Synthesis and antiproliferative evaluation of 7-aminosubstituted pyrroloiminoquinone derivatives

Article abstract of DOI:10.1016/S0960-894X(00)00450-9

Coupling of five amines on the 7-methoxy-1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline core was achieved and afforded, in particular, an opened analogue of the natural alkaloid wakayin. Evaluation of cytotoxic activity of compounds 2, 10-13 on L1210 cells afforded IC₅₀ in the range 0.25-5.3 μM. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00450-9

Bioorganic & Medicinal Chemistry Letters 10 (2000) 2231±2234
Synthesis and Antiproliferative Evaluation of 7-Aminosubstituted
Pyrroloiminoquinone Derivatives
Valerie Beneteau,a Alain Pierre,b Bruno Pfei€er,c Pierre Renardc
and Thierry Bessona,*
a
  Â
Ã
Laboratoire de Genie Proteique et Cellulaire, UPRES 2001, Pole Sciences et Technologie, Universite de La Rochelle,
Avenue Marillac, 17042 La Rochelle cedex 1, France
bInstitut de Recherche Servier, 11 Rue des Moulineaux, 92150 Surennes, France
c
Â
A.D.I.R. et Cie, 1 Rue Carle Hebert, 92415 Courbevoie cedex, France
Received 19 June 2000; revised 25 July 2000; accepted 4 August 2000
AbstractÐCoupling of ®ve amines on the 7-methoxy-1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline core was achieved and a€orded,
in particular, an opened analogue of the natural alkaloid wakayin. Evaluation of cytotoxic activity of compounds 2, 10±13 on
L1210 cells a€orded IC50 in the range 0.25±5.3 mM. # 2000 Elsevier Science Ltd. All rights reserved.
Chemistry
Introduction
Since the discovery of discorhabdin C in 1986 until
isolation and characterization of veuitamine in 1997,
more than 40 pyrroloiminoquinone alkaloids have been
isolated from sponges and ascidians.1 For these marine
organisms devoid of skeleton and immune system, ®xed
or not very mobile, secondary metabolites would have a
basic role in communication, defense or attack towards
other organisms.
The strategy used for building the tricyclic system 3 was
inspired by the work of Joule and Alvarez.5 6,7-Dime-
thoxy-4-methylquinoline 4 was formed by reaction
between 3,4-dimethoxyaniline and methylvinylketone in
re¯uxing acetic acid with iron(III) chloride. Nitration
of 4 (concentrated nitric acid, 50 ꢀC) led to the 5-
nitro compound 5 in a good yield (78%). According to
Vismara's method, oxidation of the methyl group to
aldehyde was achieved in DMSO with tri¯uoroacetic
acid, iodine, tert-butyliodide and iron(II) chloride. The
aldehyde function was then protected as a dimethylacetal
to give 7 in 87% yield. The pyridine ring and the nitro
group were simultaneously reduced by an excess of
sodium borohydride in methanol with nickel chloride to
a€ord diamine 8 in a very good yield (95%). Cyclization
of the pyrrole ring occurred by heating compound 8 at
80ꢀC in aqueous HCl and THF in a 62% yield (Scheme 2).
Pyrroloiminoquinones have recently received increasing
attention as a source of new and useful anticancer
drugs. In particular wakayin 1, isolated from Ascidian
Clavelina species, shows biological activities such as
inhibition of topoisomerase I.2 Until now, only two
approaches to structures analogous to wakayin were
reported with no biological activity described.3 As part
of our work on heterocyclic compounds with potential
pharmacological value,4 we planned to synthesize pyr-
roloiminoquinone 2 which is structurally very close to
the natural alkaloid, by the retrosynthetic pathway
shown in Scheme 1, from tryptamine and 7-methoxy-
3,4-dihydro-1H-pyrrolo[4,3,2-de]quinolin-8-one 3.
Aminoindole 9 was treated by ceric ammonium nitrate
(CAN) in aqueous acetonitrile to generate the quinone
structure. Substitution of the C-7 methoxy group by the
amine was achieved in situ, without isolating the very
unstable intermediate 3. The product of coupling was then
transformed into its tri¯uoroacetate salt (Scheme 3). In this
way, tryptamine was condensed on the pyrroloiminoqui-
none core to a€ord compound 2. Because some studies6
have proved the utility of DNA-intercalating heterocyclic
*Corresponding author. Fax: +33-5-46-45-82-65(or 47). E-mail: tbes-
son@univ-lr.fr
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00450-9

