Synthesis and antiplasmodial activity of aminoalkylamino-substituted neocryptolepine derivatives

Article abstract of DOI:10.1021/jm801490z

A series of chloro- and aminoalkylamino-substituted neocryptolepine (5-methyl-5H-indolo[2,3-b]quinoline) derivatives were synthesized and evaluated as antiplasmodial agents. The evaluation also included cytotoxicity (MRC5 cells), inhibition of β-hematin f

Full text of DOI:10.1021/jm801490z

J. Med. Chem. 2009, 52, 2979–2988
2979
Synthesis and Antiplasmodial Activity of Aminoalkylamino-Substituted Neocryptolepine
Derivatives
Ibrahim El Sayed,† Pieter Van der Veken,† Koen Steert,† Liene Dhooghe,‡ Steven Hostyn,§ Gitte Van Baelen,§ Guy Lemie`re,§
Bert U. W. Maes,§ Paul Cos,| Louis Maes,| Jurgen Joossens,† Achiel Haemers,† Luc Pieters,‡ and Koen Augustyns*,†
Laboratory of Medicinal Chemistry and Laboratory of Pharmacognosy and Pharmaceutical Analysis, UniVersity of Antwerp,
UniVersiteitsplein, 1, 2610, Antwerp, Belgium, Laboratory of Organic Chemistry and Laboratory of Microbiology, UniVersity of Antwerp,
Groenenborgerlaan, 171, 2020, Antwerp, Belgium
ReceiVed NoVember 26, 2008
A series of chloro- and aminoalkylamino-substituted neocryptolepine (5-methyl-5H-indolo[2,3-b]quinoline)
derivatives were synthesized and evaluated as antiplasmodial agents. The evaluation also included cytotoxicity
(MRC5 cells), inhibition of ꢀ-hematin formation, and DNA interactions (DNA-methyl green assay).
Introduction of aminoalkylamino chains increased the antiplasmodial activity of the neocryptolepine core
substantially. The most efficient compounds showed antiplasmodial activities in the nanomolar range. N1,N1-
Diethyl-N4-(5-methyl-5H-indolo[2,3-b]quinolin-8-yl)pentane-1,4-diamine 11c showed an IC50 of 0.01 µM
and a selectivity index of 1800.
Introduction
(5-methyl-5H-indolo[2,3-c]quinoline) (5),5-7 which also showed
antiplasmodial activity against chloroquine-resistant P. falci-
parum. Neocryptolepine appeared to have lower affinity for
DNA and topoisomerase II compared to cryptolepine.8,9
In a previous paper, we reported on the synthesis and
biological activity of a series of substituted neocryptolepine
derivatives. 2-Bromo-5-methyl-5H-indolo[2,3-b]quinoline (2-
bromoneocryptolepine) was the most promising compound. It
showed an IC50 of 4.0 µM against chloroquine resistant P.
falciparum in the absence of obvious cytotoxicity (MRC5 cells:
IC50 > 32 µM). It showed low affinity for DNA and no
topoisomerase II inhibition. Inhibition of ꢀ-hematin formation
could be demonstrated.10,11 However, several analogues have
been described for DNA interfering activity and are under
investigation as anticancer drugs.12,13
In this paper, we report on the further exploration of the
antimalarial potential of the neocryptolepine core. We tried to
reduce the cytotoxicity by introducing halo-substituents as in
2-bromoneocryptolepine in order to reduce the DNA-intercalat-
ing properties of the parent compound. Therefore, a functional
assay was used to measure DNA-interactions, i.e., the DNA-
methyl green assay. In addition, we tried to improve the
biological activity of the parent compound by substituting it
with basic (aminoalkylamino) side chains. A basic side chain
is indeed an important feature for the activity of chloroquine
and is required for the accumulation into the food vacuole and,
hence, for inhibition of hemozoin formation. Therefore, a
functional assay was used to measure the inhibition of ꢀ-hematin
formation, the in vitro process that is equivalent to hemozoin
formation in the parasite. We prepared a series of neocryptol-
epine analogues with chloro-substituents, an N1,N1-diethylpen-
tane-1,4-diamine group (the side chain of chloroquine), and a
combination of both in various positions. This series was
extended to other aminoalkylamino groups and to norneocryp-
tolepine (quinindoline, 6H-indolo[2,3-b]quinoline) for the 11-
substituted compounds.
Plants are still important resources for the discovery of new
drugs. The potential of natural compounds as new drug leads
is clearly illustrated by the discovery and development of
artemisinin-inspired endoperoxides as antimalarial drugs. The
importance of artemisinins as antimalarials has encouraged
research for other plant derived antiparasitic agents. A promising
plant appeared to be Cryptolepis sanguinolenta. The roots of
this climbing shrub are used in Central and West Africa in
traditional medicine for the treatment of malaria. Its main
alkaloid, cryptolepine (5-methyl-5H-indolo[3,2-b]quinoline) (1)
has been shown to have potent antiplasmodial activity both
against chloroquine-sensitive and chloroquine-resistant Plas-
modium falciparum (Figure 1).1,2 Further experiments indicated
that cryptolepine inhibits the formation of ꢀ-hematin, a mech-
anism also responsible for the antiplasmodial activity of
chloroquine (2). Unfortunately, cryptolepine is also a DNA
intercalating agent and an inhibitor of topoisomerase II, resulting
in a high level of cytotoxicity. It was speculated that substitution
of cryptolepine could be favorable for more selective antima-
larial activity by decreasing the DNA interfering action, and
several series of substituted cryptolepines have been synthesized.1,2
A dibromoanalogue, 2,7-dibromo-5-methyl-5H-indolo[3,2-b]-
quinoline, was found 10 times more potent than cryptolepine,
did not show cross-resistance with chloroquine, and appeared
not toxic in mice but was still DNA-intercalating. Moreover,
compounds with a 5H-indolo[3,2-b]quinoline core displayed
antihyperglycemic, anticholinergic, and antiadrenergic activity.1,2
In a search for novel antimalarial compounds, we focused
on minor alkaloids of C. sanguinolenta such as neocryptolepine
(5-methyl-5H-indolo[2,3-b]quinoline, cryptotackieine) (3), isoc-
ryptolepine (5-methyl-5H-indolo[3,2-c]quinoline, cryptosan-
guinolentine) (4),3,4 and the non-natural isoneocryptolepine
* To whom correspondence should be addressed. Phone: +32(0)38202703.
Fax: +32(0)38202739. E-mail: koen.augustyns@ua.ac.be.
†
Laboratory of Medicinal Chemistry, University of Antwerp.
Laboratory of Pharmacognosy and Pharmaceutical Analysis, University
During the course of our work, this strategy was applied to
cryptolepine. 11-Substituted cryptolepine derivatives were re-
ported, and these derivatives appeared more potent and less toxic
than the parent compound although the selectivity ratios were
still rather moderate (<50).14 Basic side chain analogues of
‡
of Antwerp.
§
Laboratory of Organic Chemistry, University of Antwerp.
Laboratory of Microbiology, Parasitology, and Hygiene, University of
|
Antwerp.
10.1021/jm801490z CCC: $40.75
2009 American Chemical Society
Published on Web 04/13/2009

2980 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9
El Sayed et al.
Figure 1. Structures of cryptolepine (1), chloroquine (2), neocryptolepine (3), isocryptolepine (4), and isoneocryptolepine (5).
Scheme 1. Synthesis of Neocryptolepines with A or D-Ring
norcryptolepine were reported as telomerase inhibitors.15 Weak
telomerase inhibiting properties had already been demonstrated
for neocryptolepine.16 Amino-substituted derivatives of neoc-
ryptolepine were not reported until now, apart from 11-anilino
analogues of norneocryptolepine that were studied as anticancer
agents.17
Substitutionsa
Chemistry
Several pathways for the synthesis of the neocryptolepine core
have been developed. Cyclizations starting from a quinoline,
an indole, and double cyclizations are described.
Double cyclizations include thermal biradical or Lewis acid
induced cyclizations of N-[2-(alk-1-yn-1-yl)phenyl]-N′-phenyl-
carbodiimide10,18-20 and N-[2-(alk-1-en-1-yl)phenyl]-N′-phe-
nylcarbodiimides21 and reductive cyclizations of 2,3-bis(2-ni-
trophenyl)propanoate derivatives.22,23 Other methodologies start
from (2-nitrobenzyl)triphenylphosphonium bromide and an
aldehyde to construct the quinoline and indole ring consecu-
tively.24 Cyclizations starting from quinolines use 2-(1H-benzo-
triazol-1-yl)quinolines in a Graebe-Ullmann type reaction,25,26
2-azido-4-chloro-3-phenylquinoline in an intramolecular nitrene
insertion reaction,27 2-(2-chloroquinolin-3-yl)aniline28 or 3-(2-
aminophenyl)-1-methylquinolin-2(1H)-one (after activation with
POCl3) in an intramolecular nucleophilic aromatic substitution
reaction,29 and N-phenylquinolin-2-amine via a heteroatom
directed photoannulation.30 Indole based strategies have been
published starting from N-methylisatine,31 3-[(methylthio)m-
ethylene]-1,3-dihydro-2H-indol-2-one,32 methyl 1H-indole-3-
carboxylate,33 or 2-chloro-1H-indole-3-carbaldehyde.34
Our general synthetic strategy was based on the amination
of chloro-substituted neocryptolepines. The main reason for this
is the incapability to perform a selective methylation of the
quinoline nitrogen atom when the basic side chain is already
present on the neocryptolepine nucleus. In addition, this
approach offers the advantage to easily modify the basic side
chain as it is introduced in the last reaction step. The chloro-
neocryptolepines were synthesized through two methods.
