New benzo[5,6]pyrrolizino[1,2-b]quinolines as cytotoxic agents

Article abstract of DOI:10.1016/j.bmcl.2004.01.097

An assessment of structure-activity relationships associated with the new benzo[5,6]pyrrolizino[1,2-b]quinoline system displaying potent in vitro cytotoxic activity against the MCF7 cell line is described.

Full text of DOI:10.1016/j.bmcl.2004.01.097

Bioorganic & Medicinal Chemistry Letters 14 (2004) 2363–2365
New benzo[5,6]pyrrolizino[1,2-b]quinolines as cytotoxic agents
ꢀ ꢀ
Aurore Perzyna, Frederique Klupsch, Raymond Houssin, Nicole Pommery,
*
ꢀ
Amelie Lemoine and Jean-Pierre Henichart
ꢀ
Institut de Chimie Pharmaceutique Albert Lespagnol, EA 2692, Universitꢀe de Lille, 2, rue du Professeur Laguesse, BP 83,
59006 Lille, France
Received 24 September 2003; revised 23 January 2004; accepted 23 January 2004
Abstract—An assessment of structure–activity relationships associated with the new benzo[5,6]pyrrolizino[1,2-b]quinoline system
displaying potent in vitro cytotoxic activity against the MCF7 cell line is described.
ꢀ 2004 Elsevier Ltd. All rights reserved.
The quinoline pattern is found in a large number of
natural products and drug-like compounds known as
antitumoural agents, such as camptothecin,1 luotonin,2
ascididemin,3 TAS-103,4 cryptolepin,5 indolo[2,3-
b]quinolines6. . . Similarly, the alkoxyindole nucleus is
often seen in various compounds (Fig. 1) known for
their cytotoxic activity such as rebeccamycin7 or aza-
toxin derivatives,8 retelliptine9 or voacangine.10
Our approach was to link these two bicyclic skeletons by
a pyrrolidine ring, as is found in camptothecin (CPT),
leading to a new condensed pentacyclic skeleton,
benzo[5,6]pyrrolizino[1,2-b]quinoline. The correspond-
ing compounds retain their originality as to the
arrangement of the quinoline, pyrrolidine and indole
moieties giving the molecule a more extended and linear
geometry than camptothecin offers and, in this way,
improving their DNA-binding activity.
O
O
N
N
N
N
N
O
We report here the synthesis and cytotoxic properties of
some substituted benzo[5,6]pyrrolizino[1,2-b]quinolines.
II
I
OH
O
N
In order to establish significant structure–activity rela-
tionships for this class of compounds (Fig. 2), different
substituents were investigated on positions 2, 8 and 13:
a hydrogen -donor/-acceptor bond (hydroxyl and/or
methoxy) on the lateral homocycles and a positively
charged chain able to engage electrostatic bonds with
DNA phosphates (piperidinoethoxy fragment) on car-
bons 2and 8 and a methyl or an ethyl group on carbon
13 of quinoline.
H
N
HN
O
O
H3C
CH3O
N
H
N
N
H
CH3
OH
Cl
Cl
IV
OH
OMe
OH
III
R
13
Figure 1. Structures of camptothecin (I), luotonin (II), rebeccamycin
(III) and retelliptine (IV).
2
R1O
N
N
8
OR2
* Corresponding author. Tel.: +33-3-2096-4374; fax: +33-3-2096-4906;
e-mail: henicha@pharma.univ-lille2.fr
Figure 2. Structure of benzo[5,6]pyrrolizino[1,2-b]quinolines.
0960-894X/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.01.097

