Enantioselective synthesis and anti-parasitic properties of aporphine natural products

Article abstract of DOI:10.1016/j.tet.2019.130814

Chagas disease and visceral leishmaniasis are neglected protozoan diseases with significant impact in developing countries. Due to the limited number and toxicity of current therapies, new drug leads are urgently needed. In this work, four aporphine natural products were synthesized using an enantioselective, modular and convergent strategy, comprising eight steps in the longest linear sequence; key steps included Bischler-Napieralski cyclization/Noyori asymmetric reduction to construct the tetrahydroisoquinolines, and palladium-catalyzed arylation to close the C ring. Norglaucine, nordicentrine and dicentrine showed promising bioactivity against T. cruzi and L. infantum, suggesting potential for further development of these scaffolds as antiparasitic agents.

Full text of DOI:10.1016/j.tet.2019.130814

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Enantioselective synthesis and anti-parasitic properties of aporphine natural products
Pauline Pieper, Eliza McHugh, Maiara Amaral, Andre G. Tempone, Edward A.
Anderson
PII:
S0040-4020(19)31221-9
https://doi.org/10.1016/j.tet.2019.130814
TET 130814
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To appear in: Tetrahedron
Received Date: 1 October 2019
Revised Date: 15 November 2019
Accepted Date: 19 November 2019
Please cite this article as: Pieper P, McHugh E, Amaral M, Tempone AG, Anderson EA, Enantioselective
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Graphical Abstract
Enantioselective synthesis and anti-parasitic
properties of aporphine natural products
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Pauline Pieper, Eliza McHugh, Maiara Amaral, Andre G. Tempone and Edward A. Anderson
Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K.

1
Tetrahedron
Tetrahedron
journal homepage: www.elsevier.com
Enantioselective synthesis and anti-parasitic properties of aporphine natural products
Pauline Piepera, Eliza McHugha, Maiara Amaralb, Andre G. Temponec* and Edward A. Andersona*
a Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K.
b Programa de Pós-Graduação em Medicina Tropical do Instituto de Medicina Tropical da Universidade de São Paulo, Av. Dr. Eneas de Carvalho Aguiar 470,
05403-000, São Paulo, Brazil
c Centre for Parasitology and Mycology, Instituto Adolfo Lutz, Av. Dr. Arnaldo 351, 01246-000, São Paulo, Brazil.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Chagas disease and visceral leishmaniasis are neglected protozoan diseases with significant
impact in developing countries. Due to the limited number and toxicity of current therapies, new
drug leads are urgently needed. In this work, four aporphine natural products were synthesized
using an enantioselective, modular and convergent strategy, comprising eight steps in the
Available online
longest linear sequence; key steps included Bischler-Napieralski cyclization / Noyori
asymmetric reduction to construct the tetrahydroisoquinolines, and palladium-catalyzed
arylation to close the C ring. Norglaucine, nordicentrine and dicentrine showed promising
bioactivity against T. cruzi and L. infantum, suggesting potential for further development of
these scaffolds as antiparasitic agents.
Keywords:
Natural products
Aporphine
Leishmania infantum
Trypanosoma cruzi
Alkaloid
2009 Elsevier Ltd. All rights reserved
.
Palladium catalyzed arylation
Dedicated to Prof. Steve Davies in recognition of his contributions to organic chemistry
Corresponding author. Tel.: +44 1865 285000; fax: +44 1865
285002; e-mail: edward.anderson@chem.ox.ac.uk
Introduction
The aporphines comprise a large group of plant-derived
tetracyclic alkaloids featuring a 1,2,3,4-tetrahydroisoquinoline
motif. Many members of the aporphine family display interesting
biological activities, such as anti-inflammatory [1], antimicrobial
[2], anticancer [3,4] and antiparasitic [5,6] properties. In the latter
context, a handful of aporphines have been evaluated for
bioactivity against protozoan parasites; for example dicentrine,
isolated from Cassytha filiformis L., demonstrated antiparasitic
activity against Trypanosoma T. brucei, potentially by acting as
an intercalating agent with the parasite DNA (the kinetoplast) [7].
perspective of limited treatments (benznidazole and nifurtimox)
and economic / health consequences. Particularly prevalent in
South America, Chagas disease leads to eventual cardiac failure
and enlargement of the colon / oesophagus, and is fatal in >90%
cases when untreated.
The search for new drug leads for both diseases therefore
remains a pressing goal, especially for developing countries
where they predominate. In the past few years, our laboratory has
been interested in exploiting natural products as prototypes for
the discovery of new antiparasitic agents for the treatment of the
causal parasites of VL (Leishmania infantum and L. donovani)
and Chagas disease (Trypanosoma cruzi) [11, 12]. Our initial
focus was on semi-synthetic derivatives of the neolignan
dehydrodieugenol B, a number of which were found to exhibit
promising activity against intracellular forms of L. infantum, with
a phenotypic mechanism of action suggestive of impairment of
mitochondria and cell division machinery [11]. In light of the
potential anti-parasitic activity of the aporphine natural products,
four aporphines that have been shown to possess anti-
trypanosomal properties against other parasites were identified as
synthetic targets (norglaucine 1[13], nordicentrine 2 [14], and
their N-methylated analogues glaucine 3 [15, 16] and dicentrine 4
[7], Figure 1). Here we report enantioselective syntheses of these
four natural products, along with the evaluation of their anti-
parasitic properties against L. infantum and T. cruzi.
Leishmaniases, neglected tropical diseases caused by
protozoan parasites of the Leishmania genus, affect more than 12
million people worldwide [8]. Human visceral leishmaniasis
(VL) is the most severe clinical form of the disease, affecting
internal organs such as the spleen, liver, bone marrow and lymph
nodes [9]; it is the second largest cause of parasitic death after
malaria. The VL chemotherapeutic arsenal consists of just three
frontline drugs: pentavalent antimonials, amphotericin
B
(administered as a liposomal formulation), and miltefosine.
These exhibit several limitations, including long administration
periods (often with hospitalization), high cost, and adverse side
effects [10]. The related protozoan disease Chagas disease, which
affects some 8 million people worldwide, presents a similar
challenge from the

2
Tetrahedron
Results and Discussion
Scheme 1. Retrosynthetic Analysis of the Aporphines.
O
R1O
NO2
R1O
R1O
R1O
A number of synthetic approaches have been developed to
a
b
H
access the aporphine scaffold. These can broadly be classified
into two categories, according to which is the final ring built
during the synthesis, specifically: i) B-ring formation by
heterocyclization [17], or ii) C-ring formation by connection of
NH2
R1O
R1O
10a: R1 = Me, 91%
8a: R1 = Me, 89%
R1 = Me or -CH2-
10b: R1 = -CH2-, 88%
8b: R1 = -CH2-, 95%
the A and D rings through C–C bond formation including
a
MeO
MeO
O
MeO
MeO
O
c
AIBN-Bu3SnH induced aryl radical cyclization [18, 19]. Among
the latter methodologies, the most widely used are direct Pd-
catalyzed C–H arylations of halo-benzyltetrahydroisoquinolines
[20, 21], and intramolecular oxidative coupling using hypervalent
iodine reagents [22, 23]. In light of the modular and potentially
enantioselective nature of the latter approach, we also elected to
study the A–D connection tactic for the preparation of aporphines
1–4.
d
OH
OH
Br
91%
9
R1O
R1O
R1O
NH
HN
O
e
R1O
MeO
MeO
MeO
MeO
Br
Br
MeO
O
O
5a: R1 = Me, 57%
7a: R1 = Me, 76%
A
A
D
B
5b: R1 = -CH2-, 54%
B
7b: R1 = -CH2-, 81%
N
N
MeO
H
H
C
C
Scheme 2. Reagents and conditions: a) CH3NO2, AcOH, ethylenediamine, 70
°C, 12 h (10a: 91%, 10b: 88%); b) LiAlH4, THF, 70 °C, 12 h (8a: 89%, 8b:
95%); c) Br2, AcOH, 0 °C to 60 °C, 1 h, 91%; d) EDC.HCl, HOBt, NMM,
DMF, 0 °C to rt, 4h (7a: 76%, 7b: 81%); e) 1. Tf2O, 2-chloropyridine, DCM,
-78 °C to 0 °C, 15 min. 2. RuCl[(R,R)-TsDPEN](p-cymene), Et3N / HCO2H
(2:5), 0 °C to rt, 10 h (5a: 57% over 2 steps, 93% ee, 5b: 54% over 2 steps,
94% ee).
