Synthesis of pyrido[2,1-a]isoquinolin-4-ones and oxazino[2,3-a]isoquinolin- 4-ones: New inhibitors of mitochondrial respiratory chain

Article abstract of DOI:10.1016/j.ejmech.2013.08.013

Benzo[a]quinolizine is an important heterocyclic framework that can be found in numerous bioactive compounds. The general scheme for the synthesis of these compounds was based on the preparation of the appropriate dihydroisoquinolines by Bischler-Napieral

Full text of DOI:10.1016/j.ejmech.2013.08.013

European Journal of Medicinal Chemistry 69 (2013) 69e76
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis of pyrido[2,1-a]isoquinolin-4-ones and oxazino[2,3-a]
isoquinolin-4-ones: New inhibitors of mitochondrial respiratory chain
,
c
a
a
Laura Moreno a, Nuria Cabedo b , Agathe Boulangé , Javier Párraga , Abraham Galán ,
*
Stéphane Leleu c, María-Jesús Sanz d e, Diego Cortes a, Xavier Franck c
,
,
**
a Departamento de Farmacología, Facultad de Farmacia, Universidad de Valencia, Burjassot, 46100 Valencia, Spain
b Centro de Ecología Química Agrícola-Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, UPV, Campus de Vera s/n, Edificio 6C, 46022
Valencia, Spain
c Normandie Univ, COBRA, UMR 6014 et FR 3038, CNRS, Univ Rouen, INSA Rouen, 1 rue Tesnières, 76821 Mont-Saint-Aignan Cedex, France
d Departamento de Farmacología, Facultad de Medicina, Universidad de Valencia, 46013 Valencia, Spain
e Institute of Health Research-INCLIVA, University Clinic Hospital of Valencia, Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Benzo[a]quinolizine is an important heterocyclic framework that can be found in numerous bioactive
compounds. The general scheme for the synthesis of these compounds was based on the preparation of
the appropriate dihydroisoquinolines by BischlereNapieralski cyclization with good yields, followed by
the Pemberton method to form the oxazinones or pyridones derivatives via acyl-ketene imine cyclo-
condensation. All the synthesized compounds were assayed in vitro for their ability to inhibit mito-
chondrial respiratory chain. Most of the tested compounds were able to inhibit the integrated electron
transfer chain, measured as NADH oxidation, which includes complexes I, III and IV, in the low micro-
molar range. Oxazino[2,3-a]isoquinolin-4-ones displayed greater activity than their pyrido[2,1-a]iso-
quinolin-4-ones analogs. Indeed, the presence of a furan ring in C2 position of oxazino[2,3-a]isoquinolin-
4-ones provided the compound (1g) with the most potent biological activity. Therefore, these com-
pounds and especially the oxazinone derivatives are in the tendency of the new less toxic antitumor
agents that target mitochondrial electron transport chain in a middle range potency.
Received 13 May 2013
Received in revised form
9 August 2013
Accepted 10 August 2013
Available online 19 August 2013
Keywords:
Benzo[a]quinolizines
BischlereNapieralski cyclodehydration
Acyl-ketene imine cyclocondensation
Respiratory chain inhibition
Cytotoxicity
Ó 2013 Elsevier Masson SAS. All rights reserved.
1. Introduction
and cytochrome c. In the electron transport chain a transfer of
electrons occurs during the oxidative phosphorylation and a proton
Isoquinoline alkaloids are a large family of natural products with
a variety of powerful biological activities [1e3], including the in-
hibition of cellular proliferation [4]. Our research group has for a
long time been focused on the isolation and synthesis of
isoquinoline-containing compounds and a variety of chemically
diverse structures with dopaminergic activity were obtained [5e9].
In addition, we have also been interested in the search of new
compounds with antitumor properties via inhibition of mito-
chondrial respiratory chain, such as Annonaceous acetogenins [10e
12]. Mitochondrial electron transport chain, comprises the enzy-
matic respiratory complexes (IeIV), the coenzyme Q (ubiquinone)
gradient is established as the energy source for the ATP generation.
In addition, when an electron escapes, it may react with molecular
ꢀ
oxygen to form the superoxide radical (O2 ꢁ) which can be con-
verted to hydrogen peroxide (H2O2) and other reactive oxygen
species (ROS). Therefore, mitochondria play essential roles in the
ATP synthesis, ROS metabolism and apoptosis. It is important that
cells preserve an apposite level of intracellular ROS to keep redox
balance and signaling cellular proliferation [13]. An increase of
intracellular ROS leads to cellular damage, including lipid peroxi-
dation, oxidative DNA modifications, protein oxidation, enzyme
inactivation and finally, the cell death. Furthermore, DNA damage
and mutations in the enzymatic complexes are related to the most
common human neurodegenerative diseases, including Parkinson’s
disease [14] and aging [15]. Damage to the mitochondria has been
also detected in cancer cells that increase the glycolytic activity
(Warburg effect) to produce the ATP required for cellular functions
[16]. Some anticancer agents have the ability to inhibit mitochon-
drial electron transport and/or increase superoxide radical
* Corresponding author. Tel.: þ34 963 87 90 58.
** Corresponding author. UMR-CNRS 6014 COBRA, Université de Rouen, 1 rue
Tesnière, 76131 Mont Saint Aignan Cedex, France. Tel.: þ33 (0) 2 35 52 24 59.
E-mail addresses: ncabedo@ceqa.upv.es, ncabedo@uv.es (N. Cabedo),
xavier.franck@insa-rouen.fr (X. Franck).
0223-5234/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2013.08.013

70
L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
depicted approaches we are now interested in the study of the
reactivity of imines since it can lead to original and biologically
unexplored frameworks. Indeed, the microwave-assisted acyl-
ketene imine cyclocondensation has been a useful strategy to
generate oxazinones. In this regard, Presset et al. [33] reported the
use of cyclic 2-diazo-1,3-diketones as acyl-ketene source by Wolff
rearrangement, and Pemberton et al. [34] started from either
Meldrum’s acid derivatives or 1,3-dioxine-4-ones to react with
dihydroisoquinolines. Therefore, we have applied the Pemberton
method using dioxinones as acyl-ketenes precursors taking
advantage of the chemical diversity generated by this procedure.
The structureeactivity relationship (SAR) of the synthesized
products was further evaluated.
Fig. 1. Structure of benzo[a]quinolizine framework and examples of natural products
containing it.
2. Results and discussion
generation in tumor cells, causing apoptosis by reducing ATP levels
and/or cell-damaging. Indeed, the research on respiratory chain
inhibitors has been focused on pharmacological [17] and agro-
chemical targets, providing compounds with high potential for
antitumor therapy [18] and pest control [19]. In addition, mito-
chondrial respiratory chain inhibitors have been also extremely
useful to establish the functional mechanisms and crystal struc-
tures of complex I [20].
Benzo[a]quinolizine is an important heterocyclic framework
that can be found in numerous bioactive compounds (Fig. 1) [1]
such as berberine [21] and emetine [22]. Furthermore, many
biologically-relevant 2-pyridones like the yohimbane-type alkaloid
sempervilam [23] and the antineoplasic agent camptothecin are
natural products that contain multi ring-fused systems (Fig. 2).
