Direct metalation of heteroaromatic esters and nitriles using a mixed lithium-cadmium base. Subsequent conversion to dipyridopyrimidinones

Article abstract of DOI:10.1021/jo902385h

(Chemical Equation Presented) All pyridine nitriles and esters were metalated at the position next to the directing group using (TMP) ₃CdLi in tetrahydrofuran at room temperature. The 2-, 3-, and 4-cyanopyridines were treated with 0.5 equiv of base for 2 h to afford, after subsequent trapping with iodine, the corresponding 3-iodo, 2-iodo, and 3-iodo derivatives, respectively, in yields ranging from 30 to 61%. Cyanopyrazine was similarly functionalized at the 3 position in 43% yield. Ethyl 3-iodopicolinate and -isonicotinate were synthesized from the corresponding pyridine esters in 58 and 65% yield. Less stable ethyl 4-iodonicotinate also formed under the same conditions and was directly converted to ethyl 4-(pyrazol-1-yl)nicotinate in a two-step 38% yield. All three ethyl iodopyridinecarboxylates were involved in a one-pot palladium-catalyzed cross-coupling reaction/cyclization using 2-aminopyridine to afford new dipyrido[1,2-a:3′,2′-d]pyrimidin-11- one, dipyrido[1,2-a:4′,3′-d]pyrimidin-11-one, and dipyrido[1,2-a:3′,4′-d]pyrimidin-5-one in yields ranging from 50 to 62%. A similar crosscoupling/ cyclization sequence was applied to methyl 2-chloronicotinate using 2-aminopyridine, 2-amino-5-methylpyridine, and 1-aminoisoquinoline to give the corresponding tricyclic or tetracyclic compounds in 43-79% yield. Dipyrido[1,2-a:4′,3′-d]pyrimidin-11-one and dipyrido[1,2-a:3′,4′-d]pyrimidin-5-one showed a good bactericidal activity against Pseudomonas aeroginosa. Dipyrido-[1,2-a:2′,3′-d] pyrimidin-5-one and pyrido[2′,3′:4,5]pyrimidino[2,1-a]isoquinolin-8- one showed a fungicidal activity against Fusarium and dipyrido[1,2-a:4′, 3′-d]pyrimidin-11-one against Candida albicans. Ethyl 4-(pyrazol-1-yl) nicotinate and dipyrido[1,2-a:2′,3′-d]pyrimidin-5-one have promising cytotoxic activities, the former toward a liver carcinoma cell line (HEPG2) and the latter toward a human breast carcinoma cell line (MCF7).

Full text of DOI:10.1021/jo902385h

pubs.acs.org/joc
Direct Metalation of Heteroaromatic Esters and Nitriles Using a Mixed
Lithium-Cadmium Base. Subsequent Conversion
to Dipyridopyrimidinones
†
,§
,z
Ghenia Bentabed-Ababsa,†,‡ Sidaty Cheikh Sid Ely, Stephanie Hesse,* Ekhlass Nassar,*
ꢀ
Floris Chevallier,† Tan Tai Nguyen,† Aıcha Derdour,‡ and Florence Mongin*,†
†
ꢀ
ꢀ
^
Chimie et Photonique Moleculaires, UMR 6510 CNRS, Universite de Rennes 1, Batiment 10A, Case 1003,
‡
Campus Scientifique de Beaulieu, 35042 Rennes, France, Laboratoire de Synthese Organique Appliquee, Faculte
ꢁ
des Sciences de l’Universite, BP 1524 Es-Senia, Oran 31000, Algeria, Laboratoire d’Ingenierie Moleculaire et
ꢀ
ꢀ
§
ꢀ
ꢀ ꢀ
ꢀ
Biochimie Pharmacologique, Institut Jean Barriol, FR CNRS 2843, Universite Paul Verlaine-Metz, 1 Boulevard
ꢀ
Arago, 57070 Metz Technopole, France, and Department of Chemistry, Faculty of Women for Arts, Science and
z
^
Education, Ain Shams University, Asma Fahmy Street, Heleopolis (El-Margany), Cairo, Egypt
florence.mongin@univ-rennes1.fr
Received November 7, 2009
All pyridine nitriles and esters were metalated at the position next to the directing group using
(TMP)3CdLi in tetrahydrofuran at room temperature. The 2-, 3-, and 4-cyanopyridines were treated
with 0.5 equiv of base for 2 h to afford, after subsequent trapping with iodine, the corresponding
3-iodo, 2-iodo, and 3-iodo derivatives, respectively, in yields ranging from 30 to 61%. Cyanopyrazine
was similarly functionalized at the 3 position in 43% yield. Ethyl 3-iodopicolinate and -isonicotinate
were synthesized from the corresponding pyridine esters in 58 and 65% yield. Less stable ethyl
4-iodonicotinate also formed under the same conditions and was directly converted to ethyl
4-(pyrazol-1-yl)nicotinate in a two-step 38% yield. All three ethyl iodopyridinecarboxylates were
involved in a one-pot palladium-catalyzed cross-coupling reaction/cyclization using 2-aminopyri-
dine to afford new dipyrido[1,2-a:30,20-d]pyrimidin-11-one, dipyrido[1,2-a:40,30-d]pyrimidin-11-one,
and dipyrido[1,2-a:30,40-d]pyrimidin-5-one in yields ranging from 50 to 62%. A similar cross-
coupling/cyclization sequence was applied to methyl 2-chloronicotinate using 2-aminopyridine,
2-amino-5-methylpyridine, and 1-aminoisoquinoline to give the corresponding tricyclic or tetracyclic
compounds in 43-79% yield. Dipyrido[1,2-a:40,30-d]pyrimidin-11-one and dipyrido[1,2-a:30,40-
d]pyrimidin-5-one showed a good bactericidal activity against Pseudomonas aeroginosa. Dipyrido-
[1,2-a:20,30-d]pyrimidin-5-one and pyrido[20,30:4,5]pyrimidino[2,1-a]isoquinolin-8-one showed a fun-
gicidal activity against Fusarium and dipyrido[1,2-a:40,30-d]pyrimidin-11-one against Candida
albicans. Ethyl 4-(pyrazol-1-yl)nicotinate and dipyrido[1,2-a:20,30-d]pyrimidin-5-one have promising
cytotoxic activities, the former toward a liver carcinoma cell line (HEPG2) and the latter toward a
human breast carcinoma cell line (MCF7).
Introduction
such as material science, has resulted in extensive efforts on
synthesis methodologies.1 The deprotonative metalation
Interest in pyridine natural products and pharmaceuticals,
as well as pyridine building blocks for various applications
(1) (a) Katritzky, A. R. Handbook of Heterocyclic Chemistry, 1st ed.;
Pergamon: New York, 1985. (b) Eicher, T.; Hauptmann, S.; Speicher, A. The
Chemistry of Heterocycles, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2003;
Chapter 6.
*To whom correspondence should be addressed. Phone: þ33 2 2323 6931.
Fax: þ33 2 2323 6955.
DOI: 10.1021/jo902385h
r
Published on Web 12/23/2009
J. Org. Chem. 2010, 75, 839–847 839
2009 American Chemical Society

Bentabed-Ababsa et al.
JOCArticle
using lithium bases has been widely used as a powerful
method for the regioselective functionalization of such sub-
strates.2 Nevertheless, the incompatibility of lithium com-
pounds with reactive functions or sensitive heterocycles can
be a limit to their use for the elaboration of complex
molecules. Recourse to softer magnesium bases can improve
the chemoselectivity of deprotonation reactions, but it is to
the detriment of their efficiency since a large excess of base
has, in general, to be used.3
The use of metal additives to get more efficient or more
chemoselective bases (synergic superbases) has been, respec-
tively, developed by Schlosser4 and Lochmann5 with LIC-
KOR, mixture of butyllithium (LIC) and potassium tert-
ꢁ
butoxide (KOR), and by Caubere, Gros and Fort in the
pyridine series with BuLi-LiDMAE (DMAE = 2-dimethyl-
0
aminoethoxide). More recently, other (R)n(R )n MLi-type
bases, but with M different from an alkali metal, have been
described by different groups.8 By combining alkali additives
with soft organometallic compounds, bases such as R2Zn-
and Mulvey),12 Al(TMP)3 3LiCl (Knochel),13 (Me3SiCH2)2-
3
Mn(TMP)Li TMEDA (Mulvey),14 and MeCu(TMP)(CN)-
3
Li2 (Uchiyama and Wheatley)15 have been prepared, character-
ized, and used to generate functionalized aromatic compounds.
