Discovery of potent and selective small molecule NPY Y5 receptor antagonists.

Article abstract of DOI:10.1016/S0960-894X(02)00287-1

The discovery of a new class of sulfonamide NPY Y5 receptor antagonists is described. Optimization of this series led to the identification of compounds with high affinity for the hY5 subtype and excellent selectivity over the other NPY receptor subtypes. The SAR for this series was examined and a model for understanding the ligand-receptor interactions was developed.

Full text of DOI:10.1016/S0960-894X(02)00287-1

Bioorganic & Medicinal Chemistry Letters 12 (2002) 1767–1769
Discovery of Potent and Selective Small Molecule
NPY Y5 Receptor Antagonists
Imadul Islam, Dale Dhanoa, John Finn,* Ping Du, Mary W. Walker,
John A. Salon, Jack Zhang and Charles Gluchowski
Synaptic Pharmaceutical Corporation, 215 College Road, Paramus, NJ 07652, USA
Received 7 December 2001; accepted 29 March 2002
Abstract—The discovery of a newclass of sulfonamide NPY Y5 receptor antagonists is described. Optimization of this series led to
the identification of compounds with high affinity for the hY5 subtype and excellent selectivity over the other NPY receptor sub-
types. The SAR for this series was examined and a model for understanding the ligand–receptor interactions was developed. # 2002
Elsevier Science Ltd. All rights reserved.
Neuropeptide Y (NPY) is a 36 amino acid peptide neuro-
transmitter widely expressed in both the peripheral and
central nervous system.1 Cloned receptors for NPY and
related family members (peptide YY and pancreatic
polypeptide) are classified as Y-type receptors (Y1, Y2,
Y4, and Y5; note there is also a Y6 receptor gene that is
absent in the rat and a pseudogene in human). NPY is
considered to regulate a variety of physiological pro-
cesses, including vasoconstriction, nasal congestion,
blood pressure, intestinal motility, anxiety, depression,
pain, feeding, reproductive endocrinology, neuronal
excitability and memory retention.2 As such, receptor-
specific ligands to modulate NPY receptor signaling
may have therapeutic value. In this report, we describe
the discovery of potent and selective sulfonamide Y5
antagonists and provide a model of howthese antago-
nist bind to the NPY Y5 receptor.3
groups and to identify the number of basic amines
required for binding. Symmetrical bis-2-naphthyl-
methylamines such as 2–4 with shorter (two, four, and
six) methylene linker groups and containing either two
or four basic sites were found to have similar potency to
benextramine. In an effort to discover more potent and
selective ligands, sulfonamides 5 and 6 were prepared.
These arylsulfonamide amines were based on a common
GPCR ligand motif or privileged structure5,6 where an
arylamide (or sulfonamide) functionality is separated by
an alkyl spacer from a basic benzylic amine or an aryl
piperazine. Both 5 and 6 demonstrate improved selec-
tivity for the hY5 receptor. Sulfonamide 6, containing
the longer linker, has significant (120 nM) potency for
the hY5 receptor in addition to good selectivity. It is
interesting that the sulfonamide functionality is present
in SR 120107A, a Sanofi NPY Y1 selective antagonist.7
While we had hoped for an improvement in potency
with the introduction of the sulfonamide, the sig-
nificant enhancement in selectivity for Y5 versus Y1
was unexpected.
When this project was initiated, limited information
about small molecule NPY ligands was available. Our
starting point was the weakly potent ligand benex-
tramine 1 (Fig. 1).4 Due to its flexible and polybasic
structure, benextramine binds with little selectivity to
multiple GPCRs and provides limited structural infor-
mation to guide the discovery of more potent and
selective ligands. Consequently, we used symmetrical
polyamine benextramine analogues as probe molecules
to explore shorter linking chains, different aromatic
To improve the affinity of sulfonamide amine 6, w e
examined more rigid linking chains that could orient the
arylsulfonamide and benzylic amine functionalities cor-
rectly in the Y5 receptor’s binding pockets. Overlays
between sulfonamide 6 and multiple HTS hits suggested
the more rigid bis-(1,4-aminomethylene)cyclohexane as
a linker. Testing this hypothesis, lead to the synthesis
and testing of sulfonamide 11, a potent (Ki=8 nM) Y5
receptor subtype antagonist with greater than 500-fold
selectivity over the other NPY receptor subtypes. The
*Corresponding author at current address: Cubist Pharmaceuticals, 65
Hayden Ave., Lexington, MA 02421, USA; Fax: +1-781-861-1164;
e-mail: john.finn@cubist.com
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00287-1

