Synthetic studies and pharmacological evaluations on the MDMA ('Ecstasy') antagonist nantenine

Article abstract of DOI:10.1016/j.bmcl.2009.11.053

The naturally occurring aporphine alkaloid nantenine, has been shown to antagonize behavioral and physiological effects of MDMA in mice. We have synthesized (±)-nantenine via an oxidative cyclization reaction with PIFA and evaluated its binding profile against a panel of CNS targets. To begin to understand the importance of the chiral center of nantenine with regards to its capacity to antagonize the effects of MDMA in vivo, (R)- and (S)-nantenine were prepared and evaluated in a food-reinforced operant task in rats. Pretreatment with either nantenine enantiomer (0.3 mg/kg ip) completely blocked the behavioral suppression induced upon administration of 3.0 mg/kg MDMA. (±)-Nantenine displayed high affinity and selectivity for the α_1A adrenergic receptor among several other receptors suggesting that this α₁ subtype may be significantly involved in the anti-MDMA effects of the enantiomers.

Full text of DOI:10.1016/j.bmcl.2009.11.053

Bioorganic & Medicinal Chemistry Letters 20 (2010) 628–631
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthetic studies and pharmacological evaluations on the MDMA (‘Ecstasy’)
antagonist nantenine
Onica LeGendre a, Stevan Pecic a, Sandeep Chaudhary a, Sarah M. Zimmerman b, William E. Fantegrossi b,
Wayne W. Harding a,
*
a Department of Chemistry, Hunter College and the Graduate Center of the City University of New York, 695 Park Avenue, New York, NY 10065, USA
b University of Arkansas for Medical Sciences, Department of Pharmacology and Toxicology, Little Rock, AR 72205, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The naturally occurring aporphine alkaloid nantenine, has been shown to antagonize behavioral and
physiological effects of MDMA in mice. We have synthesized ( )-nantenine via an oxidative cyclization
reaction with PIFA and evaluated its binding profile against a panel of CNS targets. To begin to understand
the importance of the chiral center of nantenine with regards to its capacity to antagonize the effects of
MDMA in vivo, (R)- and (S)-nantenine were prepared and evaluated in a food-reinforced operant task in
rats. Pretreatment with either nantenine enantiomer (0.3 mg/kg ip) completely blocked the behavioral
suppression induced upon administration of 3.0 mg/kg MDMA. ( )-Nantenine displayed high affinity
Received 18 October 2009
Revised 11 November 2009
Accepted 16 November 2009
Available online 20 November 2009
Keywords:
Nantenine
MDMA
Adrenergic
Rate suppression
PIFA
and selectivity for the
a1A adrenergic receptor among several other receptors suggesting that this a1 sub-
type may be significantly involved in the anti-MDMA effects of the enantiomers.
Published by Elsevier Ltd.
MDMA (‘Ecstasy’) is a synthetic amphetamine which produced
both stimulant-like and hallucinogen-like effects in humans.1
Abuse of this designer drug is particularly prevalent among young
adults. Recent data shows that 6% and 4% of 12th grade students
had used ‘Ecstasy’ in their lifetime and in the past year respec-
tively.2 MDMA causes acute adverse physiological effects including
the development of hyperthermia.3–6 Use of MDMA is also associ-
ated with memory and cognitive impairment as well as the devel-
opment of dependence on the drug in some consumers.6–13 At this
time, there are no therapeutic agents which are specifically ap-
proved to treat the acute adverse effects of MDMA or MDMA
dependence.
and in vivo pharmacological profile of nantenine, we have synthe-
sized racemic nantenine and nantenine enantiomers and evaluated
the CNS receptor binding profile and behavioral effects in rats
trained to respond for food-reinforcement, respectively. Our efforts
in this regard are reported herein.
A commonly used route to synthesize aporphines involves oxida-
tivebiarylcouplingofphenolicorphenoletherbenzyltetrahydroiso-
quinoline intermediates in an essentially biomimetic process.18 In
the past, the oxidizing agents commonly used for this reaction in-
clude VOCl3, VOF3, Pb(OAc)4 and Tl(OCOCF3)3.19–24 These reagents
are toxic and furthermore the yields obtained in these reactions
are often quite low.