We recently accomplished the room temperature depro-
tometalation of a large range of substrates including sensitive
heterocycles and functionalized benzenes using a newly
developed lithium-cadmium base, (TMP)3CdLi, prepared
from CdCl2 TMEDA and 3 equiv of LiTMP.16 If TMEDA
3
is often employed in solvents of low or modest polarities to
enhance the reactivity of a base9d,e or to obtain a specific
regioselectivity,2 it was here rather used in order to simplify
the reaction protocol, CdCl2 TMEDA being much less
3
sensitive to hydration than free CdCl2.17
6
7
We here describe the use of (TMP)3CdLi for the functio-
nalization of pyridine esters and nitriles. Ethyl iodopyridine-
carboxylates thus obtained appeared as useful key synthetic
intermediates for the synthesis of polycyclic compounds con-
taining a dipyridopyrimidinone skeleton. Some compounds
were evaluated for their antimicrobial and cytotoxic activity.
0
t
(TMP)Li( TMEDA) (R = Bu, Bu; TMP = 2,2,6,6-tetra-
3
methylpiperidino) (described by the groups of Kondo,
Uchiyama, Mulvey, and Hevia),9 (TMP)2Zn 2MgCl2 2LiCl10
Results and Discussion
3
3
and TMPZnCl LiCl11 (Knochel), iBu3Al(TMP)Li (Uchiyama
3
Synthetic Aspects. Due to their electrophilic functional
group and to their ring prone to nucleophilic attacks, cyano-
pyridines have never been metalated at room temperature.
Reactions using cyano as a group to direct ortho-lithiation
have been reported in the benzene series from 1982,18 but the
first example in the pyridine series only appeared 20 years
later. Larock and co-workers showed in 2002 that it was
possible to lithiate 3-cyanopyridine using LiTMP in tetrahy-
drofuran (THF) at -78 °C. This result was evidenced by
subsequent trapping with iodine to afford a 1:1 mixture of the
2- and 4-iodo compounds in a 50% total yield.19 Rault and
co-workers achieved in 2005 the regioselective20 functionali-
zation of the other cyanopyridine isomers using 2 equiv of the
same hindered lithium amide in THF at -80 °C for 0.75 h.21
ꢀ
(2) (a) Queguiner, G.; Marsais, F.; Snieckus, V.; Epsztajn, J. Adv.
Heterocycl. Chem. 1991, 52, 187–304. (b) Mongin, F.; Queguiner, G. Tetra-
hedron 2001, 57, 4059–4090. (c) Turck, A.; Ple, N.; Mongin, F.; Queguiner,
G. Tetrahedron 2001, 57, 4489–4505. (d) Schlosser, M.; Mongin, F. Chem.
Soc. Rev. 2007, 36, 1161–1172. (e) Chevallier, F.; Mongin, F. Chem. Soc. Rev.
2008, 37, 595–609.
(3) (a) Schlecker, W.; Huth, A.; Ottow, E.; Mulzer, J. J. Org. Chem. 1995,
60, 8414–8416. (b) Schlecker, W.; Huth, A.; Ottow, E.; Mulzer, J. Liebigs
Ann. Chem. 1995, 1441–1446. (c) Schlecker, W.; Huth, A.; Ottow, E.; Mulzer,
J. Synthesis 1995, 1225–1227.
(4) Schlosser, M. Pure Appl. Chem. 1988, 60, 1627–1634.
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(6) Caubere, P. Chem. Rev. 1993, 93, 2317–2334.
(7) Gros, P.; Fort, Y. Eur. J. Org. Chem. 2002, 3375–3383.
(8) For reviews, see: (a) Mulvey, R. E. Organometallics 2006, 25, 1060–
1075. (b) Mulvey, R. E.; Mongin, F.; Uchiyama, M.; Kondo, Y. Angew.
Chem., Int. Ed. 2007, 46, 3802–3824. (c) Mulvey, R. E. Acc. Chem. Res. 2009,
42, 743–755.
(9) (a) Kondo, Y.; Shilai, M.; Uchiyama, M.; Sakamoto, T. J. Am. Chem.
Soc. 1999, 121, 3539–3540. (b) Uchiyama, M.; Miyoshi, T.; Kajihara, Y.;
Sakamoto, T.; Otani, Y.; Ohwada, T.; Kondo, Y. J. Am. Chem. Soc. 2002,
124, 8514–8515. (c) Barley, H. R. L.; Clegg, W.; Dale, S. H.; Hevia, E.;
Honeyman, G. W.; Kennedy, A. R.; Mulvey, R. E. Angew. Chem., Int. Ed.
2005, 44, 6018–6021. (d) Clegg, W.; Dale, S. H.; Hevia, E.; Honeyman,
G. W.; Mulvey, R. E. Angew. Chem., Int. Ed. 2006, 45, 2370–2374. (e) Clegg,
W.; Dale, S. H.; Harrington, R. W.; Hevia, E.; Honeyman, G. W.; Mulvey,
R. E. Angew. Chem., Int. Ed. 2006, 45, 2374–2377. (f) Clegg, W.; Dale, S. H.;
Drummond, A. M.; Hevia, E.; Honeyman, G. W.; Mulvey, R. E. J. Am.
Chem. Soc. 2006, 128, 7434–7435. (g) Uchiyama, M.; Kobayashi, Y.;
Furuyama, T.; Nakamura, S.; Kajihara, Y.; Miyoshi, T.; Sakamoto, T.;
Kondo, Y.; Morokuma, K. J. Am. Chem. Soc. 2008, 130, 472–480. (h) Clegg,
W.; Conway, B.; Hevia, E.; McCall, M. D.; Russo, L.; Mulvey, R. E. J. Am.
Chem. Soc. 2009, 131, 2375–2384.
ꢀ
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(14) Garcia-Alvarez, J.; Kennedy, A. R.; Klett, J.; Mulvey, R. E. Angew.
Chem., Int. Ed. 2007, 46, 1105–1108.
(15) Usui, S.; Hashimoto, Y.; Morey, J. V.; Wheatley, A. E. H.; Uchiyama,
M. J. Am. Chem. Soc. 2007, 129, 15102–15103.
(16) (a) L’Helgoual’ch, J.-M.; Bentabed-Ababsa, G.; Chevallier, F.;
Yonehara, M.; Uchiyama, M.; Derdour, A.; Mongin, F. Chem. Commun.
2008, 5375–5377. (b) L’Helgoual’ch, J.-M.; Bentabed-Ababsa, G.; Chevallier,
F.; Derdour, A.; Mongin, F. Synthesis 2008, 4033–4035. (c) Bentabed-Ababsa,
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G.; Blanco, F.; Derdour, A.; Mongin, F.; Trecourt, F.; Queguiner, G.;
Ballesteros, R.; Abarca, B. J. Org. Chem. 2009, 74, 163–169. (d) Snegaroff,
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Yonehara, M.; Uchiyama, M.; Derdour, A.; Mongin, F. Chem.;Eur. J. 2009,
15, 10280–10290.
(17) CdCl2 TMEDA can be prepared in large amounts (∼20 g) and
3
stored for several months in a desiccator, whereas free CdCl2 has to be
heated with a heat gun under vacuum for 30 min before each use.
(18) (a) Krizan, T. D.; Martin, J. C. J. Org. Chem. 1982, 47, 2681–2682.
(b) Krizan, T. D.; Martin, J. C. J. Am. Chem. Soc. 1983, 105, 6155–6157.
(19) Pletnev, A. A.; Tian, Q.; Larock, R. C. J. Org. Chem. 2002, 67, 9276–
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(10) (a) Wunderlich, S. H.; Knochel, P. Angew. Chem., Int. Ed. 2007, 46,
7685–7688. (b) Wunderlich, S.; Knochel, P. Chem. Commun. 2008, 6387–
6389. (c) Wunderlich, S. H.; Knochel, P. Org. Lett. 2008, 10, 4705–4707.
(d) Mosrin, M.; Knochel, P. Chem.;Eur. J. 2009, 15, 1468–1477.
(11) Mosrin, M.; Knochel, P. Org. Lett. 2009, 11, 1837–1840.