The Graebe-Ullman condensation,25,26 starting from com-
mercially available or prepared chloroquinolines 6 and chlo-
robenzotriazoles 7, appeared the most versatile synthesis of
neocryptolepines with substitutions on the A or D ring (2-, 3-,
8-, and 9-substitution). The Graebe-Ullman condensation was
performed under thermolytic conditions and yielded intermediate
2-(1H-benzotriazol-1-yl)quinolines 8 and norneocryptolepines
9. The 5-methyl group was introduced with iodomethane, giving
rise to neocryptolepines 10. As basic side chain, we used the
chloroquine-derived N1,N1-diethylpentane-1,4-diamine. This chain
was introduced on 2-, 3-, 8-, and 9-chloroneocryptolepines with
a palladium-catalyzed amination reaction (Scheme 1).
a Reagents and conditions: (i) 110-120 °C, 2 h. (ii) Polyphosphoric acid,
130 °C, 2-6 h, then 180 °C, 30 min. (iii) (a) MeI, dry THF, reflux, 18-24
h; (b) NH4OH, CH2Cl2, room temperature. (iv) Pd(OAc)2, DCPB, NaOtBu,
N1,N1-diethylpentane-1,4-diamine, toluene, reflux, 2 h. (v) Pd(OAc)2,
DTPB, NaOtBu, N1,N1-diethylpentane-1,4-diamine, 1,4-dioxane, reflux,
2-24 h.
higher dilution prompted us to additionally select reflux condi-
tions under classical heating.
Neocryptolepines with a substitution in position 11 were
prepared from 1H-methyl indole-3-carboxylate (12) and anilines
13 (Scheme 2).33 The intermediate methyl 2-(phenylamino)-
1H-indole-3-carboxylates (14), obtained via chlorination with
N-chlorosuccinimide in the presence of 1,4-dimethylpiperazine,
followed by addition of the aniline as trichloroacetate, were
cyclized in boiling diphenyl ether to 5,6-dihydro-11H-in-
dolo[2,3-b]quinolin-11-ones (15), which were dehydroxychlo-
rinated with POCl3 (16a). Methylation afforded 11-chlorone-
ocryptolepine (17a), which was aminated via an SNAr reaction
in neat N1,N1-diethylpentane-1,4-diamine at high temperature,
yielding target compound 18a. Using 3- and 4-chloroanilines
13b-c as starting materials, 1-, 2-, and 3-chlorosubstituted
compounds 18b-d were similarly obtained. The similarity of
chloroneocryptolepines 18b-d to chloroquine prompted us to
prepare also their norneocryptolepine analogues 19b-d by
amination of compounds 16b-d with N1,N1-diethylpentane-1,4-
diamine via an SNAr reaction. A series of analogues of 18d
(20a-g) and 19d (21a-g) with other aminoalkylamino-sub-
stituents were synthesized by following the same synthetic
strategy from 17 and 16, respectively.
First, we tried to implement the microwave-assisted amination
protocol for aryl chlorides reported by us previously.35 Unfor-
tunately, these reaction conditions proved not very useful as
the starting chloroneocryptolepines are only moderately soluble
in toluene or dioxane. A better result was obtained when using
the same catalyst system under more diluted conditions. The

Aminoalkylamino-Substituted Neocryptolepine DeriVatiVes
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9 2981
Scheme 2. Synthesis of Neocryptolepines with 11-Substitutiona
a Reagents and conditions: (i) (a) N-Chlorosuccinimide, 1,4-dimethylpiperazine, CH2Cl2, 0 °C, 2 h; (b) trichloroacetic acid, 13a-c, room temperature,
2 h. (ii) Diphenyl ether, reflux, 45 min-3 h. (iii) POCl3, toluene, reflux, 6-12 h. (iv) N1,N1-Diethylpentane-1,4-diamine (for 18) or appropriate amine (for
20) (neat), 135-155 °C, 12 h. (v) (a) MeI, THF, reflux, 18-24 h; (b) NH4OH, CH2Cl2, room temperature. (vi) N1,N1-Diethylpentane-1,4-diamine (for 19)
or appropriate amine (for 21), 135-155 °C, 1-4 h.
All compounds used for biological screening and functional
tests are listed in Table 1.
We also prepared a small series of 2-chloro-neo- and
-norneocryptolepines with various aminoalkylaminogroups in
position 11. Unfortunately, these compounds, 20a-g and
21a-g, although fairly potent, showed a remarkable increase
in cytotoxicity.
Results and Discussion
a. Antiplasmodial Activity and Cytotoxicity. All ami-
noalkylamino-substituted compounds and their chloro-substi-
tuted precursors were evaluated for in vitro antiplasmodial
activity against a chloroquine-sensitive P. falciparum strain and
for cytotoxicity on a human cell (MRC5) line.
b. DNA Interactions. Cryptolepine alkaloids are known as
DNA intercalating agents and topoisomerase inhibitors, resulting
in cytotoxicity. Although neocryptolepines are less prone to this
interaction, we tested our compounds as DNA-interacting agents
in the DNA-methyl green assay. Cryptolepine as well as
neocryptolepine are active in this assay. It had been observed
in our previous work on neocryptolepine derivatives that
introduction of substituents such as bromine could lead to a
decrease of DNA-interacting properties and a reduced cyto-
toxicity.10,11 Indeed, all mono- and disubstituted chloro-deriva-
tives of neocryptolepine 10a-d and 17a-d tested in this assay
were inactive, as well as the dichlorinated nor-derivatives
16b-d.
All mono- and dichlorosubstituted neocryptolepines (10a-d,
17a-d) and norneocryptolepines (16b-d) were poorly potent,
showing lower activity than neocryptolepine. Most chlorone-
ocryptolepines were less cytotoxic than the parent compound,
except 11-chloroneocryptolepine 17a, which was marginally
more cytotoxic. Introduction of the N1,N1-diethylpentane-1,4-
diamine side chain resulted in a substantial increase of the
antiplasmodial activity. The 8-substituted compound 11c ap-
peared the most potent, with an IC50 of about 0.01 µM, which
is as equally potent as the reference compound chloroquine.
11-Substituted neocryptolepine 18a was less potent, but its
activity increased by adding a chlorine substituent on the A-ring,
as in compounds 18b-d. Although it has been reported for
cryptolepine as well as neocryptolepine derivatives that the
presence of an N-methyl group is essential for antiplasmodial
activity, removal of the 5-methyl group in compounds 18,
affording chloroquine like compounds 19, resulted only in a 1-
to 3-fold loss in potency.10,36 This shows that not the N-methyl
group as such, but rather the presence of a basic nitrogen atom,
is important for the biological activity, i.e., accumulation in the
acid food vacuole where hemozoin formation occurs. The
cytotoxicity of the N1,N1-diethylpentane-1,4-diamine substituted
compounds remained in the same range as the chloroneocryp-
tolepines, compounds 11b-c, 18d, and 19d showing the highest
selectivity indices.
On the contrary, introduction of the N1,N1-diethylpentane-
1,4-diamine side chain in various positions of neocryptolepine
as in 11a-d and 18a did not result in a loss of DNA-interacting
properties. However, an additional chloro-substituent in position
1 (18b) or 2 (18d), but not 3 (18c), yielded compounds showing
no DNA-interacting activity in this assay. Nevertheless, when
the 11-N1,N1-diethylpentane-1,4-diamine side chain of the 2-Cl
derivative 18d was replaced by a shorter basic side chain as in
20a-g, the DNA interacting activity was restored.
Finally, it could be noted that the neocryptolepine derivatives
20a-g showing DNA interacting activity in spite of the presence
of a chloro-substituent lost this property by removing the
N-methyl group as in 21a-g. The latter observation is in
agreement with the results obtained for the dichlorinated nor-
derivatives 16b-d. The absence of DNA-interacting properties
is not necessarily accompanied by an absence of cytotoxicity,

2982 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9
El Sayed et al.
Table 1. Biological Results: Cellular Toxicity (MRC5 cells), Antiplasmodial Activity (Pf), Selectivity Index (SI), Inhibition of ꢀ-Hematin Formation,
and DNA Interaction of Substituted Neocryptolepines
a SD ) standard deviation. b n ) number of independent measurements. c ND ) not determined. d No inhibition of ꢀ-hematin formation at 5 meq.
e Inhibition of ꢀ-hematin formation at 5 meq was less than 20%. f The data of these reference compounds are taken from reference 11.

Aminoalkylamino-Substituted Neocryptolepine DeriVatiVes
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9 2983
indicating that other mechanisms of cytotoxicity may play a
role as well. On the other hand, all compounds showing DNA-
interacting activity are cytotoxic to various degrees, indicating
that the assay is valid but not exclusive to predict cytotoxicity.
c. Inhibition of ꢀ-Hematin Formation. The antiplasmodial
mechanism of action of chloroquine and analogues is based on
inhibition of hemozoin formation from hematin. This process
can be simulated in vitro by measuring the conversion of hemin
(hematin as chloride) to ꢀ-hematin (synthetic hemozoin). In our
previous research, we found that introduction of a chloro- or a
bromo-substituent in position 2 or 3 of neocryptolepine increased
the potency of the parent compound to inhibit ꢀ-hematin
formation, yielding compounds more potent than chloroquine
in this assay.11
tolepine is due to a combination of nonselective DNA interac-
tions that are accompanied by a general cytotoxicity and a
selective mechanism of action, i.e., inhibition of hemozoin
formation, still stands and is further confirmed. In the absence
of inhibition of ꢀ-hematin formation, only DNA-interacting and
cytotoxic compounds showed antiplasmodial activity. Com-
pounds that are not active in both functional assays do not show
a pronounced cytotoxicity or antiplasmodial activity.
d. In Vivo Activity. These results prompted us to evaluate
compounds 18d and 19d in an in vivo drug screening model
against Plasmodium berghei in Swiss mice. After daily intra-
peritoneal dosing at 50 mg/kg for five consecutive days,
neocryptolepine analogue 18d showed 100% reduction in
parasitaemia on day 4, however, 50% of the animals died by
day 7 due to drug toxicity. Administration of a lower dose (20
mg/kg intraperitoneal) was ineffective. The norcompound 19d
was less potent, as 100% reduction in parasitaemia could not
be obtained.
