Application of Bivalent Bioisostere Concept on Design and Discovery of Potent Opioid Receptor Modulators

Article abstract of DOI:10.1021/acs.jmedchem.9b01767

Here, we described the structural modification of previously identified μ opioid receptor (MOR) antagonist NAN, a 6α-N-7′-indolyl substituted naltrexamine derivative, and its 6β-N-2′-indolyl substituted analogue INTA by adopting the concept of "bivalent bioisostere". Three newly prepared opioid ligands, 25 (NBF), 31, and 38, were identified as potent MOR antagonists both in vitro and in vivo. Moreover, these three compounds significantly antagonized DAMGO-induced intracellular calcium flux and displayed varying degrees of inhibition on cAMP production. Furthermore, NBF produced much less significant withdrawal effects than naloxone in morphine-pelleted mice. Molecular modeling studies revealed that these bivalent bioisosteres may adopt similar binding modes in the MOR and the "address" portions of them may have negative or positive allosteric modulation effects on the function of their "message" portions compared with NAN and INTA. Collectively, our successful application of the "bivalent bioisostere concept" identified a promising lead to develop novel therapeutic agents toward opioid use disorder treatments.

Full text of DOI:10.1021/acs.jmedchem.9b01767

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Article
Application of Bivalent Bioisostere Concept on Design
and Discovery of Potent Opioid Receptor Modulators
Hongguang Ma, Samuel Obeng, Huiqun Wang, Yi Zheng, Mengchu Li, Abdulmajeed
M Jali, David Stevens, William L Dewey, Dana E Selley, and Yan Zhang
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jmedchem.9b01767 • Publication Date (Web): 29 Nov 2019
Downloaded from pubs.acs.org on November 29, 2019
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Application of Bivalent Bioisostere Concept on Design and
Discovery of Potent Opioid Receptor Modulators
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Hongguang Ma, † Samuel Obeng,† Huiqun Wang,† Yi Zheng,† Mengchu Li, † Abdulmajeed M. Jali, ‡
David L. Stevens,‡ William L. Dewey,‡ Dana E. Selley,‡ Yan Zhang†,*
†Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University,
800 E Leigh Street, Richmond, Virginia 23298, United States
‡Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th
Street, Richmond, Virginia 23298, United States
* Corresponding author: Tel: +1 (804) 828-0021. E-mail address: yzhang2@vcu.edu (Y. Zhang).
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Abstract
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Here we described the structural modification of previously identified MOR antagonist NAN, a 6α-N-7′-
indolyl substituted naltrexamine derivative, and its 6β-N-2′-indolyl substituted analogue INTA by adopting
the concept of “bivalent bioisostere”. Three newly prepared opioid ligands 25 (NBF), 31 and 38, were
identified as potent MOR antagonists both in vitro and in vivo. Moreover, these three compounds significantly
antagonized DAMGO-induced intracellular calcium flux and displayed varying degree of inhibition on cAMP
production. Furthermore, NBF produced much less significant withdrawal effects than naloxone in morphine-
pelleted mice. Molecular modeling studies revealed that these bivalent bioisosteres may adopt similar binding
modes in the MOR and the “address” portions of them may have negative or positive allosteric modulation
effects on the function of their “message” portions compared with NAN and INTA. Collectively, our
successful application of the “bivalent bioisostere concept” identified a promising lead to develop novel
therapeutic agents toward opioid use disorder treatments.
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Introduction
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It has been several decades since opioid binding sites were initially investigated in the 1950s.1 During this
period of time, different types of opioid receptors have been pharmacologically designated and characterized.2-
5 Among them, three main types, the μ opioid receptor (MOR), the κ opioid receptor (KOR), and the δ opioid
receptor (DOR), have been extensively studied.6-8 As members of G protein-coupled receptor (GPCR)
superfamily, opioid receptors are widely distributed in the central and peripheral nervous system,9-11 and they
exert critical functions not only in modulation of pain experience, but also in other physiological and
pathophysiological processes.12-20 It has been proven that activation of different types of opioid receptors can
pose various biological effects.21-25 Based on these observations, a considerable number of opioid agonists and
antagonists have been developed with varying degree of success to treat different diseases.26-28 Among them,
MOR ligands with different degrees of selectivity and efficacy have received significant attention as they
played critical roles in the treatment of opioid use disorder (OUD).29,30
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The latest statistics show that OUD remains a major threat to human health with growing economic cost and
considerable impact on the health care system. Particularly in the United States, it has become a national
epidemic due to the illicit use of non-medical prescription opioids over the past decades. The annual number
of overdose deaths in the United States, largely caused by opioids, have nearly increased four-fold from 2001
to 2016 and the opioids-related mortality rate has reached the highest level with an increasing of 11.4% in
2016,31 underlying an urgent need of efficacious medications to treat side effects attributable to opioids.
Presently, the FDA-approved treatments for OUD include opioid agonists, such as methadone and
buprenorphine, and opioid antagonists, such as naltrexone (Figure 1).29,30 As a MOR full agonist, methadone
possessed great efficacy for opioid addiction maintenance, however, the respiratory depression and long
period of withdrawal symptom precipitation have largely compromised its therapeutic efficiency.32 Similarly,
buprenorphine, a MOR partial agonist, also suffered undesirable effects.33 As for the opioid antagonist
naltrexone, it did not produce side effects associated with opioid agonists. However, high dose of naltrexone
primarily contributes to undesirable effects, which could be attributable to the interactions between naltrexone
and the DOR or KOR.34 Therefore, it is still imperative to develop highly potent and selective MOR ligands
devoid of undesired side effects.
With a continuous endeavor on developing selective opioid receptor ligands, we have established a small
molecule library, which is mainly designed based on the “message-address concept”, by introducing various
heterocyclic substituents onto the epoxymorphinan skeleton. From this library, several potent and highly
selective MOR ligands have been identified and characterized as lead compounds in treating OUD.35-42 More
recently, introduction of an indole moiety at the 6-position of epoxymorphinan group resulted in a series of
novel
ligands,
among
which
17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(indole-7-
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carboxamido)morphinan (NAN) acted as a potent MOR antagonist both in vitro and in vivo (Figure 1).42
Interestingly, a structurally similar compound, 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-
(indole-2-carboxamido)morphinan (INTA) was identified previously as a MOR full agonist (Figure 1).43
Further molecular modeling studies revealed that INTA and NAN may be bitopic ligands in which their
identical “message” portion, namely the epoxymorphinan moiety, may bind to the MOR orthosteric binding
site in a similar fashion, while their indole rings, referred to as the “address” portion, may interact with
different domains of the MOR allosteric binding site. These results indicated that even subtle changes of
allosteric interactions may influence the functional activity of opioid ligands. In addition, it has been reported
that bitopic ligands may possess favorable pharmacological properties, e.g., high affinity and selectivity, on
their target receptors.44-47 Based on these observations, we thus decided to conduct structural modification of
the indole rings at the 6-position of epoxymorphinan skeleton in INTA and NAN to further explore their
structure-activity relationship (SAR).
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N
N
OH
OH
N
O
O
O
O
O
OH
OH
3 naltrexone
1 methadone
2 buprenorphine
N
N
OH
O
OH
O
HN
O
N
N
H
H
HN
O
4 INTA
5 NAN
OH
OH
Figure 1. Chemical Structures of FDA-Approved Opioid Ligands, and NAN and INTA.
Since the concept of “bioisostere” was proposed by Harris Friedman in 1951,48 the application of bioisosteres
has become a tactical approach in drug design and lead optimization.49 Among all bioisosteres, bivalent
biososteres represented by -NH-, -O- and -S- moieties have been studied extensively because interchanges
among them have facilitated identification of bioactive compounds.50 Some of those representative
applications are depicted in Figure 2. For example, the replacement of -NH- moiety in clozapine with -O-
resulted in another marketed antipsychotic agent loxapine.51,52 Further replacement of the oxygen atom in the
loxapine skeleton with a sulfur atom led to approval of quetiapine in treating schizophrenia and other mental
illnesses with favorable side-effect profile.53
Another successful application was found in a study of indolones derivatives (9−11).54 Introduction of
different bivalent bioisosteres resulted in retained inhibitory activities against cardiac phosphodiesterase, a
potential target in the development of cardiotonic agent. In a study of adenosine 3',5'-cyclic phosphate
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phosphodiesterase III (cAMP PDE III) inhibitors, introduction of -NH- and -O- moieties (compounds 12 and
13) retained their inhibitory activities, while the sulfur derivative 14 showed greater potency for inhibition
and turned out to be a more potent cardiotonic agent.55 To summarize, numerous of studies have shown that
the bioactivity of a specific bioisostere largely relies on the context, such as size, shape, polarity,
electronegativity, and pKa, which potentially play critical roles in the molecule and target protein
recognition.50 To be noticed, introduction of bioisosteres may cause beneficial or deleterious effects while an
effective bioisostere in one application may not be applicable in another case. Nevertheless, the application of
bivalent bioisosteres is apparently a promising approach with significant value in drug design and discovery.
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(CH2)2O(CH2)2OH
N
N
N
N
N
N
N
N
N
Cl
Cl
Cl
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H
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S
6 Clozapine
7 Loxapine
8 Quetiapine
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12 X NH
=
=
NH
10 X
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13 X
O
=
=
=
=
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O
11 X
14 X
S
O
N
H
N
H
Figure 2. Representative Applications of Bivalent Bioisosteres.
We thus decided to apply the concept of “bivalent bioisostere” for the structural modification of INTA and
NAN by replacing the -NH- moiety in indole ring with a -O- or -S- moiety, which resulted in two series of
novel opioid ligands bearing benzofuran and benzothiophene moieties. In addition, complementary analogues
in which an α and β amide linkages were also incorporated on different positions of heterocyclic substituents
were also prepared in order to further understand the contributions of these structural changes to binding
affinity and efficacy profiles at the MOR and the other two opioid receptors.
Results and Discussion
Chemical Synthesis. All newly designed compounds (except for two previously reported ones, compounds
15 and 16)43 were synthesized following previously reported procedure,36,39,42 and the synthetic route is shown
in Scheme 1. Briefly, using naltrexone as the start material, 6α- and 6β-naltrexamine were obtained under
different stereoselective conditions with yield of 75% and 50%, respectively. Then various heterocyclic
carboxylic acids, either purchased from commercial resources or prepared according to reported methods (see
Supporting Information), reacted with 6α- or 6β-naltrexamine via EDCI/HOBt coupling reaction under mild
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basic conditions. By treating with K2CO3 in methanol, the 6-monosubstitued free bases were obtained in
reasonable yields. After transferring to hydrochloride salts, all target compounds were fully characterized and
then submitted for biological studies.
