Synthesis and pharmacological activities of 6-glycine substituted 14-phenylpropoxymorphinans, a novel class of opioids with high opioid receptor affinities and antinociceptive potencies

Article abstract of DOI:10.1021/jm101211p

The synthesis and the effect of a combination of 6-glycine and 14-phenylpropoxy substitutions in N-methyl- and N-cycloproplymethylmorphinans on biological activities are described. Binding studies revealed that all new 14-phenylpropoxymorphinans (11-18) d

Full text of DOI:10.1021/jm101211p

980 J. Med. Chem. 2011, 54, 980–988
DOI: 10.1021/jm101211p
Synthesis and Pharmacological Activities of 6-Glycine Substituted
14-Phenylpropoxymorphinans, a Novel Class of Opioids with High Opioid
Receptor Affinities and Antinociceptive Potencies†
§
§
‡
Mariana Spetea,‡,# Petra Windisch,‡,# Yan Guo, Indre Bileviciut^e-Ljungar, Joha^nnes Schutz,
€
Muhammad Faheem Asim, Ilona P. Berzetei-Gurske, Pal Riba, Kornel Kiraly, Susanna Furst,
‡
^
€
Mahmoud Al-Khrasani,^ and Helmut Schmidhammer*,‡
‡Department of Pharmaceutical Chemistry, Institute of Pharmacy and Center for Molecular Biosciences Innsbruck,
University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria, §Department of Physiology and Pharmacology,
Karolinska Institutet, S-171 77 Stockholm, Sweden, Biosciences Division, SRI International, 333 Ravenswood Avenue,
Menlo Park, California 94025, United States, and ^Department of Pharmacology and Pharmacotherapy,
Medical Faculty, Semmelweis University, Nagyvarad ter 4, POB 370, H-1445 Budapest, Hungary.
# These authors contributed equally to this work.
Received September 16, 2010
The synthesis and the effect of a combination of 6-glycine and 14-phenylpropoxy substitutions in N-
methyl- and N-cycloproplymethylmorphinans on biological activities are described. Binding studies
revealed that all new 14-phenylpropoxymorphinans (11-18) displayed high affinity to opioid receptors.
Replacement of the 14-methoxy group with a phenylpropoxy group led to an enhancement in affinity to
all three opioid receptor types, with most pronounced increases in δ and κ activities, hence resulting in a
loss of μ receptor selectivity. All compounds (11-18) showed potent and long-lasting antinociceptive
effects in the tail-flick test in rats after subcutaneous administration. For the N-methyl derivatives 13
and 14, analgesic potencies were in the range of their 14-methoxy analogues 9 and 10, respectively. Even
derivatives 15-18 with an N-cyclopropylmethyl substituent acted as potent antinociceptive agents,
being several fold more potent than morphine. Subcutaneous administration of compounds 13 and 14
produced significant and prolonged antinociceptive effects mediated through peripheral opioid
mechanisms in carrageenan-induced inflammatory hyperalgesia in rats.
Introduction
work on 14-alkoxymorphinans led to the development of 14-
methoxymetopon13 (2; Figure 1). It was reported as a selective
and high efficacy μ opioid receptor agonist showing potent
centrally mediated antinociceptive effects and less pronounced
typical opioid adverse actions.12-18 A derivative of the 14-alk-
oxymorphinan series of opioids, 14-phenylpropoxymetopon19
(3; Figure 1), has been described as an extremely powerful
analgesic with high affinity for all three opioid receptor types
(μ, δ, and κ).19 Similar results were provided on differently N-
substituted 14-phenylpropoxymorphinan-6-ones (e.g.,N-allyl
and N-cyclopropylmethyl substituted morphinans 5 and 6).20
It was established that the presence of a 14-phenylpropoxy
group increases both the agonist potency and the affinity
for all three opioid receptor types while concurrently dimin-
ishing the selectivity for any of the receptors. The two classical
opioid antagonists naloxone (7) and naltrexone (8) were
converted into highly active analgesic agents by introducing
a phenylpropoxy group in position 14 (compounds 5 and 6,
respectively).20 Moreover, derivatives of the selective μ opioid
receptor antagonist cyprodime having a phenylpropoxy
group at C-14 have also acted as potent antinociceptives
in different pain models in mice after subcutaneous (sc)
administration.21 Thus, the presence of this substituent
directs to a profound alteration in the pharmacological
profile of morphinan-6-ones.
The clinical management of pain, especially severe and
chronic pain, is still a major challenge.1,2 Analgesic drugs
such as opioids play a central role in pain control.2,3 Together
with endogenous opioids, they modulate nociceptive trans-
mission at different levels in the pain modulating pathways
via interaction with opioid receptors.4-6 The efficacy of
currently used opioid analgesics, including morphine, oxy-
morphone, oxycodone, and fentanyl, is frequently asso-
ciated with the occurrence of undesired dose-limiting side
effects.2,3 There is a continued search for opioids that are
highly efficacious with reduced complications and improved
patient compliance.
Work in our laboratory has been focused on the development
of new opioid agonists and antagonists from the morphinan
class of compounds.7-9 Introduction of a 14-methoxy group
in oxymorphone resulted in 14-O-methyloxymorphone10
(1; Figure 1), which not only increases affinity to opioid
receptors while retaining the μ receptor selectivity but also
markedly enhances the antinociceptive potency.10-12 Further
†This paper is dedicated to Dr. Kenner C. Rice on the occasion of his
70th birthday.
*To whom correspondence should be addressed. Phone: (43) 512-
507-5248. Fax: (43) 512-507-5248. E-mail: helmut.schmidhammer@
uibk.ac.at.
r
pubs.acs.org/jmc
Published on Web 01/14/2011
2011 American Chemical Society

Article
Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4 981
Scheme 1. Synthesis of 14-Phenylpropxymorphinans 11-18a
Figure 1. Structures of ligands related to 14-O-methyloxymor-
phone (1), naloxone (7), and naltrexone (8). CPM, cycloproply-
methyl; Ph, phenyl.
a Reagents and conditions: (a) glycine-t-butylester hydrochloride,
NaCNBH3, DMF/MeOH 10:1, RT; (b) separation of the diastereo-
isomers using column chromatography (silica gel); (c) 4 M HCl in
dioxane, reflux.
Traditionally, analgesic effects of opioids have been asso-
ciated with exclusive activation of opioid receptors in the
central nervous system (CNSa). There is large evidence that
intrinsic pain control can also occur at peripheral sites,6,22-24
which is supported by the identification of peripheral opioid
receptors on sensory neurons.25,26 The contribution of the
opioid system to peripheral pain control mechanisms gained
considerable attention during the past years, leading to new
directions in research focusing on exploration of the thera-
peutic potential of peripheral opioid receptors for superior
management of pain.6,23,24,27,28 Targeting peripheral mecha-
nisms can provide selective peripheral analgesia by avoiding the
central complications associated with the use of opioids.6,23,27
Our research in the field of peripherally acting opioid
antinociceptive agents has led us to obtain a series of 6-amino
acid substituted derivatives (glycine, alanine, and phenylalanine)
of 14-O-methyloxymorphone (1).29 These compounds dis-
played high affinities at the μ opioid receptor and showed
potent agonism.30 A number of pharmacological studies
reported that amino acid substitution in position 6 of 14-O-
methyloxymorphone affords derivatives that produce potent
antinociceptive actions in rodent models of acute nociception,
inflammatory, visceral, and neuropathic pain.18,31-33 These
antinociceptive effects were shown to be mediated by activating
primarily peripheral opioid receptors. They showed markedly
long-lasting antinociceptive actions compared to the conven-
tional centrally acting μ opioids, fentanyl, morphine, the parent
compound 1, and 14-methoxymetopon (2).8,31-33 The most
potentcompoundswerethe 6-glycine, 14-methoxysubstituted
derivatives 9 and 10, respectively (Figure 1). The 6β-glycine
analogue 10 exhibited an antinociceptive potency comparable
to fentanyl and was only 2-fold lower than that of 14-O-methyl-
oxymorphone (1) after sc administration.31
the biological profile represented by in vitro binding and
antinociceptive activities after sc administration to rats.