In agreement with our previous work, the monochlorinated
neocryptolepine derivatives 10a,c,d showed a high inhibitory
activity. In the series of the dichlorinated derivatives 17b-d
and 16b-d, only 17c was active. Nevertheless, 17c showed no
antiplasmodial activity. On the contrary, all neocryptolepine
derivatives only containing a N1,N1-diethylpentane-1,4-diamine
side chain in various positions 11a-d and 18a inhibited
ꢀ-hematin formation, and the same was true for the chlorinated
11-N1,N1-diethylpentane-1,4-diamine derivatives 18b-d. The
activity was increased by removing the N-methyl group as in
19b-d. All analogues of 18d having a 2-Cl and 5-methyl
substituent but a different basic side chain at position 11
(20a-g) were not active. However, the ꢀ-hematin inhibiting
properties were restored by removal of the N-methyl group as
in 21a-g except for 21c. This is exactly the opposite of that
observed in the DNA-methyl green assay.
Conclusion
Neocryptolepine has been confirmed as a useful lead com-
pound for the development of new antimalarial agents. Our
initial goal to prepare synthetic derivatives with higher anti-
plasmodial activity and lower cytotoxicity could be achieved,
resulting in several compounds with in vitro selectivity indices
>500. Two compounds were selected for in vivo evaluation in
infected mice, but they were not sufficiently potent or toxic to
the animals. Further variations in substituents and substitution
pattern may be necessary to obtain nontoxic compounds showing
in vivo activity.
With regard to the ꢀ-hematin inhibitory assay, it should be
noted that the amount of material needed to carry out the test
is rather high and that the available amounts did not allow
measurement of IC50 values >5 meq. In Table 1, all compounds
showing no activity at 5 meq were marked as inactive, whereas
some compounds such as 11d, and 18b,d showing some activity
(<20% inhibition) at this concentration were marked as active.
Since this assay has been developed quite recently, it is not
completely clear yet which range of IC50 values has biological
significance. Obviously also, IC50 values (much) higher than 5
meq may still be relevant because compounds such as 18b,d
did not show DNA interactions but had antiplasmodial activity
in spite of a relatively low inhibitory activity of ꢀ-hematin
formation (unless a completely different mechanism of action
would be involved). On the other hand, this inhibitory activity
is not necessarily associated with antiplasmodial activity (e.g.,
10a,c), possibly because the compound does not reach its target
or is not sufficiently accumulated in the acid food vacuole.
Taking this into account, the validity of the functional assay is
demonstrated by the fact that all compounds containing a basic
side chain (and hence are capable of accumulating in the acid
food vacuole), and showing inhibition of ꢀ-hematin formation,
are indeed antiplasmodially active. However, the range of
measured IC50 values for inhibition of ꢀ-hematin formation was
rather small (from 1 to >5 meq), and it was not possible to
observe a more detailed correlation with the antiplasmodial
activity. It should be noted that compound 21c, which was
surprisingly not active in the ꢀ-hematin inhibitory assay, was
the only compound in the 21 series without a pronounced
antiplasmodial activity.
Experimental Section
General Methods. Starting materials were either commercially
available or prepared as reported in literature (2,7-dichloroquino-
line37). Anhydrous THF, toluene, and dioxane were obtained from
Sigma-Aldrich or Acros. Moisture-sensitive reactions were done
under a nitrogen or an argon atmosphere. Analytical thin-layer
chromatography was performed on silica gel 60 F254 (Merck).
Column chromatography was carried out on silica gel 60 (230-400
mesh, Merck). Characterization of all compounds was done with
1H NMR and mass spectrometry. H NMR spectra were recorded
1
on a 400 MHz Bruker Avance DRX-400 spectrometer with NMR
shifts being expressed in ppm downfield from internal TMS. NMR
assignments for the regioisomers were determined on the basis of
2D experiments, and NMR coupling constants are reported in hertz.
ES mass spectra were obtained from an Esquire 3000 plus ion trap
mass spectrometer from Bruker Daltonics. Purity was verified using
two diverse HPLC systems using respectively a mass and UV
detector. Water (A) and ACN (B), were used as eluents. LC-MS
spectra were recorded on an Agilent 1100 Series HPLC system
using a Alltech Prevail C18 column (2.1 mm × 50 mm, 3 µm)
coupled with an Esquire 3000plus as MS detector and a 5-100%
B, 20 min-gradient was used with a flow rate of 0.2 mL/min. Then
0.1% formic acid was added to solvent A and B. Reversed phase
HPLC was run on a Gilson instrument equipped with an Ultrasphere
ODS column (4.6 mm × 250 mm, 5 µm). A 10-100% B, 35 min
gradient was used with a flow rate of 1 mL/min. TFA (0.1%) was
added to solvent A and B. The wavelength used was 214 nm. Flash
chromatography was carried out using FlashMaster II (Jones
Chromatography) using Merck silica gel 60 (230-400 mesh).
General Procedure for the Synthesis of 2-(1H-benzotriazol-1-
yl)quinolines (8a-d). A mixture of chloroquinoline (6) (5 mmol)
and benzotriazole (7) (5 mmol) was heated at 110-120 °C for 2 h
until the exothermic reaction finished (TLC monitoring). After the
mixture was cooled to room temperature, the resulting solid was
dissolved in DMF (20 mL) and precipitated by slow addition of
water. The resulting precipitate was collected by filtration, washed
Summarizing the results of both functional assays, DNA-
interactions and inhibition of ꢀ-hematin formation, it can be
concluded that our initial hypothesis that the antiplasmodial
activity of parent compounds such as cryptolepine or neocryp-

2984 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9
El Sayed et al.
with water, and dried to give a crude solid, which was recrystallized
from EtOH to afford pure compounds 8 as colorless crystals.
2-(1H-Benzotriazol-1-yl)-6-chloroquinoline (8a). Yield: 1.30 g
(93%), colorless crystals.
2-(1H-Benzotriazol-1-yl)-7-chloroquinoline (8b). Yield: 1.25 g
(88.5%), colorless crystals.
1H), 7.95 (d, 1H, J ) 7.6 Hz), 8.44 (s, 1H). HPLC: 214 nm; tr
19.67 min 100%. LC/MS: tr 13.2 min 100%. MS (ESI): m/z ) 267
[M + H]+.
General Procedure for the Synthesis of N1,N1-diethyl-N4-(5-
methyl-5H-indolo[2,3-b]quinolin-2-yl)pentane-1,4-diamines (11a-d).
A round-bottom flask was charged with chloroindoloquinoline
(10a-d) (0.5 mmol), N1,N1-diethylpentane-1,4-diamine (0.75 mmol),
and NaOtBu (67.30 mg, 0.7 mmol) followed by dry toluene or dry
dioxane (1 mL) in air. Subsequently, the flask was flushed with Ar
for a few minutes under magnetic stirring. Then 1 mL of a stock
solution of Pd catalyst (4 mol%) was added via a syringe and the
flask was flushed with Ar for an additional 3 min. [Preparation of
4 mol % stock solution of the catalyst: A 250 mL bottle was charged
with Pd(OAc)2 as Pd(0) source (89.8 mg, 0.4 mmol), DCPB
[2-(dicyclohexylphosphanyl)biphenyl] or DTPB [2-(di-t-butylphos-
phanyl)biphenyl] as ligand (0.8 mmol), and toluene (10 mL) in
air. Subsequently, the bottle was flushed with argon for 10 min
under magnetic stirring. The stock solutions were stored under an
argon atmosphere. When DTPB was used as ligand for the catalyst,
the stock solution was stirred for 16 h prior to its use.] The resulting
mixture was heated at reflux (oil bath temperature: 105-110 °C)
for 2-24 h under magnetic stirring and an argon atmosphere. After
cooling to room temperature, CH2Cl2 (25 mL) was added and the
suspension filtered over a pad of celite and rinsed with CH2Cl2 (30
mL). The solvent was removed under reduced pressure, and the
residue purified by flash chromatography using DCM-2.0 N
ammonia in MeOH (9:1) as the eluent to yield title compounds
11a-d.
2-(5-Chloro-1H-benzotriazol-1-yl)quinoline and 2-(6-Chloro-
1H-benzotriazol-1-yl)quinoline (8c,d). Yield: 1.10 g (79%), colorless
crystals obtained as an inseparable 1:1 mixture of two regioisomers.
General Procedure for the Synthesis of Chloro-6H-indolo[2,3-
b]quinolines (9a-d). A mixture of 8a-d (3 mmol) and polyphos-
phoric acid (15 mL) was heated at 130 °C for 2-6 h until the
formation of N2 had ceased. The mixture was heated at 180 °C for
30 min. The dark solution was allowed to attain room temperature,
poured into ice water (30 mL), and neutralized with a saturated
Na2CO3 solution until pH 8.5 was obtained. The product was
extracted with CH2Cl2 (3 × 20 mL), the organic layer was dried
over anhydrous Na2SO4, and evaporated in vacuo. The resulting
light-yellow precipitate was purified with flash chromatography
using EtOAc-hexane (1:1) as the eluent to afford pure compounds
9a and 9b and an inseparable 1:1 mixture of 9c and 9d.
2-Chloro-6H-indolo[2,3-b]quinoline (9a). Yield: 0.22 g (29%),
light-yellow solid.
3-Chloro-6H-indolo[2,3-b]quinoline (9b). Yield: 0.23 g (30%),
light-yellow solid.
8- and 9-Chloro-6H-indolo[2,3-b]quinoline (9c-d). Yield: 0.25 g
(33.2%), light-yellow solid obtained as an inseparable 1:1 mixture
of two regioisomers.
