α-substituted n-(sulfonamido)alkyl-β-aminotetralins: Potent and selective neuropeptide Y Y5 receptor antagonists [2]

Full text of DOI:10.1021/jm990468g

346
J . Med. Chem. 2000, 43, 346-350
from arylalkylamines are reported to be sub-micromolar
r-Su bstitu ted
Y5 antagonists.22 Structurally related sulfonamides that
contain heterocyclic systems such as a series of 2,4-
diaminoquinazolines are being developed as well;23-26
the nanomolar Y5 antagonist 1 is reported to reduce
food consumption in animal models of feeding.27 In
addition, structurally diverse series of pyrazoles, ami-
nopyridines, and various amide derivatives have been
claimed as nanomolar Y5 receptor ligands.28-31
N-(Su lfon a m id o)a lk yl-â-a m in otetr a lin s:
P oten t a n d Selective Neu r op ep tid e Y Y5
Recep tor An ta gon ists
Mark A. Youngman,† J ames J . McNally,†
Timothy W. Lovenberg,‡ Allen B. Reitz,†
Nicole M. Willard,† Diane H. Nepomuceno,‡
Sandy J . Wilson,‡ J effrey J . Crooke,†
Daniel Rosenthal,† Anil H. Vaidya,† and
Scott L. Dax*,†
Drug Discovery, The R. W. J ohnson Pharmaceutical
Research Institute, Welsh and McKean Roads,
Spring House, Pennsylvania 19477, and
3210 Merryfield Row, San Diego, California 92121
Received September 16, 1999
Herein we report on a novel series of R-substituted
N-(sulfonamido)alkyl-â-aminotetralins and -â-amido-
tetralins that are among the most potent and selective
NPY Y5 receptor antagonists identified to date. Certain
members of this series possess good chemical and
metabolic stability along with high aqueous solubility
thus making these compounds extremely useful for
elucidating the physiological role of the Y5 receptor.
Furthermore, a prototypic compound was effective in
reducing food consumption in an ad libitum fasted rat
model of feeding.
In tr od u ction . Neuropeptide Y (NPY), first isolated
from porcine brain,1 is a powerful stimulant of food
intake.2-5 In landmark studies by Stanley and Leibow-
itz,4,5 injection of 100 ng of NPY into the hypothalamic
paraventricular nucleus of live rats caused satiated
animals to overeat. A dose of 1 µg induced animals to
consume, within 4 h, an amount of food approximately
equivalent to the normal daily intake in an age-
matched, vehicle-treated group.
Endogenous receptors that bind NPY and related
peptides are members of the superfamily of G-protein-
coupled receptors, and most NPY receptors have been
cloned and expressed in viable functional cell lines. Five
different NPY receptor subtypes (Y1, Y2, Y4(PP), Y5,
and Y6 (formerly designated as a Y5 receptor and
expressed as a pseudogene)) are recognized today based
upon binding profile, pharmacology, and composition if
identity is known.6-16 Some studies have suggested that
an “atypical Y1” receptor is responsible for invoking
NPY-stimulated food consumption17 in animals. For
example, the NPY fragment NPY2-36 has been shown
to be a potent inducer of feeding despite poor binding
at the Y1 receptor.18 In contrast, a potent and selective
Y1 agonist has been reported to be ineffective at
stimulating feeding in animals,19 whereas the Y5 recep-
tor agonist, [D-Trp32]NPY, stimulated food intake when
injected into the hypothalamus of rats.20 Since [D-Trp32]-
NPY appears to be a full agonist of the Y5 receptor with
no appreciable Y1 activity, the Y5 receptor is hypoth-
esized to be at least partially responsible for the feeding
response. Furthermore, antisense oligodeoxynucleotides
to the Y5 receptor are reported to reduce food consump-
tion in animal models of feeding.21 Accordingly, com-
pounds that antagonize the Y5 receptor should be
effective in inhibiting food intake, particularly that
stimulated by NPY.
Ch em istr y. Screening of our in-house chemical li-
brary identified novel aminotetralin 2 as having low
micromolar binding affinity for the human Y5 recep-
tor.32 With this lead in-hand, we chose to construct the
R-substituted â-aminotetralin nucleus and carry out
acylations and alkylations of the nitrogen center in the
hope of improving receptor binding affinity. Accordingly,
â-tetralone 3 was reacted with pyrrolidine to give the
corresponding enamine which underwent alkylation
upon reaction with benzyl or alkyl halides to afford
iminium salt 4. Hydrolysis generated the corresponding
tetralone 5 which was subjected to reductive amination
to produce cis-R-substituted â-aminotetralin 6 (along
with traces of the trans-product). Heteroaryl groups
were introduced via condensation of â-tetralone 3 with
heteroarylcarboxaldehydes in the presence of piperidine,
followed by hydrogenolysis and/or reductive amination.