D
MeO
MeO
OMe
Norglaucine (1)
OMe
Nordicentrine (2)
MeO
O
A
A
D
B
B
N
N
O
MeO
The syntheses commenced (Scheme 2) with the preparation of
amides 7a and 7b. These were constructed by an EDC/HOBt-
mediated coupling of phenylethylamines 8a and 8b with
carboxylic acid 9 [26]. Amines 8a and 8b were in turn readily
prepared from veratraldehyde and piperonal respectively by a
sequence of Henry reaction with nitromethane and LiAlH4
reduction of the resulting β-nitrostyrenes 10a/b (81-84% over
two steps); acid 9 was synthesized in a single step by
bromination of 2-(3,4-dimethoxyphenyl)acetic acid [27]. On
treatment of 7a and 7b with trifluoromethanesulfonic anhydride
in the presence of 2-chloropyridine at low temperature
(conditions optimized by Movassaghi et al.) [24], Bischler-
Napieralski cyclodehydration occurred to form air-sensitive
benzyldihydroisoquinolines, which were directly reduced by
Noyori asymmetric transfer hydrogenation to form
tetrahydroisoquinolines 5a and 5b (5a: 57% yield over two steps,
93% ee; 5b: 54%, 94% ee).
C
C
D
MeO
MeO
OMe
Glaucine (3)
OMe
Dicentrine (4)
Figure 1. Aporphine natural products targeted in this work.
Our strategy for construction of aporphines 1–4 is outlined in
more detail in Scheme 1. As discussed above, we anticipated
using either palladium-catalyzed arylation of a halogenated
benzyltetrahydroisoquinoline (BI) 5, or oxidative C–C coupling
re action of a non-halogenated BI 6 in the late phase of the
synthesis. The required BIs would be obtained via Bischler-
Napieralski cyclization upon mild electrophilic activation of an
amide 7 [24], followed by an asymmetric Noyori hydrogenation
reduction [25]. Disconnection of the amide 7 reveals the
constituent amine (8) and carboxylic acid (9) building blocks. Of
the two cyclization strategies, the Pd-catalyzed cyclization has
significantly greater precedent, and we therefore prioritized this
approach to the aporphine scaffold.
Before C ring formation, amines 5a and 5b were first N-
protected as either the tert-butyl carbamates (11a/c, Scheme 3) or
methyl carbamates (11b/d). The direct palladium-catalyzed
ortho-arylation was next achieved using Pd(OAc)2 with di-tert-
butyl(methyl)phosphine as ligand (added as the air-stable HBF4
salt) [21], which gave the aporphine carbamates 12a-d in good
yields (52-87%). The nature of the catalyst proved crucial, as low
yields were obtained with PhDavePhos (11a: 12%, 11c: 30%)
[21]. Even under the former conditions, a significant amount of
starting material remained after a reaction time of 24 h; under
prolonged heating for 48 h, or with addition of fresh catalyst, the
reaction did not proceed to completion.
R1
R1
[Pd] or
PIFA
N
N
R1
R2
R1
R2
MeO
MeO
MeO
X
OMe
5: X = Halogen (Pd)
6: X = H (PIFA)
1–4
R1 = OMe or -OCH2O-
R2 = H or Me
Bischler-Napieralski /
Noyori
The syntheses of (+)-norglaucine (1) and (+)-nordicentrine (2)
were completed by deprotection of the Boc groups in 12a/c
respectively using anhydrous ZnBr2 (Scheme 3); the use of
Brønsted acids (e.g. trifluoroacetic acid) led to low yields due to
degradation of the sensitive aporphine products. Reduction of the
methyl carbamate-protected aporphines 12b/d using LiAlH4 gave
(+)-glaucine 3 and (+)-dicentrine 4. The spectroscopic data for
the four natural products matched that reported in the literature
[28, 29, 14, 30]. We also briefly examined the alternative
R1
R1
R1
NH2
Amide
coupling
R1
HN
O
8
X
MeO
MeO
HO
O
X
OMe
7
OMe
9

3
Tetrahedron
approach to obtain (+)-glaucine and (+)-dicentrine using
hypervalent iodine- mediated oxidative biaryl coupling (PIFA) of
intracellular amastigotes. In previous work, glaucine showed
poor activity against the insect-borne form of T. cruzi
(epimastigotes), with an EC50 value of 90 ꢀM [16]. Despite the
lack of antiparasitic activity of glaucine in our assays, the
compound showed
norglaucine, with a CC50 value of 70 ꢀM.
R1O
R1O
NH
a similar mammalian cytotoxicity to
R1O
N
a or b
R1O
R2
MeO
MeO
Finally, dicentrine (4) has been shown to exhibit activity
against Trypanosoma brucei brucei [7] with an EC50 value of 14
ꢀM; however considerable mammalian cytotoxicity was
observed for dicentrine on HeLa cells, with a CC50 value of 8.2
ꢀM. In our studies, 4 was found to be bioactive against L. (L.)
infantum, with an EC50 value of 10.5 ꢀM against the intracellular
amastigote form. In contrast, 4 lacked activity against the
intracellular amastigotes of T. cruzi, with a weak activity against
the trypomastigote form (EC50 71 ꢀM). However, it also showed
similar levels of mammalian cytotoxicity as nordicentrine.
MeO
Br
MeO
Br
5a: R1 = Me
5b: R1 = -CH2-
11a: R1 = OMe, R2 = CO2t-Bu, 78%
11b: R1 = OMe, R2 = CO2Me, 77%
11c: R1 = -CH2-, R2 = CO2t-Bu, 83%
11d: R1 = -CH2-, R2 = CO2Me, 65%
c
R1O
R1O
N
N
R1O
R2
R1O
R2
d or e
To our knowledge, this is the first report on the bioactivities
against L. infantum and T. cruzi of the aporphines norglaucine,
nordicentrine and dicentrine. In spite of the relatively high levels
of cytotoxicity, that three of the four aporphines tested showed
respectable activity against at least one of the parasites suggests
potential for further development of these scaffolds as
antiparasitic agents.
MeO
MeO
OMe
OMe
1: R1 = OMe, R2 = H, 40%
2: R1 = OMe, R2 = Me, 48%
3: R1 = -CH2-, R2 = H, 35%
4: R1 = -CH2-, R2 = Me, 53%
12a: R1 = OMe, R2 = CO2t-Bu, 55%
12b: R1 = OMe, R2 = CO2Me, 65%
12c: R1 = -CH2-, R2 = CO2t-Bu, 52%
12d: R1 = -CH2-, R2 = CO2Me, 87%
Conclusion
Scheme 3. Reagents and conditions: a) Boc2O, i-Pr2EtN, DMAP, CH2Cl2, rt, 2
h (11a: 78%, 11c: 83%); b) MeOCOCl, i-Pr2EtN, DMAP, CH2Cl2, rt, 10 h
(11b: 77%, 11d: 65%); c) Pd(OAc)2, (t-Bu)2PMeHBF4, K2CO3, DMA, 130
°C, 52%-87%; d) ZnBr2, CH2Cl2, rt, 8 h (1: 40%, 3: 35%); e) LiAlH4, THF, 0
°C to rt, 20 h (2: 48%, 4: 53%).
In conclusion, four aporphine natural products were
synthesized using an enantioselective, modular and convergent
eight step strategy. Key processes in these syntheses were the
Bischler-Napieralski cyclization / Noyori asymmetric transfer
hydrogenation to form the tetrahydroisoquinoline ring, and Pd-
catalyzed C–H arylation to construct the C ring. The natural
products were evaluated for bioactivity against T. cruzi and L.
infantum, the causal parasites of visceral leishmaniasis and
Chagas disease. Three of the four compounds showed promising
bioactivity in these assays.
the
corresponding
non-halogenated
benzyltetrahydroisoquinolines (6 (X = H), Scheme 1) [23];
however, this led only to decomposition of starting material, even
at low temperatures (-40 °C).