(12) (a) Uchiyama, M.; Naka, H.; Matsumoto, Y.; Ohwada, T. J. Am.
Chem. Soc. 2004, 126, 10526–10527. (b) Garcia-Alvarez, J.; Graham, D. V.;
Kennedy, A. R.; Mulvey, R. E.; Weatherstone, S. Chem. Commun. 2006, 30,
3208–3210. (c) Garcia-Alvarez, J.; Hevia, E.; Kennedy, A. R.; Klett, J.;
(20) Using Me3SiCl and I2 as electrophile, difunctionalized derivatives
concomitantly formed, probably through an homotransmetalation type
ꢀ
mechanism: Mallet, M.; Queguiner, G. Tetrahedron 1985, 16, 3433–3440.
(21) (a) Cailly, T.; Fabis, F.; Lemaitre, S.; Bouillon, A.; Rault, S. Tetrahedron
^
^
Mulvey, R. E. Chem. Commun. 2007, 2402–2404. (d) Conway, B.; Hevia, E.;
Garcı
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Lett. 2005, 46, 135–137. (b) Cailly, T.; Fabis, F.; Bouillon, A.; Lemaitre, S.;
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a-Alvarez, J.; Graham, D. V.; Kennedy, A. R.; Mulvey, R. E. Chem.
Sopkova, J.; de Santos, O.; Rault, S. Synlett 2006, 53–56. See also: (c) Cailly, T.;
Fabis, F.; Rault, S. Tetrahedron 2006, 62, 5862–5867. An in situ deprotona-
tion-trapping protocol has also been used for the synthesis of the corresponding
Commun. 2007, 5241–5243. (e) Naka, H.; Uchiyama, M.; Matsumoto, Y.;
Wheatley, A. E. H.; McPartlin, M.; Morey, J. V.; Kondo, Y. J. Am. Chem.
Soc. 2007, 129, 1921–1930. (f) Naka, H.; Morey, J. V.; Haywood, J.; Eisler,
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boronic esters: (d) Hansen, H. M.; Lysen, M.; Begtrup, M.; Kristensen, J. L.
^
Tetrahedron 2005, 61, 9955–9960. (e) Cailly, T.; Lemaitre, S.; Fabis, F.; Rault, S.
Synthesis 2007, 3247–3251. Note that butyllithium in a mixture of THF and
hexane has also been used, albeit in a low yield, to metalate 4-cyanopyridine at the
2 position: (f) Su, Y.-J.; Ko, C.-W. Chinese Pat. 1616471, 2005.
840 J. Org. Chem. Vol. 75, No. 3, 2010

Bentabed-Ababsa et al.
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The deprotonation of cyanopyridines (1-3) as well as
cyanopyrazine (4) was attempted using (TMP)3CdLi in
THF (Table 1), with this base being suitable to metalate
benzonitrile.16a Conducting the reaction from 2-cyanopyri-
dine (1) using 0.5 equiv of base at 0 °C for 2 h resulted, after
quenching with iodine, in the formation of a mixture from
which the main compound, 2-cyano-3-iodopyridine (5a),
was isolated in 39% yield (entry 1). When the reaction was
carried out at room temperature, the iodide 5a formed in
30% yield, due to the more important formation of side
products (entry 2). By using 1 equiv of base at room
temperature, the di- and triiodide 5b,c were obtained in 28
and 20% yield, respectively (entry 3). If the formation of a
diiodinated compound can be rationalized as the result of a
dimetalation, (TMP)3CdLi being able to dideprotonate sub-
strates such as pyrazine,16b thiazole,16a N-Boc pyrrole,16a
thiophenes,16a and [1,2,3]triazolo[1,5-a]pyridines,16c the
triiodide 5c could rather result from a metalation of 5b
during the trapping step with iodine, as already suggested
in the case of 3-(2-pyridyl)-[1,2,3]triazolo[1,5-a]pyridine.16c
The reaction from 4-cyanopyridine (2) was then attempted
using 0.5 equiv of base at 0 °C for 2 h; subsequent trapping
with iodine afforded a mixture of 4-cyano-3-iodo- and
4-cyano-3,5-diodopyridine (6a,b) in 30 and 20% yield, respec-
tively (entry 4). By performing the reaction at room tempera-
ture, the diiodide was not observed, but a 72:28 ratio of
4-cyano-3-iodopyridine (6a) and isomeric 4-cyano-2-iodopyri-
dine (6c) was obtained instead, the latter being isolated in
44and 10% yield, respectively (entry 5). Surprisingly, carrying
out the reaction with 1 equiv of base resulted in the formation
of the diiodide 6d under the same conditions (entry 6).
TABLE 1. Deprotonation of 1-4 Using (TMP)3CdLi Followed by
Trapping with I2
The results obtained with 3-cyanopyridine (3) were less
disappointing. Indeed, when exposed to 0.5 equiv of base at
room temperature for 2 h, this substrate was regioselectively
metalated at the 2 position. This was demonstrated by
subsequent interception with iodine to afford the derivative
7 in 61% yield (entry 7). This regioselectivity is different to
that previously documented by other teams using LiTMP in
THF at low temperatures; indeed, by using the lithium
amide, the metalation took place unregioselectively at the
positions adjacent to the cyano group.19,21a Such a result
could be partly explained by the presence of a different
directing group for the metalation using LiTMP than for that
using (TMP)3CdLi; whereas a first equivalent of LiTMP adds
to the cyano group in the study performed by Rault et al., it
does not seem to be the case with (TMP)3CdLi (Scheme 1).
These conditions were extended to cyanopyrazine (4) for
which metalation mainly took place at the position next to
the cyano group to furnish the iodide 8 in 43% yield (entry 8).
The compatibility of an ester function with (TMP)3CdLi
in THF at room temperature has been recently evidenced
with the possible metalation of methyl benzoate.16a Using
ethyl thiophene-2-carboxylate (9) as substrate also resulted
in its cadmation.22 After a 2 h contact with 0.5 equiv of base
followed by quenching with iodine, the 5-iodo derivative 10
was obtained in 77% yield (Scheme 2).
aOther compounds including 2-cyano-3,4-diiodopyridine and 2-cya-
no-3,6-diiodopyridine were identified in the crude. Other compounds
including 2-cyano-6-iodopyridine and 2-cyano-3,6-diiodopyridine were
identified in the crude. cA mixture of 8 and an unidentified diiodide was
obtained in a 75:25 ratio.
b
their ring. In 2007, Knochel and co-workers reported the
magnesiation of ethyl isonicotinate using (TMP)2Mg 2LiCl
Deprotonation of ethyl pyridinecarboxylates is a much
more difficult challenge due to easy nucleophilic attacks on
3
in THF at -40 °C for 12 h to give, after trapping with iodine,
the corresponding 3-iodo derivative in 66% yield.23
(22) Ethyl thiophene-2-carboxylate (9) has previously been metalated
using Pr2NMgCl (2 equiv) in THF at room temperature for 10 min and
i
trapped with iodine to provide the iodide 10 in 77% yield: Shilai, M.; Kondo,
Y.; Sakamoto, T. J. Chem. Soc., Perkin Trans. 1 2001, 442–444.
(23) Clososki, G. C.; Rohbogner, C. J.; Knochel, P. Angew. Chem., Int.
Ed. 2007, 46, 7681–7684.
J. Org. Chem. Vol. 75, No. 3, 2010 841

Bentabed-Ababsa et al.
SCHEME 1. 3-Cyanopyridine (3): Comparisons of the Species before Ring Deprotonation Using LiTMP and (TMP)3CdLi
JOCArticle
SCHEME 2. Functionalization of Ethyl Thiophene-2-carboxy-
late (9) Using (TMP)3CdLi
TABLE 2. Deprotonation of 11-14 Using (TMP)3CdLi Followed by
Trapping with I2
The deprotonation of the different pyridine or pyridazine
esters 11-14 was attempted using (TMP)3CdLi in THF at
room temperature for 2 h, and the metalated species was
intercepted with iodine (Table 2). Conducting the reaction
from ethyl picolinate (11) using 0.5 equiv of base resulted in
the major formation of the 3-iodo derivative 15, which was
isolated in 58% yield (entry 1). Ethyl isonicotinate (12) simi-
larly furnished the 3-iodo compound 16, and the yield of 65%
could be slightly improved to 72% using 1 equiv of base (entries
2 and 3). Surprisingly, methyl pyridazine-4-carboxylate (13)
behaved differently when submitted to 0.5 equiv of base, with a
complex mixture of mono- and diiodides formed (entry 4).