N1,N1-Diethyl-N4-(5-methyl-5H-indolo[2,3-b]quinolin-2-yl)pen-
General Procedure for the Synthesis of Chloro-5-methyl-5H-
indolo[2,3-b]quinolines (10a-d). Chloroindoloquinoline 9a-d (1
mmol), THF (15 mL), and iodomethane (0.62 mL, 10 mmol) were
heated at reflux under N2 atmosphere (oil bath temperature: 68 °C)
for 18-24 h under magnetic stirring in a round-bottom flask. After
cooling to room temperature, the precipitated material was filtered
off and rinsed well with THF. The residue was dissolved in MeOH
(50 mL) and the solvent subsequently evaporated to dryness under
reduced pressure. The crude product was purified by flash chro-
matography on silica gel using CHCl3-MeOH (9:1) affording the
hydroiodide salt of 10a-d as yellowish-orange solids in 37-78%
yield. To obtain the free base, the hydroiodide salt of 10a-d was
brought in a mixture of DCM (50 mL) and 30% ammonia in water
(50 mL). The organic phase was separated and the aqueous phase
subsequently extracted with CH2Cl2 (2 × 30 mL). The combined
organic phase was dried over anhydrous MgSO4, filtered, and
evaporated to dryness to yield 10a-d as a red residue. Finally, the
residue was purified by flash chromatography on silica gel using
hexane-EtOAc (4:1) and hexane-EtOAc (1:1) as eluent to give
pure 10a-d as red solids. The regioisomeric mixture of 10c and
10d could be separated at this point using the same chromatographic
conditions.
1
tane-1,4-diamine (11a). Yield: 0.11 g (58%). H NMR (CDCl3) δ
1.06 (t, 6H, J ) 7.6 Hz), 1.29 (d, 3H, J ) 6.4 Hz), 1.63 (m, 4H),
2.48 (t, 2H, J ) 6.8 Hz), 2.58 (q, 4H, J ) 7.2 Hz), 3.62 (m, 1H),
3.87 (s, 1H), 4.34 (s, 3H), 7.07 (m, 1H), 7.12 (m, 1H), 7.19 (m,
1H), 7.52 (m, 1H), 7.60 (d, 1H, J ) 8.8 Hz), 7.72 (d, 1H, J ) 8.0
Hz), 8.03 (d, 1H, J ) 7.2 Hz), 8.43 (s, 1H). HPLC: 214 nm; tr
15.03 min 100%. LC/MS: tr 9.15 min 100%. MS (ESI): m/z ) 389
[M + H]+.
N1,N1-Diethyl-N4-(5-methyl-5H-indolo[2,3-b]quinolin-3-yl)pen-
1
tane-1,4-diamine (11b). Yield: 0.11 g (55%). H NMR (CDCl3) δ
1.05 (t, 6H, J ) 7.6 Hz), 1.28 (d, 3H, J ) 6.4 Hz), 1.64 (m, 4H),
2.46 (t, 2H, J ) 6.8 Hz), 2.55 (q, 4H, J ) 7.2 Hz)), 3.69 (m, 1H),
4.29 (s, 3H), 6.63 (s, 1H), 6.65 (d, 1H, J ) 9.2 Hz), 7.17 (m, 1H),
7.45 (m, 1H), 7.51 (m, 1H), 7.70 (m, 2H), 7.96 (d, 1H, J ) 7.2
Hz), 8.36 (s, 1H). HPLC: 214 nm; tr 15.68 min 100%. LC/MS: tr
11.2 min 100%. MS (ESI): m/z ) 389 (M + H)+.
N1,N1-Diethyl-N4-(5-methyl-5H-indolo[2,3-b]quinolin-8-yl)pen-
1
tane-1,4-diamine (11c). Yield: 0.13 g (67%). H NMR (CDCl3) δ
1.04 (t, 6H, J ) 7.2 Hz), 1.27 (d, 3H, J ) 6.0 Hz), 1.60 (m, 4H), 2.47
(t, 2H, J ) 7.2 Hz), 2.57 (q, 4H, J ) 7.2 Hz), 3.65 (m, 1H), 4.04 (d,
1H, J ) 8.0 Hz), 4.32 (s, 3H), 6.45 (m, 1H), 6.92 (d, 1H, J ) 2.0 Hz),
7.38 (m, 1H), 7.67 (m, 2H), 7.76 (d, 1H, J ) 8.4 Hz), 7.88 (d, 1H, J
) 7.6 Hz), 8.17 (s, 1H). HPLC: 214 nm; tr 16.04 min 100%. LC/MS:
tr 10.4 min 96%. MS (ESI): m/z ) 389 [M + H]+.
2-Chloro-5-methyl-5H-indolo[2,3-b]quinoline (10a). Yield: 0.23 g
1
(86%), red solid. H NMR (CDCl3) δ 4.28 (s, 3H), 7.18 (m, 1H),
7.50 (m, 1H), 7.63 (m, 2H), 7.67 (d, 1H, J ) 8.0 Hz), 7.88 (s, 1H),
7.98 (d, 1H, J ) 7.6 Hz), 8.35 (s, 1H). HPLC: 214 nm; tr 16.39
min 100%. LC/MS: tr 12.5 min 100%. MS (ESI): m/z ) 267 [M +
H]+.
N1,N1-Diethyl-N4-(5-methyl-5H-indolo[2,3-b]quinolin-9-yl)pen-
tane-1,4-diamine (11d). Yield: 0.054 g (28%). 1H NMR (CDCl3) δ
1.23 (t, 6H, J ) 7.2 Hz), 1.27 (d, 3H, J ) 6.0 Hz), 1.60 (m, 4H),
2.83 (t, 2H, J ) 7.2 Hz), 2.90 (q, 4H, J ) 7.2 Hz), 3.61 (m, 1H),
4.32 (s, 3H), 5.93 (m, 1H), (6.90 (m, 1H), 7.40 (m, 2H), 7.57 (d,
1H, J ) 8.8 Hz), 7.73 (m, 2H), 7.97 (d, 1H, J ) 8.4 Hz), 8.52 (s,
1H). HPLC: 214 nm; tr 15.95 min 100%. LC/MS: tr 13.2 min 97%.
MS (ESI): m/z ) 389 [M + H]+.
3-Chloro-5-methyl-5H-indolo[2,3-b]quinoline (10b). Yield: 0.23 g
1
(87%), red solid. H NMR (CDCl3) δ 4.28 (s, 3H), 7.18 (m, 1H),
7.50 (m, 1H), 7.63 (m, 2H), 7.67 (d, 1H, J ) 8.0 Hz), 7.88 (s, 1H),
7.98 (d, 1H, J ) 7.6 Hz), 8.35 (s, 1H). HPLC: 214 nm; tr 15.95
min 100%. LC/MS: tr 12.1 min 100%. MS (ESI): m/z ) 267 (M +
H)+.
General Procedure for the Synthesis of Methyl 2-(Pheny-
lamino)-1H-indole-3-carboxylates (14a-c). To a solution of methyl
1H-indole-3-carboxylate (12) (2.08 g, 11.9 mmol) in CH2Cl2 (50
mL) at 0 °C under argon, 1,4-dimethylpiperazine (0.75 g, 6.56
mmol) and N-chlorosuccinimide (1.75 g, 13.1 mmol) were added.
The reaction mixture was allowed to stand at 0 °C for 2 h, and a
solution of trichloroacetic acid (0.5 g, 3 mmol) and the appropriate
aniline 13a-c (23.4 mmol) in CH2Cl2 (50 mL) was added and the
reaction mixture was allowed to attain room temperature. After 2 h,
the reaction mixture was washed with 10% aqueous NaHCO3 and
8-Chloro-5-methyl-5H-indolo[2,3-b]quinoline (10c). Yield: 0.16 g
1
(60%). H NMR (CDCl3) δ 4.29 (s, 3H), 7.14 (m, 1H), 7.43 (m,
1H), 7.65 (m, 1H), 7.90 (d, 1H, J ) 8.4 Hz), 7.75 (m, 1H), 7.84
(d, 1H, J ) 8.4 Hz), 7.92 (m, 1H), 8.39 (s, 1H). HPLC: 214 nm;
tr 19.72 min 100%. LC/MS: tr 12.1 min, 96%. MS (ESI): m/z )
267 (M + H)+.
9-Chloro-5-methyl-5H-indolo[2,3-b]quinoline (10d). Yield: 0.08 g
1
(30%). H NMR (CDCl3) δ 4.31 (s, 3H), 7.44 (m, 2H), 7.61 (d,
1H, J ) 8.4 Hz), 7.71 (d, 1H, J ) 8.4 Hz), 7.77 (m, 1H), 7.91 (m,

Aminoalkylamino-Substituted Neocryptolepine DeriVatiVes
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9 2985
1.0 M aqueous HCl and finally with water and brine. The resulting
solution was dried, filtered, and evaporated. The residue was
chromatographed using hexane-EtOAc (3:1) as eluent to yield title
compounds 14a-c.
Methyl 2-(Phenylamino)-1H-indole-3-carboxylate (14a). Yield:
1.77 g (56%).
1,11-Dichloro-5-methyl-5H-indolo[2,3-b]quinoline (17b). Yield:
0.09 g (60%). 1H NMR (CDCl3) δ 4.29 (s, 3H), 7.30 (m, 1H), 7.45
(m, 1H), 7.60 (m, 1H), 7.72 (m, 1H), 8.32 (d, 1H, J ) 8.8 Hz),
8.24 (d, 1H, J ) 8.8 Hz), 8.38 (d, 1H, J ) 7.6 Hz). HPLC: 214
nm; tr 20.55 min 97.97%. LC/MS: tr 13.2 min 100%. MS (ESI):
m/z ) 301 [M + H]+.
