Synthesis and pharmacological evaluation of 1,2-dihydrospiro[isoquinoline- 4(3H),4′-piperidin]-3-ones as nociceptin receptor agonists

Article abstract of DOI:10.1021/jm7009606

Some synthesized 1,2-dihydrospiro[isoquinoline-4(3H),4′-piperidin]-3- ones were evaluated as ligands for nociceptin receptor (NOP receptor). Their affinity was established by binding studies, and efficacy was investigated by GTP binding experiments. Selec

Full text of DOI:10.1021/jm7009606

1058
J. Med. Chem. 2008, 51, 1058–1062
Synthesis and Pharmacological Evaluation of
1,2-Dihydrospiro[isoquinoline-4(3H),4′-piperidin]-3-ones as Nociceptin Receptor Agonists
Carlo Mustazza,* Anna Borioni, Isabella Sestili, Maria Sbraccia, Andrea Rodomonte, and Maria Rosaria Del Giudice
Dipartimento del Farmaco, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Roma, Italy
ReceiVed August 2, 2007
Some synthesized 1,2-dihydrospiro[isoquinoline-4(3H),4′-piperidin]-3-ones were evaluated as ligands for
nociceptin receptor (NOP receptor). Their affinity was established by binding studies, and efficacy was
investigated by GTP binding experiments. Selectivity toward DOP, KOP, and MOP receptors was assessed,
and structural requirements affecting affinity and selectivity were remarked. Most notably, compound 6d
displayed nanomolar NOP receptor affinity and showed more than 800-fold selectivity. The new structures
exerted full or partial agonistic activity.
Introduction
In 1994, a receptor clearly related to the opioid receptors was
discovered. It was named ORL1 receptor1 (NOP, according to
the current nomenclature2), and one year later its endogenous
ligand the heptadecapeptide nociceptin or orphanin N/OFQ3 was
identified. The NOP-N/OFQ system is widely distributed in both
central and peripheral nervous system and is also present in
some non-neural tissues.4 This complex system is involved in
many physiological processes including pain, anxiety, learning
and memory, blood pressure regulation, and others,5 but until
now, the diverse biological actions of nociceptin have not been
Figure 1. Structures of Roche NOP agonists and 1,2-dihydrospiro[iso-
quinoline-4(3H),4′-piperidin]-3-ones 5 and 6.
fully clarified. Efforts in drug discovery led to the identification
of small molecules active on NOP receptor. Agonists are
potential therapeutic agents for anxiety, neuropatic pain, cough,
proved to enhance NOP affinity in analogous structures.8
drug abuse, and urinary incontinence, and antagonists could find
Molecular modeling methods were employed to gather informa-
application as analgesics and memory enhancers and in the
tion on the structural requirements for affinity and selectivity
treatment of Parkinson’s disease, depression and obesity. Among
of the studied ligands.
NOP receptor–ligands, piperidine derivatives bearing in the
Chemistry. The synthetic pathway to the compounds 5 and
4-position either a spiro junction with systems as 4-imidazoli-
6 is outlined in Scheme 1.
dinone,6,7 2-indolinone,8 isobenzofuran9 and hexahydropyr-
Reductive amination of 4-alkylcyclohexanones with 4-cyano-
role[3,4-c]pyrrole10 or cyclic substituents such as phenyl,6a
4-arylpiperidines 115 and sodium triacetoxyborohydride16 af-
benzimidazolinone,11 and dihydroindolinone12 received the most
attention. These derivatives bear a lipophilic moiety on the
forded the cis- and trans-1-(4-alkylcyclohexyl)-4-aryl-4-cyan-
opiperidines 2. They were separated by chromatography and
piperidine nitrogen atom. Zaveri et al. hypothesized that the
unambiguously characterized by 1D and 2D 1H and 13C NMR,
heterocyclic moiety of the 4-spiropiperidine was a determinant
by measurement of the coupling constants of axial and equatorial
of affinity and selectivity and that the lipophilic N-substituent
protons in cyclohexane, and by comparison with literature
was responsible for intrinsic activity.12 A valuable representative
reports on analogous structures.14 Literature on NOP ligands
of this class of compounds is the potent agonist Ro 64-6198,6a
bearing a 4-alkylcyclohexyl substituent reported that cis isomers
whose pharmacology and potential therapeutic applications were
are always more potent than the corresponding trans.6b In this
recently reviewed.13 In a previous work,14 we reported a series
paper, the trans isomers were not taken into account, and the
of spiropiperidinequinazolinones that resembled the Ro 64-6198
following synthetical steps were carried on the cis isomers.
