Synthesis and evaluation of nuciferine and roemerine enantiomers as 5-HT2 and α1 receptor antagonists

Article abstract of DOI:10.1039/c7md00629b

In this study, the (S)-enantiomers of the aporphine alkaloids, nuciferine and roemerine, were prepared via a synthetic route involving catalytic asymmetric hydrogenation and both stereoisomers were evaluated in vitro for functional activity at human 5-HT2 and adrenergic α1 receptor subtypes using a transforming growth factor-α shedding assay. Both enantiomers of each of the compounds were found to act as antagonists at 5-HT2 and α1 receptors. (R)-roemerine was the most potent compound at 5-HT2A and 5-HT2C receptors (pKb = 7.8-7.9) with good selectivity compared to (S)-roemerine at these two receptors and compared to its activity at 5-HT2B, α1A, α1B and α1D receptors.

Full text of DOI:10.1039/c7md00629b

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RESEARCH ARTICLE
Synthesis and evaluation of nuciferine and
roemerine enantiomers as 5-HT2 and α1 receptor
antagonists†
Cite this: DOI: 10.1039/c7md00629b
ab
ab
Hui Li Heng, a Chin Fei Chee,
Sek Peng Chin,
*
Yifan Ouyang,c
Hao Wang,c Michael J. C. Buckle,
a Deron R. Herr, d Ian C. Paterson,
e
Stephen W. Doughty, f Noorsaadah Abd. Rahman
and Lip Yong Chung
b
a
*
In this study, the (S)-enantiomers of the aporphine alkaloids, nuciferine and roemerine, were prepared via a
synthetic route involving catalytic asymmetric hydrogenation and both stereoisomers were evaluated
in vitro for functional activity at human 5-HT2 and adrenergic α1 receptor subtypes using a transforming
growth factor-α shedding assay. Both enantiomers of each of the compounds were found to act as antag-
onists at 5-HT2 and α1 receptors. (R)-roemerine was the most potent compound at 5-HT2A and 5-HT2C re-
ceptors (pKb = 7.8–7.9) with good selectivity compared to (S)-roemerine at these two receptors and com-
pared to its activity at 5-HT2B, α1A, α1B and α1D receptors.
Received 15th December 2017,
Accepted 9th February 2018
DOI: 10.1039/c7md00629b
rsc.li/medchemcomm
found to behave as moderate antagonists, with the (S)-
enantiomer being slightly more potent than the (R)-enantio-
Introduction
Aporphines are tetracyclic compounds that form a subset of
the tetrahydroisoquinoline alkaloids and contain a single chi-
ral centre at position C6a (Fig. 1). They have been found to ex-
hibit a number of different pharmacological activities, includ-
ing at dopamine, serotonin (5-HT) and adrenergic
receptors.1,2 At dopamine D1 and D2 receptors, it has been
observed that the (R)-enantiomers tend to act as agonists,
whereas the (S)-enantiomers are usually antagonists. Experi-
ments on some pairs of aporphine enantiomers at the 5-HT1A
receptor suggested the same pattern of activity as that ob-
served with dopamine receptors.3 However, very few studies
have been reported on the stereoselectivity of aporphines at
5-HT2A and adrenergic α1A receptors and no clear patterns
have been observed. In one of these studies, the two isomers
of nantenine (1) at the 5-HT2A and α1A receptors were both
mer at the 5-HT2A receptor, but with the pattern of stereo-
selectivity being reversed at the α1A receptor.4 Conversely, in
another study, the (S)-enantiomers of apomorphine (2a) and
N-n-propyl norapomorphine (2b) have been found to have
higher affinities for α1A, α1B and α1D receptors than their cor-
responding (R)-enantiomers.5
Previously, we reported that ( )-nuciferine (3a) and (R)-
roemerine (3b), which differ from nantenine in that they lack
a methylenedioxy substituent at positions C9 and C10 in the
D ring, possess high binding affinity and selectivity for the
a Department of Pharmacy, Faculty of Medicine, University of Malaya, 50603
Kuala Lumpur, Malaysia. E-mail: buckle@um.edu.my, chungly@um.edu.my;
Fax: +60 3 79674964; Tel: +60 3 79674959
b Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala
Lumpur, Malaysia
c School of Pharmacy, Ningxia Medical University, Yinchuan, 750004, P. R. China
d Department of Pharmacology, Yong Loo Lin School of Medicine, National
University of Singapore, 117597 Singapore
e Department of Oral Biology and Craniofacial Sciences and Oral Cancer Research
and Coordinating Centre, Faculty of Dentistry, University of Malaya, 50603 Kuala
Lumpur, Malaysia
f Penang Medical College, 4 Jalan Sepoy Lines, 10450 George Town, Pulau Pinang,
Malaysia
Fig.