As noted above, a number of aporphine alkaloids have been
shown to display bioactivity against protozoan parasites, and
continuing with our interests in antiparasitic natural products [11,
12], we studied the effects of 1–4 against Trypanosoma cruzi and
Leishmania infantum (Table 1). Norglaucine (1) has previously
been shown to possess antimalarial activity, with an EC50 value
of 66 ꢀM against a chloroquine-sensitive strain (D10) and 94 ꢀM
against a chloroquine-resistant strain (Dd2) of Plasmodium
falciparum [13]. In this work, 1 reduced the number of
intracellular amastigotes of Leishmania-infected macrophages,
with an EC50 value of 21.7 ꢀM. Although norglaucine showed no
mammalian cytotoxicity in previous work in a CHO cell line
(>300 ꢀM) [13], our studies demonstrated a potential toxicity to
NCTC cells, with a CC50 value of 71 ꢀM. 1 also showed activity
against the intracellular amastigote form of T. cruzi (EC50 = 38
Experimental Section
(E)-1,2-Dimethoxy-4-(2-nitrovinyl)benzene (10a) [32]. To a
flask containing acetic acid and activated 4Å molecular sieves
was added 3,4-dimethoxybenzaldehyde (3.00 g, 18.0 mmol).
Nitromethane (4.86 mL, 90.0 mmol) and ethylenediamine (0.12
mL, 1.80 mmol) were added sequentially, and the reaction was
stirred at 70 °C overnight. Upon completion, the reaction mixture
was cooled to room temperature, poured into cold water, filtered,
and washed with more cold water to give the title compound 10a
(3.43 g, 16.4 mmol, 91%) as yellow solid. Rf 0.37 (1:1
pentane/EtOAc); 1H NMR (400 MHz, CDCl3) δ 7.95 (d, J = 13.5
Hz, 1 H), 7.53 (d, J = 13.6 Hz, 1 H), 7.17 (dd, J = 8.4, 2.0 Hz,
1H), 7.00 (d, J = 2.1 Hz, 1H), 6.91 (d, J = 8.3 Hz, 1H), 3.93 (s,
3H), 3.92 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 152.8, 149.5,
ꢀM), and against the extracellular trypomastigote form (EC50
62 ꢀM).
=
139.4, 135.2, 124.7, 122.8, 111.3, 110.2, 56.1, 56.0; IR (νmax
/
Nordicentrine (2) has also been reported to exhibit activity
against P. falciparum with an EC50 of 0.3 ꢀg/mL [31], and
against P. falciparum (strain D6) with an EC50 value of 0.47
ꢀg/mL [14]. We observed activity against both the intracellular
amastigote (EC50 of 7 ꢀM) and extracellular trypomastigote (EC50
of 19 ꢀM) forms of T. cruzi, but no activity against L. infantum
amastigotes. This compound exhibited the highest mammalian
cytotoxicity among the four aporphines, with a CC50 value of 21
ꢀM.
cm-1) 3128, 2958, 2923, 1500, 1334; HRMS (ES+) calc. for
C10H12O4N [M+H]+ 210.0766, found 210.0763; mp 138–140 °C.
(E)-5-(2-Nitrovinyl)benzo[d][1,3]dioxole (10b) [33]. 10b was
prepared from benzo[d][1,3]dioxole-5-carbaldehyde (3.50 g, 23.3
mmol) following the same procedure as for 10a to give the title
compound 10b (3.96 g, 20.5 mmol, 88%) as a yellow solid. Rf
1
0.77 (1:1 pentane/EtOAc); H NMR (400 MHz, CDCl3) δ 7.93
(d, J = 13.5 Hz, 1H), 7.47 (d, J = 13.5 Hz, 1H), 7.08 (dd, J = 8.2,
1.7 Hz, 1H), 7.00 (d, J = 1.8 Hz, 1H), 6.87 (d, J = 8.0 Hz, 1H),
6.06 (s, 2H); 13C NMR (101 MHz, CDCl3) δ 151.4, 148.8, 139.1,
In contrast to the secondary amine-containing aporphines, the
N-methylated glaucine (3) demonstrated neither antileishmanial
nor antitrypanosomal activity against the clinically relevant

4
Tetrahedron
135.4, 126.6, 124.2, 109.1, 107.0, 102.1; IR (νmax / cm-1) 3105,
2918,

5
Tetrahedron
Table 1. Bioactivity against Trypanosoma cruzi and Leishmania (L.) infantum, and mammalian cytotoxicity of aporphine
alkaloids 1–4.a
EC50
EC50
CC50
EC50 Trypomastigote T.cruzi
Compound
Amastigote T.cruzi
(µM) ± SD
Amastigote L.infantum
(µM) ± SD
NCTC cells
(µM) ± SD
(µM) ± SD
Norglaucine (1)
Nordicentrine (2)
Glaucine (3)
62.6 ± 0.4
19.8 ± 0.6
>150
38.4 ± 15.3
7.0 ± 2.0
NA
21.7 ± 7.5
NA
71.3 ± 8.5
21.2 ± 12.7
70.6 ± 5.7
NA
Dicentrine (4)
miltefosine
71.8 ± 0.2
ND
NA
10.5 ± 5.4
6.5 ± 3.0
ND
27.6 ± 5.9
ND
119.7 ± 4.2
190.6 ± 13.4
benznidazole
17.7 ± 1.9
5.0 ± 1.5
a EC50: 50% Effective Concentration; CC50: 50% Cytotoxic Concentration; SD: Standard Deviation; ND: Not Determined; NA: Not Active.
2852, 1654, 1602, 1578, 1501, 1448, 1420, 1336, 1262, 1099,
1036, 814, 655; HRMS (ES+) calc. for C9H7O4NNa [M+Na]+
216.0273, found 216.0273; mp 163 °C.
(s, 1H), 3.86 (s, 3H), 3.86 (s, 3H), 3.77 (s, 2H); 13C NMR (126
MHz, CDCl3) δ 176.4, 149.1, 148.5, 125.4, 115.5, 115.2, 114.0,
56.3, 56.2, 41.0; IR (νmax / cm-1) 3550, 1688, 1417, 1281, 1189,
1144, 1045 ; HRMS (ES+) calc. for C10H10O479Br [M-H]–
272.9768, found 272.9767; mp 113–114 °C.
2-(3,4-Dimethoxyphenyl)ethanamine (8a) [34]. To a flask
containing anhydrous THF (60 mL) was added LiAlH4 (4 M
solution in Et2O, 8.96 mL, 35.8 mmol), and the solution was
cooled to 0 °C. A solution of nitroalkene 10a (2.50 g, 11.9 mmol)
in anhydrous THF (20 mL) and added dropwise. The mixture
was allowed to reach rt and was then refluxed under N2
overnight. Upon completion, the reaction mixture was cooled to
0 °C. Et2O (5 mL) and water (1.15 mL) were added slowly. After
15 mins, 15 % (w/w) aq. sodium hydroxide (1.15 mL) was
added. After another 15 mins, water (3.41 mL) was added. The
resultant mixture was stirred for 30 mins at rt. Following this,
MgSO4 was added, and the mixture was filtered through a Celite
pad (CH2Cl2 wash). The filtrate was concentrated to give the title
compound 8a (1.92 g, 10.9 mmol, 89%) as an amber oil, which
was of sufficient purity to use without further purification. Rf
2-(2-Bromo-4,5-dimethoxyphenyl)-N-(3,4-
dimethoxyphenethyl)acetamide (7a) [35]. To a solution of amine
8a (981 mg, 5.41 mmol) and carboxylic acid 9 (1.48 g, 5.41
mmol) in dry DMF (20 mL) was added 1-hydroxybenzotriazole
(1.07 g, 7.95 mmol). The reaction mixture was cooled to 0 °C,
then
1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide
hydrochloride (1.30 g, 6.62 mmol) and N-methylmorpholine
(2.03 mL, 18.0 mmol) were added. The reaction mixture was
warmed slowly to room temperature, and then stirred for 4 h
before being quenched by addition of NaHCO3 (10 mL, sat., aq.)
and extracted with ethyl acetate (3 × 10mL). The combined
organic layers were washed with brine, dried over MgSO4,
filtered and concentrated. The residue was purified by flash
chromatography over silica gel (2:1 petroleum ether/EtOAc) to
give the title compound 7a (1.80 g, 4.11 mmol, 76%) as a white
solid. Rf 0.8 (2:1 petrol ether/EtOAc). 1H NMR (400 MHz,
CDCl3) δ 6.99 (s, 1H), 6.76 (s, 1H), 6.71 (d, J = 8.1 Hz, 1H), 6.64
(d, J = 2.0 Hz, 1H), 6.58 (dd, J = 8.2, 2.0 Hz, 1H), 5.44 (br s,
1H), 3.88 (s, 3H), 3.85 (s, 3H), 3.84 (s, 3H), 3.83 (s, 3H), 3.59 (s,
2H), 3.46 (app q, J = 6.7 Hz, 2H), 2.71 (t, J = 6.9 Hz, 2H); 13C
NMR (101 MHz, CDCl3) δ 166.7, 149.0, 148.9, 148.7, 147.6,
131.0, 126.5, 120.5, 115.5, 114.7, 113.7, 111.7, 111.2, 56.1, 56.0,
55.8, 55.8, 43.6, 40.7, 34.9; IR (νmax / cm-1) 3414, 2935, 1633,
1549, 1463, 1384, 1244, 1028; HRMS (ES+) calc. for
C20H24O5N79BrNa [M+Na]+ 460.0730, found 460.0729; mp 150–
151 °C.
