Potent and Selective 1,2,3-Trisubstituted Indole NPY Y-1 Antagonists

Full text of DOI:10.1021/jm970512x

3712
J . Med. Chem. 1997, 40, 3712-3714
P oten t a n d Selective 1,2,3-Tr isu bstitu ted
In d ole NP Y Y-1 An ta gon ists
Philip A. Hipskind,* Karen L. Lobb, J ames A. Nixon,
Thomas C. Britton, Robert F. Bruns, J ohn Catlow,
Donna K. Dieckman-McGinty,
Susan L. Gackenheimer, Bruce D. Gitter,
Smriti Iyengar, Douglas A. Schober,
Rosa M. A. Simmons, Steve Swanson,
Hamideh Zarrinmayeh, Dennis M. Zimmerman, and
Donald R. Gehlert
Lilly Research Laboratories, A Division of Eli Lilly and
Company, Lilly Corporate Center,
Indianapolis, Indiana 46285
Received August 4, 1997
Neuropeptide Y (NPY) was originally isolated from
extracts of porcine brain and is named for the presence
of an N-terminal tyrosine (tyr ) “Y”) and a C-terminal
tyrosine amide. NPY is a 36 amino acid peptide and a
member of the family of neurotransmitter peptides that
also includes peptide YY (PYY) and pancreatic polypep-
tide (PP).1 NPY is the most abundant peptide neu-
rotransmitter in the brain, and its receptors are promi-
nent in both the central nervous system and peripheral
tissues.2,3 While several NPY receptor subtypes have
been characterized at the molecular level (Y1, Y2, Y4,
Y5, and Y6), the various pharmacological responses of
NPY have not, in many cases, been definitively ascribed
to a particular subtype.4 However, based on NPY
physiological responses and anatomical localization,
NPY has been implicated in a variety of disorders
including obesity and diabetes.5-11
One of the fundamental difficulties in defining the
functional roles of NPY has been the absence of specific
receptor ligands. The synthesis of peptide analogs or
chimeric peptides provided selective agonists, but few
useful peptide antagonists are available. Over the last
several years, nonpeptidyl NPY Y1 receptor antagonists
(BIBP3226,12,13 SR120819A,14 and PD16017015) have
appeared in the literature. While these NPY Y1 tools
do exist, the description of unique NPY Y1 receptor
subtype pharmacology has been ambiguous due to lack
of potency, selectivity, or in vivo efficacy of these agents.
Considerable interest remains in the discovery of selec-
tive Y1 antagonists. Herein we disclose a totally novel
series of selective and potent NPY Y1 antagonists that
should help elucidate of the role of the Y1 receptor
subtype.
Biased library screening and follow-up similarity
searching of the Lilly compound files uncovered the
trisubstituted indole 1 (Ki ) 2.1 µM). On the basis of
this low molecular weight lead, a series of trisubstituted
indoles were pursued using traditional medicinal chem-
istry. In this paper the effects of substituent pattern
modifications at N-1, C-2, and C-3 will be reported. In
addition to chemical synthesis, radioligand binding
affinities for the cloned human Y1 receptor, in vitro
functional activity, and selectivity data verses Y1, Y2,
Y4 and Y5 receptor lines will be reported. Initial in vivo
data showing antagonism by S-18 of the feeding induced
by intracerebroventricularly injected NPY is also pre-
sented.
Ch em ist r y. Synthesis of compounds 1 and 10
through 18 was accomplished as described in Scheme
1. Deprotonation of 2 with sodium hydride followed by
alkylation with the appropriate alkyl iodide or bromide
gave 3. Reduction with lithium aluminum hydride
followed by nucleophilic aromatic substitution of a
fluorobenzene yielded 5. Alternatively the aryloxy
group could be installed via Mitsunobu reaction of 4 and
the appropriate phenol. Mannich reaction of 5 using
paraformaldehyde and the appropriate amine gave 6.
