A novel series of piperidin-4-yl-1,3-dihydroindol-2-ones as agonist and antagonist ligands at the nociceptin receptor

Article abstract of DOI:10.1021/jm034249d

A series of N-(4-piperidinyl)-2-indolinones were discovered as a new structural class of nociceptin receptor (NOP) ligands. Unlike other previously reported classes of NOP receptor ligands, modifications of the piperidine N substituents afforded both pote

Full text of DOI:10.1021/jm034249d

J . Med. Chem. 2004, 47, 2973-2976
2973
Ch a r t 1. Structures of Reported NOP Agonist and
Antagonist Ligands
A Novel Ser ies of
P ip er id in -4-yl-1,3-Dih yd r oin d ol-2-on es a s
Agon ist a n d An ta gon ist Liga n d s a t th e
Nocicep tin Recep tor
Nurulain T. Zaveri,*,§ Faming J iang,§ Cris M. Olsen,§
J effrey R. Deschamps,† Damon Parrish,†
Willma Polgar,§ and Lawrence Toll§
Biosciences Division, SRI International,
333 Ravenswood Avenue, Menlo Park, California 94025,
and Laboratory for the Structure of Matter, Code 6030,
Naval Research Laboratory, Washington, D.C. 20375
Received December 10, 2003
molecule antagonists of NOP have been shown to
potentiate analgesia in tolerant mice.9
Abstr a ct: A series of N-(4-piperidinyl)-2-indolinones were
discovered as a new structural class of nociceptin receptor
(NOP) ligands. Unlike other previously reported classes of
NOP receptor ligands, modifications of the piperidine N
substituents afforded both potent agonists and antagonists,
with modest selectivities over other opioid receptors. The SAR
revealed in this new series will provide important insights for
the development of pharmacophores for agonist and antagonist
actions at the NOP receptor.
Several peptide and small-molecule NOP ligands have
now been reported.10 Among the small-molecule ligands,
Roche has reported an extensive series of NOP agonists
based on the spirodecanone (e.g., Ro 64-6198) and
hexahydropyrrolopyrrole (I) heterocyclic moieties (Chart
1).11 NOP antagonists such as the benzimidazolone
J 113397,12 the quinoline J TC-801,13 and recently the
phenylpiperidine SB-6121119a (Chart 1) have also been
reported and pharmacologically characterized. Except
for J TC-801, almost all small-molecule ligands contain
a common central piperidine core, with a 4-position
heterocyclic moiety and a lipophilic group on the pip-
eridine nitrogen.10 Despite the extensive series of ago-
nists and antagonists studied, there is no clear under-
standing about the pharmacophoric features that confer
NOP agonist or antagonist activity, or selectivity versus
opioid receptors. Furthermore, among the different
classes of ligands reported thus far, only agonists or only
antagonists have been reported within the same struc-
tural class. These series therefore do not offer much
insight for the rational design of specific NOP agonists
or antagonists at the NOP receptor.
We report a new series of NOP ligands based on a
1,3-dihydroindol-2-one heterocyclic scaffold. This series
is particularly interesting because subtle structural
changes in the nature of the piperidine N-1 substituent
resulted in converting potent antagonists into potent
agonists with modest selectivities. Thus, unlike the
previously reported series of NOP ligands, this new
series of indolinone ligands produced both potent NOP
agonists and antagonists within the same structural
series.
The nociceptin receptor (NOP receptor, previously
known as the opioid receptor-like receptor ORL1) was
discovered in 1994 because of its homology to the opioid
receptors.1 Interestingly, this fourth member of the
opioid receptor family did not bind classical opioids with
appreciable affinity. Soon after, two groups indepen-
dently identified its endogenous ligand, a heptadeca-
peptide named nociceptin2 or orphanin FQ (N/OFQ).3
Since then, the physiological role of the NOP receptor
and its ligand N/OFQ has been the focus of intense
research. Although both the NOP receptor and its ligand
share significant homology with the classical opioid
receptors and their ligands, none of the mature experi-
ence with the opioid pharmacology can be brought to
bear on the study of the NOP-N/OFQ system because
none of the known opioid ligands or synthetic opiates
bind appreciably to the NOP receptor.
The NOP-N/OFQ system has been shown to be
involved in pain and analgesia, anxiety, learning and
memory, tolerance development, and reward pathways.4
The ligand N/OFQ has been shown to have a potent
anxiolytic effect in rodent models,5 inhibits release of
serotonin and dopamine in reward pathways,6 and
blocks conditioned place preference to morphine,7 sug-
gesting a role for NOP agonists as anxiolytics and drug
abuse treatments. Studies in NOP -/- mice showed
that they exhibited improved memory and attention8a,b
and reduced tolerance development to morphine anal-
gesia,8c suggesting that NOP antagonists could be useful
for improving memory and modulating tolerance devel-
opment when given in combination with potent anal-
gesics such as morphine. Indeed, peptide and small-
Our discovery of this new class of ligands began with
the random screening hit 1a (Table 1), which had higher
affinity for the µ and κ opioid receptors. Modification of
the piperidine N-1 substituent of the lead compound
resulted in potent NOP ligands, a trend that has been
observed with other reported series of NOP ligands. We
first replaced the N-1 benzyl group of 1a with the
cyclooctylmethyl group to give 1b. This resulted in a
dramatic improvement in the affinity at the NOP
receptor and reduced the affinity for the opioid recep-
tors, resulting in a 38-fold selectivity versus the κ
* To whom correspondence should be addressed. Phone: 650-859-
6041. Fax: 650-859-3153. E-mail: nurulain.zaveri@sri.com.
§ SRI International.
† Naval Research Laboratory.
10.1021/jm034249d CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/04/2004

2974 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 12
Letters
Ta ble 1. Binding Affinities and Functional Activities of the New Dihydroindolinone Ligands
a
Receptor binding and [35S]GTPγS binding were conducted as described previously.18,20 Ki values were derived from the equation Ki
) IC50/(1 + [L]/Kd), where [L] (the concentration of the radioligand) is approximately 0.2, 1.9, 1.1, and 1.2 nM for NOP, µ, κ, and δ
binding, respectively. Each experiment was conducted at least twice in triplicate. An EC50 value of >10000 for [35S]GTPγS binding could
b
indicate either low affinity or lack of agonist activity. ND not determined. These ligands appear to have very low affinity for the δ opioid
d
receptor. c Ke ) [A]/(dose ratio - 1); [A] ) antagonist concentration. Agonist activities were confirmed with the cAMP assay, as described
in the Supporting Information.
receptor. When tested for functional activity in the [35S]-
GTPγS assay (described below), 1b completely lacked
agonist activity and was found to be an antagonist (Ke
) 15 nM). However, when the N-1 substituent was
replaced with a cyclooctyl (1c), it not only improved the
binding affinity at the NOP receptor but, to our surprise,
converted the compound into a potent agonist with an
EC50 of 20 nM in the [35S]GTPγS functional assay. 1c
also had a 21-fold and 30-fold selectivity versus µ and κ
receptors, respectively. Encouraged by the effect of this
subtle structural change in the functional activity of our
new ligands, we examined a range of lipophilic N-1
substituents to gain an understanding of the predict-
ability of the structural changes that could afford both
potent NOP agonists and antagonists. The different N-1
substituents examined are shown in Table 1 (1b-1q).
The ligands were synthesized as shown in Scheme 1.
Most ligands were synthesized by reductive amination
of the appropriate aldehyde or ketone with the common
intermediate N-1-(4-piperidinyl)-1,3-dihydroindol-2-one
5, which was obtained from 1a by debenzylation.
Initially, 1a was prepared by a literature method
starting from N-benzylpiperidone 2.14 However, for
larger scale preparations of 5, we resorted to the more
convenient route, starting from di-tert-butyl malonate
6, also reported in the literature.15 This route also
worked well for those target compounds where the
ketone synthons corresponding to the piperidine N

Letters
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 12 2975
Sch em e 1a
a
Reagents and conditions: (a) aniline, NaBH(OAc)3, AcOH, DCE, room temp, 3 h (90%); (b) Cl-CO-CH2-Cl, DCM, room temp, 16 h
(90%); (c) AlCl3, 160 °C, 3 h, (70%); (d) Pd-C, HCOOH, MeOH, 60 °C, 4 h (78%); (e) ketone or aldehyde, NaBH(OAc)3, AcOH, DCE, room
temp (10-70%); (f) (1) NaH/DMF-THF, 0 °C, 30 min; (2) o-nitrofluorobenzene, room temp, 2 h (83%); (g) Pd-C/H2, EtOAc, room temp,
3 h (100%); (h) N-1 substituted 4-piperidone, NaBH(OAc)3, AcOH, DCE, room temp, 3-16 h (75-90%); (i) pTsOH, toluene, reflux, 1-4 h
(70-90%); (j) MeI, acetone, room temp, 18 h (95%); (k) R-NH2, K2CO3, EtOH-H2O, reflux, 1 h (55-100%).
substitutent did not afford appreciable yields by direct
reductive aminations of 5. For 1c, 1e, 1h , 1j, and 1q,
the requisite ketones (corresponding to the R group on
the piperidine nitrogen) were first converted to the
amine using a standard amination procedure (NH4OAc,
NaCNBH3).16 The appropriate amine was then con-
densed with 1-ethyl-1-methyl-4-oxopiperidinium iodide
via an elimination-addition sequence17 to afford the
substituted piperidone 12, which was then condensed
with 8, followed by a decarboxylative cyclization to give
the target compounds 1c, 1e, 1h , 1j, and 1q. Most
aldehydes and ketones used were commercially avail-
able or could be easily accessed by Swern oxidation of
their hydroxyl precursors. In the cases of 1f,g and 1n ,o,
the cis and trans isomers were separated by chroma-
tography and their structures were confirmed by X-ray
crystallography. The endo and exo isomers 1k and 1l
were also separated by chromatography and analyzed
separately. The endo configuration of 1l was also
confirmed by X-ray crystallography.
These new indolinone-based compounds were tested
for binding affinity at human NOP receptors transfected
into Chinese hamster ovary (CHO) cells and at human
µ, δ, and κ opioid receptors also transfected into CHO
cells. Binding to NOP was conducted with [3H]N/OFQ,
as described previously.18 Binding to the opioid receptors
utilized the selective agonists [3H]DAMGO, [3H]Cl-
DPDPE, and [3H]U69593 for the µ, δ, and κ receptors,
respectively.19 Functional activity of these compounds
was determined by stimulation of [35S]GTPγS binding
to cell membranes19,20 and was confirmed with cAMP
inhibition assays for selected compounds 1b, 1c, and
1m .21 Binding affinities and functional activity are
shown in Table 1.
different structural classes have been reported for the
NOP receptor, no pharmacophore models for selectivity
or for agonist versus antagonist activity have been
proposed. We have been interested in defining struc-
tural requirements not only for selectivity but also for
efficacy at the NOP receptor. In our new series of
dihydroindolinone ligands, we observed that a subtle
structural change in the piperidine N-1 substituent
converted the NOP antagonist 1b to an agonist (1c). We
therefore explored the effects of the piperidine N-1
substituents on this new heterocyclic series by synthe-
sizing several analogues, 1b -q , containing lipophilic
piperidine N-1 substituents of different sizes.
In general, we find that saturated alicyclic or bicyclic
N-1 substitution affords ligands of higher affinity than
those containing aromatic character (1f,g versus 1d ,i,j).
Among the saturated N-1 substituents, potent agonist
ligands were obtained with the cyclooctyl (1c), decahy-
dronaphthyl (1f and 1g), bicyclooctyl (1m ), and 4-iso-
propylhexyl (1n ) groups. The tolerated size of the
saturated cyclic group is also limited because the
biscyclohexylmethyl-containing compound (1q) has no
affinity for the NOP receptor. Interestingly, the decahy-
dronaphthyl and 4-isopropylhexyl groups on the indoli-
none scaffold did not afford the same selectivity (∼40-
fold versus κ) versus the opioid receptors, as seen when
the same N-1 substituents were on the hexahydropyr-
rolopyrrole scaffold (∼1000-fold) reported by Roche (I,
Chart 1).11b This indicates that the heterocyclic moiety
at the 4-position of the piperidine-containing NOP
ligands is an important determinant of selectivity of that
structural class over the opioid receptors. On the other
hand, our results show that the piperidine N-1 sub-
stituent plays a role in determining agonist versus
antagonistic activity and that one can modulate efficacy
at the NOP receptor by modifying the piperidyl N-1
substituent, within the same structural class. We find
that when the saturated lipophilic substituent on the
piperidyl N-1 is directly linked to the cyclic substituent
For the rational design of ligands for the NOP
receptor, as tools or therapeutics, two issues need to be
addressed: one of selectivity versus the opioid receptors
and the other of agonist/antagonist activity at the NOP
receptor. Although several small-molecule ligands of

2976 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 12
Letters
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Ack n ow led gm en t. This work was supported by a
grant from the National Institutes on Drug Abuse
(Grant DA14026 to N.T.Z.).
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails, analytical and spectral data, and X-ray crystal structure
data for final compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
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