Recently, synthetic benzo[a]quinolizine derivatives have shown
effect in reversing tumor cell resistance with IC50 values in the
micromolar range [24].
The biological properties and chemical features of these mole-
cules have attracted the chemists’ interest leading to the descrip-
tion of a large number of synthetic routes [25]. Therefore, both the
attractive structure of the benzo[a]quinolizine moiety together
with their potential activity as inhibitors of cellular proliferation,
encouraged us to prepare pyrido[2,1-a]isoquinolin-4-ones and the
oxygenated analogs oxazino[2,3-a]isoquinolin-4-ones in order to
explore their properties as mitochondrial respiratory chain
inhibitors.
Several approaches for the synthesis of benzo[a]quinolizines
have been described in the literature [26], most of which involved
B-ring closure by formation of de C11aeC11b bond either by Bis-
chlereNapieralski cyclodehydration or by related palladium-
catalyzed cyclization [27,28]. Other reported methods include the
formation of C1eC11b bond via Mannich cyclization of a dihy-
droisoquinolinium ion [29] or B-ring closure by the formation of
the C7eC7a bond from the appropriate N-substituted 2-
arylpiperidine or pyridine derivatives [30]. Roy et al. [31] also
showed an effective procedure for the synthesis of benzo[a]qui-
nolizin-4-thiones through the reaction of 3,4-dihydroisoquinolines
2.1. Chemistry
The general synthetic plan to obtain these compounds was
based on the preparation of the appropriate b-phenylacetamides
(1e3) by standard methods [6,35] and further cyclization by Bis-
chlereNapieralski cyclodehydration (Scheme 1). First, 3,4-
dimethoxyphenethylamine was subjected to Ac2O/Pyr or Schot-
teneBauman conditions to give the appropriate amides (1e3).
Then, amides 1e3 were treated with POCl3 to lead to the expected
dihydroisoquinolines 1ae3a by BischlereNapieralski cyclization
with good yields.
Once the different imines were prepared following Pemberton’s
procedure [34], imine 1a was reacted with the commercially
available 2,2,6-trimethyl-4H-1,3-dioxin-4-one (4a) under neutral
or basic conditions, either using microwave irradiation or conven-
tional heating. Similar to Pemberton et al. [34], the formation of
oxazinone 1c was favored by basic conditions and it was almost
exclusively formed by the use of conventional heating. Neutral
conditions clearly favored the formation of pyridone 1b under
either conventional or microwave activation (Table 1, Scheme 2).
Once the reaction conditions were set up [38], this methodology
was applied to the synthesis of oxazinones (1ce3c, 1e, 1g) and
pyridones (1be3b, 1d, 1f) from different 1-substituted dihy-
droisoquinolines (1ae3a) and dioxinones (4ae4c). When 1-
benzyldihydroisoquinolines (2a, 3a) were used, yields were lower
than those for 1-methyldihydroisoquinoline (1a) (Schemes 3 and
4). In addition, in order to explore their biological activity, depro-
tection of the methoxy groups of compound 1b was performed.
Catechol 1h was then obtained in good yield using BBr3. To our
knowledge, compounds 1c, 1fe1h, 2b, 2c, 3b and 3c are here re-
ported for the first time and their structures were confirmed by
NMR spectral data and mass spectrometry.
2.2. Respiratory chain inhibition (SAR)
with different
b
-oxodithioesters. Furthermore,
a
conjugate
All the synthesized compounds were assayed in vitro against the
NADH oxidase activity of beef-heart submitochondrial particles, as
a model of mammalian respiratory chain. Most of the tested
addition-dipolar cycloaddition cascade has been described for the
synthesis of benzo[a]quinolizines [32]. Among the different
Fig. 2. Examples of natural 2-pyridones and structures of pyrido[2,1-a]isoquinolin-4-ones and oxazino[2,3-a]isoquinolin-4-ones.

L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
71
Scheme 1. Synthesis of dihydroisoquinolines 1ae3a. Reagents and Conditions: (a) Ac2O, Pyr, rt, 3 h; (b) POCl3, CH3CN, N2, reflux, 1 h; (c) 2-bromophenylacetyl chloride or 2-
phenylacetyl chloride, CH2Cl2, 5% aq NaOH, rt, 16 h.
Table 1
complex I or from complex II (succinate:cytochrome c reductase) to
complex III by ubiquinone, and then from complex III to complex IV
by the peripheral membrane protein cytochrome c. Thus, the
inhibitory action of the active compounds might be affecting one or
more of the electron transfer chain enzymatic complexes [39].
Compared with the highly toxic rotenone (a high-affinity in-
hibitor of complex I), the pyridone (1b, 1f, 1h, 2b and 3b) and
oxazinone (1c, 1e, 1g, 2c and 3c) cytotoxic derivatives showed a
moderate inhibitor activity that was in the same order of magni-
tude that the structural-related mycotoxins such as circumdatins
Reaction of dihydroisoquinoline 1a with 2,2,6-trimethyl-4H-1,3-dioxin-4-one under
different reaction conditions.
Solvent
Heating
Pyridone (1b)
Oxazinone (1c)
-
Toluene
MW
MW
Conventional
Conventional
70%
TEA þ Toluene
Complex mixture
78%
2%
Toluene
1%
68%
TEA þ Toluene
compounds were able to inhibit the whole respiratory chain in the
micromolar range. Indeed, this enzymatic assay detected a decay of
the NADH oxidase activity in the integrated electron transfer
chain which involves all three energy-conserving enzymatic com-
plexes: NADH:ubiquinone oxidoreductase (complex I), ubiq-
uinol:cytochrome c reductase (complex III) and cytochrome c
oxidase (complex IV). NADH is the physiological electron donor of
complex I that catalyzes the reduction of lipid soluble endogenous
coenzyme Q or ubiquinone (CoQ10 in beef heart). In fact, in the
integrated electron transfer chain, electrons are first carried from
(circumdatin E and H, IC50 ¼ 2.5 and 1.5
mM, respectively) and
flavacol (IC50 ¼ 13 M) [40]. Given that most of the respiratory
m
chain inhibitors with potential therapeutic interest act in the high
nanomolar and low micromolar ranges to avoid an extreme
toxicity, as it happens with Annonaceus acetogenins (IC50 values in
the low nanomolar range), these compounds and especially the
oxazinone derivatives can be consider effective inhibitors of the
whole respiratory chain [41] (Table 2).
In general, oxazino[2,3-a]isoquinolin-4-ones seemed to display
greater activity than their respective pyrido[2,1-a]isoquinolin-4-
Table 2
Inhibitory potency of compounds 1be3c against the NADH oxidase activity of mammalian respiratory chain.
Compound
IC50
(
m
M) ꢂ SEa
1b
8.23 ꢂ 0.98*
1c
1d
1.36 ꢂ 0.50*
>30
1e
1f
1g
1h
2b
2c
3b
3c
1.32 ꢂ 0.03*
12.50 ꢂ 1.66*
0.90 ꢂ 0.03*
3.44 ꢂ 0.05*
4.24 ꢂ 0.03*
1.39 ꢂ 0.20*
4.69 ꢂ 0.11*
1.53 ꢂ 0.10*
5.10 ꢂ 0.90* (nM)
Rotenone
*p < 0.05.
a
Data are presented as the mean ꢂ SD of thee independent determinations for each compound.