Alternatively, 5 could be treated with oxalyl chloride
in ether, followed by an amine to yield compounds such
as 7. Reduction of 7 with borane-dimethyl sulfide
produced compound 8 in reasonable yield. Finally,
compound 5 could also be treated with bromoacetyl
bromide and powdered lithium carbonate in diethyl
ether under ultrasound conditions, followed by treat-
ment with the desired amine to give 9 in modest yield.
Deprotection of tritylamino or tert-butyl carbamate
groups, if necessary (see compounds 17, S-18, and R-18),
to yield free amino functionalities was accomplished via
standard techniques. Chiral alkyl bromides necessary
for compounds S-18 and R-18 were prepared via clas-
sical resolution techniques, and enantiomeric purities
were verified (>99% ee) via intermediate Mosher amide
* Author to whom all correspondence should be addressed. (v) (317)
276-8067. (f) (317) 277-1125. (e-mail) hipskind philip a@lilly.com.
S0022-2623(97)00512-8 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 23 3713
Sch em e 1.a General Synthetic Strategy for 1,2,3-Trisubstituted Indoles
a
Reagents: (a) NaH, R1I or R1Br, DMF, 0 °C to room temperature; (b) LAH, THF, 0 °C to room temperature; (c) NaH, ArF, DMF, 80
°C; (d) piperidine, paraformaldehyde, concentrated aqueous HCl, NaOAc, EtOAc; (e) oxalyl chloride, diethyl ether; (f) amine, THF; (g)
borane-dimethyl sulfide complex, THF; (h) bromoacetyl bromide, Li2CO3, diethyl ether; (i) amine, THF.
Ta ble 1. Chemical Structures and Binding Affinities at Cloned
NPY-1 Receptors Expressed in AV-12 Cells
lead to improvement, further examination of the C-3
structure-activity relationships proved to be more
fruitful. Studies of the substitution pattern around the
C-3 piperidine ring revealed that additional basic sub-
stituents at the 4-position of this ring could improve
affinity at the Y1 receptor significantly. Compound 12
was an early example wherein the affinity improved
nearly 4-fold. Optimization of the C-3 chain length was
achieved with compound 13 (93 nM).
During the synthesis of 13, dicarbonyl compounds
similar to 7 were employed as synthetic intermediates.
Y1 binding affinity Ki,
mean ( SEM (nM)
compound
X
R3
Examination of their binding properties revealed they
possessed reasonable affinity for the Y1 receptor (14,
0.44 µM). This variation of affinity based on differential
oxidation states of the C-3 linker (13 vs 14) piqued our
interest in other carbonyl variants that might act as
acyclic conformational restraints at C-3. Among those
compounds examined, 15 (26 nM) was uncovered,
representing a 100-fold improvement over the original
lead structure 1.
BIBP3226
1
NA
CH2
NA
H
4.6 ( 0.3
2315 ( 193
2875 ( 75
559 ( 83
93 ( 4
440 ( 20
26 ( 1.8
11
12
13
14
15
CH2CH2
CH2
CH2CH2
COCO
COCH2
H
1-piperidinyl
1-piperidinyl
1-piperidinyl
1-piperidinyl
formation followed by capillary GC analysis. Absolute
configurations of intermediates were determined via
X-ray crystallographic analysis of mandelic acid salts.
Resu lts a n d Discu ssion . A Topliss decision analy-
sis of the C-2 side chain SAR lead to a modest improve-
ment in activity over the 4-chloro substitution pattern
with the 2,4-dichloro compound 10 (1.3 µM). All other
substitution patterns lead to derivatives of lower affin-
ity. For simplicity, the remaining structure-activity
study is exemplified as the 4-monochloro derivative.
Structure-activity relationships for C-3 modifications
are summarized in Table 1. Early concerns regarding
the stability of “gramine” structures 6 motivated a
desire toward additional C-3 modifications. Homologa-
tion of the C-3 side chain gave compound 11 (2.9 µM).