2364
A. Perzyna et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2363–2365
CH3O
HO
R2O
b
O
O
O
O
O
O
R1O
HO
HO
a
R
R
R
a
b
N
N
N
7
8
9
NO2
NO2
3a,b
1a,b
2a,b
R2 = (CH2)2piperidine
Scheme 3. Synthesis of pyrroloindoles 8, 9. Reagents and conditions:
(a) BBr3, CH2Cl2, rt, 3 h, 55%; (b) Cl(CH2)2piperidine, DMF, 80 ꢁC,
4 h, 52%.
c
c
R
a
b
1 = (CH2)2piperidine
R = CH3
R = CH2CH3
O
O
R1O
HO
R
CH3
NH2
NH2
€
Finally, the Friedlander reaction between o-acylanilines
5a,b
4
and pyrroloindoles (Scheme 4) was carried out in the
previous conditions,14 namely butan-1-ol with pyridi-
nium p-toluenesulfonate as catalyst and azeotropic dis-
tillation of water.
Scheme 1. Synthesis of o-aminoketones 4, 5. Reagents and conditions:
(a) (i) HNO3–AcOH, 70 ꢁC; (ii) column chromatography CH2Cl2–
AcOEt, 30–35%; (b) Cl(CH2)2piperidine, K2CO3, DMF, 80 ꢁC, 3 h,
66–92%; (c) Fe, HCl, EtOH–AcOH–H2O, reflux, 15 min, 66–88%.
All the compounds, except 11d, were tested for in vitro
cytotoxic activity against the mouse leukemic cell line
L1210,15 the human breast cancer cell line MCF7 and the
prostatic one PC3.16 The results are shown in Table 1.
The benzo[5,6]pyrrolizino[1,2-b]quinoline scaffold was
€
synthesised on the basis of the Friedlander method for
the quinoline preparation, using the appropriate
o-aminoketone and the enolisable pyrroloindole. O-
aminoacetophenones 4 and 5a were obtained (Scheme 1)
by nitrating11 3-hydroxyacetophenone 1a followed by
the O-alkylation of the phenol, or Bechamp reduction of
the nitro group.
If compounds with a hydroxyl group on the quinoline
moiety show a slight antiproliferative activity (10f,g),
their analogues 10c–e with a side chain on this scaffold
exhibit a higher cytotoxic effect. The piperidinoethoxy
group, borne by the quinoline moiety, seems to be cru-
cial for cytotoxic activity, as we have demonstrated in a
previous study on indolizino[1,2-b]quinolines17 whose
condensed tetracyclic structure is derived from cam-
ptothecin. Comparison of cytotoxic activity against the
O-Aminopropiophenone 5b was prepared from 3-hy-
droxypropiophenone12 (1b) whose nitration (HNO3–
CH3COOH) gave the 6- and 4- (2b) regioisomers; after
separation by column chromatography (SiO2, CH2Cl2–
AcOEt 9/1) the phenol group of 2b was alkylated and
the nitro group reduced. Pyrroloindole 7 (Scheme 2) was
obtained according to the pathway described13 for the
analogue devoid of methoxy substituent.
Table 1. In vitro cytotoxicity activities of benzopyrrolizinoquinoline
derivatives 10, 11
Compound
IC50 (lM)
Boron tribromide enabled O-demethylation (Scheme 3),
before O-alkylation (Williamson conditions) to give
pyrroloindole 9.
Mouse leukemia Human breast Human prostate
L1210
MCF7
PC3
10c
10d
10e
10f
0.55
3.93
0.55
3.40
0.60
0.55
––a
0.55
5.30
4.60
>50
4.94
5.50
5.30
>10
>50
4.80
––a
CH3O
b
CH3O
CH3O
a
O
O
COOEt
N
N
H
N
10g
11c
11d
CPT
12.0
6.30
––a
COOEt
7
Scheme 2. Synthesis of pyrroloindole 7. Reagents and conditions: (a)
t-BuOK, CH2@CHCOOEt, toluene, reflux, 4 d, 90%; (b) AcOH,
reflux, 24 h, 80%.
0.06
0.320.31
a Relative insolubility in culture medium (DMSO ꢀ 1&).
R
O
R2O
R1O
R1O
R
O
a
N
+
N
N
NH2
OR2
4 or 5a,b
7, 8 or 9
10c-g R = CH3
11c,d R = CH2CH3
R1
R2
H
CH3
(CH2)2piperidine
(CH2)2piperidine
c
d
e
f
(CH2)2piperidine (CH2)2piperidine
H
H
H
CH3
g
Scheme 4. Synthesis of benzo[5,6]pyrrolizino[1,2-b]quinolines 10, 11. Reagents and conditions: (a) PPTS, butan-1-ol, reflux, 2h, 38–57%.

A. Perzyna et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2363–2365
2365
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15. Cytotoxic assay: Leukemic L1210 cells were maintained in
RPMI 1640 culture medium supplemented with 10% FCS.
For growth assay, the cells were seeded onto 24-well plates
at a density approximatively 105 cells/well. The tested
compounds were added to the culture medium and
incubation was performed for 72h. Cell growth was
assessed by numeration on Nageotte hemacytometer.
16. Cytotoxic assay: Human breast cancer MCF7 and pros-
tate cancer PC3 cells were, respectively, maintained in
MEM and RPMI culture medium supplemented with 10%
FCS. For growth assay, the cells were seeded onto 24-well
plates at a density of, respectively, 3 · 105 cells/well and
2 · 105 cells/well. After 24 h, the tested compounds were
added to the culture medium for 72h. Cell growth was
assessed by the colorimetric MTT test.
Acknowledgements
This work was partly supported by the ÔAssociation
pour la Recherche sur le CancerÕ (Grant no 4287).
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