72
L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
Scheme 2. Mechanism of reaction.
Scheme 3. Synthesis of pyrido[2,1-a]isoquinolin-4-ones and oxazino [2,3-a]isoquinolin-4-ones 1be1g. Reagents and Conditions: (a) 2,2,6-trimethyl-4H-1,3-dioxin-4-one 4a,
toluene, N2, MW, 150 ꢃC, 5 min; (b) 2,2,6-trimethyl-4H-1,3-dioxin-4-one 4a, Et3N, toluene, N2, reflux, 3 h; (c) 2,2-dimethyl-6-phenyl-4H-1,3-dioxin-4-one 4b, toluene, N2, MW,
110 ꢃC, 5 min; (d) 2,2-dimethyl-6-phenyl-4H-1,3-dioxin-4-one 4b, Et3N, toluene, N2, reflux, 3h; (e) 6-(furan-2-yl)-2,2-dimethyl-4H-1,3-dioxin-4-one 4c, toluene, N2, MW, 110 ꢃC,
5 min; (f) 6-(furan-2-yl)-2,2-dimethyl-4H-1,3-dioxin-4-one 4c, Et3N, toluene, N2, reflux, 3 h; (g) BBr3, CH2Cl2, N2, rt, 2 h.

L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
73
position of oxazino[2,3-a]isoquinolin-4-ones provided the com-
pound (1g) with the most potent biological activity. Therefore,
these compounds and especially the oxazinone derivatives are in
the tendency of the new less toxic antitumor agents that target
mitochondrial electron transport chain in a middle range potency.
4. Experimental section
4.1. Chemistry
Melting points were taken on a Cambridge microscope instru-
ment coupled with a Reichert-Jung. EIMS was recorded in a VG
Auto Spec Fisons spectrometer instrument (Fisons, Manchester,
United Kingdom). Microwave reactions were performed using a
CEM Focused Microwave Synthesis System apparatus, Model
Discover. The device is a continuous focused microwave power
delivery system with operator selectable power output from 0 to
300 W. All the reactions were performed in special 10 mL glass
vessels under argon atmosphere. Reaction mixture temperatures
were measured during microwave heating with an IR surface
sensor located at the base of the Discover. The temperature was
fixed at 150 ꢃC or 110 ꢃC and maintained for 5 min (i.e., hold time:
time in which the system maintains the control parameters) and
was usually reached within 1 min (i.e., run time: maximum run
time for the method in situations where the control point is not
reached). 1H NMR and 13C NMR spectra were recorded with CDCl3
as a solvent in a Bruker AC-300, AC-400 or AC-500. Multiplicities of
13C NMR resonances were assigned by DEPT experiments. COSY,
HSQC and HMBC correlations were recorded at 400 and 500 MHz
(Bruker AC-400 or AC-500). The assignments of all compounds
were made by COSY, DEPT, HSQC and HMBC. All the reactions were
monitored by analytical TLC with silica gel 60 F254 (Merck 5554).
Scheme 4. Synthesis of pyrido[2,1-a]isoquinolin-4-ones and oxazino[2,3-a]iso-
quinolin-4-ones 2be3c. Reagents and Conditions: (a) 2,2,6-trimethyl-4H-1,3-dioxin-4-
one 4a, toluene, N2, reflux, 3 h; (b) 2,2,6-trimethyl-4H-1,3-dioxin-4-one 4a, Et3N,
toluene, N2, reflux, 3 h.
ones analogs. For instance, while the IC50 of the compound 1c was
1.36
mM, its pyridone analog (1b) showed decreased NADH oxidase
activity (IC50 ¼ 8.33
m
M). In addition, when the methyl group in C2
position of the pyridone was replaced by an aromatic group, the
activity decreased or almost disappeared (1d and 1f). By contrast,
the size and nature of the substituent in 2-position of the oxazine
did not seem to affect NADH oxidase activity. In this regard, not only
the existence of a phenyl group (1e) kept the activity but the
presence of a furan ring in C2 position provided the most potent
compound 1g. Interestingly, the deprotection of the methoxy
groups in A ring to obtain a catechol (1h) maintained the activity.
On the other hand, when the aromatic ring was placed on C1
position (series 2 and 3), the pyrido[2,1-a]isoquinolin-4-ones were
able to inhibit respiratory chain at moderated potencies (com-
Residues were purified by silica gel 60 (40e63 mm, Merck 9385)
column chromatography. Solvents and reagents were purchased
from commercial sources. Quoted yields are of purified material.
pounds 2b and 3b with IC50 of 4.24 mM and 4.69 mM respectively)
4.1.1. General procedure for the synthesis of dihydroisoquinolines
(1ae3a)
without any noticeable influence of the halogen group. However
and in agreement with the previous observations, the oxazine an-
alogs displayed greater NADH oxidase inhibition than their
4.1.1.1. 6,7-Dimethoxy-1-methyl-3,4-dihydroisoquinoline
(1a).
A solution of 3,4-dimethoxyphenethylamine (1 g, 5.52 mmol) in
dry Ac2O (10 mL) and pyridine (0.5 mL) was stirred under nitrogen
atmosphere at room temperature for 3 h. Then, the reaction
mixture was diluted with water (15 mL) and extracted with CH2Cl2.
The combined organic phases were dried over Na2SO4 and evapo-
rated to dryness to give 1.02 g (81%) of 1 as a white solid, which was
used in the next step with no further purification. Next, a solution
of N-(3,4-dimethoxyphenethyl)acetamide 1 (500 mg, 2.24 mmol)
in dry CH3CN (20 mL) was treated with POCl3 (0.37 mL, 4.1 mmol)
and refluxed for 1 h in a nitrogen atmosphere. The reaction mixture
was concentrated to dryness, re-dissolved in water and basified
with NH4OH until pH ¼ 9. The mixture was extracted with CH2Cl2.
The organic solution was dried over Na2SO4 and evaporated to
dryness to give 312 mg of 1a (67%) which was used in the next step
with no further purification. Characterization data for 1 and 1a
were in agreement with published data [35].
respective pyridones (compounds 2c and 3c with IC50 of 1.39 mM
and 1.53 respectively). Likewise, the presence of a bromine atom in
the aromatic ring did not seem to affect the activity. Therefore,
pyridone and mainly oxazine derivatives can interfering with the
mitochondrial respiratory chain by direct inhibition of one or more
enzyme complexes and/or, similar to many potent inhibitors that
mimic the quinoid head of ubiquinone, they can function as false
electron acceptors (carriers) by extracting electrons from in-
termediates in the respiratory chain in competition with their
natural substrates [42]. We could hypothesize that the different
electron density of oxazine and pyridone nucleus might establish
their different electron acceptor properties whereas substituents
on C1 or C2 positions favors the passage through the hydrophobic
environment of the ubiquinone catalytic binding site.