When treated under the same conditions, ethyl nicotinate (14)
allowed the synthesis of the 4-iodo derivative 17 (entry 5). The
latter could not be isolated due its instability over silica gel but
could be identified by NMR. It was involved without purifica-
tion in a known copper-catalyzed reaction24 with pyrazole to
provide the expected derivative 18 in a two-step 38% yield
(Scheme 3).
It was then decided to involve in the deprotonation-trapping
sequence methyl pyridine-2,6-dicarboxylate (19). By using 0.5
equiv of (TMP)3CdLi, the 3-iodo, 4-iodo and 3,4-diiodo deri-
vatives 20-22 were obtained in a 63:28:9 ratio. Whereas the
main compounds 20 and 21 were isolated from the mixture in 35
and 3% yield, respectively, methyl 3,4-diiodopyridine-2,6-di-
carboxylate (22) was only identified from the NMR spectra of
the crude. Turning to 1 equiv of base resulted in the formation of
a fourth derivative, methyl 3,5-diiodopyridine-2,6-carboxylate
(23), together with the previous iodides. It was isolated from the
22:25:4:49 mixture of the 3-iodo, 4-iodo, 3,5-diiodo, and 3,4-
diiodo compounds in a modest 14% yield (Scheme 4).
Aiming to valorize the newly synthesized ethyl iodopyr-
idinecarboxylates 15-17, we studied their reactivity in
palladium-catalyzed cross-coupling reactions. Especially,
as done previously on ethyl halogenothiophenecarboxy-
lates,25 we decided to couple those compounds, as well as
methyl 2-chloronicotinate (24), with 2-aminopyridines
25-27 in order to access to polycyclic compounds contain-
ing a pyridopyrimidinone moiety (Scheme 5 and Table 3).
SCHEME 3. Synthesis of Ethyl 4-(pyrazol-1-yl)nicotinate (18)
Indeed, the pyridopyrimidinone core is present in a
number of biologically active substances. For example, aza
analogues of methaqualone26 and 2-substituted 3-arylpy-
rido[2,3-d]pyrimidinones27 proved to be anticonvulsant
agents, whereas some aza-quinazolinones28 were described
(26) Vaidya, N. A.; Panos, C. H.; Kite, A.; Ben Iturrian, W.; De Witt
Blanton, C. J. Med. Chem. 1983, 26, 1422–1425.
(27) White, D. C.; Greenwood, T. D.; Downey, A. L.; Bloomquist, J. R.;
Wolfe, J. F. Bioorg. Med. Chem. Lett. 2004, 5711–5717.
(24) Cristau, H.-J.; Cellier, P. P.; Spindler, J.-F.; Taillefer, M. Eur. J. Org.
Chem. 2004, 695–709.
(25) Begouin, A.; Hesse, S.; Queiroz, M. J. R. P.; Kirsch, G. Synthesis
2006, 2794–2798.
(28) Johnson, M.; Li, A.-R.; Liu, J.; Fu, Z.; Zhu, L.; Miao, S.; Wang, X.;
Xu, Q.; Huang, A.; Marcus, A.; Xu, F.; Ebsworth, K.; Sablan, E.; Danao, J.;
Kumer, J.; Dairaghi, D.; Lawrence, C.; Sullivan, T.; Tonn, G.; Schall, T.;
Collins, T.; Medina, J. Bioorg. Med. Chem. Lett. 2007, 3339–3343.
842 J. Org. Chem. Vol. 75, No. 3, 2010

Bentabed-Ababsa et al.
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SCHEME 4. Deprotonation of 19 Using (TMP)3CdLi Followed by Trapping with I2
SCHEME 5. Synthetic Scheme for the Synthesis of Tricyclic (or Tetracyclic) Compounds
as antagonists of CXCR3. Aza-tryptanthrins exhibited anti-
trypanosomal activity29 and inhibited Plasmodium falciparum
cyclin-dependent kinases.30
TABLE 3. Buchwald-Hartwig Cross-Coupling of 24, 15-17
Optimization of the reaction conditions was conducted by
coupling methyl 2-chloronicotinate (24) with 2-aminopyridine
(25). Whereas ethyl bromothiophenecarboxylates were very
sensitive to the reaction conditions (several cycles of evacua-
tion-backfilling with argon were needed) and required high
catalyst loading (7 mol % of palladium acetate and 5 mol % of
Xantphos), halogenopyridinecarboxylates gave good results
using only 3 mol % of palladium acetate and 3.5 mol % of
Xantphos. Moreover, a simple purge of argon was sufficient.
The C-N coupling followed by the intramolecular cyclization
involving the nitrogen atom of the pyridine ring and the
carbonyl moiety of the carboxylate took place at room tem-
perature but in a very low yield. Turning to 55 °C and 18 h of
reaction allowed the formation of the expected product 28 in
20% yield. Finally, the best yield (66%) was obtained conduct-
ing the reaction at 95 °C for 24 h (entry 1). Those conditions
were then extended to the use of 2-amino-5-methylpyridine (26)
and 1-aminoisoquinoline (27). The methylated compound 29
was obtained after only 2.5 h of reaction in 79% yield (entry 2),
and the tetracyclic compound 30 in a lower 43% yield (entry 3).
Involving the iodo esters 15-17 in the reaction similarly
resulted in the formation of the tricyclic compounds 31-33
(entries 4-6). Whereas 30-33 are new compounds, 28 and 29
were soon described in the literature;31 they were obtained
thanks to a two-step process including Ullman reaction of
2-halogenonicotinic acid with 2-aminopyridine-1-oxides and
subsequent intramolecular cyclization of the resulting 3-car-
boxy-2,20-bipyridylamin-10-oxides using PCl3.
Pharmacology. Applying the agar plate diffusion techni-
que,32 the newly synthesized compounds 28-33 were
(29) (a) Scovill, J.; Blank, E.; Konnick, M.; Nenortas, E.; Shapiro, T.
Antimicrob. Agents Chemother. 2002, 46, 882–883. (b) Bhattacharjee, A. K.;
Skancky, D. J.; Jennings, B.; Hudson, T. H.; Brendle, J. J.; Werbovetz, K. A.
Bioorg. Med. Chem. 2002, 10, 1979–1989.
(30) Bhattacharjee, A. K.; Geyer, J. A.; Woodard, C. L.; Kathcart, A. K.;
Nichols, D. A.; Prigge, S. T.; Mott, B. T.; Waters, N. C. J. Med. Chem. 2004,
47, 5418–5426.
aFor two steps.
(31) Rylowski, A.; Pucko, W. Acta Pol. Pharm. 1997, 54, 325–330.
(32) Bauer, A. W.; Mkriby, W. W.; Sherris, J. C.; Turck, M. Am. J. Clin.
Pathol. 1966, 45, 493.
screened in vitro for their bactericidal activity against Gram
positive bacteria (Staphylococcus aureus) and Gram negative
J. Org. Chem. Vol. 75, No. 3, 2010 843

Bentabed-Ababsa et al.
JOCArticle
TABLE 4. Bactericidal and Fungicidal Activity of Compounds 28-33 and Ciprofloxacin and Nystina
entry
compound
Staphylococcus aureus Escherichia coli Pseudomonas aeroginosa
Fusarium
27 (þþþ)
17 (þþ)
Aspergillus niger Candida albicans
1
2
3
4
5
6
7
8
28
19 (þþ)
18 (þþ)
-
-
-
-
24 (þþ)
19 (þþ)
-
-
-
22 (þþ)
16 (þþ)
19 (þþ)
18 (þþ)
25 (þþþ)
22 (þþ)
29
30
31
32
33
56 (þþþþþþ) 18 (þþ)
16 (þþ)
17 (þþ)
17 (þþ)
-
-
-
-
-
-
18 (þþ)
25 (þþþ)
25 (þþþ)
þþþ
20 (þþ)
-
-
ciprofloxacin þþþ
þþþ
nystin
þþþ
þþþ
þþþ
aThe diameters of zones of inhibition are given in millimeters. Stock solution: 5 μg in 1 mL of DMF; 1 mL of stock solution in each hole of each paper
disk. þ: <15 mm; þþ: 15-24 mm; þþþ: 25-34 mm; þþþþ: 35-44 mm, etc.