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V. Beneteau et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2231±2234
2232
(concentration reducing the cell proliferation by 50%)
are reported in Table 1. Because all the IC50s were
less than 20 mM, cell cycle perturbations were also
investigated.
Results and Discussion
Compound 2, a strict analogue of wakayin, is the least
active of the tested molecules on the L1210 cell line.
Compared to the natural alkaloid, the enhanced ¯ex-
ibility of the substituent at C-7 may not be favorable for
interaction with biological targets. The most cytotoxic
compounds (10, 11 and 13) inhibit the growth of L1210
cells at concentrations less than 0.5 mM. These water
soluble products are substituted by a primary amino or
an aminoalkyl group. Makaluvamine D (12), bearing
a hydrophobic side chain, showed a moderate anti-
proliferative activity in accordance with those reported for
di€erent cell lines (IC50(HCT116)=23.4 mM, IC50(xrs-6)
=19.1 mM).9
Figure 1.
compounds possessing a cationic side chain, products 10
and 11 were prepared by treatment of 3 with N,N-
dimethylethylenediamine and 1-(2-amino-ethyl)pyrroli-
dine, respectively. Finally, makaluvamines D (12) and I
(13) were obtained by reaction of 3 with tyramine and
ammonium chloride, respectively.7
Pharmacology
Compounds 2 and 10±13 were evaluated in vitro for
their antiproliferative activity using the murine L1210
leukemia cell line.8 The results expressed as IC50
Despite interesting antiproliferative properties, none of
the pyrroloiminoquinone derivatives 2 and 10±13 induce
signi®cant modi®cation of the L1210 cells cycle. This may
Scheme 1.
Scheme 2. Reaction conditions and yields: (a) AcOH, FeCl3, re¯ux, 2 h, 37%; (b) concd HNO3, 50 ꢀC, 1.5 h, 78%; (c) I2, tBuI, FeCl2, DMSO,
TFA, 100 ꢀC, 4 h, 83%; (d) HCl in Et2O, CH3OH, re¯ux, 48 h, 87%; (e) NaBH4, NiCl2, CH3OH, rt, 1 h, 95%: (f) HCl 1 N, THF, 80 ꢀC, 1 h, 62%.

