Design, synthesis and SAR of a series of 2-substituted 4-amino-quinazoline neuropeptide Y Y5 receptor antagonists

Article abstract of DOI:10.1016/S0960-894X(00)00177-3

The design of a novel series of NPY-Y₅ receptor antagonists is described. Key elements for the design were the identification of weak Y₅ hits from a Y₁ program, results from a combinatorial approach and database mining. This led to the discovery of the quinazoline 4 and the aryl-sulphonamide moiety as major components of the pharmacophore for Y₅ affinity. The synthesis and SAR towards CGP71683A is described. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00177-3

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1175±1179
Design, Synthesis and SAR of a Series of 2-Substituted 4-
Amino-quinazoline Neuropeptide Y Y5 Receptor Antagonists
Heinrich Rueeger, a,* Pascal Rigollier, a Yasuchika Yamaguchi, a Tibur Schmidlin, a
Walter Schilling, a Leoluca Criscione, a Steven Whitebread, a Michele Chiesi, a
Mary W. Walker, b Dale Dhanoa b,y, Imadul Islam b,{
Jack Zhang b and Charles Gluchowski b,x
,
aNovartis Pharma AG, Metabolic and Cardiovascular Diseases, CH-4002 Basel, Switzerland
bSynaptic Pharmaceutical Corporation, 215 College Road, Paramus, NJ, USA
Received 8 October 1999; accepted 16 March 2000
AbstractÐThe design of a novel series of NPY-Y5 receptor antagonists is described. Key elements for the design were the identi®-
cation of weak Y5 hits from a Y1 program, results from a combinatorial approach and database mining. This led to the discovery of
the quinazoline 4 and the aryl-sulphonamide moiety as major components of the pharmacophore for Y5 anity. The synthesis and
SAR towards CGP71683A is described. # 2000 Elsevier Science Ltd. All rights reserved.
Neuropeptide Y (NPY), a 36 amino acid peptide, has been
the focus of much attention since its discovery as the most
abundant peptide in the mammalian brain.1 It is present in
a highly conserved manner across species and is involved
in a number of physiological responses and implicated in
the pathophysiology of several disorders. Within the
hypothalamus, NPY is intimately involved in the regula-
tion of several aspects of neuroendocrine function and
behavior, in particular food intake.2 At least six receptor-
subtypes have been characterized to date by pharmacolo-
gical and molecular cloning techniques.3,4 However, their
speci®c involvement in NPY mediated food intake reg-
ulation remains to be fully validated.
tion that the NPY-Y1 receptor is also involved in the
control of NPY-induced food intake.8 10 Our ®ndings,
however, indicate that the Y5-subtype shows more
robust evidence for an involvement in the regulation of
food intake.12 Antagonists for the NPY-Y5-subtype are,
therefore, required and targeted.
Herein, we disclose a novel series of potent and selective
NPY-Y5 antagonists that demonstrate that the Y5-sub-
type plays a major role in mediating food intake induced
by NPY.
We used an integrated approach of selected screening
and combinatorial chemistry to identify Y5-subtype
selective compounds. Exploitation of weak Y5 hits from
a previous Y1 program and exploration of the internal
compound library by Y5 pharmacophore models gener-
ated with Catalyst1, revealed the 2-substituted 4-ami-
noquinazolines 1±3 with sub-micromolar anity and
some selectivity towards the Y5-subtype.
Recently, the hypothetical ``feeding'' receptor, named
Y5, was cloned and expressed by Synaptic Pharmaceu-
tical Corporation.5 In collaboration with Novartis, evi-
dence was generated indicating that the NPY-Y5
receptor is the primary mediator of NPY-induced feed-
ing.6,7 However, other investigators made the observa-
In parallel to the optimization of the quinazoline scaf-
fold 4 by traditional methodology, a small biased com-
binatorial library was prepared in solution12 and on
solid support,13 based on the weak Y5 hit 5, con-
taining at least two distal hydrophobic moieties
namely a basic nitrogen containing sca€old and an
H-bond acceptor functionality. These e€orts resulted in
the identi®cation of compounds 6 and 7 (SNAP6608A),
*Corresponding author. Fax:+41-61-6965966;
e-mail: heinrich.rueeger@pharma.novartis.com
yPresent address: 3-D Pharmaceuticals Inc., 665 Stockton Drive,
Exton, PA 9341, USA.
{Present address: Berlex Bioscience, 15049 San Pablo Avenue, Rich-
mond, CA 94804-0099, USA.
xPresent address: RiboGene Inc., 26118 Research Rd. Hayward, CA
94545, USA.
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00177-3