3,11-Dichloro-5-methyl-5H-indolo[2,3-b]quinoline (17c). Yield:
0.10 g (68%). 1H NMR (CDCl3) δ 4.26 (s, 3H), 7.29 (m, 1H), 7.59
(d, 1H, J ) 7.2 Hz), 7.65 (d, 1H, J ) 8.8 Hz), 7.69 (m, 1H), 7.71
(m, 1H), 8.38 (m, 1H), 8.40 (d, 1H, J ) 7.6 Hz). HPLC: 214 nm;
tr 19.47 min 71.02%. LC/MS: tr 13.5 min 85%. MS (ESI): m/z )
301 [M + H]+.
Methyl 2-[(3-Chlorophenyl)amino]-1H-indole-3-carboxylate (14b).
Yield: 1.68 g (47%).
Methyl 2-[(4-Chlorophenyl)amino]-1H-indole-3-carboxylate (14c).
Yield: 1.75 g (49%).
General Procedure for Synthesis of 5,6-Dihydro-11H-indolo[2,3-
b]quinolin-11-one (15a-d). The ester 14a-c (4 mmol) was heated
for 45 min to 3 h in diphenyl ether (5 mL) at reflux (250 °C), and
the reaction mixture was allowed to attain room temperature. The
solid formed was isolated by filtration and washed with a large
quantity of diethyl ether, yielding title compounds 15a-d.
5,6-Dihydro-11H-indolo[2,3-b]quinolin-11-one (15a). Yield: 0.60 g
(65%).
1-Chloro-5,6-dihydro-11H-indolo[2,3-b]quinolin-11-oneand3-Chlo-
ro-5,6-dihydro-11H-indolo[2,3-b]quinolin-11-one (15b-c). Yield:
0.94 g (88%), as an inseparable 1:1 mixture of two regioisomers.
2-Chloro-5,6-dihydro-11H-indolo[2,3-b]quinolin-11-one (15d).
Yield: 0.57 g (53%).
General Procedure for Synthesis of 11-Chloro-6H-indolo[2,3-
b]quinolines (16a-d). A solution of 15a-d. (2.17 mmol) in dry
toluene (5 mL) and POCl3 (5 mL) was refluxed for 6-12 h. The
reaction mixture was cooled, poured into ice, neutralized with a
cold saturated solution of NaHCO3 while keeping the internal
temperature below 30 °C, and then extracted with CH2Cl2 (3 × 30
mL). The combined CH2Cl2 extract was washed with water and
brine, dried (anhydrous Na2SO4), and then concentrated. Purification
by flash chromatography, eluting with EtOAc-hexane (1:1) afford
16a-d as yellow solids. The 1- and 3-Cl derivatives were separated
during this procedure.
2,11-Dichloro-5-methyl-5H-indolo[2,3-b]quinoline (17d). Yield:
1
0.11 g (73%). H NMR (CDCl3) δ 4.35 (s, 3H), 7.27 (t, 1H, J )
7.6 Hz), 7.53 (dd, 1H, J ) 0.8 Hz), 7.58 (d, 1H, J ) 8.4 Hz), 7.63
(d, 1H, J ) 8.0 Hz), 7.7 (m, 2H), 8.5 (d, 1H, J ) 7.6 Hz). HPLC:
214 nm; tr 17.86 min 82.51%; LC/MS: tr 13.2 min 87%. MS (ESI):
m/z ) 301 [M + H]+.
General Procedure for the Synthesis of 11-Aminoalkylamino-
neocryptolepines (18a-d) and (20a-g). Chloroindoloquinoline
17a-d (0.3 mmol) and an excess of the appropriate aminoalky-
lamine (3.0 mmol) were heated together at 135-155 °C for 1-4
h. TLC monitoring was used to ensure the completion of reaction.
The resulting brown crude oil was purified by flash chromatography
using CH2Cl2-2 N ammonia in MeOH (9:1) as the eluent to yield
pure 18a-d and 20a-g as yellowish-orange solids.
N1,N1-Diethyl-N4-(5-methyl-5H-indolo[2,3-b]quinolin-11-yl)pen-
1
tane-1,4-diamine (18a). Yield: 0.09 g (77%). H NMR (CDCl3) δ
0.92 (t, 6H, J ) 9.2 Hz), 1.38 (d, 3H, J ) 6.4 Hz), 1.68 (m, 4H),
2.36 (t, 2H, J ) 7.2 Hz), 2.42 (q, 4H, J ) 6.8 Hz), 4.29 (s, 3H),
4.33 (s, 1H), 5.10 (d, 1H, J ) 10.8 Hz), 7.21 (m, 1H), 7.39 (m,
1H), 7.46 (m, 1H), 7.75 (m, 3H), 7.91 (d, 1H, J ) 7.6 Hz), 8.17
(d, 1H, J ) 8.4 Hz). HPLC: 214 nm; tr 14.22 min 100%. LC/MS:
tr 10.3 min 100%. MS (ESI): m/z ) 389 [M + H]+.
N4-(1-Chloro-5-methyl-5H-indolo[2,3-b]quinolin-11-yl)-N1,N1-di-
1
11-Chloro-6H-indolo[2,3-b]quinoline (16a). Yield: 0.38 g (69%).
1H NMR (DMSO-d6) δ 7.31 (m, 1H), 7.59 (m, 3H), 7.82 (m, 1H),
8.05 (1H, d, J ) 8.5 Hz), 8.37 (d, 1H, J ) 8.5 Hz), 8.54 (d, 1H,
J ) 7.7 Hz), 12.02 (s, 1H). MS (ESI): m/z ) 253 [M + H]+.
1,11-Dichloro-6H-indolo[2,3-b]quinoline (16b). Yield: 0.08 g
ethyl-pentane-1,4-diamine (18b). Yield: 0.11 g (85%). H NMR
(CDCl3) δ 0.92 (t, 6H, J ) 9.2 Hz), 1.38 (d, 3H, J ) 6.4 Hz), 1.61
(m, 4H), 2.36 (t, 2H, J ) 7.2 Hz), 2.42 (q, 4H, J ) 6.8 Hz), 4.22
(m, 1H), 4.29 (s, 3H), 4.93 (d, 1H, J ) 10.8 Hz), 7.2 (t, 1H, J )
7.6 Hz), 7.37 (dd, 1H, J ) 1.6, 7.2 Hz), 7.54 (t, 1H, J ) 7.2 Hz),
7.71 (m, 2H), 8.24 (d, 1H, J ) 8.8 Hz), 8.30 (d, 1H, J ) 7.6 Hz).
HPLC: 214 nm; tr 14.8 min 95%. LC/MS: tr 13.2 min 100%. MS
(ESI): m/z ) 423 [M + H]+.
1
(13%). H NMR (DMSO-d6) δ 7.45 (s, 1H), 7.65 (m, 1H), 7.75
(m, 3H), 8.12 (d, 1H, J ) 8.0 Hz), 8.71 (d, 1H, J ) 7.2 Hz), 12.20
(s, 1H). HPLC: 214 nm; tr 19.67 min 100%. LC/MS: tr 13.2 min
100%. MS (ESI): m/z ) 287 [M + H]+.
N4-(3-Chloro-5-methyl-5H-indolo[2,3-b]quinolin-11-yl)-N1,N1-di-
1
3,11-Dichloro-6H-indolo[2,3-b]quinoline (16c). Yield: 0.24 g
(38%). 1H NMR (DMSO-d6) δ 7.36 (m, 1H), 7.55 (d, 1H, J ) 8.4
Hz), 7.65 (m, 2H), 8.07 (d, 1H, J ) 2.0 Hz), 8.36 (d, 1H, J ) 9.2
Hz), 8.50 (d, 1H, J ) 8.0 Hz), 12.18 (s, 1H). MS (ESI): m/z ) 287
[M + H]+.
2,11-Dichloro-6H-indolo[2,3-b]quinoline (16d). Yield: 0.49 g
(79%). 1H NMR (DMSO-d6) δ 7.37 (m, 1H), 7.56 (d, 1H, J ) 8.0
Hz), 7.64 (m, 1H), 7.82 (m, 1H), 8.07 (d, 1H, J ) 9.2 Hz), 8.34
(d, 1H, J ) 2.4 Hz), 8.53 (d, 1H, J ) 7.6 Hz), 12.10 (s, 1H). MS
(ESI): m/z ) 287 [M + H]+.
ethyl-pentane-1,4-diamine (18c). Yield: 0.10 g (79%). H NMR
(CDCl3) δ 1.04 (t, 6H, J ) 7.2 Hz), 1.4 (d, 3H, J ) 6.0 Hz), 1.70
(m, 4H), 2.55 (t, 2H, J ) 6.8 Hz), 2.61 (q, 4H, J ) 7.2 Hz), 4.20
(m, 1H), 4.28 (s, 3H), 5.10 (d, 1H, J ) 10.8 Hz), 7.23 (m, 1H),
7.45 (m, 1H), 7.66 (m, 2H), 7.67 (d, 1H, J ) 8.0 Hz), 7.89 (d, 1H,
J ) 7.6 Hz), 8.18 (s, 1H). HPLC: 214 nm; tr 15.29 min 97.40%.
LC/MS: tr 15.2 min 93%. MS (ESI): m/z ) 423 [M + H]+.
N4-(2-Chloro-5-methyl-5H-indolo[2,3-b]quinolin-11-yl)-N1,N1-di-
1
ethyl-pentane-1,4-diamine (18d). Yield: 0.09 g (71%). H NMR
(CDCl3) δ 0.96 (t, 6H, J ) 7.2 Hz), 1.36 (d, 3H, J ) 6.4 Hz), 1.70
(m, 4H), 2.40 (t, 2H, J ) 7.2 Hz), 2.47 (q, 4H, J ) 7.2 Hz), 4.21 (m,
1H), 4.23 (s, 3H), 4.91 (d, 1H, J ) 10.4 Hz), 7.21 (t, 1H, J ) 7.2 Hz),
7.33 (dd, 1H, J )7.20, 2.0 Hz), 7.46 (t, 1H, J ) 8.0 Hz), 7.66 (d, 1H,
J ) 8.0 Hz), 7.76 (d, 1H, J ) 8.0 Hz), 7.87 (d, 1H, J ) 7.6 Hz), 8.09
(d, 1H, J ) 8.8 Hz). HPLC: 214 nm; tr 14.23 min 100%. LC/MS: tr
14.58 min 97%. MS (ESI): m/z ) 423 [M + H]+.