Structure-activity relationship (SAR) studies relating to
the substitution pattern in positions 6 and 14 within this series
were pursued. To this aim, 6-glycine derivatives having a 14-
phenylpropoxy group (compounds 13, 14, 17, and 18) were
synthesized and their in vitro and in vivo opioid activities were
evaluated. We have also assessed the peripheral mechanisms
of antinociceptive effects of derivative 13 and 14 after sc
administration to rats with carrageenan-induced inflamma-
tory pain. In addition, the pharmacological properties of the
corresponding tert-butyl esters 11, 12, 15, and 16 were in-
vestigated in order to extend the SAR in the series of 14-
alkoxymorphinans.
Chemistry. Reductive amination of the 14-phenylpropoxy-
morphinan-6-ones 421 and 620 was performed with glycine
tert-butyl ester hydrochloride and NaCNBH3 in DMF/
MeOH 10:1 at room temperature (Scheme 1). The diastereo-
isomers were separated by medium pressure liquid chroma-
tography (MPLC) to obtain 11, 12, 15, and 16. Ester cleavage
of the tert-butyl derivatives in dioxane/HCl generated the
amino acids 13, 14, 17, and 18. Configuration assignments
at C(6) are based on the coupling constants (J(5,6)) between
H-C(5) and H-C(6). J(5,6) values for 6R-amino epimers
are smaller (3.2-4.0 Hz) than for 6β-amino epimers (6.5-
7.8 Hz).29,34,35 The results for compounds 11-18 agree with
the earlier findings.
Results and Discussion
In Vitro Opioid Receptor Binding Affinities. Binding affi-
nities of the newly synthesized compounds 11-18 at opioid
receptors were determined by in vitro competition binding
assays using rat brain (μ, δ) and guinea pig brain (κ) mem-
branes and employing [3H][D-Ala2,Me-Phe4,Gly-ol5]enkephalin
([3H]DAMGO, μ),36 [3H][Ile5,6]deltorphin II (δ),37 and [3H]-
(5R,7R,8β-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4-
5)dec-8-yl]benzeneacetamide) ([3H]U69,593, κ)38 as specific
opioid radioligands.30 The μ, δ, and κ opioid receptor
binding affinities expressed as inhibition constants (Ki) are
summarized in Table 1. The selectivity for the μ opioid
receptor vs δ and κ receptors was defined by the ratio of
In the present study, we have investigated the effect of a
combination of 6-amino acid and 14-phenylpropoxy substitu-
tions in N-methyl- and N-cycloproplymethylmorphinans on
a Abbreviations: CHO, Chinese hamster ovary; CNS, central nervous
system; DAMGO, [D-Ala2,Me-Phe4,Gly-ol5]enkephalin; DMF, N,N-
dimethylformamide; DPDPE, [D-Pen2,D-Pen5]enkephalin; HEPES,
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; GDP, guanosine
diphosphate; [35S]GTPγS, guanosine-50-O-(3-[35S]thio)-triphosphate;
MPLC, medium pressure liquid chromatography; SAR, structure-
activity relationship; Tris, tris-(hydroxymethyl)-aminomethane; U69,593,
5R,7R,8β-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4-5)dec-8-yl]-
benzeneacetamide.

982 Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4
Table 1. Binding Affinities at μ, δ and κ Opioid Receptors
Spetea et al.
Ki (nM)a
selectivity ratio
compd
morphined
μ receptor [3H]DAMGOb
δ receptor [3H][Ile5,6]deltorphin IIb
κ receptor [3H]U69,593c
δ/μ
κ/μ
6.55 ( 0.74
0.20 ( 0.05
0.34 ( 0.06
0.89 ( 0.09
0.83 ( 0.02
1.40 ( 0.07
1.03 ( 0.25
0.19 ( 0.02
0.16 ( 0.02
1.38 ( 0.21
1.01 ( 0.21
0.27 ( 0.02
0.20 ( 0.04
217 ( 19
113 ( 9a
33
17
3e
0.14 ( 0.02
0.48 ( 0.05
15.4 ( 1.4
0.54 ( 0.15
0.41 ( 0.09
43.2 ( 7.0a
44.8 ( 0.1a
1.26 ( 0.30
2.02 ( 0.68
0.73 ( 0.01
0.81 ( 0.03
1.49 ( 0.27
1.77 ( 0.37
0.64 ( 0.01
0.65 ( 0.01
0.7
1.4
17
2.7
1.2
49
6f
9g
10g
11
12
13
14
15
16
17
18
7.86 ( 0.64
1.01 ( 0.06
0.92 ( 0.16
0.22 ( 0.02
0.19 ( 0.01
1.11 ( 0.07
0.40 ( 0.07
0.33 ( 0.10
0.35 ( 0.04
10
54
0.7
0.9
1.2
1.2
0.8
0.4
1.2
1.7
0.9
2.0
3.8
5.1
1.1
1.8
2.4
3.2
a Values represent the mean ( SEM. b Rat brain membranes were used. c Guinea pig brain membranes were used. d From ref 17. e From ref 19. f From
ref 20. g From ref 30.
the Ki values. For comparison purposes, the opioid binding
affinity data for morphine, 3, the 6R- and 6β-glycine con-
jugates of 14-O-methyloxymorphone, 9 and 10, respectively,
and the 14-phenylpropoxy analogue of naltrexone, com-
pound 6, are included. All compounds 11-18 bound with
high affinity at the μ opioid receptor (Ki=0.16-1.40 nM),
having considerably improved interaction with the μ site
compared to morphine. As shown in Table 1, they also exhibit
increased binding affinities at δ and κ receptors as indicated
by the Ki values in the subnanomolar or low nanomolar
range.
substitution, indicating that small alkoxy groups are supe-
rior over arylalkoxy groups in this respect.11 In contrast,
replacement of the 14-methoxy with a phenylpropoxy group
in cyprodime and other 4,5-oxygen bridge opened morphi-
nan-6-ones was found to markedly increase binding affinities
at μ but also at δ and κ receptors, however retaining μ
selectivity.21
The effect on the opioid receptor binding profile upon
different substitution at the nitrogen of the morphinan
skeleton was also investigated. Replacement of the N-methyl
group in 13 and 14 by a cyclopropylmethyl group resulted in
analogues 17 and 18, respectively. The N-cyclopropylmethyl
substitution was well-tolerated as indicated by the high
affinity for all μ, δ, and κ receptors (Ki values in the subnano-
molar range; Table 1). Further evidence for this observation
comes from our previous works where nearly identical affinities
for all opioid receptor types were noted for 319 and naltrex-
one derivative 6.20 It appears that modification of the N-
substituent, methyl vs cyclopropylmethyl, causes no major
alterations in binding affinity and selectivity in this series of
opioid compounds. In other series of morphinans which are
unsubstituted or have a hydroxyl or a small alkoxy group at
C-14, substitution of the N-methyl by a N-cyclopropyl-
methyl group leads to an increase in affinity at δ and κ opioid
receptors but also to a raise in μ affinity, resulting in reduced
μ receptor selectivity.11,41,42 A representative example is the
comparison of binding affinities of oxymorphone (μ:δ:κ =
0.97:80.5:61.6)11 with its N-cyclopropylmethyl analogue nal-
trexone (μ:δ:κ = 0.20:8.70:0.40).42 On the other hand, it has
been shown that replacement of the N-methyl group in 14-
methoxymetopon (2) with a 2-phenylethyl group left the
binding affinities at μ and δ opioid receptors essentially
unchanged but affected interaction with the κ receptor.11
In view of these results, the nature of the substituent at the
nitrogen has a significant effect on both opioid receptor
binding affinity and selectivity of the morphinan class of
opioid compounds, depending on the character and length of
the substituent in position 14.