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H. Rueeger et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1175±1179
and suggested that the naphthylsulfonamide moiety
might be an important part of the Y5 pharmacophore.
Results and Discussion
On the basis of the low molecular weight quinazoline hits
1±3, a series of substituted 2,4-diamino quinazolines were
synthesized using traditional medicinal chemistry and
applying the decision tree by Topliss14 (11a±e) followed
by a Hansch analysis15 for the optimization of the 2-
arylamino substituent. High binding anity is predicted
for compounds bearing substituents that possess a large
p- and s-value like p-NEt2 in 11g of Table 1. At this
point in time the results of the combinatorial e€ort
became available suggesting that an aryl-sulphonamide
moiety as encountered in 6 and 7 is an important com-
ponent of the pharmacophore for Y5 anity. Therefore,
we explored the e€ect of H-bonding acceptor head-
groups at the 2-aryl- and 2-cyclohexyl-moieties. Sub-
stitution of the methyl group of 11b (IC50=200 nM) in
the para-position by attachment of a sulfonamide (11h)
or sulfone (11i) moiety improved anity >100-fold to
the sub-nanomolar range, whereas other H-bond
acceptors (e.g., P(O)(OEt)2 11j) were less optimal. In the
cyclohexyl series compounds 12f and 12g possessing a
sulfonamide moiety in which the sulfonyl and NH had
been reversed as compared to compound 11h showed
Linking this moiety by a semi-rigid spacer to the hetero-
aryl fragment A led to the preparation of sulfonamide-
tethered 2,4-diamino-quinazolines and ultimately to 8
(CGP71 683A), a potent and selective antagonist of the
Y5 subtype.
Chemistry
The synthesis of the quinazoline-sulfonamide derivatives is
outlined in Scheme 1. Starting from 2,4-dichloroquinazo-
line 9, sequential amination with the corresponding amine
for the 4-position, followed by the amine for the 2-position
led to compounds 11a±j. The amine intermediate 15a was
obtained from trans-4-aminomethyl-cyclohexyl-car-
boxylic acid (14) by sulfonylation with 1-naphthylsulfo-
nylchloride, amide formation via the mixed anhydride
with ammonia followed by reduction of the amide group
with BH3-THF. Standard procedures were applied for the
one carbon contraction and extension of the semi-rigid
spacer starting from the same precursor 14.