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V. Beneteau et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2231±2234
2233
Scheme 3.
References and Notes
Table 1. Antiproliferative activity of compounds 2 and 10±13 on
L1210 cells
1. Sakemi, S.; Sun, H. H.; Je€ord, C. W.; Bernardinelli, G.
Tetrahedron Lett. 1989, 30, 2517. Venables, D. A.; Concep-
cion, G. P.; Matsumoto, S. S.; Barrows, L. R.; Ireland, C. M.
J. Nat. Prod. 1997, 60, 408. Gunasekera, S. P.; McCarthy, P.
J.; Longley, R. E.; Pomponi, S. A.; Wright, A. E.; Lobkovsky,
E.; Clardy, J. J. Nat. Prod. 1999, 62, 173. D'Ambrosio, M.;
Guerriero, A.; Chiasera, G.; Pietra, F. Tetrahedron 1996, 52,
8899. Copp, B. R.; Ireland, C. M.; Barrows, L. R. J. Org.
Chem. 1991, 56, 4596. Venables, D. A.; Barrows, L. R.; Lassota,
P.; Ireland, C. M. Tetrahedron Lett. 1997, 38, 721. Hooper,
G. J.; Davies Coleman, M. T.; Kelly Borges, M.; Coetzee, P. S.
Tetrahedron Lett. 1996, 37, 7135.
Compound
Formula
IC50 (mM)
E€ect on cellular cycle
2
C22H19N4O3F3
5.3
0.3
0.38
2.1
Nonspeci®c
Nonspeci®c
Nonspeci®c
Nonspeci®c
Nonspeci®c
10
11
12
13
C
18H20N4O5F6
C20H22N4O5F6
20H18N3O4F3
C12H10N3O3F3
C
0.25
prove that the pyrroloiminoquinone skeleton on its own is
not able to exert a speci®c cytotoxic action.
2. Kokoshka, J. M.; Capson, T. L.; Holden, J. A.; Ireland, C.
M.; Barrows, L. R. Anti-Cancer Drug Des. 1996, 7, 758.
3. Zhang, L.; Cava, M. P.; Rogers, R. D.; Rogers, L. M.
Tetrahedron Lett. 1998, 39, 7677. Barret, R.; Roue, N. Tetra-
hedron Lett. 1999, 34, 1053.
Conclusion
In conclusion, we achieved the synthesis of an opened
analogue of wakayin whose structure is the closest to
the natural compound yet published. Two products
with basic side chains were also formed as well as the
marine alkaloids makaluvamines D and I. These pro-
ducts, especially water soluble compounds 10, 11 and
13, proved to be quite good cytotoxic agents despite
their lack of interaction with the L1210 cellular cycle.
4. Beneteau, V.; Besson, T.; Guillard, J.; Leonce, S.; Pfei€er,
B. Eur. J. Med. Chem. 1999, 34, 1053.
5. Roberts, D.; Joule, J. A.; Bros, M. A.; Alvarez, M. J. Org.
Chem. 1997, 62, 568. Alvarez, M.; Bros, M. A.; Gras, G.;
Ajana, U.; Joule, J. A. Eur. J. Org. Chem. 1999, 1173. For a
review see Alvarez, M.; Bros, M. A.; Joule, J. A. Recent Res.
Devel. Org. Bioorg. Chem. 1999, 3, 29.
6. Xie, G.; Gupta, R.; Atchinson, K.; Lown, J. W. J. Med.
Chem. 1996, 39, 1049. Krapcho, A. P.; Menta, E.; Oliva, A.;
Domenico, R. D.; Fiocchi, L.; Maresh, M. E.; Gallagha, C. E.;
Hacker, M. P.; Beggiolin, G.; Giuliani, F. C.; Pezzoni, G.;
Spinelli, S. J. Med. Chem. 1998, 41, 5429. Todd, A. K.;
Adams, A.; Thorpe, J. H.; Denny, W. A.; Wakelin, L. P. G.;
Cardin, C. J. J. Med. Chem. 1999, 42, 536.
We are now focusing our e€orts on the introduction of
a C C bond at C-6 in order to mimic veiutamine, the
most active pyrroliminoquinone alkaloid recently iso-
lated from the Fijian sponge Zyzzya fuliginosa.
7. Selected data for compound 2: IR (KBr) n 3121, 1680,
1555, 1403, 1338, 1206 cm
1
.
1H NMR (DMSO-d6) 2.87 (t,
Acknowledgements
2H, J 7.5 Hz), 3.03 (t, 2H, J 7.5 Hz), 3.59 (m, 2H), 3.79 (dt, 2H,
J 7.5 Hz and J 3 Hz), 5.49 (s, 1H), 6.99 (t, 1H, J 7.3 Hz), 7.07
(t, 1H, J 7.3 Hz), 7.22 (d, 1H, J 2.4 Hz), 7.34 (d, 1H, J 7.3 Hz),
We thank the Comite de Charente-Maritime de la Ligue
contre le Cancer for ®nancial support.

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V. Beneteau et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2231±2234
2234
7.34 (s, 1H), 7.56 (d, 1H, J 7.3 Hz), 9.11 (t, 1H, J 6.2 Hz), 10.43
(s, 1H), 10.92 (s, 1H), 13.10 (s, 1H). 13C NMR (DMSO-d6)
18.15; 23.30; 42.43; 44.15; 83.96; 110.62; 110.63; 111.49;
118.18; 118.42; 118.70; 121.10; 122.64; 123.12; 123.81; 126.97;
136.24; 153.12; 157.07; 167.48. MS (FAB) m/z 331 (M+H,
100%), 201 (M C9H8N, 21), 188 (10). Anal. calcd for
C22H19N4O3F3: C, 59.46; H, 4.31; N, 12.61; found: C, 59.51;
H, 4.35; N, 12.76. All compounds were fully characterized by
spectroscopic and elemental analysis. Structural data for
compounds 13 and 14 are consistent with those previously
reported.
8. Leonce, S.; Perez, V.; Casabianca-Pignede, M. R.; Anstett,
M.; Bisagni, E.; Atassi, G. Invest. New Drugs 1996, 14, 169.
9. Barrows, L. R.; Radisky, D. C.; Copp, B. R.; Swa€ar, D.
S.; Kramer, R. A.; Warters, R. L.; Ireland, C. M. Anti-Cancer
Drug Des. 1993, 8, 333.