1
Structures of the aporphines,
( )-nantenine (1), (S)-
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c7md00629b
apomorphine (2a), (S)-N-n-propyl norapomorphine (2b), ( )-nuciferine
(3a) and (R)-roemerine (3b).
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rat 5-HT2A receptor compared to the 5-HT1A, D1 and D2 recep-
tors.6 In addition, other researchers have shown that these
compounds have good oral bioavailability and a wide tissue
distribution in rats, including brain penetration.7,8 They
therefore have potential for use as pharmacological probes or
agents for conditions such as psychotic disorders and drug
addiction.9,10 However, it was not known if both enantiomers
are active or whether they act as agonists or antagonists. Only
the (R)-isomers are commercially available so we embarked
on the stereoselective synthesis of the (S)-isomers in order to
determine the functional activity of each pair of isomers at
human 5-HT2 and α1 receptors.
Pharmacological evaluation
Both the (R)- and (S)-enantiomers of nuciferine (3a) and
roemerine (3b) were evaluated for functional activity at
human 5-HT2 and α1 receptor subtypes using a recently-
developed transforming growth factor-α shedding assay that
measures ligand-mediated receptor activation.13 Representa-
tive pIC50 curves are shown in Fig. 2 and the results are
summarised in Tables 1 and 2.
The compounds were all observed to act as competitive
antagonists at both sets of receptor subtypes. This was con-
firmed by Schild analysis which resulted in agonist dose–
response curves that were increasingly shifted to the right
with increasing concentrations of test compound (see Fig. 3)
and linear Schild plots with slopes which were not signifi-
cantly different from unity.
The pKb values at the 5-HT2A and α1A receptors obtained
from the Schild analyses (see Table 3) were essentially similar
to those obtained from the pIC50 curves, although some dif-
ferences were noted for (S)-roemerine. The values obtained
from the Schild analyses are likely to be more accurate be-
cause about 6 times as many data points are involved in their
determination.
(R)-Roemerine was found to be the most potent com-
pound at 5-HT2A and 5-HT2C receptors (pKb = 7.97 and 7.82,
respectively). This is in agreement with our previous results6
from radioligand binding studies at rat 5-HT2A receptors
which showed that (R)-roemerine has more than twice the
affinity of ( )-nuciferine and confirms (R)-roemerine to have
the highest potency at 5-HT2 receptors of any naturally-
occurring aporphine identified to date. (R)-Roemerine also
displayed 4- and 5-fold stereoselectivity compared to (S)-
roemerine at the 5-HT2A and 5-HT2C receptor subtypes, re-
spectively. However, the two isomers of nuciferine were ob-
served to have similar activities at all three 5-HT2 receptor
subtypes. In comparison, the two isomers of nantenine (1)
have previously been found to have activities at the 5-HT2A
Results and discussion
Synthesis
(S)-Nuciferine (3a) and (S)-roemerine (3b) were prepared
using the synthetic route depicted in Scheme 1 based on the
asymmetric hydrogenation of 1-benzyl-3,4-dihydroisoquinoline
intermediates 7a or 7b.11,12 Coupling of commercially-available
2-bromophenylacetic acid (4) with 2-(3,4-dimethoxyphenyl)-
ethylamine (5a) or 2-(3,4-methylenedioxyphenyl)ethylamine
(5b) gave amides 6a and 6b. Bischler–Napieralski cyclisation
using phosphorus oxychloride in refluxing dichloromethane,
followed by catalytic asymmetric hydrogenation of the
resulting imines 7a and 7b using Noyori's ruthenium-based
catalyst, (R,R)-8, gave the (S)-1-benzyltetrahydroisoquinolines
9a and 9b. Oxidative cyclisation of the methylcarbamate-
protected amines 10a and 10b using catalytic palladiumIJII) in
complex with 2-dicyclohexylphosphino-2′-(N,N-dimethylamino)
biphenyl (DavePhos) (11) in dimethylacetamide (DMA) at 130
°C produced (S)-aporphines 12a and 12b. Finally, reduction of
the methyl carbonate group using lithium aluminium hydride
gave the target compounds (S)-3a and (S)-3b in 30–40% overall
yield and with 96% and 99% e.e., respectively, determined by
chiral HPLC.