1
0.05 (9:1 EtOAc/MeOH); H NMR (400 MHz, CDCl3) δ 6.82–
6.79 (m, 1H), 6.76–6.71 (m, 2H), 3.87 (s, 3H), 3.86 (s, 3H), 2.94
(t, J = 6.8 Hz, 2H), 2.69 (t, J = 6.8 Hz, 2H); 13C NMR (101 MHz,
CDCl3) δ 149.0, 147.5, 132.4, 120.8, 112.1, 111.3, 56.0, 55.9,
43.7, 39.5; IR (νmax / cm-1) 3370, 2934, 1606, 1591, 1516, 1464,
1417, 1331, 1261, 1237, 1190, 1157, 1142, 1028, 935, 855, 808,
764, 633; HRMS (ES+) calc. for C10H16O2N [M+H]+ 182.1176,
found 182.1176; mp 154–155 °C.
2-(Benzo[d][1,3]dioxol-5-yl)ethanamine (8b) [34]. Amine 8b
was prepared following from 10b (3.10 g, 48.1 mmol) using the
same procedure as for 8a, to give the title compound (2.52 g, 15.2
1
mmol, 95%) as an amber oil. Rf 0.16 (9:1 EtOAc/MeOH); H
NMR (400 MHz, CDCl3) δ 6.74 (d, J = 7.8 Hz, 1H), 6.68 (d, J =
1.5 Hz, 1H), 6.64 (dd, J = 7.8, 1.6 Hz, 1H), 5.92 (s, 2H), 2.91 (t,
J = 6.8 Hz, 2H), 2.66 (t, J = 6.8 Hz, 2H); 13C NMR (101 MHz,
CDCl3) δ 147.7, 145.9, 133.6, 121.7, 109.1, 108.2, 100.8, 43.7,
39.8; IR (νmax / cm-1) 3636, 3368, 2923, 1846, 1607, 1503, 1489,
1443, 1362, 1246, 1190, 1123, 1098, 1040, 933, 928, 864, 818,
637, 601; HRMS (ES+) calc. for C9H12O2N [M+H]+ 166.0863,
found 166.0864.
N-(2-(Benzo[d][1,3]dioxol-5-yl)ethyl)-2-(2-bromo-4,5-
dimethoxyphenyl)acetamide (7b). Amide 7b was prepared from
8b (675 mg, 4.08 mmol) and 9 (1.12 g, 4.08 mmol) following the
same procedure as for 9a to give the title compound 7b (1.40 g,
3.32 mmol, 81%) as a white solid. Rf 0.33 (1:1 pentane/EtOAc);
1H NMR (400 MHz, CDCl3) δ 7.01 (s, 1H), 6.76 (s, 1H), 6.66 (d,
J = 7.8 Hz, 1H), 6.55 (d, J = 1.7 Hz, 1H), 6.50 (dd, J = 7.8, 1.7
Hz, 1H), 5.92 (s, 2H), 5.42 (br s, 1H), 3.88 (s, 3H), 3.84 (s, 3H),
3.59 (s, 2H), 3.43-3.40 (m, 2H), 2.66 (t, J = 6.7 Hz, 2 H); 13C
NMR 101 MHz, CDCl3): δ 169.9, 149.1, 148.8, 147.9, 146.2,
132.4, 126.7, 121.7, 115.7, 114.9, 113.8, 109.1, 108.4, 101.0,
56.3, 56.2, 43.8, 40.9, 35.3; IR (νmax / cm-1) 3271, 2981, 2889,
1634, 1606; HRMS (ES+) calc. for C19H21O5N79Br [M+H]+
422.0598, found 422.0595; mp 138–141 °C.
2-(2-Bromo-4,5-dimethoxyphenyl)acetic acid (9) [27]. 2-(3,4-
dimethoxyphenyl)acetic acid (5.00 g, 25.5 mmol) was dissolved
in glacial acetic acid (10 mL) and cooled to 0 °C. Br2 (1.31 mL,
25.5 mmol) dissolved in glacial acetic acid (10 mL) was added
dropwise. The ice bath was removed, and the reaction was heated
at 60 °C for 1 h. Upon completion, the reaction mixture was
cooled, poured into ice water, and the precipitate was filtered off.
This solid was washed with Na2S2O3 (sat., aq.) and H2O to afford
the title compound 9 (6.41 g, 23.3 mmol, 91%) as white solid. Rf
(S)-1-(2-Bromo-4,5-dimethoxybenzyl)-6,7-dimethoxy-1,2,3,4-
tetrahydroisoquinoline (5a) [24]. Trifluoromethanesulfonic
anhydride (419 ꢀL, 2.49 mmol) was added via syringe over 5 min
1
0.48 (EtOAc); H NMR (500 MHz, CDCl3) δ 7.04 (s, 1H), 6.79

Tetrahedron
to a stirred mixture of amide 7a (1.00 g, 2.49 mmol) and 2-
rotamers in a 3:1 ratio denoted Major (M) and minor (m)) δ 7.04
(s, 1H, (M)), 6.97 (s, 0.33H, (m)), 6.74 (s, 1H, (M)), 6.66 (s,
0.33H (m)), 6.62 (s, 1H, (M)), 6.58 (s, 0.33, (m)), 6.52 (s, 1H,
(M)), 6.48 (s, 0.33H, (m)), 5.40–5.36 (m, 0.33H, (m)), 5.25 (dd, J
= 10.0, 3.9 Hz, 1H, (M)), 4.34 (ddd, J = 13.2, 6.0, 2.4 Hz, 1H,
(M)), 3.86 (s, 6H, (M)), 3.85 (s, 4H, both rotamers), 3.83 (s, 1H,
(m)), 3.80 (s, 4H, both rotamers), 3.74 (s, 1H, (m)), 3.40–3.34
(m, 1H, (m)), 3.30–3.19 (m, 2.33H, both rotamers), 3.06–3.01
(m, 0.33H, (m)), 2.95–2.86 (m, 2H, (M)), 2.82–2.76 (m, 0.33H,
(m)), 2.65–2.63 (m, 1H, (M)), 2.59–2.55 (m, 0.33H, (m)), 1.39 (s,
3H, (m)), 1.18 (s, 9H, (M)); 13C NMR (101 MHz, CDCl3, major
rotamer): δ 154.2, 148.5, 148.4, 147.9, 147.4, 130.3, 128.8,
126.6, 115.5, 114.9, 114.4, 111.5, 110.0, 79.4, 56.3, 56.2, 56.0,
55.9, 54.3, 42.1, 36.5, 28.4, 28.0; IR (νmax / cm-1) 3661, 3021,
2981, 1678, 1639, 1609; HRMS (ES+) calc. for C25H33O6N79Br
[M+H]+ 522.1486, found 522.1487; 93% ee. The ee value was
determined by comparison of HPLC analyses of the optically
enriched product (+)-11a, and (±)-11a obtained by reduction of
9a with NaBH4. Daicel Chiralpak IB-3 (ɸ 0.46 cm × 25 cm), 5.0
ꢀL/min, room temperature, 5% isopropyl alcohol / 95% n-
hexane, 210 nm, t = 16.02 min; [α]D20 +51 (c 0.95, CHCl3).
chloropyridine (259 ꢀL, 2.74 mmol) in CH2Cl2 (10 mL) at –78
°C. After 10 min, the reaction mixture was warmed to 0 °C by
placing in an ice-water bath. After 5 min, the solution was
allowed to warm to 23 °C, and then quenched by addition of
NaOH (15 mL, 1N aq.). CH2Cl2 (10 mL) was added and the
layers were separated. The organic layer was dried over
anhydrous MgSO4, and filtered. The solvent was removed under
reduced pressure to afford the crude imine, which was
immediately used in the next step without further purification.