Because of the toxicity of cadmium compounds,33 the
use of other ate bases was before considered. Polar mix-
TABLE 5. In Vitro Cytotoxic Activity (IC50) of Compounds 18, 28-33,
and Doxorubicin Against a Liver Carcinoma Cell Line (HEPG2), a
Human Breast Carcinoma Cell Line (MCF7), and a Cervix Carcinoma
tures including alkali (or alkaline-earth metal) were ruled
Cell Line (HeLa)a
out because of their lack of compatibility with both reac-
HEPG2
(μg mL-1
MCF7
(μg mL-1
HeLa
(μg mL-1
tive functions and sensitive aromatic heterocycles. Lithium
aluminate and cuprate were similarly discarded, sen-
sitive heterocycles being converted with these bases at
low temperatures.12,15 The 1:1 LiTMP/(TMP)2Zn lithium-
entry compound
)
)
)
3
3
3
1
2
3
4
5
6
7
8
18
28
29
30
31
32
0.89
1.70
2.27
1.77
1.47
1.81
1.58
0.60
2.38
0.78
2.99
1.73
2.50
2.34
1.96
0.70
1.51
1.39
3.11
1.09
3.26
2.31
1.70
0.85
zinc combination, prepared from ZnCl2 TMEDA and
3
3 equiv of LiTMP, allows efficient deprotonation reac-
tions of aromatic substrates.34 Nevertheless, it was not
employed here because reactions using it are, in general,
more weakly chemoselective,16b probably due to the pre-
sence of free LiTMP. Real lithium zincates could be more
suitable for the functionalization of heteroaromatic esters
and nitriles; studies in order to identify bases allowing more
efficient and chemoselective reactions are currently under
investigation.
33
doxorubicin
aIC50 is defined as the concentration which results in a 50% decrease
in cell number as compared with that of the control structures in the
absence of an inhibitor.
bacteria (Escherichia coli and Pseudomonas aeroginosa)
and for their fungicidal activity against Fusarium, Aspergillus
niger, and Candida albicans (Table 4). The compounds
32 and 33 showed a good bactericidal activity, similar to
that of ciprofloxacin, against Pseudomonas aeroginosa,
whereas 28 and 30 showed a good fungicidal activity, similar
to that of nystin, against Fusarium and 32 against Candida
albicans.
The compounds 18 and 28-33 were also tested against a
human liver carcinoma cell line (HEPG2), a human breast
carcinoma cell line (MCF7), and a cervix carcinoma cell line
(HeLa) (Table 5). Moderate cytotoxic activities were ob-
served; the compounds 18 and 28 were found to have more
promising activities toward HEPG2 and MCF7, respec-
tively, compared to a reference drug (doxorubicin).
Experimental Section
General Procedure A (Deprotonation Using 0.5 equiv of
CdCl2 TMEDA and 1.5 equiv of LiTMP Followed by Trapping
3
Using I2). To a stirred, cooled (0 °C) solution of 2,2,6,6-tetra-
methylpiperidine (0.52 mL, 3.0 mmol) in THF (5 mL) were
added BuLi (1.6 M hexanes solution, 3.0 mmol) and, 5 min later,
CdCl2 TMEDA35 (0.30 g, 1.0 mmol). The mixture was stirred
3
for 10 min at 0 °C before introduction of the substrate (2.0
mmol). After 2 h at room temperature, a solution of I2 (0.76 g,
3.0 mmol) in THF (5 mL) was added. The mixture was stirred
overnight before addition of an aq saturated solution of
Na2S2O3 (10 mL) and extraction with EtOAc (3 ꢀ 20 mL).
The combined organic layers were dried over MgSO4, filtered,
and concentrated under reduced pressure.
Conclusion
General Procedure B (Deprotonation Using 1.0 equiv of
CdCl2 TMEDA and 3.0 equiv of LiTMP Followed by Trapping
3
All pyridine nitriles and esters were metalated at the
position next to the directing group using 0.5 equiv of
(TMP)3CdLi in tetrahydrofuran at room temperature for
2 h. Subsequent trapping with iodine afforded the iodo
derivatives in yields ranging from 30 to 65%. The ethyl
iodopyridinecarboxylates thus obtained were then involved
in a one-pot palladium-catalyzed cross-coupling reaction/
cyclization using 2-aminopyridine to afford new polycyclic
compounds containing a pyridopyrimidinone moiety, which
were evaluated for their bactericidal and fungicidal activity.
Some of the newly synthesized compounds were tested for
their antitumor activity.
Using I2). To a stirred, cooled (0 °C) solution of 2,2,6,6-tetra-
methylpiperidine (1.1 mL, 6.0 mmol) in THF (5 mL) were
successively added BuLi (1.6 M hexanes solution, 6.0 mmol)
and, 5 min later, CdCl2 TMEDA35 (0.60 g, 2.0 mmol). The
3
mixture was stirred for 10 min at 0 °C before introduction of the
substrate (2.0 mmol). After 2 h at room temperature, a solution
of I2 (1.5 g, 6.0 mmol) in THF (5 mL) was added. The mixture
was stirred overnight before addition of an aq saturated solution
of Na2S2O3 (10 mL) and extraction with EtOAc (3 ꢀ 20 mL).
The combined organic layers were dried over MgSO4, filtered,
and concentrated under reduced pressure.
(34) L’Helgoual’ch, J.-M.; Seggio, A.; Chevallier, F.; Yonehara, M.;
Jeanneau, E.; Uchiyama, M.; Mongin, F. J. Org. Chem. 2008, 73, 177-183
and references cited therein.
(33) Shannon, M. Heavy Metal Poisoning. In Clinical Management of
Poisoning and Drug Overdose, 3rd ed.; Haddad, L. M., Shannon, M.,
Winchester, J. F., Eds.; W.B. Saunders: Philadelphia, PA, 1998. The use of
salts reduces the risk of cadmium absorption.
(35) CdCl2 TMEDA was prepared as described: Kedarnath, G.;
Kumbhare, L. B.; Jain, V. K.; Phadnis, P. P.; Nethaji, M. Dalton Trans.
2006, 2714–2718.
3
844 J. Org. Chem. Vol. 75, No. 3, 2010

Bentabed-Ababsa et al.
JOCArticle
2-Cyano-3-iodopyridine (5a).21a 5a was obtained according to
the general procedure A starting from 2-cyanopyridine (0.21 g),
but keeping the metalation temperature at 0 °C, and was isolated
after purification by flash chromatography on silica gel (eluent:
heptane/EtOAc 80/20) as a white powder (0.18 g, 39%): mp
98 °C; 1H NMR (200 MHz, CDCl3) δ 7.26 (dd, 1 H, J = 8.2 and
4.6 Hz), 8.24 (dd, 1 H, J = 8.2 and 1.4 Hz), 8.68 (dd, 1 H, J = 4.6
and 1.4 Hz); 13C NMR (50 MHz, CDCl3) δ 117.4, 127.5, 137.9,
138.5, 146.6, 149.4; HRMS calcd for C6H3IN2 (Mþ•) 229.9341,
found 229.9345.
(75 MHz, CDCl3) δ 110.6, 119.1, 121.0, 127.1, 133.1, 151.7;
HRMS calcd for C6H2I2N2 (Mþ•) 355.8307, found 355.8341.
3-Cyano-2-iodopyridine (7). 7 was obtained according to the
general procedure A starting from 3-cyanopyridine (0.21 g) and
isolated after purification by flash chromatography on silica gel
(eluent: heptane/EtOAc 80/20) as a beige powder (0.28 g, 61%):
mp 127 °C; 1H NMR (200 MHz, CDCl3) δ 7.43 (dd, 1 H, J = 7.7
and 4.9 Hz), 7.82 (dd, 1 H, J = 7.7 and 2.0 Hz), 8.54 (dd, 1 H,
J = 4.9 and 2.0 Hz); 13C NMR (50 MHz, CDCl3) δ 117.7, 119.9,
121.0, 122.5, 141.2, 152.9; HRMS calcd for C6H3IN2 (Mþ•
)
2-Cyano-6-iodopyridine was identified by its 1H NMR spectra
(300 MHz, CDCl3): δ 7.49 (t, 1 H, J = 7.8 Hz), 7.68 (dd, 1 H, J =
7.6 and 1.0 Hz), 7.95 (dd, 1 H, J = 7.8 and 1.0 Hz).