To investigate the SAR for the novel 14-alkoxymorphi-
nans, the following structural modifications were targeted:
(i) replacement of the methoxy group with a phenylpropoxy
group in position 14, (ii) substitution of the N-methyl with an
N-cyclopropylmethyl group, (iii) modification of the sub-
stituent at position 6 (e.g., 6-glycine vs 6-glycine ester vs
6-keto), and (iv) R vs β orientation of the amino acid residue
at C-6 of the morphinan skeleton. First, we have examined
the result of the replacement of the 14-methoxy group in N-
methyl substituted morphinans 9 and 10 with a phenylpro-
poxy group, leading to compounds 13 and 14, respectively,
on the in vitro opioid binding profile. While the μ affinity was
less affected, affinities at δ and κ receptors were increased
significantly after introduction of a phenylpropoxy substi-
tuent (Table 1). Compared to analogues 9 and 10, affinities
of the 14-phenylpropoxy substituted derivatives 13 and 14
were increased by about 7- and 5-fold at μ, 70- and 42-fold at
δ, and 59- and 55-fold at κ receptors, respectively. On the
basis of these data, it appears that a phenylpropoxy group in
position 14 is not favorable for selective binding to μ, δ, or κ
receptors by causing a notable loss in μ receptor selectivity,
thus, corroborating and extending our previous findings in
other series of 14-phenylpropoxy substituted morphinans.19,20
The present observations together with earlier reports10,11,19,20,39,40
provide additional evidence that interaction with opioid
receptors is sensitive to the character and length of the
substituent in position 14. It has been shown that different
substitution patterns at C-14 in morphinan-6-ones give rise
to compounds with improved or decreased selectivity for the μ
receptor. An enhancement in the binding affinity at δ and κ
receptors has been reported with other substituents at position
14 such as benzyloxy or naphthylmethoxy.11 We have described
that a 14-methoxy group results in higher selectivity for
the μ receptor than 14-benzyloxy or 14-naphthylmethoxy
The effect on opioid receptor binding affinities upon
substitution of a keto group with a glycine residue in position
6 in the N-methyl and N-cyclopropylmethyl 14-phenylpro-
poxy substituted morphinans was examined. The 6-glycine
conjugates 13 and 14 displayed similar binding affinities to
all three opioid receptors as the 6-keto derivative 3. Moreover,
in the N-cyclopropylmethyl series, in a direct comparison of

Article
Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4 983
Table 2. Antinociceptive Potencies in the Tail-Flick Test in the Rat after sc Administration
ED50 (nmol/kg, sc), 95% CLa
time after drug administration
relative potencyb
morphine = 1
compd
0.5 h
6053c
1 h
2 h
13285
3 h
morphine
7626
(5084-11439)
58.5c
1
103
209
104
66
(4037-9080)
137
(8856-19929)
143
9d
437
(243-786)
(85.7-219)
50.8
(36.5-93.7)
29.0c
(86.8-237)
43.3
10d
11
12
13
14
15
16
17
18
(32.7-78.7)
63.5
(18.8-44.9)
58.3c
(27.9-67.1)
84.0
148
(28.4-775)
189
(15.4-262)
164
(18.0-188)
92.3c
(31.4-255)
124
(78.6-341)
127
(39.5-215)
81.1c
(53.0-292)
87.9
(69.8-514)
116
75
(65.0-246)
180
(46.4-139)
143
(43.9-176)
130c
(48.5-278)
192
47
(122-247)
365
(85.8-238)
348c
(73.4-231)
363
(90.0-414)
427
17
(195-687)
33.8
(212-570)
26.8c
(215-615)
34.4
(205-692)
56.0
226
17
(18.8-60.5)
1388
(14.1-51.0)
349c
(17.7-66.8)
433
(21.9-143)
543
(117-16526)
1561
(113-1072)
183
(172-1084)
147c
(180-1636)
e
-
41
(199-12223)
(17.7-1877)
(13.9-1554)
a Values in paranthesis are 95% confidence limits. b Relative potencies were calculated at the peak of action. c Peak of effect. d From ref 31.
e -: no dose-response relationship.
the 14-phenylpropoxy analogue of naltrexone (6) with the
6-glycine derivatives 17 and 18, all compounds showed
comparable affinities at μ, δ, and κ receptors (Table 1).
According to the present results, the 6-glycine derivatives
having a 14-phenylpropoxy group maintained the high affinity
at the μ opioid receptor of the nonzwitterionic compounds 3
and 6, which is in agreement with a further SAR report in
other series of 14-methoxymorphinans containing zwitterionic
moieties such as amino acid residues.29,30 Thus, it is evident
that replacement of the 6-keto group with a glycine residue
does not have a detrimental effect on affinity at the μ
receptor. Analogous observations were made for β-oxymor-
phamine43 and β-naltrexamine44 when having ionizable
moieties at C-6. Also, it has been shown in 4,5-oxygen bridge
opened N-methylmorphinans that a 6-cyano substituent in
comparison to a 6-keto group has a minor impact on the
ability to interact with opioid receptors.45 These findings indicate
that replacement of the 6-keto group with other substituents
such as amino acids or a cyano group produces only minor
changes in the opioid binding profile of morphinans.
The consequence of esterification of the glycine residue at
C-6 on binding affinity and selectivity was also investigated.
As shown in Table 1, the tert-butyl ester derivatives 11, 12,
15, and 16 exhibited a decrease in the affinity at μ, δ, and κ
opioid receptors compared to the 6-glycine analogues 13, 14,
17, and 18, respectively. An exception was ester 16, which
showed comparable δ receptor affinity to analogue 18 (0.40
vs 0.35 nM). However, all esters still display high interaction
with opioid receptors as indicated by the Ki values in the low
nanomolar range (1.01-1.40 nM at μ, 0.40-1.11 nM at δ,
and 1.26-2.02 nM at κ receptors). On the other hand, the
esters also showed to lack selectivity to a receptor type
similar to the corresponding 6-glycine analogues.
it was noted that binding affinities and selectivities of R vs β
epimers did not vary greatly in this series of newly synthe-
sized 14-phenylpropoxymorphinans (Table 1).
Pharmacological Activities. The 6-glycine substituted 14-
phenylpropoxymorphinans 11-18 were further evaluated in
vivo for antinociceptive effects in rats after sc administration
using the tail-flick test.31 Their antinociceptive properties
were compared to those of morphine and derivatives 9 and
10. The antinociceptive ED50 values are listed in Table 2. All
compounds acted as potent antinociceptive agents with long-
lasting action when administered sc, with peak ED50s of
26.8-349 nmol/kg. Peak antinociception occurred generally
one hour after drug sc administration, and only derivatives
14 and 18 had a peak of action at two hours postinjection.
Compared to morphine, the 14-phenylpropoxymorphinans
of this series showed 17- to 226-fold increased analgesic
potency, with compound 16 displaying the highest potency
(Table 2). Antinociceptive potencies of the 6-glycine sub-
stituted 14-phenylpropoxy derivatives 13 and 14 were in the
range of their 14-methoxy analogues 9 and 10, respectively
(Table 2). It appears that a 14-phenylpropoxy substitution
maintains the high analgesic activity, while it largely affects
opioid binding affinities and μ receptor selectivity (Table 1).