Following these synthetic routes, a host of racemic
R-substituted â-aminotetralins containing aralkyl, het-
eroaralkyl, alkyl, or alkenyl appendages were readily
prepared (Scheme 1).
With this premise in mind, a variety of small molecule
Y5 antagonists have been developed within the past
years. Arylsulfonamides and arylsulfamides derived
* To whom correspondence should be addressed. Tel: 215-628-5211.
In keeping with the general structural features of our
lead compound 2 and finding that aminotetralins lack-
ing N-substitution are inactive in terms of Y5 receptor
Fax: 215-628-4985. E-mail: sdax@prius.jnj.com.
† Pennsylvania.
‡ California.
10.1021/jm990468g CCC: $19.00 © 2000 American Chemical Society
Published on Web 01/19/2000

Communications to the Editor
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 3 347
Sch em e 1. Synthesis of cis-R-Substituted
â-Aminotetralins
Similarly, an R-aminopentyl scaffold was introduced via
reaction of aminotetralin 6 with sulfonylated lysine.
Resu lts a n d Discu ssion . R-Substituted N-(sulfon-
amido)alkyl-â-aminotetralins 8 and -â-amidotetralins 7
were evaluated for binding affinity to the human NPY
Y5 receptor using a stably transfected HEK293 cell line
and measuring competitive inhibition of binding of [125I]-
PYY (Table 1).32 Replacement of the N-phenethyl sub-
stituent found in the lead compound 2 (IC50 ) 910 (
153 nM, n ) 4) with (arylsulfonamido)alkyl groups
afforded aminotetralins 8 with enhanced binding affin-
ity (e.g., 8a : IC50 ) 443 ( 155 nM). The length of the
hydrocarbon tether (L group) was found to be important
indicating that proper spacing between the aminote-
tralin nucleus and sulfonamide group is needed for
potent binding. The optimum distance was demon-
strated to be between five and six carbon atoms;
compounds with shorter or longer alkyl tethers were
poorly active (not shown).
In general, R-aralkylaminotetralin sulfonamides con-
taining bulky hydrocarbon R2 substituents such as
phenyl (8a ), substituted phenyl, and naphthyl (not
shown) displayed weak receptor affinity and were
typically plagued by poor physical properties (low aque-
ous solubility, high lipophilicity). For this reason, we
chose to introduce smaller hydrocarbon groups and
various heterocyclic systems. In particular, pyridine
substituents afforded aminotetralins with enhanced
solubility and the 3-pyridyl congeners maintained good
affinity for the Y5 receptor (8b: IC50 ) 337 nM). Rather
surprisingly, replacement of the pyridyl (R2) substituent
with a simple allyl group also gave potent compounds.
A dramatic increase in potency was observed in going
from naphthylsulfonamides to the smaller phenyl and
substituted phenyl analogues (8d : IC50 ) 10 nM).
Substitution on the ortho position of the benzene-
sulfonamide was tolerated; for example, electron-
withdrawing groups such as fluoro gave equipotent
compounds. However, the introduction of substituents
onto other positions of the benzenesulfonamide dimin-
ished binding affinity.
binding, we decided to tether terminal arylsulfonamido
groups onto the aminotetralin nitrogen center. We chose
to utilize Ω-sulfonamidocarboxylic acids derived from
simple aliphatic amino acids to see if there was any
preferred spacing between the aminotetralin ring sys-
tem and the arylsulfonamido group. We also investi-
gated constrained versions of the tether (L) thus leading
to the trans-methyl(cyclohexyl)methyl scaffold present
in other series of Y5 antagonists.22,25 Using known
peptide coupling protocols (i.e., HBTU/DMF), amino-
tetralins 6 underwent acylation to afford the corre-
sponding amide adducts 7 which were subsequently
reduced to aminotetralin sulfonamides 8 (Scheme 2).
We tailored our strategy to include scaffolds derived
from lysine and cyclic amines in an attempt to lower
lipophilicity and enhance aqueous solubility. Accord-
ingly, N-Boc-protected aminopyrrolidines and aminopi-
peridines were reacted with ethyl bromoacetate and
subsequently hydrolyzed to give the desired pyrrolidi-
nyl- and piperidinylacetic acids. These substrates coupled
smoothly with aminotetralins 6 to give the correspond-
ing amides 9. Treatment with acid removed the Boc
group giving intermediates 10 which were sulfonylated
to the desired acetylated aminotetralins 7 (Scheme 2).
An additional enhancement of receptor binding was
achieved by examining aminotetralin substituents (R1).