229.9341, found 229.9345. These data are analogous to those
previously described.19
2-Cyano-3-iodopyrazine (8).37 8 was obtained according
to the general procedure A starting from cyanopyrazine
(0.21 g) and isolated after purification by flash chromato-
graphy on silica gel (eluent: heptane/EtOAc 90/10) as a
2-Cyano-3,4-diiodopyridine was identified by its 1H NMR
spectra (300 MHz, CDCl3): δ 7.62 (d, 1 H, J = 8.4 Hz), 7.79
(d, 1 H, J = 8.4 Hz).
2-Cyano-3,6-diiodopyridine (5b).21a 5b was obtained accord-
ing to the general procedure B starting from 2-cyanopyridine
(0.21 g) and isolated after purification by flash chromatography
on silica gel (eluent: heptane/EtOAc 90/10) as a beige powder
(0.20 g, 28%): mp 140 °C; 1H NMR (300 MHz, CDCl3) δ 7.62
(d, 1 H, J = 8.4 Hz), 7.80 (d, 1 H, J = 8.4 Hz); 13C NMR (75
MHz, CDCl3) δ 97.7, 116.3, 116.5, 139.1, 140.0, 147.5; HRMS
calcd for C6H3I2N2 ([M þ H]þ) 356.8386, found 356.8387.
2-Cyano-3,4,6-triiodopyridine (5c). 5c was obtained according
to the general procedure B starting from 2-cyanopyridine (0.21
g) and isolated after purification by flash chromatography on
silica gel (eluent: heptane/EtOAc 90/10) as a yellow powder
(0.19 g, 20%): mp 211 °C; 1H NMR (300 MHz, CDCl3) δ 8.39
(s, 1 H); 13C NMR (75 MHz, CDCl3) δ 113.2, 115.9, 117.0,
122.4, 139.7, 147.1; HRMS calcd for C6H2I3N2 ([M þ H]þ)
482.7352, found 482.7352.
1
yellow powder (0.20 g, 43%): mp 107 °C; H NMR (300 MHz,
CDCl3) δ 8.54 (d, 1 H, J = 2.4 Hz), 8.65 (d, 1 H, J = 2.4 Hz); 13
C
NMR (75 MHz, CDCl3) δ 116.3, 120.7, 138.2, 143.2, 147.2;
HRMS calcd for C5H2IN3Na ([M þ Na]þ) 253.9191, found
253.9192.
Ethyl 5-iodothiophene-2-carboxylate (10). 10 was obtained
according to the general procedure A starting from ethyl
thiophene-2-carboxylate (0.31 g) and isolated after purification
by flash chromatography on silica gel (eluent: heptane/CH2Cl2
90/10) as a yellow oil (0.43 g, 77%): 1H NMR (300 MHz,
CDCl3) δ 1.36 (t, 3 H, J = 7.1 Hz), 4.33 (q, 2 H, J = 7.1 Hz),
7.25 (d, 1 H, J = 3.9 Hz), 7.42 (d, 1 H, J = 3.9 Hz); these data are
similar to those described;22 13C NMR (75 MHz, CDCl3) δ 14.4,
61.5, 82.6, 134.4, 137.8, 139.8, 161.0.
Ethyl 3-iodopicolinate (15).38 15 was obtained according to
the general procedure A starting from ethyl picolinate (0.30 g)
and isolated after purification by flash chromatography on silica
gel (eluent: heptane/EtOAc 80/20) as a yellow oil (0.32 g, 58%):
1H NMR (200 MHz, CDCl3) δ 1.45 (t, 3 H, J = 7.1 Hz), 4.47 (q,
2 H, J = 7.1 Hz), 7.11 (dd, 1 H, J = 8.2 and 4.7 Hz), 8.25 (dd,
4-Cyano-3-iodopyridine (6a).21a 6a was obtained according to
the general procedure A starting from 4-cyanopyridine (0.21 g)
and isolated after purification by flash chromatography on
silica gel (eluent: heptane/EtOAc 70/30) as a beige pow-
1
1 H, J = 8.2 and 1.4 Hz), 8.62 (dd, 1 H, J = 4.7 and 1.4 Hz); 13
C
der (0.20 g, 44%): mp 122 °C; H NMR (200 MHz, CDCl3)
δ 7.52 (dd, 1 H, J = 4.8 and 0.6 Hz), 8.71 (d, 1 H, J = 5.0 Hz),
9.10 (s, 1 H); 13C NMR (75 MHz, CDCl3) δ 96.4, 117.0, 127.1,
127.9, 148.9, 158.0; HRMS calcd for C6H3IN2 (Mþ•) 229.9341,
found 229.9345.
NMR (50 MHz, CDCl3) δ 14.1, 62.1, 92.1, 126.1, 126.2, 148.2,
152.3, 165.7; HRMS calcd for C8H8INO2 (Mþ•) 276.9600,
found 276.9609.
Ethyl 3-iodoisonicotinate (16).23 16 was obtained according to
the general procedure A starting from ethyl isonicotinate (0.30
g) and isolated after purification by flash chromatography on
silica gel (eluent: heptane/EtOAc 80/20) as an orange oil (0.36 g,
65%): 1H NMR (200 MHz, CDCl3) δ 1.41 (t, 3 H, J = 7.1 Hz),
4.42 (q, 2 H, J = 7.1 Hz), 7.62 (d, 1 H, J = 4.9 Hz), 8.60 (d, 1 H,
J = 4.8 Hz), 9.08 (s, 1H); 13C NMR (50 MHz, CDCl3) δ 14.0,
62.4, 92.3, 124.3, 142.3, 149.0, 159.4, 164.9; HRMS calcd for
C8H8INO2 (Mþ•) 276.9600, found 276.9609.
4-Cyano-3,5-diiodopyridine (6b).21a 6b was obtained accord-
ing to the general procedure A starting from 4-cyanopyridine
(0.21 g), but keeping the metalation temperature at 0 °C, and
was isolated after purification by flash chromatography on silica
gel (eluent: heptane/EtOAc 90/10) as a beige powder (0.14 g,
20%): mp 153 °C; 1H NMR (300 MHz, CDCl3) δ 8.97 (s, 2 H);
13C NMR (75 MHz, CDCl3) δ 97.3 (2C), 118.4, 134.5, 156.4
(2C); HRMS calcd for C6H2I2N2Na ([M þ Na]þ) 378.8205,
found 378.8207.
Methyl 3-iodopyridazine-4-carboxylate. A pure fraction was
isolated (eluent: heptane/EtOAc 85/15) from the crude obtained
according to the general procedure A as a yellow solid
4-Cyano-2-iodopyridine (6c).36 6c was obtained according to
the general procedure A starting from 4-cyanopyridine (0.21 g)
and isolated after purification by flash chromatography on silica
gel (eluent: heptane/EtOAc 70/30) as a beige powder (46 mg,
10%): mp 76 °C; 1H NMR (300 MHz, CDCl3) δ 7.50 (dd, 1 H,
J = 5.0 and 1.4 Hz), 7.96 (t, 1 H, J = 1.4 Hz), 8.56 (dd, 1 H, J =
5.0 and 1.4 Hz); 13C NMR (75 MHz, CDCl3) δ 114.6, 117.8,
1
(degradation to a dark residue upon standing): H NMR (300
MHz, CDCl3) δ 7.66 (d, 1 H, J = 5.0 Hz), 9.26 (d, 1 H, J = 5.0
Hz), 4.01 (s, 3 H); 13C NMR (75 MHz, CDCl3) δ 53.7, 77.4,
126.2, 135.3, 150.6, 164.4.
Methyl 3,5-diiodopyridazine-4-carboxylate. A pure fraction
was isolated (eluent: heptane/EtOAc 85/15) from the crude
obtained according to the general procedure A as a yellow solid
121.5, 124.1, 136.0, 151.3; HRMS calcd for C6H3IN2 (Mþ•
229.9341, found 229.9345.