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OH
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i) Bn2NH, Toluene
NH2
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ii) NaCNBH3, EtOH
iii) Pd/C, MeOH
O
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β-naltrexamine
OH
O
N
i) RCOOH, EDCI, HOBt,
TEA, DMF
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
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R
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OH
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OH
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i) BnNH2, Benzene
NH2
ii) NaBH4, EtOH
iii) Pd/C, MeOH
OH
α-naltrexamine
Scheme 1. Synthetic Route of Target Compounds Carrying Benzofuran and Benzothiophene Moieties.
In Vitro Pharmacological Studies. In order to characterize the binding affinity and selectivity of all newly
synthesized ligands on the three opioid receptors, competitive radioligand binding assay was adopted on
monoclonal mouse opioid receptor-expressed CHO cell membranes following reported protocol,36,39,42 in
which the MOR, DOR and KOR were labeled by [3H]naloxone, [3H]naltrindole, and [3H]norBNI, respectively.
The [35S]-GTPγS functional assay was then carried out in an effort to characterize whether each ligand acted
as a full agonist, partial agonist, or antagonist at the MOR as previously reported by measuring its relative
efficacy to the full agonist DAMGO for MOR stimulation.36
As shown in Table 1, compounds 15 − 26 possessed subnanomolar binding affinity for the MOR and
subnanomolar to nanomolar binding affinity at the KOR, while most of them bond to the DOR with low
affinity of Ki value at two-digit nanomolar level, indicating that their opioid receptor selectivity profile was
similar to that of INTA. In details, INTA exhibited low selectivity to the MOR over the KOR and DOR (Ki
ratios κ/μ ≈ 0.6, δ/μ ≈ 5.3), after replaced the -NH- of the indole ring with oxygen and sulfur atoms, no
significant binding selectivity change in its counterparts compound 15 (Ki ratios κ/μ ≈ 1.4, δ/μ ≈ 12.1) and
compound 16 (Ki ratios κ/μ ≈ 1.4, δ/μ ≈ 9.9) was observed. This result corroborated previously reported finding
that compounds 15 and 16 afforded low selectivity in intracellular calcium release assay in human embryonic
kidney 293 (HEK293) cells.43 For other compounds, introduction of oxygen or sulfur atom appeared to have
various effects on the selectivity of the MOR over the KOR and the DOR. For example, compounds 17 (Ki
ratios κ/μ ≈ 2.3, δ/μ ≈ 79.2) and 18 (Ki ratios κ/μ ≈ 3.4, δ/μ ≈ 133.21) showed slightly improved selectivity for
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the MOR over the KOR and the DOR in comparison with their bioisosteric counterpart bearing 3′-indolyl (Ki
ratios κ/μ ≈ 0.8, δ/μ ≈ 37.7).42 While compound 21(Ki ratios κ/μ ≈ 1.4, δ/μ ≈ 35.4) and 22 (Ki ratios κ/μ ≈ 1.5,
δ/μ ≈ 9.7), in which the 5′-benzofuryl and 5′-benzothiophenyl were incorporated, respectively, at the 6-position
of epoxymorphinan skeleton, possessed retained selectivity for the MOR over the KOR but relatively reduced
selectivity for the MOR over the DOR compared with their corresponding bioisosteric counterpart (Ki ratios
κ/μ ≈ 2.0, δ/μ ≈ 68.0).42
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Among the 6α-configuration analogues in Table 2, it was observed that the replacement of -NH- in the indole
ring with oxygen and sulfur atoms resulted in retention of binding affinity at the MOR and the KOR and
slightly increased selectivity of the MOR over the KOR and DOR (except for compounds 32, 34 and 38).
Interestingly, NAN possessed moderate selectivity on the MOR over the KOR and DOR (Ki ratios κ/μ ≈ 7.3,
δ/μ ≈ 59.5), after -O- moiety was applied to replace the -NH- moiety, the resulting compound 37 showed
higher selectivity with about 18-fold selectivity for the MOR over the KOR and about 104-fold selectivity for
the MOR over the DOR. Introduction of a sulfur atom into the heterocyclic ring, however, somewhat retained
selectivity of the MOR over the KOR but slightly decreased selectivity on the MOR over the DOR (compound
38, Ki ratios κ/μ ≈ 8.5, δ/μ ≈ 26.9). Additionally, it was also noticed that the different substituent positions of
benzofuran and benzothiophene moieties seemed not to have very significant impact on MOR affinity and
selectivity. That suggested that the “address” portion of these ligands in recognizing the MOR allosteric
binding site was not influenced by the orientation of benzofuran and benzothiophene groups, which is
consistent with our observations in INTA and NAN analogues.42
The [35S]-GTPγS functional assay was then conducted using MOR-expressed CHO cell line as illustrated
before.36 As seen in Table 1, all target compounds primarily exhibited partial agonism with different levels of
potency and efficacy. In details, INTA was known as a MOR full agonist, while among all 6β-configuration
analogues, its bioisosteric counterparts, compounds 15 and 16 bearing 2′-benzofuryl and 2′-benzothiophenyl,
respectively, turned out to be partial agonists with around 60% MOR stimulation. Meanwhile, it was also
found that, after bivalent bioisosteric exchange, the efficacies of compounds 17 and 18 as well as compounds
23 and 24 were relatively decreased in comparison with their corresponding bioisosteric counterpart.42 While
the potencies and efficacies of compounds 21 and 22 (compound 21, EC50 = 0.41 ± 0.02 nM, Emax = 52.23 ±
1.42%; compound 22, EC50 = 0.19 ± 0.03 nM, Emax = 75.43 ± 2.30%) were largely increased compared to
their bioisosteric counterpart carrying -NH- moiety (EC50 = 2.98 ± 1.25 nM, Emax = 22.32 ± 3.50%).42 For the
rest of compounds, no obvious change in potency and efficacy was observed after bivalent bioisosteric
replacement. Based on the functional assay results of target compounds with 6α-configuration, a trend was
found that introduction of oxygen and sulfur atoms produced distinct reduction in MOR efficacy compared to
corresponding -NH- counterpart (except for compound 35).42 Particularly, NAN has been identified as a MOR
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antagonist as it had relative low efficacy of 19% compared to DAMGO. After -O- and -S- moieties were
adopted to replace the -NH- moiety, the resulting counterparts 37 and 38 produced considerably lower
efficacies (compound 37 Emax = 12.89 ± 1.78%; compound 38 Emax = 10.59 ± 0.93%). It demonstrated that the
application of bivalent bioisosteres led to a beneficial impact on reducing the efficacy of NAN.
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Previous observations have indicated that the configurational arrangement at 6-position of epoxymorphinan
skeleton is critical for the affinity and selectivity of opioid receptor ligands,56 which was also supported by
our investigation regarding INTA and NAN series.42 In the current study, comparisons were conducted in
bioisosteric counterparts of INTA and NAN in an effort to further understand the impact of the stereochemistry
at 6-position of the skeleton on ligand binding affinity and efficacy. Switching the linkage stereochemistry of
counterparts of INTA, namely compounds 15 and 16, from β-configuration to α-configuration (compounds 27
and 28) did not change their MOR binding affinity but improved somewhat their selectivity on the MOR over
the KOR and DOR (compound 15, Ki ratios κ/μ ≈ 1.4, δ/μ ≈ 12.1; compound 27, Ki ratios κ/μ ≈ 3.8, δ/μ ≈
81.6; compound 16, Ki ratios κ/μ ≈ 1.4, δ/μ ≈ 9.9; compound 28, Ki ratios κ/μ ≈ 4.5, δ/μ ≈ 53.0). Meanwhile,
distinct reductions in MOR efficacy were also observed. On the other hand, changing the linkage
stereochemistry of compounds 37 and 38, which are bioisosteric counterparts of NAN, from α-configuration
to β-configuration (compounds 25 and 26) did not lead to significant changes in MOR binding affinity, but
had various effects on their selectivity profiles. Moreover, such changes in configuration also slightly
increased their MOR efficacy. Collectively, our observations of the impact of the stereochemistry at 6-position
of the epoxymorphinan skeleton on binding affinity and efficacy in bioisosteric counterparts of INTA and
NAN were basically consistent with our previous results in INTA and NAN analogues.42
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Table 1. The Binding Affinity, Selectivity, and MOR [35S]-GTPγS Functional Assay Results of 6β
Configuration Ligands Bearing Benzofuran and Benzothiophene Moieties. a
N
OH
O
N
R
H
O
HCl
OH
Ki (nM)
Selectivity
MOR [35S]-GTPγS binding
Compd
-R
Μ
Κ
δ
κ/μ
δ/μ
EC50 (nM)
% Emax of
DAMGO
4b
0.29 ± 0.04
0.18 ± 0.00
1.54 ± 0.47
0.6
5.3
0.21 ± 0.01
92.42 ± 2.81
N
H
(INTA)
15
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0.23 ± 0.02
1.940 ± 0.37
1.4
12.1
0.39 ± 0.07
64.52 ± 1.41
O
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16
17
18
0.14 ± 0.01
0.13 ± 0.01
0.14 ± 0.03
0.20 ± 0.02
0.30 ± 0.02
0.48 ± 0.06
1.39 ± 0.14
10.29 ± 2.53
18.65 ± 2.96
1.4
2.3
3.4
9.9
79.2
0.24 ± 0.03
0.47 ± 0.09
0.37 ± 0.05
59.05 ± 1.16
43.23 ± 2.00
29.91 ± 1.18
1
2
3
4
S
O
5
133.21
6
S
7
8
9
19
0.17 ± 0.03
0.16 ± 0.03
0.15 ± 0.03
0.14 ± 0.02
0.18 ± 0.03
0.15± 0.03
0.18 ± 0.03
0.19 ± 0.03
0.80 ± 0.10
0.75 ± 0.08
0.21 ± 0.02
0.21 ± 0.03
0.30 ± 0.05
0.20 ± 0.01
0.81 ± 0.14
1.62 ± 0.18
70.55 ± 10.60
24.04 ± 3.36
5.31 ± 1.05
1.36 ± 0.12
12.26 ± 2.53
2.04 ± 0.21
17.56 ± 3.17
38.93 ± 6.00
4.7
4.7
1.4
1.5
1.7
1.3
4.5
8.5
415.0
150.3
35.4
9.7
0.59 ± 0.17
0.32 ± 0.06
0.41 ± 0.02
0.19 ± 0.03
0.59 ± 0.09
0.21 ± 0.02
0.95 ± 0.18
2.97 ±1.08
23.61 ± 1.29
23.06 ± 2.2