3. Conclusions
4.1.1.2. 6,7-Dimethoxy-1-(2-bromobenzyl)-3,4-dihydroisoquinoline
(2a). 2-Bromophenylacetyl chloride (1.2 mL, 8.25 mmol) was added
dropwise at 0 ꢃC to a solution of 3,4-dimethoxyphenetylamine (2 g,
5.50 mmol) in 15 mL of CH2Cl2 and 5% aqueous NaOH (2.5 mL). The
reaction was stirred at room temperature overnight and then
extracted with CH2Cl2 (3 ꢄ 10 mL). The combination of the organic
phases was washed with brine (2 ꢄ10 mL) and H2O (2 ꢄ10 mL), dried
over Na2SO4 and evaporated to dryness. The residue was purified by
silica gel column chromatography (hexane-EtOAc, 5:5) to afford 1.8 g
In conclusion, we have synthesized via Pemberton method
eleven benzo[a]quinolizines including pyrido[2,1-a]isoquinolin-4-
ones (1b, 1d, 1f, 1h, 2b and 3b) and oxazino[2,3-a]isoquinolin-4-
ones (1c, 1e, 1g, 2c and 3c). Most of these compounds were found
to be moderate inhibitors of the electron transport chain in the
same range that known mycotoxins. Oxazino[2,3-a]isoquinolin-4-
ones displayed greater activity than their pyrido[2,1-a]iso-
quinolin-4-ones analogs. Indeed, the presence of a furan ring in C2

74
L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
of amide 2 as a white powder (4.73 mmol, 86%). Next, a solution of 2
(100 mg, 0.27 mmol) in dry CH3CN (5 mL) was treated with POCl3
(0.07 mL, 0.75 mmol) and refluxed for 1 h in a nitrogen atmosphere
under the same conditions described above to obtain 1a. The residue
was used in the next step with no further purification. Characteriza-
tion data for 2 and 2a were in agreement with published data [36].
CH2Cl2 (5 mL) was cooled to ꢁ78 ꢃC. Then, BBr3 (0.05 mL,
0.50 mmol) was added dropwise under nitrogen atmosphere. After
15 min, the reaction mixture was warmed up to room temperature
and stirred for 2 h. The reaction was terminated by the addition of
MeOH (1 mL) dropwise and the mixture was further stirred for
another 30 min. The solvent was concentrated to dryness. The
residue was purified by silica gel column chromatography (CH2Cl2e
MeOH, 90:10) to afford 70 mg of 1h (87%) as a brown solid. Mp:
281e283 ꢃC; IR (cmꢁ1): 3328, 2971, 2734, 2589, 1646, 1509, 1298;
4.1.1.3. 6,7-Dimethoxy-1-benzyl-3,4-dihydroisoquinoline
(3a).
The compound was 3 prepared according to the procedure
described above to obtain 2a. Firstly, 2-phenylacetyl chloride
(2.18 mL, 16.5 mmol), 3,4-dimethoxyphenetylamine (2 g, 11 mmol)
and NaOH 5% (2.5 mL). The residue was purified by silica gel column
chromatography (hexane/EtOAc 5:5) to afford 1.9 g of amide 3 as a
white powder (6.27 mmol, 57%). Next, a solution of 3 (200 mg,
0.65 mmol) in dry CH3CN (15 mL) was treated with POCl3 (0.12 mL,
1.35 mmol) and refluxed for 1 h in a nitrogen atmosphere under the
same conditions described above to obtain 1a. The residue was
used in the next step with no further purification. Characterization
data for 3 and 3a were in agreement with published data [37].
1H NMR (500 MHz, CDCl3):
d
¼ 7.59 (s, 1H, H-11), 6.98 (s, 1H, H-8),
6.46 (d, J ¼ 1.1 Hz, 1H, H-3), 6.37 (d, J ¼ 1.1 Hz, 1H, H-1), 4.19 (m, 2H,
CH2-6), 2.66 (m, 2H, CH2-7), 2.03 (s, 3H, CH3); 13C NMR (125 MHz,
CDCl3):
d
¼ 165.2 (CO), 153.3 (C-9), 151.9 (C-10), 148.6 (C-2), 145.8
(C-11b), 130.5 (C-7a), 120.9 (C-11a), 117.6 (CH-1), 117.4 (CH-8), 115.6
(CH-11), 106.6 (CH-3), 41.9 (CH2-6), 29.5 (CH2-7), 23.3 (CH3); ESMS
m/z (%) 234 (100) [M]þ
4.1.3. General procedure for the synthesis of oxazino[2,3-a]
isoquinolin-4-ones (1c, 1e, 1g)
4.1.3.1. 9,10-Dimethoxy-2,11b-dimethyl-7,11b-dihydro-4H,6H- [1,3]
oxazino[2,3-a]isoquinolin-4-one (1c).
4.1.2. General procedure for the synthesis of pyrido[2,1-a]
isoquinolin-4-ones (1b, 1d, 1f)
2,2,6-Trimethyl-4H-1,3-dioxin-4-one (0.06 mL, 0.44 mmol) was
added to a stirred solution of imine 1a (46 mg, 0.22 mmol) dis-
solved in dry toluene (5 mL). Et3N (0.06 mL, 0.44 mmol) was added
and the heated mixture was refluxed for 3 h and then cooled to
room temperature. The resulting solution was diluted with CH2Cl2
and washed with saturated aq. NaHCO3, water and brine. The
combined organic extracts were dried with Na2SO4, filtered and
concentrated. Purification by column chromatography (CH2Cl2-
AcOEt, 60:40) gave 1c (43 mg, 68%). IR (cmꢁ1): 2932, 1662, 1515,
4.1.2.1. 9,10-Dimethoxy-2-methyl-6,7-dihydro-4H-pyrido[2,1-a]iso-
quinolin-4-one (1b). 2,2,6-Trimethyl-4H-1,3-dioxin-4-one (0.065 mL,
0.48 mmol) was added to a stirred solution of imine 1a (50 mg,
0.24 mmol) dissolved in dry toluene (0.5 mL). The mixture was
irradiated at 150 ꢃC, 300 W, for 5 min and then cooled to room
temperature. The resulting solution was diluted with CH2Cl2 and
washed with saturated aq. NaHCO3, water and brine. The combined
organic extracts were dried with Na2SO4, filtered and concentrated.
Purification by column chromatography (CH2Cl2eMeOH, 98:2) gave
1b (42 mg, 70%) as a white powder. Characterization data were in
agreement with published data [33,31].
1409; 1H NMR (500 MHz, CDCl3):
H-11), 5.26 (s, 1H, H-3), 4.62 (ddd, J ¼ 12.7, 5.1, 2.7 Hz; 1H, H-6
3.91 (s, 3H, OCH3-9), 3.66 (s, 3H, OCH3-10), 3.01 (m, 1H, H-6 ), 2.91
(m, 1H, H-7 ), 2.66 (m, 1H, H-7
), 1.97 (CH3-2), 1.81 (CH3-11b); 13
NMR (125 MHz, CDCl3):
¼ 163.4 (CO), 162.1 (C-2), 149.2 (C-10),
d
¼ 6.99 (s, 1H, H-8), 6.96 (s, 1H,
a),
b
a
b
C
4.1.2.2. 9,10-Dimethoxy-2-phenyl-6,7-dihydro-4H-pyrido[2,1-a]iso-
quinolin-4-one (1d). This compound was prepared following the
same procedure described above for the synthesis of 1b, and using
1a (0.24 mmol) and 2,2-dimethyl-6-phenyl-4H-1,3-dioxin-4-one
(89 mg, 0.46 mmol). The mixture was irradiated at 110 ꢃC, 300 W,
for 5 min and then cooled to room temperature. Purification by
column chromatography (CH2Cl2-AcOEt, 60:40) gave 1d (35 mg,
60%) as a yellow powder. Characterization in agreement with
published data [33,31].
