Aminopyrazoles with high affinity for the human neuropeptide Y5 receptor

Article abstract of DOI:10.1016/S0960-894X(01)00448-6

1,3-Disubstituted-5-aminopyrazoles were prepared based on a lead compound found through high-throughput screening of our corporate compound library in an assay measuring affinity for the human neuropeptide Y5 receptor. The target compounds were prepared b

Full text of DOI:10.1016/S0960-894X(01)00448-6

Bioorganic & Medicinal Chemistry Letters 11 (2001) 2283–2286
Aminopyrazoles with High Affinity for the Human Neuropeptide
Y5 Receptor
Cheryl P. Kordik,a,* Chi Luo,a Brian C. Zanoni,a Scott L. Dax,a James J. McNally,a
Timothy W. Lovenberg,b Sandy J. Wilsonb and Allen B. Reitza
aDrug Discovery Division, The R. W. Johnson Pharmaceutical Research Institute, Welsh and McKean Roads,
Spring House, PA19477, USA
bDrug Discovery Division, The R. W. Johnson Pharmaceutical Research Institute, 3210 Merryfield Row,
San Diego, CA92121, USA
Received 26 March 2001; accepted 11 June 2001
Abstract—1,3-Disubstituted-5-aminopyrazoles were prepared based on a lead compound found through high-throughput screening
of our corporate compound library in an assay measuring affinity for the human neuropeptide Y5 receptor. The target compounds
were prepared by cyclization of a-cyanoketones with appropriate hydrazines, followed by reduction and coupling to various sul-
fonamido-carboxylic acids. Several of these arylpyrazoles (e.g., 19 and 45) displayed high affinity for the human NPY Y5 receptor
(<20 nM IC50s). # 2001 Elsevier Science Ltd. All rights reserved.
Neuropeptide Y (NPY) is a 36-amino acid C-amidated
peptide, which is a member of the pancreatic polypep-
tide family.1 It is highly expressed in several regions of
the brain and is released into the circulation from neu-
ronal stores in times of stress. In the CNS, NPY has
been implicated in obesity and feeding,2,3 as NPY is a
powerful stimulant of food intake when administered
directly into the hypothalamus. Recent discoveries have
revealed six G-protein coupled receptors that bind with
high affinity to NPY and related peptides such as pep-
tide YY, pancreatic polypeptide and truncated NPY
analogues.4ꢀ13 The most likely receptor subtypes
responsible for centrally-mediated NPY-induced feeding
responses are NPY Y1 and NPY Y5.12,14ꢀ16 Antago-
nists at the NPY Y5 receptor have been shown to be
effective in reducing food intake in various animal
models of feeding.17 Consequently, NPY Y5 receptor
antagonists may provide new treatments for obesity and
other eating disorders.18
have low nanomolar affinity at the Y5 receptor. Other
sulfonamides bearing a b-aminotetralin substructure,
typified by 2, are also potent NPY Y5 antagonists.21ꢀ23
One of the most potent NPY Y5 antagonists is amide
derivative 3, reported to have an IC50 value of 0.47 nM
at the Y5 receptor.24 Aminopyrazoles 4 and 5 have both
been shown to have low nanomolar affinity for the Y5
NPY Y5 antagonists that have been reported in the lit-
erature encompass many diverse structural types (Fig. 1).
The first NPY Y5-selective antagonists appeared in
mid-1997.19,20 Quinazoline sulfonamide 1 was found to
*Corresponding author. Fax: +1-215-628-4985; e-mail: ckordik@
prius.jnj.com
Figure 1. Non-peptide NPY 5 receptor antagonists.
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00448-6