52.23 ± 1.42
75.43 ± 2.30
21.14 ± 1.33
58.71 ± 1.29
27.31 ± 3.26
13.49 ± 1.94
O
20
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
S
21
22
O
S
23
68.1
13.6
97.6
204.9
O
24
S
25 (NBF)
26
O
S
aThe values are the mean ± SEM of three independent experiments. bData has been reported in Reference 42
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Table 2. The Binding Affinity, Selectivity, and MOR [35S]-GTPγS Functional Assay Results of 6α
Configuration Ligands Bearing Benzofuran and Benzothiophene Moieties.a
N
OH
O
N
R
H
O
HCl
OH
Ki (nM)
Selectivity
MOR [35S]-GTPγS binding
Compd
-R
Μ
Κ
δ
κ/μ
δ/μ
EC50 (nM)
% Emax of
DAMGO
5b
N
H
0.23 ± 0.02
1.69 ± 0.35
13.69 ± 1.39
7.3
59.5
3.85 ± 2.32
19.11 ± 3.31
(NAN)
27
0.44 ± 0.04
1.67 ± 0.31
35.90 ± 9.90
3.8
81.6
5.52 ± 0.95
33.99 ± 1.45
O
S
28
29
30
31
0.27 ± 0.02
0.27 ± 0.04
0.20 ± 0.01
0.26 ± 0.04
1.21 ± 0.10
3.37± 0.34
2.39 ± 0.19
4.98 ± 0.68
14.31 ± 1.88
16.83 ± 3.35
9.07 ± 1.96
16.91 ± 2.10
4.5
53.0
62.3
45.4
65.0
4.02 ± 0.85
1.57 ± 0.41
1.85 ± 0.37
0.77 ± 0.16
22.91 ± 0.72
18.68 ± 0.65
14.26 ± 1.13
10.00 ± 0.48
12.5
11.9
19.2
O
S
O
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33
34
35
36
37
38
0.26 ± 0.05
0.35 ± 0.03
0.39 ± 0.07
0.29 ± 0.03
0.28 ± 0.04
0.28 ± 0.04
0.31 ± 0.04
2.35 ± 0.49
4.23 ± 0.86
2.19 ± 0.28
1.66 ± 0.19
3.72 ± 0.67
5.12 ± 0.96
2.65 ± 0.32
6.85 ± 0.87
29.00 ± 5.46
11.87 ± 1.26
30.67 ± 3.83
22.28 ± 2.59
29.79 ± 4.60
8.35 ± 0.99
9.0
12.1
5.6
26.3
82.9
1.05 ± 0.26
3.72 ± 0.28
2.47 ± 0.36
2.23 ± 0.27
3.01 ± 0.68
0.97 ± 0.19
6.21 ± 2.08
16.09 ± 0.92
1
2
3
4
5
6
7
8
S
17.66 ± 0.63
18.88 ± 1.29
30.49 ± 2.19
18.11 ± 1.13
12.89 ± 1.78
10.59 ± 0.93
O
30.4
S
5.7
105.8
79.6
O
9
13.3
18.3
8.5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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S
106.4
26.9
O
S
aThe values are the mean ± SEM of three independent experiments. bData has been reported in Reference 42
Molecular Modeling Study. As described above, INTA, compounds 15 and 16 (Figure S1) acted as partial
agonists with around 60% MOR stimulation. NAN, compounds 37 and 38 (Figure S1) acted as antagonists
produced low efficacies to the MOR. In order to understand the effects of bioisosteres on the binding modes
of these compounds with the MOR, GOLD 5.657 was applied to dock INTA and its bioisosteric counterparts
(compounds 15 and 16) into the crystal structure of the agonist-bound (PDB ID: 5C1M) MOR.58 Meanwhile,
NAN and its bioisosteric counterparts (compounds 37 and 38) were docked into the crystal structure of
antagonist-bound (PDB ID: 4DKL) MOR.59 The docking poses with the highest CHEM-PLP score were
selected as the optimal binding poses of each compound, namely INTA-MORactive, Compound 15-MORactive
Compound 16-MORactive, NAN-MORinactive, Compound 37-MORinactive and Compound 38-MORinactive
,
,
respectively. These six optimal binding poses were energy-minimized by a 10,000-iterations minimization in
Sybyl-X 2.0 and displayed in Figures 3 and 4.
Comparing the chemical structures of INTA, NAN, and compounds 15, 16, 37, and 38, their “message”
portions (epoxymorphinan moiety) are identical. Similar to INTA and NAN, the “message” portions of
compounds 15, 16, 37, and 38 also interacted with the MOR orthosteric binding site.42 The ionic interactions
with D3.32 (superscript numbers follow the Ballesteros-Weinstein numbering method for GPCRs60), hydrogen
bond interactions with Y3.33, and hydrophobic interactions with residues M3.36, W6.48, and H6.52 were observed
with the “message” portion of each compound.
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Figure 3. The binding modes of INTA-MORactive (a), Compound 15-MORactive (b), and Compound 16-
MORactive (c) from molecular docking studies. Protein shown as cartoon model in light-pink; INTA, compound
15, compound 16, and key amino acid residues shown as stick model. Carbon atoms: INTA (green), compound
15 (magentas), compound 16 (blue), key amino acid residues (yellow), oxygen atom (red), nitrogen atom
(blue), sulfur atom (light-orange). The red dash line represents the hydrogen bond. The orange line represents
the ionic interaction between D3.32 and ligand. The inactive MOR crystal structure PDB ID, 4DKL.59
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As reported in our previous study, the “address” portion of INTA formed hydrophobic interactions with H54N-
terminus and π-π stacking interactions with W7.35 located at the allosteric binding site.42 Meanwhile, a hydrogen
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bond existed between the -NH- moiety in indole ring of INTA and H54N-terminus (Figure 3 and Table S1).
However, since the -NH- moiety in indole ring (“address” portion) of INTA was replaced by oxygen and
sulfur atoms in compounds 15 and 16, respectively, the hydrogen bond between the “address” portion of INTA
and H54N-terminus didn’t exist in Compound 15-MORactive and Compound 16-MORactive complexes. Hence, the
“address” portions of compounds 15 and 16 were observed to have moved away from H54N-terminus. Together
with the effect of the larger atomic radius of sulfur atom,61 the distance between the “address” portion of
compound 16 and H54N-terminus was longer than that in INTA-MORactive and Compound 15-MORactive
complexes. This movement may further cause the “address” portions of compounds 15 and 16 moved closer
to W7.35 (Table S1). Thus, the hydrophobic interactions with W7.35 in Compound 15-MORactive and Compound
16-MORactive complexes seemed to be increased. Since the -NH- moiety in indole ring of INTA had direct
interaction with H54N-terminus of MOR, changing the -NH- moiety in the “address” portion of INTA to -O- and
-S- moieties may decrease the binding affinities of the “address” portions of compounds 15 and 16 with H54N-
terminus. However, due to the increase of the hydrophobic interactions with W7.35 in Compound 15-MORactive
and Compound 16-MORactive complexes, the binding affinities of INTA, compounds 15 and 16 in active MOR
basically had no significant differences.
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Figure 4. The binding modes of NAN-MORinactive (a), Compound 37-MORinactive (b), and Compound 38-
MORinactive (c) from molecular docking studies. Protein shown as cartoon model in light-pink; NAN,
compound 37, compound 38, and key amino acid residues shown as stick model. Carbon atoms: NAN (cyan),
compound 37 (orange), compound 38 (pink), key amino acid residues (yellow), oxygen atom (red), nitrogen
atom (blue), sulfur atom (light-orange). The red dash line represents the hydrogen bond. The orange line
represents the ionic interaction between D3.32 and ligand. The active MOR crystal structure PDB ID, 5C1M.58
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From Figure 4, the binding modes of the “address” portions of NAN, compounds 37 and 38 were very similar.
As described in our previous studies, the binding subdomain of the “address” portion of NAN shifted from
K6.58 and W7.35 to L5.38 and K5.39 after 10 ns MD simulations. The “address” portion of NAN formed
hydrophobic interactions with L5.38 and K5.39.42 In the case of compounds 37 and 38, it showed that the “address”
portions of compounds 37 and 38 also formed hydrophobic interactions with L5.38 and K5.39 (Figure 4 and
Table S1). Moreover, the distances listed in Table S1 suggested that the hydrophobic interactions with L5.38
and K5.39 in NAN-MORinactive, Compound 37-MORinactive and Compound 38-MORinactive complexes were
almost the same. Since the -NH- moiety in indole ring of NAN had no direct interaction with MOR, bivalent
bioisosteric exchange in the “address” portion of NAN from -NH- moiety to -O- and -S- moieties showed no
significant effects on the binding of NAN, compounds 37 and 38 with inactive MOR.
In addition, the binding of the “address” portions of compounds 15 and 16 with W7.35 at the allosteric binding
site may cause the “message” portions of compounds 15 and 16 to form favorable interactions with W6.48
(Table S1) to further stabilize the conformation of MOR in an active state. Such positive modulation effects
of the “address” portions of compounds 15 and 16 were similar to that of INTA.42 On the other hand, the
hydrophobic interactions between residues L5.38 and K5.39 and the “address” portions of compounds 37 and 38
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may cause the “message” portions of compounds 37 and 38 away from W6.48 (Table S1).42 In consequence,
the binding of the “message” portions with the orthosteric binding site weakened. Therefore, the “address”
portions of compounds 37 and 38 may induce negative modulation effects on the function of the “message”
portions of compounds 37 and 38, which were similar to that of NAN.42 Collectively, the benzofuran and
benzothiophene moieties of compounds 15 and 16 seemed to exert the same function as that of a positive
allosteric modulator (PAM), while the benzofuran and benzothiophene moieties of compounds 37 and 38
seemed to carry the same function as that of a negative allosteric modulator (NAM) at the MOR.
Additionally, INTA, NAN and compounds 15, 16, 37, 38 were also docked into the KOR and DOR to compare
their selectivity to the MOR over the KOR and DOR (Figures S2 and S3).62-64 Similar to the six compounds
binding with the MOR, their “message” portions interacted with the orthosteric binding sites of the KOR and
DOR. The ionic interactions with D3.32, hydrogen bond interactions with Y3.33, and hydrophobic interactions
with residues M3.36, W6.48, and H6.52 were formed between the six compounds and the KOR and DOR.