The imine was dissolved in anhydrous DMF (10 mL) at room
temperature, then RuCl[(R,R)-TsDPEN](p-cymene) (52 mg,
0.092 mmol) was added, and the mixture was placed under a
nitrogen atmosphere. The mixture was then cooled to 0 °C, then
Et3N (910 ꢀL) and formic acid (2.0 mL) were added. The
reaction was allowed to warm to room temperature and stirred for
24 h before being quenched by addition of NaHCO3 (10 mL, sat.,
aq.), and extracted with CH2Cl2 (3 × 10mL). The combined
organic layers were washed with brine, dried over MgSO4,
filtered and concentrated. The residue was purified by flash
chromatography (1:0→0:1 petrol/EtOAc, silica gel deactivated
with 0.1% Et3N) to afford the title compound 5a (598 mg, 1.42
mmol, 57% over 2 steps) as a green oil. Rf 0.06 (99 : 1 EtOAc /
MeOH); 1H NMR (400 MHz, CDCl3) δ 7.04 (s, 1H), 6.89 (s, 1H),
6.60 (s, 1H), 6.38 (s, 1H), 4.59–4.49 (m, 1H), 3.87 (s, 3H), 3.86
(s, 3H), 3.85 (s, 3H), 3.69 (s, 3H), 3.50–3.16 (m, 4H), 3.03–2.89
(m, 2H); 13C NMR (101 MHz, CDCl3) δ 148.9, 148.7, 148.6,
147.4, 127.3, 123.9, 123.2, 115.6, 115.4, 115.2, 111.3, 109.9,
56.5, 56.2, 55.9, 55.6, 54.4, 40.8, 39.1, 25.5; IR (νmax / cm-1)
3662, 3283, 2980, 2890, 1641; HRMS (ES+) calc. for
C20H25O4N79Br [M+H]+ 422.0962, found 422.0966; mp 205–207
°C; [α]D20 +33 (c 0.94, CHCl3).
(S)-Tert-butyl 5-(2-bromo-4,5-dimethoxybenzyl)-7,8-dihydro-
[1,3]dioxolo[4,5-g]isoquinoline-6(5H)-carboxylate
(11c).
Prepared following General procedure A from 5b (347 mg,
0.86 mmol) to give compound the title compound 11c (360 mg,
0.71 mmol, 83%) as a white solid. Rf 0.35 (7:3 pentane / EtOAc);
1H NMR (400 MHz, CDCl3, analysis revealed the presence of
two amide rotamers in a 1:0.39 ratio, denoted Major (M) and
minor (m)) δ: 7.04 (s, 1H, M), 6.98 (s, 0.39H, m), 6.79 (s, 1H,
(M)), 6.62-6.56 (m, 2.17H, both rotamers), 6.52 (s, 1H, (M)),
5.92 (dd, J = 5.2, 1.3 Hz, 2H, (M)), 5.90-5.88 (m, 0.78H, (m)),
5.36-5.34 (m, 0.39, (m)), 5.23 (dd, J = 10.4, 3.4 Hz, 1H, (M)),
4.33-4.28 (m, 1H, (M)), 3.86 (s, 3H, (M)), 3.83 (s, 1.17H, (m)),
3.80 (s, 4.27H, both), 3.38-3.37 (m, 0.39H, (m)), 3.29-3.15 (m,
3H, (M)), 3.01-2.95 (m, 0.39H, (m)), 2.92-2.83 (m, 2H, (M)),
2.77-2.71 (m, 0.39H, (m)), 2.65-2.61 (m, 0.78H, (m)), 2.58-2.54
(m, 0.39, (m)), 1.36 (s, 3.51H, (m)), 1.14 (s, 9H, (M)); 13C NMR
(400 MHz, CDCl3, major rotamer) δ 148.7, 148.5, 148.3, 146.6,
146.2, 130.2, 130.2, 127.9, 115.7, 115.1, 114.5, 108.9, 107.2,
101.0, 79.5, 56.5, 56.3, 54.8, 42.3, 28.8, 28.5, 22.1. HRMS (ES+)
calc. for C24H29NO6 [M+H]+ 506.1172, found: 506.1152. 94% ee.
The ee value was determined by comparison of HPLC analyses
of the optically enriched product (+)-11b, and (±)-11b obtained
by reduction of 9b with NaBH4. Daicel Chiralpak IB-3 (ɸ 0.46
cm× 25 cm), 5.0 ꢀL/min, room temperature, 5% isopropyl
(S)-5-(2-Bromo-4,5-dimethoxybenzyl)-5,6,7,8-tetrahydro-
[1,3]dioxolo[4,5-g]isoquinoline (5b). Tetrahydroisoquinoline 5b
was prepared from 7b (1.50 g, 3.56 mmol) following the same
procedure as for 5a to afford the title compound 5b (786 mg, 1.94
1
mmol, 54% over 2 steps) as a green oil. Rf 0.17 (EtOAc); H
NMR (400 MHz, CDCl3) δ 7.06 (s, 1H), 6.81 (s, 1H), 6.79 (s,
1H), 6.58 (s, 1H), 5.91 (s, 2H), 4.25–4.18 (m, 1H), 3.88 (s, 3H),
3.86 (s, 3H), 3.29 (dd, J = 13.8, 3.5 Hz, 1H), 3.23 (ddd, J = 12.0,
6.8, 3.5 Hz, 1H), 2.94 (ddd, J = 11.7, 6.2, 5.2 Hz, 1H), 2.87 (dd,
J = 13.8, 10.2 Hz, 1H), 2.81-2.67 (m, 2H); 13C NMR (101 MHz,
CDCl3) δ 148.3, 148.3, 145.9, 145.7, 131.5, 130.4, 128.3, 115.8,
114.7, 114.3, 108.8, 106.4, 100.6, 56.2, 56.1, 55.6, 42.7, 40.4,
30.0; IR (νmax / cm-1) 3322, 2959, 2928, 1602; HRMS (ES+) calc.
for C19H21O4N79Br [M+H]+ 406.0649, found 406.0654; mp 124–
125 °C; [α]D20 +28 (c 0.98, CHCl3).
20
alcohol / 95% n-hexane, 210 nm, t = 10.02 min; [α]D +56 (c
0.98, CHCl3).
General
procedure
A
for
the
synthesis
of
General
procedure
B
for
the
synthesis
of
benzyltetrahydroisoquinoline carbamates 11a and 11c. To a
stirred solution of the tetrahydroisoquinoline (5a and 5b) (1.0
equiv.), diisopropylethylamine (2.0 equiv.), and 4-
dimethylaminopyridine (1–3 mg) in CH2Cl2 (0.2 M) was slowly
added di-tert-butyl dicarbonate (1.2 equiv.), and the resulting
mixture was stirred for 2 h at room temperature. Upon
completion, the reaction was quenched by addition of NH4Cl (sat.
aq.), and extracted with CH2Cl2 (x 3). The combined organic
layers were dried over MgSO4, concentrated in vacuo and
purified by flash chromatography (1:1 pentane/EtOAc).
benzyltetrahydroisoquinoline carbamates 11b and 11d.
Methyl chloroformate (2 eq.) was added slowly to a solution of
tetrahydroisoquinoline (5a and 5b) (1 eq.), diisopropylethylamine
(2 eq.) and 4-(dimethylamino)pyridine (1-5 mg) in CH2Cl2 (0.2
M) and the resulting mixture was stirred overnight at room
temperature. The reaction mixture was then quenched by adding
saturated ammonium chloride solution and extracted with
CH2Cl2. The combined organic phases were purified by column
chromatography on silica gel (pentane/EtOAc, 1:1).