General Procedure for the Synthesis of 11-Chloroneocryptol-
epines (17a-d). A suspension of 16a-d (0.5 mmol) in dry THF
(10 mL) and iodomethane (0.31 mL, 5.0 mmol) was heated at 85
°C for 18-24 h under argon atmosphere. After cooling to room
temperature, the precipitated material was filtered off and rinsed
with THF (20 mL) to afford the hydroiodide salt of 16a-d as
orange solids. The free base was liberated from its hydroiodide by
treatment with 28-30% ammonia in water and extraction with
CH2Cl2 (3 × 20 mL). The combined organic layers were dried over
Na2SO4, the solvent was evaporated, and the red residue was
purified by flash chromatography using hexane-EtOAc (1:2) as
the eluent to afford title compounds 17a-d as red solids.
N1-(2-Chloro-5-methyl-5H-indolo[2,3-b]quinolin-11-yl)-N2,N2-
dimethylethane-1,2-diamine (20a). Yield: 0.09 g (83%). 1H NMR
(CDCl3) δ 2.41 (s, 6H), 2.59 (t, 2H, J ) 5.6 Hz), 3.85 (q, 2H, J )
3.2 Hz), 4.25 (s, 3H), 6.57 (br s, 1H), 7.21 (t, 1H, J ) 7.2 Hz),
7.45 (t, 1H, J ) 7.2 Hz), 7.62 (m, 2H), 7.76 (d, 1H, J ) 8.0 Hz),
8.08 (d, 1H, J ) 8.0 Hz), 8.20 (d, 1H, J ) 2.0 Hz). HPLC: 214
nm; tr 11.67 min 100%. LC/MS: tr 9.2 min 100%. MS (ESI): m/z
) 353 [M + H]+.
11-Chloro-5-methyl-5H-indolo[2,3-b]quinoline (17a). Yield: 0.10 g
1
(75%). H NMR (CDCl3) δ 4.34 (s, 3H), 7.30 (m, 1H), 7.51 (m,
1H), 7.73 (m, 3H), 8.36 (d, 1H, J ) 8.4 Hz), 8.44 (m, 1H), 8.87
(d, 1H, J ) 8.4 Hz). HPLC: 214 nm; tr 16.79 min 100%. LC/MS:
tr 11.9 min 94%. MS (ESI): m/z ) 267 [M + H]+.
2-Chloro-5-methyl-N-(2-pyrrolidin-1-ylethyl)-5H-indolo[2,3-
b]quinolin-11-amine (20b). Yield: 0.08 g (70%). 1H NMR (CDCl3)
δ 1.93 (m, 4H), 2.68 (m, 4H), 2.81 (t, 2H, J ) 5.6 Hz), 3.88 (q,

2986 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9
El Sayed et al.
2H, J ) 5.2 Hz), 4.26 (s, 3H), 6.70 (br s, 1H), 7.20 (t, 1H, J ) 8.4
Hz), 7.45 (t, 1H, J ) 8.4 Hz), 7.64 (m, 2H), 7.77 (d, 1H, J ) 8.0
Hz), 8.11 (d, 1H, J ) 8.0 Hz), 8.24 (d, 1H, J ) 2.0 Hz). HPLC:
214 nm; tr 14.57 min 94.3%. LC/MS: tr 13.2 min 100%. MS (ESI):
m/z ) 409 [M + H]+.
2-Chloro-5-methyl-N-(2-morpholin-4-ethyl)-5H-indolo[2,3-b]quin-
olin-11-amine (20c). Yield: 0.10 g (87%). 1H NMR (CDCl3) δ 2.61
(m, 4H), 2.68 (t, 2H, J ) 6.8 Hz), 3.87 (m, 4H), 3.9 (q, 2H, J )
3.8 Hz), 4.27 (s, 3H), 6.43 (br s, 1H), 7.22 (t, 1H, J ) 7.6 Hz),
7.42 (m, 2H), 7.59 (m, 1H), 7.81 (d, 1H, J ) 8.8 Hz), 8.14 (d, 1H,
J ) 8.0 Hz), 8.50 (s, 1H). HPLC: 214 nm; tr 11.89 min 100%.
LC/MS: tr 10.7 min 97%. MS (ESI): m/z ) 395 [M + H]+.
N4-(2-Chloro-6H-indolo[2,3-b]quinolin-11-yl)-N1,N1-diethyl-pen-
tane-1,4-diamine (19d). Yield: 0.09 g (56%). H NMR (CDCl3) δ
1
0.96 (t, 6H, J ) 7.2 Hz), 1.36 (d, 3H, J ) 6.4 Hz), 1.62 (m, 2H),
1.73 (m, 2H), 2.42 (t, 2H, J ) 7.2 Hz), 2.47 (q, 4H, J ) 7.2 Hz),
4.20 (m, 1H), 4.65 (d, 1H, J ) 10.8 Hz), 7.29 (m, 1H), 7.46 (m,
2H), 7.62 (m, 1H), 7.93 (d, 1H, J ) 9.2 Hz), 8.00 (d, 1H, J ) 8.8
Hz), 8.14 (d, 1H, J ) 2.4 Hz), 11.32 (s, 1H). HPLC: 214 nm; tr
14.63 min 99.14%. LC/MS: tr 14.2 min 100%. MS (ESI): m/z )
409 [M + H]+.
N2-(2-Chloro-6H-indolo[2,3-b]quinolin-11-yl)-N1,N1-dimethyl-
ethane-1,2-diamine (21a). Yield: 0.10 g (73%). 1H NMR (DMSO-
d6) δ 2.26 (s, 6H), 2.59 (br s, 2H), 3.77 (m, 2H), 6.36 (br s, 1H),
7.24 (m, 1H), 7.42 (m, 2H), 7.59 (m, 1H), 7.82 (d, 1H, J ) 8.8
Hz), 8.10 (d, 1H, J ) 8.0 Hz), 8.46 (s, 1H), 11.53(s, 1H). HPLC:
214 nm; tr 12.09 min 100%. LC/MS: tr 9.6 min 94%. MS (ESI):
m/z ) 339 [M + H]+.
2-Chloro-N-[(1-ethylpyrrolidin-2-yl)methyl]-5-methyl-5H-indo-
1
lo[2,3-b]quinolin-11-amine (20d). Yield: 0.09 g (79%). H NMR
(CDCl3) δ 1.27 (t, 3H, J ) 7.2 Hz), 1.50 (m, 1H), 1.68 (m, 4H),
1.82 (m, 1H), 1.85 (m, 1H), 2.80 (m, 1H), 3.02 (m, 1H), 3.45 (m,
1H), 3.82 (m, 1H), 4.02 (m, 1H), 4.26 (s, 3H), 6.82 (m, 1H), 7.20
(t, 1H, J ) 7.2 Hz), 7.65 (m, 2H), 7.76 (d, 1H, J ) 8.0 Hz), 8.10
(d, 1H,, J ) 8.0 Hz), 8.21 (d, 1H, J ) 2.0 Hz). HPLC: 214 nm; tr
12.44 min 100%. LC/MS: tr 9.7 min 100%. MS (ESI): m/z ) 393
[M + H]+.
2-Chloro-5-methyl-11-(4-methylpiperazin-1-yl)-5H-indolo[2,3-
b]quinoline (20e). Yield: 0.089 g (81%). 1H NMR (CDCl3) δ 2.53
(s, 3H), 2.81 (t, 4H, J ) 4.8 Hz), 3.61 (t, 4H, J ) 4.4 Hz), 4.34 (s,
3H), 7.27 (m, 1H), 7.54 (t, 1H, J ) 7.2 Hz), 7.70 (s, 2H), 7.74 (d,
1H, J ) 7.6 Hz), 8.33 (d, 1H, J ) 7.6 Hz), 8.50 (s, 1H). HPLC:
214 nm; tr 9.98 min 100%. LC/MS: tr 8.8 min 100%. MS (ESI):
m/z ) 365 [M + H]+.
2-Chloro-N-(2-pyrrolidin-1-ylethyl)-6H-indolo[2,3-b]quinolin-11-
1
amine (21b). Yield: 0.09 g (62%). H NMR (DMSO-d6) δ 1.70
(m, 4H), 2.50 (m, 4H), 2.73 (m, 2H), 3.77 (m, 2H), 6.40 (br s,
1H), 7.23 (m, 1H), 7.42 (m, 2H), 7.60 (m, 1H), 7.82 (d, 1H, J )
8.8 Hz), 8.12 (d, 1H, J ) 8.8 Hz), 8.47 (s, 1H), 11.52 (br s, 1H).
HPLC: 214 nm; tr 12.1 min 100%. LC/MS: tr 10.2 min 97%. MS
(ESI): m/z ) 365 [M + H]+.
2-Chloro-N-(2-morpholin-4-ylethyl)-6H-indolo[2,3-b]quinolin-11-
amine (21c). Yield: 0.12 g (77%). 1H NMR (DMSO-d6) δ 2.31 (br
s, 4H), 2.55 (br m, 2H), 3.42 (br s, 4H), 3.76 (m, 2H), 6.33 (br m,
1H), 7.23 (m, 1H), 7.42 (m, 2H), 7.59 (m, 1H), 7.81 (d, 1H, J )
8.8 Hz), 8.14 (d, 1H, J ) 8.0 Hz), 8.50 (s,1H), 11.51 (s, 1H). HPLC:
214 nm; tr 12.28 min 100%. LC/MS: tr 9.8 min 95%. MS (ESI):
m/z ) 381 [M + H]+.