d
148.8 (C-9), 128.5 (C-11a), 126.9 (C-7a), 110.7 (CH-8), 108.8 (CH-11),
98.4 (CH-3), 90.3 (C-11b), 56.1 (OCH3-10), 55.8 (OCH3-9), 35.9 (CH2-
6), 27.6 (CH2-7), 23.1 (CH3-11b), 19.8 (CH3-2); ESMS m/z (%) 290
[M þ H]þ (100)
4.1.3.2. 9,10-Dimethoxy-11b-methyl-2-phenyl-7,11b-dihydro-4H,6H-
[1,3]oxazino[2,3-a]isoquinolin-4-one (1e). This compound was pre-
pared following the same procedure described above for the syn-
thesis of 1c, and using 1a (75 mg, 0.36 mmol) and 2,2-dimethyl-6-
phenyl-4H-1,3-dioxin-4-one (178 mg, 0.88 mmol), Et3N (0.12 mL,
0.88 mmol), and dry toluene (3 mL). Purification by column chro-
matography (CH2Cl2-AcOEt, 90:10) gave 1e (40 mg, 50%). Charac-
terization data were in agreement with published data [33].
4.1.2.3. 2-(Furan-2-yl)-9,10-dimethoxy-6,7-dihydro-4H-pyrido[2,1-
a]isoquinolin-4-one (1f). This compound was prepared following
the same procedure described above for the synthesis of 1b, and
using 1a (0.24 mmol) and 6-(furan-2-yl)-2,2-dimethyl-4H-1,3-
dioxin-4-one (93 mg, 0.48 mmol). The mixture was irradiated at
110 ꢃC, 300 W, for 5 min and then cooled to room temperature.
Purification by column chromatography (CH2Cl2-AcOEt, 70:30)
gave 1f (23 mg, 31%) as a yellow oil. IR (cmꢁ1): 2932, 1648, 1566,
4.1.3.3. 2-(Furan-2-yl)-9,10-dimethoxy-11b-methyl-7,11b-dihydro-
4H,6H- [1,3]oxazino[2,3-a]isoquinolin-4-one (1g). This compound
was prepared following the same procedure described above for
the synthesis of 1c, and using 1a (50 mg, 0.24 mmol) and 6-(furan-
2-yl)-2,2-dimethyl-4H-1,3-dioxin-4-one (126 mg, 0.66 mmol), Et3N
(0.06 mL, 0.33 mmol), and dry toluene (2 mL). Purification by col-
umn chromatography (CHCl2-AcOEt, 90:10) gave 1g (20 mg, 26%) as
a white powder. Mp: 123e125 ꢃC; IR (cmꢁ1): 2943, 1653, 1515, 1414,
1504, 1459, 1341; 1H NMR (500 MHz, CDCl3):
d
¼ 7.57 (d, J ¼ 1.3 Hz,
1H, H-30), 7.23 (s, 1H, H-11), 6.87 (d, J ¼ 3.3 Hz, 1H, H-50), 6.85 (d,
J ¼ 1.7 Hz, 1H, H-1), 6.79 (d, J ¼ 1.7 Hz, 1H, H-3), 6.75 (s, 1H, H-8),
6.54 (dd, J ¼ 3.5, 1.8 Hz, 1H, H-40), 4.27 (m, 2H, CH2-6), 3.98 (OCH3-
9), 3.94 (OCH3-10), 2.92 (m, 2H, CH2-7); 13C NMR (125 MHz, CDCl3):
d
¼ 162.7 (CO), 151.1 (C-9), 151.0 (C-10), 148.5 (C-2), 144.0 (CH-30),
1364; 1H NMR (500 MHz, CDCl3):
d
¼ 7.53 (d, J ¼ 1.1 Hz, 1H, H-30),
143.5 (C-11b), 139.6 (C-10), 129.1 (C-7a), 121.5 (C-11a), 112.1 (CH-40),
110.4 (CH-8), 109.9 (CH-3), 109.4 (CH-50), 108.2 (CH-11), 98.0 (CH-
1), 56.3 (OCH3-9), 56.0 (OCH3-10), 39.1 (CH2-6), 27.6 (CH2-7); ESMS
m/z (%) 324 [M þ H]þ (100).
7.02 (s, 1H, H-11), 6.80 (d, J ¼ 3.3 Hz,1H, H-50), 6.62 (s, 1H, H-8), 6.50
(dd, J ¼ 3.4, 1.8 Hz, 1H, H-40), 5.89 (s, 1H, H-3), 4.67 (ddd, J ¼ 13.0,
5.3, 2.8 Hz, 1H, H-6
a), 3.94 (OCH3-10), 3.87 (OCH3-9), 3.09 (m, 1H,
H-6 ), 2.97 (m, 1H, H-7
b
a
), 2.70 (dt, J ¼ 13.5, 3.3 Hz, 1H, H-7
b), 1.89
¼ 162.2 (CO), 152.3 (C-2),
(CH3-11b); 13C NMR (125 MHz, CDCl3):
d
4.1.2.4. 9,10-Dihydroxy-2-methyl-6,7-dihydro-4H-pyrido[2,1-a]iso-
quinolin-4-one (1h). A solution of 1b (75 mg, 0.33 mmol) in dry
149.4 (C-9), 148.1 (C-10), 147.1 (C-10), 145.1 (CH-30), 128.4 (C-11a),
127.1 (C-7a), 111.8 (CH-40, CH-50), 110.7 (CH-8), 108.9 (CH-11), 94.9

L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
75
(CH-3), 90.7 (C-11b), 56.1 (OCH3-10), 55.9 (OCH3-9), 36.2 (CH2-6),
1H, H-7
CDCl3):
a
d
), 2.50 (m, 1H, H-7
¼ 162.7 (CO), 161.9 (C-2), 149.3 (C-9), 147.3 (C-10), 134.6
b
), 2.05 (s, 3H, CH3); 13C NMR (125 MHz,
27.6 (CH2-7), 23.0 (CH3-11b); ESMS m/z (%) 341 [M]þ (100).
