-
bined organic solutions were washed with water (2×) and
brine, dried (Na2SO4), filtered, and concentrated to give about
1
35.2 g (120 mmol, 98%) of the title compound. H NMR (400
MHz, CDCl3): δ 7.30-7.20 (m, 2H), 7.17-7.10 (m, 2H), 4.83
(s, 1H), 4.79 (s, 2H), 3.61-3.56 (m, 4H), 2.93-2.89 (m, 4H),
1.48 (s, 9H). LRMS (ES+): 293.2 (M + 1).
1-Boc-4-(2-(im idazol-1-ylm eth yl)ph en yl)piper azin e (13).
To a solution of 1-Boc-4-(2-(hydroxymethyl)phenyl)piperazine
12 (300 mg, 1.02 mmol, 1.0 equiv), imidazole (104 mg, 1.53
mmol, 1.5 equiv), triphenylphosphine (535 mg, 2.04 mmol, 2.0
equiv), and THF at 0 °C under nitrogen was added DEAD
(0.321 mL, 2.04 mmol, 2.0 equiv) slowly so that the temper-
ature of reaction did not rise above 10 °C. After addition was
completed, the ice bath was removed and the reaction mixture
was stirred at room temperature overnight. Methanol was
added and the mixture was stirred for about 15 min. The
mixture was then concentrated. Purification by flash chroma-
tography (35 g of SiO2, linear gradient from 50 to 70% EtOAc/
hexane for 15 min and 70% EtOAc for 18 min) afforded the
title compound (109 mg, 0.32 mmol, 31%). 1H NMR (400 MHz,
CDCl3): δ 7.62 (s, 1H), 7.34 (dt, 1H, J ) 7.6, 1.5 Hz), 7.19 (dd,
1H, J ) 8.1, 1.0 Hz), 7.13 (dt, 1H, J ) 7.5, 1.1 Hz), 7.08 (s,
1H), 7.03 (dd, 1H, J ) 7.6, 1.3 Hz), 6.92 (s, 1H), 5.23 (s, 2H),
3.59-3.51 (m, 4H), 2.82-2.69 (m, 4H), 1.48 (s, 9H). LRMS
(ES+): 343.2 (M + 1).
1-Boc-4-[2-((2-m eth ylim id a zol-1-yl)m eth yl)p h en yl]p ip -
er a zin e (14). To a solution of 1-Boc-4-(2-(hydroxymethyl)-
phenyl)piperazine 12 (300 mg, 1.03 mmol, 1.0 equiv), trieth-
ylamine (0.17 mL, 1.2 mmol, 1.2 equiv), and DMAP (6 mg, 0.05
mmol, 0.05 equiv) in CH2Cl2 (10 mL) was added methane-
sulfonyl chloride (0.085 mL, 1.1 mmol, 1.1 equiv). The solution
was stirred at room temperature under N2 for about 2 h. A
solution of 2-methylimidazole (410 mg, 5.0 mmol, 5.0 equiv)
in THF (3 mL) was added, and the mixture was allowed to
stir at room temperature overnight. The mixture was diluted
with EtOAc (50 mL) and washed with saturated aqueous
NaHCO3 (15 mL) and brine (15 mL). The combined organic
extracts were dried (Na2SO4), filtered, and concentrated.
Purification by flash chromatography (35 g of SiO2, 40 mL/
min, linear gradient from 0 to 10% 0.2 M NH3 in MeOH/CH2-
Cl2 for 25 min and 10% 2.0M NH3 in MeOH/CH2Cl2 for 7 min)
afforded the title compound as a white solid (192 mg, 0.54
1-Boc-4-(2-((d iet h yla m in o)m et h yl)p h en yl)p ip er a zin e
(16a ). The title compound was prepared from 2-(N-Boc-
piperazin-1-yl)benzaldehyde 15 and diethylamine in a manner
1
similar to that described for 16c. H NMR (300 MHz, CDCl3):
δ 7.54 (d, J ) 7.3 Hz, 1H), 7.19-7.26 (m, 1H), 7.03-7.11 (m,
2H), 3.63 (s, 2H), 3.56 (t, J ) 4.4 Hz, 4H), 2.88 (t, J ) 4.6 Hz,
4H), 2.54 (q, J ) 7.2 Hz, 4H), 1.49 (s, 9H), 1.03 (t, J ) 7.2 Hz,
6H). LRMS (APCI): 348 (M + H).
1-Boc-4-(2-((d ip r op yla m in o)m e t h yl)p h e n yl)p ip e r a -
zin e (16b). The title compound was prepared from 2-(N-Boc-
piperazin-1-yl)benzaldehyde 15 and dipropylamine in a man-
ner similar to that described for 16c. 1H NMR (300 MHz,
CDCl3): δ 7.54-7.57 (m, 1H), 7.01-7.26 (m, 3H), 3.58 (s, 2H),
3.49-3.53 (m, 4H), 2.85-2.90 (m, 4H), 2.38 (t, J ) 7.3 Hz, 4H),
1.40-1.50 (m, 13H), 0.84 (t, J ) 7.3 Hz, 6H). LRMS (APCI):
376 (M + H).
1-Boc-4-(2-(p ip er id in -1-ylm et h yl)p h en yl)p ip er a zin e
(16d ). The title compound was prepared from 2-(N-Boc-
piperazin-1-yl)benzaldehyde 15 and piperidine in a manner
1
similar to that described for 16c. H NMR (300 MHz, CDCl3):
δ 7.38 (d, J ) 7.6 Hz, 1H), 7.20-7.26 (m, 1H), 7.03-7.08 (m,
2H), 3.54-3.57 (m, 4H), 3.50 (s, 2H), 2.92-2.95 (m, 4H), 2.40
(m, 4H), 1.23-1.59 (m, 15H). LRMS (APCI): 360 (M + H).
1-Boc-4-{2-[h ydr oxy(1-m eth yl-1H-im idazol-2-yl)m eth yl]-
p h en yl}p ip er a zin e (18). To a solution of 1-methylimidazole
°
(350 µL, 4.4 mmol) in 15 mL of THF at -78 C was added
nBuLi (1.5 mL of a 1.6 M solution in hexane, 2.4 mmol). After
stirring for about 30 min, the solution was warmed to about 0
°C and then stirred for about 15 min. The mixture was then
cooled to about -78 °C. A solution of 2-(N-Boc-piperazin-1-
yl)benzaldehyde 15 (580 mg, 1.0 mmol) in 5 mL of THF was
added via cannula. The solution was allowed to warm slowly
to room temperature overnight. After addition of saturated
aqueous NH4Cl and brine, the solution was extracted with
EtOAc (2×). The combined organic solutions were dried (Na2-

Novel Arylpiperazines as Melanocortin Agonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3 751
SO4), filtered, and concentrated. Purification by silica gel
chromatography (35 g of SiO2, linear gradient from 0 to 10%
0.2 M NH3 in MeOH/CH2Cl2 over 30 min at 35 mL/min)
afforded about 592 mg (1.59 mmol, 79%) of the title compound.
1H NMR (400 MHz, CDCl3): δ 7.29 (dt, 1H, J ) 7.7, 1.5 Hz),
7.21 (dd, 1H, J ) 8.0, 0.9 Hz), 7.11 (dt, 1H, J ) 7.4, 1.1 Hz),
7.02 (dd, 1H, J ) 7.7, 1.4 Hz), 6.92 (d, 1H, J ) 1.1 Hz), 6.82
(d, 1H, J ) 1.2 Hz), 6.20 (s, 1H), 3.65-3.40 (m, 2H), 3.49 (s,
3H), 3.13-3.02 (m, 2H), 2.87-2.76 (m, 2H), 1.47 (s, 9H). LRMS
(ES+): 373.2 (M + 1).
1-Boc-4-[2-((1-m eth yl-1H-im id a zol-2-yl)m eth yl)p h en yl]-
p ip er a zin e (19). To a solution of 1-Boc-4-{2-[hydroxy(1-
methyl-1H-imidazol-2-yl)methyl]phenyl}piperazine 18 (93 mg,
0.25 mmol) in 5 mL of THF was added NaH (30 mg, 0.75
mmol). After stirring for about 45 min, CS2 (75 µL, 1.25 mmol)
was added. After stirring for about 30 min, 5 mL of THF was
added, followed by MeI (78 µL, 1.25 mmol). After stirring for
about 1 h, saturated aqueous NH4Cl and brine were added.
The solution was extracted EtOAc (2×). The combined organic
solutions were dried (Na2SO4), filtered, and concentrated.