The aporphine alkaloid (S)-(+)-nantenine (1) ex Nandina domes-
tica was shown to block and reverse a range of behavioral and
physiological effects mediated by MDMA in mice.14 At present,
there is a paucity of knowledge concerning the receptor targets
which may be involved in the reported antagonist effects of nant-
enine vs MDMA in vivo, although it would appear that 5-HT2A and
a1 adrenergic receptors are involved.14 Prior reports have estab-
lished that ( )-nantenine is an antagonist at the 5-HT2A receptor
and a1 adrenoceptors;15–17 its pharmacological activity at other
CNS receptors has not been ascertained. To date, (R)-(ꢀ)-nantenine
has not been evaluated for its anti-MDMA effects in animal models.
As part of our research endeavors to better understand the in vitro
The reagent phenyliodine bis(trifluoroacetate) (PIFA) has
emerged as an environmentally-friendly alternative for these biar-
yl cyclizations, providing aporphines in good yields. For example,
Anakabe et al. have reported conversion of laudanosine (2, Fig. 1)
4
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
1
NCH3
H
NCH3
H
NCH3
H
H3CO
H3CO
O
9
O
OCH3
OCH3
1
2
3
* Corresponding author. Tel.: +1 212 772 5359; fax: +1 212 772 5332.
E-mail address: wayne.harding@hunter.cuny.edu (W.W. Harding).
Figure 1. Structures of (+)-nantenine (1), laudanosine (2) and (+)-glaucine (3).
0960-894X/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2009.11.053

O. LeGendre et al. / Bioorg. Med. Chem. Lett. 20 (2010) 628–631
629
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
i-iv
v
NH2
NCH3
NCH3
H
4
5
H
+
O
O
O
( )-1
6
O
O
OH
O
O
vi
vii
H3CO
H3CO
H3CO
NCH3
NCH3
H3CO
O
H
H
O
O
O
(S)-(+)-1
(R)-(-)-1
Scheme 1. Reagents and conditions: (i) CDI, THF, 99%; (ii) POCl3, CH2Cl2, reflux, 87%; (iii) NaBH4, MeOH, ꢀ78 °C, 77%; (iv) HCHO, Na(OAc)3BH, DCM, 95%; (v) PIFA, BF3ꢁOEt2,
HFIP, rt, 45 min, 16%; (vi) (ꢀ)-2,3-di-p-toluoyl-
L-tartaric acid, EtOH then 10% aq NaOH, 30%, 96% ee; (vii) (+)-2,3-di-p-toluoyl-D-tartaric acid, EtOH then 10% aq NaOH, 32%, 97%
ee.
to glaucine (3) in 75% yield using PIFA.25 Others have recently re-
ported the synthesis of ( )-nantenine in moderate (36%) yield with
PIFA.26 We initially engaged this method to prepare nantenine,
with a secondary goal of optimizing reported conditions for the
PIFA-mediated biaryl cyclization.
(R)-(ꢀ)-Nantenine (96% ee as determined by chiral HPLC; ½a D24
ꢂ
ꢀ117.0 (c 0.58, CHCl3); stereochemistry determined by CD spec-
troscopy31) was then evaluated in a food-reinforced operant assay
in rats trained under a fixed-ratio 20 (FR20) schedule in the pres-
ence of an illuminated stimulus light. This behavior was main-
tained by delivery of one 94 mg food pellet. Behavioral sessions
were run daily and consisted of 4 discrete components; each com-
ponent was terminated after rats earned 20 pellets, or after
20 min—whichever happened first. Each component was separated
by a 10 min timeout where stimulus lights were extinguished and
lever presses had no programmed consequences. The (S)-enantio-
mer [obtained by resolution of the racemate with (ꢀ)-2,3-di-p-tol-
Following established protocols,25 the tetrahydroisoquinoline 6
was prepared starting from amine 4 and acid 5 in a sequence
involving amide coupling, Bischler–Napieralski cyclization, imine
reduction and N-methylation as shown in Scheme 1. Cyclization
of 6 with PIFA at ꢀ40 °C in DCM has been reported to give a mod-
erate yield of 1.26 In our hands however, only a 12% yield was ob-
tained under these conditions.