)
1
4-Cyano-2,3-diiodopyridine (6d). 6d was obtained according
to the general procedure B starting from 4-cyanopyridine
(0.21 g) and isolated after purification by flash chromatography
on silica gel (eluent: heptane/EtOAc 80/20) as a beige powder
(0.36 g, 51%): mp 215 °C; 1H NMR (300 MHz, CDCl3) δ 7.84
(d, 1 H, J = 5.3 Hz), 8.08 (d, 1 H, J = 5.3 Hz); 13C NMR
(degradation to a dark residue upon standing): H NMR (300
MHz, CDCl3) δ 9.41 (s, 1 H), 4.03 (s, 3 H); 13C NMR (75 MHz,
CDCl3) δ 54.1, 97.4, 120.2, 145.6, 157.9, 165.4.
(37) Rodgers, J. D.; Robinson, D. J.; Arvanitis, A. G.; Maduskuie, T. P.,
Jr.; Shepard, S.; Storace, L.; Wang, H.; Rafalski, M.; Jalluri, R. K.; Combs,
A. P. PCT Int. Appl. WO2005105814, 2005.
(36) Jones, P.; Kinzel, O.; Llauger Bufi, L.; Muraglia, E.; Pescatore, G.;
Torrisi, C. PCT Int. Appl. WO2007138355, 2007.
(38) Giblin, G. M. P.; Hall, A.; Hurst, D. N. PCT Int. Appl.
WO2005037794, 2005.
J. Org. Chem. Vol. 75, No. 3, 2010 845

Bentabed-Ababsa et al.
JOCArticle
Ethyl 4-iodonicotinate (17). 17 was obtained according to the
general procedure A starting from ethyl nicotinate (0.30 g) but
could not be purified by flash chromatography on silica gel
because of its low stability. It was identified by NMR: 1H NMR
(200 MHz, CDCl3) δ 1.42 (t, 3 H, J = 7.1 Hz), 4.14 (q, 2 H, J =
7.1 Hz), 7.94 (d, 1 H, J = 5.3 Hz), 8.23 (d, 1 H, J = 5.3 Hz), 8.93
(s, 1 H); 13C NMR (50 MHz, CDCl3) δ 14.1, 62.1, 106.1, 131.0,
136.2, 151.0, 152.0, 164.7. The crude was directly involved in the
reactions giving the compounds 18 and 32.
Ethyl 4-(pyrazol-1-yl)nicotinate (18). 18 was obtained from
the crude compound 17 by adapting a procedure described24 and
was isolated after purification by flash chromatography on silica
gel (eluent: heptane/EtOAc 70/30) as an orange oil (0.17 g, two
steps, 38%): 1H NMR (300 MHz, CDCl3) δ 1.24 (t, 3 H, J = 7.1
Hz), 4.31 (q, 2 H, J = 7.2 Hz), 6.50 (dd, 1 H, J = 2.4 and 1.8 Hz),
7.48 (d, 1 H, J = 5.4 Hz), 7.75 (d, 1 H, J = 1.5 Hz), 7.83 (d, 1 H,
J = 2.7 Hz), 8.75 (d, 1 H, J = 5.1 Hz), 8.92 (s, 1H); 13C NMR
(75 MHz, CDCl3) δ 14.1, 62.1, 108.8, 117.1, 121.9, 129.5, 142.6,
145.1, 151.5, 152.9, 165.9; HRMS calcd for C11H12N3O2 ([M þ
H]þ) 218.0930, found 218.0932.
2-chloronicotinate (0.26 g) and 2-aminopyridine (0.17 g) and
was isolated after purification by chromatography on silica gel
(CHCl3 as eluent) as a yellow solid (0.20 g, 66%): mp 220-
221 °C (lit.40 223 °C); 1H NMR (250 MHz, CDCl3) δ 6.99 (m, 1
H), 7.43 (dd, 1 H, J = 8.0 and 4.4 Hz), 7.64-7.69 (m, 2H), 8.78
(dd, 1 H, J = 8.0 and 2.1 Hz), 8.89 (m, 1 H), 9.12 (dd, 1 H, J =
4.4 and 2.1 Hz); 13C NMR (62.5 MHz, CDCl3) δ 111.3, 113.5,
120.6, 126.7, 127.0, 135.7, 137.0, 149.8, 157.4, 157.8, 159.7; IR
(KBr) ν 1698, 1641, 1593, 1543, 1526, 1411 cm-1; HRMS calcd
for C11H8N3O ([M þ H]þ) 198.0662, found 198.0668.
8-Methyldipyrido[1,2-a:20,30-d]pyrimidin-5-one (29). 29 was
obtained according to the general procedure C starting from
methyl 2-chloronicotinate (0.26 g) and 2-amino-5-methylpyri-
dine (0.19 g) and was isolated after purification by chromatog-
raphy on silica gel (CHCl3 as eluent) as a yellow solid (0.25 g,
79%): mp 201-202 °C (lit.40 203 °C); 1H NMR (250 MHz,
CDCl3) δ 2.48 (s, 3 H), 6.82 (dd, 1 H, J = 7.5 and 1.8 Hz), 7.38
(dd, 1 H, J = 8.0 and 4.4 Hz), 7.45 (br s, 1 H), 8.74 (dd, 1 H, J =
8.0 and 2.1 Hz), 8.79 (d, 1 H, J = 7.5 Hz), 9.08 (dd, 1 H, J = 4.4
and 2.1 Hz); 13C NMR (62.5 MHz, CDCl3) δ 21.6, 110.9, 116.5,
120.1, 124.4, 126.0, 137.0, 147.8, 149.9, 157.7, 157.8, 159.8; IR
(KBr) ν 1693, 1651, 1592, 1543, 1412 cm-1; HRMS calcd for
C12H10N3O ([M þ H]þ) 212.0818, found 212.0826.
Methyl 3-iodopyridine-2,6-dicarboxylate (20). 20 was ob-
tained according to the general procedure A starting from
methyl pyridine-2,6-dicarboxylate (0.39 g) and isolated by flash
chromatography on silica gel (eluent: heptane/CH2Cl2 80/20) as
Pyrido[20,30:4,5]pyrimidino[2,1-a]isoquinolin-8-one (30). 30 was
obtained according to the general procedure C starting from
methyl 2-chloronicotinate (0.26 g) and 1-aminoisoquinoline
(0.26 g) and was isolated after purification by chromatography
onsilicagel (eluent:EtOAc/C6H12 70/30) asa yellow solid(95mg,
1
a pale orange powder (0.22 g, 35%): mp 88-90 °C; H NMR
(300 MHz, CDCl3) δ 4.00 (s, 3 H), 4.01 (s, 3 H), 7.89 (d, 1 H, J =
8.1 Hz), 8.42 (d, 1 H, J = 8.1 Hz); 13C NMR (50 MHz, CDCl3) δ
53.3 (2C), 95.3, 127.1, 146.8, 149.6, 152.6, 164.7, 165.5; HRMS
calcd for C9H8INO4 (Mþ•) 320.9498, found 320.9496.
1
43%): mp 242-244 °C; H NMR (250 MHz, CDCl3) δ 7.17
Methyl 4-iodopyridine-2,6-dicarboxylate (21). 21 was ob-
tained according to the general procedure A starting from
methyl pyridine-2,6-dicarboxylate (0.39 g) and isolated by flash
chromatography on silica gel (eluent: heptane/CH2Cl2 80/20) in
3% (18 mg) yield: 1H NMR (300 MHz, CDCl3) δ 4.02 (s, 6H),
8.66 (s, 2H); 13C NMR (50 MHz, CDCl3) δ 53.2 (2C), 106.8,
136.9 (2C), 148.0 (2C), 163.6 (2C); these data are similar to those
previously described;39 HRMS calcd for C7H6INO2 [(M -
C2H2O2)þ•] 262.9443, found 262.9469.
(d, 1 H, J = 7.8Hz), 7.48(dd, 1 H, J = 8.0 and4.5Hz), 7.70-7.83
(m, 3 H), 8.67 (d, 1 H, J = 7.8 Hz), 8.81 (dd, 1 H, J = 8.0 and
2.1 Hz), 9.13 (dd, 1 H, J = 4.5 and 2.1 Hz), 9.30 (d, 1 H,
J = 8.0 Hz); 13C NMR (62.5 MHz, CDCl3) δ 112.8, 114.2, 121.2,
121.5, 126.5, 127.0, 128.2, 128.9, 133.1, 133.4, 137.0, 149.1, 156.9,
157.2, 160.1; IR (KBr) ν 1679, 1645, 1593, 1555, 1423 cm-1
;
HRMS calcd for C15H10N3O ([M þ H]þ) 248.0818, found
248.0808.