Meanwhile, in the KOR and DOR, their “address” portions binding with the same domain as those of the six
compounds binding with the MOR. However, as some residues located at the allosteric binding sites among
the three receptors were non-conserved (L5.38, K6.58, and W7.35 in the MOR; M5.38, K6.58, and Y7.35 in the KOR;
and T5.38, W6.58, and L7.35 in the DOR), the interactions between the “address” portions of the six compounds
and the allosteric binding sites of the three receptors showed some differences. For INTA, compounds 15 and
16, their “address” portions mainly formed hydrophobic interactions with K6.58 and W7.35 of the KOR and W6.58
and L7.35 of the DOR, which was similar to their binding with K6.58 and W7.35 of the MOR. For NAN,
compounds 37 and 38, their “address” portions formed hydrophobic interactions with M5.38 and K5.39 of the
KOR and T5.38 and K5.39 of the DOR. As the hydrophobicity of L5.38 in the MOR, M5.38 in the KOR, and T5.38
in the DOR was L5.38 > M5.38 > T5.38, the hydrophobic interactions between the “address” portions of NAN,
compounds 37 and 38 and the allosteric binding site of the three receptors was MOR > KOR > DOR. Thus,
the similar interactions between INTA, compounds 15 and 16 with the MOR, KOR, and DOR may explain
why these three compounds displayed no selectivity to the MOR, KOR and DOR. The different hydrophobic
interactions between the “address” portions of NAN, compounds 37 and 38 with the allosteric binding site of
the MOR, KOR and DOR may lead to certain degree of selectivity of NAN, compounds 37 and 38 to the
MOR, KOR, and DOR.
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In Vivo Warm-Water Tail Immersion Assay. Warm-water tail immersion assay was then conducted to
examine the ability of each ligand to elicit antinociception or to antagonize the antinociception of morphine
in mice as previously reported.36 As seen in Figure 5A and 5B, compounds 15, 16, 21, 22, 23 and 24 (10
mg/kg) produced comparable percentage of maximum possible effect (% MPE) values as morphine, indicating
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that these six compounds acted as agonists in vivo. Figure 5C depicted the potency of each ligand at 10 mg/kg
to antagonize the antinociceptive effect of morphine at 10 mg/kg. As shown, compounds 19, 25 (NBF), 27,
29, 31, 33 and 38 were found to be potent antagonists of morphine and the other nine analogues had marginal
to moderate impact on the antinociceptic effect of morphine. Dose response studies showed (Table 3) that
compounds 19, 27, 29 and 33 possessed AD50 values ranging from 2.03 mg/kg to 3.21 mg/kg while compounds
31 and 38 carried greater potencies (AD50 values of 0.29 mg/kg) in comparison with NAN (AD50 = 2.07
mg/kg).42 More notably, the AD50 value of NBF was determined as 0.18 mg/kg, which is 12-fold more potent
compared to NAN.
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Figure 5. Warm-water tail immersion assay of synthesized analogues in mice (n = 5) at 56 ± 0.1 °C. All tested
compounds were administered subcutaneously. (A) Antinociceptive effects of compounds 15-26 (10 mg/kg).
(B) Antinociceptive effects of compounds 27-38 (10 mg/kg). (C) Blockage of the morphine-mediated
antinociception of selected compounds (10 mg/kg) in the presence of morphine (10 mg/kg). Saline and
morphine were adopted as negative and positive controls. Data are presented as mean values ± SD. ∗ indicates
P < 0.05; ∗∗∗ indicates P < 0.005.
Table 3. AD50 Values of Selected Compounds to Antagonize Morphine-mediated Antinociception in Warm-
Water Tail Immersion Assay in Vivo.
Compound
AD50 values (mg/kg (95% CL))
5 (NAN)a
2.07 (0.40-10.74)
2.79 (1.75-4.43)
0.18 (0.03-0.97)
3.21 (1.50-6.85)
2.51 (1.36-4.62)
0.29 (0.25-0.34)
2.03 (0.70-5.88)
0.29 (0.23-0.37)
19
25 (NBF)
27
29
31
33
38
a
Data has been reported in Reference 42.
Calcium Flux Assay. It has been reported that the activation of Gq G-protein/calcium pathway may result in
the rapid and transient increase of cytosolic calcium concentration.65 Calcium flux measurement has become
a key approach to evaluate GPCR function. To further profile three selected potent antagonists, NBF,
compounds 31 and 38 in this G-protein mediated signaling cascade, calcium flux assay was conducted
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following previously reported procedure.66 The results suggested that all three tested compounds displayed no
apparent agonism to increase intracellular calcium concentration (Figure 6A). On the other hand, all three of
them concentration-dependently antagonized DAMGO-induced calcium flux (Figure 6B). In details,
compound 38 was equipotent with the MOR antagonist naltrexone with IC50 value of 15.59 ± 1.96 nM, while
compounds 31 and NBF showed lower potencies with IC50 values of 50.7 ± 2.88 nM and 566.14 ± 7.68 nM,
respectively. The lack of agonism of these three compounds could be attributable to several factors. Firstly,
the adoption of chimeric Gαqi5 to transfect mMOR-CHO cells may result in such a phenomenon. Actually,
similar results was also observed in 5-HT1A receptor agonist ipsapirone, which efficaciously inhibited adenylyl
cyclase (AC) activity but did not display any agonism in calcium flux assay.67 Secondly, compounds 31 and
38 may act as neutral MOR antagonists in this signaling pathway according to their very low efficacy in
GTPγS functional assay. As for NBF, it may behave similarly to compounds 31 and 38, although NBF was
found to act as low efficacy partial agonist (Table 2).
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Figure 6. The calcium flux assay of compound 31, NBF, and compound 38 in Gαqi5 transfected mMOR-CHO
cells. (A) Compound 31, NBF, and compound 38 exhibited no apparent agonism to increase intracellular
calcium level. DAMGO was used as a control. The assay was repeated at least three times. The EC50 value of
DAMGO was 97.34 ± 1.35 nM. (B) Compound 31, NBF, and compound 38 significantly antagonized
DAMGO-induced intracellular calcium increase. Naltrexone was used as a control. DAMGO in assay buffer
(500 nM) was used in this antagonism studies. The assay was repeated at least three times and the data is
shown as the mean ± SEM. The IC50 values of naltrexone, compound 31, NBF, and compound 38 were 15.37
± 1.92 nM, 50.7 ± 2.88 nM, 566.14 ± 7.68 nM and 15.59 ± 1.96 nM, respectively.
Inhibition of cAMP Synthesis Assay. Cyclic adenosine monophosphate (cAMP) is a critical second
messenger in GPCR signal transduction, which is acutely inhibited after opioid agonist couples to Gi/Go
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classes of the G-proteins.68 We, therefore, evaluated the inhibitory effect of selected compounds on forskolin-
stimulated cAMP formation compared to DAMGO in mMOR-CHO cells. Figure 7 shows that all tested
ligands caused lower acute inhibition of cAMP production compared to DAMGO. As expected, the MOR full
agonist DAMGO was a potent inhibitor of forskolin-stimulated cAMP formation (Emax = 82.4 ± 1.7%, EC50
= 19 ± 5 nM). Compound 31 showed an Emax value of 18.9 ± 3.7% inhibition at an EC50 value of 80 ± 21 nM,
while NBF produced somewhat greater inhibition, with an Emax value of 35.7 ± 2.2% and an EC50 value of 37
± 10 nM. On the other hand, compound 38 acted as an MOR neutral antagonist because it did not produce
concentration-dependent inhibition of cAMP production at concentrations that bind to the MOR (Table 2).
These results basically corresponded well with the results in [35S]-GTPγS functional assays, in which the order
of decreasing relative efficacy was DAMGO >> NBF > compound 31 ≈ compound 38.
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Figure 7. The inhibition of cAMP synthesis assay of NBF and compounds 31 and 38 (n = 3). NBF, compounds
31 and 38 displayed varying degree of inhibition of 10 μM forskolin-stimulated cAMP. Data are presented as
mean % inhibition values ± SEM of the percentage of cAMP inhibition, where stimulation by 10 μM forskolin
alone is designated as 0%.
In Vivo Opioid-Withdrawal Studies. It has been reported that the well-known opioid antagonists such as
naltrexone and naloxone may precipitate significant withdrawal symptoms when administered to opioid
dependent patients.69,70 Since NBF and compounds 31 and 38 showed potent antagonisms in vivo, it is
necessary to examine whether they would produce withdrawal effects in morphine-pelleted mice. Thus
somatic symptoms of opioid withdrawal (wet-dog shakes, escape jumps, and paw tremors) were monitored
and recorded over a 20 min period after each injection with tested compound.71 As shown in Figure 8, naloxone
precipitated significant withdrawal symptoms at 1 mg/kg (Figure 8, the second columns), which were similar
to previous reports.41,72 Meanwhile, a 20 mg/kg dose of NBF did not show any significant withdrawal signs
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in placebo-pelleted mice (Figure 8, the first columns). A 1 mg/kg dose of NBF produced significantly fewer
wet-dog shakes, escape jumps, and paw tremors than 1 mg/kg NLX (Figure 8A, 8B and 8C,) in morphine-
pelleted mice. Moreover, the number of wet-dog shakes, escape jumps, and paw tremors for NBF at high dose
of 50 mg/kg were still dramatically lower than that of 1 mg/kg naloxone. On the other hand, a 1 mg/kg dose
of compound 31 produced wet-dog shakes, escape jumps, and paw tremors similar to naloxone at 1 mg/kg
(Figure S4). For compound 38, it produced significantly fewer escape jumps and slightly fewer wet-dog shakes
and paw tremors at 1 mg/kg than naloxone at 1 mg/kg (Figure S5). More interestingly, at a dose of 8 mg/kg
compound 38 still produced significantly fewer paw tremors (Figure S5C) than naloxone at 1 mg/kg. Overall,
these results suggest NBF produced much less significant withdrawal effects than NLX, which may indicate
its potential application in opioid abuse and addiction treatment.
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Figure 8. In vivo withdrawal assays of NBF in morphine-pelleted mice (n = 5). (A) Wet-dog shakes, (B)
escape jumps, and (C) paw tremors. The first column in each figure represents placebo-pelleted mice, while
the second to the fifth columns represent morphine-pelleted mice. ∗ indicates P < 0.05, ∗∗ indicates P < 0.005,
∗∗∗ indicates P < 0.0005, compared to 1 mg/kg naloxone (NLX, s.c.).
Conclusions
Bivalent bioisosteres represented by -NH-, -O- and -S- moieties have been widely used in drug design and
lead optimization for decades. Our previous studies revealed that NAN acted as a potent MOR antagonist
while its structurally similar analogue INTA actually produced agonism both in vitro and in vivo. On the basis
of these observations, we thus applied the concept of “bivalent bioisostere” for the structural modification of
INTA and NAN by replacing the -NH- in their indole ring with a -O- or -S- moiety. Twenty-four opioid
ligands carrying benzofuran and benzothiophene moieties were prepared and pharmacologically evaluated.