While additional efforts toward higher homologs did not
Concurrent with the structure-activity studies at
C-3, an analysis of the N-1 SAR was pursued. Early
on in our efforts, it was hypothesized that additional
basic substituents might further improve the potency
of this series. This notion was supported by the
reported importance of the -Arg33-X34-Arg35- substruc-
ture in the carboxamide terminus of NPY.17 The initial
example of this type of compound was 16 which exhib-
ited a 6-fold improvement in affinity over 12. Optimal
side chains for the N-1 position eventually proved to be
alkylpiperidines with a free N-H. Combining this with
our earlier findings within the C-2 and C-3 structure-
activity studies resulted in the discovery of compounds
17 (1.3 nM) and S-18 (0.75 nM). Apparently little

3714 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 23
Communications to the Editor
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails and spectroscopic information (15 pages). Ordering
information is given on any current masthead page.
stereodifferentiation occurs at the binding site on the
receptor as the opposite enantiomer, R-18, was only
2-fold less potent.
In addition to the Y1 binding assay, the binding
affinity of all compounds at cloned human Y2, Y4, and
Y5 receptors was examined. Affinities (Ki’s) at these
subtypes were in all cases greater than 10 µM. Further
compound S-18 reversed NPY-induced inhibition of
forskolin-stimulated cAMP (Ki ) 1.8 nM) and inhibited
NPY-induced intracellular Ca2+ mobilization (Ki ) 3.2
nM) in SK-N-MC cells.16 All compounds in this series
were found to be antagonists. No partial or full agonism
was observed.
Refer en ces
(1) For a review, see: Hipskind, P. A.; Gehlert, D. R. Neuropeptide
Y: At the dawn of subtype selective antagonists. Annu. Rep.
Med. Chem. 1996, 31, 1-10.
(2) Allen, Y. S.; Adrain, T. E.; Allen, J . M.; Tatemoto, K.; Crow, J .;
Bloom, S. R.; Polak, J . M. Neuropeptide Y distribution in the
rat brain. Science 1983, 221, 877-879.
(3) Wahlestedt, C.; Reis, D. J . Neuropeptide Y-related peptides and
their receptors. Are the receptors potential therapeutic drug
targets? Annu. Rev. Pharmacol. Toxicol. 1993, 33, 309-52.
(4) Gehlert, D. R.; Hipskind, P. A. Neuropeptide Y Antagonists:
Clinical Promise and Recent Developments. Curr. Pharm. Des.
1995, 1, 295-304.
The ability of S-18 to antagonize an in vivo NPY-
induced (230 pmol, icv) food consumption effect was
examined. When injected into the lateral ventricle of
mice, very low doses of NPY (69-2300 pmol, icv) rapidly
produced a specific and robust dose-dependent increase
in food intake which peaks within 30 min of the injection
and lasted for approximately 90 min. For example, a
submaximal dose of NPY (230 pmol, icv), elicits a 200%
increase in time spent feeding over vehicle control mice.
The ability of S-18 to block this central NPY-induced
food consumption was tested by co-administering S-18
with NPY (230 pmol, icv) into the lateral ventricle. S-18
was found to block the increase in food consumption
elicited by NPY [ED50 ) 17 nmol (lower and upper
confidence limits of 11-26 nmol)] in a dose dependent
manner. Moreover, at doses found to antagonize NPY-
induced feeding, icv-administered S-18 did not exhibit
neuromuscular dysfunction as measured by the hori-
zontal screen test or general behavior malaise. Thus,
the antagonism of central NPY-induced feeding behavior
by S-18 appears to be mediated by the Y-1 receptor.
Unfortunately serum levels of S-18 upon oral or sub-
cutaneous administration were inadequate to evaluate
the compound systemically in these models.
Biased library screening at cloned human NPY Y-1
receptors followed by a traditional medicinal chemistry
strategy produced a novel series of 1,2,3-trisubstituted
indole NPY Y1 antagonists. Structure-activity studies
at N-1, C-2, and C-3 of the indole nucleus were exam-
ined, and the importance of a distally opposed diamine
motif (N-1 and C-3 amine containing side chains) as well
as homologation and optimal oxidation of the C-3 side
chain was delineated. This resulted in the discovery of
S-18 (LY357897), the first selective, subnanomolar NPY
Y1 antagonist. A more detailed description of our
investigations within this class as well as complete
pharmacological characterization of members of this and
related series will be reported in subsequent papers.