Scheme 1 Reagents and conditions: a) (COCl)2, CH2Cl2; b) 5, Et3N, CH2Cl2; c) POCl3, CH2Cl2, reflux; d) (R,R)-8 (3 mol%), HCO2H/NEt3, DMF, rt; e)
MeOCOCl, DIPEA, CH2Cl2, rt; f) Pd(OAc)2 (5 mol%), DavePhos 11 (10 mol%), KOAc (2 eq.), DMA, 130 °C; g) LiAlH4, Et2O, 0 °C.
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Fig. 2 Representative pIC50 curves. A. For (R)- and (S)-roemerine (3b) compared to ketanserin at the 5-HT2A receptor in the presence of 1 μM
serotonin. B. For (R)- and (S)-nuciferine (3a) compared to prazosin at the α1A receptor in the presence of 0.1 μM noradrenaline. Data points are
normalised and shown as the mean SD from triplicate readings.
Table 1 Antagonist potencies and selectivities of nuciferine (3a) and roemerine (3b) enantiomers for 5-HT2 receptor subtypes calculated from pIC50
curves
Subtype selectivityb
a
pKb
Kb (nM)
Compound
5-HT2A
5-HT2B
5-HT2C
5-HT2A
5-HT2B
5-HT2C
5-HT2A/5-HT2B
5-HT2A/5-HT2C
5-HT2C/5-HT2B
(R)-Nuciferine
(S)-Nuciferine
(R)-Roemerine
(S)-Roemerine
Ketanserinc
7.18 0.03
7.07 0.17
7.97 0.18
7.37 0.10
8.69 0.03
7.51 0.21
7.38 0.01
7.08 0.43
7.03 0.33
5.70 0.04
7.44 0.01
7.51 0.22
7.82 0.08
7.12 0.13
6.95 0.08
65.3
84.3
10.8
42.9
2.0
31.0
41.7
84.0
92.7
1980
36.4
41.7
15.1
76.9
112
0.5
0.5
8
2
1000
0.6
0.4
1
2
60
1
1
6
1
20
a
b
Values are expressed as mean SEM from at least 2 separate experiments. Selectivities for receptor X/receptor Y were calculated as the ratio
c
of Kb receptor Y/Kb receptor X
. Positive control.
Table 2 Antagonist potencies and selectivities of nuciferine (3a) and roemerine (3b) enantiomers for α1 receptor subtypes calculated from pIC50 curves
Subtype selectivityb
a
pKb
Kb (nM)
Compound
α1A
α1B
7.22 0.01
6.50 0.01
6.57 0.05
6.81 0.03
11.41 0.09
α1D
6.78 0.01
6.94 0.01
7.34 0.15
7.04 0.07
10.60 0.02
α1A
α1B
α1B
α1A/α1B
α1A/α1D
α1B/α1D
(R)-Nuciferine
(S)-Nuciferine
(R)-Roemerine
(S)-Roemerine
Prazosinc
7.42 0.07
7.17 0.08
6.47 0.08
7.07 0.01
9.69 0.07
37.8
67.1
338
86.0
0.20
60.6
316
266
154
0.004
165
116
46.0
92.2
0.025
2
5
0.8
2
0.02
4
2
0.1
1
0.1
3
0.4
0.2
0.6
6
a
b
Values are expressed as mean SEM from at least 2 separate experiments. Selectivities for receptor X/receptor Y were calculated as the ratio
c
of Kb receptor Y/Kb receptor X
. Positive control.