(S)-Methyl 1-(2-bromo-4,5-dimethoxybenzyl)-6,7-dimethoxy-
3,4-dihydroisoquinoline-2(1H)-carboxylate (11b). Prepared
following General procedure B from 5a (459 mg, 1.09 mmol)
to give compound the title compound 11b (414 mg, 0.86 mmol,
77%). Rf 0.43 (2:1 pentane / EtOAc); 1H NMR (400 MHz,
CDCl3, analysis revealed the presence of two rotamers in a 1:0.75
ratio, denoted Major (M) and minor (m)) δ 7.03 (s, 1H, (M)),
(S)-Tert-butyl
dimethoxy-3,4-dihydroisoquinoline-2(1H)-carboxylate
1-(2-bromo-4,5-dimethoxybenzyl)-6,7-
(11a)
[35]. Prepared following General procedure A from 5a (362
mg, 0.86 mmol) to give the title compound 11a (350 mg, 0.67
1
mmol, 78%) as a white solid. Rf 0.14 (2:1 pentane/EtOAc); H
NMR (400 MHz, CDCl3. Analysis revealed the presence of two

7
Tetrahedron
6.97 (s, 0.75H (m)), 6.63-6.58 (m, 3.5H, both rotamers), 6.49 (s,
1H, (M)), 6.36 (s, 0.75H, (m)), 5.37 (t, J = 6.9 Hz, 0.75H, (m)),
5.28 (m, 1H, (M)), 4.25 (ddd, J = 13.0, 5.7, 3.0 Hz, 1H, (M)),
3.95-3.89 (m, 0.75H, (m)), 3.87 (s, 6H, (M)), 3.85-3.84 (m, 4.5H,
(m)), 3.79 (s, 2.25H, (m)), 3.77 (s, 6H, (M)), 3.70 (s, 2.25H,
(m)), 3.67 (s, 2.25H, (m)), 3.46-3.42 (m, 0.75H, (m)), 3.39 (s,
3H, (M)), 3.55-3.31 (m, 0.75H (m)), 3.26-3.19 (m, 1.75H, both
rotamers), 3.12-3.07 (m, 0.75H, (m)), 3.03-2.97 (m, 0.75H, (m)),
2.92-2.80 (m, 2H, (M)), 2.68-2.60 (m, 2H, (M)); 13C NMR (101
MHz, CDCl3 major rotamer) δ 156.0, 148.4, 148.2, 148.0, 147.4,
129.9, 128.2, 126.6, 115.4, 114.3, 113.9, 111.5, 110.2, 56.4, 56.3,
56.0, 56.1, 54.5, 52.5, 42.3, 37.7, 28.2; IR (νmax / cm-1) 2953,
2363, 1689, 1508, 1216, 905; HRMS (ES+) calc. for
(S)-Methyl
1,2,9,10-tetramethoxy-6a,7-dihydro-4H-
dibenzo[de,g]quinoline-6(5H)-carboxylate (12b). Prepared from
11b (404 mg, 0.84 mmol) following General procedure C to
give the title compound 12b (219 mg, 0.55 mmol, 65%) as a
white solid. Rf 0.42 (4:1 pentane / EtOAc); 1H NMR (500 MHz,
CDCl3) δ 8.16 (s, 1H), 6.79 (s, 1H), 6.63 (s, 1H), 4.75 (d, J =
12.8 Hz, 1H), 4.45 (br s, 1H), 3.93 (s, 3H), 3.91 (s, 3H), 3.90 (s,
3H), 3.77 (s, 3H), 3.66 (s, 3H), 3.00 (m, 1H), 2.91–2.77 (m, 3H),
2.65 (m, 1H); 13C NMR (126 MHz, CDCl3) δ 156.2, 152.2,
148.4, 147.6, 144.9, 130.1, 129.86, 127.8, 125.5, 124.2, 111.9,
111.3, 110.7, 60.1, 56.1, 56.0, 55.9, 55.8, 52.8, 52.0, 39.2, 30.5.
IR (νmax / cm-1) 2981, 2358, 1698, 1509, 1457, 1394, 1253, 1110,
904; HRMS (ES+) calc. for C22H26O6N [M+H]+ 400.1755, found
400.1756; [α]D20 +99 (c 1.0, CHCl3).
20
C22H26O6N79Br [M+H]+ 480.10163, found 480.1093. [α]D +77
(c 1.0, CHCl3).
(S)-Tert-butyl
10,11-dimethoxy-7a,8-dihydro-5H-
(S)-Methyl-5-(2-bromo-4,5-dimethoxybenzyl)-7,8-dihydro-
[1,3]dioxolo[4',5':4,5]benzo[1,2,3-de]benzo[g]quinoline-7(6H)-
carboxylate (12c). Prepared from 11c (360mg, 0.71mmol)
following General procedure C to give the title compound 12c
(157 mg, 0.36 mmol, 52%) as a white solid. Rf 0.38 (4:1
[1,3]dioxolo[4,5-g]isoquinoline-6(5H)-carboxylate
(11d).
Prepared following General procedure B from 5b (646 mg,
1.59 mmol) to give the title compound 11d (481 mg, 1.03 mmol,
65%). Rf 0.45 (2:1 pentane / EtOAc); 1H NMR (400 MHz,
CDCl3, analysis revealed the presence of two amide rotamers in a
1:0.75 ratio, denoted Major (M) and minor (m)) δ 7.03 (s, 1H,
(M)), 6.97 (s, 0.67H (m)), 6.59 (br s, 1.67H, both rotamers), 6.56
(s, 0.67H, (m)), 6.48 (s, 1H, (M)), 6.47 (s, 0.67H, (m)), 5.92 (s,
2H, (M)), 5.89 (d, J = 2.2 Hz, 1.34H, (m)), 5.36 (t, J = 6.9 Hz,
0.67H, (m)), 5.26 (dd, J = 9.5, 4.2 Hz, 1H, (M)), 4.21 (ddd, J =
13.0, 5.7, 3.4 Hz, 1H, (M)), 3.86 (s, 3H, (M)), 3.85 (s, 2H, (m)),
3.79 (s, 3H, (M)), 3.78 (s, 2H, (m)), 3.45-3.36 (m, 1.34, (m)),
3.34 (s, 3H, (M)), 3.25-3.17 (m, 2H, (M)), 3.08-3.02 (m, 0.67H,
(m)), 2.99-2.93 (m, 1H, (M)), 2.89-2.81 (m, 1.34H, (m)), 2.79-
2.73 (m, 0.65H, (m)), 2.67-2.57 (m, 2H, (M)); 13C NMR (101
MHz, CDCl3 major rotamer) δ 156.0, 148.4, 148.2, 146.6, 146.2,
129.8, 129.6, 127.7, 115.4, 115.3, 114.2, 108.7, 107.2, 101.0,
56.4, 56.3, 54.8, 52.4, 42.4, 37.8, 28.6. IR (νmax / cm-1) 2952,
2361, 1696, 1603, 1505, 1284, 1449, 1259, 1273, 1036, 930;
HRMS (ES+) calc. for C21H23O6N79Br [M+H]+ 464.07033, found
464.07043; [α]D20 +75 (c 0.92, CHCl3).
1
pentane/EtOAc); H NMR (400 MHz, CDCl3) δ 7.70 (s, 1H),
6.77 (s, 1H), 6.56 (s, 1H), 6.09 (d, J = 1.5 Hz, 1H), 5.97 (d, J =
1.5 Hz, 1H), 4.85–4.72 (m, 1H), 4.45–4.30 (m, 1H), 3.93 (s, 3H),
3.91 (s, 3H), 3.04–2.76 (m, 4H), 2.60 (td, J = 15.4, 2.3 Hz, 1H),
1.51 (s, 9H); 13C NMR (126 MHz, CDCl3) δ 154.7, 148.4, 147.6,
146.6, 142.1, 131.33, 129.0, 128.0, 127.3, 125.3, 123.2, 111.4,
110.6, 106.8, 100.8, 86.18, 79.9, 56.1, 55.9, 51.9, 31.9, 30.9,
30.5, 28.6; IR (vmax / cm-1) 2971, 2925, 2852, 2252, 1688; HRMS
(ES+) calc. for C24H27O6NNa [M+Na]+ 448.1731, found
448.1729; [α]D20 +78 (c 1.0, CHCl3).