H. Rueeger et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1175±1179
1177
Table 1.
Compound
R
IC50 (nM)a
Compound
R1
R2
IC50 (nM)a
11a
11b
11c
11d
11e
11f
11g
11h
11i
3,4-Cl2
4-Me
4-Cl
H
4-MeO
270
200
100
80
12a
12b
12c
12d
12e
12f
12g
12h
12i
Cl
Cl
Cl
Cl
Cl
H
H
H
H
H
CH2NHCOMe
CH2NHCOPh
CH2NHMe
390
310
510
250
58
4
2
50
CH2N(Me)COPh
CH2N(Me)COMe
CH2NHSO2Ph(4-Me)
CH2NHSO2Me
H
33
4-C6H11
4-NEt2
4-CH2SO2NMe2
4-CH2SO2Et
4-CH2P(O)(EtO)2
20 (2)b
4 (2)b
0.9
0.6
33
OCOMe
OCOPh
6
400
11j
12j
aBinding anities to Y5-receptor subtype stable expressed in LM(tk-) cells (n=3±6), values determined at Novartis Pharma AG.
bPredicted IC50 value by the Hantsch equation: -log(IC50)=0.18 p2±1.65s+0.01 Es+1.00.
Scheme 1. Reagents and conditions: (a) Ph-NH2, DIPEA, iPrOH, re¯ux, 97%; (b) R-NH2, isopentanol, 155 ꢀC; 48%; (c) NH3, MeOH, rt, 100%; (d)
(1-C10H8)SO2Cl, 1 N NaOH, rt, 80%; (e) (i) ClCO2Et, Et3N, THF; (ii) aq NH3, 90%, (f) BH3-THF, THF, re¯ux, 90%; (g) (i) isopentanol, 120 ꢀC,
(ii) 4N HCl/dioxane, CH2Cl2, 58±73%; (h) (i) ClCO2Et, Et3N, THF, (ii) NaN3, H2O, (iii) toluene, re¯ux, (iv) aq 4N HCl, re¯ux, 68%; (i) LiAlH4,
THF, re¯ux, 80%; (j) TsCl, Et3N, cat. DMAP, CH2Cl2, rt, 90%; (k) NaCN, DMF, 50 ꢀC, 99%; (l) H2, Ra-Ni, NH3-MeOH, rt, 89%.
equally high anities. The aryl-substituted sulfonamide
12f showed a somewhat weaker anity compared to the
methyl analogue 12g. These results suggest that the
presence of the sulfonyl group or an equally well posi-
tioned carbonyl group as in analogue 12i are important
for receptor binding possibly through H-bonding to
H398 identi®ed by site-directed mutagenesis.16
able length (8, 26, 27) are optimal. N-Methylation as in
23±25 resulted in a drastic drop in anity indicating
that the NH function might act as an H-bond donor.
The superimposition of the low-energy conformations
of 11h (phenyl spacer), 12g (cyclohexyl spacer) and 8
(methyl-cyclohexyl spacer) is shown in Figure 1. The
good overlap of the equally potent compounds point to
a common pharmacophore: the hydrophobic element
and the H-bond donor/acceptor principle of the quina-
zoline, the H-bond acceptor of the sulfonamide moiety
and the hydrophobic element of the spacer. In the
phenyl- and the cyclohexyl-spacer series, an additional
hydrophobic pocket is occupied by the 4-phenylamino-
A more detailed exploration of the distance require-
ments to link the two pharmacophoric elements 2,4-
diamino-quinazoline 4 and the sulfonamide moiety
together, is depicted in Table 2. Compounds 16±18
illustrate that long linear spacers are superior to short
restricted ones (19±21) and semi-rigid spacers of vari-

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H. Rueeger et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1175±1179
Table 2. SAR of the spacer
Compound
Spacer
IC50 (nM)a
28
Compound
Spacer
IC50 (nM)a
2.9
16
17
18
19b
HN-(CH2)6-NH
HN-(CH2)7-NH
HN-(CH2)8-NH
8 CGP71683A
44
46
23
24
25
710
110
16
4900
20
380
290
38
26
27
28
2.7
2.9
51
21
22c
aBinding anities to Y5-receptor subtype stable expressed in LM(tk-) cells (n=3±6), values determined at Novartis Pharma AG.
bRacemic.
cRacemic cis/trans ratio=4:1.
The best compounds of these series were selected for in
vivo studies and tested in the rat food deprivation model.11
Compound 8 was selected for further concept validation
studies based upon its activity and Y-type selectivity (hY5,
rY5, [IC50ÆSEM; nM] 2.9Æ0.16, 1.4Æ0.09 and hY1, hY2,
hY4 [IC50ÆSEM; nM] 8370Æ530, 1890Æ260, 5740Æ230).
Furthermore, 8 was active in the following functional
assays:11 the NPY-induced intracellular Ca2+ mobiliza-
tion (Kb=5.8Æ1.2 nM) and in an assay of the reversal of
NPY-induced inhibition of forskolin stimulated cAMP
production (Kb=1.9Æ0.6 nM) in LM(tk-) cells.
In summary, key pharmacophoric elements of hits
identi®ed by screening of biased libraries prepared in
solution and on solid support and 3-D-database mining
were combined and optimized. This resulted in the
design of 8 (CGP71683A), the ®rst selective, nanomolar
Y5 antagonist. This new compound helped to elucidate
the Y5-subtype involvement in mediating food intake
induced by NPY.11
Figure 1. Superimposition of 11h (in silver), 12g (in gold) and 8
(CGP71683A, in green).
substituent, whereas in the methyl-cyclohexyl spacer
series, this pocket is not used and a di€erent pair of
nitrogen atoms of the quinazoline moiety make up the
H-bond donor/acceptor principle.
Acknowledgements
The loss of hydrophobic interaction is probably com-
pensated by the additional hydrophobic substituent
attached at the sulfonamide.
The authors would like to thank S. Di Bello, U. Dies-
senbacher, P. Huber, F. Lugrin, M. Mele, D. Monna
and R. Wicki for their excellent technical assistance.

H. Rueeger et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1175±1179
1179
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