receptor that are one to one and a half orders of magnitude
lower, with the (S)-enantiomer being slightly more potent
than the (R)-enantiomer.4 The greater than 6-fold selectivity
of (R)-roemerine for the 5-HT2A and 5-HT2C receptors com-
pared to the 5-HT2B receptor is also notable. Taken together,
these results suggest that the presence of a methylenedioxy
substituent at positions C1 and C2 in the A ring favours the
action of the (R)-enantiomer of roemerine at 5-HT2A and
5-HT2C receptors. This in agreement with a previous study
on analogues of nantenine which showed that variation of
the alkoxy substituent at position C1 has a substantial effect
on 5-HT2A activity.14–16
(pKb = 7.42 and 7.22, respectively), with 3- to 4-fold selectivity
compared to the α1D receptor. (R)-roemerine was the most
potent compound at the α1D subtype (pKb = 7.34) with 6- to
7-fold selectivity compared to the α1A and α1B receptors. (R)-
Roemerine has, in fact, previously been subjected to a com-
petitive radioligand binding assay at α1 receptor subtypes
and found to have a similar activity to that obtained in the
current study at the α1A receptor (pKi = 6.6), but activities that
are an order of magnitude lower for the α1B and α1D recep-
tors (pKi = 5.5 and 6.2, respectively).17 These inconsistencies
may be due to the difficulty of comparing values obtained
from different assays. During the course of our investigation,
another group has also determined that nuciferine functions
as an antagonist at the three α1 receptor subtypes.18
From the results for the α1 receptors, (R)-nuciferine was
the most potent compound at the α1A and α1B subtypes
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Fig. 3 Agonist dose–response curves in the presence of varying concentrations of antagonist. A. For serotonin at the 5-HT2A receptor in the
presence of (R)-roemerine (3b). B. For noradrenaline at the α1A receptor in the presence of (R)-nuciferine (3a). Data points are normalised and
shown as the mean SD from triplicate readings.
Regarding the stereoselectivities observed in the current
study at α1 subtypes, these were relatively modest, except in
the cases of (S)-roemerine at the α1A receptor and (R)-
nuciferine at the α1B receptor, which showed 4- to 5-fold
selectivities over their corresponding enantiomers. This sug-
gests that small changes in the substituents can have a pro-
found effect on stereoselectivity at α1 subtypes. This phenom-
enon can also be seen from comparison of the results from
two previous studies.4,5 In one of the studies, nantenine (1)
showed 3-fold stereoselectivity in favour of the (R)-enantio-
mer at the α1A receptor whereas, in the other study, apomor-
phine (2a) and N-n-propyl norapomorphine (2b) showed 8- to
16-fold stereoselectivity in favour of the (S)-enantiomer for all
three adrenergic receptor subtypes. However, it should be
noted that the latter two compounds lack the alkoxy substitu-
ents that are present at positions C1 and C2 in the A ring of
the other compounds and the activities were one and a half
to two orders of magnitude lower than those obtained in the
current study and so comparison of the stereoselectivities
may not be meaningful.
5-HT2A and 5-HT2C receptors, with 18- to 32-fold selectivity
compared to α1A and α1B receptors and 3- to 4-fold selectivity
compared to α1D receptors.
Molecular modelling studies
In order to determine the binding modes of the test com-
pounds at 5-HT2 receptors and to explain the stereoselectivity
of roemerine at the 5-HT2A and 5-HT2C receptors, the com-
pounds were docked into homology models generated from a
crystal structure of the 5-HT2B receptor in complex with ergot-
amine (PDB code: 4IB4).19 The test compounds were all
found to bind to the orthosteric site of 5-HT2A and 5-HT2C re-
ceptors through electrostatic interactions between their pro-
tonated nitrogen atoms and the carboxylate group of Asp155/
134 and the phenolic ring of Tyr370/358 and non-polar inter-
actions between their aromatic rings and hydrophobic resi-
dues, Val156/135 and Phe339/327. Nevertheless, it was ob-
served that the binding poses of (R)-roemerine were rotated
180° around the axis of the tetrahydroisoquinoline ring com-
pared to those of (S)-roemerine (see Fig. 4). This change in
orientation appears to enable (R)-roemerine to have an addi-
tional π–π interaction with Phe340/328, which could account
for the marked difference in activity between the (R)- and (S)-
enantiomers. This residue has been previously identified by
site-directed mutagenesis experiments as being important for
the binding of orthosteric ligands at 5-HT2 receptors.20,21 The
equivalent residue in the 5-HT2B receptor (Phe341) appeared
to make less of a contribution to the complex of (R)-
roemerine with this receptor (see Fig. 5), thus giving a possi-
ble reason for the lower activity compared to that observed at
the 5-HT2A and 5-HT2C receptors.