Traditional and generally accepted SAR models have
assigned critical importance in defining the pharmacological
profile of agonist/antagonist action of morphinan-6-ones to
the substitutent at the morphinan nitrogen.46-48 Substitu-
ents such as cyclopropylmethyl or allyl at the nitrogen have
been commonly associated with an antagonist character in
this series of opioids. On the other hand, there are a number
of examples where substitution at C-14 affords potent analge-
sics independent of the substituent nature at the morphinan
nitrogen.11,19-21,39,40 Even with a N-substituent that is linked
with distinct antagonist character such as cyclopropyl-
methyl, antinociceptive agents can be obtained and examples
When examining the impact of R/β orientation of the
amino acid residue at position 6 on the in vitro opioid activity,

984 Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4
Spetea et al.
Table 3. Stimulation of [35S]GTPγS Bindinga
μ receptor
δ receptor
κ receptor
compd
17
18
EC50 (nM)
% stimb
EC50 (nM)
% stimc
EC50 (nM)
% stimd
0.69 ( 0.10
1.06 ( 0.28
15.6 ( 0.5
34.7 ( 6.6
24.2 ( 3.0
93 ( 2.8
0.69 ( 0.29
4.24 ( 0.47
316 ( 5
26.1 ( 3.0
34.7 ( 0.6
103 ( 7
1.28 ( 0.35
11.0 ( 1.4
484 ( 213
28.2 ( 1.0
30.4 ( 3.3
62 ( 7
morphine
a Membranes from CHO cells stably transfected with human μ, δ, or κ opioid receptors were incubated with varyingconcentrations of the compounds.
b Compared to DAMGO. c Compared to DPDPE. d Compared to U69,593. Data represent mean ( SEM.
Figure 2. (A) Antinociceptive effects of 6-glycine substituted 14-phenylpropoxymorphinans 13 and 14 after sc administration to rats with
carrageenan-induced inflammatory hyperalgesia. (B) Antagonism by naloxone methiodide (NM) on the antinociceptive effect of compound 13
and 14 after sc coadministration on the inflamed paw withdrawal latencies to mechanical stimulation. Values are presented as % changes in
withdrawal latencies of the inflamed paw from the pretreatment (pre-) values obtained at 3 h after carrageenan injection. Areas under the curves
(AUC) of the respective time curves are represented. Data are shown as mean ( SEM *p<0.05, **p<0.01, and ***p<0.001 vs vehicle-treated
controls; #p<0.05 vs agonist-treated animals.
include the clinically used buprenorphine,49 nalfurafine
(TRK-820) and its analogues,50,51 and 14-aminomorphinone
derivatives.39,40 In the present study, the N-cyclopropyl-
methyl substituted compounds 17 and 18 and their corre-
sponding tert-butyl esters 15 and 16 showed potent
antinociceptive activities in rats after sc administration
(Table 2). The in vivo pharmacology of derivatives 17 and
18 as antinociceptive agents was also supported by the
functional data on the ligand-stimulated guanosine-50-
O-(3-[35S]thio)-triphosphate ([35S]GTPγS) binding to mem-
branes from Chinese hamster ovary (CHO) stably transfected
with human opioid receptors21 (Table 3). Both compounds
were highly potent partial agonists at the μ receptor and also
at δ and κ receptors so that no significant selectivity for any
receptor type was apparent. It is suggested that such com-
pounds which interact with multiple receptor types may have
an overall increased potency derived from the combined action
at μ, δ, and κ opioid receptors.52 Moreover, as found in this
and our earlier studies11,19-21 and also by others,39,40,53-55
not necessarily the nature of the substituent at the nitrogen in
morphine-like compounds but rather residues occupying a
defined position in the vicinity to the morphinan nitrogen
seem to be responsible for agonist/antagonist activity. Our
SAR study also showed that replacement of the N-methyl
group of compounds 13 and 14 with a cyclopropylmethyl
group resulted in analogues 17 and 18, respectively, which
retained the high antinociceptive potency after sc adminis-
tration (Table 2). This holds also true when evaluating the
N-methyl substituted 319 and naltrexone derivative 6,20
which show comparable antinociceptive potencies in differ-
ent analgesic tests in mice after sc administration.
As shown in Table 2, esterification of the glycine residue in
position 6 did not result in major alterations in antinocicep-
tive activities and all tert-butyl esters were found to be greatly
active displaying similar potencies to their corresponding
glycine analogues. Notably, the N-cyclopropylmethyl tert-
butyl ester 16 was about 6-fold more potent than derivative
18. In the tail-flick test, antinociceptive potencies did not
significantly differ between the R and β epimers, which is in
agreement with the in vitro biological data where also no
major changes in opioid binding affinities were observed.
Their ED50 ratios were ranging between 0.6 and 2.4 after sc
administration, except for the pair 15 vs 16, where a 13-fold
difference in the potency was calculated.
Opioids with hydrophilic groups such as amino acid
residues attached to the C-6 position of the morphinan skeleton
were targeted in an effort to obtain opioid compounds that
would have potentially limited access to the CNS and thus to

Article
Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4 985
reduce the activation of central opioid receptors. We have
reported on the potent antinociceptive action of the 6-glycine
conjugate of 14-O-methyloxymorphone, compound 10, after
systemic sc administration to rats with carrageenan-induced
inflammatory hyperalgesia.18 Further in vivo pharmacolo-
gical studies were undertaken in the present study with the
14-phenylpropoxy derivative of 10, compound 14, and its
corresponding 6R-glycine analogue 13 to assess their anti-
nociceptive actions in a rat model of inflammatory pain.
Subcutaneous administration of compounds 13 and 14, in a
dose of 170 nmol/kg, produced a significant attenuation in
pain-related behavior in the inflamed paw by increasing
withdrawal latencies to mechanical stimulation having a
long duration of action (up to 4 h) (Figure 2A). These
observations are in line with the earlier pharmacological
findings on potent and prolonged inhibitory effects of the 14-
methoxy 6-glycine analogue 10 in rats with inflammatory
hyperalgesia.18 Moreover, its antinociceptive actions after sc
administration was shown to be mediated through periph-
eral mechanisms not only in carrageenan-induced hindpaw
inflammation18 but also in other rodent pain models in-
cluding tail-flick test,31 formalin test,31 and acetic acid-
induced writhing.32 The antinociceptive efficacy of deriva-
tives 13 and 14 in tested sc doses in carrageenan-induced
inflammatory pain was comparable to that reported for
compound 10 after a sc dose of 100 μg/kg (i.e., 183 nmol/kg)
and with markedly longer duration of action than morphine
and 14-methoxymetopon (2).18 To evaluate whether the
antinociceptive effect of the 14-phenylpropoxy substituted
derivatives 13 and 14 in rats with carrageenan-induced
hyperalgesia is peripherally mediated, naloxone methio-
dide, the peripherally acting opioid antagonist, was sc
coadministered with each opioid. As shown in Figure 2B,
naloxone methiodide (426 nmol/kg) significantly reversed
the antinociceptive effect of a 170 nmol/kg dose of com-
pound 13 and 14 on mechanical hyperalgesia. Hence,
replacement of the 14-methoxy group in compound 10 with
a phenylpropoxy group gave rise to new derivatives show-
ing peripherally mediated antinociceptive action in a rat
model of inflammatory pain. Outcomes of these studies
extend our earlier reports on 6-amino acid substituted
derivatives (i.e., glycine, alanine and phenylalanine) of 14-
O-methyloxymorphone (1)18,29-33 described as high affi-
nity μ opioid receptor agonists that can induce potent
antinociceptive effects via peripheral opioid receptor-
specific mechanisms.
not appreciably affected upon substitution of the N-methyl
with a cyclopropylmethyl group. Besides the increasedaffinity
for opioid receptors, another attribute of the new 6-glycine
substituted 14-phenylpropoxymorphinans is the potent and
long-lasting antinociceptive effects in rats after sc administra-
tion, displaying considerably increased potency than mor-
phine. For the N-methyl derivatives13 and 14, antinociceptive
potencies were in the range of their 14-methoxy analogues.