The competitive radioligand binding assays indicated that introduction of oxygen or sulfur atom resulted in
retention of binding affinity at the MOR but somewhat changed selectivity on the MOR over the KOR or/and
DOR. The [35S]-GTPγS functional assay demonstrated various effects on MOR efficacy in 6β-configuration
analogues and distinct reduction on MOR efficacy in 6α-configuration analogues. Molecular modeling studies
revealed that NAN and INTA as well as their corresponding bioisosteric counterparts, compounds 15, 16, 37,
and 38 seemed bind to the MOR in similar fashions. It also suggested that compounds 15, 16, 37, and 38 may
act as bitopic allosteric modulators at the MOR similar to INTA and NAN. Meanwhile, similar interactions
between INTA, compounds 15 and 16 and the MOR, KOR, and DOR resulted in their low selectivity to the
MOR over the KOR and DOR. However, differentiated interactions between the “address” portions of NAN,
compounds 37 and 38 with the allosteric binding site of the MOR, KOR, and DOR may cause NAN,
compounds 37 and 38 exhibiting moderate selectivity to the MOR over the KOR and DOR. Further in vivo
studies showed that three new compounds were more potent than NAN in blocking antinociceptic effect of
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morphine. Particularly, compound 25 (NBF) bearing 7′-benzofuryl moiety exhibited 12-fold antagonist
potency in comparison to NAN. Further investigation on the MOR-activated downstream signaling indicated
that NBF, compounds 31 and 38 significantly antagonized DAMGO-induced intracellular calcium flux and
exhibited varying degree of inhibition against cAMP production. Among these three potent antagonists, NBF
showed much less significant withdrawal symptoms than naloxone in morphine-pelleted mice, suggesting its
potential application to treat OUD. Taken together, these data demonstrated that our application of the
“bivalent bioisostere concept” for structural modification of opioid ligands INTA and NAN implemented
several new members of potent antagonists for the opioid receptors as well as a potential lead to develop novel
therapeutic agents treating OUD.
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Experimental Section.
Chemistry. All nonaqueous reactions were carried out under a pre-dried nitrogen gas atmosphere. All solvents
and reagents were purchased from either Sigma-Aldrich or Alfa Aesar, and were used as received without
further purification. Melting points were measured on a MPA100 OptiMelt automated melting point apparatus
without correction. IR spectra were recorded on Thermo Scientific Nicolet iS10 FT-IR Spectrometer.
Analytical thin-layer chromatography (TLC) analyses were carried out on Analtech Uniplate F254 plates and
flash column chromatography (FCC) was performed over silica gel (230−400 mesh, Merck). 1H (400 MHz)
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and C (100 MHz) nuclear magnetic resonance (NMR) spectra were recorded on a Bruker Ultrashield 400
Plus spectrometer, and chemical shifts were expressed in ppm. Mass spectra were obtained on an Applied
BioSystems 3200 Q trap with a turbo V source for TurbolonSpray. Analytical reversed-phase high
performance liquid chromatography (HPLC) was performed on a Varian ProStar 210 system using Agilent
Microsorb-MV 100-5 C18 column (250 x 4.6 mm). All analyses were conducted at ambient temperature with
a flow rate of 0.8 mL/min. Mobile phase is acetonitrile/water (90/10) with 0.1% trifluoroacetic acid (TFA).
The UV detector was set up at 210 nm. Compounds purities were calculated as the percentage peak area of
the analyzed compound, and retention times (Rt) were presented in minutes. The purity of all newly
synthesized compounds was identified as ≥ 95%.
General Procedure for Amide Coupling/Hydrolysis Reaction. A solution of carboxylic acid (2.5 equiv) in
dry DMF (1.5 mL) was added with hydrobenzotriazole (HOBt, 3 equiv), N-(3-dimethylaminopropyl)-N′-
ethylcarbodiimide hydrochloride (EDCI, 3 equiv), 4 Å molecular sieves, and triethylamine (5 equiv) on an
ice-water bath. After 1h, a solution of 6α-naltrexamine or 6β-naltrexamine (1 equiv) in pre-dried DMF (1.5
mL) was added dropwise. The resulting mixture was stirred at room temperature. Once TLC indicated
complete consumption of the starting material, the reaction mixture was filtered through celite. The filtrate
was concentrated to dryness, and dissolved in anhydrous methanol (3 mL), then K2CO3 (2.5 equiv) was added.
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The resulting mixture was stirred overnight at room temperature and filtered again over celite. After
concentration, the residue was purified by flash column chromatography with CH2Cl2/MeOH (1% NH3·H2O)
as the eluent to give the free base. After structural confirmation by 1H NMR, the corresponding free base was
then converted into a hydrochloride salt, which was fully characterized by 1H NMR, 13C NMR, IR, MS, and
HPLC.
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17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzofuran-2-carboxamido)morphinan (15)
The title compound was prepared following the general procedure as a white solid in 36% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.36 (s, 1H, exchangeable), 9.01 (d, J = 8.3 Hz, 1H, exchangeable),
8.90 (s, 1H, exchangeable), 7.79 (d, J = 7.6 Hz, 1H), 7.67 (d, J = 8.4 Hz, 1H), 7.59 (s, 1H), 7.49 (t, J = 7.5 Hz,
1H), 7.35 (t, J = 7.5 Hz, 1H), 6.74 (d, J = 8.1 Hz, 1H), 6.66 (d, J = 8.1 Hz, 1H), 6.25 (s, 1H, exchangeable),
4.90 (d, J = 7.8 Hz, 1H), 3.90 (d, J = 5.1 Hz, 1H), 3.69 (m, 1H), 3.37 (m, 1H), 3.30 (m, 1H), 3.08 (m, 1H),
3.03 (m, 1H), 2.88 (m, 1H), 2.46–2.44 (m, 2H), 1.96 (m, 1H), 1.80 (m, 1H), 1.58 (m, 1H), 1.46 (m, 1H), 1.40
(m, 1H), 1.09 (m, 1H), 0.68 (m, 1H), 0.60 (m, 1H), 0.52 (m, 1H), 0.42 (m, 1H). 13C NMR (100 MHz, DMSO-d6)
δ 157.76, 154.19, 149.02, 142.09, 141.35, 129.63, 127.11, 126.83, 123.69, 122.78, 120.60, 119.31, 117.92,
111.73, 109.47, 89.62, 69.68, 61.67, 56.67, 55.00, 50.82, 45.60, 29.40, 27.31, 23.69, 23.02, 5.72, 5.10, 2.62.
[α]25D –201.7o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M + H]+ (m/z): 487.2262.
IR (diamond, cm-1) νmax : 3064, 1652, 1597, 1448, 1313, 1177, 1028, 746. Mp 199–201 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzothiophene-2-carboxamido)morphinan
(16)
The title compound was prepared following the general procedure as a white solid in 52% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H, exchangeable), 8.99 (d, J = 8.2 Hz, 1H, exchangeable),
8.84 (s, 1H, exchangeable), 8.15 (s, 1H), 8.03 (d, J = 7.6 Hz, 1H), 7.97 (d, J = 7.6 Hz, 1H), 7.50–7.43 (m, 2H),
6.73 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 8.1 Hz, 1H), 6.13 (s, 1H, exchangeable), 4.81 (d, J = 7.8 Hz, 1H), 4.08
(m, 1H), 3.85 (d, J = 5.3 Hz, 1H), 3.66 (m, 1H), 3.37 (m, 1H), 3.26 (m, 1H), 3.10 (m, 1H), 3.05 (m, 1H), 2.85
(m, 1H), 2.43 (m, 1H), 1.91 (m, 1H), 1.76 (m, 1H), 1.63 (m, 1H), 1.50 (m, 1H), 1.43 (m, 1H), 1.07 (m, 1H),
0.68 (m, 1H), 0.60 (m, 1H), 0.51 (m, 1H), 0.42 (m, 1H). 13C NMR (100 MHz, DMSO-d6) δ 161.05, 142.09,
141.35, 140.21, 140.01, 139.14, 129.58, 126.19, 125.18, 124.89, 124.76, 122.79, 120.59, 119.36, 117.95,
89.73, 69.69, 61.72, 56.72, 51.38, 46.49, 45.62, 29.34, 27.32, 23.76, 23.03, 5.71, 5.09, 2.63. [α]25D –172.0o (c
0.2, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z): 503.1991. IR (diamond,
cm-1) νmax : 3061, 1647, 1538, 1451, 1319, 1126, 1018, 759. Mp 273–275 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzofuran-3-carboxamido)morphinan (17)
The title compound was prepared following the general procedure as a white solid in 49% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.36 (s, 1H, exchangeable), 8.87 (s, 1H, exchangeable), 8.63 (s, 1H),
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Journal of Medicinal Chemistry
8.61 (d, J = 8.2 Hz, 1H, exchangeable), 8.07 (d, J = 7.3 Hz, 1H), 7.66 (d, J = 8.1 Hz, 1H), 7.40 (t, J = 7.5 Hz,
1H), 7.35 (t, J = 7.5 Hz, 1H), 6.74 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 8.1 Hz, 1H), 6.18 (s, 1H, exchangeable),
4.77 (d, J = 7.8 Hz, 1H), 3.87 (d, J = 4.9 Hz, 1H), 3.71 (m, 1H), 3.38 (m, 1H), 3.35 (m, 1H), 3.10 (m, 1H),
3.05 (m, 1H), 2.86 (m, 1H), 2.46–2.44 (m, 2H), 1.90 (m, 1H), 1.78 (m, 1H), 1.65 (m, 1H), 1.49 (m, 1H), 1.41
(m, 1H), 1.08 (m, 1H), 0.69 (m, 1H), 0.60 (m, 1H), 0.51 (m, 1H), 0.43 (m, 1H). 13C NMR (100 MHz, DMSO-d6)
δ 161.62, 158.15, 154.62, 147.38, 142.12, 141.32, 129.60, 125.08, 123.69, 121.93, 120.57, 119.29, 117.93,
116.85, 111.51, 89.90, 69.70, 61.72, 56.69, 54.85, 50.58, 45.61, 29.35, 27.32, 23.84, 22.59, 5.68, 5.07, 2.59.
[α]25D –147.3o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M + H]+ (m/z): 487.2190.
IR (diamond, cm-1) νmax : 3181, 1648, 1536, 1447, 1314, 1124, 1038, 755. Mp 241–243 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzothiophene-3-carboxamido)morphinan
(18)
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The title compound was prepared following the general procedure as a white solid in 43% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H, exchangeable), 8.84 (s, 1H, exchangeable), 8.68 (d, J =
7.9 Hz, 1H, exchangeable), 8.46 (d, J = 7.2 Hz, 1H), 8.43 (s, 1H), 8.05 (d, J = 7.2 Hz, 1H), 7.46–7.40 (m, 2H),
6.73 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 8.1 Hz, 1H), 6.13 (s, 1H, exchangeable), 4.80 (d, J = 7.7 Hz, 1H), 3.85
(d, J = 5.6 Hz, 1H), 3.71 (m, 1H), 3.36 (m, 1H), 3.28 (m, 1H), 3.15 (m, 1H), 3.09–3.02 (m, 2H), 2.85 (m, 1H),
2.42 (m, 1H), 1.90 (m, 1H), 1.77 (m, 1H), 1.67 (m, 1H), 1.49 (m, 1H), 1.43 (m, 1H), 1.07 (m, 1H), 0.68 (m,
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1H), 0.59 (m, 1H), 0.50 (m, 1H), 0.42 (m, 1H). C NMR (100 MHz, DMSO-d6) δ 162.67, 142.18, 141.35,
139.44, 137.18, 130.75, 130.72, 129.68, 124.84, 124.76, 124.58, 122.71, 120.60, 119.30, 117.95, 89.88, 69.75,
61.74, 56.72, 50.79, 46.51, 45.65, 29.43, 27.35, 23.79, 23.04, 5.72, 5.11, 2.62. [α]25D –129.0o (c 0.1, MeOH).
HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z): 503.1980. IR (diamond, cm-1) νmax
2981, 1656, 1507, 1450, 1325, 1127, 1034, 765. Mp 254–256 oC, dec.
:
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzofuran-4-carboxamido)morphinan (19)
The title compound was prepared following the general procedure as a white solid in 42% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.33 (s, 1H, exchangeable), 8.84 (s, 1H, exchangeable), 8.70 (d, J =
8.0 Hz, 1H, exchangeable), 8.09 (d, J = 2.1 Hz, 1H), 7.79 (d, J = 8.0 Hz, 1H), 7.77 (d, J = 7.9 Hz, 1H), 7.42
(t, J = 7.9 Hz, 1H), 7.31 (d, J = 2.1 Hz, 1H), 6.73 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 8.1 Hz, 1H), 6.13 (s, 1H,
exchangeable), 4.86 (d, J = 7.9 Hz, 1H), 3.86 (d, J = 5.1 Hz, 1H), 3.73 (m, 1H), 3.37 (m, 1H), 3.28 (m, 1H),
3.10 (m, 1H), 3.04 (m, 1H), 2.85 (m, 1H), 2.46–2.44 (m, 2H), 1.91 (m, 1H), 1.77 (m, 1H), 1.65 (m, 1H), 1.49
(m, 1H), 1.42 (m, 1H), 1.06 (m, 1H), 0.68 (m, 1H), 0.60 (m, 1H), 0.50 (m, 1H), 0.42 (m, 1H). 13C NMR (100
MHz, DMSO-d6) δ 165.77, 154.72, 146.90, 142.21, 141.32, 129.69, 127.60, 126.39, 123.72, 121.73, 120.58,
119.24, 117.93, 114.01, 107.31, 89.88, 69.76, 61.74, 54.87, 51.10, 46.50, 45.63, 29.45, 27.35, 23.76, 23.04,
5.71, 5.09, 2.63. [α]25D –138.4o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M + H]+
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(m/z): 487.2206. IR (diamond, cm-1) νmax : 3182, 1646, 1505, 1447, 1313, 1124, 1032, 754. Mp 239–241 oC,
dec.
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(20)
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The title compound was prepared following the general procedure as a white solid in 53% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.36 (s, 1H, exchangeable), 8.89 (s, 1H, exchangeable), 8.72 (d, J =
8.1 Hz, 1H, exchangeable), 8.17 (d, J = 8.1 Hz, 1H), 7.90–7.85 (m, 2H), 7.72 (d, J = 7.7 Hz, 1H), 7.46 (t, J =
7.7 Hz, 1H), 6.75 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 8.1 Hz, 1H), 6.23 (s, 1H, exchangeable), 4.83 (d, J = 7.8
Hz, 1H), 3.90 (d, J = 5.3 Hz, 1H), 3.74 (m, 1H), 3.36 (m, 1H), 3.29 (m, 1H), 3.10 (m, 1H), 3.04 (m, 1H), 2.88
(m, 1H), 2.47–2.42 (m, 2H), 1.93 (m, 1H), 1.80 (m, 1H), 1.68 (m, 1H), 1.47 (m, 1H), 1.47 (m, 1H), 1.09 (m,
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1H), 0.68 (m, 1H), 0.60 (m, 1H), 0.52 (m, 1H), 0.42 (m, 1H). C NMR (100 MHz, DMSO-d6) δ 166.98,
142.21, 141.33, 140.27, 137.15, 130.60, 129.68, 128.44, 125.02, 123.72, 123.54, 123.46, 120.57, 119.22,
117.93, 89.85, 69.73, 61.69, 56.68, 51.17, 46.47, 45.61, 29.44, 27.32, 23.68, 23.02, 5.69, 5.06, 2.59. [α]25
–
D
194.0o (c 0.05, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z): 503.1953. IR
(diamond, cm-1) νmax : 2973, 1655, 1505, 1323, 1298, 1126, 1034, 765. Mp 250 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzofuran-5-carboxamido)morphinan (21)
The title compound was prepared following the general procedure as a white solid in 40% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.33 (s, 1H, exchangeable), 8.86 (s, 1H, exchangeable), 8.70 (d, J =
8.0 Hz, 1H, exchangeable), 8.24 (d, J = 1.7 Hz, 1H), 8.09 (d, J = 2.2 Hz, 1H), 7.88 (dd, J = 8.7, 1.7 Hz, 1H),
7.68 (d, J = 8.7 Hz, 1H), 7.08 (d, J = 2.2 Hz, 1H), 6.73 (d, J = 8.1 Hz, 1H), 6.66 (d, J = 8.1 Hz, 1H), 6.15 (s,
1H, exchangeable), 4.86 (d, J = 7.8 Hz, 1H), 3.86 (d, J = 5.1 Hz, 1H), 3.71 (m, 1H), 3.37 (m, 1H), 3.34 (m,
1H), 3.10 (m, 1H), 3.04 (m, 1H), 2.85 (m, 1H), 2.47–2.44 (m, 2H), 1.89 (m, 1H), 1.77 (m, 1H), 1.62 (m, 1H),
1.48 (m, 1H), 1.41 (m, 1H), 1.07 (m, 1H), 0.68 (m, 1H), 0.59 (m, 1H), 0.51 (m, 1H), 0.42 (m, 1H). 13C NMR
(100 MHz, DMSO-d6) δ 165.70, 155.76, 147.19, 142.20, 141.31, 129.69, 129.45, 127.02, 123.86, 120.88,
120.58, 119.23, 117.92, 110.91, 107.16, 89.91, 69.75, 61.75, 54.87, 51.26, 46.50, 45.61, 29.39, 27.37, 23.80,
23.04, 5.71, 5.09, 2.63. [α]25D –162.1o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M
+ H]+ (m/z): 487.2230. IR (diamond, cm-1) νmax : 3098, 1644, 1503, 1464, 1311, 1253, 1124, 748. Mp 298–
300 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzothiophene-5-carboxamido)morphinan
(22)
The title compound was prepared following the general procedure as a white solid in 55% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H, exchangeable), 8.88 (s, 1H, exchangeable), 8.77 (d, J =
8.1 Hz, 1H, exchangeable), 8.45 (s, 1H), 8.11 (d, J = 8.1 Hz, 1H), 7.88 (d, J = 8.1 Hz, 1H), 7.87 (d, J = 5.2
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Hz, 1H), 7.56 (d, J = 5.2 Hz, 1H), 6.73 (d, J = 8.1 Hz, 1H), 6.66 (d, J = 8.1 Hz, 1H), 6.21 (s, 1H, exchangeable),
4.88 (d, J = 7.8 Hz, 1H), 3.88 (d, J = 5.1 Hz, 1H), 3.74 (m, 1H), 3.37 (m, 1H), 3.27 (m, 1H), 3.09 (m, 1H),
3.04 (m, 1H), 2.87 (m, 1H), 2.48–2.44 (m, 2H), 1.91 (m, 1H), 1.78 (m, 1H), 1.63 (m, 1H), 1.48 (m, 1H), 1.41
(m, 1H), 1.09 (m, 1H), 0.68 (m, 1H), 0.60 (m, 1H), 0.51 (m, 1H), 0.42 (m, 1H). 13C NMR (100 MHz, DMSO-d6)
δ 165.77, 142.19, 141.74, 141.31, 139.15, 130.67, 129.68, 128.76, 124.38, 122.89, 122.78, 122.38, 120.58,
119.25, 117.92, 89.91, 69.75, 61.76, 56.70, 51.27, 46.50, 45.61, 29.38, 27.37, 23.79, 23.04, 5.71, 5.09, 2.62.
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[α]25 –130.6o (c 0.05, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z):
D
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17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzofuran-6-carboxamido)morphinan (23)
The title compound was prepared following the general procedure as a white solid in 44% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H, exchangeable), 8.85 (s, 1H, exchangeable), 8.72 (d, J =
7.9 Hz, 1H, exchangeable), 8.16 (d, J = 2.1 Hz, 1H), 8.15 (s, 1H), 7.84 (dd, J = 8.2, 1.3 Hz, 1H), 7.75 (d, J =
8.2 Hz, 1H), 7.05 (d, J = 2.1 Hz, 1H), 6.73 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 8.1 Hz, 1H), 6.13 (s, 1H，
exchangeable), 4.86 (d, J = 7.8 Hz, 1H), 3.85 (d, J = 5.3 Hz, 1H), 3.72 (m, 1H), 3.37 (m, 1H), 3.29 (m, 1H),
3.09 (m, 1H), 3.04 (m, 1H), 2.84 (m, 1H), 2.47–2.42 (m, 2H), 1.89 (m, 1H), 1.76 (m, 1H), 1.63 (m, 1H), 1.49
(m, 1H), 1.41 (m, 1H), 1.08 (m, 1H), 0.69 (m, 1H), 0.60 (m, 1H), 0.50 (m, 1H), 0.42 (m, 1H). 13C NMR (100
MHz, DMSO-d6) δ 165.44, 153.93, 148.34, 142.19, 141.31, 130.54, 129.88, 129.68, 122.17, 120.87, 120.59,
119.25, 117.92, 110.22, 106.82, 89.88, 69.75, 61.74, 56.71, 51.31, 46.50, 45.61, 29.38, 27.35, 23.79, 23.02,
5.71, 5.06, 2.63. [α]25D –147.4o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M + H]+
(m/z): 487.2238. IR (diamond, cm-1) νmax : 3102, 1637, 1527, 1448, 1312, 1126, 1032, 747. Mp 283–284 oC,
dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzothiophene-6-carboxamido)morphinan
(24)
The title compound was prepared following the general procedure as a white solid in 47% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H, exchangeable), 8.89 (s, 1H, exchangeable), 8.78 (d, J =
8.0 Hz, 1H, exchangeable), 8.56 (s, 1H), 7.97 (d, J = 8.4 Hz, 1H), 7.95 (d, J = 5.4 Hz, 1H), 7.91 (d, J = 8.4
Hz, 1H), 7.54 (d, J = 5.4 Hz, 1H), 6.74 (d, J = 8.1 Hz, 1H), 6.66 (d, J = 8.1 Hz, 1H), 6.23 (s, 1H, exchangeable),
4.87 (d, J = 7.8 Hz, 1H), 3.89 (d, J = 5.1 Hz, 1H), 3.73 (m, 1H), 3.37 (m, 1H), 3.32 (m, 1H), 3.09 (m, 1H),
3.05 (m, 1H), 2.87 (m, 1H), 2.47–2.44 (m, 2H), 1.92 (m, 1H), 1.79 (m, 1H), 1.63 (m, 1H), 1.48 (m, 1H), 1.41
(m, 1H), 1.09 (m, 1H), 0.68 (m, 1H), 0.60 (m, 1H), 0.52 (m, 1H), 0.42 (m, 1H). 13C NMR (100 MHz, DMSO-d6)
δ 165.50, 142.16, 141.40, 141.29, 138.85, 130.40, 130.21, 129.65, 123.83, 123.27, 123.25, 121.85, 120.56,
119.23, 117.90, 89.89, 69.72, 61.71, 56.68, 51.28, 46.47, 45.58, 29.34, 27.33, 23.75, 23.01, 5.68, 5.06, 2.59.