Comparison of the activities of the test compounds at
5-HT2 and α1 receptors showed that they generally had equal
or higher activities at 5-HT2 receptors than at α1 receptors. Of
particular note is the strong preference of (R)-roemerine for
Table 3 Antagonist potencies and selectivities of nuciferine (3a) and
roemerine (3b) enantiomers for 5-HT2A and α1A receptors determined
from Schild analysis
a
pKb
5-HT2A/α1A selectivityb
Compound
5-HT2A
α1A
(R)-Nuciferine
(S)-Nuciferine
(R)-Roemerine
(S)-Roemerine
7.26 0.12
6.85 0.14
7.88 0.13
7.06 0.11
7.31 0.11
6.91 0.07
6.38 0.11
6.62 0.11
1
1
32
3
Experimental
Chemicals
a
b
(S)-Nuciferine and (S)-roemerine were prepared as described
in the supplementary information. (R)-Nuciferine and (R)-
Values are expressed as mean SD. Selectivities for receptor X/
receptor Y were calculated as the ratio of Kb receptor Y/Kb receptor X
.
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Fig. 4 The docking poses of the two enantiomers of roemerine in complex with the 5-HT2A and 5-HT2C receptors. A and C. The poses of (R)-
roemerine enable a π–π interaction with Phe340/327 as depicted by the black dotted lines. B and D. The poses of (S)-roemerine do not allow a π–π
interaction with Phe340/327. For the purpose of clarity, only the principal binding residues are depicted and some of the transmembrane helices
are not shown.
roemerine were obtained from Chengdu Biopurify Phyto-
chemicals Ltd. (Chengdu, China) and Pharmeks Ltd. (Mos-
cow, Russia), respectively, and their identity and purity was
confirmed by 1H NMR spectroscopy, polarimetry and chiral
HPLC analysis.
All other chemicals were purchased from Sigma-Aldrich
(St. Louis, MO, USA) or Merck (Darmstadt, Germany) unless
otherwise stated.
forming growth factor-α (TGFα) shedding assay, which was
performed essentially as previously described.13 Briefly,
HEK293 cells (ATCC #CRL-1573) were co-transfected with the
respective receptor expression construct and alkaline
phosphatase-tagged TGFα using Lipofectamine 3000 reagent
(Thermo Fisher Scientific, Waltham, MA, USA), collected by
trypsinization, washed with phosphate-buffered saline, and
seeded into 96-well plates in Hank's balanced salt solution
(HBSS). For agonism testing, the cells were incubated for 1
hour at 37 °C with varying concentrations (0.1 nM to 30 μM
final concentration) of test compound or endogenous agonist
(serotonin for 5-HT receptors, noradrenaline for α1 receptors)
in stimulation buffer. For antagonist testing, the cells were
Functional assays at 5-HT2 and α1 receptors
The pharmacological activity of the test compounds at
human 5-HT2 and α1 receptors was evaluated using a trans-
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Fig. 5 The docking poses of the two enantiomers of roemerine in complex with the 5-HT2B receptor. A. (R)-Roemerine. B. (S)-Roemerine. For the
purpose of clarity, only the principal binding residues are depicted and some of the transmembrane helices are not shown.
pre-treated with varying concentrations (0.1 nM to 30 μM
final concentration) of test compound or positive control
(ketanserin for 5-HT receptors, prazosin for α1 receptors) in
stimulation buffer for 15 minutes, followed by addition of a
fixed concentration of serotonin (1 μM, 0.1 μM or 0.1 μM fi-
nal concentration for 5-HT2A, 5-HT2B and 5-HT2C, respec-
tively) or noradrenaline (0.1 μM, 1 μM or 1 μM final concen-
tration for α1A, α1B and α1D receptors, respectively) and the
mixture was incubated for 1 hour at 37 °C. Alkaline phos-
phatase activity in the cells and in the supernatant was de-
termined by measuring the absorbance of p-nitrophenol
(from hydrolysis of p-nitrophenyl phosphate) at 405 nm
using a Cytation 3 cell imaging multi-mode microplate
reader (Biotek Instruments, Inc., Winooski, VT, USA). Each
assay was performed in triplicate. Receptor response was de-
fined as the alkaline phosphatase activity of the superna-
tant/total alkaline phosphatase activity (cells + supernatant)
and normalised against the maximal response obtained with
the endogenous agonist. For Schild analysis, a similar proce-
dure was followed as for antagonist testing, except that each
experiment involved pre-treatment with fixed concentrations
of test compound or positive control, followed by addition
of varying concentrations of serotonin (10 pM to 100 μM fi-
nal concentration) or noradrenaline (1 pM to 10 μM final
concentration).
tio of the EC50 value for the agonist in the presence of antag-
onist concentration [B] to the EC50 value for the agonist in
the absence of antagonist.