(C-10), 132.8 (CH-30), 132.5 (CH-60), 128.6 (CH-40), 127.5 (C-20), 126.9
(CH-50),126.8 (C-7a),126.4 (C-11a),110.3 (CH-8),109.6 (CH-11), 98.8
(CH-3), 91.7 (C-11b), 55.8 (OCH3-9), 55.8 (OCH3-10), 41.8 (CH2Ph),
36.7 (CH2-6), 27.1 (CH2-7), 19.8 (CH3); ESMS m/z (%) 444 (100)
[Mþ1]þ
4.1.4. General procedure for the synthesis of pyrido[2,1-a]
isoquinolin-4-ones 2be3b
4.1.4.1. 1-(2-Bromophenyl)-9,10-dimethoxy-2-methyl-6,7-dihydro-
4H-pyrido[2,1-a]isoquinolin-4-one (2b). A residue of the imine 2a
(from 100 mg, 0.27 mmol of amide 2) was dissolved in dry toluene
(5 mL), and treated with 2,2,6-trimethyl-4H-1,3-dioxin-4-one
(0.06 mL, 0.44 mmol). The reaction mixture was refluxed under ni-
trogen atmosphere for 3 h and then cooled to room temperature. The
resulting solution was diluted with CH2Cl2 and washed with satu-
rated aq. NaHCO3, water and brine. The combined organic extracts
were dried with Na2SO4, filtered and concentrated. Purification by
column chromatography (CH2Cl2-AcOEt, 10:90) gave 2b (40 mg, 33%
from amide 2) as a white solid. Mp: 216e218 ꢃC. IR: 2961, 1639,1491,
4.1.5.2. 11B-Benzyl-9,10-dimethoxy-2-methyl-7,11b-dihydro-4H,6H-
[1,3]oxazino[2,3-a]isoquinolin-4-one (3c). This compound was pre-
pared following the same procedure described above for the syn-
thesis of 2c, and using a residue of the imine 3a (from 200 mg,
0.65 mmol of amide 3) in dry toluene (10 mL), and treated with
2,2,6-trimethyl-4H-1,3-dioxin-4-one (0.18 mL,1.30 mmol) and Et3N
(0.18 mL). The reaction mixture was refluxed under nitrogen at-
mosphere for 2.5 h and then cooled to room temperature. Purifi-
cation by column chromatography (CH2Cl2eMeOH, 95:5) gave 3c
(80 mg, 33% from amide 3). IR (cmꢁ1): 2933, 1698, 1515, 1373, 1324,
1466, 1450, 1212; 1H NMR (500 MHz, CDCl3):
d
¼ 7.65 (dd, 1H,
J ¼ 8.02, 1.12 Hz, CH-20), 7.31 (td,1H, J ¼ 7.49, 1.19 Hz, CH-60), 7.20 (td,
1H, J ¼ 7.77,1.71 Hz, CH-40), 7.14 (dd,1H, J ¼ 7.55,1.65 Hz, CH-40), 6.66
1212; 1H NMR (500 MHz, CDCl3):
d
¼ 7.18 (m, 3H, CH-30, CH-40, CH-
(s, 1H, H-8), 6.52 (s, 1H, H-3), 6.43 (s, 1H, H-11), 4.45 (m, 1H, H-6
a),
50), 7.83 (m, 2H, CH-20, CH-60), 6.70 (s, 1H, H-11), 6.54 (s, 1H, H-8),
3.97 (m, 1H, H-6
b
), 3.86 (OCH3-9), 3.23 (OCH3-10), 2.85 (m, 2H, CH2-
5.36 (s, 1H, H-3), 4.16 (m, 1H, H-6
3.53 (m, 2H, CH2Ph), 2.87 (m, 1H, H-6
1H, H-7 d
), 2.04 (s, 3H, CH3); 13C NMR (125 MHz, CDCl3):
a
), 3.86 (OCH3-9), 3.75 (OCH3-10),
), 2.72 (m, 1H, H-7 ), 2.35 (m,
¼ 163.1
7), 1.88 (s, 3H, CH3); 13C NMR (125 MHz, CDCl3):
d
¼ 161.7 (CO), 150.2
b
a
(C-9),149.5 (C-10),146.5 (C-2),140.4 (C-1),140.1 (C-10), 133.2 (CH-30),
132.7 (CH-50),131.6 (C-11b),129.2 (CH-40), 128.2 (CH-60), 126.5 (C-20),
121.4 (C-11a), 118.4 (C-7a), 117.7 (CH-3), 112.4 (CH-11), 109.6 (CH-8),
55.7 (OCH3-9), 55.3 (OCH3-10), 40.3 (CH2-6), 28.6 (CH2-7), 21.0
(CH3); ESMS m/z (%) 425 [M þ H]þ (100).
b
(CO), 162.2 (C-2), 149.2 (C-9), 147.4 (C-10), 134.6 (C-10), 130.9 (CH-20,
CH-60), 128.0 (CH-30, CH-50), 127.8 (C-7a), 127.0 (CH-40), 126.3 (C-
11a), 110.4 (CH-11), 109.7 (CH-8), 99.1 (CH-3), 91.8 (C-11b), 55.9
(OCH3-9), 55.8 (OCH3-10), 42.7 (CH2Ph), 37.2 (CH2-6), 27.2 (CH2-7),
19.8 (CH3); ESMS m/z (%) 366 (100) [M þ H]þ.
4.1.4.2. 9,10-Dimethoxy-2-methyl-1-phenyl-6,7-dihydro-4H-pyrido
[2,1-a] isoquinolin-4-one (3b). This compound was prepared
following the same procedure described above for the synthesis of
2b, and using a residue of the imine 3a (from 200 mg, 0.65 mmol of
amide 3) and treated with 2,2,6-trimethyl-4H-1,3-dioxin-4-one
(0.18 mL, 1.30 mmol) in dry toluene (10 mL). Purification by col-
umn chromatography (CH2Cl2eMeOH, 95:5) gave 3b (75 mg, 33%
from amide 3). IR (cmꢁ1): 2933, 1690, 1517, 1373, 1262, 1212; 1H
4.2. Biological assays
NADH and other biochemical reagents were purchased from
SigmaeAldrich Chemical Co. Stock solutions (30 mM in absolute
EtOH) of target compounds were prepared and kept in the dark
at ꢁ20 ꢃC. Appropriate dilutions (10e30 mM) were made before the
experiments. Inverted submitochondrial particles (SMP) from beef
heart were obtained following Fato’s method [39] by extensive
ultrasonic disruption of frozen-thawed mitochondria to produce
open membrane fragments where permeability barriers to sub-
strates were lost, and they were stored at ꢁ70 ꢃC at 28 mg/mL
(protein measured by the Bradford method). The beef heart SMP
were transferred to glass test tubes, diluted to 0.5 mg/mL in
250 mM sucrose and 10 mM TriseHCl buffer, pH 7.4, and treated
NMR (500 MHz, CDCl3):
d
¼ 7.45 (m, 2H, CH-30, CH-50), 7.30 (m, 1H,
CH-40), 7.29 (m, 2H, CH-20, CH-60), 6.96 (s, 1H, H-8), 6.89 (s, 1H, H-
11), 6.16 (s, 1H, H-3), 4.63 (m, 1H, H-6
(OCH3-9), 3.25 (OCH3-10), 2.92 (m, 2H, CH2-7), 1.93 (s, 3H, CH3); 13
NMR (125 MHz, CDCl3):
a), 3.98 (m, 1H, H-6b), 3.83
C
d
¼ 161.0 (CO), 148.9 (C-9), 148.1 (C-2),
146.5 (C-10), 140.2 (C-1), 135.6 (C-11b), 132.5 (C-10), 128.9 (CH-20,
CH-60), 128.7 (C-7a), 128.6 (CH-30, CH-50), 127.9 (CH-40), 123.5 (C-
11a), 118.7 (CH-3), 111.4 (CH-8), 109.7 (CH-11), 55.8 (OCH3-9), 55.4
(OCH3-10), 41.3 (CH2-6), 27.2 (CH2-7), 19.0 (CH3); ESMS m/z (%) 347
(100) [M]þ
with 300
periments. Aliquots of the stocks solutions (1
successively to 500 L of the SMP preparations with 5 min of in-
mM NADH to activate complex I before starting the ex-
m
L) were added
m
cubation on ice after each addition (ethanol never exceeded 2% of
the total volume). After incubation, aliquots of the treated SMP
4.1.5. General procedure for the synthesis of oxazino[2,3-a]
isoquinolin-4-ones (2ce3c)
(25
buffer (pH 7.4) and 1 mM EDTA, in a cuvette at 22 ꢃC, always in the
presence of 75 M NADH. Immediately, NADH oxidase activity was
mL) were diluted to 6 mg/mL in 50 mM potassium phosphate
4.1.5.1. 11B-(2-Bromobenzyl)-9,10-dimethoxy-2-methyl-7,11b-dihy-
dro-4H,6H- [1,3]oxazino[2,3-a]isoquinolin-4-one (2c). A residue of
the imine 2a (from 100 mg, 0.27 mmol of amide 2) in dry toluene
(5 mL) was treated with 2,2,6-trimethyl-4H-1,3-dioxin-4-one
(0.06 mL, 0.44 mmol) and Et3N (0.06 mL, 0.44 mmol). The reac-
tion mixture was refluxed under nitrogen atmosphere for 3 h and
then cooled to room temperature. The resulting solution was
diluted with CH2Cl2 and washed with saturated aq. NaHCO3, water
and brine. The combined organic extracts were dried with Na2SO4,
filtered and concentrated. Purification by column chromatography
(Toluene-AcOEt, 70:30) gave 2c (15 mg, 12% from amide 2). IR
(cmꢁ1): 2938, 1664, 1515, 1460, 1264, 1212; 1H NMR (500 MHz,
m
measured as the aerobic oxidation of NADH. Reaction rates were
calculated for each inhibitor (at increasing concentrations) from the
linear decrease of NADH concentration (
l
¼ 340 nm,
3
¼ 6.22 mMꢁ1
cmꢁ1) measured in an end-window photomultiplier spectropho-
tometer ATI-Unicam UV4-500. The inhibitory concentration (IC50
)
was taken as the final compound concentration in the assay cuvette
that yielded 50% inhibition of the NADH oxidase activity. Data from
individual titrations were used to assess the means and standard
deviations of three independent assays for each compound.