We found that variations in temperature (ꢀ78 °C, ꢀ20 °C and rt)
did not improve this outcome in yield. We also substituted DCM
with polar, non-nucleophilic solvents such as hexafluoroisopropa-
nol (HFIP),27,28 trifluoroethanol (TFE) and CH3CN; only HFIP gave
the required product albeit in low (16%) yield. No nantenine was
detected when RuO2ꢁxH2O or Ce(OH)4 were used as oxidant (i.e.,
instead of PIFA). Our failed attempts at optimizing this reaction
have since led us to opt for more efficient and versatile direct biaryl
coupling procedures to prepare ( )-nantenine as well as several
analogs (Scheme 2).29,30
uoyl-
L
-tartaric acid; 97% ee by chiral HPLC; ½a D24
ꢂ
+115.5 (c 0.51,
CHCl3)] was also evaluated in this assay for comparison. As a posi-
tive control, the 5-HT2A/2C antagonist ketanserin was also tested
against the rate suppressant effects of MDMA.
Importantly, ketanserin has previously been shown to block a
range of behavioral and physiological effects of MDMA in mice,3
The naturally occurring enantiomer of 1 (i.e., the (S)-(+)-enan-
tiomer) has been shown to antagonize locomotor stimulant,
head-twitch, lethality and hyperthermic effects of MDMA.14 To
gain some insight into the capacity of the (R)-(ꢀ)-enantiomer to
function as an antagonist of MDMA’s effects, we first resolved this
compound from racemic 1 with (+)-2,3-di-p-toluoyl-
D
-tartaric acid.
PPh2
P
Me2N
HBF4
B
A
H3CO
H3CO
H3CO
H3CO
NCH3
NCO2Et
i
NCO2Et
H3CO
O
H3CO
ii
O
Br
O
O
7
(
)-1
8
O
O
Scheme 2. Reagents and conditions: (i) Pd(OAc)2, solvent (DMA, DMF or DMSO),
pivalic acid, K2CO3, ligand A or B, microwaves, 5 min, 15–88%; (ii) LiAlH4, THF, 0 °C,
16 h, 90%.
Figure 2. Rate suppressant assay with nantenine enantiomers and ketanserin.

630
O. LeGendre et al. / Bioorg. Med. Chem. Lett. 20 (2010) 628–631
Table 1
Affinity of ( )-nantenine (1) at CNS receptors
Receptor
Ki (nM)
Receptor
Ki (nM)
Receptor
Ki (nM)
Receptor
Ki (nM)
5-HT1B
5-HT1D
5-HT1E
5-HT2A
5-HT2B
5-HT2C
5-HT3
5-HT5A
5-HT6
5-HT7
100
49
>10,000
832 164
543 53
1069 131
>10,000
2224 224
257 24
3
5
a
a
a
a
a
a
1A-AR
1B-AR
1D-AR
2A-AR
2B-AR
2C-AR
2
0.2
D1
D2
D3
D4
895 94
858 86
309 50
262 28
2397 410
>10,000
244 41
>10,000
>10,000
>10,000
MOR
H1
H2
H3
H4
M1
M2
M3
M4
7265 910
>10,000
672 23
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
1191 145
340 34
1288 155
252 21
181 14
8565 1084
>10,000
D5
DAT
SERT
NET
DOR
KOR
b1-AR
b2-AR
b3-AR
>10,000
67
7
Sigma 2
rats,32 rhesus monkeys33 and humans34,35 which guided our selec-
tion of this compound as a standard against which to compare the
effects of the nantenine enantiomers.
Screening Program. Experimental details for these assays may be
found at the PDSP website (http://pdsp.med.unc.edu/). The data
(Table 1) indicates that ( )-nantenine is a very selective
a1A ligand.
Rats were injected with various dose combinations of ketan-
serin, (R)- or (S)-nantenine, and 3.0 mg/kg racemic MDMA.
Responding during the first behavioral component following drug
administration, normalized to baseline data collected in sessions
where no injections were administered, is presented in Figure 2.
At a dose of 3.0 mg/kg (IP), MDMA profoundly suppresses operant
behavior in this first component in all subjects, although respond-
ing gradually recovered throughout the remainder of the session.