Molecular modelling
Homology models of the 5-HT2A and 5-HT2C receptors were
generated based on a crystal structure of the 5-HT2B receptor
in complex with ergotamine (PDB code: 4IB4) using Modeller
9v6.23 Sequence alignment was carried out within Modeller
(align2D.py) and was inspected manually to ensure that the
highly conserved residues of each of the transmembrane
(TM) helices and motifs were aligned and that there were no
gaps in the TM core. The engineered protein, apocytochrome
b562 RIL (BRIL), that replaced intracellular loop 3 (ICL3) in
the crystal structure, was deleted prior to modelling and ICL3
was not modelled. Other loops were modelled directly using
the template and the missing residues in extracellular loop 2
were also added. A total of 5 models were generated for each
receptor and the model with lowest DOPE energy was se-
lected. The crystal structure of the 5-HT2B receptor was pre-
pared for docking using Discovery Studio (DS) 4.0 (BIOVIA,
San Diego, CA, USA) and the missing residues in ECL2 were
added. The three receptor structures were minimised using
the CHARMM force field implemented in DS.
Data processing was performed using Prism 5 (GraphPad
Software, San Diego, CA, USA). Antagonist dissociation con-
stant (Kb) values for the test compounds were calculated from
pIC50 curves using a modified form of the Gaddum equation:
IC50/([A]/EC50 − 1) where IC50 = the IC50 value of the antago-
nist, [A] = the concentration of the agonist and EC50 = the
EC50 value of the agonist.22 Kb values from Schild analysis
were determined from linear regression using the equation:
log (dose ratio – 1) = log[B] – log Kb where dose ratio = the ra-
The 3D structures of the test compounds were
downloaded from the PubChem substances and compound
database24 and were prepared using LigPrep 2.3 (Schrödinger
LLC, New York, USA). Receptor and ligand coordinate files
were prepared using AutoDockTools 1.5.6.25
Docking studies were performed with AutoDock Vina 1.0.2
with an exhaustiveness of 100.26 The grid box was set to cover
the orthosteric binding pocket with 1 Å grid spacing. The
resulting ligand-receptor complexes were viewed using DS
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and the lowest energy conformation with the protonated ni-
trogen atom of the ligand suitably positioned to interact with
the carboxylate group of the conserved aspartic acid residue
was selected for further study. The ligand–receptor interac-
tions were then optimised using the Minimization protocol
in DS,27 with the residues in the binding pocket being
allowed to move. Images of the optimised ligand-receptor
complexes were generated using PyMOL (Schrödinger LLC).
7 S. Gu, G. Zhu, Y. Wang, Q. Li, X. Wu, J. Zhang, G. Liu and X.
Li, J. Chromatogr. B: Anal. Technol. Biomed. Life Sci.,
2014, 961, 20–28.
8 Y.-Q. Liu, G.-H. He, H.-L. Li, J.-C. He, E.-F. Feng, L. Bai, C.-Y.
Wang and G.-L. Xu, J. Chromatogr. B: Anal. Technol. Biomed.
Life Sci., 2014, 969, 249–255.
9 T. A. Mestre, M. Zurowski and S. H. Fox, Expert Opin. Invest.
Drugs, 2013, 22, 411–421.
10 O. LeGendre, S. Pecic, S. Chaudhary, S. M. Zimmerman,
W. E. Fantegrossi and W. W. Harding, Bioorg. Med. Chem.
Lett., 2010, 20, 628–631.
11 L. F. Tietze, N. Rackelmann and G. Sekar, Angew. Chem., Int.
Ed., 2003, 42, 4254–4257.
12 M. Lafrance, N. Blaquiere and K. Fagnou, Eur. J. Org. Chem.,
2007, 2007, 811–825.
13 A. Inoue, J. Ishiguro, H. Kitamura, N. Arima, M. Okutani, A.
Shuto, S. Higashiyama, T. Ohwada, H. Arai and K. Makide,
Nat. Methods, 2012, 9, 1021–1029.
14 S. Chaudhary, S. Pecic, O. LeGendre, H. A. Navarro and
W. W. Harding, Bioorg. Med. Chem. Lett., 2009, 19,
2530–2532.
15 S. Chaudhary, S. Ponnala, O. LeGendre, J. A. Gonzales, H. A.
Navarro and W. W. Harding, Bioorg. Med. Chem. Lett.,
2011, 19, 5861–5868.
