Discovery of the first potent and selective small molecule opioid receptor-like (ORL1) antagonist: 1-[(3R,4R)-1-cyclooctylmethyl-3- hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J- 113397)

Full text of DOI:10.1021/jm990517p

© Copyright 1999 by the American Chemical Society
Volume 42, Number 25
December 16, 1999
Communications to the Editor
Ch a r t 1
Discover y of th e F ir st P oten t a n d
Selective Sm a ll Molecu le Op ioid
Recep tor -lik e (ORL1) An ta gon ist:
1-[(3R,4R)-1-Cyclooctylm eth yl-3-
h yd r oxym eth yl-4-p ip er id yl]-3-eth yl-
1,3-d ih yd r o-2H-ben zim id a zol-2-on e
(J -113397)
learning and memory,6 food intake,7 anxiety,8 the
cardiovascular system,9 locomotor activity,10 and so on.11
Unfortunately, further pharmacological evaluation of
the NC/OFQ-ORL1 system has been hampered due to
the lack of selective ORL1 antagonists. To understand
the physiological roles of the NC/OFQ-ORL1 system,
development of potent and selective ORL1 antagonists
has been desired. Recently, a mutant of NC/OFQ,
[Phe1ψ(CH2-NH)Gly2]OFQ/N(1-13)-NH2, was reported
to be a selective antagonist of ORL1 in guinea pig ileum
and mouse vas deferens.12 On the other hand, this
pseudopeptide was described as an agonist in controlling
cAMP levels in both CHO cells transfected with human
ORL1 and mouse N1E-115 neuroblastoma.13 Thus, it
is still debatable whether this pseudopeptide acts as an
antagonist or agonist on ORL1. Naloxonebenzoylhydra-
zone (NalBzOH) was shown to act as an ORL1 antago-
nist;14 however, this compound was also reported to
interact with κ3-opioid receptor subtypes.15 Thus, phar-
macological results using NalBzOH may be complicated.
In this paper, we describe our studies resulting in the
development of a potent and selective small molecule
NC/OFQ antagonist. 1-[(3R,4R)-1-Cyclooctylmethyl-3-
hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-
benzimidazol-2-one (J -113397, 1) (Chart 1) binds to
ORL1 at nanomolar concentration with a selectivity
greater than 600-fold over µ-, κ-, and δ-receptors and
inhibits ORL1 function. To the best of our knowledge,
this is the first potent and selective small molecule
ORL1 antagonist reported. We identified the lead
compound 1-(1-benzyl-4-piperidyl)-1,3-dihydro-2H-ben-
zimidazol-2-one (2) in our chemical library, as it showed
high affinity for ORL1 with an IC50 of 200 nM but poor
selectivity for ORL1 over µ- and κ-receptors.
Hiroshi Kawamoto, Satoshi Ozaki, Yoshiki Itoh,
Mitsuru Miyaji, Sachie Arai, Hiroshi Nakashima,
Tetsuya Kato, Hisashi Ohta, and
Yoshikazu Iwasawa*
Banyu Tsukuba Research Institute in collaboration with
Merck Research Laboratories, Banyu Pharmaceutical
Company Ltd., Okubo 3, Tsukuba, Ibaraki 300-2611, J apan
Received October 14, 1999
In tr od u ction . Classical opioid receptors (µ, δ, and
κ) have important physiological and pharmacological
roles, especially in pain regulation. A fourth opioid
receptor, opioid receptor-like 1 (ORL1), was identified
in 1994 through cDNA expression cloning techniques.1
ORL1 is a member of the G-protein coupled receptor
superfamily with a high degree of amino acid sequence
homology to the classical opioid receptors. Despite this
homology, native opioid peptides and synthetic agonists
selective for µ-, δ-, or κ-receptors do not show significant
affinity to ORL1. As an endogenous ligand for ORL1, a
peptide containing 17 amino acids, termed nociceptin
as well as orphanin FQ (NC/OFQ), was isolated from
brain and identified.2 The amino acid sequence of NC/
OFQ has notable homology to that of opioid peptide
dynorphin A; however, this new peptide does not show
significant affinity to the other opioid receptors. As for
the classical opioid receptors, ORL1 is coupled to activa-
tion of inwardly rectifying K+ (GIRK) channels and/or
negatively coupled to adenylate cyclase.3
NC/OFQ and ORL1 are widely distributed in the
central nervous system. Pharmacological studies using
NC/OFQ and ORL1-deficient mice have shown that the
NC/OFQ-ORL1 system may have important roles in
the regulation of pain response,4 morphine tolerance,5
Ch em istr y. Synthetic methods to derivatize 4-pip-
eridyl-1,3-dihydro-2H-benzimidazol-2-one are summa-
10.1021/jm990517p CCC: $18.00 © 1999 American Chemical Society
Published on Web 11/19/1999

5062 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 25
Communications to the Editor
Ta ble 1. Structure and Biological Properties of Benzimidazolidinone Derivatives
GTPγS
binding IC50 (nM)
antagonism
IC50 (nM)e
agonism
a
no.