(S)-Methyl
10,11-dimethoxy-7a,8-dihydro-5H-
[1,3]dioxolo[4',5':4,5]benzo[1,2,3-de]benzo[g]quinoline-7(6H)-
carboxylate (12d). Prepared from 11d (470 mg, 1.03 mmol)
following General procedure C to give the title compound 12d
(348 mg, 0.90 mmol, 87%) as a white solid. Rf 0.49 (4:1
1
pentane/EtOAc); H NMR (500 MHz, CDCl3) δ 7.70 (s, 1H),
6.78 (s, 1H), 6.56 (s, 1H), 6.09 (d, J = 1.4 Hz, 1H), 5.97 (d, J =
1.4 Hz, 1H), 4.84 (d, J = 13.6 Hz, 1H), 4.43 (br s, 1H), 3.93 (s,
3H), 3.92 (s, 3H), 3.77 (s, 3H), 3.02–2.96 (m, 2H), 2.87–2.78 (m,
2H), 2.62-2.59 (m, 1H). 13C NMR (126 MHz, CDCl3) δ 13C NMR
(126 MHz, CDCl3) δ 156.1, 148.6, 147.8, 146.8, 142.9, 128.8,
128.0, 125.0, 123.3, 117.6, 111.6, 110.8, 106.9, 100.9, 56.2, 56.0,
52.8, 52.1, 39.3, 30.9, 30.5; IR (νmax / cm-1) 2984, 1691, 1515,
1453, 1390, 1214, 1119, 906; HRMS (ES+) calc. for C21H22O6N
[M+H]+ 384.1442, found 384.1442; [α]D20 +85 (c 1.0, CHCl3).
General procedure C for the synthesis of Aporphine
carbamates
(12a-d).
K2CO3
(3.0
eq.),
di-tert-
butyl(methyl)phosphonium tetrafluoroborate (0.1 eq.), Pd(OAc)2
(0.2 eq.) and the tetrahydroisoquinoline carbamate 11a-d (1.0
eq.) were weighed out into a vial, which was purged with N2
three times. Degassed the anhydrous DMA (0.2M) is then added
and the resulting mixture heated to 130 °C for 8 h. The reaction
mixture was then washed with water and extracted with EtOAc
(x 3). The combined organic layers were washed with brine,
dried over MgSO4, concentrated in vacuo and purified by column
chromatography (28 : 1 pentane / EtOAc).
General procedure D for the deprotection of carbamates
11a and 11c to synthesise (+)-norglaucine (1) and (+)-
nordicentrine (3). Anhydrous ZnBr2 (4 equiv.) was added to a
solution of compound 12a or 12c (1 equiv.) in dry CH2Cl2 (0.1M)
under a nitrogen atmosphere, and the mixture was stirred at room
temperature for 8 h. The reaction was quenched by addition of
with a NaHCO3 (10 mL, sat., aq.), and then extracted with
CH2Cl2 (x 3). The combined organic layers were dried over
MgSO4, and concentrated. The residue was dissolved in a 1 M
solution of HCl in diethyl ether (5 mL), stirred for 5 min at 0 °C,
and then filtered to give the natural product hydrochloride salt as
a yellow solid.
(S)-Tert-butyl
1,2,9,10-tetramethoxy-6a,7-dihydro-4H-
dibenzo[de,g]quinoline-6(5H)-carboxylate (12a) [35]. Prepared
from 11a (348 mg, 0.66 mmol) following General procedure C
to give the title compound 12a (163 mg, 0.37 mmol, 55%) as a
white solid. Rf 0.60 (1:1 pentane / EtOAc); 1H NMR (500 MHz,
CDCl3) δ 8.15 (s, 1H), 6.77 (s, 1H), 6.63 (s, 1H), 4.67 (d, J =
10.9 Hz, 1H), 4.40 (d, J = 11.2 Hz, 1H), 3.92 (s, 3H), 3.92 (s,
3H), 3.90 (s, 3H), 3.66 (s, 3H), 3.05–2.73 (m, 4H), 2.68–2.60
(m, 1H), 1.50 (s, 9H); 13C NMR (101 MHz, CDCl3) δ 154.6,
151.9, 148.2, 147.4, 144.7, 130.1, 130.0, 127.7, 125.8, 124.1,
111.7, 110.9, 110.5, 79.8, 60.0, 55.9, 55.8, 51.9, 31.9, 30.5, 29.4,
28.6; IR (νmax / cm-1) 2922, 2852, 1688, 1596, 1513; HRMS
(ES+) calc. for C25H31O6NNa [M+Na]+ 464.2044, found
464.2045. [α]D20 +95 (c 1.0, CHCl3).
(S)-1,2,9,10-Tetramethoxy-5,6,6a,7-tetrahydro-4H-
dibenzo[de,g]quinoline ((+)-norglaucine, 1) [36]. Prepared from
12a (101 mg, 0.29mmol) following General Procedure D to
give the title compound 1 (40 mg, 0.12 mmol, 40%) as yellow
1
solid. Rf 0.38 (4:1 CH2Cl2/MeOH); H NMR (500 MHz, MeOD)
δ 8.08 (s, 1H), 6.98 (s, 1H), 6.89 (s, 1H), 4.33 (dd, J = 14.0, 4.3

Tetrahedron
Hz, 1H), 3.93 (s, 3H), 3.92 (s, 3H), 3.90 (s, 3H), 3.83–3.81 (m,
found 340.1543; mp 166–169 °C. [Lit. mp 176–177 °C][38].
1H), 3.73 (dd, J = 12.0, 5.8 Hz, 1H), 3.68 (s, 3H), 3.39 (td, J =
12.7, 4.7 Hz, 1H), 3.28–3.25 (m, 1H), 3.09–3.03 (m, 2H), 2.97–
2.87 (m, 1H); 13C NMR (126 MHz, MeOD) δ 155.2, 150.4,
149.6, 146.7, 127.9, 127.5, 127.5, 125.3, 121.9, 121. 1, 113.6,
[α]D20 +72 (c 1.0, CHCl3) [Lit. +62 (c 1.0, CHCl3)] [38].
Biological Assays: Animals. Male golden hamsters
(Mesocricetus auratus) and female BALB/c mice were obtained
from the animal breeding facility at the Instituto Adolfo Lutz,
Brazil. The animals were maintained in sterilized cages under a
controlled environment, receiving water and food ad libitum. All
procedures performed were previously approved by the Animal
Care and Use Committee from Instituto Adolfo Lutz – Secretary
of Health of São Paulo State (Project number CTC 21H/2015,
CEUA 04/2016) in agreement with the Guide for the Care and
Use of Laboratory Animals from the National Academy of
Sciences.
112.7, 112.2, 60.6, 56.7, 56.5, 54.4, 42.6, 34.5, 26.3; IR (νmax
/
cm-1) 3019, 1578, 1514, 1466, 1110; HRMS (ES+) calc. for
C20H24O4N [M+H]+ 342.1700, found 342.1699. [α]D20 +83 (c 1.0,
MeOH) [Lit. +80 (c 1.0, MeOH)] [28].
(S)-10,11-Dimethoxy-6,7,7a,8-tetrahydro-5H-
[1,3]dioxolo[4',5':4,5]benzo[1,2,3-de]benzo[g]quinoline
((+)-
nordicentrine, 3) [14]. Prepared from 12c (135 mg, 0.31 mmol)
following General procedure D to give the title compound 3 (38
mg, 0.11 mmol, 35%) as yellow solid. Rf 0.43 (4:1
Parasites and mammalian cell maintenance. Leishmania
(L.) infantum amastigotes were obtained from the spleen of
golden hamsters previously infected and purified by differential
centrifugation [39]. Peritoneal macrophages were collected by
washing the peritoneal cavity of BALB/c mice with RPMI-1640
medium (Sigma-Aldrich) supplemented with 10% FBS, and were
maintained at 37 ºC in a 5% CO2 humidified incubator [40].
Murine fibroblasts NCTC (clone L929, ATCC) were maintained
in RPMI-1640 supplemented with 10% FBS at 37 ºC in a 5%
CO2 humidified incubator. Trypanosoma cruzi (Y strain)
trypomastigotes were maintained in Rhesus monkey kidney cells
(LLC-MK2 – ATCC CCL 7), cultivated in RPMI-1640 medium
supplemented with 2% fetal calf serum at 37ºC in 5% CO2
humidified incubator.