2-{4-(2-Chloro-5-methyl-5H-indolo[2,3-b]quinolin-11-yl)piper-
1
azin-1-yl}ethanol (20f). Yield: 0.09 g (76%). H NMR (CDCl3) δ
1.25 (s, 1H), 2.80 (t, 2H, J ) 5.2 Hz), 2.91 (t, 4H, J ) 4.4 Hz),
3.61 (t, 4H, J ) 4.8 Hz), 3.78 (t, 2H, J ) 5.2 Hz), 4.33 (s, 3H),
7.26 (m, 1H), 7.54 (t, 1H, J ) 8.40 Hz), 7.68 (m, 2H), 7.74 (d,
1H, J ) 8.0 Hz), 8.27 (d, 1H, J ) 7.6 Hz), 8.47 (s, 1H). HPLC:
214 nm; tr 9.67 min 100%. LC/MS: tr 8.7 min 94%. MS (ESI): m/z
) 395 [M + H]+.
11-(1,4′-Bipiperidin-1′-yl)-2-chloro-5-methyl-5H-indolo[2,3-b]quin-
oline (20g). Yield: 0.09 g (65%). 1H NMR (CDCl3) δ 1.26 (m, 2H),
1.72 (m, 4H), 2.02 (m, 2H), 2.14 (m, 2H), 2.70 (m, 5H), 3.54 (m,
2H), 3.67 (m, 2H), 4.33 (s, 3H), 7.24 (m, 1H), 7.53 (t, 1H, J ) 7.6
Hz), 7.68 (m, 2H), 7.74 (d, 1H, J ) 7.6 Hz), 8.24 (d, 1H, J ) 8.0
Hz), 8.43 (s, 1H). HPLC: 214 nm; tr 12.64 min 100%. LC/MS: tr
9.7 min 95%. MS (ESI): m/z ) 433 [M + H]+.
2-Chloro-N-[(1-ethylpyrrolidin-2-yl)methyl]-6H-indolo[2,3-b]quin-
olin-11-amine (21d). Yield: 0.11 g (75%). 1H NMR (CDCl3) δ 1.27
(t, 3H, J ) 7.2 Hz), 1.62 (m, 1H), 1.75 (m, 2H), 1.85 (m, 1H),
2.34 (m, 2H), 2.78 (m, 1H), 3.05 (m, 1H), 3.46 (m, 1H), 3.87 (m,
1H), 4.02 (m, 1H), 6.52 (d, 1H, J ) 6.8 Hz), 7.27 (m, 1H), 7.43 (t,
1H, J ) 7.6), 7.49 (d, 1H, J ) 8.0 Hz), 7.60 (m, 1H), 8.00 (d, 1H,
J ) 9.2 Hz), 8.21 (d, 1H, J ) 7.6 Hz), 8.27 (d, 1H, J ) 2.4 Hz),
11.51 (s, 1H). HPLC: 214 nm; tr 12.25 min 100%. LC/MS: tr 9.8
min 100%. MS (ESI): m/z ) 379 [M + H]+.
2-Chloro-11-(4-methylpiperazin-1-yl)-6H-indolo[2,3-b]quino-
1
lin (21e). Yield: 0.11 g (78%). H NMR (CDCl3) δ 2.50 (s, 3H),
2.82 (m, 4H), 3.49 (m, 4H), 7.34 (m, 4H), 7.75 (d, 1H, J ) 8.8
Hz), 8.42 (s, 2H), 12.19 (br s,1H). HPLC: 214 nm; tr 11.31 min
100%. LC/MS: tr 11.3 min 100%. MS (ESI): m/z ) 351 [M +
H]+.
General Method for the Synthesis of 11-Aminoalkylaminonor-
neocryptolepines (19b-d) and (21a-g). A mixture of 16b-d (0.40
mmol) and an excess of the appropriate aminoalkylamine (4 mmol)
was heated slowly from room tempertaure to 135 °C over 1 h with
stirring and subsequently heated at 155 °C for 12 h with continued
stirring to drive the reaction to completion (TLC monitoring). The
resulting brownish residue was purified by flash chromatography
using CH2Cl2-MeOH (9:1) as the eluent to yield 19b-d and
21a-g as colorless viscous oils.
2-{4-(2-Chloro-6H-indolo[2,3-b]quinolin-11-yl)piperazin-1-
yl}ethanol (21f). Yield: 0.10 g (68%). 1H NMR (CDCl3) δ 2.80 (t,
2H, J ) 5.6 Hz), 2.94 (m, 5H, J ) 4.8 Hz), 3.62 (t, 4H, J ) 4.4
Hz), 3.79 (t, 2H, J ) 5.2 Hz), 3.52 (m, 2H), 7.33 (t, 1H, J ) 8
Hz), 7.47 (d, 1H, J ) 7.6 Hz), 7.52 (t, 1H, J ) 7.2 Hz), 7.64 (m,
1H), 8.02 (d, 1H, J ) 8.8 Hz), 8.48 (m, 2H), 10.10 (br s, 1H).
HPLC: 214 nm; tr 10.57 min 100%. LC/MS: tr 8.7 min 95%. MS
(ESI): m/z ) 381 [M + H]+.
N4-(1-Chloro-6H-indolo[2,3-b]quinolin-11-yl)-N1,N1-diethyl-pen-
1
tane-1,4-diamine (19b). Yield: 0.19 g (73%). H NMR (CDCl3) δ
11-(1,4′-Bipiperidin-1′-yl)-2-chloro-6H-indolo[2,3-b]quinoline (21g).
1
0.96 (t, 6H, J ) 7.2 Hz), 1.29 (d, 3H, J ) 6.4 Hz), 1.47 (m, 2H),
1.57 (m, 2H), 2.35 (t, 2H, J ) 7.2 Hz), 2.48 (q, 4H, J ) 7.2 Hz),
4.11 (m, 1H), 6.8 (d, 1H, J ) 10.8 Hz), 7.3 (m, 1H), 7.38 (m, 1H),
7.47 (m, 2H), 7.53 (d, 1H, J ) 7.6 Hz), 7.92 (d, 1H, J ) 8.0 Hz),
7.99 (dd, 1H, J ) 8.0, 1.2 Hz), 11.37(s, 1H). HPLC: 214 nm; tr
14.57 min 94.3%. LC/MS: tr 13.2 min 100%. MS (ESI): m/z )
409 [M + H]+.
Yield: 0.10 g (60%). H NMR (CDCl3) δ 1.72 (m, 6H), 2.03 (m,
2H), 2.15 (m, 2H), 2.71 (m, 5H), 3.52 (m, 2H), 3.66 (m, 2H), 7.33
(m, 1H), 7.45 (d, 1H, J ) 7.6 Hz), 7.50 (t, 1H, J ) 7.6 Hz), 7.61
(m, 1H), 8.00 (d, 1H, J ) 8.8 Hz), 8.42 (m, 2H), 10.26 (s,1H).
HPLC: 214 nm; tr 13.46 min 100%. LC/MS: tr 13 min 100%. MS
(ESI): m/z ) 419 [M + H]+.
In Vitro Biological Screening Tests. Standard screening meth-
odologies were adopted as described.38 For antiplasmodial activity,
the chloroquine-susceptible P. falciparum Ghana strain was used.
Parasites were cultured in human erythrocytes at 37 °C under a
low oxygen atmosphere (3% O2, 4% CO2, and 93% N2) in RPMI-
1640 culture medium. After 72 h exposure to the compounds,
parasite multiplication was measured by the Malstat method.39
Absorbance was spectrophotometrically read at 655 nm, and
percentage growth inhibition was calculated compared to the
negative blanks.
N4-(3-Chloro-6H-indolo[2,3-b]quinolin-11-yl)-N1,N1-diethyl-pen-
1
tane-1,4-diamine (19c). Yield: 0.13 g (82%). H NMR (CDCl3) δ
0.94 (t, 6H, J ) 7.2 Hz), 1.35 (d, 3H, J ) 6.4 Hz), 1.60 (m, 2H),
1.67 (m, 2H), 2.38 (t, 2H, J ) 7.2 Hz), 2.45 (q, 4H, J ) 7.2 Hz),
4.20 (m, 1H), 4.70 (d, 1H, J ) 10.8 Hz), 7.31 (m, 1H), 7.48 (t,
1H, J ) 7.6 Hz), 7.54 (d, 1H, J ) 7.6 Hz), 7.88 (d, 1H, J ) 8.0
Hz), 7.96 (d, 1H, J ) 8.0 Hz), 7.99 (d, 1H, J ) 7.6 Hz), 8.09 (m,
1H), 11.01(s, 1H). HPLC: 214 nm; tr 15.41 min 94.14%. LC/MS:
tr 13.9 min 100%. MS (ESI): m/z ) 409 [M + H]+.

Aminoalkylamino-Substituted Neocryptolepine DeriVatiVes
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 9 2987
(3) Jonckers, T. H. M.; Maes, B. U. W.; Lemie`re, G. L. F.; Rombouts,
G.; Pieters, L.; Haemers, A.; Dommisse, R. A. Synthesis of isocryp-
tolepine via a Pd-catalyzed “amination-arylation” approach. Synlett
2003, 6015–6018.
(4) Meyers, C.; Rombouts, G.; Loones, K. T. J.; Coelho, A.; Maes,
B. U. W. Auto-tandem catalysis: synthesis of substituted 11H-
indolo[3,2-c]quinolines via palladium-catalyzed intermolecular C-N
and intramolecular C-C bond formation. AdV. Synth. Catal. 2008,
350, 465–470.