Even derivatives 15-18 having a N-cyclopropylmethyl sub-
stituent acted as highly active antinociceptive agents, being
several fold more potent than morphine. Subcutaneous ad-
ministration of the N-methyl 6R- and 6β-glycine substituted
14-phenylpropoxymorphinans 13 and 14, respectively, signif-
icantly reduced mechanical hypersensitivity in rats with car-
rageenan-induced inflammatory pain, effects shown to be
mediated via activation of peripheral opioid receptors. Such
peripherally acting opioids may represent novel drug candi-
dates for pain treatment.
Experimental Section
General Methods. The starting material thebaine was obtained
from Tasmanian Alkaloids Ltd., Westbury, Tasmania, Australia.
Melting points were determined on a Kofler melting point micro-
scope and are uncorrected. 1H NMR spectra were obtained on a
Varian Gemini 200 (200 MHz) spectrometer using tetramethyl-
silane (TMS) as internal standard for CDCl3 and 3-(trimethylsilyl)-
1-propanesulfonic acid sodium salt (DSS) for D2O. Coupling
constants (J) are given in Hz. IR spectra were taken on a Mattson
Galaxy FTIR series 3000 in KBr pellets (in cm-1). Mass spectra
were recorded on a Varian MAT 44 S apparatus. Elemental
analysis was performed at the Institute of Physical Chemistry of
the University of Vienna, Austria. For column chromatography
(MPLC), Silica Gel 60 (0.040-0.063 mm, Fluka, Switzerland) was
used. Thin-layer chromatography (TLC) was performed on silica
gel plates Polygram SIL G/UV254 (Macherey-Nagel, Germany)
with CH2Cl2/MeOH/NH4OH 90:9:1 as an eluent.
Radioligands [3H]DAMGO, [3H]U69,593, and [35S]GTPγS
were purchased from PerkinElmer (Boston, MA, USA).
[3H][Ile5,6]deltorphin II was obtained from the Institute of
Isotopes Co. Ltd. (Budapest, Hungary). Naloxone hydrochloride,
tris-(hydroxymethyl)-aminomethane (Tris), carrageenan (λ-car-
rageenan), naloxone methiodide, GTPγS, guanosine diphosphate
(GDP), and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
(HEPES) were obtained from Sigma Chemicals (St. Louis, MO,
USA). All other chemicals were of analytical grade and obtained
from standard commercial sources. Compounds 11, 12, 15, and
16 were used as bases and compounds 13, 14, 17, and 18 were
used as hydrochloride salts. Purities of tested compounds were
determined by elemental analysis and were g95%.
Conclusions
General Procedure for the synthesis of 13, 14, 17, and 18 (13 as
example). 11 (0.18 g; 0.35 mmol) was dissolved in 5 mL of 4 M
HCl in dioxane and stirred under reflux for 2 h. The colorless
crystals were filtered off under nitrogen, washed with anhydrous
diethyl ether, and dried.
We have described the synthesis and biological activities of
a series of new 6-glycine substituted 14-phenylpropoxymor-
phinans which emerged as high affinity and potent opioid
antinociceptive agents. Specific modifications in the substitu-
tion pattern, such as introduction of a 14-phenylpropoxy
group and a glycine residue at position 6, led to an interesting
alteration in opioid activity by influencing the biological
profile of these compounds interacting with μ, δ, and κ opioid
receptors. On the basis of the SAR that has emerged, it could
be observed that there is a significant enhancement in affinity
at all opioid receptor types upon introduction of a phenyl-
propoxy group at position 14 in 6-glycine substituted mor-
phinans, with most pronounced increases in activity at δ and κ
receptors, leading to a loss in μ receptor selectivity. In vitro
binding affinities to all opioid receptors and selectivity were
[[4,5r-Epoxy-3-hydroxy-17-methyl-14β-[(3-phenylpropyl)oxy]-
morphinan-6r-yl]amino]acetic Acid Dihydrochloride (13 2HCl).
3
Colorless crystals (89%); mp>207 ꢀC (dec). IR (KBr) 1744
(CdO). 1H NMR (D2O) δ 7.47-7.35 (m, 5 arom H), 6.96 (d, J=
8.3, 1 arom H), 6.87 (d, J=8.3, 1 arom H), 5.09 (d, J=3.2,
H-C(5)), 3.01 (s, CH3N). MS (ESI) m/z 479 [M þ 1]þ. Anal.
(C28H34N2O5 2HCl 1.9H2O) C, H, N.
3
3
[[4,5r-Epoxy-3-hydroxy-17-methyl-14β-[(3-phenylpropyl)oxy]-
morphinan-6β-yl]amino]acetic Acid Dihydrochloride (14 2HCl).
3
Colorless crystals (93%). mp>217 ꢀC (dec). IR (KBr) 1740
(CdO). 1H NMR (D2O) δ 7.44 (s, 5 arom H), 6.94 (s, 2 arom H),
4.96 (d, J=7.0, H-C(5)), 2.99 (s, CH3N). MS (ESI) m/z 479 [M þ
1]þ. Anal. (C28H34N2O5 2HCl 2H2O) C, H, N.
3
3

986 Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4
Spetea et al.
[[17-Cyclopropylmethyl-4,5r-epoxy-3-hydroxy-14β-[(3-phenyl-
propyl)oxy]morphinan-6r-yl]amino]acetic Acid Dihydrochloride
limits were calculated according to the method of Litchfield and
Wilcoxon.56
(17 2HCl). Colorless crystals (97%); mp>218 ꢀC (dec). IR
Carrageenan-Induced Hindpaw Inflammation. Unilateral in-
flammation was induced to nonanesthetized rats by injection of
100 μL of 1% carrageenan into the plantar surface of the right
hindpaw as previously described.18 All treatments were per-
formed 3 h after carrageenan injection. Compounds were dis-
solved in physiological saline (0.9%) and administered sc in a
volume of 100 μL. Control animals received the same volume of
sc physiological saline solution. Each experimental group included
four to seven animals. The Randall-Selitto test (Ugo Basile)
was used to assess the hindpaw withdrawal latencies to mechanical
stimulation as described.18 A wedge-shaped, blunt piston with
an area of 1 ꢀ 10 mm2 and a loading rate of 48 g/s was applied to
the dorsal surface of the manually handled hindpaw, and the
time required to initiate the struggle response was assessed and
expressed in seconds. A cutoff time of 20 s was applied. With-
drawal latencies to mechanical stimulation were measured
before injection of carrageenan (basal values), prior to admin-
istration of the drug 3 h postcarrageenan (pretreatment values),
and after drug administration. The antinociceptive response is
expressed as percentage (%) changes in hindpaw withdrawal
latencies from the pretreatment value obtained at 3 h after
carrageenan injection, and was calculated as 100 [(PX - P0)/
P0], where P0 is the latency prior to drug administration at 3 h
postcarrageenan and PX is the latency after drug administration
at corresponding time points.
3
(KBr) 1741 (CdO). 1H NMR (D2O) δ 7.29 (s, 5 arom H), 6.85
(d, J=8.2, 1 arom H), 6.75 (d, J=8.2, 1 arom H), 4.99 (d, J=3.0,
H-C(5)), 0.93 (m, CH-cp), 0.66 (m, CH2-cp), 0.36 (m, CH2-cp)
(cp=cyclopropyl). MS (CI) m/z 519 [M þ 1]þ. Anal. (C31H38-
N2O5 2HCl 1.4H2O) C, H, N.