1768
I. Islam et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1767–1769
Figure 1. Binding affinities for benextramine and analogues (Ki in mM).
Scheme 1.
preferred stereochemistry of the 1,4-cyclohexane ring
substituents is trans. Synthesis of sulfonamide 11
(Scheme 1) is illustrative of the synthetic route to a ser-
ies of sulfonamide amines. Sulfonylation of the mono-
protected diamine 8 followed by deprotection affords
arylsulfonamides 9. Reductive amination of 9 with
2-formyl-tetrahydronaphthalene yielded 11 directly.
Alternatively, 9 was acylated to yield a sulfonamide
amide 10. Reduction of 10 with borane afforded the
desired sulfonamide amine 11.
Table 1 shows the binding affinities of selected sulfon-
amide analogues for human NPY receptor subtypes.
Common to this set of potent hY5 ligands are two
hydrophobic, preferably aromatic, groups. Naphthyl
and 2-substituted phenyl groups are favored in the aryl
sulfonamide binding region. The second aryl pocket is
considerably more permissive and a range of different
groups are compatible with good affinity. The ability to
vary this second aromatic group allowed us to prepare a
set of ligands with a range of physicochemical properties.
Table 1. Binding affinities for arylsulfonamide amines
Compd
Ar
L
Y
R
Ki hY1 (nM)
Ki hY5 (nM)
6
2-Naphthyl
2-NO2C6H4
2-Naphthyl
2-NH2C6H4
2-NO2C6H4
1-Naphthyl
2-CF3C6H4
1-Naphthyl
2-CF3C6H4
2-NO2C6H4
(CH2)6
CHX
CHX
CHX
CHX
CHX
CHX
CHX
CHX
CHX
CH2
CH2
CH2
CH2
CH2
CH2
CH2
2-Naphthyl
THN
THN
THN
2-Quinoline
THN
1-Naphthyl
4-Cl-benzyl
2-Naphthyl
4-Quinoline
7300
16,032
5546
17,179
23,714
3548
14,454
3236
12,981
48,697
123
8
11
12
13
14
15
16
17
18
19
14
10
14
11
26
17
10
28
CH(CH2OH)
CH2
CH2

I. Islam et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1767–1769
1769
receptor is the only NPY subtype to contain a histidine
residue in TM6. Other important interactions high-
lighted by the model, include an acid-base pair formed
with the amine of the sulfonamide amine and Glu211
and hydrophobic interactions between the aromatic
groups and hydrophobic regions of the receptor.
In summary, we have shown that a weak and non-
selective flexible molecule, benextramine, can be used as
a starting point for the design of potent and selective
ligands. Central to this improvement was the incor-
poration of a sulfonamide group that provides a bias
towards the NPY Y5 receptor. Systematic exploration
of this series led to a series of NPY Y5 antagonists of
high potency. A model for howthese ligands bind to the
receptor is presented that is consistent with the SAR
trends.
Figure 2. Model of sulfonamide 6 binding to hY5 receptor.
The sulfonamide amines were found to be very selective
for the Y5 over the other NPY receptors (Y1, Y2, and
Y4) and therefore represent excellent tools for studying
the physiological roles of the Y5 receptor.
Acknowledgements
We thank Zoya Shaposhnik and Nancy Rogacki for
their efforts in Ki determinations.
All of the sulfonamide amines in Table 1 were pharma-
cologically characterized in binding and functional
assays (n ꢀ2). Radioligand binding assays were per-
formed with membranes from COS-7 cells transiently
transfected with NPY receptor subtypes, labeled with
125I-PYY plus or minus test compounds.8 Functional
assays were conducted with HEK-293 or LMTK- cells
stably transfected with NPY receptor subtypes; intact
cells were stimulated with forskolin and NPY plus or
minus test compounds, then cAMP levels were detected
by radioimmunoassay. All sulfonamides (6 and 11–19)
are pure antagonists, in that they competitively attenu-
ate the ability of NPY to inhibit forskolin-stimulated
cAMP. These antagonists are potent inhibitors of the
functional response to NPY with Kb values very similar
to the Ki values (e.g., 11 hY5 Ki=8 nM, hY5
Kb=26 nM; 12 hY5 Ki=14 nM, hY5 Kb=6 nM). The
compounds were tested in a panel of GPCRs and found
to be selective for the NPY hY5 receptor (>100-fold for
most receptors). The main cross reactivity being with
the cloned human a2c and D2 receptors (e.g., 11
Ki=100 nM on human a2c and Ki=63 nM on human
D2). The sulfonamide series of NPY antagonists are
also potent and selective for the rat NPY Y5 subtype
(e.g., 11 Ki rY5=18 nM, Ki rY1=22,000 nM).
References and Notes
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