R1
R2
R3
R4
ORL1
200
µb
κc
δd
EC50 (nM)f
2
H
H
H
Et
Et
Et
H
H
H
H
H
Me
H
H
H
Ph
1700
43
780
950
2200
3300
110
32
12
440
1400
2600
>10000
1900
>10000
>10000
>10000
>10000
>10000
>10000
270
20
5.6
>10000
6900
25
>10000
>10000
>10000
>10000
13
14
15
2-Cl-Ph
c-Oct
c-Oct
c-Oct
c-Oct
5.9
6.8
6.8
2.3
J -113397 (3R,4R)
J -112444 (3S,4S)
CH2OH
CH2OH
H
820
a-d
c
Displacement of a [125I]Tyr14-nociceptin, b[3H]diprenorphin, [3H]U-69593, d[3H][D-Ala2,D-Leu5]enkephalin binding from the CHO
cells stably expressing cloned human ORL1, opioid µ-, opioid κ- and opioid δ-receptors, respectively. e IC50 values on nociceptin-produced
[
35S]GTPγS binding to ORL1 expressed in CHO cells. f EC50 values relative to the maximal [35S]GTPγS binding produced by nociceptin
in ORL1 expressed CHO cells. All values are the means of three independent determinations performed in duplicate.
Sch em e 1a
achieved by using a chiral column (CHIRALPAK AD),
and the resultant free base was converted to a water-
soluble hydrochloride powder for use in biological stud-
ies. The absolute stereochemistry of the active enan-
tiomer (J -113397) was determined by X-ray crystallog-
raphy of its D-tartaric acid salt.
a
Reagents: (a) R3-CHO, NaB(OAc)3H, THF or R3R4CH-X,
Resu lts a n d Discu ssion . The compounds described
here were tested for their inhibitory effects on ligand
binding to the human ORL1 receptor and also on GTPγS
binding to proteins using membrane fractions of CHO
cells expressing ORL1. Binding affinities for the ORL1
were determined by displacement of [125I]Tyr14-NC/
OFQ, and agonist/antagonist activities were measured
by the [35S]GTPγS binding method.16 Affinities for
human µ-, κ-, and δ-receptors were assayed similarly
to ORL1 using membrane fractions of CHO cells ex-
pressed in each receptor.
K2CO3, DMF; (b) EtI, NaH, DMF.
Sch em e 2a
Because the amino acid sequences of ORL1 and the
classical opioid receptors are highly homologous and the
selectivity of the lead compound 2 for ORL1 over µ- and
κ-receptors was poor, the most important issue in
identifying selective ORL1 antagonists was to determine
the structural requirements of the ligands to show
potent affinity for each receptor. In addition, since 2
showed weak agonistic activity for ORL1, identification
of the structural requirements to show full antagonistic
activity was also critical.
a
Reagents: (a) NaB(OAc)3H, THF, 64%; (b) AcONH4, MeOH;
(c) 2-fluoronitrobenzene, NaBH3CN, Na2CO3, n-BuOH, reflux, 37%
(2 steps); (d) H2, Pd-C, MeOH; (e) CDI, CHCl3, 84% (2 steps); (f)
EtI, NaH, DMF, 90%; (g) LiAlH4, THF, 89%; (h) optical resolution
by CHIRALPAK AD, hexane/2-propanol/Et2NH ) 800/200/1.
rized in Schemes 1 and 2. Reductive alkylation of
commercially available 3 with alkyl aldehydes or N-
alkylation with alkyl halides in the presence of K2CO3
afforded 4. The synthesis of N-ethylbenzimidazolidino-
nes 5 was achieved by treating 4 with NaH followed by
ethyl iodide. J -113397 was synthesized as shown in
Scheme 2. Commercially available keto ester 6 was
converted to 8 by reductive alkylation with cyclooctyl
aldehyde (7) in the presence of NaB(OAc)3H in THF.
Treatment of 8 with ammonium acetate in MeOH gave
stable enamine 9, and reduction with NaBH3CN fol-
lowed by coupling reaction of 9 with 2-fluoronitroben-
zene in n-BuOH at reflux temperature afforded 10 as a
mixture of trans- and cis-isomers. After separation of
the isomers by silica gel column chromatography, the
trans-isomer was hydrogenated in the presence of Pd-C
and the resultant phenylenediamine was cyclized with
carbonyldiimidazole (CDI) to give 11. Treatment of 11
with NaH and ethyl iodide followed by reduction with
LiAlH4 gave 1 as a racemate. Optical resolution was
We studied structure-activity relationships around
the lead compound 2, and Table 1 highlights the results.
The introduction of substituents into the benzyl group
improved binding affinity; o-chlorophenethyl analogue
13 showed nanomolar affinity for ORL1. Unfortunately,
this compound lacked selectivity over µ- and κ-receptors
and antagonistic activity. Efforts to identify fully an-
tagonistic compounds by changing the benzyl part with
a variety of groups resulted in the discovery of the
cyclooctyl analogue 14. 14 showed full antagonistic
activity in the GTPγS assay, although the IC50 value
was rather large (IC50 270 nM). To improve selectivity
and antagonistic activity, we introduced a variety of
substituents into the benzimidazolidinone nitrogen (R1)
and found that an ethyl analogue 15 dramatically
improved not only the antagonistic activity but also the
selectivity (>50-fold). Improvement of selectivity was

Communications to the Editor
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 25 5063
(5) Ueda, H.; Yamaguchi, T.; Tokuyama, S.; Inoue, M.; Nishi, M.;
Takeshima H. Partial loss of tolerance liability to morphine
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accomplished by introducing a hydroxymethyl group
into the piperidine ring; J -113397 having (R,R)-stereo-
chemistry showed excellent potency (IC50 2.3 nM),
antagonistic activity (IC50 5.6 nM), and selectivity over
µ, κ, and δ (>600-fold). The affinity for ORL1 of the less
active enantioisomer (J -112444) was approximately 400-
fold weaker than that of J -113397. This compound was
confirmed to be active in vivo via testing antagonism
against hyperalgesia produced by NC/OFQ (preliminary
observation).
In conclusion, we discovered the first potent and
selective small molecule ORL1 antagonist, 1 (J -113397),
through chemical modifications of the lead compound
2 found in our chemical library. J -113397 should be a
useful pharmacological tool to elucidate the physiologi-
cal roles of the NC/OFQ-ORL1 system as well as the
therapeutic potential of ORL1 antagonists and/or ago-
nists.
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Ack n ow led gm en t. We thank Dr. Susumu Nish-
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Kamata for conducting the X-ray crystallographic analy-
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reading of this manuscript.
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