3
3
[[17-Cyclopropylmethyl-4,5r-epoxy-3-hydroxy-14β-[(3-phenyl-
propyl)oxy]morphinan-6β-yl]amino]acetic Acid Dihydrochloride
(18 2HCl). Colorless crystals (89%); mp > 223 ꢀC (dec).IR (KBr)
3
1741 (CdO).1H NMR (D2O) δ 7.42 (s, 5 arom H), 6.94 (s, 2
arom H), 4.99 (d, J=7.0 H-C(5)), 1.02 (m, CH-cp), 0.82-0.68
(m, CH2-cp), 0.46 (m, CH2-cp) (cp=cyclopropyl.MS (CI) m/z
519 [M þ 1]þ. Anal. (C31H38N2O5 2HCl 1.7H2O) C, H, N.
3
3
Opioid Receptor Binding Assays. Membranes were prepared
from Sprague-Dawley rat or guinea pig brains, obtained from
€
the Institut fur Labortierkunde and Laborgenetik, Medizinische
Universitat Wien (Himberg, Austria), as previously described.
30
€
Binding experiments were performed in 50 mM Tris-HCl buffer
(pH 7.4.) in a final volume of 1 mL containing 0.3-0.5 mg of
protein and at least 10 concentrations of test compound as
described.18 Rat brain homogenates were incubated either with
[3H]DAMGO (1 nM, 45 min, 35 ꢀC) or [3H][Ile5,6]deltorphin II
(0.5 nM, 45 min, 35 ꢀC). Guinea pig brain homogenates were
incubated with [3H]U69,593 (1 nM, 30 min, 30 ꢀC). Reactions
were terminated by rapid filtration through Whatman glass
fiber filters using a Brandel M24R cell harvester, followed by
washing with 50 mM Tris-HCl buffer (pH 7.4). Nonspecific
binding was determined using 10 μM naloxone. The bound
radioactivity was measured by liquid scintillation counting.
Inhibition constant (Ki) values were calculated from competition
binding curves using the nonlinear least-squares curve fitting by
GraphPad Prism program. All experiments were performed in
duplicate and repeated at least three times.
Statistical Analysis. Data are expressed as mean ( SEM. The
areas under the curves (AUC) were calculated by the trapezoidal
rule using NCSS software. Statistical analysis was carried out using
one-way analysis of variances (ANOVA) with Dunnett’s post
hoc test using SPSS software. A p value <0.05 was considered
statistically significant.
Acknowledgment. We thank Tasmanian Alkaloids Pty.
Ltd., Westbury, Tasmania, Australia, for the generous gift
of thebaine. We acknowledge A. Kaletsch, I. Wachtl, and K.
Parina for technical assistance. This work was supported by
CAST, LISA, the Austrian Science Fund (FWF; P15481,
P21350, and TRP 16-B18), the Hungarian grant OTKA-K
60999, and a contract from the National Institute on Drug
Abuse (N01DA-1-8816).
[35S]GTPγS Functional Assays. Functional assays were con-
ducted on human opioid receptors stably transfected into CHO
cells as described.21 Aliquots of cell membranes (15 μg) in buffer
A (20 mM HEPES, 10 mM MgCl2 and 100 mM NaCl, pH 7.4)
were incubated with 0.05 nM [35S]GTPγS, 10 μM GDP, and test
compounds, in a total volume of 1 mL, for 60 min at 25 ꢀC.
Nonspecific binding was determined using 10 μM GTPγS.
Samples are filtered over glass fiber filters and counted as
described for binding assays. Potency (EC50, nM) and percentage
of stimulation (% stim) with respect to the standard agonists
DAMGO (μ), DPDPE (δ), and U69,593 (κ) were calculated
using GraphPad Prism program. The results are mean (
SEM from at least three determinations, each performed in
triplicates.
Supporting Information Available: Additional experimental,
spectroscopic data, elemental analysis results, and supplemen-
tary pharmacology figures. This material is available free of
charge via the Internet at http://pubs.acs.org.
References
In Vivo Assays. General Methods. Male Wistar rats (120-150 g)
used in the tail-flick test were purchased from Charles River
(Budapest, Hungary). Male Sprague-Dawley rats (250 g) used
in carrageenan-induced inflammatory pain were purchased
form B&K Universal Lab (Sollentuna, Sweden). Animals were
maintained on a 12 h light/dark cycle with free access to food
and water at all times except during testing. Experiments were
carried out in accordance to the Declaration of Helsinki and the
Guide for Care and Use of Laboratory Animals. The experi-
mental protocols were approved by the Ethical Board of Sem-
melweis University, Budapest, and Ethics Committee for Animal
Research (North Stockholm, Sweden).
Tail-Flick Test. The tail-flick test was performed according to
the described procedure.31 A beam light was focused on the tip
of the tail and the latency required for the rat to remove its tail
was determined before (basal latencies) and after drug admin-
istration, using an arbitrary cutoff time of twice the basal reaction
time. Compounds were dissolved in distilled water and adminis-
tered sc to rats in a volume of 5 mL/kg of body weight. Each
drug dose or vehicle (distilled water) was tested in at least five
animals. The effective dose 50%(ED50) values and 95% confidence
(1) Breivik, H.; Collett, B.; Ventafridda, V.; Cohen, R.; Gallacher, D.
Survey of Chronic Pain in Europe: Prevalence, Impact on Daily
Life, and Treatment. Eur. J. Pain 2006, 10, 287–333.
(2) Marcus, D. A.; Cope, D. K.; Deodhar, A.; Payne, R. Chronic Pain:
An Atlas of Investigation and Management; Clinical Publishing:
Oxford, 2009.
(3) Benyamin, R.; Trescot, A. M.; Datta, S.; Buenaventura, R.;
Adlaka, R.; Sehgal, N.; Glaser, S. E.; Vallejo, R. Opioid Complica-
tions and Side Effects. Pain Physician 2008, 11, S105–S120.
(4) McNally, G. P.; Akil, H. Opioid Peptides and Their Receptors:
Overview and Function in Pain Modulation. In Neuropsychophar-
macology: The Fifth Generation of Progress; Davis, K. L., Charney,
D., Coyle, J. T., Nemeroff, C., Eds.; Lippincott Williams & Wilkins:
Philadelphia, 2002; pp 34-46.
(5) Kieffer, B. L.; Evans, C. J. Opioid Receptors: From Binding Sites
to Visible Molecules In Vivo. Neuropharmacology 2009, 56, 205–
212.
(6) Stein, C.;Clark, J. D.; Oh, U.;Vasko, M. R.;Wilcox, G. L.;Overland,
A. C.; Vanderah, T. W.; Spencer, R. H. Peripheral Mechanisms of
Pain and Analgesia. Brain Res. Rev. 2009, 60, 90–113.
(7) Schmidhammer, H. 14-Alkoxymorphinans: A Series of Highly
Potent Opioid Agonists, Antagonists, and Partial Agonists. Curr.
Top. Med. Chem. 1993, 1, 261–276.

Article
Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4 987
(8) Schmidhammer, H. Opioid Receptor Antagonists. In Progress in
Medicinal Chemistry; Ellis, G. P., Luscombe, D. K., Oxford, A. W.,
Eds.; Elsevier: Amsterdam, 1998; 35, 83-132.
(9) Schmidhammer, H.; Spetea, M. Synthesis of 14-Alkoxymorphinan
Derivatives and Their Pharmacological Actions. Top. Curr. Chem.
2011, 299, 63-91.
(10) Schmidhammer, H.; Aeppli, L.; Atwell, L.; Fritsch, F.; Jacobson,
A. E.; Nebuchla, M.; Sperk, G. Synthesis and Biological Evalua-
tion of 14-Alkoxymorphinans. 1. Highly Potent Opioid Agonists in
the Series of (-)-14-Methoxy-N-methylmorphinan-6-ones. J. Med.