16 S. Ponnala, N. Kapadia, S. Madapa, I. L. Alberts and W. W.
Harding, Bioorg. Med. Chem. Lett., 2015, 25, 5102–5106.
17 M. Valiente, P. D'ocon, M. Noguera, B. Cassels, C. Lugnier
and M. Ivorra, Planta Med., 2004, 70, 603–609.
18 M. S. Farrell, J. D. McCorvy, X.-P. Huang, D. J. Urban, K. L.
White, P. M. Giguere, A. K. Doak, A. I. Bernstein, K. A. Stout
and S. M. Park, PLoS One, 2016, 11, e0150602.
19 D. Wacker, C. Wang, V. Katritch, G. W. Han, X.-P. Huang, E.
Vardy, J. D. McCorvy, Y. Jiang, M. Chu and F. Y. Siu, Science,
2013, 340, 615–619.
20 M. Choudhary, S. Craigo and B. L. Roth, Mol. Pharmacol.,
1993, 43, 755–761.
21 B. Roth, M. Shoham, M. Choudhary and N. Khan, Mol.
Pharmacol., 1997, 52, 259–266.
22 S. Lazareno and N. Birdsall, Br. J. Pharmacol., 1993, 109,
1110–1119.
23 A. Šali and T. L. Blundell, J. Mol. Biol., 1993, 234, 779–815.
24 S. Kim, P. A. Thiessen, E. E. Bolton, J. Chen, G. Fu, A.
Gindulyte, L. Han, J. He, S. He, B. A. Shoemaker, J. Wang, B.
Yu, J. Zhang and S. H. Bryant, Nucleic Acids Res., 2016, 44,
D1202–D1213.
Conclusions
In this study, a reaction sequence involving catalytic asym-
metric hydrogenation has been shown to be an efficient
method for the synthesis of enantiomerically-pure
aporphines. Both enantiomers of nuciferine and roemerine
were observed to have moderate to good 5-HT2 and α1 antag-
onist activity. (R)-Roemerine was the most potent compound
at 5-HT2A and 5-HT2C receptors with good selectivity com-
pared to (S)-roemerine at these two receptors and compared
to its activity at 5-HT2B and α1 receptor subtypes. These re-
sults will inform ongoing medicinal chemistry efforts to de-
termine the structure–activity relationships of aporphines at
5-HT2 and α1 receptors and evaluate their potential as phar-
macological probes or agents for the treatment of psychotic
disorders and drug addiction.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
This study was funded by grants from the Ministry of Science,
Technology and Innovation, Malaysia (02-01-03-SF0937) and
the Ministry of Higher Education, Malaysia, High Impact Re-
search Grant (HIR-MoHE: UM.C/625/1/HIR/MOHE/MED/17 &
UM.C/625/1/HIR/MOHE/MED/33).
Notes and references
1 A. Zhang, Y. Zhang, A. R. Branfman, R. J. Baldessarini and
J. L. Neumeyer, J. Med. Chem., 2007, 50, 171–181.
2 B. K. Cassels and M. Asencio, Nat. Prod. Commun., 2008, 3,
643–653.
3 J. G. Cannon, S. T. Moe and J. P. Long, Chirality, 1991, 3,
19–23.
4 S. Ponnala, J. Gonzales, N. Kapadia, H. A. Navarro and W. W.
Harding, Bioorg. Med. Chem. Lett., 2014, 24, 1664–1667.
5 M. D. Ivorra, M. Valiente, S. Martínez, Y. Madrero, M. A.
Noguera, B. K. Cassels, E. M. Sobarzo and P. D'Ocon, Planta
Med., 2005, 71, 897–903.
25 G. M. Morris, R. Huey, W. Lindstrom, M. F. Sanner, R. K.
Belew, D. S. Goodsell and A. J. Olson, J. Comput. Chem.,
2009, 30, 2785–2791.
26 O. Trott and A. J. Olson, J. Comput. Chem., 2010, 31,
455–461.
6 V. Munusamy, B. K. Yap, M. J. Buckle, S. W. Doughty and
L. Y. Chung, Chem. Biol. Drug Des., 2013, 81, 250–256.
27 S. Lim, R. Othman, R. Yusof and C. Heh, Curr. Comput.-
Aided Drug Des., 2016, 13, 160–169.
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