[α]25D –142.0o (c 0.1, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z): 503.1989.
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IR (diamond, cm-1) νmax : 3095, 1645, 1502, 1425, 1310, 1187, 1032, 748. Mp 266–267 oC, dec.
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17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzofuran-7-carboxamido)morphinan (25)
The title compound was prepared following the general procedure as a white solid in 45% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.37 (s, 1H, exchangeable), 8.91 (s, 1H, exchangeable), 8.47 (d, J =
8.3 Hz, 1H, exchangeable), 8.14 (d, J = 2.1 Hz, 1H), 7.84 (dd, J = 7.7, 1.0 Hz, 1H), 7.71 (d, J = 7.7 Hz, 1H),
7.36 (t, J = 7.7 Hz, 1H), 7.09 (d, J = 2.1 Hz, 1H), 6.75 (d, J = 8.1 Hz, 1H), 6.66 (d, J = 8.1 Hz, 1H), 6.35 (s,
1H, exchangeable), 4.91 (d, J = 7.7 Hz, 1H), 3.91 (d, J = 5.0 Hz, 1H), 3.79 (m, 1H), 3.34 (m, 1H), 3.30 (m,
1H), 3.09 (m, 1H), 3.04 (m, 1H), 2.88 (m, 1H), 2.47–2.43 (m, 2H), 1.99 (m, 1H), 1.79 (m, 1H), 1.65 (m, 1H),
1.46 (m, 1H), 1.39 (m, 1H), 1.09 (m, 1H), 0.68 (m, 1H), 0.60 (m, 1H), 0.52 (m, 1H), 0.42 (m, 1H). 13C NMR
(100 MHz, DMSO-d6) δ 163.35, 151.01, 146.36, 142.19, 141.29, 129.66, 128.23, 124.54, 124.40, 122.79,
120.59, 119.24, 119.10, 117.91, 106.86, 90.01, 69.72, 61.58, 56.68, 51.18, 46.47, 45.66, 29.45, 27.32, 23.66,
22.98, 5.68, 5.06, 2.59. [α]25D –99.8o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M
+ H]+ (m/z): 487.2190. IR (diamond, cm-1) νmax : 3064, 1644, 1505, 1451, 1316, 1125, 1032, 749. Mp 270–
272 oC, dec.
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17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(benzothiophene-7-carboxamido)morphinan
(26)
The title compound was prepared following the general procedure as a white solid in 55% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H, exchangeable), 8.96 (d, J = 8.0 Hz, 1H, exchangeable),
8.88 (s, 1H, exchangeable), 8.10 (d, J = 7.7 Hz, 1H), 8.07 (d, J = 7.7 Hz, 1H), 7.81 (d, J = 5.6 Hz, 1H), 7.53
(t, J = 7.7 Hz, 1H), 7.49 (d, J = 5.6 Hz, 1H), 6.74 (d, J = 8.1 Hz, 1H), 6.68 (d, J = 8.1 Hz, 1H), 6.22 (s, 1H,
exchangeable), 4.91 (d, J = 7.8 Hz, 1H), 3.89 (d, J = 5.2 Hz, 1H), 3.76 (m, 1H), 3.37 (m, 1H), 3.29 (m, 1H),
3.10 (m, 1H), 3.05 (m, 1H), 2.87 (m, 1H), 2.47–2.42 (m, 2H), 1.94 (m, 1H), 1.80 (m, 1H), 1.65 (m, 1H), 1.49
(m, 1H), 1.42 (m, 1H), 1.09 (m, 1H), 0.69 (m, 1H), 0.60 (m, 1H), 0.51 (m, 1H), 0.43 (m, 1H). 13C NMR (100
MHz, DMSO-d6) δ 165.30, 142.14, 141.30, 140.82, 138.11, 130.88, 129.62, 127.32, 126.79, 123.84, 122.86,
122.52, 120.55, 119.26, 117.94, 89.71, 69.73, 61.73, 56.69, 51.34, 46.47, 45.62, 29.40, 27.33, 23.73, 23.02,
5.68, 5.05, 2.60. [α]25 –114.0o (c 0.1, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M +
D
H]+ (m/z): 503.1984. IR (diamond, cm-1) νmax : 3096, 1647, 1502, 1425, 1312, 1128, 1033, 748. Mp 259–261
oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzofuran-2-carboxamido)morphinan (27)
The title compound was prepared following the general procedure as a white solid in 56% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.26 (s, 1H, exchangeable), 8.85 (s, 1H, exchangeable), 8.13 (d, J =
7.9 Hz, 1H, exchangeable), 7.79 (d, J = 7.6 Hz, 1H), 7.70 (d, J = 8.4 Hz, 1H), 7.65 (s, 1H), 7.49 (t, J = 7.6 Hz,
1H), 7.35 (t, J = 7.6 Hz, 1H), 6.74 (d, J = 8.1 Hz, 1H), 6.60 (d, J = 8.1 Hz, 1H), 6.32 (s, 1H, exchangeable),
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4.79 (d, J = 3.8 Hz, 1H), 4.63 (m, 1H), 3.92 (d, J = 6.7 Hz, 1H), 3.34 (m, 1H), 3.27 (m, 1H), 3.09 (m, 1H),
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3.05 (m, 1H), 2.96 (m, 1H), 2.73 (m, 1H), 2.47 (m, 1H), 1.92 (m, 1H), 1.65 (m, 1H), 1.56 (m, 1H), 1.47 (m,
4
5
13
1H), 1.17 (m, 1H), 1.07 (m, 1H), 0.70 (m, 1H), 0.62 (m, 1H), 0.48 (m, 1H), 0.41 (m, 1H). C NMR (100
6
7
MHz, DMSO-d6) δ 157.61, 154.23, 148.71, 145.92, 138.87, 128.65, 127.10, 126.92, 123.75, 122.77, 122.07,
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119.27, 118.37, 111.85, 109.99, 87.09, 69.34, 64.86, 61.02, 57.04, 45.61, 45.29, 30.18, 29.15, 23.48, 19.44,
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5.68, 5.15, 2.56. [α]25 –227.3o (c 0.25, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M +
D
H]+ (m/z): 487. 2233. IR (diamond, cm-1) νmax: 3061, 1645, 1505, 1449, 1316, 1117, 1032, 749. Mp 244–246
oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzothiophene-2-carboxamido)morphinan
(28)
The title compound was prepared following the general procedure as a white solid in 43% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.24 (s, 1H, exchangeable), 8.86 (s, 1H, exchangeable), 8.48 (d, J =
7.5 Hz, 1H, exchangeable), 8.28 (s, 1H), 8.03 (d, J = 7.1 Hz, 1H), 7.95 (d, J = 7.1 Hz, 1H), 7.49–7.45 (m, 2H),
6.73 (d, J = 8.1 Hz, 1H), 6.59 (d, J = 8.1 Hz, 1H), 6.34 (s, 1H, exchangeable), 4.79 (d, J = 3.8 Hz, 1H), 4.60
(m, 1H), 3.93 (d, J = 6.7 Hz, 1H), 3.39 (m, 1H), 3.27 (m, 1H), 3.08 (m, 1H), 3.04 (m, 1H), 2.96 (m, 1H), 2.73
(m, 1H), 2.47 (m, 1H), 1.93 (m, 1H), 1.65 (m, 1H), 1.54 (m, 1H), 1.46 (m, 1H), 1.22 (m, 1H), 1.07 (m, 1H),
0.69 (m, 1H), 0.62 (m, 1H), 0.49 (m, 1H), 0.41 (m, 1H). 13C NMR (100 MHz, DMSO-d6) δ 161.13, 146.05,
140.19, 139.63, 139.14, 138.80, 128.63, 126.19, 125.37, 125.13, 124.90, 122.75, 122.04, 119.12, 118.31,
86.97, 69.35, 61.04, 57.01, 51.97, 46.25, 45.23, 30.24, 29.17, 23.46, 19.17, 5.65, 5.13, 2.54. [α]25D –197.7o (c
0.2, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z): 503.1952. IR (diamond,
cm-1) νmax : 2942, 1621, 1505, 1455, 1303, 1117, 1032, 755. Mp 240–242 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzofuran-3-carboxamido)morphinan (29)
The title compound was prepared following the general procedure as a white solid in 60% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.23 (s, 1H, exchangeable), 8.87 (s, 1H, exchangeable), 8.74 (s, 1H),
8.11 (d, J = 7.8 Hz, 1H, exchangeable), 8.08 (dd, J = 7.2, 1.1 Hz, 1H), 7.66 (dd, J = 7.2, 1.1 Hz, 1H), 7.41–
7.35 (m, 2H), 6.72 (d, J = 8.1 Hz, 1H), 6.58 (d, J = 8.1 Hz, 1H), 6.34 (s, 1H, exchangeable), 4.80 (d, J = 3.9
Hz, 1H), 4.64 (m, 1H), 3.94 (d, J = 6.8 Hz, 1H), 3.37 (m, 1H), 3.28 (m, 1H), 3.08 (m, 1H), 3.04 (m, 1H), 2.96
(m, 1H), 2.73 (m, 1H), 2.53 (m, 1H), 1.93 (m, 1H), 1.65 (m, 1H), 1.54 (m, 1H), 1.46 (m, 1H), 1.16 (m, 1H),
13
1.09 (m, 1H), 0.69 (m, 1H), 0.62 (m, 1H), 0.49 (m, 1H), 0.41 (m, 1H). C NMR (100 MHz, DMSO-d6) δ
161.61, 154.54, 147.83, 146.07, 138.80, 128.69, 125.26, 125.03, 123.73, 122.05, 121.80, 119.09, 118.34,
116.58, 111.53, 87.19, 69.36, 61.06, 57.01, 45.42, 45.21, 30.22, 29.20, 23.47, 19.39, 5.65, 5.12, 2.54. [α]25
–
D
145.0o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found [M + H]+ (m/z): 487.2225. IR
(diamond, cm-1) νmax : 2973, 1646, 1505, 1451, 1316, 1117, 1031, 748. Mp 229–231 oC, dec.