(5) Clark, J . T.; Kalra, P. S.; Crowley, W. R.; Kalra, S. P. Neuropep-
tide Y and human pancreatic polypeptide stimulate feeding
behavior in rats. Endocrinology 1984, 115, 427-429.
(6) Clark, J . T.; Sahu, A.; Kalra, P. S.; Balasubramaniam, A.; Kalra,
S. P. Neuropeptide Y (NPY)-induced feeding behavior in female
rats: comparison with human NPY ([Met17]NPY), NPY analog
([norLeu4]NPY) and peptide YY. Regul. Pept. 1987, 17, 31-39.
(7) Kalra, S. P.; Clark, J . T.; Sahu, A.; Dube, M. G.; Kalra, P. S.
Control of feeding and sexual behaviors by neuropeptide Y:
physiological implications. Synapse 1988, 2, 254-257.
(8) Stanley, B. G.; Kyrkouli, S. E.; Lampert, S.; Leibowitz, S. F.
Neuropeptide Y chronically injected into the hypothalamus: a
powerful neurochemical inducer of hyperphagia and obesity.
Peptides 1986, 7, 1189-1192.
(9) Stanley, B. G.; Magdalin, W.; Seirafi, A.; Nguyen, M. M.;
Leibowitz, S. F. Evidence for neuropeptide Y mediation of eating
produced by food deprivation and for a variant of the Y1 receptor
mediating this peptide’s effect. Peptides 1992, 13, 581-587.
(10) Stanley, B. G.; Leibowitz, S. F. Neuropeptide Y: stimulation of
feeding and drinking by injection into the paraventricular
nucleus. Life Sci. 1984, 35, 2635-2642.
(11) Gehlert, D. R.; Goldstein, D. J .; Hipskind, P. A. Treating obesity
in the 21st century. Annu. Rep. Med. Chem. 1996, 31, 201-
210.
(12) Doods, H. N.; Wienen, W.; Entzeroth, M.; Rudolf, K.; Eberlein,
W.; Engel, W.; Wieland, H. A. Pharmacological characterization
of the selective nonpeptide neuropeptide-Y Y1 receptor antago-
nist BIBP-3226. J . Pharmacol. Exp. Ther. 1995, 275, 136-142.
(13) Rudolf, K.; Eberlein, W.; Engel, W.; Wieland, H. A.; Willim, K.
D.; Entzeroth, M.; Wienen, W.; Beck-Sickinger, A. G.; Doods, H.
N. The first highly potent and selective nonpeptide neuropep-
tide-Y Y-1-receptor antagonist - BIBP3226. Eur. J . Pharmacol.
1994, 271, R11-R13.
(14) Serradeil-Le Gal, C.; Valeet, G.; Rouby, P. E.; Pellet, A.; Oury-
Donat, F.; Brossard, G.; Lespy, L.; Marty, E.; Neliat, G.; de
Cointet, P.; Maffrand, J . P.; LeFur, G. SR120819A, an orally-
active and selective neuropeptide Y Y1 receptor antagonist.
FEBS Lett. 1995, 362, 192-196.
(15) Wright, J .; Bolton, G.; Creswell, M.; Downing, D.; Georgic, L.;
Heffner, T.; Hodges, J .; MacKenzie, R.; Wise, L. 8-Amino-6-(aryl-
sulfonyl)-5-nitroquinolines: novel nonpeptide neuropeptide Y1
receptor antagonists. Bioorg. Med. Chem. Lett. 1996, 6, 1809.
(16) Daniels, A. J .; Lazarowski, E. R.; Mathews, J . E.; Lapetina, E.
G. Neuropeptide-Y mobilize intracellular Ca2+
and increases
inositol phosphate production in human erythroleukemia cells.
Biochem. Biophys. Res. Commun. 1989, 165, 1138-1144.
(17) Beck-Sickinger, A. G.; J ung, G. Structure-activity relationships
of neuropeptide Y analogs with respect to Y1 and Y2 receptors.
Biopolymers 1995, 37, 123-42.
J M970512X