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C. P. Kordik et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2283–2286
Figure 2. Aminopyrazole lead structures from HTS.
Scheme 2. Reagents: (a) isobutylchloroformate, Et3N, DCE; (b) NaH,
THF; (c) 14 h; (d) TFA, DCE; (e) arylhydrazine hydrochloride, Et3N,
EtOH, reflux.
receptor.25,26 Aminothiazole 6 has also been described
as an NPY Y5 antagonist.27
Screening of our corporate compound library identified
aminopyrazole bis-sulfonamide 7 (Fig. 2), obtained
through a compound aquisition program, as having
nanomolar binding affinity for the human Y5 receptor.
Structural characterization of the sample revealed,
unexpectedly, that it was a 1:1 mixture of two com-
pounds, which were found to bis-sulfonamide 7 and
aminopyrazole 8. Evaluation of the individual compo-
nents of the mixture revealed that all of the original
activity resided in aminopyrazole 8, having a 40 nM
IC50. The bis-sulfonamide 7 was inactive with a 6 mM
IC50. An intensive effort to develop structure–activity
relationships (SARs) based on aminopyrazole lead 8
was then undertaken.
amido group had previously been shown to be present
in high-affinity NPY Y5 ligands.19ꢀ21 The mixed anhy-
dride of the trans-cyclohexyl acid 13 was reacted with
the anion of t-butyl cyanoacetate 14 to yield cyclohexyl
b-ketoester 15. T het-butyloxycarbonyl group was
removed by treatment with TFA. The pyrazoles were
formed by reacting a-cyano ketone 16 with a substituted
hydrazine in the presence of Et3N in ethanol at reflux to
provide the cyclohexylmethyl pyrazoles 17 in fair to
moderate yields. The analogous phenylmethyl sulfon-
amido compounds were prepared in the same manner
starting with the corresponding benzoic acid 13.
The aminopyrazole sulfonamides were evaluated for
binding affinity to the human neuropeptide Y Y5
receptor using a stably transfected HEK293 cell line and
measuring competitive inhibition of binding of 125I-
PYY (Table 1). Table 1 illustrates aminopyrazole sulfo-
namides in which the substituent on the pyrazole ring
(R1) was varied to develop an SAR profile. The parent
N-phenyl derivative 18 had a 100 nM IC50 for the
human NPY Y5 receptor. In general, when the R1
group was a substituted phenyl the compounds were
found to be the more potent NPY ligands. In particular,
the best affinity was found when R1 was 4-methylphenyl
(19), for which a 15 nM IC50 was observed.28 3-Sub-
stitution on the phenyl ring resulted in a slight loss of
The target aminopyrazoles were synthesized in four
steps from commercially available 2-bromo-40-nitroace-
tophenone 9 (Scheme 1). This compound was reacted
with NaCN in aqueous ethanol at 0 ꢁC to provide 2-
cyano-40nitroacetophenone 10. Formation of the pyra-
zole core stucture was effected by cyclization of the a-
cyanoketone with an arylhydrazine in the presence of
triethylamine in refluxing ethanol, which yielded pyra-
zole 11. The nitro group was then reduced to an amine
under hydrogenation conditions and the amine was
coupled to an aryl sulfonyl chloride to afford desired
aminopyrazoles 12 in excellent yields.
Table 1. Human NPY Y5 receptor binding affinity of aminopyr-
azoles with R1 variationa
Alternatively, aminopyrazoles that contained a cyclo-
hexylmethyl- or phenylmethyl-sulfonamido group were
prepared as illustrated in Scheme 2. These compounds
were designed because the cyclohexylmethylsulfon-
Compd
R1
Y5 IC50 (nM)
18
19
20
21
22
23
24
25
26
27
Phenyl
4-Methylphenyl
3-Methylphenyl
100
15
37
30
3-(Dimethylamino)phenyl
3,5-(Bistrifluoromethyl)phenyl
4-Fluorophenyl
1-Naphthyl
2-Pyridyl
4-Trifluoromethyl-2-pyridyl
4-Trifluoromethyl-2-pyrazine
>1000
37
48
436
>1000
709
Scheme 1. Reagents: (a) NaCN, H2O, EtOH, 0 ꢁC; (b) R1NHNH2,
Et3N, EtOH, reflux; (c) H2, 10% Pd–C, EtOAc, 30 psig; (d) R2SO2Cl,
K2CO3, THF, H2O.
aHEK 293 cells were stably transfected with the human NPY Y5
cDNA, and the receptor affinity was determined as described in ref 21.