(5) Hostyn, S.; Maes, B. U. W.; Pieters, L.; Lemie`re, G. L. F.; Ma´tyus,
P.; Hajo´s, G.; Dommisse, R. A. Synthesis of the benzo-ꢀ-carboline
isoneocryptolepine: the missing indoloquinoline isomer in the alkaloid
series cryptolepine, neocryptolepine and isocryptolepine. Tetrahedron
2005, 61, 1571–1577.
(6) Van Miert, S.; Hostyn, S.; Maes, B. U. W.; Cimanga, K.; Brun, R.;
Kaiser, M.; Ma´tyus, P.; Dommisse, R.; Lemie`re, G.; Vlietinck, A.;
Pieters, L. Isoneocryptolepine, a synthetic indoloquinoline alkaloid,
as an antiplasmodial lead compound. J. Nat. Prod. 2005, 68, 674–
677.
(7) Hostyn, S.; Maes, B. U. W.; Van Baelen, G.; Gulevskaya, A.; Meyers,
C.; Smits, K. Synthesis of 7H-indolo[2,3-c]quinolines: study of the
Pd-catalyzed intramolecular arylation of 3-(2-bromophenylamino)-
quinolines under microwave irradiation. Tetrahedron 2006, 62, 4676–
4684.
(8) Bailly, C.; Laine, W.; Baldeyrou, B.; De Pauw-Gillet, M. C.; Colson,
P.; Houssier, C.; Cimanga, K.; Van Miert, S.; Vlietinck, A. J.; Pieters,
L. DNA intercalation, topoisomerase II inhibition and cytotoxic activity
of the plant alkaloid neocryptolepine. Anti-Cancer Drug Des. 2000,
15, 191–201.
(9) Dassonneville, L.; Lansiaux, A.; Wattelet, A.; Wattez, N.; Mahieu,
C.; Van Miert, S.; Pieters, L.; Bailly, C. Cytotoxicity and cell cycle
effects of the plant alkaloids cryptolepine and neocryptolepine: relation
to drug-induced apoptosis. Eur. J. Pharmacol. 2000, 409, 9–18.
(10) Jonckers, T. H. M.; Van Miert, S.; Cimanga, K.; Bailly, C.; Colson,
P.; De Pauw-Gillet, M.-C.; Van Den Heuvel, H.; Claeys, M.; Lemie`re,
F.; Esmans, E. L.; Rozenski, J.; Quirijnen, L.; Maes, L.; Dommisse,
R.; Lemie`re, G. L. F.; Vlietinck, A.; Pieters, L. Synthesis, cytotoxicity
and antiplasmodial and antitrypanosomal activity of new neocryptol-
epine derivatives. J. Med. Chem. 2002, 45, 3497–3508.
(11) Van Miert, S.; Jonckers, T.; Cimanga, K.; Maes, L.; Maes, B.; Lemie`re,
G.; Dommisse, R.; Vlietinck, A.; Pieters, L. In vitro inhibition of
ꢀ-haematin formation, DNA interactions, antiplasmodial activity, and
cytotoxicity of synthetic neocryptolepine derivatives. Exp. Parasitol.
2004, 108, 163–168.
For cytotoxity evaluation, MRC-5 SV2 cells (human fetal lung
fibroblasts) were cultivated in MEM supplemented with L-glutamine
(20 mM) and 5% FCS at 37 °C and 5% CO2. For the assay, 104
MRC-5 cells/well were seeded onto the 96-well test plates contain-
ing the prediluted compounds and incubated at 37 °C and 5% CO2
for 72 h. Cell viability was determined fluorimetrically after addition
of resazurin.40
In Vivo Antiplasmodial Evaluation. Swiss mice are intraperi-
toneally infected with 4 × 108 erythrocytes infected with chloro-
quine-sensitive P. berghei (ANKA-strain) and intraperitoneally
treated with the test compounds at 50 mg/kg for five consecutive
days. On days 4 and 7, levels of parasitaemia are determined on
Giemsa-stained blood smears. A more detailled description can be
found in the Supporting Information.
DNA-Methyl Green Assay. The DNA-methyl green reagent
was prepared by suspending 20 mg of DNA-methyl green (Sigma-
Aldrich Chemie Gmbh, Steinheim, Germany) in 100 mL of 0.05
M Tris HCl buffer (pH 7.5) containing 7.5 mM MgSO4 and stirred
at 37 °C for 24 h. The samples were transferred to a 96-well
microtiter plate, and the solvent was removed under vacuum. Then
200 µL of the DNA-methyl green reagent was added to the test
compounds. The absorbance at 620 nm was measured at t ) 0 and
after 24 h of incubation at 25 °C. Cryptolepine was used as a
positive control.11 The IC50 value was calculated by comparing the
initial and the final absorbance. It corresponds to the concentration
where 50% displacement of methyl green from DNA occurs.41
Inhibition of ꢀ-Hematin Formation. This microassay was
performed in a 96-well V-bottom microplate.42 First, 50 µL of an
8 mM hemin (Sigma-Aldrich Chemie Gmbh, Steinheim, Germany)
solution in DMSO was added to 50 µL of the test compound in
water (or for water-insoluble compounds, 25 µL of a 16 mM hemin
solution in DMSO was added to 25 µL of the test compound in
DMSO, 50 µL of water was added afterward in order to keep the
DMSO concentration constant at 25%). Then as a negative control,
50 µL of water was used instead of the test solution, and chloroquine
(Sigma-Aldrich Chemie Gmbh, Steinheim, Germany) served as a
positive control. Then 100 µL of an 8 M acetate buffer (pH 5) was
added, and the plate was incubated at 37 °C for 18 h. After 15 min
of centrifugation at 3000 rpm, the soluble fraction was removed
and 200 µL of DMSO was added to the wells. The plate was
centrifuged again for 15 min at 3000 rpm, and all supernatant was
removed. The residual pellet of pure ꢀ-hematin remaining in the
well was dissolved in 200 µL of 0.1 M NaOH solution. Then 75
µL from each well was transferred into a U-bottom microplate,
and a serial 4-fold dilution in 0.1 M NaOH was prepared. The
absorbance was measured at 414 nm using a microtiter plate reader.
The IC50 value was calculated compared to the control (100%
ꢀ-hematin formation).
(12) Kaczmarek, L.; Peczyn´ska-Czoch, W.; Opolski, A.; Wietrzyk, J.;
Marcinkowska, E.; Boratynski, J.; Osiadacz, J. Methoxy- and methyl-,
methoxy-5,6,11-trimethyl-6H-indolo[2,3-b]quinolinium derivatives as
novel cytotoxic agents and DNA topoisomerase II inhibitors. Anti-
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indolo[2,3-b]quinoline as cytotoxic compounds and topoisomerase II
inhibitors. Radiol. Oncol. 2004, 38, 137–144.
(14) Lavrado, J.; Paulo, A.; Gut, J.; Rosenthal, P. J.; Moreira, R.
Cryptolepine analogues containing basic aminoalkyl side-chains at
C-11: synthesis, antiplasmodial activity, and cytotoxicity. Bioorg. Med.
Chem. Lett. 2008, 18, 1378–1381.
(15) Zhou, J.-L.; Lu, Y.-J.; Ou, T.-M.; Zhou, J.-M.; Huang, Z.-S.; Zhu,
X.-F.; Du, C.-J.; Bu, X.-Z.; Ma, L.; Gu, L. Q.; Li, Y.-M.; Sun-Chi,
C. A. Synthesis and evaluation of quindoline derivatives as G-
quadruplex inducing and stabilizing ligands and potential inhibitors
of telomerase. J. Med. Chem. 2005, 48, 7315–7321.
(16) Guittat, L.; Alberti, P.; Rosu, F.; Van Miert, S.; Thetiot, E.; Pieters,
L.; Gabelica, V.; De Pauw, E.; Ottaviani, A.; Riou, J.-F.; Mergny,
J.-L. Interactions of cryptolepine and neocryptolepine with unusal DNA
structures. Biochimie 2003, 85, 535–547.
Acknowledgment. We gratefully acknowledge support of
the Research Fund of the University of Antwerp. P. Van der
Veken and P. Cos are postdoctoral fellows of the Research
Foundation Flanders (FWOsVlaanderen). S. Hostyn and G. van
Baelen are fellows of the Institute of Promotion of Innovation
in Science and Technology of Flanders (IWT). The excellent
technical assistance of W. Bollaert is greatly appreciated.
(17) Chen, Y. L.; Hung, H. M.; Lu, C.-M.; Li, K. C.; Tzeng, C. C. Synthesis
and anticancer evaluation of certain indolo[2,3-b]quinoline derivatives.
Bioorg. Med. Chem. 2004, 12, 6539–6546.
(18) Shi, C.; Zhang, Q.; Wang, K. J. Biradicals from thermolysis of N-[2-
(1-alkynyl)phenyl]-N′-phenylcarbodiimides and their subsequent trans-
formations to 6H-indolo[2,3-b]quinolines. J. Org. Chem. 1999, 64,
925–932.
(19) Schmittel, M.; Steffen, J. P.; Engels, B.; Lennartz, C. Two novel
thermal biradical cyclisations in theory and experiment: new synthetic
routes to 6H-indolo[2,3-b]quinolines and 2-aminoquinolines from
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(21) Saito, T.; Ohmori, H.; Ohkubo, T.; Motoki, S. Periselective, Lewis
acid-induced intramolecular Diels-Alder reaction of conjugated
carbodiimides: efficient synthesis of nitrogen heterocycles, indolo-
Supporting Information Available: A table with HPLC data
demonstrating purity of target compounds, a detailled description
of the in vivo drug screening model against Plasmodium berghei
in Swiss mice, and spectroscopic details of the intermediate
compounds 8a, 8b, 8c-d, 9a, 9b, 9c-d, 14a, 14b, 14c, 15a,
15b-c, 15d. This material is available free of charge via the Internet
at http://pubs.acs.org.
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