Purification by silica gel chromatography (35 g of SiO2, linear
gradient from 0 to 5% MeOH/CH2Cl2 over 30 min at 35 mL/
min) afforded about 97 mg (0.21 mmol, 84%) of the xanthate
as a yellow oil. LRMS (ES+): 463.2 (M + 1).
dried (Na2SO4), filtered through a pad of Celite, and concen-
trated. Purification by flash chromatography (35 g of SiO2, 40
mL/min, linear gradient from 0 to 15% EtOAc/hexane for 20
min and 15% EtOAc/hexane for 13 min) gave 480 mg (1.57
mmol, 97%) of the title compound as a solid. 1H NMR (400
MHz, CDCl3): δ 7.07-6.80 (m, 4H), 3.57 (s, 4H), 3.06 (s, 4H),
2.83 (s, 6H), 1.48 (s, 9H). LRMS (ES+): 306.2 (M + H).
1-Boc-4-(2-h yd r oxyp h en yl)p ip er a zin e. To a solution of
N-(2-hydroxyphenyl)piperazine 24 (2.8 g, 15.7 mmol) and
NaHCO3 (2.3 g, 21.9 mmol) in 50 mL of THF, 50 mL of dioxane,
and 50 mL of water was added di-tert-butyl dicarbonate (4.1
g, 18.8 mmol). After stirring overnight, the solution was
neutralized with 1 M HCl and extracted with CH2Cl2 (2 × 100
mL). The combined organic solutions were dried (Na2SO4),
filtered, and concentrated to give 4.0 g (14.4 mmol, 92%) of
1
the title compound. H NMR (400 MHz, CDCl3): δ 7.17-7.08
(m, 2H), 6.98 (d, 1H, J ) 8.0 Hz), 6.88 (t, 1H, J ) 7.6 Hz),
3.66-3.59 (m, 4H), 2.93-2.82 (m, 4H), 1.49 (s, 9H). LRMS
(ES+): 279.2 (M + 1).
1-Boc-4-(2-(ben zyloxy)p h en yl)p ip er a zin e (25a ). To a
solution of 1-Boc-4-(2-hydroxyphenyl)piperazine (500 mg, 1.79
mmol) in 15 mL of DMF was added K2CO3 (592 mg, 4.29
mmol). After stirring for 5 min benzyl bromide (260 µL, 2.16
mmol) was added. After stirring overnight at 60 °C, the
solution was cooled to room temperature, diluted with EtOAc;
washed with water twice, saturated sodium bicarbonate, and
brine; dried (Na2SO4); filtered; and concentrated. Purification
by silica gel chromatography (35 g of SiO2, 40 mL/min, from
10 to 30% EtOAc/hexanes, over 20 min and 30% EtOAc/
hexanes for 13 min) afforded 344 mg (0.93 mmol, 54%) of the
To a solution of the xanthate (90 mg, 0.195 mmol) and Bu3-
SnH (260 µL, 0.967 mmol) in 2 mL of toluene at 80°C was
added AIBN (50 µL of a 0.4 M solution in toluene, 0.02 mmol).
Another 50 µL of the AIBN solution was added every 2-3 h
for 8 h. After stirring overnight, another 50 µL of the AIBN
solution was added. After stirring for about 8 h more, the
solution was concentrated and filtered through Celite with
CH2Cl2. Purification by silica gel chromatography (35 g of SiO2,
linear gradient from 0 to 5% 0.2 M NH3 in MeOH/CH2Cl2 over
30 min at 35 mL/min) afforded about 46 mg (0.13 mmol, 66%)
1
title compound. H NMR (400 MHz, CDCl3): δ 7.47-7.43 (m,
2H), 7.41-7.36 (m, 2H), 7.35-7.29 (m, 1H), 7.03-6.91 (m, 4H),
5.13 (s, 2H), 3.60-3.53 (m, 4H), 3.09-3.01 (m, 4H), 1.5 (s, 9H).
LRMS (ES+): 269.1 (M + H).
1
of the title compound. H NMR (400 MHz, CDCl3): δ 7.21 (m,
1-Boc-4-[2-((1-m eth yl-1H-im id a zol-2-yl)m eth oxy)p h en -
yl]p ip er a zin e (25c). To a solution of 1-Boc-4-(2-hydroxyphen-
yl)piperazine (556 mg, 2.0 mmol, 1.0 equiv), (1-methyl-1H-
imidazol-2-yl)-methanol (448 mg, 4.0 mmol, 2.0 equiv), tri-
phenylphosphine (1.04 g, 4.0 mmol, 2.0 equiv), and THF at 0
°C under nitrogen was added DEAD (0.629 mL, 4.0 mmol, 2.0
equiv) slowly so that the temperature of the reaction did not
rise above 10 °C. After addition was complete, the ice bath
was removed and the reaction mixture was stirred at room
temperature overnight. After this time, methanol was added
and the reaction was stirred for 15 min. The reaction mixture
was then concentrated. Purification by flash chromatography
(35 g of SiO2, 40 mL/min, linear gradient from 0 to 8% 2.0 M
NH3 in MeOH/CH2Cl2 for 25 min and 8% 2.0 M NH3 in MeOH
for 7 min) afforded the title compound (279 mg, 0.75 mmol,
37%). 1H NMR (400 MHz, CDCl3): δ 7.06 (td, 1H, J ) 10.8,
3.9 Hz), 7.00 (d, 1H, J ) 1.2 Hz), 6.98 (d, 1H, J ) 1.6 Hz),
6.87 (d, 1H, J ) 1.0 Hz), 6.81-6.71 (m, 2H), 4.35 (d, 2H, J )
5.4 Hz), 4.0-3.2 (s, br, 4H), 3.67 (s, 3H), 2.90-2.77 (s, br, 4H),
1.48 (s, 9H). LRMS (ES+): 373.3 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-p h en ylp ip er a zin e (26). Step 1. To
a solution of N-Boc-D-Tic-4-Cl-D-Phe-OH 3 (156 mg, 0.34 mmol,
1.1 equiv), phenylpiperazine 4a (50 mg, 0.31 mmol, 1.0 equiv),
HOAt (710 µL of a 0.5 M solution in DMF, 0.36 mmol, 1.15
equiv), diisopropylethylamine (160 µL, 0.92 mmol, 3.0 equiv),
and CH2Cl2 (4 mL) was added HATU (135 mg, 0.36 mmol, 1.15
equiv). After stirring at room temperature overnight, the
solution was diluted with ethyl acetate; washed with 1 M HCl,
water, saturated sodium bicarbonate, and brine; dried over
Na2SO4; filtered; and concentrated. Purification by flash
chromatography (10 g of SiO2, linear gradient from 0 to 100%
EtOAc/CH2Cl2, 35 mL/min, over 30 min) gave about 152 mg
(0.25 mmol, 81%) of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-phenylpip-
erazine. LRMS (ES+): 603.2 (M + H).
1H), 7.08 (d, 1H, J ) 7.6 Hz), 7.03-7.01 (m, 2H), 6.95 (d, 1H,
J ) 1.2 Hz), 6.79 (d, 1H, J ) 1.2 Hz), 4.17 (s, 2H), 3.52-3.50
(m, 4H), 3.36 (s, 3H), 2.56-2.58 (m, 4H), 1.48 (s, 9H). LRMS
(ES+): 357.2 (M + 1).
1-Boc-4-(2-a m in op h en yl)p ip er a zin e (21). To a solution
of N-(2-nitrophenyl)piperazine 20 (30 g, 145 mmol) and tri-
ethylamine (28.3 mL, 203 mmol) in 600 mL of CH2Cl2 was
added di-tert-butyl dicarbonate (38 g, 174 mmol). After stirring
overnight, the solution was washed with saturated aqueous
sodium bicarbonate and brine, dried (Na2SO4), filtered, and
concentrated to afford 1-Boc-4-(2-nitrophenyl)piperazine as an
orange oil. To a solution of the oil in 2 L of ethanol was added
6 g of 5% Pd/C. After shaking under an atmosphere of 60 psi
hydrogen overnight, the solution was filtered and concentrated
to afford about 39 g (140 mmol, 97%) of the title compound.
1H NMR (400 MHz, CDCl3): δ 7.00-6.94 (m, 2H), 6.78-6.72
(m, 2H), 4.21 (s, 2H), 3.60 (s, 4H), 2.90 (s, 4H), 1.49 (s, 9H).
LRMS: 278.1 (M + 1).