C. P. Kordik et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2283–2286
2285
activity versus 4-substitution (19 vs 20). Compounds
with nitrogens that could be protonated were of interest
to us because they could perhaps increase aqueous
solubility. Therefore, it was gratifying that dimethyl-
amino compound 21 had a 30 nM IC50 at the human
NPY Y5 receptor. Surprisingly, the 3,5-bis(tri-
fluoromethyl)phenyl congener (22) was devoid of activ-
ity at a concentration of 1 mM. 4-Fluorophenyl and 1-
naphthyl derivatives 23 and 24 demonstrated good
receptor affinity with 37 and 48 nM IC50s, respectively.
Heteroaryls 25, 26, and 27 had greatly diminished
activity.
Fig. 3). In addition, the 1,4-orientation of the pyrazole
and the sulfonamide on the middle phenyl ring is also
necessary for activity. When the groups were transposed
into a 1,3-orientation (43), affinity for the NPY Y5
receptor was lost (>1 mM IC50). Methylation of the
amino group attached to the pyrazole ring of 35 pro-
vided 44, which resulted in a 3-fold decrease in activity
(487 nM IC50).
When a cyclohexylmethyl group replaced the phenyl
ring, resultant compounds 45 and 46 were slightly better
or similar in activity when compared with phenyl deri-
vative 19. The 2-NO2 and 2-NH2 substitution on R3 was
selected for these compounds because of literature pre-
cedent with compounds of type 2.21 Phenyl methyl lin-
ker congener 47 had an IC50 of 114 nM. Replacement of
the sulfonamido group with either an amide (48) or a
reverse amide (49) resulted in a loss of activity, indicat-
ing that the sulfonamide is critical for activity here as it
is for some of the other NPY Y5 chemical series, as seen
for 1 and 2 previously (Table 3).
Variations were also made to the sulfonamide sub-
stituent (R2, Table 2). For this analysis, the R1 group
was held constant at 4-MePh because of the potent
receptor affinity of 19. In general, phenyl (28) and 4-
substituted phenyls (19 and 29–35) provided the best
affinity for the NPY Y5 receptor. Electon-donating
substituents 4-Me (29) and 4-MeO (19) displayed 40 and
15 nM IC50s for the NPY Y5 receptor, respectively.
Electron-withdrawing groups in the 4-position were also
tolerated, such as with 4-CF3Ph 30, 4-(CF3O)Ph 31, 4-
FPh 32 (29 nM IC50), and 4-NO2Ph 33. The 4-NH2Ph
congener 34, obtained by reduction of 33, was equipo-
tent to 33, indicating a broad tolerance for substitution
in this position. 4-(Me2N)Ph 35 was less active with a
162 nM IC50. Direct comparison of 4- and 3-substitu-
tion revealed a loss of activity when moving an amino
group to the 3-position (viz. 36 vs 34), whereas the 3-
(Me2N)Ph analogue (37) was nearly equivalent in activ-
ity to 4-substituted 35. Compounds 38 and 39 with 2-
substitution showed moderate activity. Incorporation of
bicyclic quinoline and naphthyl groups (40 and 41)
abolished the receptor affinity.
Several of the aminopyrazole sulfonamides we report
here show high affinity for the human neuropeptide Y5
receptor. This series contains an arylpyrazole and an
arylsulfonamide that are connected via a suitable linker.
For example, among the most active compounds are
those in which there is a substituted phenyl pyrazole on
one side and a 4-substituted phenyl sulfonamide on the
other with a 1,4-phenyl linker in the middle (viz. 19, 21,
23, and 28). Additionally, derivatives with a (cyclohex-
yl)methylamino spacer (viz. 45 and 46) have significant
activity, with 45 exhibiting a 10 nM IC50 at the human
NPY Y5 receptor. These compounds may be useful for
the treatment of human feeding disorders and obesity,
especially if a compound with favorable pharmacoki-
netic properties can be obtained with this level of in
vitro affinity.
The sulfonamide NꢀH in 19 appears to be crucial for
activity because N-methyl 42 was inactive (>1 mM IC50;
Table 2. Human NPY Y5 receptor binding affinity of aminopyr-
azoles with R2 modifications
Compd
R2
Y5 IC50 (nM)
28
29
19
30
31
32
33
34
35
36
37
38
39
40
41
Phenyl
4-Methylphenyl
4-Methoxyphenyl
4-Trifluoromethyl
4-(Trifluoromethoxy)phenyl
4-Fluorophenyl
4-Nitrophenyl
4-Aminophenyl
4-(Dimethylamino)phenyl
3-Aminophenyl
25
40
15
63
67
29
79
74
162
303
145
178
229
>1000
>1000
3-(Dimethylamino)phenyl
2-Nitrophenyl
2-Aminophenyl
8-Quinolinyl
1-Naphthyl
Figure 3. Variably substituted pyrazole derivatives.

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C. P. Kordik et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2283–2286
Table 3. NPY Y5 receptor binding affinity of aminopyrazoles with
variation of the middle linker portion
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