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17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzothiophene-3-carboxamido)morphinan
(30)
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9
The title compound was prepared following the general procedure as a white solid in 33% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.19 (s, 1H, exchangeable), 8.89 (s, 1H, exchangeable), 8.47 (s, 1H),
8.45 (dd, J = 7.2, 1.5 Hz, 1H), 8.17 (d, J = 7.7 Hz, 1H, exchangeable), 8.06 (dd, J = 7.2, 1.5 Hz, 1H), 7.49 (t,
J = 7.2 Hz, 1H), 7.43 (t, J = 7.2 Hz, 1H), 6.72 (d, J = 8.1 Hz, 1H), 6.58 (d, J = 8.1 Hz, 1H), 6.35 (s, 1H,
exchangeable), 4.83 (d, J = 3.9 Hz, 1H), 4.64 (m, 1H), 3.95 (d, J = 6.8 Hz, 1H), 3.38 (m, 1H), 3.28 (m, 1H),
3.09 (m, 1H), 3.05 (m, 1H), 2.97 (m, 1H), 2.74 (m, 1H), 2.54 (m, 1H), 1.94 (m, 1H), 1.67 (m, 1H), 1.56 (m,
1H), 1.47 (m, 1H), 1.18 (m, 1H), 1.08 (m, 1H), 0.70 (m, 1H), 0.62 (m, 1H), 0.49 (m, 1H), 0.42 (m, 1H). 13C
NMR (100 MHz, DMSO-d6) δ 162.68, 146.06, 139.35, 138.80, 137.17, 131.05, 130.82, 128.71, 124.82,
124.77, 124.34, 122.74, 122.07, 119.09, 118.30, 87.13, 69.36, 61.06, 57.02, 56.09, 45.62, 45.22, 30.21, 29.23,
23.47, 19.40, 5.66, 5.13, 2.54. [α]25D –233.2o (c 0.2, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999.
Found [M + H]+ (m/z): 503.1935. IR (diamond, cm-1) νmax : 2942, 1621, 1505, 1455, 1303, 1117, 1032, 755.
Mp 225 oC, dec.
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17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzofuran-4-carboxamido)morphinan (31)
The title compound was prepared following the general procedure as a white solid in 45% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.17 (s, 1H, exchangeable), 8.88 (s, 1H, exchangeable), 8.10 (d, J =
2.2 Hz, 1H), 8.09 (d, J = 7.2 Hz, 1H, exchangeable), 7.79 (d, J = 8.2 Hz, 1H), 7.72 (d, J = 7.2 Hz, 1H), 7.41
(t, J = 7.9 Hz, 1H), 7.31 (dd, J = 2.2, 0.8 Hz, 1H), 6.72 (d, J = 8.1 Hz, 1H), 6.58 (d, J = 8.1 Hz, 1H), 6.33 (s,
1H, exchangeable), 4.84 (d, J = 3.8 Hz, 1H), 4.64 (m, 1H), 3.94 (d, J = 6.7 Hz, 1H), 3.38 (m, 1H), 3.27 (m,
1H), 3.09 (m, 1H), 3.06 (m, 1H), 2.97 (m, 1H), 2.74 (m, 1H), 2.54 (m, 1H), 1.94 (m, 1H), 1.67 (m, 1H), 1.55
(m, 1H), 1.47 (m, 1H), 1.17 (m, 1H), 1.09 (m, 1H), 0.70 (m, 1H), 0.63 (m, 1H), 0.49 (m, 1H), 0.41 (m, 1H).
13C NMR (100 MHz, DMSO-d6) δ 165.93, 154.61, 146.93, 146.06, 138.85, 128.75, 127.98, 126.21, 123.74,
122.21, 122.10, 119.14, 118.31, 113.93, 107.05, 87.19, 69.36, 61.08, 57.06, 51.39, 45.88, 45.24, 30.21, 29.29,
24.84, 19.45, 5.67, 5.15, 2.56. [α]25 –257.0o (c 0.2, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227.
D
Found [M + H]+ (m/z): 487.2236. IR (diamond, cm-1) νmax : 2972, 1645, 1505, 1449, 1316, 1118, 1032, 748.
Mp 224–226 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzothiophene-4-carboxamido)morphinan
(32)
The title compound was prepared following the general procedure as a white solid in 41% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 8.21 (d, J = 7.7 Hz, 1H, exchangeable), 8.15 (d, J = 8.1 Hz, 1H), 7.87–
7.82 (m, 2H), 7.67 (d, J = 7.7 Hz, 1H), 7.44 (t, J = 7.7 Hz, 1H), 6.70 (d, J = 8.1 Hz, 1H), 6.59 (d, J = 8.1 Hz,
1H), 4.84 (d, J = 3.8 Hz, 1H), 4.62 (m, 1H), 3.91 (d, J = 6.9 Hz, 1H), 3.29 (m, 1H), 3.25 (m, 1H), 3.09 (m,
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Journal of Medicinal Chemistry
1H), 3.04 (m, 1H), 2.94 (m, 1H), 2.74 (m, 1H), 2.53 (m, 1H), 1.90 (m, 1H), 1.66 (m, 1H), 1.55 (m, 1H), 1.45
(m, 1H), 1.13 (m, 1H), 1.04 (m, 1H), 0.70 (m, 1H), 0.62 (m, 1H), 0.47 (m, 1H), 0.40 (m, 1H). 13C NMR (100
MHz, DMSO-d6) δ 167.08, 146.04, 140.11, 138.83, 137.08, 130.92, 128.73, 128.48, 124.89, 123.82, 123.57,
123.55, 122.08, 119.09, 118.26, 87.10, 69.34, 61.05, 57.02, 45.90, 45.22, 30.18, 29.25, 23.48, 19.43, 5.65,
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5.12, 2.54. [α]25 –182.5o (c 0.2, MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+
D
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(m/z): 503.1940. IR (diamond, cm-1) νmax : 2956, 1622, 1504, 1455, 1303, 1117, 1031, 769. Mp 242–243 oC,
dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzofuran-5-carboxamido)morphinan (33)
The title compound was prepared following the general procedure as a white solid in 51% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.18 (s, 1H, exchangeable), 8.86 (s, 1H, exchangeable), 8.23 (d, J =
1.5 Hz, 1H), 8.10 (d, J = 2.2 Hz, 1H), 8.09 (d, J = 8.1 Hz, 1H, exchangeable), 7.87 (dd, J = 8.6, 1.5 Hz, 1H),
7.69 (d, J = 8.6 Hz, 1H), 7.08 (d, J = 2.2 Hz, 1H), 6.72 (d, J = 8.1 Hz, 1H), 6.58 (d, J = 8.1 Hz, 1H), 6.31 (s,
1H, exchangeable), 4.80 (d, J = 3.9 Hz, 1H), 4.62 (m, 1H), 3.93 (d, J = 6.8 Hz, 1H), 3.38 (m, 1H), 3.27 (m,
1H), 3.08 (m, 1H), 3.05 (m, 1H), 2.96 (m, 1H), 2.73 (m, 1H), 2.53 (m, 1H), 1.92 (m, 1H), 1.65 (m, 1H), 1.53
(m, 1H), 1.46 (m, 1H), 1.18 (m, 1H), 1.07 (m, 1H), 0.69 (m, 1H), 0.62 (m, 1H), 0.49 (m, 1H), 0.41 (m, 1H).
13C NMR (100 MHz, DMSO-d6) δ 166.07, 155.74, 147.19, 146.07, 138.79, 129.62, 128.72, 126.92, 124.16,
122.07, 121.08, 119.06, 118.30, 110.88, 107.13, 87.22, 69.38, 61.03, 57.00, 46.02, 45.20, 30.21, 29.23, 23.50,
19.40, 5.67, 5.14, 2.55. [α]25D –183.1o (c 0.25, MeOH). HRMS calcd for C29H31N2O5 m/z: 487.2227. Found
[M + H]+ (m/z): 487. 2308. IR (diamond, cm-1) νmax : 2972, 1624, 1505, 1452, 1317, 1237, 1115, 1031, 746.
Mp 257–258 oC, dec.
17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(benzothiophene-5-carboxamido)morphinan
(34)
The title compound was prepared following the general procedure as a white solid in 36% yield. Hydrochloride
salt: 1H NMR (400 MHz, DMSO-d6) δ 9.20 (s, 1H, exchangeable), 8.88 (s, 1H, exchangeable), 8.44 (s, 1H),
8.16 (d, J = 7.6 Hz, 1H, exchangeable), 8.11 (d, J = 8.4 Hz, 1H), 7.89–7.85 (m, 2H), 7.57 (d, J = 7.6 Hz, 1H),
6.73 (d, J = 8.1 Hz, 1H), 6.58 (d, J = 8.1 Hz, 1H), 6.36 (s, 1H, exchangeable), 4.81 (d, J = 3.8 Hz, 1H), 4.64
(m, 1H), 3.95 (d, J = 6.7 Hz, 1H), 3.37 (m, 1H), 3.26 (m, 1H), 3.08 (m, 1H), 3.05 (m, 1H), 2.97 (m, 1H), 2.73
(m, 1H), 2.53 (m, 1H), 1.94 (m, 1H), 1.65 (m, 1H), 1.54 (m, 1H), 1.46 (m, 1H), 1.21 (m, 1H), 1.09 (m, 1H),
0.69 (m, 1H), 0.62 (m, 1H), 0.49 (m, 1H), 0.41 (m, 1H). 13C NMR (100 MHz, DMSO-d6) δ 166.15, 146.04,
141.72, 139.04, 138.79, 130.81, 128.73, 128.71, 124.34, 123.22, 122.94, 122.33, 122.05, 119.08, 118.29,
87.19, 69.37, 61.06, 57.01, 46.03, 45.21, 30.21, 29.21, 23.48, 19.40, 5.66, 5.13, 2.54. [α]25 –156.1o (c 0.1,
D
MeOH). HRMS calcd for C29H31N2O4S m/z: 503.1999. Found [M + H]+ (m/z): 503.1934. IR (diamond, cm-1)
νmax : 2942, 1620, 1560, 1454, 1320, 1116, 1073, 730. Mp 256–258 oC, dec.
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