CDCl3):
d
¼ 7.44 (m, 1H, C-20), 7.16 (m, 1H, CH-50), 7.07 (m, 1H, CH-
Acknowledgments
40), 6.94 (m, 1H, CH-60), 6.56 (s, 1H, H-11), 6.55 (s, 1H, H-8), 5.29 (s,
1H, H-3), 4.33 (m, 1H, H-6
3.66 (OCH3-10), 3.65 (m, 1H, CH2Ph-
a
), 3.84 (OCH3-9), 3.80 (m, 1H, CH2Ph-
a
),
This study was supported by grants SAF2011-23777, Spanish
Ministry of Economy and Competitiveness, RIER RD08/0075/0016,
b
), 3.18 (m, 1H, H-6 ), 2.81 (m,
b

76
L. Moreno et al. / European Journal of Medicinal Chemistry 69 (2013) 69e76
[18] V. Gogvadze, S. Orrenius, B. Zhivotovsky, Mitochondria in cancer cells, what is
so special about them? Trends Cell Biol. 18 (2008) 165e173.
[19] F. Schuler, J.E. Casida, The insecticide target in the PSST subunit of complex I,
Pest. Manag. Sci. 57 (2001) 932e940.
[20] R. Baradaran, J.M. Berrisford, G.S. Minhas, L.A. Sazanov, Crystal structure of the
entire respiratory complex I, Nature 494 (2013) 443e448.
Carlos III Health Institute, Spanish Ministry of Health and the Eu-
ropean Regional Development Fund (FEDER). A. Galán was the
recipient of a fellowship from FPU program of Spanish Ministry of
Education, Culture and Sport.
[21] G. Memetzidis, J. Stambach, L. Jung, C. Schott, C. Heitz, J.C. Stocklet, Structure-
affinity relationships of berbines or 5,6,13,13a-tetrahydro-8H-dibenzo[a,g]
Appendix A. Supplementary data
quinolizines at a-adrenoceptors, Eur. J. Med. Chem. 26 (1991) 605e611.
[22] C. Szantay, L. Toke, P. Kolonits, Synthesis of protoemetine. A new total syn-
thesis of emetine, J. Org. Chem. 31 (1966) 1447e1451.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.ejmech.2013.08.013.
[23] N. Kogure, C. Nishiya, M. Kitajima, H. Takayama, Six new indole alkaloids from
Gelsemium sempervirens Ait. f. Tetrahedron Lett. 46 (2005) 5857e5861.
[24] Y. Kanintronkul, R. Worayuthakarn, N. Thasana, P. Winayanuwattikun,
K. Pattanapanyasat, R. Surarit, S. Ruchirawat, J. Svasti, Overcoming multidrug
resistance in human lung cancer with novel benzo[a]quinolizin-4-ones,
Anticancer Res. 31 (2011) 921e927.
References
[1] K.W. Bentley, b-Phenylethylamines and the isoquinoline alkaloids, Nat. Prod.
[25] W. Du, Towards new anticancer drugs: a decade of advances in synthesis of
camptothecins and related alkaloids, Tetrahedron 59 (2003) 8649e8687.
[26] S.U. Saraf, The chemistry of the benzo(a)- and benzo(c)quinolizinium ions,
Heterocycles 16 (1981) 803e841.
Rep. 22 (2005) 249e268.
[2] S.S. Kulkarni, S. Singh, J.R. Shah, W.-K. Low, T.T. Talele, Synthesis and SAR
optimization of quinazolin-4(3H)-ones as poly(ADP-ribose)polymerase-1 in-
hibitors, Eur. J. Med. Chem. 50 (2012) 264e273.
[27] S. Kirschbaum, H. Waldeman, Construction of the tricyclic benzoquinolizine
ring system by combination of a tandem Mannich-Michael reaction with a
Heck reaction, Tetrahedron Lett. 38 (1997) 2829e2832.
[28] S. Kirschbaum, H. Waldeman, Three-step access to the tricyclic benzo[a]qui-
nolizine ring system, J. Org. Chem. 63 (1998) 4936e4946.
[29] M. Strandtmann, M.P. Cohen, J. Shravel, A new general synthesis of benzo[a]
quinolizines, dibenzo[a, f]quinolizines, and related compounds, J. Org. Chem.
31 (1966) 797e802.
[3] O.P.J. van Lindena, C. Farenc, W.H. Zoutmanc, L. Hameetmanc, M. Wijtmans,
R. Leurs, C.P. Tensenc, G. Siegal, I.J.P. de Escha, Fragment based lead discovery
of small molecule inhibitors for the EPHA4 receptor tyrosine kinase, Eur. J.
Med. Chem. 47 (2012) 493e500.
[4] R.J. Juszczak, J.H. Russell, Inhibition of cytotoxic T lymphocyte-mediated lysis
and cellular proliferation by isoquinoline sulfonamide protein kinase in-
hibitors. Evidence for the involvement of protein kinase C in lymphocyte
function, J. Biol. Chem. 264 (1989) 810e815.
[30] M. Rubiralta, A. Diez, A. Balet, J. Bosch, New synthesis of benzo[a]quinolizidin-
2-ones via protected 2-aryl-4-piperidones, Tetrahedron 43 (1987) 3021e
3030.