In general, substitution onto the aryl ring of the tetralin
system was well-tolerated. However, the C-6 center was
Sch em e 2. Synthesis of R-Substituted N-(Sulfonamido)alkyl-â-aminotetralins 8 and -â-Amidotetralins 7

348 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 3
Communications to the Editor
Ta ble 1. Y5 Receptor Affinities of cis-R-Substituted
â-Aminotetralin Sulfonamides 8 (Y ) -CH2-) and
â-Amidotetralins 7 (Y ) CdO)
mg/mL) and were problematic in terms of isolating well-
characterized salts suitable for dosing in animals. We
attributed these undesired properties to the presence
of the cycloalkyl tether, and for this reason, we inves-
tigated amine-containing variations which would be
expected to impart lower lipophilicity and possibly
enhance solubility.
To our satisfaction, the incorporation of aminopiper-
idinyl-, aminopyrrolidinyl-, or aminopentyl-derived scaf-
folds resulted in a slight augmentation of binding
affinity (7k : IC50 ) 10 nM, 7n : IC50 ) 5 nM vs 7e: IC50
) 40 nM; 8p : IC50 ) 1 nM vs 8h : IC50 ) 7 nM), and
water solubility was improved as well (7n : >50 mg/mL;
8p : >50 mg/mL). Interestingly, â-amidotetralins con-
taining these tethers are very potent Y5 receptor
antagonists without the need to reduce to the amine.
This finding differentiates our series of compounds from
other known sulfonamide-based Y5 receptor antagonists
and may be indicative of a unique binding motif with
the receptor.
Chromatographic separation of racemic 8i using a
chiral stationary phase provided the individual enan-
tiomers, and it was demonstrated that essentially all
of the Y5 affinity resided in one enantiomer (8i ent-1:
IC50 ) 439 nM, [R]D ) +35.9°, c ) 0.81 g/dL (MeOH) vs
8i ent-2: IC50 ) 12 nM, [R]D ) -35.1°, c ) 0.67 g/dL
(MeOH)). The â-amidotetralins containing aminopentyl
and aminopyrrolidinyl scaffolds could be derived from
lysine and aminopyrrolidines of known stereochemical
configurations, and thus sets of diastereomers were
readily obtained via chromatographic separation. Upon
separation, a single diastereomer was shown to be
responsible for Y5 receptor affinity (7o diast-1: IC50
)
22 nM vs 7o diast-2: IC50 ) 869 nM (not shown)), and
in one case, a single pure diastereomer had exquisite
affinity for the Y5 receptor (8p : IC50 ) 1 nM).
Receptology studies of members of this series reveal
that R-substituted N-(sulfonamido)alkyl-â-aminotetra-
lins and -â-amidotetralins are highly selective Y5
antagonists. A panel of compounds (8i,p and 7n ) did
not stimulate binding of labeled GTPγS in a Bowes
melanoma cell line transfected with the human Y5
receptor but, in the presence of PYY, was able to inhibit
incorporation of label. Several compounds of this series
(e.g., 8g,i) were screened against over 30 G-protein-
coupled receptors and ion channels and found to have
only weak (g1 µM) affinity for the central muscarinic
receptor and the L-type calcium channel. Members of
this series are also Y receptor subtype specific and do
not bind to either Y1 or Y2 receptors in radioligand
([125I]PYY) displacement assays (e.g., 8g: 0% vs hY1,
0% vs hY2; 8i: 0% vs hY1, 30% vs hY2 @ 10 µM). In
vitro metabolism studies reveal that these aminotetra-
lins possess good stability when incubated with human
(and rat) S9 hepatic fractions (8g: 92% unchanged and
8i: 95% unchanged after 1 h).
a
b
Compound is racemic mixture. Compound is mixture of
diastereomers; chiral center of known configuration is shown (L
column). c Compound is single pure diastereomer of unknown
absolute configuration; chiral center of known configuration is
shown (L column). NPY (human) was purchased from Bachem
(Torrance, CA).
a preferred site and the hydroxy group was an excep-
tional substituent that routinely gave a severalfold
increase in potency compared to methoxy and fluoro
analogues (8h : IC50 ) 7 nM vs 8g: IC50 ) 23 nM and
8f: IC50 ) 19 nM; 8j: IC50 ) 5 nM vs 8i: IC50 ) 21
nM). Combining these structural features routinely gave
R-(3-pyridylmethyl)-â-aminotetralin-derived sulfona-
mides that exhibited nanomolar binding affinity for the
Y5 receptor.