1-Boc-4-(2-((m e t h ylsu lfon yl)a m in o)p h e n yl)p ip e r a -
zin e (22). To a solution of 1-Boc-4-(2-aminophenyl)piperazine
21 (5.55 g, 20 mmol) and triethyamine (5.6 mL, 40 mmol) in
200 mL of CH2Cl2 was added methanesulfonyl chloride (1.55
mL, 20 mmol). After stirring for 4 h, the solution was
concentrated and the residue dissolved in 200 mL of EtOAc.
The solution was washed twice with 1 M HCl, water, and
brine; dried (Na2SO4); filtered; and concentrated to afford 6.68
g (18.8 mmol, 94%) of the title compound. 1H NMR (400 MHz,
CDCl3): δ 7.51 (dd, 1H, J ) 8.3, 1.5 Hz), 7.21-7.15 (m, 2H),
7.09 (dt, 1H, J ) 1.4, 7.2 Hz), 3.63-3.53 (m, 4H), 3.08 (s, 3H),
2.85-2.75 (m, 4H), 1.49 (s, 9H). LRMS (ES+): 356.1 (M + H).
1-Boc-4-(2-(d im eth yla m in o)p h en yl)p ip er a zin e (23). To
a solution of 1-Boc-4-(2-nitrophenyl)piperazine (500 mg, 1.63
mmol, 1.0 equiv), prepared as described above for 1-Boc-4-(2-
aminophenyl)piperazine 21, in IPA (20 mL) was added form-
aldehyde (3.3 mL of a 37% solution in H2O, 4.07 mmol, 2.5
equiv) and 10% Pd/C (125 mg). The reaction mixture was
shaken under an atmosphere of hydrogen at 60 psi overnight.
The mixture was filtered and diluted with CH2Cl2. The
aqueous solution was separated and the organic solution was
St ep 2. To a solution of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-
phenylpiperazine (53 mg, 0.078 mmol) in CH2Cl2 (2 mL) and
DMS (0.2 mL) was added TFA (2 mL). After stirring for about
2 h, the solution was azeotroped with heptane (2×). The
residue was loaded onto an SCX ion exchange column with
MeOH and flushed with MeOH. The product was eluted with

752 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3
Richardson et al.
2 M NH3 in MeOH and concentrated. Purification by flash
chromatography (10 g of SiO2, linear gradient from 0 to 10%
methanol/CH2Cl2, 30 mL/min, over 30 min) afforded a white
solid. The solid is dissolved in CH2Cl2 and precipitated with 1
M HCl in Et2O. The solution was concentrated to afford 68
mg (0.126 mmol, 55%) of the HCl salt of the title compound.
1H NMR (400 MHz, CD3OD): δ 8.96 (d, 1H, J ) 7.0 Hz), 7.50-
7.44 (m, 2H), 7.39-7.23 (m, 11H), 5.20 (dd, 1H, J ) 15.2, 7.3
Hz), 4.43 (s, 2H), 4.23 (dd, 1H, J ) 11.9, 4.8 Hz), 3.96-3.86
(m, 3H), 3.73 (m, 1H), 3.50-3.42 (m, 3H), 3.30 (m, 1H), 3.19-
3.06 (m, 3H), 2.92 (m, 1H). LRMS (ES+): 503.2 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-(2-m eth ylph en yl)piper azin e (27).
The title compound was prepared from N-Boc-D-Tic-4-Cl-D-Phe-
OH 3 and N-(2-methylphenyl)piperazine 4b in a manner
Tic-4-Cl-D-Phe-OH 3 and N-(2-isopropoxyphenyl)piperazine 6c
in a manner similar to that described for 26. 1H NMR (400
MHz, MeOD): δ 7.51-7.47 (m, 2H), 7.38-7.24 (m, 9H), 7.12
(dt, 1H, J ) 1.2, 7.8 Hz), 5.20 (m, 1H), 4.42 (s, 2H), 4.24 (dd,
1H, J ) 4.7, 11.7 Hz), 4.16-4.03 (m, 3H), 3.82 (m, 1H), 3.79-
3.60 (m, 3H), 3.49 (m, 1H), 3.47 (dd, 1H, J ) 5.0, 16.8 Hz),
3.19-3.03 (m, 4H), 1.43 (d, 6H, J ) 6.2 Hz). LRMS (ES+):
561.2 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-p h en oxyp h en yl)p ip er a zin e
(34). The title compound was prepared from N-Boc-D-Tic-4-
Cl-D-Phe-OH 3 and N-(2-phenoxyphenyl)piperazine 6d in a
1
manner similar to that described for 26. H NMR (400 MHz,
MeOD): δ 9.00 (d, 1H, J ) 6.4 Hz), 7.60 (d, 1H, J ) 7.8 Hz),
7.50-7.22 (m, 14H), 7.20-7.14 (m, 2H), 6.93 (d, 1H, J ) 4.8
Hz), 5.19 (m, 1H), 4.42 (s, 2H), 4.23 (dd, 1H, J ) 11.1, 3.9 Hz),
4.05-3.88 (m, 3H), 3.82-3.63 (m, 3H), 3.54 (m, 1H), 3.43 (dd
1H, J ) 4.5, 17.5 Hz), 3.22-3.05 (m, 4H). LRMS (ES+): 595.2
(M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-(b en zyloxy)p h en yl)p ip er a -
zin e (35). Step 1. To a solution of 4-Boc-1-(2-benzyloxyphe-
nyl)piperazine 25a and dimethyl sulfide (0.25 mL) in 6 mL of
CH2Cl2 was added 3 mL of TFA. After stirring for 30 min the
solution was concentrated to give an oil. The oil was loaded
onto a 10-g SCX ion exchange column with MeOH. The column
was flushed with 20 mL of MeOH then and 20 mL of 2 M NH3
in MeOH. The fractions containing desired product were
combined and concentrated to give 230 mg of 1-(2-(benzyloxy)-
phenyl)piperazine as an oil. LRMS (ES+): 269.1 (M+H).
Step 2. To a solution of N-Boc-D-Tic-4-Cl-D-Phe-OH 3 (307
mg, 0.67 mmol, 1.0 equiv), 1-(2-(benzyloxy)phenyl)piperazine
(180 mg, 0.67 mmol, 1.0 equiv), diisopropylethylamine (300
µL, 1.67 mmol, 2.5 equiv), and CH2Cl2 (7 mL) was added HATU
(254 mg, 0.67 mmol, 1.0 equiv). After stirring at room tem-
perature overnight, the solution was diluted with ethyl acetate;
washed with 1 M HCl, water, saturated sodium bicarbonate,
and brine; dried over Na2SO4; filtered; and concentrated.
Purification by flash chromatography (35 g of SiO2, linear
gradient from 30 to 80% EtOAc/hexanes for 20 min and then
80% EtOAc/hexanes for 13 min, 35 mL/min) gave about 327
mg (0.46 mmol, 69%) of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-
(benzyloxy)phenyl)piperazine. LRMS (ES+): 709.1 (M + H).
1
similar to that described for 26. H NMR (400 MHz, CD3OD):
δ 8.97 (d, 1H, J ) 6.6 Hz), 7.38-7.20 (m, 12H), 5.20 (m, 1H),
4.43 (s, 2H), 4.23 (dd, 1H, J ) 4.3, 11.7 Hz), 4.00-3.70 (m,
4H), 4.00-3.70 (m, 4H), 3.46 (dd, 1H, J ) 3.9, 16.8 Hz), 3.30-
3.05 (m, 6H), 2.70 (m, 1H), 2.44 (s, 3H). LRMS (ES+): 517.2
(M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-eth ylp h en yl)p ip er a zin e (28).
The title compound was prepared from N-Boc-D-Tic-4-Cl-D-Phe-
OH 3 and N-(2-ethylphenyl)piperazine 6a in a manner similar
to that described for 26. 1H NMR (400 MHz, CD3OD): δ 7.37-
7.19 (m, 9H), 7.13 (dt, 1H, J ) 1.8, 7.9 Hz), 7.04 (dt, 1H, J )
1.2, 7.3 Hz), 6.95 (d, 1H, J ) 7.9 Hz), 5.20 (t, 1H, J ) 7.9 Hz),
4.32 (s, 2H), 4.15 (m, 1H), 3.80 (m, 1H), 3.63-3.49 (m, 3H),
3.35 (m, 1H), 3.15-3.00 (m, 3H), 2.82-2.55 (m, 5H), 2.25 (m,
1H), 1.20 (t, 3H, J ) 7.7 Hz). LRMS (ES+): 531.3 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-isop r op ylp h en yl)p ip er a zin e
(29). The title compound was prepared from N-Boc-D-Tic-4-
Cl-D-Phe-OH 3 and N-(2-isopropylphenyl)piperazine 6b in a
1
manner similar to that described for 26. H NMR (400 MHz,
MeOD): δ 8.95 (d, 1H, J ) 5.7 Hz), 7.6-7.19 (m, 12H), 5.2
(m, 1H), 4.42 (s, 2H), 4.24 (dd, 1H, J ) 4.7, 12.1 Hz), 4.00-
3.60 (m, 3H), 3.68-3.51 (m, 3H), 3.20-2.80 (m, 7H), 1.25 (d,
3H, J ) 6.6 Hz), 1.24 (d, 3H, J ) 6.6 Hz). LRMS (ES+): 545.2
(M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-h ydr oxyph en yl)piper azin e (30).
The title compound was prepared from N-Boc-D-Tic-4-Cl-D-Phe-
OH 3 and N-(2-hydroxyphenyl)piperazine 24 in a manner
1
similar to that described for 26. H NMR (400 MHz, MeOD):
Step 3. To a solution of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-
(benzyloxy)phenyl)piperazine (315 mg, 0.44 mmol) in CH2Cl2
(5 mL) and DMS (0.25 mL) was added TFA (3 mL). After
stirring for about 1 h, the solution was azeotroped from
heptane (2×). The residue was loaded onto an SCX ion
exchange column with MeOH and flushed with MeOH. The
product was eluted with 2 M NH3 in MeOH and concentrated.
Purification by flash chromatography (35 g SiO2, step gradient
from 0 to 11% 2 M NH3 in methanol/CH2Cl2, 40 mL/min, over
36 min) afforded a white solid. The solid was dissolved in CH2-
Cl2 and precipitated with 1 M HCl in Et2O. The solution was
concentrated to afford 253 mg (0.39 mmol, 89%) of the HCl
salt of the title compound. 1H NMR (400 MHz, MeOD): δ 9.00
(d, 1H, J ) 6.6 Hz), 7.54-7.49 (m, 2H), 7.46-7.22 (m, 14H),
7.13 (t, 1H, J ) 7.7 Hz), 5.30 (s, 2H), 5.16 (m, 1H), 4.42 (s,
2H), 4.22 (dd, 1H, J ) 11.9, 4.6 Hz), 4.12-3.33 (m, 6H), 3.38
(m, 1H), 3.44 (dd, 1H, J ) 16.9, 4.8 Hz), 3.24-2.91 (m, 4H).
LRMS (ES+): 609.2 (M + 1).
δ 7.43-7.23 (m, 10H), 7.06-7.01 (m, 2H), 5.19 (t, 1H, J ) 7.8
Hz), 4.42 (s, 2H), 4.24 (dd, 1H, J ) 6.8, 4.9 Hz), 4.06-3.94 (m,
3H), 3.79 (bs, 1H), 3.70-3.60 (m, 2H), 3.50-3.42 (m, 3H),
3.19-3.06 (m, 3H). LRMS (ES+): 519.5 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-m et h oxyp h en yl)p ip er a zin e
(31). The title compound was prepared from N-Boc-D-Tic-4-
Cl-D-Phe-OH 3 and N-(2-methoxyphenyl)piperazine 4c in a
1
manner similar to that described for 26. H NMR (400 MHz,
CD3OD): δ 9.01 (d, 1H, J ) 7.0 Hz), 7.46-7.23 (m, 11H), 7.12
(t, 1H, J ) 7.4 Hz), 5.19 (m, 1H), 4.43 (s, 2H), 4.23 (dd, 1H, J
) 4.7, 11.7 Hz), 3.99 (s, 3H), 4.02-3.88 (m, 3H), 3.76 (m, 1H),
3.60-3.50 (m, 2H), 3.45 (dd, 1H, J ) 4.7, 18.4 Hz), 3.35 (m,
1H), 3.20-3.08 (m, 3H), 2.96 (m, 1H). LRMS (ES+): 533.2 (M
+ 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-eth oxyp h en yl)p ip er a zin e (32).
1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-ethoxyphenyl)piperazine was
prepared from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and N-(2-ethoxy-
phenyl)piperazine 4d in a manner similar to that described
in step 1 for 26. To a solution of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-
4-(2-ethoxyphenyl)piperazine (180 mg, 028 mmol) and dim-
ethyl sulfide (0.5 mL) in 2 mL of CH2Cl2 was added 2 mL of
TFA. After stirring for 1 h the solution was concentrated. The
residue was dissolved in methylene chloride and precipitated
with ether to obtain 170 mg (0.26 mmol) of the TFA salt of
the title compound. 1H NMR (400 MHz, DMSO): δ 9.0 (d, 1H,
J ) 2.8 Hz), 7.36-7.25 (m, 4H), 7.24-7.19 (m, 4H), 6.92-6.77
(m, 4H), 5.20 (m, 1H), 4.39-4.22 (m, 2H), 4.14 (m, 1H), 4.01
(d, 1H, J ) 6.6 Hz), 3.98 (d, 1H, J ) 6.6 Hz), 3.64-3.42 (m,
4H), 3.04-2.74 (m, 7H), 2.64 (m, 1H), 1.32 (t, 3H, J ) 7.0 Hz).
LRMS (ES+): 547.1 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-n itr op h en yl)p ip er a zin e (36).
The title compound was prepared from N-Boc-D-Tic-4-Cl-D-Phe-
OH 3 and N-(2-nitrophenyl)piperazine 20 in a manner similar
1
to that described for 26. H NMR (400 MHz, MeOD): δ 7.76
(dd, 1H, J ) 1.2, 7.8 Hz), 7.57 (dt, 1H, J ) 1.6, 7.4 Hz), 7.37-
7.17 (m, 10H), 5.19 (t, 1H, J ) 7.8 Hz), 4.41 (s, 2H), 4.19 (dd,
1H, J ) 4.7, 11.7 Hz), 3.82 (m, 1H), 3.60-3.40 (m, 4H), 3.18-
2.90 (m, 5H), 2.81 (m, 1H), 2.42 (m, 1H). LRMS (ES+): 548.2
(M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-a m in op h en yl)p ip er a zin e (37).
1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-nitrophenyl)piperazine was pre-
pared from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and N-(2-nitrophen-
yl)piperazine 20 in a manner similar to that described in step
1 for 26. A solution of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-nitro-
phenyl)piperazine (260 mg, 0.4 mmol) and PtO2 (70 mg) in 30
1-(D-Tic-4-Cl-D-P h e )-4-(2-isop r op oxyp h e n yl)p ip e r a -
zin e (33). The title compound was prepared from N-Boc-D-

Novel Arylpiperazines as Melanocortin Agonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3 753
mL of 2-propanol was shaken in a Parr hydrogenation ap-
paratus under 45 psi of H2 for about 1 h. The solution was
filtered through Celite and concentrated to yield about 263
mg (0.4 mmol, 100%) of 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-ami-
nophenyl)piperazine, which was used without further purifica-
tion. 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-aminophenyl)piperazine
was deprotected with TFA in a manner similar to that
described in step 2 for 26. 1H NMR (400 MHz, MeOD): δ 7.41-
7.29 (m, 12H), 5.2 (dd, 1H, J ) 4.7, 3.1 Hz), 4.43 (s, 2H), 4.24
(dd, 1H, J ) 7.0, 4.7 Hz), 3.94 (m, 1H), 3.71-3.40 (m, 4H),
3.20-3.03 (m, 3H), 2.90-2.70 (m, 2H), 2.65 (m, 1H), 2.19 (m
1H). LRMS (ES+): 518.3 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-(d im eth yla m in o)p h en yl)p ip -
er a zin e (38). The title compound was prepared from N-Boc-
D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-(dimethylamino)phenyl)-
piperazine 23 in a manner similar to that described for 35.
1H NMR (400 MHz, MeOD): δ 7.85 (d, 1H, J ) 8.1 Hz), 7.66-
7.50 (m, 3H), 7.48-7.23 (m, 8H), 5.21 (m, 1H), 4.50 (m, 1H),
4.44 (s, 2H), 4.24 (dd, 1H, J ) 12.0, 4.6 Hz), 3.94 (m, 1H), 3.62
(m, 1H), 3.43 (m, 1H), 3.29 (s, 6H) 3.22-3.00 (m, 4H), 2.92-
2.81 (m, 2H), 2.70 (m, 1H), 2.50 (m, 1H). LRMS (ES+): 546.2
(M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-((m eth ylsu lfon yl)a m in o)p h en -
yl)p ip er a zin e (39). The title compound was prepared from
N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-((methylsulfonyl)-
amino)phenyl)piperazine 22 in a manner similar to that
described for 35. 1H NMR (400 MHz, MeOD): δ 8.91 (d, 1H, J
) 7.3 Hz), 7.49-7.14 (m, 11H), 5.21 (m, 1H), 4.42 (s, 2H), 4.22
(dd, 1H, J ) 11.7, 4.7 Hz), 3.90 (m, 1H), 3.60-3.58 (m, 3H),
3.45 (dd, 1H, J ) 4.7, 17.2 Hz), 3.20-3.08 (m, 4H), 3.08 (s,
3H), 2.95-2.80 (m, 2H), 2.74 (m, 1H), 2.34 (m, 1H). LRMS
(ES+): 596.2 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-(h yd r oxym eth yl)p h en yl)p ip -
er a zin e (40). The title compound was prepared from N-Boc-
D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-(hydroxymethyl)phenyl)-
piperazine 12 in a manner similar to that described for 35.
1H NMR (400 MHz, CD3OD): δ 9.02 (d, 1H, J ) 6.8 Hz), 7.50-
7.22 (m, 12H), 5.20 (m, 1H), 5.00 (s, 2H), 4.43 (s, 2H), 4.24
(dd, 1H, J ) 11.7, 4.9 Hz), 4.03-3.70 (m, 4H), 3.55-3.41 (m,
3H), 3.29 (m, 1H), 3.21-3.05 (m, 3H), 2.89 (m, 1H). LRMS
(ES+): 533.2 (M + 1).
δ 7.47 (d, 1H, J ) 7.4 Hz), 7.34-7.30 (m, 2H), 7.27-7.01 (m,
9H), 5.33 (q, 1H, J ) 6.3 Hz), 5.16 (t, 1H, J ) 7.0 Hz), 3.97 (s,
2H), 3.80 (m, 1H), 3.62-3.35 (m, 4H), 3.08-2.95 (m, 4H), 2.85-
2.80 (m, 2H), 2.78-2.65 (m 2H), 2.16 (m, 1H), 1.41 (d, 3H, J )
6.3 Hz). LRMS (ES+): 547.3 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-[2-(((m eth ylsu lfon yl)a m in o)m e-
th yl)p h en yl]p ip er a zin e (43). 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-
[2-(((methylsulfonyl)amino)methyl)phenyl]piperazine was pre-
pared from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-[2-
(((methylsulfonyl)amino)methyl)phenyl]piperazine 9 in
a
manner similar to that described in steps 1 and 2 for 35. The
TFA salt of the title compound was prepared from 1-(N-Boc-
D-Tic-4-Cl-D-Phe)-4-[2-(((methylsulfonyl)amino)methyl)phenyl]-
piperazine in a manner similar to that described for 32. 1H
NMR (300 MHz, DMSO): δ 9.30-9.60 (m, 2H), 9.00-9.10 (m,
1H), 7.20-7.60 (m, 11H), 6.85-7.10 (m, 2H), 4.80-5.10 (m,
1H), 4.10-4.50 (m, 5H), 2.35-3.85 (m, 9H), 2.50 (s, 3H). LRMS
(APCI): 610 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-(2-((dim eth ylam in o)m eth yl)ph en -
yl)p ip er a zin e (44). The title compound was prepared from
N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-((dimethylamino)-
methyl)phenyl)piperazine 10 in a manner similar to that
1
described for 35. H NMR (400 MHz, CD3OD): δ 8.90 (d, 1H,
J ) 7.0 Hz), 7.52-7.47 (m, 2H), 7.39-7.22 (m, 10H), 5.21 (m,
1H), 4.44 (s, 2H), 4.43 (d, 1H, J ) 13.2 Hz), 4.38 (d, 1H, J )
13.2 Hz), 4.24 (dd, 1H, J ) 4.8, 12.3 Hz), 3.79-3.56 (m, 3H),
3.46 (dd, 1H, J ) 4.8, 17.1 Hz), 3.26-3.04 (m, 4H), 2.92-2.76
(m, 3H), 2.88 (s, 3H), 2.87 (s, 3H), 2.64 (m, 1H). LRMS (ES+):
560.2 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-{2-[2-(d im et h yla m in o)et h oxy]-
p h en yl}p ip er a zin e (45). To a solution of 1-Boc-4-(2-hydroxy-
phenyl)piperazine (300 mg, 1.08 mmol), 2-(dimethylamino)-
ethyl chloride hydrochloride (233 mg, 1.62 mmol), K2CO3 (450
mg, 3.26 mmol), and KI (357 mg, 2.15 mmol) in DMF (10 mL)
was added 18-crown-6 (1.42 g, 5.37 mmol). After stirring
overnight, water was added and the solution extracted with
CH2Cl2 (3×). The combined organic extracts were concentrated
to an oil. The oil was loaded onto a 10 g SCX ion exchange
column equilibrated with MeOH. The column was flushed with
20 mL of MeOH, 20 mL of 0.2 M NH3 in MeOH, and 20 mL of
2 M NH3 in MeOH. The fractions containing desired product
were combined and concentrated to an oil. To a solution of the
oil in MeOH (2 mL) was added 1 M HCl (6 mL) in Et2O. After
stirring overnight, the solution was concentrated to an oil
to obtain N-{2-[2-(dimethylamino)ethoxy]phenyl}piperazine.
LRMS: 250.2 (M + 1). The title compound was prepared from
N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and N-{2-[2-(dimethylamino)-
ethoxy]phenyl}piperazine in a manner similar to that de-
scribed for 26. NMR (400 MHz, CD3OD): δ 8.99 (d, 1H, J )
6.8 Hz), 7.40-7.12 (m, 12H), 5.20 (m, 1H), 4.52-4.46 (m, 2H),
4.43 (s, 2H), 4.24 (dd, 1H, J ) 12.0, 4.9 Hz), 4.14-3.74 (m,
4H), 3.72-3.66 (m, 2H), 3.55-3.20 (m, 3H), 3.45 (dd, 1H, J )
16.9, 4.9 Hz), 3.19-3.05 (m, 4H), 3.00 (s, 6H). LRMS (ES+):
590.3 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-((dieth ylam in o)m eth yl)ph en yl)-
p ip er a zin e (46). 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-((diethyl-
amino)methyl)phenyl)piperazine was prepared from N-Boc-D-
Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-((diethylamino)methyl)-
phenyl)piperazine 16a in a manner similar to that described
in steps 1 and 2 for 35. The TFA salt of the title compound
was prepared from 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-((diethyl-
amino)methyl)phenyl)piperazine in a manner similar to that
described for 32. 1H NMR (300 MHz, CD3OD): δ 7.47-7.53
(m, 2H), 7.21-7.39 (m, 10H), 5.20 (t, J ) 7.4 Hz, 1H), 4.42 (s,
2H), 4.39 (s, 2H), 4.20-4.25 (m, 1H), 3.40-3.80 (m, 5H), 3.05-
3.25 (m, 8H), 2.60-2.90 (m, 3H), 1.34 (t, J ) 7.2 Hz, 6H).
LRMS (APCI): 588 (M + H).
(S)-1-(D-Tic-4-Cl-D-P h e)-4-[2-(1-h yd r oxyeth yl)p h en yl]-
p ip er a zin e (41). (S)-1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-{2-[1-((tert-
butyldimethylsilanyl)oxy)ethyl]phenyl}piperazine was pre-
pared from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and (S)-N-{2-[1-((tert-
butyldimethylsilanyl)oxy)ethyl]phenyl}piperazine 6e in
a
manner similar to that described in step 1 for 26. To a solution
of (S)-1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-{2-[1-((tert-butyldimeth-
ylsilanyl)oxy)ethyl]phenyl}piperazine (100 mg, 0.13 mmol) in
2 mL of CH2Cl2 was added 1 drop of water and 1 mL of TFA.
After stirring for 3 h, heptane was added and the solution
concentrated to an oil. To a solution of the oil in a polyprop-
ylene tube in 2 mL of THF cooled to 0 °C was added 1 mL of
HF-pyridine. The solution was allowed to warm slowly to
room temperature with stirring overnight. The solution was
diluted with CH2Cl2, washed twice with saturated aqueous
sodium bicarbonate and brine, dried (Na2SO4), filtered, and
concentrated. Purification by flash chromatography (10 g of
SiO2, linear gradient from 0 to 10% methanol/CH2Cl2, 30 mL/
min, over 30 min) afforded a white solid. The solid was
dissolved in CH2Cl2 and precipitated with 1 M HCl in Et2O.
The solution was concentrated to afford 63 mg (0.11 mmol,
82%) of the HCl salt of the title compound. 1H NMR (400 MHz,
CD3OD): δ 7.47 (dd, 1H, J ) 1.6, 7.8 Hz), 7.34-7.32 (m, 2H),
7.27-7.00 (m, 9H), 5.32 (q, 1H, J ) 6.6 Hz), 5.17 (dd, 1H, J )
6.6, 8.2 Hz), 3.97 (s, 2H), 3.80 (m, 1H), 3.45-3.35 (m, 4H),
3.08-3.94 (m, 3H), 2.88 (m, 1H), 2.81 (dd, 1H, J ) 10.2, 16.0
Hz), 2.65 (m, 1H), 2.52 (m, 1H), 2.28 (m, 1H), 1.41 (d, 3H, J )
6.6 Hz). LRMS (ES+): 547.3 (M + 1).
1-(D-Tic-4-Cl-D-P h e)-4-(2-((dipr opylam in o)m eth yl)ph en -
yl)p ip er a zin e (47). 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-((dipropyl-
amino)methyl)phenyl)piperazine was prepared from N-Boc-D-
Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-((dipropylamino)methyl)-
phenyl)piperazine 16b in a manner similar to that described
in steps 1 and 2 for 35. The TFA salt of the title compound
was prepared from 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-((dipropyl-
(R)-1-(D-Tic-4-Cl-D-P h e)-4-[2-(1-h yd r oxyeth yl)p h en yl]-
p ip er a zin e (42). The title compound was prepared from
N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and (R)-N-{2-[1-((tert-butyldi-
methylsilanyl)oxy)ethyl]phenyl}piperazine 6f in a manner
1
similar to that described for 41. H NMR (400 MHz, CD3OD):

754 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3
Richardson et al.
amino)methyl)phenyl)piperazine in a manner similar to that
described for 32. 1H NMR (300 MHz, CD3OD): δ 7.47-7.53
(m, 2H), 7.21-7.39 (m, 10H), 5.20 (t, J ) 7.5 Hz, 1H), 4.42 (s,
4H), 4.20-4.25 (m, 1H), 3.40-3.70 (m, 5H), 2.98-3.18 (m, 8H),
2.70-2.85 (m, 3H), 1.69-1.86 (m, 4H), 0.96 (t, J ) 7.3 Hz, 6H).
LRMS (APCI): 616 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-(2-(pyr r olidin -1-ylm eth yl)ph en yl)-
p ip er a zin e (48). 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-(pyrrolidin-
1-ylmethyl)phenyl)piperazine was prepared from N-Boc-D-Tic-
to identify competitive inhibitors of 125I-NDP-R-MSH binding
using membranes prepared from human embryonic kidney
(HEK) 293 cells stably transfected with cloned human mel-
anocortinin receptors. Cells are grown as adherent monolayers
in roller bottle cultures at 37 °C and 5% CO2/air atmosphere
in a 3:1 mixture of Dulbecco’s modified Eagle medium (DMEM)
and Ham’s F12 containing 25 mM L-glucose, 100 units/mL
penicillin G, 100 µg/mL streptomyocin, 250 ng/mL amphoterin
B, and 300 µg/mL genticin and supplemented with 5% fetal
bovine serum. For large-scale production, monolayer cells are
adapted to suspension culture (Berg et al. Biotechniques 1993,
14, no. 6) and are grown in either spinner or shaker flasks
(37 °C and 7.5% CO2/air overlay) in a modified DME/F12
medium containing 0.1 mM CaCl2, 2% equine serum, and 100
µg/mL sodium heparin to prevent cell-cell aggregation. Cells
are harvested by centrifugation and washed in PBS, and
pellets are stored frozen at -80 °C until required for prepara-
tion of membranes.
For the preparation of membranes, frozen cell pellets are
resuspended in 10 volumes of membrane prep buffer (10 mL
buffer/g of cell paste) consisting of 50 mM Tris pH 7.5 at 4°C,
250 mM sucrose, 1 mM MgCl2, Complete EDTA-free protease
inhibitor tablet (Roche Applied Science, Indianapolis, IN), and
24 µg/mL DNase I (Sigma, St. Louis, MO). The cells are
homogenized with a motor-driven Teflon-glass dounce ho-
mogenizer using 20 strokes, followed by centrifugation at
38000g at 4 °C for 40 min. The pellets are resuspended in
membrane prep buffer at a concentration of 2.5-7.5 mg/mL,
aliquoted, quick frozen in liquid nitrogen, and stored at -80
°C.
Standard competitive receptor/ligand binding experiments
consisted of testing serial dilutions of test compound (30 µM
to 300 pM) or unlabeled NDP-R-MSH (100 nM to 1 pM) in
binding buffer (25 mM HEPES pH 7.5; 10 mM CaCl2; 0.3%
BSA) containing 0.5-5.0 µg membrane protein, 100 pM 125I-
NDP-R-MSH (Amersham Biosciences, Piscataway, NJ ), and
0.25 mg of wheat germ agglutinin SPA beads. The resulting
mixture is agitated briefly on a plate shaker and incubated
for 10 h at room temperature. The radioactivity bound to the
receptor is quantified in a PE Life Sciences Trilux microplate
scintillation counter. Nonlinear regression analysis of competi-
tion binding data using a four-parameter logistic fit yields IC50
values which are converted to affinity constants (Ki values)
using the Cheng-Prusoff equation, Ki ) IC50/(1 + D/Kd), where
D is the concentration of radioligand and Kd is the equilibrium
dissociation constant determined from saturation binding
anlaysis.
F u n ction a l Assa y. Functional activity was determined
using a standard cAMP assay testing serial dilutions of test
compound (10 µM to 0.1 nM) or the control agonist NDP-R-
MSH (100 nM to 1 pM). HEK 293 cells stably transfected with
the human MC3 or MC4 receptor were grown in DMEM
containing 10% FBS and 1% antibiotic/antimycotic solution.
On the day of the assay, the cells were dislodged with enzyme-
free cell dissociation solution and resuspended in cell buffer
(Hank’s balanced salt solution without phenol red HBSS-092,
0.1% BSA, 10 mM HEPES) at 1 × 106 cells/mL. Cell suspen-
sion (40 µL) was added to PET 96-well plates containing 20
µL of diluted compound or control agonist. Plates were
incubated at 37 °C for 20 min, and the assay was stopped by
the addition of 50 µL of quench buffer (50 mM sodium acetate,
0.25% Triton X-100).
4-Cl-D-Phe-OH
3
and 1-Boc-4-(2-(pyrrolidin-1-ylmethyl)-
phenyl)piperazine 16c in a manner similar to that described
in steps 1 and 2 for 35. The TFA salt of the title compound
was prepared from 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-(pyrrolidin-
1-ylmethyl)phenyl)piperazine in a manner similar to that
described for 32. 1H NMR (300 MHz, CD3OD): δ 7.45-7.50
(m, 2H), 7.19-7.39 (m, 10H), 5.20 (t, J ) 7.2 Hz, 1H), 4.42 (s,
4H), 4.19-4.25 (m, 1H), 3.65-3.78 (m, 1H), 3.40-3.96 (m, 6H),
3.02-3.24 (m, 5H), 2.60-2.85 (m, 3H), 2.00-2.17 (m, 5H).
LRMS (APCI): 586 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-(2-(piper idin -1-ylm eth yl)ph en yl)-
p ip er a zin e (49). 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-(piperidin-
1-ylmethyl)phenyl)piperazine was prepared from N-Boc-D-Tic-
4-Cl-D-Phe-OH
3
and 1-Boc-4-(2-(piperidin-1-ylmethyl)-
phenyl)piperazine 16d in a manner similar to that described
in steps 1 and 2 for 35. The TFA salt of the title compound
was prepared from 1-(N-Boc-D-Tic-4-Cl-D-Phe)-4-(2-(piperidin-
1-ylmethyl)phenyl)piperazine in a manner similar to that
described for 32. 1H NMR (300 MHz, CD3OD): δ 7.47-7.52
(m, 2H), 7.21-7.39 (m, 10H), 5.21 (t, J ) 7.1 Hz, 1H), 4.42 (s,
2H), 4.37 (s, 2H), 4.19-4.25 (m, 1H), 3.41-3.87 (m, 6H), 3.02-
3.18 (m, 6H), 2.64-2.98 (m, 4H), 1.52-2.20 (m, 6H). LRMS
(APCI): 600 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-(2-(im id a zol-1-ylm eth yl)p h en yl)-
p ip er a zin e (50). The title compound was prepared from
N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-(2-(imidazol-1-yl-
methyl)phenyl)piperazine 13 in a manner similar to that
1
described for 35. H NMR (400 MHz, MeOD): δ 8.98 (s, 1H),
7.55 (s, 2H), 7.46-7.16 (m, 12H), 5.53 (s, 2H), 5.21 (m, 1H),
4.43 (s, 2H), 4.23 (dd, 1H, J ) 12.2, 4.9 Hz), 3.85 (m, 1H), 3.62-
3.50 (m, 3H), 3.45 (dd, 1H, J ) 5.1, 17.4 Hz), 3.18-3.03 (m,
3H), 2.80-2.52 (m, 3H), 2.18 (m, 1H). LRMS (ES+): 583.2 (M
+ H).
1-(D-Tic-4-Cl-D-P h e)-4-[2-((2-m eth ylim id a zol-1-yl)m eth -
yl)p h en yl]p ip er a zin e (51). The title compound was prepared
from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-[2-((2-meth-
ylimidazol-1-yl)methyl)phenyl]piperazine 14 in a manner simi-
lar to that described for 35. 1H NMR (400 MHz, MeOD): δ
8.93 (d, 1H, J ) 7.3 Hz), 7.47-7.23 (m, 11H), 7.22-7.16 (m,
2H), 7.07 (dd, 1H, J ) 7.6, 1.3 Hz), 5.45 (s, 2H), 5.22 (m, 1H),
4.43 (s, 2H), 4.23 (dd, 1H, J ) 12.2, 4.6 Hz), 3.84 (m, 1H), 3.68-
3.52 (m, 2H), 3.45 (dd, 1H, J ) 4.6, 12.5 Hz), 3.19-3.02 (m,
4H), 2.84-2.69 (m, 2H), 2.62 (m, 1H), 2.56 (s, 3H), 2.22 (m,
1H). LRMS (ES+): 597.2 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-[2-((1-m eth yl-1H-im id a zol-2-yl)-
m eth yl)p h en yl]p ip er a zin e (52). The title compound was
prepared from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-[2-
((1-methyl-1H-imidazol-2-yl)methyl)phenyl]piperazine 19 in a
1
manner similar to that described for 35. H NMR (400 MHz,
MeOD): δ 7.47 (d, 1H, J ) 2.0 Hz), 7.41 (d, 1H, J ) 2.0 Hz),
7.42-7.13 (m, 12H), 5.18 (m, 1H), 4.43 (s, 2H), 4.42 (s, 2H),
4.22 (dd, 1H, J ) 12.1, 4.5 Hz), 3.70 (s, 3H), 3.44 (dd,1H, J )
4.4, 17.2 Hz), 3.53-3.35 (m, 2H), 3.18-3.01 (m, 4H), 2.76-
2.49 (m, 4H), 2.13 (m, 1H). LRMS (ES+): 597.2 (M + H).
1-(D-Tic-4-Cl-D-P h e)-4-[2-((1-m eth yl-1H-im id a zol-2-yl)-
m eth oxy)p h en yl]p ip er a zin e (53). The title compound was
prepared from N-Boc-D-Tic-4-Cl-D-Phe-OH 3 and 1-Boc-4-[2-
((1-methyl-1H-imidazol-2-yl)methoxy)phenyl]piperazine 25c in
a manner similar to that described for 35. 1H NMR (400 MHz,
MeOD): δ 7.64 (d, 1H, J ) 1.6 Hz), 7.60 (d, 1H, J ) 1.6 Hz),
7.40-7.19 (m, 12H), 5.60 (s, 2H), 5.19 (m, 1H), 4.42 (s, 2H),
4.22 (dd, 1H, J ) 11.6, 4.7 Hz), 3.95 (s, 3H), 4.05-3.71 (m,
4H), 3.44 (dd, 1H, J ) 4.8, 17.2 Hz), 3.32-3.43 (m, 2H), 3.24-
3.02 (m, 4H), 2.81 (m, 1H). LRMS (ES+): 613.2 (M + H).
Bin d in g Assa y. A radioligand binding assay was performed
cAMP was determined by an SPA-based competition assay
using 125I-cAMP (Amersham Biosciences), goat anti-cAMP
antibody (ICN), and PVT anti-sheep antibody binding SPA
beads as per manufacturer instructions (Amersham Bio-
sciences). Assay buffer contained 50 mM sodium acetate and
0.1% BSA. A mixture containing SPA beads (1 mg/mL),
antibody (0.65%), and radioligand (61 pM) was prepared in
assay buffer, and 100 µL was added to each quenched well of
the 96-well assay plate to yield a final volume of 210 µL.
Following a 12 h incubation, the plates were counted in a PE
Life Sciences Trilux microplate scintillation counter. The data
were converted to picomoles of cAMP using a standard curve

Novel Arylpiperazines as Melanocortin Agonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 3 755
(4) (a) Herpin, T. F.; Yu, G.; Carlson, K. E.; Morton, G. C.; Wu, X.;
Kang, L.; Tuerdi, H.; Khanna, A.; Tokarski, J . S.; Lawrence, R.
M.; Macor, J . E. Discovery of Tyrosine-Based Potent and
Selective Melanocortin-1 Receptor Small-Molecule Agonists with
Antiinflammatory Properties. J . Med. Chem. 2003, 46, 1123-
1126. (b) Sebhat, I. K.; Martin, W. J .; Ye, Zhixiong; B. K.; Mosley,
R. T.; J ohnston, D. B. R.; Bakshi, R.; Palucki, B.; Weinberg, D.
H.; MacNeil, T.; Kalyani, R. N.; Tang, R.; Stearns, R. A.; Miller,
R. R.; Tamvakopoulos, C.; Strack, A. M.; McGowan, E.; Cashen,
D. E.; Drisko, J . E.; Hom, G. J .; Howard, A. D.; MacIntyre, D.
E.; Van der Ploeg, L. H. T.; Patchett, A. A.; Nargund, R. P.
Design and pharmacology of N-[(3R)-1,2,3,4-tetrahydroisoquino-
linium-3-ylcarbonyl]-(1R)-1-(4-chlorobenzyl)-2-[4-cyclohexyl-4-
(1H-1,2,4-triazol-1-ylmethyl)piperidin-1-yl]-2-oxoethylamine (1),
a potent, selective, melanocortin subtype-4 receptor agonist. J .
Med. Chem. 2002, 45, 4589-4593. (c) Pan, K.; Scott, M. K.; Lee,
D. H. S.; Fitzpatrick, L. J .; Crooke, J . J .; Rivero, R. A.; Rosenthal,
D. I.; Vaidya, A. H.; Zhao, B.; Reitz, A. B. 2,3-Diaryl-5-anilino-
[1,2,4]thiadiazoles as melanocortin MC4 receptor agonists and
their effects on feeding behavior in rats. Bioorg. Med. Chem.
2003, 11, 185-192. (d) Bondebjerg, J .; Xiang, Z.; Bauzo, R. M.;
Haskell-Luevano, C.; Meldal, M. A Solid-Phase Approach to
Mouse Melanocortin Receptor Agonists Derived from a Novel
Thioether Cyclized Peptidomimetic Scaffold. J . Am. Chem. Soc.
2002, 124, 11046-11055. (e) J oseph, C. G.; Bauzo, R. M.; Xiang,
Z.; Haskell-Luevano, C. Urea small molecule agonists on mouse
melanocortin receptors. Bioorg. Med. Chem. Lett. 2003, 13,
2079-2082. (f) Mutulis, F.; Mutule, I.; Wikberg, J . E. S.
N-Alkylamino acids and their derivatives interact with melano-
cortin receptors. Bioorg. Med. Chem. Lett. 2002, 12, 1039-1042.
(g) Mutulis, F.; Mutule, I.; Lapins, M.; Wikberg, J . E. S.
Reductive amination products containing naphthalene and
indole moieties bind to melanocortin receptors. Bioorg. Med.
Chem. Lett. 2002, 12, 1035-1038.
assayed under the same conditions in the presence of varying
concentrations of unlabeled cAMP. The data were analyzed
using a four-parameter logistic nonlinear regression to gener-
ate agonist potencies (EC50) and percent efficacy data relative
to the maximum stimulation obtained with NDP-R-MSH.
Bioa va ila bility P r otocol. Fischer 344 rats (Harlan Labo-
ratories) weighing between 200 and 250 g were used in the
exposure studies (n ) 3 per time point). Oral doses were
administered at 30 mg/kg in a 10% acacia vehicle via gavage,
and intravenous doses were administered at 5 mg/kg. Rats
were bled via the retro-orbital route 0.5, 1, 2 and 6 h after
oral dosing and 0.083, 1, 2, 4, 6, 8 and 24 h after intravenous
dosing. All blood samples were collected into heparinized
syringes. Plasma was harvested using centrifugation and
stored at -70 °C until assayed. Plasma was assayed by
electrospray LC/MS/MS on a Sciex API 3000 mass spectrom-
eter using fast gradient elution on a 2 × 50 mm C18 HPLC
column. Least squares regression of the standard concentra-
tions was used for sample quantitation. Pharmacokinetic
analysis using a model-independent analysis was used to
generate pharmacokinetic parameter estimates.
Ack n ow led gm en t. The authors would like to thank
Clifford M. Paicely, J r. and the Physical Chemistry
Department of Lilly Research Laboratories for spectral
data and LC/MS analysis.
Su p p or tin g In for m a tion Ava ila ble: HPLC and HRMS
data for all new compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
(5) Mayer, J . P. Discovery of Selective Melanocortin-4 Ligands
through Combinatorial Modification of Privileged Structures.
18th American Peptide Symposium, J uly 19-23, 2003, Boston,
MA.
(6) Wolfe, J . P.; Buchwald, S. L. Scope and Limitations of the Pd/
BINAP-Catalyzed Amination of Aryl Bromides. J . Org. Chem.
2000, 65, 1144-1157.
Refer en ces
(1) (a) Cone, R. D., Ed. The Melanocortin Receptors; Humana
Press: Totowa, NJ , 2000, 551 pp. (b) MacNeil, D. J .; Howard,
A. D.; Guan, X.; Fong, T. M.; Nargund, R. P.; Bednarek, M. A.;
Goulet, M. T.; Weinberg, D. H.; Strack, A. M.; Marsh, D. J .;
Chen, H. Y.; Shen, C.-P.; Chen, A. S.; Rosenblum, C. I.; MacNeil,
T.; Tota, M.; MacIntyre, E. D.; Van der Ploeg, L. H. T. The role
of melanocortins in body weight regulation: Opportunities for
the treatment of obesity. Eur. J . Pharmacol. 2002, 440, 141-
157. (c) Wikberg, J . E. S. Melanocortin receptors: Perspectives
for novel drugs. Eur. J . Pharmacol. 1999, 375, 295-310.
(2) (a) Mountjoy, K. G.; Robbins, L. S.; Mortrud, M. T.; Cone, R. D.
The cloning of a family of genes that encode the melanocortin
receptors. Science 1992, 257, 1248-1251. (b) Cone, R. D.;
Mountjoy, K. G.; Robbins, L. S.; Nadeau, J . H.; J ohnson, K. R.;
Roselli-Rehfuss, L.; Mortrud, M. T. Cloning and functional
characterization of a family of receptors for the melanotropic
peptides. Ann. N. Y. Acad. Sci. 1993, 680, 342-363. (c) Chhajlani,
V.; Wikberg, J . E. S. Molecular cloning and expression of the
human melanocyte stimulating hormone receptor cDNA. FEBS
Lett. 1992, 309, 417-420. (d) Gantz, I.; Konda, Y.; Tashiro, T.;
Shimoto, Y.; Miwa, H.; Munzert, G.; Watson, S. J .; DelValle, J .;
Yamada, T. Molecular cloning of a novel melanocortin receptor.
J . Biol. Chem. 1993, 268, 8246-8250. (e) Mountjoy, K. G.;
Mortrud, M. T.; Low, M. J .; Simerly, R. B.; Cone, R. D.
Localization of the melanocortin-4 receptor (MC4-R) in neuroen-
docrine and autonomic control circuits in the brain. Mol.
Endocrinol. 1994, 8, 1298-1308. (f) Gantz, I.; Miwa, H.; Konda,
Y.; Shimoto, Y.; Tashiro, T.; Watson, S. J .; DelValle, J .; Yamada,
T. Molecular cloning, expression, and gene localization of a
fourth melanocortin receptor. J . Biol. Chem. 1993, 268, 15174-
15179. (g) Chhajlani, V.; Muceniece, R.; Wikberg, J . E. S.
Molecular cloning of a novel human melanocortin receptor.
Biochem. Biophys. Res. Commun. 1993, 195, 866-873.
(7) (a) Evans, B. E.; Rittle, K. E.; Bock, M. G.; DiPardo, R. M.;
Freidinger, R. M.; Whitter, W. L.; Lundell, G. F.; Veber, D. F.;
Anderson, P. S.; Chang, V. J .; Loti, V. J .; Cerino, D. J .; Chen, P.
J .; Kling, P. J .; Kunkel, K. A.; Springer, J . P.; Hirshfield, J .
Methods for drug discovery: Development of potent, selective,
orally effective cholecystokinin antagonists. J . Med. Chem. 1988,
31, 2235-2246. (b) Nargund, R. P.; Patchett, A. A.; Bach, M.
A.; Murphy, M. G.; Smith, R. G. Peptidomimetic Growth
Hormone Secretagogues. Design Considerations and Therapeutic
Potential. J . Med. Chem. 1998, 41, 3103-3127. (c) Patchett, A.
A.; Nargund, R. P. Chapter 26. Privileged structuressAn update.
Ann. Rep. Med. Chem. 2000, 35, 289-298.
(8) (a) Dyck, B. P.; Goodfellow, V.; Parker, J .; Phillips, T.; Wade,
W.; Tran, J . A. Pyrroles as ligands of melanocortin receptors.
PCT Int. Appl. WO2003068738, 2003. (b) Boyce, R.; Chu, D.
Guanidino compounds. PCT Int. Appl. WO2003066597, 2003. (c)
Dyck, B. P.; Goodfellow, V.; Phillips, T.; Parker, J .; Zhang, X.;
Chen, C.; Tran, J . A.; Pontillo, J .; Tucci, F. C. Ligands of
melanocortin receptors and compositions and methods related
thereto. PCT Int. Appl. WO2003031410, 2003. (d) Fotsch, C. H.;
Arasasingham, P.; Bo, Y.; Chen, N.; Goldberg, M. H.; Han, N.;
Hsieh, F.-Y.; Kelly, M. G.; Liu, Q.; Norman, M. H.; Smith, D.
M.; Stec, M.; Tamayo, N.; Xi, N.; Xu, S. Substituted piperazines
as modulators of the melanocortin receptor. PCT Int. Appl.
WO2003009850, 2003. (e) Carpino, P. A.; Cole, B. M.; Morgan,
B. P. Melanocortin receptor ligands. PCT Int. Appl. WO2002000-
654, 2002. (f) Bakshi, R. K.; Barakat, K. J .; Nargund, R. P.;
Palucki, B. L.; Patchett, A. A.; Sebhat, I.; Ye, Z.; Van Der Ploeg,
L. H. T. Substituted piperidines as melanocortin-4 receptor
agonists. PCT Int. Appl. WO2000074679, 2000. (g) Nargund, R.
P.; Ye, Z.; Palucki, B. L.; Bakshi, R. K.; Patchett, A. A.; Van Der
Ploeg, L. H. T. Spiropiperidine derivatives as melanocortin
receptor agonists. PCT Int. Appl. WO9964002, 1999.
(3) (a) Chen, A. S.; Marsh, D. J .; Trumbauer, M. E.; Frazier, E. G.;
Guan, X.-M.; Yu, H.; Rosenblum, C. I.; Vongs, A.; Feng, Y.; Cao,
L.; Metzger, J . M.; Strack, A. M.; Camacho, R. E.; Mellin, T. N.;
Nunes, C. N.; Min, W.; Fisher, J .; Gopal-Truter, S.; MacIntyre,
D. E.; Chen, H. Y.; Van der Ploeg, L. H. T. Inactivation of the
mouse melanocortin-3 receptor results in increased fat mass and
reduced lean body mass. Nature Genet. 2000, 26, 97-102. (b)
Butler, A. A.; Kesterson, R. A.; Khong, K.; Cullen, M. J .;
Pelleymounter, M. A.; Dekoning, J .; Baetscher, M.; Cone, R. D.
A unique metabolic syndrome causes obesity in the melanocor-
tin-3 receptor-deficient mouse. Endocrinology 2000, 141, 3518-
3521.
J M0304109