[5] A. Bermejo, P. Protais, M.A. Blázquez, K.S. Rao, M.C. Zafra-Polo, D. Cortes,
Dopaminergic isoquinoline alkaloids from roots of Xylopia papuana, Nat. Prod.
Lett. 6 (1995) 57e62.
[31] A. Roy, S. Nandi, H. Ila, H. Junjappa, An expedient route to 2,3-substituted and
[6] I. Berenguer, N. El Aouad, S. Andujar, V. Romero, F. Suvire, T. Freret,
A. Bermejo, M.D. Ivorra, R.D. Enriz, M. Boulouard, N. Cabedo, D. Cortes, Tet-
rahydroisoquinolines as dopaminergic ligands: 1-butyl-7-chloro-6-hydroxy-
tetrahydroisoquinoline, a new compound with antidepressant-like activity in
mice, Bioorg. Med. Chem. 17 (2009) 4968e4975.
[7] N. El Aouad, I. Berenguer, V. Romero, P. Marín, A. Serrano, S. Andujar, F. Suvire,
A. Bermejo, M.D. Ivorra, R.D. Enriz, N. Cabedo, D. Cortes, Structure-activity
relationship of dopaminergic halogenated 1-benzyl-tetrahydroisoquinoline
derivatives, Eur. J. Med. Chem. 44 (2009) 4616e4621.
[8] N. Cabedo, I. Berenguer, B. Figadère, D. Cortes, An overview on benzyliso-
quinoline derivatives with dopaminergic and serotonergic activities, Curr.
Med. Chem. 16 (2009) 2441e2467.
[9] S. Andujar, F. Suvire, I. Berenguer, N. Cabedo, P. Marín, L. Moreno, M.D. Ivorra,
D. Cortes, R.D. Enriz, Tetrahydroisoquinolines acting as dopaminergic ligands.
A molecular modeling study using MD simulations and QM calculations,
J. Mol. Model. 18 (2012) 419e431.
[10] A. Bermejo, B. Figadere, M.C. Zafra-Polo, I. Barrachina, E. Estornell, D. Cortes,
Acetogenins from annonaceae. Recent progress in isolation, synthesis, and
mechanisms of action, Nat. Prod. Rep. 22 (2005) 269e303.
[11] S. Granell, I. Andreu, D. Marti, A. Cave, R. Aragon, E. Estornell, D. Cortes,
M.C. Zafra-Polo, Bisbenzyltetrahydroisoquinolines, a new class of inhibitors
of the mitochondrial respiratory chain complex I, Planta Med. 70 (2004)
266e268.
fused benzo[a]quinolizine-4-thione framework via ring annulation with
oxodithioesters, J. Org. Lett. 3 (2001) 229e232.
b-
[32] C.J. Stearman, M. Wilson, A. Padwa, Conjugate addition-dipolar cycloaddition
cascade for the synthesis of benzo[a]quinolizine and indolo[a]quinolizine
scaffolds: application to the total synthesis of (ꢂ)-yohimbenone, J. Org. Chem.
74 (2009) 3491e3499.
[33] M. Presset, Y. Coquerel, J. Rodriguez, Microwave-assisted domino and multi-
component reactions with cyclic acylketenes: expeditious syntheses of oxa-
zinones and oxazindiones, Org. Lett. 11 (2009) 5706e5709.
[34] N. Pemberton, L. Jakobsson, F. Almqvist, Synthesis of multi ring-fused 2-
pyridones via an acyl-ketene imine cyclocondensation, Org. Lett. 8 (2006)
935e938.
[35] M.R. Pitts, J.R. Harrison, C.J. Moody, Indium metal as a reducing agent in
organic synthesis, J. Chem. Soc. Perkin Trans. 1 (2001) 955e977.
[36] M. Lafrance, N. Blaquière, K. Fagnou, Direct intramolecular arylation of
unactivated arenes: application to the synthesis of aporphine alkaloids, Chem.
Commun. 24 (2004) 2874e2875.
[37] M. Ariza, A. Díaz, R. Suau, M. Valpuesta, Synthesis of new dopamine D1
antagonist SCH 23390 analogues by the stereoselective Stevens rearrange-
ment, Eur. J. Org. Chem. (2011) 6507e6518.
[38] P.A. Peixoto, A. Boulangé, S. Leleu, X. Franck, Versatile synthesis of acylfur-
anones by reaction of acylketenes with a-hydroxy ketones: application to the
one-step multicomponent synthesis of cadiolide B and its analogues, Eur. J.
Org. Chem. (2013) 3316e3327.
[12] I. Andreu, N. Cabedo, J.R. Tormo, A. Bermejo, R. Mello, D. Cortes, Synthesis of
N-diisopropyl phosphoryl benzyltetrahydroisoquinoline,
a new class of
[39] R. Fato, E. Estornell, S. Bernando, F. Palloti, G. Parenti-Castelli, G. Lenaz,
Steady-state kinetics of the reduction of coenzyme Q analogs by complex I
(NADH:ubiquinone oxidoreductase) in bovine heart mitochondria and sub-
mitochondrial particles, Biochemistry 35 (1996) 2705e2716.
[40] M.P. López-Gresa, M.C. González, J. Primo, P. Moya, V. Romero, E. Estornell,
Circumdatin H, a new inhibitor of mitochondrial NADH oxidase from Asper-
gillus ochraceous, J. Antibiot. 58 (2005) 416e419.
[41] A. Bermejo, J.R. Tormo, N. Cabedo, E. Estornell, B. Figadère, D. Cortes, Enan-
tiospecific semisynthesis of (þ)-almuheptolide-A, a novel natural heptolide
inhibitor of the mammalian mitochondrial respiratory chain, J. Med. Chem. 41
(1998) 5158e5166.
[42] M. Degli Esposti, A. Ngo, A. Ghelli, B. Benelli, V. Carelli, H. McLennan,
A.W. Linnane, The interaction of Q analogs, particularly hydroxydecyl ben-
zoquinone (idebenone), with the respiratory complexes of heart mitochon-
dria, Arch. Biochem. Biophys. 330 (1996) 395e400.
mitochondrial complexes I and III inhibitors, Bioorg. Med. Chem. Lett. 10
(2000) 1491e1494.
[13] D. Trachootham, W. Lu, M.A. Ogasawara, N. Rivera-del Valle, P. Huang, Redox
regulation of cell survival, Antioxid. Redox Signal. 10 (2008) 1343e1374.
[14] T.M. Dawson, V.L. Dawson, Molecular pathways of neurodegeneration in
Parkinson’s disease, Science 302 (2003) 819e822.
[15] R.S. Balaban, S. Nemoto, T. Finkel, Mitochondria, oxidants, and aging, Cell 120
(2005) 483e495.
[16] H. Pelicano, L. Feng, Y. Zhou, J.S. Carew, E.O. Hileman, W. Plunkett,
M.J. Keating, P. Huang, Inhibition of mitochondrial respiration.
A novel
strategy to enhance drug-induced apoptosis in human leukemia cells by a
reactive oxygen species-mediated mechanism, J. Biol. Chem. 278 (2003)
37832e37839.
[17] A. Szewczyk, L. Wojtczak, Mitochondria as a pharmacological target, Phar-
macol. Rev. 54 (2002) 101e127.