structure and that displayed moderate affinity but high selectiv-
Hydrolysis of nitriles 2 in an acetic acid/sulfuric acid/water 2:1:1
mixture gave carboxylic acids 3. These were treated with SOCl2
to obtain the acyl chlorides and subsequently reacted with
benzylamine or methylamine to obtain the N-substituted amides
ity. Because selectivity more than affinity represents the problem
with the development of NOP ligands, these results encouraged
us to further exploit the spiropiperidine scaffold. Now, to better
understand the structural requirements for receptor interaction,
4. The Pictet-Spengler reaction of compounds 4 with paraform-
we report an investigation on a new series of 1,2-dihy-
aldehyde17 gave the 1,2-dihydrospiro[isoquinoline-4(3H),4′-
drospiro[isoquinoline-4(3H),4′-piperidin]-3-ones (Figure 1, com-
piperidin]-3-ones 5. Debenzylation of compounds 5p-u by
pounds 5 and 6) that differ from Ro 64-6198 analogues in having
reaction with phenol, and 85% phosphoric acid18 afforded
compounds 6d,f,g,i. This reaction when applied to compounds
5q and 5t led to the isoquinolinone ring opening and afforded
the unsubstituted carboxamides 7e and 7h instead of the
a fused benzene ring instead of a phenyl substituent and in
having a dihydroisoquinolinone ring instead of an imidazolinone.
We also inserted a fluorine atom in the aromatic ring as fluorine
expected 6e and 6h. Attempts to synthesize 6 by direct
cyclization of the corresponding unsubstituted 1-(4-alkylcyclo-
* To whom correspondence should be addressed. Tel.: +390649902385.
Fax: +390649902516. E-mail: carlo.mustazza@iss.it.
10.1021/jm7009606 CCC: $40.75
2008 American Chemical Society
Published on Web 01/31/2008

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 4 1059
Scheme 1. Synthetic Route to Compounds 5 and 6
hexyl)-4-aryl-4-piperidinecarboxamides 7 only afforded the
methylated compounds 5j-o in very low yield (5–8%) (Sup-
porting Information).
Pharmacology. Binding affinities for NOP, KOP, MOP, and
DOP receptors were measured.14,19 The ligand efficacy was
evaluated as the ability to enhance the binding of [35S]GTPγS
at fixed and increasing ligand concentration14,19 (Figures 2
and 3).
compounds were anchored by a salt bridge between the basic
nitrogen and Asp130 residue as reported for structurally similar
opioid ligands.20 The lactamic sequence that characterized our
molecules as well as several NOP ligands6,8 assured their
affinity. Compounds 6 interacted with Thr305 using the amide
portion as hydrogen bond donor (Figure 4, top) in agreement
with what Bröer et al. described for Ro 64-6198.20 The
introduction of a methyl group on the 2-nitrogen atom (com-
pounds 5j,m) was not detrimental for affinity as the amide
maintained interaction with Thr305 by acting as a H-bond
acceptor (Figure 4, bottom). Changing the methyl group to a
benzyl group influenced the binding affinity only slightly. A
fluorine atom at the isoquinolinone moiety of 2-methyl com-
pounds 5j,m strongly affected affinity (up to 50-fold decrease)
especially when it was in the 5-position (5k,n). Although
fluorine and hydrogen atoms have similar steric features, the
former possesses a negative inductive effect. Thus, when the
Results and Discussion
Binding experiments results (Table 1) evidenced that the
isoquinolinonespiropiperidine moiety was suitable for NOP
receptor interaction. Molecular modeling investigations on the
ligand-NOP receptor complex (Figure 4) showed that our
Figure 2. Effect of the new piperidine derivatives on G protein
R-subunit activation. The binding of [35S]GTPγS was measured in the
presence of 300 nM GDP using membranes prepared from HEK-293
cells stable transfected with human NOP receptors. All compounds were
present at a concentration of 10 µM. Data are expressed as bound/total
ratio of the radioligand (0.1 nM) and values are the mean ( SEM (n
) 3).
Figure 3. Concentration–response curves for stimulation of GTPγS
binding by the compounds 5j, 5n, and 6d in comparison with the curves
of N/OFQ and Ro 64-6198. The binding of [35S]GTPγS was measured
in triplicate at increasing ligand concentrations and in the presence of
300 nM GDP. All data were computed by subtracting the binding in
the absence of ligand.

1060 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 4
Brief Articles
Table 1. Opioid Receptors Binding Affinity of the New Piperidine Derivatives
Ki (nM) ( SDa
selectivity
compd
NOP
DOP
KOP
MOP
KOP/NOP
MOP/NOP
N/OFQ5b
0.13 ( 0.01
0.39
3.1 ( 1.2
186 ( 74
8.9 ( 0.2
21 ( 2
395 ( 33
147 ( 45
6.6 ( 1.3
12 ( 2
>104
1380
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
>104
3030 ( 371
47
476 ( 43
2075 ( 63
540 ( 48
>77000
228
180
2
23307
121
154
11
61
48
20
24
203
542
72
4
3
Ro 64–619820
89
5j
5k
5l
557 ( 40
412 ( 12
103 ( 18
178 ( 44
3600 ( 1630
1150 ( 157
928 ( 17
123 ( 9
12
9
9
8
140
10
74
2
2
5m
5n
5o
5p
5q
5r
5s
5t
5u
6d
6f
6g
6i
1005 ( 77
7800 ( 4150
3503 ( 480
1340 ( 91
6500 ( 3050
1875 ( 119
215 ( 20
26 ( 9
51 ( 16
81 ( 4
1920 ( 110
97 ( 6
190 ( 12
1104 ( 255
3827 ( 650
3977 ( 1025
3844 ( 910
3641 ( 875
>104
247 ( 43
136 ( 38
4.7 ( 1.4
23 ( 1
1582 ( 183
5406 ( 1605
6755 ( 1325
6139 ( 916
5155 ( 1105
>104
8
12
814
173
92
1150
294
146
57
>70
40
42 ( 6
90 ( 16
130 ( 45
65 ( 23
92 ( 29
40
4j
4p
7d
>70
>150
>100
>104
2600 ( 96
>104
>104
>100
a Membrane proteins from HEK-293 cells stable transfected with the human NOP19 or DOP or KOP receptors (Perkin-Elmer Life Sciences) (3–5 µg) and
membrane proteins from CHO cells expressing human MOP receptors (Perkin-Elmer Life Sciences) (5–15 µg) were incubated with the specific receptor
radioligand (30000–50000 cpm) in a total volume of 1 mL.14,19 Increasing concentrations of compounds to be tested were added and samples were incubated
for 90 min at room temperature. Radioligands: [125I]-nociceptin for NOP, [3H]-naltrindole for DOP, and [3H]-diprenorphine for KOP and MOP receptors.
Data are given as mean ( SD (n ) 3).
(5r,u). Furthermore, small variations in the size of alkylcyclo-
hexyl tail appeared critical for affinity. As already observed,6b
4-isopropyl seemed more suitable than tert-butyl for receptor
binding. Affinity decrease observed, for instance, in compounds
5m, 5s, and 6g, compared with the analogues 5j, 5p, and 6d,
could be explained by modeling observations: receptor-5j
complex showed a bad steric contact between one methyl group
of the isopropyl substituent, Val279, and Val283 (the two
residues had to shift slightly to make room for the methyl group).
Also, Met134 was slightly displaced to accommodate the
3-methylene of the cyclohexyl ring. However, the lipophilic
pocket residues revealed a certain degree of mobility, and these
shifts did not imply a significant energy increase of the
receptor–ligand complex when compared to the complex with
Ro 64-6198. On the contrary, the presence of the more
cumbersome tert-butyl group at the cyclohexyl 4-position led
to a substantial energy increase of the receptor–ligand complex.
This behavior was caused by a bad steric contact that tert-butyl
had with Val202, a residue not reported as part of the lipophilic
pocket by Bröer.20 All of the compounds lack affinity for DOP
receptor. Their NOP vs MOP selectivity was generally greater
Figure 4. Stereoview of compounds 6d (top) and 5j (bottom) inserted
than that for NOP vs KOP. Multiple sequence alignment of
in the binding pocket of a NOP receptor 3D model.20 Intermolecular
NOP, KOP, and MOP receptor transmembrane domains21
interactions are represented by dashed lines.
evidenced that threonine at the NOP 305-position is replaced
by isoleucine in the KOP and MOP receptor transmembrane
helix TM7 at the 316- and 324-positions, respectively. The
presence of an isoleucine makes impossible the hydrogen bond
formation and determines the poor 6d affinity for KOP and MOP
receptors. This can explain compound 6d excellent selectivity
profile. In 2-substituted compounds 5j and 5p, the hydrogen
bond interaction is replaced by hydrophobic interactions between
isoquinolinone 2-methyl or 2-benzyl groups and isoleucine. This
explains the higher affinity for KOP and MOP receptors of the
2-substituted compounds compared to 6d. Moreover loss in
selectivity for NOP receptor seemed to be generally related to
the molecular hydrophobicity increase caused by introduction
of lipophilic groups as tert-butyl and/or fluorine atom. GTPγS
binding experiments at NOP receptor in the presence of
halogen was in the 5-position, its negative partial charge
generated a repulsive interaction with the negatively charged
Asp130, whose oxygen was only 2 Å far. Asp130 had to move
away to minimize repulsion, and the salt bridge with the
piperidine nitrogen was consequently weakened. When fluorina-
tion occurred at the 7-position, only a moderate decrease in
activity was observed (5l,o). This is because no interaction
between fluorine and Asp130 was present in this case. The slight
reduction in affinity might be due to repulsive effects exerted
toward Tyr309 phenolic oxygen and toward the Cys200 sulfur.
Insertion of fluorine in the 2-benzyl derivatives 5p,s was not
excessively harmful to affinity. The detrimental effect was
expressed mainly when the substituent was inserted in 7-position

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 4 1061
AcOH (0.9 mL, 16 mmol) were sequentially added to the solution,
which was stirred overnight at room temperature. Aqueous NaOH
(10%) was added, and the layers were separated. The organic phase
was evaporated under reduced pressure. Purification by chroma-
tography on Al2O3 eluting with ethyl acetate/n-hexane (15:85)
afforded cis and trans isomers 2 in an approximately 7:3 ratio.
General Procedure for the Synthesis of the cis-1-(4-Alkylcy-
clohexyl)-4-aryl-4-piperidinecarboxylic acids 3d-i. A solution
of 2 (10 mmol) in a AcOH/H2O/H2SO4 (2:1:1) mixture (120 mL)
was refluxed for 3 h. Most of the acetic acid was evaporated under
reduced pressure, and the residue was diluted with H2O and
alkalinized to pH 9 with aqueous NaOH (10%). The pH of the
cloudy solution was adjusted to 4–5 with acqueous HCl (15%).
Compounds 3 separated as white precipitates and were collected
by filtration, washed with H2O and diethyl ether, and dried under
vacuum.
General Procedure for the Synthesis of the cis-1-(4-Alkylcy-
clohexyl)-4-aryl-N-methyl-4-piperidinecarboxamides 4j-o. A
suspension of 3 (3.0 mmol) in SOCl2 (15 mL) was stirred overnight
at room temperature. SOCl2 was removed under reduced pressure,
and MeNH2 ·HCl (0.24 g, 3.6 mmol) was added to the solid residue.
The mixture was cooled to 0 °C, and pyridine (30 mL) and N,N-
ethyldiisopropylamine (2.1 mL, 12 mmol) were added dropwise.
The mixture was stirred overnight at room temperature. The
volatiles were evaporated, and the residue was suspended in H2O
and extracted three times with ethyl acetate. The solvent was
removed to afford the compounds 4j-o, which were purified by
crystallization from ethyl acetate/hexane.
compounds 5 and 6 were performed to test efficacy of our
compounds. The results are reported in Figure 2. As illustrated
by the histogram, the isopropyl derivatives 5j, 5p showed
agonism and their intrinsic activity was variously influenced
by the introduction of fluorine in the heterocyclic portion.
Efficacy decreased in the tert-butyl-substituted 5m, 5s whereas
compounds 6 were less affected by both the presence of the
halogen and the nature of the alkyl group in the lipophilic
portion. To ascertain if compounds 5j and 6d were full or partial
agonists and to exclude antagonism for the less potent 5n,
stimulation of [35S]GTPγS was measured in concentration–re-
sponse curves in comparison with N/OFQ and Ro 64-6198
(Figure 3). Compounds 5j and 6d behaved as full agonists,
whereas 5n exhibited partial agonist activity. Through a ligand-
based analysis, Zaveri et al.12 showed that the ligand lipophilic
moiety is supposedly responsible for intrinsic activity. It was
observed that when the lipophilic moiety of agonists is subject
to 1-carbon homologation at the piperidine side, antagonists are
generated. Thus, she theorized the presence of a trigger site in
the receptor lipophilic pocket that induced major conformational
changes in the receptor when activated by agonists. Antagonists
instead accommodated their lipophilic moiety in the same
receptor pocket but did not activate that trigger. To corroborate
such a theory and to find out which residue in particular may
constitute the trigger point, further docking investigations were
carried out. Upon inserting an agonist such as 5j in the 3D NOP-
receptor model, Trp276 shifted to make room for the methylene
in the 2-position at the R-cyclohexyl ring. This in turn caused
a displacement of Asn311, resulting in the disruption of the
hydrogen bonds that Asn311 forms with Cys275 and Gly308.
When analogous structures bearing a methylene bridge between
piperidine ring and the R-cyclohexyl group were docked instead,
these major conformational changes did not manifest. Therefore,
it may be reasonably assumed that those changes were linked
to the receptor activation, with Trp276 being the trigger site
envisaged by Zaveri.12 Preliminary investigation on the phar-
macological characteristics of the amides 4 and 7 showed an
affinity decrease in comparison with their cyclized analogues.
In Table 1, data regarding affinity and selectivity of 4j, 4p, and
the 2-unsubstituted derivative 7d have been reported. These
compounds, investigated for potency at the NOP receptor,
showed a non-negligible effect on G protein R-subunit activation
(Figure 2). A thorough evaluation of the biological activity of
the open amides will be conducted later and reported elsewhere.
General Procedure for the Synthesis of the cis-1-(4-Alkylcy-
clohexyl)-4-aryl-N-benzyl-4-piperidinecarboxamides 4p-u. A
suspension of 3 (3.0 mmol) in SOCl2 (15 mL) was stirred overnight
at room temperature. SOCl2 was removed under reduced pressure.
The solid residue was cooled to 5 °C, and pyridine (30 mL) and
benzylamine (6.0 mmol) were carefully added. The mixture was
stirred overnight at room temperature. The volatiles were evapo-
rated, and the residue was suspended in H2O and extracted three
times with ethyl acetate. The solvent was removed to afford the
compounds 4p-u, which were purified by crystallization from ethyl
acetate.
General Procedure for the Synthesis of the cis-2-Substituted
1,2-Dihydrospiro[isoquinoline-4(3H),4′-piperidin]-3-ones 5j-u.
A mixture of compound 4j (1.4 mmol) and paraformaldehyde (3
mmol) in AcOH (3.0 mL), Ac2O (1.5 mL), and H2SO4 (0.2 mL)
was heated at 140 °C for 3 h. An additional amount of paraform-
aldehyde (3 mmol) was added, and the solution was maintained at
140 °C for 6 h. The mixture was allowed to cool to room
temperature, diluted with H2O (15 mL), alkalinized with aqueous
NaOH (10%), and extracted three times with ethyl acetate. The
combined organic extracts were evaporated. Crude 5j was purified
by chromatography on Al2O3 eluting with ethyl acetate/n-hexane
(20:80) and crystallized from ethyl acetate (19% yield): mp 96–97
Experimental Section
1
°C; H NMR (pyridine-d5) δ 7.54 (d, 1H), 7.35 (t, 1H), 7.27 (t,
General Procedures. Compounds were purified by column
chromatography on Merck aluminum oxide 90 and their purity
checked on Merck aluminum oxide 60 F254 (type E) plates. Sodium
sulfate was used to dry organic solutions. Melting points were
determined on a Köfler apparatus. Elemental analyses were within
(0.4% of the theoretical values. The 1H and 13C NMR spectra
were performed on a Bruker Avance 400 instrument, and chemical
shifts were expressed in ppm (δ). Mass spectra were recorded on
a HP 59980 B spectrometer operating at 70 eV. GDP and GTPγS
were purchased by Sigma, N/OFQ was from Bachem, and Ro 64-
6198 was kindly provided by Roche. Receptor radioligands, [125I-
Tyr14]nociceptin, [3H]naltrindole and [3H]diprenorphine, and la-
beled nucleotide [35S]GTPγS were purchased by Perkin-Elmer Life
Sciences. Molecular modeling calculations were performed using
the Sybyl 7.1 software package (Tripos, Inc., St. Louis, MO)
running under the Linux operating system.
1H), 7.20 (d, 1H), 4.45 (s, 2H, 1-CH2) 3.07 (s, 3H, NCH3), 2.95 (t,
2H, H-2ax,H-6ax d), 2.80 (d, 2H, H-2eq,H-6eq), 2.36 (d, 2H, H-3eq,H-
5eq), 2.30 (m, 1H, H-1′eq, Jeq-ax ) 6.2 Hz, Jeq-eq ) 3.1 Hz), 2.05 (t,
2H, H-3ax, H-5ax), 1.79 (m, H-2′eq, H-6′eq), 1.60 (m, 2H, H-3′ax,
H-5′ax), 1.49 (m, 1H, isopropyl CH), 1.42 (m, 2H, H-2′ax, H-6′ax),
1.33 (m, 2H, H-3′eq, H-5′eq), 1.03 (m, 1H, H-4′ax, Jax-ax ) 11.7
Hz, Jax-isopropylCH ) 7.9 Hz, Jax-eq ) 3.8 Hz), 0.89 (d, 6H, isopropyl
CH3); 13C NMR (pyridine-d5) δ 173.9, 142.8, 134.0, 128.4, 127.1,
126.8, 125.6, 61.3, 52.7, 47.9, 44.8, 43.5, 35.5, 33.5, 30.7, 27.6,
26.4, 21.2; MS (EI) m/z 354 (M+). Anal. (C23H34N2O) C, H, N.
General Procedure for the Synthesis of the cis-1,2-Dihy-
drospiro[isoquinoline-4(3H),4′-piperidin]-3-ones 6d,f,g,i. Com-
pound 5p (1.0 mmol) was added to a solution of PhOH (3.2 mmol)
in 85% H3PO4 (7.0 mL). The mixture was kept at 150 °C, and the
progress of the reaction was monitored by TLC (Al2O3 ethyl acetate/
hexane 20:80) for about 3 h. The solution was poured on crushed
ice, acidified with aqueous HCl (5%), and washed with ethyl acetate.
The aqueous phase was alkalized with aqueous NaOH (20%) and
extracted with ethyl acetate (3 × 15 mL). The solvent was
General Procedure for the Synthesis of the cis-1-(4-Alkylcy-
clohexyl-4-aryl-4-piperidinecarbonitriles 2d-i. Compound 1 (16
mmol) and 4-isopropylcyclohexanone (16 mmol) were dissolved
in 1,2-dichloroethane (46 mL). NaBH(OAc)3 (4.6 g, 22 mmol) and

1062 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 4
Brief Articles
agents. Life Sci. 2003, 73, 663–678. (b) Röver, S.; Wichmann, J.;
Jenck, F.; Adam, G.; Cesura, A. M. ORL1 receptor ligands:
Structuresactivity relationships of 8-cycloalkyl-1-phenyl-1,3,8-
triazaspiro[4.5]decan-4-ones. Bioorg. Med. Chem. Lett. 2000, 10, 831–
834.
evaporated under vacuum. Crude 6d was crystallized from ethyl
acetate (32% yield): mp 172–174 °C; 1H NMR (pyridine-d5) δ 8.90
(bs, 1H, NH), 7.58 (d, 1H), 7.36 (t, 1H), 7.24 (t, 1H), 7.20 (d, 1H),
4.61 (s, 2H, 1-CH2), 3.05 (t, 2H, H-2ax, H-6ax), 2.88 (m, 2H, H-2eq,
H-6eq,), 2.48 (d, 2H, H-3eq, H-5eq), 2.31 (m, 1H, H-1′eq, Jeq-ax
)
(7) Caldwell, J. P.; Matasi, J. J.; Zhang, H.; Fawzi, A. Synthesis and
structure-activity relationship of N-substituted spiropiperidines as
nociceptin receptor ligands. Bioorg. Med. Chem. Lett. 2007, 17, 2281–
2284.
(8) Bignan, G. C.; Battista, K.; Connolly, P. J.; Orsini, M. J.; Liu, J.;
Middleton, S. A.; Reitz, A. B. Preparation of 3-spirocyclic indolin-
2-ones as ligands for the ORL-1 receptor. Bioorg. Med. Chem. Lett.
2005, 15, 5022–5026.
(9) Goto, Y.; Arai-Otsuki, S.; Tachibana, Y.; Ichikawa, D.; Ozaki, S.;
Takahashi, H.; Iwasawa, Y. Identification of a Novel Spiropiperidine
Opioid Receptor-like 1 Antagonist Class by a Focused Library
Approach Featuring 3D-Pharmacophore Similarity. J. Med. Chem.
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Oberhauser. Novel Hexahydrospiro[piperidine-4,1′-pyrrolo[3,4-c]pyr-
roles]: Highly Selective Small-Molecule Nociceptin/Orphanin FQ
Receptor Agonists. J. Med. Chem. 2003, 46, 255–264.
5.9 Hz, Jeq-eq ) 3.0 Hz), 2.15 (t, 2H, H-3ax, H-5ax), 1.78 (m, H-2′eq,
H-6′eq), 1.60 (m, 2H, H-3′ax, H-5′ax), 1.52 (m, 1H, isopropyl CH),
1.45 (m, 2H, H-2′ax, H-6′ax), 1.34 (m, 2H, H-3′eq, H-5′eq), 1.04 (m,
1H, H-4′ax, Jax-ax ) 11.6 Hz, Jax-isopropylCH ) 7.7 Hz, Jax-eq ) 3.9
Hz), 0.86 (d, 6H, isopropyl CH3); 13C NMR (pyridine-d5) δ 176.7,
143.3, 135.3, 128.2, 127.1, 126.8, 125.6, 61.3, 48.1, 45.5, 45.0,
43.5, 33.1, 30.8, 27.6, 26.4, 21.2; MS (EI) m/z 340 (M+). Anal.
(C22H32N2O) C, H, N.
General Procedure for the Synthesis of cis-1-(4-Alkylcyclo-
hexyl)-4-aryl-4-piperidinecarboxamides 7d-i. Compound 2 (2.5
mmol) was added to a mixture of sulfuric acid (5.6 mL) and water
(1.3 mL). The solution, kept at 75 °C for 2 h, was cooled to room
temperature, poured on crushed ice, alkalinized with aqueous
sodium hydroxide (10%), and extracted with ethyl acetate three
times. The volatiles were evaporated and the compounds 7 were
crystallized from ethyl acetate.
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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). J. Med. Chem. 1999,
42, 5061–5063.
Acknowledgment. We wish to thank Dr. Luciana Turchetto
for mass spectra and Dr. Gilda Lirangi and Mr. Antonino Puccio
for technical assistance.
(12) Zaveri, N.; Jiang, F.; Olsen, C.; Polgar, W.; Toll, L. Small-molecule
agonists and antagonists of the opioid receptor-like receptor (ORL1,
NOP): ligand-based analysis of structural factors influencing intrinsic
activity at NOP. AAPS J. 2005, 7, E345–E352, http://www.aapsj.org.
(13) Shoblock, J. R. The pharmacology of Ro 64–6198, a systemically
active, nonpeptide NOP Receptor (ORL-1) agonist with diverse
preclinical therapeutic activity. CNS Drug ReV. 2007, 13, 107–136.
(14) Mustazza, C.; Borioni, A.; Sestili, I.; Sbraccia, M.; Rodomonte, A.;
Ferretti, R.; Del Giudice, M. R. Synthesis and Evaluation as NOP
Ligands of Some Spiro[piperidine-4,2′(1′H)-quinazolin]-4′(3′H)-one
sand Spiro[piperidine-4,5′-(6′H)-[1,2,4]triazolo[1,5-c]quinazolines].
Chem. Pharm. Bull. 2006, 54, 611–622.
Supporting Information Available: Pharmacological data of
some amides 4 and 7. Molecular modeling methods. Procedure for
preparation of compounds 5j-o from 7d-i. Spectral data and
microanalyses of compounds 2-7. Procedures for pharmacological
assays. This material is available free of charge via the Internet at
http://pubs.acs.org.
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