Since this rate of behavioral recovery in subsequent components
differed among rats, we present only response data from the first
behavioral component as an index of the apparent antagonist ef-
fects of the nantenine enantiomers against MDMA-induced behav-
ioral suppression.
All pretreatments were administered 15 min prior to MDMA
injection. Following two saline injections (separated by 15 min,
open square), response rates were essentially unchanged from con-
trol. All rats responded at high rates and earned all 20 available
food pellets. When 3.0 mg/kg MDMA was injected 15 min after
an initial saline injection (filled diamond), response rates were re-
duced to approximately 20% of control levels, and rats earned 2 or
fewer food pellets.
Injection of ketanserin 15 min before MDMA administration
(filled circles) had biphasic effects on response rates. At a dose of
0.03 mg/kg ketanserin, MDMA continued to suppress operant
behavior to approximately 50% of control levels. At higher doses
(0.1 and 0.3 mg/kg), ketanserin blocked the rate suppressant ef-
fects of MDMA. At the highest ketanserin dose tested (1.0 mg/kg),
ketanserin produced lethargy in all subjects during the pretreat-
ment interval, and these effects likely explain the descending limb
of the dose-effect function in Figure 2.
In comparison, injection of (S)-nantenine 15 min before MDMA
administration (open inverted triangles) also had biphasic effects.
The lowest tested dose (0.1 mg/kg) did not alter the effects of
MDMA on operant behavior. However, 0.3 mg/kg (S)-nantenine
completely blocked MDMA-induced behavioral suppression, and
only 1 rat failed to earn all available food pellets at this dose. High-
er doses likely had direct effects of their own, and administration
of 10.0 mg/kg (S)-nantenine appeared to have sedative effects dur-
ing the pretreatment period, with most rats failing to emit even a
single response at this dose (not shown).
Based on the observed selectivity it is plausible that this receptor
plays a role in the anti-MDMA effects of the enantiomers. Another
significant finding from this study is that opioid receptors (DOR,
MOR, KOR), b-adrenergic receptors, or dopamine and norepineph-
rine transporters (DAT and NET) do not seem to be responsible for
nantenine’s anti-MDMA effects given the low affinity at these
receptors. (However, the contribution of multi-receptor effects
cannot be ruled out.) The involvement of a1 adrenergic receptors
in the effects of MDMA has become more prominent in the litera-
ture recently; a1 antagonists have been reported to reverse or
attenuate MDMA-induced hyperthermia and locomotor activity
in rodent models.36–39
In conclusion, the PIFA-mediated oxidative biaryl coupling pro-
cedure for the synthesis of ( )-nantenine is low-yielding with a
variety of conditions investigated. ( )-Nantenine was found to
have high affinity and selectivity for the a1A adrenoceptor, provid-
ing indications that this receptor plays a role in the observed
anti-MDMA effects of the nantenine enantiomers. Both (R)- and
(S)-nantenine (0.3 mg/kg ip) completely blocked behavioral sup-
pression induced by MDMA. In the context of antagonism of
MDMA’s behavioral and physiological effects, the importance of
the chiral center of nantenine towards its in vitro and in vivo phar-
macological characteristics is deserving of further investigation.
Such studies are ongoing in our laboratories and will be reported
in due course.
Acknowledgements
O.L. acknowledges the MBRS/RISE program at Hunter College
for financial support. Ki determinations, were provided by the
National Institute of Mental Health’s Psychoactive Drug Screening
Program, Contract # NO1MH32004 (NIMH PDSP). This publication
was made possible by Grant Number RR03037 and R03DA025910
from the National Center for Research Resources (NCRR) and
National Institute of Drug Abuse (NIDA) respectively, components
of the National Institutes of Health. Its contents are solely the
responsibility of the authors and do not necessarily represent the
official views of the NIH or its divisions.
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Like the other antagonists studied, administration of (R)-nante-
nine 15 min before MDMA injection (filled triangles) also had bi-
phasic effects. The lowest dose tested (0.03 mg/kg) did not alter
the effects of MDMA on operant behavior. At 0.1 mg/kg, (R)-nante-
nine partially blocked the rate suppressant effects of MDMA. The
highest two doses tested (0.3 and 1.0 mg/kg) completely blocked
the effects of MDMA on operant responding.
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