Chem. 1984, 27, 1575–1579.
(28) Smith, H. S. Peripherally-Acting Opioids. Pain Physician 2008, 11,
S121–S132.
€
(29) Schutz, J.; Brandt, W.; Spetea, M.; Wurst, K.; Wunder, G.;
Schmidhammer, H. Synthesis of 6-amino Acid Substituted Deri-
vatives of the Highly Potent Analgesic 14-O-Methyloxymorphone.
Helv. Chim. Acta 2003, 86, 2142–2148.
€
(30) Spetea, M.; Friedmann, T.; Riba, P.; Schutz, J.; Wunder, G.;
€
Langer, T.; Schmidhammer, H.; Furst, S. In Vitro Opioid Activity
Profiles of 6-Amino Acid Substituted Derivatives of 14-O-Methyl-
oxymorphone. Eur. J. Pharmacol. 2004, 483, 301–308.
€
(31) Furst, S.; Riba, P.; Friedmann, T.; Timar, J.; Al-Khrasani, M.;
Obara, I.; Makuch, W.; Spetea, M.; Schutz, J.; Przewlocki, R.;
€
€
(11) Lattanzi, R.; Spetea, M.; Schullner, F.; Rief, S. B.; Krassnig, R.;
Negri, L.; Schmidhammer, H. Synthesis and Biological Evaluation
of 14-Alkoxymorphinans. 22. Influence of the 14-alkoxy Group
and the Substitution in Position 5 in 14-Alkoxymorphinan-6-ones
on In Vitro and In Vivo Activities. J. Med. Chem. 2005, 48, 3372–
3378.
Przewlocka, B.; Schmidhammer, H. Peripheral versus Central
Antinociceptive Actions of 6-Amino Acid-substituted Derivatives
of 14-O-Methyloxymorphone in Acute and Inflammatory Pain in
the Rat. J. Pharmacol. Exp. Ther. 2005, 312, 609–618.
(32) Al-Khrasani, M.; Spetea, M.; Friedmann, T.; Riba, P.; Kiraly, K.;
€
ꢀ
(12) Riba, P.; Friedmann, T.; Kiraly, K. P.; Al-Khrasani, M.; Sobor,
Schmidhammer, H.; Furst, S. DAMGO and 6β-Glycine Substi-
M.; Asim, M. F.; Spetea, M.; Schmidhammer, H.; Furst, S. Novel
Approach to Demonstrate High Efficacy of μ Opioids in the Rat
Vas Deferens: A Simple Model of Predictive Value. Brain Res. Bull.
2010, 81, 178–184.
tuted 14-O-Methyloxymorphone but Not Morphine Show Periph-
eral, Preemptive Antinociception after Systemic Administration in
a Mouse Visceral Pain Model and High Intrinsic Efficacy in the
Isolated Rat Vas Deferens. Brain Res. Bull. 2007, 74, 369–375.
€
(13) Schmidhammer, H.; Schratz, A.; Mitterdorfer, J. Synthesis and
Biological Evaluation of 14-Alkoxymorphinans. 8. 14-Methoxy-
metopon, an Extremely Potent Opioid Agonist. Helv. Chim. Acta
1990, 73, 1784–1787.
(33) Obara, I.; Makuch, W.; Spetea, M.; Schutz, J.; Schmidhammer, H.;
Przewlocki, R.; Przewlocka, B. Local Peripheral Antinociceptive
Effects of 14-O-Methyloxymorphone Derivatives in Inflammatory
and Neuropathic Pain in the Rat. Eur. J. Pharmacol. 2007, 558,
60–67.
€
ꢀ ꢀ
(14) Furst, S.; Buzas, B.; Friedmann, T.; Schmidhammer, H.;
Borsodi, A. Highly Potent Novel Opioid Receptor Agonist in
the 14-Alkoxymetopon Series. Eur. J. Pharmacol. 1993, 236,
209–215.
(34) Jiang, J. B.; Hanson, R. N.; Portoghese, P. S.; Takemori, A. E.
Stereochemical Studies on Medicinal Agents. 23. Synthesis and
Biological Evaluation of 6-Amino Derivatives of Naloxone and
Naltrexone. J. Med. Chem. 1977, 20, 1100–1102.
(35) Sayre, L. M.; Portoghese, P. S. Stereospecific Synthesis of the 6R-
and 6β-Amino Derivatives of Naltrexone and Oxymorphone.
J. Org. Chem. 1980, 45, 3366–3368.
(15) Freye, E.; Schmidhammer, H.; Latasch, L. 14-Methoxymetopon, a
Potent Opioid, Induces No Respiratory Depression, Less Sedation,
and Less Bradycardia than Sufentanil in the Dog. Anesth. Analg.
2000, 90, 1359–1364.
(36) Handa, B. K.; Lane, A. C.; Lord, J. A. H.; Morgan, B. A.; Rance,
M. J.; Smith, C. F. C. Analogues of β-LPH61-64 possessing
selective agonist activity at μ-opiate receptors. Eur. J. Pharmacol.
€
(16) King, M. A.; Su, W.; Nielan, C. L.; Chang, A. H.; Schutz, J.;
Schmidhammer, H.; Pasternak, G. W. 14-Methoxymetopon, a
Very Potent μ-Opioid Analgesic with an Unusual Pharmacological
Profile. Eur. J. Pharmacol. 2003, 459, 203–209.
1981, 70, 531–540.
€
€
€
ꢀ
(37) Nevin, S. T.; Kabasakal, L.; Otvos, F.; Toth, G.; Borsodi, A.
Binding Characteristics of the Novel Highly Selective δ-Agonist,
[3H]Ile5,6Deltorphin II. Neuropeptides 1994, 268, 261–265.
(38) Lahti, R. A.; Mickelson, M. M.; McCall, J. M.; Von Voightlander,
P. F. [3H]U69-593, a Highly Selective Ligand for the Opioid κ
Receptor. Eur. J. Pharmacol. 1985, 109, 281–284.
ꢀ
€
€
ꢀ
(17) Spetea, M.; Toth, F.; Schutz, J.; Otvos, F.; Toth, G.; Benyhe, S.;
Borsodi, A.; Schmidhammer, H. Binding Characteristics of [3H]14-
Methoxymetopon, a High Affinity μ-Opioid Receptor Agonist.
Eur. J. Neurosci. 2003, 18, 290–295.
€
(18) Bileviciute-Ljungar, I.; Spetea, M.; Guo, Y.; Schutz, J.; Windisch,
P.; Schmidhammer, H. Peripherally Mediated Antinociception of
the μ-Opioid Receptor Agonist 2-[(4,5R-Epoxy-3-hydroxy-14β-
methoxy-17-methylmorphinan-6β-yl)amino] acetic Acid (HS-731)
after Subcutaneous and Oral Administration in Rats with Carra-
geenan-Induced Hindpaw Inflammation. J. Pharmacol. Exp. Ther.
2006, 317, 220–227.
(39) Nieland, N. P.; Moynihan, H. A.; Carrington, S.; Broadbear, J.;
Woods, J. H.; Traynor, J. R.; Husbands, S. M.; Lewis, J. W.
Structural Determinants of Opioid Activity in Derivatives of 14-
Aminomorphinones: Effect of Substitution in the Aromatic Ring
of Cinnamoylaminomorphinones and Codeinones. J. Med. Chem.
2006, 49, 5333–5338.
€
(19) Schutz, J.; Spetea, M.; Koch, M.; Aceto, M. D.; Harris, L. S.;
Coop, A.; Schmidhammer, H. Synthesis and Biological Evalua-
tion of 14-Alkoxymorphinans. 20. 14-Phenylpropoxymetopon:
An Extremely Powerful Analgesic. J. Med. Chem. 2003, 46,
4182–4187.