Although the corresponding amides displayed good
affinity (7i: IC50 ) 75 nM; 7e: IC50 ) 40 nM; 7f: IC50
) 12 nM; 7g: IC50 ) 11 nM), these compounds suffered
from poor aqueous solubility (7i: <1 mg/mL; 7e-g: e10
A prototypic compound (8i) was evaluated in an
animal model of feeding measuring food consumption
as an endpoint.33 Drug-treated, fasted male rats con-
sumed statistically significant less chow than vehicle
control group over a 6-h period (Table 2), suggesting that
antagonism of the Y5 receptor can suppress feeding
under certain conditions (i.e., food deprivation). Ad-
ditional studies are underway to determine if this effect

Communications to the Editor
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 3 349
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Model of Feeding
cumulative food consumption (g)
dose
(mg/kg)
0-2 h
0-4 h
0-6 h
2-6 h
compd (no. rats) (% change) (% change) (% change) (% change)
vehicle
ip
9.63
13.3
20.9
11.3
PEG-200 N ) 8
8i
30, ip
4.88
8.00
13.6
8.75
N ) 8
(-49%)
(-40%)
(-35%)
(-22%)
p ) 0.003 p ) 0.010 p ) 0.025 p ) 0.252
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Ack n ow led gm en t. We thank Cheryl Kordik, Carlos
Plata-Salama´n, Richard Shank, and Wu-Nan Wu for
their help and input.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
tocols for the synthesis of compounds 8j,p and 7l, intermedi-
ates supported with NMR and MS data, and high-resolution
and elemental analyses (C, H, N) of all compounds in Table 1.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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350 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 3
Communications to the Editor
frozen at -80 °C until needed. Frozen pellets were homogenized
with a polytron at full speed for 12 s in a homogenization buffer
(20 mM Tris HCl, 5 mM EDTA, pH 7.4). Homogenates were
centrifuged for 5 min at 4 °C at 200g and the supernatants were
transferred to corex tubes and centrifuged for 25 min at 28000g.
The pellets were resuspended in binding medium (20 mM
HEPES, 10 mM NaCl, 0.22 mM KH2PO4, 1.3 mM CaCl2, 0.8 mM
MgSO4, pH 7.4). Membranes were kept on ice until use.
Com p etition Bin d in g Assa y. Aminotetralin sulfonamides and
â-amidotetralins described herein compete with [125I]PYY for
binding to cell membranes containing the human Y5 receptor.
The less [125I]PYY bound to the membranes implies that a
compound is a good inhibitor (competitor). Bound [125I]PYY is
determined by centrifugation of membranes, aspirating super-
natant, washing away residual [125I]PYY, and subsequently
counting the bound sample in a γ-counter. Aminotetralin sul-
fonamides 8 and â-amidotetralins 7 were prepared as 10× stocks
in binding buffer and added to assay tubes (RIA vials, Sarstedt).
Twenty (20) µL of each 10× compound stock was transferred
via pipet into separate vials along with 80 µL of [125I]PYY (NEN
cat# NEX240), which was diluted to a concentration of 200 pM
in 0.25% BSA in binding buffer (final concentration of [125I]PYY
was 80 pM). To each tube was added 100 µL of membranes and
the mixture was agitated by pipeting. Samples were incubated
for 1 h at room temperature. Aluminum cast plates (Sarstedt)
containing the vials were then centrifuged for 10 min at 3200
nonspecific binding from the test samples (containing compound
7 or 8), taking these counts and dividing by total binding, and
multiplying by 100. Inhibitory concentration values (IC50) of
compounds were calculated by obtaining percent inhibition of
[
125I]PYY binding values at different concentrations and using
a graphing program such as GraphPad Prism to calculate the
concentration of test compound that inhibits 50% of [125I]PYY
binding.
(33) Fasted male Long-Evans rats (180-200 g) were housed individu-
ally and maintained on a once-a-day feeding schedule (10 a.m.
to 4 p.m.) for 5 days following quarantine to allow the animals
to acclimate to feeding on powdered chow (#5002 PMI Certified
Rodent Meal) during the allotted time. The chow was made
available in an open jar, anchored in the cage by a wire, with a
metal follower covering the food to minimize spillage. Water was
available ad libitum. Animals were fasted for 18 h prior to
testing. At the end of the fasting period, animals were admin-
istered compound 7 or 8 or vehicle. Vehicle and test compounds
were administered 30 min prior to the experiment and given
intraperitoneally (1 mL/kg). The test compound 7 or 8 was
individually administered intraperitoneally as a solution or
suspension in PEG 200; compound concentrations typically
ranged from 1-100 mg/kg, preferably from 10-30 mg/kg. Food
intake was measured at 2, 4, and 6 h after administration by
weighing the special jar containing the food before the experi-
ment and at the specified times. Percent reduction of food
consumption was calculated by subtracting the grams of food
consumed by the treated group from the grams of food consumed
by the control group, divided by the grams of food consumed by
the control group, multiplied by 100.
rpm in
a Sorvall RT6000 and the supernatant was then
aspirated. To each vial 400 µL of PBS was added followed by
aspiration again. Vials were put in carrier polypropylene 12 ×
75 tubes and counted in a γ-counter (Packard). Nonspecific
binding was determined in the presence of 300 nM NPY. Percent
inhibition of [125I]PYY binding was calculated by subtracting
J M990468G