1
CH2Cl2/MeOH); H NMR (500 MHz, MeOD) δ 7.76 (s, 1H),
6.98 (s, 1H), 6.72 (s, 1H), 6.18 (s, 1H), 6.05 (s, 1H), 4.46 (dd, J =
14.2, 4.5 Hz, 1H), 3.91 (s, 3H), 3.88 (s, 3H), 3.73 (dd, J = 12.6,
5.3 Hz, 1H), 3.40 (td, J = 12.8, 4.9 Hz, 1H), 3.25 (td, J = 12.2,
5.0 Hz, 1H), 3.12 (dd, J = 13.9, 5.0 Hz, 1H), 3.02 (dd, J = 18.6,
4.6 Hz, 1H), 2.94 (t, J = 14.4 Hz, 1H); 13C NMR (126 MHz,
MeOD) δ 150.5, 150.0, 149.8, 144.1, 126.3, 125.4, 124.2, 121.3,
117.4, 112.8, 112.3, 107.9, 102.8, 56.5, 56.4, 54.4, 42.8, 33.8,
26.3; IR (νmax / cm-1) 2981, 2361, 2341, 1558, 1540, 1457, 1248,
1114; HRMS (ES+) calc. for C19H20O4N [M+H]+ 326.1387,
found 326.1385. [α]D20 +70 (c 1.0, MeOH).
General procedure E for the reduction of carbamates 11b
and 11d to synthesise (+)-glaucine (2) and (+)-dicentrine (4).
LiAlH4 (2.0 M solution in THF, 1.2 equiv.) was added to a stirred
solution of aporphine carbamate 12b or 12d (1 equiv.) in dry
THF (0.2M) at 0 °C under a nitrogen atmosphere, and the
resulting mixture was allowed to warm to room temperature, and
then stirred for 24 h. The reaction was quenched by slow addition
of H2O (3 mL) and 1 M NaOH (5 mL) and then extracted with
Et2O (x 3). The combined organic layers were washed with brine,
dried over MgSO4, concentrated in vacuo and purified by flash
chromatography (1:0.2 CH2Cl2 / MeOH, silica gel deactivated
with 0.1% Et3N).
Evaluation of 50% Effective Concentration (EC50).
Leishmania (L.) infantum. Peritoneal macrophages (1x105
cells/well) were seeded in 16-well slide chambers (NUNC) and
mantained for 18 h at 37 ºC in 5% CO2 humidified incubator.
Cells were infected with amastigotes at a ratio of 10:1
(amastigotes/macrophage) and treated with compounds (20 to 1
µM) for 96 h. Stained slides (Giemsa) were observed in a light
microscope EVOS M5000 (Thermo, USA) using the EVOS
M5000 software for quantification of the infectivity index. The
infectivity index was used for the determination of the EC50
values and it was defined by the number of infected macrophages
(S)-1,2,9,10-Tetramethoxy-6-methyl-5,6,6a,7-tetrahydro-4H-
dibenzo[de,g]quinoline ((+)-glaucine, 2) [30]. Prepared from 12b
(210 mg, 0.51 mmol) following General procedure E to give
the title compound 2 (91 mg, 0.25 mmol, 48%) as white solid. Rf
0.23 (4:1 CH2Cl2/MeOH); 1H NMR (500 MHz, CDCl3) δ 8.09 (s,
1H), 6.78 (s, 1H), 6.59 (s, 1H), 3.93 (s, 3H), 3.90 (s, 3H), 3.88 (s,
3H), 3.65 (s, 3H), 3.19–3.11 (m, 1H), 3.05–2.99 (m, 3H), 2.70–
2.58 (m, 2H), 2.55 (s, 3H), 2.53–2.47 (m, 1H); 13C NMR (101
MHz, CDCl3) δ 152.0, 148.2, 147.6, 144.5, 129.5, 129.1, 127.4,
127.0, 124.7, 111.8, 111.0, 110.6, 62.7, 60.3, 56.1, 56.0, 55.9,
53.5, 44.2, 34.7, 29.5; IR (νmax / cm-1) 3052, 1579, 1321, 1170;
HRMS (ES+) calc. for C21H26O4N [M+H]+ 356.1856, found
X
number of intracellular amastigotes/number of total
macrophages [11]. Miltefosine was used as standard and
untreated cells as a negative control with 0.5% DMSO (v/v).
Trypanosoma cruzi. Trypomastigotes were counted in a
hemocytometer chamber and seeded at 1 x 106 cells/well in 96
well microplates. The compounds were dissolved in DMSO,
diluted (150 to 0.29 ꢀM) in RPMI-1640 medium and incubated
for 24h at 37ºC in a 5% CO2 humidified incubator. The parasite
viability was determined using the resazurin (0.011% in PBS).
The optical density was read at 570 nm using control wells
without drugs (100% viability) and without cells (blank). The
control group consisted of trypomastigotes incubated with 0.5%
(v/v) DMSO [41]. Benznidazole was used as a positive control.
For the intracellular amastigote assay, peritoneal macrophages
were dispensed (1 x 105/well) in 16 well chamber slides (NUNC,
Thermo, USA) and maintained for 24 h in the same medium at
37ºC in a 5% CO2 humidified incubator for attachment. Non-
adherent cells were removed by two step washings with medium.
After 24 h, these cells were infected with 5 x 105 culture
trypomastigotes for 4 h. Cells were treated with compounds for
48 h. After fixation with methanol and staining with Giemsa, the
slides were observed in a light microscope EVOS M5000
(Thermo, USA) using the EVOS M5000 software for
quantification of the infectivity index. The infectivity index was
used for the determination of the EC50 values and it was defined
by the number of infected macrophages X number of intracellular
20
356.1865; mp 110–115 °C [Lit. 117–118 °C][28]; [α]D +93 (c
1.0, CHCl3).
(S)-10,11-Dimethoxy-7-methyl-6,7,7a,8-tetrahydro-5H-
[1,3]dioxolo[4',5':4,5]benzo[1,2,3-de]benzo[g]quinoline
((+)-
dicentrine, 4) [29]. Prepared from 12d (340 mg, 0.88 mmol)
following General procedure E to give the title compound 4
(161 mg, 0.47 mmol, 53%) as a white solid. Rf 0.45 (4:1
CH2Cl2/MeOH); 1H NMR (500 MHz, CDCl3) δ 7.67 (s, 1H), 6.78
(s, 1H), 6.52 (s, 1H), 6.08 (d, J = 1.4 Hz, 1H), 5.93 (d, J = 1.4
Hz, 1H), 3.92 (s, 3H), 3.91 (s, 3H), 3.16–2.61 (m, 4H), 2.68–2.61
(m, 2H), 2.55 (s, 3H), 2.52–2.48 (m, 1H); 13C NMR (126 MHz,
CDCl3) δ 148.4, 147.8, 146.7, 141.9, 128.5, 126.8, 126.6, 123.7,
116.7, 111.4, 110.6, 106.9, 100.7, 62.6, 56.2, 56.0, 53.7, 44.1,
34.4, 29.4; IR (νmax / cm-1) 2957, 1607, 1515, 1462, 1266, 1215,
1095; HRMS (ES+) calc. for C20H22O4N [M+H]+ 340.1543,

9
Tetrahedron
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as the standard drug (50 to 0.78 ꢀM) and untreated cells as a
negative control with 0.5% DMSO (v/v).
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Acknowledgments
PP thanks the Swiss National Science Foundation for an SNSF
Fellowship, and the Marie Skłodowska-Curie actions for an
Individual Fellowship (GA No 832700). EAA thanks the Oxford
Internal GCRF Research England Fund (Grant no. 0006019), and
the EPSRC for additional support (EP/M019195/1). MA and
AGT thank the São Paulo State Research Foundation (FAPESP
2018/10279-6, 2018/25128-3). AGT thanks Conselho Nacional
de Pesquisa e Desenvolvimento for a Scientific Research Award.
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• Four aporphine natural products were prepared using a Bischler-Napieralski / Noyori
hydrogenation / palladium-catalyzed C–H arylation strategy.
• These asymmetric syntheses were completed in 8 steps in the longest linear sequence.
• The natural products were evaluated for anti-leishmanial and anti-trypanosomal activity
against L. infantum and T. cruzi respectively.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: