Discovery of a potent analgesic NOP and opioid receptor agonist: Cebranopadol

Article abstract of DOI:10.1021/ml500117c

In a previous communication, our efforts leading from 1 to the identification of spiro[cyclohexane-dihydropyrano[3,4-b]indole]-amine 2a as analgesic NOP and opioid receptor agonist were disclosed and their favorable in vitro and in vivo pharmacological properties revealed. We herein report our efforts to further optimize lead 2a, toward trans-6′-fluoro-4′, 9′-dihydro-N,N-dimethyl-4-phenyl-spiro[cyclohexane-1,1′(3′H) -pyrano[3,4-b]indol]-4-amine (cebranopadol, 3a), which is currently in clinical development for the treatment of severe chronic nociceptive and neuropathic pain.

Full text of DOI:10.1021/ml500117c

Letter
pubs.acs.org/acsmedchemlett
Discovery of a Potent Analgesic NOP and Opioid Receptor Agonist:
Cebranopadol
Stefan Schunk,*,† Klaus Linz,‡ Claudia Hinze,† Sven Frormann,† Stefan Oberborsch,†
̈
Bernd Sundermann,† Saskia Zemolka,† Werner Englberger,§ Tieno Germann,§ Thomas Christoph,∥
Babette-Y. Kogel,∥ Wolfgang Schroder,∥ Stephanie Harlfinger,⊥ Derek Saunders,⊥ Achim Kless,#
̈
̈
Hans Schick,○ and Helmut Sonnenschein○
†Departments of Medicinal Chemistry, ‡Preclinical Drug Safety, §Molecular Pharmacology, ∥Pain Pharmacology, ⊥Pharmacokinetics,
#
and Discovery Informatics, Global Drug Discovery, Grunenthal Innovation, Grunenthal GmbH, D-52099 Aachen, Germany
̈
̈
○ASCA GmbH Angewandte Synthesechemie Adlershof, Magnusstr. 11, 12489 Berlin, Germany
S
* Supporting Information
ABSTRACT: In a previous communication, our efforts leading from 1 to the identification of spiro[cyclohexane-
dihydropyrano[3,4-b]indole]-amine 2a as analgesic NOP and opioid receptor agonist were disclosed and their favorable in
vitro and in vivo pharmacological properties revealed. We herein report our efforts to further optimize lead 2a, toward trans-6′-
fluoro-4′,9′-dihydro-N,N-dimethyl-4-phenyl-spiro[cyclohexane-1,1′(3′H)-pyrano[3,4-b]indol]-4-amine (cebranopadol, 3a),
which is currently in clinical development for the treatment of severe chronic nociceptive and neuropathic pain.
KEYWORDS: NOP receptor agonists, MOP receptor agonists, cebranopadol, analgesics
ecent publications indicate that small molecules activating
both nociceptin/orphanin FQ peptide (NOP) and mu
cebranopadol), a novel potent analgesic NOP and opioid
receptor agonist, currently in clinical development for the
treatment of severe chronic nociceptive and neuropathic pain.
The structure−activity relationship (SAR) established
around the uncyclized scaffolds (e.g., 1) suggested that a
broad variety of linkers such as alcohols, ethers, and amines are
tolerated, showing high NOP and MOP receptor binding
affinities.3 As a result, we applied this knowledge through
analogous structural variations to lead structure 2a (region A,
Figure 1). These changes were also combined with a targeted
approach to improve the poor PK profile, in particular by
addressing metabolically liable regions B and C.
With this in mind, the transformation of the oxacyclic spiro
moiety into a carba-, aza-, or thio-cyclic moiety was
investigated. Advancing from the oxacyclic spiro 2a to the
azacyclic moiety 5a led to equally potent NOP and MOP
receptor binders, as well as the introduction of the N-methyl
subunit 6a. Similarly, potency was retained when moving from
the oxa-cycle 2a to the thio-cycle 7a and carbacycle 8a (Table
1).
R
opioid peptide (MOP) receptors may potentiate opiate
analgesia and at the same time display an improved side effects
profile.1,2 We have recently reported the discovery of a series of
small molecules, characterized by their high NOP and opioid
receptor agonistic activity.3 This series included uncyclized
(e.g., 1) as well as spirocyclic examples (e.g., 2a). The discovery
of spirocyclic 2a originated from the respective uncyclized
analogues, which were potent NOP and MOP receptor binders
but sometimes hampered by only partial agonistic NOP and
MOP receptor activity. In particular, the spiroindole derivates
sparked our interest due to their structural novelty and
favorable in vitro and in vivo properties. The leading spiroether
2a exhibited strong efficacy in preclinical models of acute (ED50
rat tail-flick: 3.63 nmol/kg i.v.) and neuropathic pain (ED50 rat
spinal nerve ligation: 1.05 nmol/kg i.v.) but was hampered by
poor pharmacokinetic (PK) properties in rats with high
clearance, large volume of distribution, moderate half-life (Cl
= 4.0 L/h·kg; Vss = 7.52 L/kg; t1/2 = 1.6 h), and a critically very
low oral bioavailability (F = 4%).
We herein report our efforts to further optimize the
spiroindole lead 2a, which eventually led to the discovery of
trans-6′-fluoro-4′,9′-dihydro-N,N-dimethyl-4-phenyl-spiro-
[cyclohexane-1,1′(3′H)-pyrano[3,4-b]indol]-4-amine (3a,
Received: March 19, 2014
Accepted: June 12, 2014
Published: June 24, 2014
© 2014 American Chemical Society
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give the corresponding spirocycles 2−7 under similar
conditions to the ones reported previously.3
To achieve carbacycle 8, another route was necessary: 5-
triethylsilyl-4-pentyn-1-ol 20 was converted into the corre-
sponding iodide 21, which after metal−halogen exchange with
tBuLi was added to previously described3 19 to give 22. Larock
cyclization4 of the triethylsilyl alkyne moiety with ortho-
iodoaniline gave the indole-3-yl-propyl moiety in 23.
Figure 1. Sites of modification.
After silyl deprotection with TBAF, spirocyclization of 24
was achieved with TMSOTf as promoter to give 8a after
separation from the accompanying cis diastereomer by HPLC.5
The spirocyclization of 4-methylamino-cyclohexanone 27
gave the corresponding N-monomethyl analogue 28a.
Also cyclic amino heads, such as 4-phenyl-4-pyrrolidin-1-yl-
cyclohexanone, were successfully synthesized and spirocyclized
in analogous manner to give 38b−40b.
Table 1. Modification of Spirocyclic Oxygen, Region A
As illustrated in our previous publication, compound 2a,
following intravenous administration, showed excellent efficacy
in the rat tail-flick and spinal nerve ligation model while having
a promising side effects profile. Nevertheless, it suffered from
poor oral bioavailability and high clearance. To understand this
further we subjected 2a to metabolite ID. These investigations
identified N-demethyl compound 28a (Table 2) and 6′-
hydroxy compound 48a (Table 3) as metabolites in humans
and rodents. Our optimization efforts therefore aimed at
targeting both sites of metabolism to improve the PK profile.
The dimethyl amine head was tackled first. Synthesis of the
N-demethyl metabolite, analogue 28a, resulted in a compound
with potent NOP and MOP receptor binding activity. For the
cyclic amine heads piperidine 38b, N-methyl piperazine 39b,
and morpholine 40b, we only obtained the generally less active
cis stereoisomer. However, because the introduction of cyclic
amine heads resulted in complete loss of binding affinities, we
concluded that there is little room for optimization here and
retained the dimethylamino moiety for further optimization.
We therefore turned our interest to the 6′-position of the
indole spiro scaffold with the aim to block this point of
metabolic instability.
% inhibition @ 1 μM or Ki
(nM)
compd
X
config
hNOPr
hMOPr
b
2a
O
trans
cis
0.1
0.26
310
0.39
0.24
3.1
b
2b
O
30%
0.19
0.55
3.7
c
5a
NH
NMe
S
trans
trans
trans
trans
c
6a
a
7a
8a
CH2
1.26
1.95
a
b
c
Hemicitrate. Hydrochloride. Dihydrochloride.
The wide range of tolerated moieties suggests that, upon
cyclization, the molecule has been brought into a preferred
conformation at both receptors (Figure 2). As a consequence of
As previously reported, the relative stereochemistry remained
crucial for high NOP and MOP receptor binding affinities3 with
the trans stereoisomer being the favored stereoisomer with
respect to binding affinity (2a vs 2b; 3a vs 3b). This has been
rationalized, through a bidentate, chelating binding mode to
Asp130, which is only feasible from the trans configuration.3
Pleasingly, a variety of small substituents such as Me (47a), F
(3a, 3b, and 4a), OH (48a), and OMe (49a) could be obtained
by use of trytophols 41−43 and TMS ether 45 and were well
tolerated by both receptors. Indeed, as described in Table 3, all
trans stereoisomers demonstrated binding affinities below 20
nM at both the NOP and MOP receptor.
Despite the good receptor binding properties, we decided
only to progress compounds with a NOP/MOP selectivity
factor of <5, as our focus was for equipotent NOP and MOP
receptor binders. On this basis, compounds 3a, 4a, 5a, and 48a
were advanced into in vitro functional testing.
Figure 2. Three-dimensional structural overlay of the binding modes
of 3a in the NOP and MOP receptors. NOP: Binding modes of 3a
(orange) in the NOP receptor: NOP ribbons, blue; residues, cyan.
MOP: Binding modes of 3a (green) in the MOP receptor: MOP
ribbons, red; residues, yellow. MOP ribbons of helix 7, His319/
Arg302, removed for clarity.
Equipotent binding at the MOP and NOP receptor was
rationalized by overlaying the recently published crystal
structures of the MOP and NOP receptors.6,7 Major differences
of the MOP and NOP receptor binding sites are Lys233
(MOP)/Ala216 (NOP), Asn127 (MOP)/Asp110 (NOP),
His319 (MOP)/Arg302 (NOP), and Tyr128 (MOP)/Ile111
(NOP) switches (Figure 2).
these results and employing the most favored core from a
lipophilicity point of view, we focused our efforts for further
optimization on the oxacyclic moiety.
The synthesis of chemotypes described in this letter is shown
in Scheme 1. Tryptophol 9 or its TMS ether 10, thiotryptophol
13, and commercially available tryptamines 14 and 15 were
cyclized with 4-dimethylamino-4-phenyl-cyclohexanone 19 to
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a
Scheme 1. Synthesis of Investigated Spirocycles
a
Reagents and conditions: (a) (i) HN(TMS)2, TMSCl, THF; (ii) NaHCO3, Et2O, 88−100%; (b) (i) Na2S2O3, H2O, EtOH reflux; (ii) i-PrOH
reflux, 75%; (c) 50 v/v H3PO4/H2O, Et2O, reflux, 96%; (d) (i) HY or 40 w/w HNMe2/H2O, MeOH, 4 N HCl, KCN, 0 °C to rt; (ii) H2O, Et2O,
DCM, 84−97%; (e) (i) PhMgCl, THF, 0 °C to rt; (ii) NH4Cl, H2O, 0 °C to rt, Et2O; (f) 2-butanone, TMSCl, 0 °C to rt, 35−58% over steps (e)
and (f); (g) (i) 7.5 N HCl, Et2O; (ii) NaOH, 78−97%; (h) 5-(TES)-4-pentin-1-ol, MeCN, Ph3PI2, imidazole, 70%; (j) (i) t-BuLi/pentane, Et2O,
−75 to −70 °C; (ii) 13, Et2O, 28%; (k) (i) iodoaniline, [1,3-bis(2,6-i-Pr2Ph)-imidazol-2-ylidene]-(3-Cl-Py)Pd(II)-chloride, Na2CO3, DMF, 100 °C;
(ii) Na2S2O3, 66%; (l) TBAF, THF, reflux, 50 °C, 36%; (m) TMSOTf, DCM, rt, 33−99%; (n) (i) H3PO4, conc. AcOH; (ii) NaOH, 96%; (o)
TfOH, DCM, rt; (ii) NaOH; (iii) MeOH, 65−67%; (p) TFA, DCE, 3−31%; (q) (i) TMSOMs, DCM, rt; (ii) filtration; (iii) evaporation filtrate,
recryst EtOH; (iii) citric acid, EtOH, 65 °C to rt, 11% 7a; (r) (i) MsOH, DCM; (ii) filtration, 63−99%; (s) citric acid, hot ethanol, 5 °C 12 h, 53−
99%.
Table 2. Variation of the Amine Head, Region C
Table 3. Variation of Substituents at Major Metabolic
Positions, Region B
% inhibition @ 1 μM or
Ki (nM)
% inhibition @ 1 μM or
Ki (nM)
compd
Y
config
hNOPr
hMOPr
a
compd
R1
R2
config
hNOPr
hMOPr
2a
NMe2
trans
trans
cis
0.1
0.26
b
a
28a
NHMe
1.1
0.36
3a
F
F
F
Me
Me
H
trans
cis
0.9
97.4
11
0.7
46
2
c
a
38b
piperidin-1-yl
<10%
<10%
43%
3b
d
a
39b
4-Me-piperazin-1-yl
cis
<10%
<10%
4a
trans
trans
trans
trans
c
a
40b
morpholin-4-yl
b
cis
<10%
d
47a
Me
Me
Me
Me
4.5
1
2.7
0.4
1.1
a
a
c
48a
OH
OMe
Hydrochloride. Hemicitrate. Methanesulfonate. Dimethanesulfo-
b
nate.
49a
9.4
a
b
Hemicitrate. Hydrochloride.
This should allow for similar pi−pi stacking interactions of
aromatic moieties at the NOP and MOP receptors. Hydro-
phobic cavities are conserved in both receptors. We have
subsequently docked compound 3a in both receptors and
observed only slightly different binding modes;8 therefore,
similar binding affinities at the NOP and MOP receptors are to
be expected.
More detailed characterization of 3a hemicitrate revealed
binding affinities of 2.6 nM (N = 7, SD = 1.4) and 18.0 nM
(N = 11, SD = 20.0 nM) at the hKOP and hDOP receptors.9
Functional investigations on 3a, 4a, 5a, and 48a revealed that
all compounds acted as full agonists at both the MOP and NOP
receptor and could therefore be progressed (Table 4). We
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nevertheless decided to drop 5a because of concerns with
regards to hERG (data not shown).
Table 4. Functional Assay Results for Selected Compounds
a
EC50 GTPγS (nM)
hNOPr hMOPr
13 1.2
rel. eff. GTPγS
compd
hNOPr
hMOPr
b
3a
89%
104%
110%
101%
96%
b
4a
60
2.6
0.2
1.2
101%
108%
75%
c
5a
1.3
120
b
48a
a
Efficacy of 100% is defined as maximum [35S]GTPγS binding induced
by stimulation with nociceptin (NOP receptor) and DAMGO (MOP
b
c
receptor). Hemicitrate. Dihydrochloride.
After these promising in vitro results we progressed 3a, 4a,
and 48a into in vivo PK profiling. Compound 3a showed good
mouse PK properties with low clearance (Cl = 0.96 L/h·kg),
moderate half-life (t1/2 = 2.57 h), medium volume of
distribution (Vc = 2.96 L/kg), and good oral bioavailability
(F = 44%). In rats, 3a achieved a significant improvement in
oral bioavailability (F = 23%) as compared to 2a (F = 4%).3
The mouse PK of 4a is characterized by a very high clearance
(Cl = 15.3 L/h·kg), very high volume of distribution (Vz = 72.5
L/kg), longer half-life (t1/2 = 3.50 h), and good oral
bioavailability (F = 44%).
Compounds 3a, 4a, and 48a were initially compared with
regards to their activity in a mouse tail-flick model of acute
nociceptive pain using a method modified from D’Amour and
Smith.10 Antinociceptive activity of the compounds was
quantified after i.v. and p.o. dosing by measuring the increase
in the latency for tail withdrawal from a radiant heat source in
male NMRI mice11 (Table 5). Compound 3a induced dose-
dependent inhibition of heat nociception with ED50 values of
40.1 nmol/kg i.v. and 77.0 nmol/kg p.o. (Figure 3 and Table
5). With both routes of administration, the maximum attainable
antinociceptive response was obtained, indicating full anti-
nociceptive efficacy.
Figure 3. Mouse tail-flick test: Dose−response curves of cebranopadol
(3a) hemicitrate (A) and 4a hemicitrate (B) obtained after oral
administration. Each point of the graph represents the mean SEM of
the maximum possible effect (MPE); n = 10 animals per group. *p <
0.05 versus vehicle.
In order to characterize the duration of analgesic action, equi-
effective dosages of the high dose range (>90% of the
maximum possible effect (MPE)) were chosen. After oral
administration, significant antinociceptive activity was observed
for more than 8 h (last test point measured), where 85% MPE
was still reached. The duration of action after intravenous
administration lasted up to 3 h, where 38% MPE was measured.
These investigations demonstrate that 3a is highly effective in
an animal model of acute nociceptive pain. It is about as equi-
potent to the strong opioid fentanyl citrate but shows a
significantly longer duration of action and, in contrast to
fentanyl, displays high potency and long lasting efficacy as well
after oral administration (see Table 5).
Table 5. In Vivo Results for Selected Compounds in a Mouse Tail-Flick Model of Acute Nociceptive Pain
tail-flick mouse
e
compd
ED50 (95% CI) [nmol/kg]
Emax (%MPE)
duration of action (min)
d
d
3a
i.v.: 40.1 (30.4−48.5)
p.o.: 77.0 (57.8−98.1)
i.v.: 434 (347−499)
p.o.: 1432 (1172−1758)
i.v.: 22.2 (18.0−27.6)
p.o.: 3062 (2622−3538)
i.v.: 11.2 (8.5−15.1)
p.o.: 1956 (1378−2797)
i.v.: 622 (529−778)
p.o.: 18753 (13466−25284)
>95
100
100
>95
>95
100
100
100
100
>95
180
>480
300
>600
n.d.
n.d.
40
4a
c
48a
fentanyl citrate
90
hydromorphone HCl
n.d.
n.d.
a
b
c
d
e
Hydrochloride. Dihydrochloride. Citrate. Hemicitrate. Duration of action was determined for a dose that produces approximately 90% MPE; it
describes the duration for which the antinociceptive efficacy is >20% MPE. n.d. = not determined.
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Compound 4a also exerted dose-dependent activity in the
mouse tail-flick test (Figure 3), with ED50 values of 434 nmol/
kg i.v. and 1432 nmol/kg p.o. This is about 10-fold less potent
than 3a after both i.v. and p.o. dosing, which can be clearly
explained by the observed higher volume of distribution and
clearance. The potency of 48a after oral dosing was surprisingly
low as compared to cebranopadol 3a and could only be partially
explained by its lower oral bioavailability (F = 14%).
A model of streptozotocin (STZ)-induced diabetic poly-
neuropathy was used to explore the efficacy of 3a in a
neuropathic pain state (see Supporting Information for details).
A dose of 2.1 nmol/kg i.v. of 3a was tested in STZ-treated
diabetic CD-1 mice and, for comparison, in nondiabetic control
animals. While 3a induced a significant reduction of thermal
hyperalgesia assessed in a hot plate test, it was without an
antinociceptive effect in the control animals. The antihyper-
algesic efficacy of 2.1 nmol/kg i.v. of 3a was calculated to be
54.1% MPE (n = 10, SEM 4.6% MPE; p < 0.001 vs vehicle
control) (Figure 4). Thus, in the neuropathic pain state, 3a
nM), the affinities toward these safety relevant targets are
expected to be without biological relevance. More detailed
electrophysiological investigations using the whole-cell patch-
clamp technique12 revealed that 3a did not affect hERG-
mediated potassium currents in transfected HEK293 cells up to
10 μM.
Having ensured a low potential to induce cardiac side effects
by 3a we embarked on assessing its side effects profile.
Treatment with opioid drugs can be associated with severe side
effects on the central nervous system (CNS) and gastro-
intestinal functions.13
In order to investigate its potential to affect the CNS, 3a was
investigated in a rota-rod test.14 In male CD-1 mice,
intravenous administration of 3a at doses up to 376 nmol/kg
did not significantly influence motor coordination in the rota-
rod test. At a dose of 454 nmol/kg, 3a induced a significant
impairment of the rota-rod performance. The time that animals
were able to remain on the rotating rod was shortened
transiently for about 30−60 min after administration. The
maximum effect was observed 15 min after administration,
when the time on the rod was shortened from the maximum
performance time of 120 s to 72
Concurrently, the number of failures increased significantly up
to 2.6 0.9 (mean SEM). The no observed effect level
17 s (mean
SEM).
(NOEL) for 3a was therefore considered to be 376 nmol/kg.
An ED50 value could not be calculated but is estimated to be
>454 nmol/kg. Compound 3a is, thus, characterized by a safety
margin ≥10-fold between the ED50 value in the tail-flick test
and the NOEL for effects on motor coordination (Figure 4).
This is in clear contrast to standard opioids such as morphine
or oxycodone that impair motor coordination within the
antinociceptive dose range.15
Effects of 3a on the gastrointestinal system were investigated
in the charcoal transit test in male NMRI mice.16 In this assay,
effects on gut motility were measured as changes in transit rate
of an orally administered charcoal suspension. Intravenous
administration of 3a at doses between 10 and 454 nmol/kg
induced a dose-dependent inhibition of intestinal charcoal
transit. NOEL was 21 nmol/kg i.v., and the ED50 was 87 nmol/
kg i.v. A comparison of this ED50 value to the ED50 value in the
mouse tail-flick assay points toward a separation of the analgesic
dose range from doses inhibiting gastrointestinal motility. In
contrast to standard opiates like morphine, which inhibits
intestinal transit in mice already at doses below the ED50 in the
tail-flick assay,16,17 3a clearly showed effects on gut motility at
doses higher than those required to induce antinociception.
In summary, 3a (cebranopadol) exhibited high efficacy in a
mouse model of acute pain with a potency comparable to the
strong opioid fentanyl. In a model of polyneuropathic pain, 3a
(cebranopadol) showed an about 20 times higher potency as
compared to the acute pain model. In contrast to standard
opioids, which induce marked CNS side effects and inhibition
of gastrointestinal transit at doses below or within the half-
maximum effective analgesic dose range,17,18 3a (cebranopadol)
exhibits distinctly improved margins between the analgesic dose
range and doses inducing significant gastrointestinal or CNS
side effects, which point towards a broader therapeutic window
(Figure 4).
Figure 4. Dose-dependent effects of 3a (cebranopadol) hemicitrate on
heat nociception (tail-flick and hot plate in STZ control animals), on
thermal hyperalgesia (hot plate in STZ diabetic animals), and on
#
motor coordination (rota rod) after i.v. administration in mice.
,
Relative effect refers to percentage of maximum possible effect (%
MPE) for tail-flick and STZ models, or relative decrease in
performance time on the rotating rod (rota rod). Error bars indicate
SEM (n = 10). *, p < 0.05 versus vehicle control.
showed about half-maximum antihyperalgesic activity at a dose
being 20 times lower than the ED50 value in the tail-flick model
of acute nociception.
We decided to progress 3a, due to its high efficacy and
potency after oral and intravenous administration, for in-depth
profiling. The cytochrom-P450 inhibition potential of 3a was
estimated after incubation with human CYP1A2, CYP2A6,
CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, or
CYP3A4/5 and probe substrates selectively metabolized by
these enzymes. None of the tested cytochrome P450 enzymes
were inhibited in vitro by 3a up to 250 nM.
The interaction of 3a with safety-relevant cardiovascular
targets was characterized: L-type Ca2+-channel (benzothiaze-
pine site) rat brain cortex Ki (μM) = 0.8 (N = 2); L-type Ca2+-
channel (phenylalkylamine site) rat brain cortex Ki (μM) =
0.48 (N = 2); L-type Ca2+-channel (dihydropyridine site) rat
whole brain Ki (μM) > 100 (N = 2); and hERG channel human
recombinant Ki (μM) > 100 (N = 2). Taking into account the
high affinity of 3a to interact with the primary targets (Ki < 1
A more detailed investigation of cebranopadol’s pharmaco-
logical profile has been published elsewhere.9 Currently,
cebranopadol is in clinical development for the treatment of
severe chronic nociceptive and neuropathic pain.
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ACS Medicinal Chemistry Letters
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(6) Thompson, A. A.; Liu, W.; Chun, E.; Katritch, V.; Wu, H.; Vardy,
E.; Huang, X.-P.; Trapella, C.; Guerrini, R.; Calo, G.; Roth, B. L.;
Cherezov, V.; Stevens, R. C. Structure of the nociceptin/orphanin FQ
receptor in complex with a peptide mimetic. Nature 2012, 485, 395−
399.
(7) Manglik, A.; Kruse, A. C.; Kobilka, T. S.; Thian, F. S.; Mathiesen,
J. M.; Sunahara, R. K.; Pardo, L.; Weis, W. I.; Kobilka, B. K.; Granier,
S. Crystal structure of the μ-opioid receptor bound to a morphinan
antagonist. Nature 2012, 485, 321−326.
(8) Standard modeling techniques have been applied to dock,
optimize, and visualize the binding modes of our compounds as
implemented in MOE2012.10 (Molecular Operating Environment
2012, CCG, Montreal, Canada).
ASSOCIATED CONTENT
* Supporting Information
Assay description and experimental procedures for the
synthesis and characterization of selected compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
AUTHOR INFORMATION
■
Corresponding Author
*(S.S.) E-mail: stefan.schunk@grunenthal.com.
Notes
(9) Linz, K.; Christoph, T.; Tzschentke, T. M.; Koch, T.; Schiene, K.;
The authors declare no competing financial interest.
Gautrois, M.; Schroder, W.; Kogel, B. Y.; Beier, H.; Englberger, W.;
̈
̈
Schunk, S.; De Vry, J.; Jahnel, U.; Frosch, S. Cebranopadol: A novel
potent analgesic nociceptin/orphanin FQ peptide and opioid receptor
agonist. J. Pharmacol. Exp. Ther. 2014, 349, 535−548.
ACKNOWLEDGMENTS
■
We would like to thank H. Steinhagen, P. Ratcliffe, S. Frosch,
and E. Hoppe for very helpful discussions, F. Theil (ASCA
GmbH) for conception and realization of compounds, T. Koch
for obtaining NOP and MOP receptor binding data,and S.
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ABBREVIATIONS
■
CHO, Chinese hamster ovary cells; CI, confidence interval;
CNS, central nervous system; DOP, delta opioid peptide; EC50,
concentration with half-maximum inducible [35S]GTPγS bind-
ing; ED50, half-maximum effective dose; Emax, maximum
possible effect for the agonist; GTPγS, guanosine-5′-[γ-
thio]triphosphate; hNOPr, Human nociceptin/orphanin FQ
receptor; hMOPr, Human μ opioid receptor; HCl, hydro-
chloride; IC50, half-maximum inhibitory concentration; i.v.,
intravenous; Ki, dissociation constant for inhibitor binding;
KOP, kappa opioid peptide; MeCN, acetonitrile; MOP, mu
opioid peptide; MPE, maximum possible effect; NOEL, no
observed effect level; NOP, nociceptin/orphanin FQ peptide;
SNL, spinal nerve ligation; TES, triethylsilyl
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