Dipyrido[1,2-a:30,20-d]pyrimidin-11-one (31). 31 was obtained
according to the general procedure C starting from ethyl
3-iodopicolinate (0.42 g) and 2-aminopyridine (0.17 g) and
was isolated after purification by chromatography on silica gel
(CHCl3 as eluent) as a yellow solid (0.12 g, 62%): mp 211 °C; 1H
NMR (250 MHz, CDCl3) δ 6.94-7.00 (m, 1 H), 7.55-7.67 (m,
2 H), 7.75 (dd, 1 H, J = 8.5 and 4.1 Hz), 8.14 (dd, 1 H, J = 8.5
and 1.5 Hz), 8.91 (dd, 1 H, J = 4.1 and 1.5 Hz), 9.00-9.04 (m,
1H); 13C NMR (62.5 MHz, CDCl3) δ 113.1, 126.3, 127.4, 129.0,
132.5, 135.1, 135.3, 145.6, 148.2, 148.9, 157.7; IR (KBr) ν 1702,
1641, 1543, 1519, 1469, 1413 cm-1; HRMS calcd for C11H8N3O
([M þ H]þ) 198.0662, found 198.0662.
Methyl 3,4-diiodopyridine-2,6-dicarboxylate (22). 22 formed
using the general procedures A and B and was identified by its
1
NMR data: H NMR (300 MHz, CDCl3) δ 3.98 (s, 6H), 8.88
(s, 1H); HRMS calcd for C8H5I2NO3 [(M - CH2O)þ•] and
C7H5I2NO2 [(M - C2H2O2)þ•] 416.8359 and 388.8410, found
416.8379 and 388.8426.
Methyl 3,5-diiodopyridine-2,6-dicarboxylate (23). 23 was ob-
tained according to the general procedure B starting from
methyl pyridine-2,6-dicarboxylate (0.39 g) and isolated by flash
chromatography on silica gel (eluent: heptane/CH2Cl2 80/20)
as a beige powder (0.13 g, 14%): mp 128-130 °C; 1H NMR (300
MHz, CDCl3) δ 3.99 (s, 6 H), 8.88 (s, 1 H); 13C NMR (50 MHz,
CDCl3) δ 53.4 (2C), 93.4 (2C), 150.6, 159.5, 164.9 (2C); HRMS
calcd for C9H7I2NO4 (Mþ•) 446.8465, found 446.8447.
General Procedure C for Buchwald-Hartwig Cross-Coupling.
A solution of Pd(OAc)2 (10 mg, 3 mol %), Xantphos (30 mg,
3.5 mol %), and Cs2CO3 (675 mg, 1.4 equiv) was prepared under
argon in dioxane. When the temperature reached 55 °C, the
appropriate halogenopyridine (1.5 mmol, 1 equiv) was added
under argon, and then 5-10 min later (temperature about
80 °C), the aminopyridine (1.8 mmol, 1.2 equiv) was finally
introduced. The reaction mixture was stirred at 95 °C for 2.5
to 24 h under argon (reaction was followed by thin layer
chromatography). After cooling to room temperature, the
reaction mixture was filtered, and the cake was washed with
EtOAc. The filtrate was concentrated under reduced pressure.
Dipyrido[1,2-a:20,30-d]pyrimidin-5-one (28). 28 was obtained
according to the general procedure C starting from methyl
Dipyrido[1,2-a:40,30-d]pyrimidin-11-one (32). 32 was obtained
according to the general procedure C starting from crude ethyl
4-iodonicotinate (general procedure A) and 2-aminopyridine
(0.23 g) and was isolated after purification by chromatography
on silica gel (eluent: CH2Cl2/Et3N 98/2) as a brown solid (0.20 g,
50% for two steps): mp 130 °C; 1H NMR (300 MHz, CDCl3) δ
6.99 (m, 1H), 7.54 (m, 2H), 7.68 (ddd, 1H, J = 9.2, 6.5, and 1.6
Hz), 8.80 (d, 1H, J = 6.0 Hz), 8.93 (m, 1H), 9.64 (s, 1H); 13C
NMR (75 MHz, CDCl3) δ 111.9, 113.7, 119.7, 126.4, 127.2,
139.4, 151.1, 152.0, 152.7, 152.9, 158.2; HRMS calcd for
C11H7N3O ([M þ H]þ) 198.0667, found 198.0670.
Dipyrido[1,2-a:30,40-d]pyrimidin-5-one (33). 33 was obtained
according to the general procedure C starting from ethyl
3-iodoisonicotinate (0.42 g) and 2-aminopyridine (0.17 g) and
was isolated after purification by chromatography on silica gel
(eluent: CH2Cl2/Et3N 98/2) as an orange solid (0.15 g, 52%): mp
164 °C; 1H NMR (300 MHz, CDCl3) δ 6.96 (m, 1H), 7.59
€
(39) Storm, O.; Luning, U. Eur. J. Org. Chem. 2002, 3680–3685.
(40) Rylowski, A.; Pucko, W. Acta Pol. Pharm. 1997, 54, 325–330.
846 J. Org. Chem. Vol. 75, No. 3, 2010

Bentabed-Ababsa et al.
JOCArticle
(m, 2H), 8.14 (dd, 1H, J = 5.4 and 0.7 Hz), 8.62 (br d, 1H, J =
5.4 Hz), 8.86 (dt, 1H, J = 7.4 and 1.2 Hz), 9.25 (br s, 1H); 13
attachment of cell to the wall of the plate. Different concentra-
tions of the compound under test (0, 1.0, 2.5, 5.0, and 10 μg/mL)
were added to the cell monolayer in triplicate wells in individual
dose, and monolayer cells were incubated with the compounds
for 48 h at 37 °C and in atmosphere of 5% CO2. After 48 h, cells
were fixed, washed, and stained with SRB stain, excess stain was
washed with acetic acid, and attached stain was recovered with
Tris-EDTA buffer. Color intensity was measured in an ELISA
reader, and the relation between surviving fraction and drug
concentration is plotted to get the survival curve of each tumor
cell line after the specified compound and the IC50 was calcu-
lated.
C
NMR (75 MHz, CDCl3) δ 113.8, 118.6, 120.2, 126.8, 127.0,
135.1, 143.1, 143.7, 149.1, 151.9, 158.3; HRMS calcd for
C11H7N3O ([M þ H]þ) 198.0667, found 198.0672.
Pharmacology. Applying the agar plate diffusion technique,32
the compounds were screened in vitro for their bactericidal
activity against Gram positive bacteria (Staphylococcus aureus)
and Gram negative bacteria (Escherichia coli and Pseudomonas
aeroginosa) and for their fungicidal activity against Fusarium,
Aspergillus niger, and Candida albicans. In this method, a
standard 5 mm diameter sterilized filter paper disk impregnated
with the compound (0.3 mg/0.1 mL of DMF) was placed on an
agar plate seeded with the test organism. The plates were
incubated for 24 h at 37 °C for bacteria and 28 °C for fungi.
The zone of inhibition of bacterial and fungi growth around the
disk was observed.
ꢀ
Acknowledgment. We are grateful to Region Bretagne
(France) and to MESRS (Algeria) for financial support to
G.B., and to MESR (France) for financial support to T.T.N.
ꢀ
We thank Rennes Metropole. We are also grateful to Faculty
The compounds were tested against a liver carcinoma cell line
(HEPG2), a human breast carcinoma cell line (MCF7), and a
cervix carcinoma cell line (HeLa). The method applied is similar
to that reported by Skehan et al.41 using 20 sulfo-rhodamine-B
stain (SRB). Cells were plated in 96-multiwell plate (104 cells/
well) for 24 h before treatment with the test compound to allow
of Women, Ain Shams University, and National Institute
of Cancer, Cairo University (Egypt) for pharmacological
measurements.
Supporting Information Available: General procedures and
1
copies of the H and 13C NMR spectra for compounds 5a-c,
(41) Skehan, P.; Storeng, R.; Scudiero, D.; Monks, A.; McMahon, J.;
Vistica, D.; Warren, J. T.; Bokesch, H.; Kenney, S.; Boyd, M. R. J. Natl.
Cancer Inst. 1990, 82, 1107–1112.
6a-d, 7, 8, 10, 15-18, 20, 23, 28-33. This material is available
free of charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 3, 2010 847