(40) Rennison, D.; Moynihan, H.; Traynor, J. R.; Lewis, J. W.; Hus-
bands, S. M. Structural Determinants of Opioid Activity in Deri-
vatives of 14-Aminomorphinones: Effects of Changes to the Chain
Linking of the C14-Amino Group to the Aryl Ring. J. Med. Chem.
2006, 49, 6104–6110.
€
(20) Greiner, E.; Spetea, M.; Krassnig, R.; Schullner, F.; Aceto, M.;
Harris, L. S.; Traynor, J. R.; Woods, J. H.; Coop, A.; Schmid-
hammer, H. Synthesis and Biological Evaluation of 14-Alkoxy-
morphinans. 18. N-Substituted 14-Phenylpropyloxymorphinan-6-
ones with Unanticipated Agonist Properties: Extending the Scope
of Common Structure-Activity Relationships. J. Med. Chem.
2003, 46, 1758–1763.
(41) Kobylecki, R. J.; Carling, R. W.; Lord, J. A. H.; Smith, C. F. C.;
Lane, A. C. Common Anionic Receptor Site Hypothesis: Its
Relevance to the Action of Naloxone. J. Med. Chem. 1982, 25,
116–120.
€
(42) Schullner, F.; Meditz, R.; Krassnig, R.; Morandell, G.; Kalinin,
V. N.; Sandler, E.; Spetea, M.; White, A.; Schmidhammer, H.;
Berzetei-Gurske, I. P. Synthesis and Biological Evaluation of 14-
Alkoxymorphinans. 19. Effect of 14-O-Benzylation on the Opioid
Receptor Affinity and Antagonist Potency of Naltrexone. Helv.
Chim. Acta 2003, 86, 2335–2341.
€
(21) Spetea, M.; Schullner, F.; Moisa, R. C.; Berzetei-Gurske, I. P.;
€
Schraml, B.; Dorfler, C.; Aceto, M. D.; Harris, L. S.; Coop, A.;
Schmidhammer, H. Synthesis and Biological Evaluation of 14-
Alkoxymorphinans. 21. Novel 4-Alkoxy and 14-Phenylpropoxy
Derivatives of the μ-Opioid Receptor Antagonist Cyprodime.
J. Med. Chem. 2004, 47, 3242–3247.
(43) Botros, S.; Lipkowski, A. W.; Larson, D. L.; Stark, A. P.; Take-
mori, A. E.; Portoghese, P. S. Opioid Agonist and Antagonist
Activities of Peripherally Selective Derivatives of Naltrexamine
and Oxymorphamine. J. Med. Chem. 1989, 32, 2068–2071.
(44) Larson, D. L.; Hua, M.; Takemori, A. K.; Portoghese, P. S.
Possible Contribution of a Glutathione Conjugate to the Long-
duration Action of β-Funaltrexamine. J. Med. Chem. 1993, 36,
3669–3673.
(45) Spetea, M.; Greiner, E.; Aceto, M. D.; Harris, L. S.; Coop, A.;
Schmidhammer, H. Effect of a 6-Cyano Substituent in 14-
Oxygenated N-Methylmorphinans on Opioid Receptor Binding
and Antinociceptive Potency. J. Med. Chem. 2005, 48, 5052–
5055.
(22) Barber, A.; Gottschlich, R. Opioid Agonists and Antagonists: An
Evaluation of Their Peripheral Actions in Inflammation. Med. Res.
Rev. 1992, 12, 525–562.
€
(23) Stein, C.; Schafer, M.; Machelska, H. Attacking Pain at its Source:
New Perspectives on Opioids. Nature Med. 2003, 9, 1003–1008.
(24) Kapitzke, D.; Vetter, I.; Cabot, P. J. Endogenous Opioid Analgesia
in Peripheral Tissues and the Clinical Implications for Pain Con-
trol. Ther. Clin. Risk Manag. 2005, 1, 279–297.
(25) Stein, C. Opioid Receptors on Peripheral Sensory Neurons. Adv.
Exp. Med. Biol. 2003, 521, 69–76.
(26) Pol, O.; Puig, M. M. Expression of Opioid Receptors During
Peripheral Inflammation. Curr. Top. Med. Chem. 2004, 4, 51–61.
(27) DeHaven-Hudkins, D. L.; Dolle, R. E. Peripherally Restricted
Agonists as Novel Analgesic Agents. Curr. Pharm. Des. 2004, 10,
743–757.
(46) Feinberg, A. P.; Creese, I.; Snyder, S. H. The Opiate Receptor: A
Model Explaining Structure-Activity Relationships of Opiate
Agonists and Antagonists. Proc. Natl. Acad. Sci. U.S.A. 1976,
73, 4215–4219.

988 Journal of Medicinal Chemistry, 2011, Vol. 54, No. 4
Spetea et al.
(47) Casy, A. F.; Parfitt, R. T. Opioid Analgesics: Chemistry and
Receptors; Plenum Press: New York, 1986.
(48) Schmidhammer, H.; Burkard, W. P.; Eggstein-Aeppli, L. Syn-
thesis and Biological Evaluation of 14-Alkoxymorphinans. 4.
Opioid Agonists and Partial Opioid Agonists in a Series
of N-(Cyclobutylmethyl)-14-methoxymorphinan-6-ones. Helv.
Chim. Acta 1989, 72, 1233–1240.
(52) Lester, P. A.; Traynor, J. R. Comparison of the in Vitro Efficacy of
μ, δ, κ, and ORL1 Receptor Agonists and Nonselective Opioid
Agonists in Dog Brain Membranes. Brain Res. 2006, 1073-1074,
290–26.
(53) Portoghese, P. S.; Moe, S. T.; Takemori, A. E. A Selective δ1
Opioid Receptor Agonist Derived from Oxymorphone. Evi-
dence for Separate Recognition Sites for δ1 Opioid Receptor
Agonists and Antagonists. J. Med. Chem. 1993, 36, 2572–
2574.
(49) Kintz, P.; Marquet, P. Opioid Therapy of Drug Addiction; Humana
Press: Totowa, NJ, 2002.
(50) Kawai, K.; Hayakawa, J.; Miyamoto, T.; Imamura, Y.; Yamane,
S.; Wakita, H.; Fujii, H.; Kawamura, K.; Matsuura, H.; Izumimoto,
N.; Kobayashi, R.; Endo, T.; Nagase, H. Design, Synthesis, and
Structure-Activity Relationship of Novel Opioid κ-Agonists.
Bioorg. Med. Chem. 2008, 16, 9188–9201.
(51) Nagase, H.; Watanabe, A.; Nemoto, T.; Yamaotsu, N.; Hayashida,
K.; Nakajima, M.; Hasebe, K.; Nakao, K.; Mochizuki, H.; Hirono,
S.; Fujii, H. Drug Design and Synthesis of a Novel κ Opioid
Receptor Agonist with an Oxabicyclo[2.2.2]Octane Skeleton and
its Pharmacology. Bioorg. Med. Chem. Lett. 2010, 20, 121–124.
(54) Portoghese, P. S.; Sultana, M.; Moe, S. T.; Takemori, A. E.
Synthesis of Naltrexone-Derived δ-Opioid Antagonists. Role of
Conformation of the δ Address Moiety. J. Med. Chem. 1994, 37,
579–585.
(55) Brandt, W. A Uniform Molecular Model of δ Opioid Agonist and
Antagonist Pharmacophore Conformations. J. Comp.-Aided Mol.
Des. 1998, 12, 615–621.
(56) Litchfield, J. T., Jr.; Wilcoxon, F. A Simplified Method of Evalu-
ating Dose-Effect Experiments. J. Pharmacol. Exp. Ther. 1949, 96,
99–113.