New 1,4-di-N-oxide-quinoxaline-2-ylmethylene isonicotinic acid hydrazide derivatives as anti-Mycobacterium tuberculosis agents

Article abstract of DOI:10.1016/j.bmcl.2011.04.072

The increase in the prevalence of drug-resistant tuberculosis cases demonstrates the need of discovering new and promising compounds with antimycobacterial activity. As a continuation of our research and with the aim of identifying new antitubercular drugs candidates, a new series of quinoxaline 1,4-di-N-oxide derivatives containing isoniazid was synthesized and evaluated for in vitro anti-tuberculosis activity against Mycobacterium tuberculosis H37Rv strain. Moreover, various drug-like properties of new compounds were predicted. Taking into account the biological results and the promising drug-likeness profile of these compounds, make them valid leads for further experimental research.

Full text of DOI:10.1016/j.bmcl.2011.04.072

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3699–3703
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
New 1,4-di-N-oxide-quinoxaline-2-ylmethylene isonicotinic acid hydrazide
derivatives as anti-Mycobacterium tuberculosis agents
Enrique Torres, Elsa Moreno, Saioa Ancizu, Carlos Barea, Silvia Galiano, Ignacio Aldana, Antonio Monge,
⇑
Silvia Pérez-Silanes
Unidad de Investigación y Desarrollo de Medicamentos, Centro de Investigación en Farmacobiología Aplicada (CIFA), University of Navarra, C/ Irunlarrea 1, 31008 Pamplona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The increase in the prevalence of drug-resistant tuberculosis cases demonstrates the need of discovering
new and promising compounds with antimycobacterial activity. As a continuation of our research and
with the aim of identifying new antitubercular drugs candidates, a new series of quinoxaline 1,4-di-N-
oxide derivatives containing isoniazid was synthesized and evaluated for in vitro anti-tuberculosis activity
against Mycobacterium tuberculosis H37Rv strain. Moreover, various drug-like properties of new com-
pounds were predicted. Taking into account the biological results and the promising drug-likeness profile
of these compounds, make them valid leads for further experimental research.
Received 9 March 2011
Revised 15 April 2011
Accepted 19 April 2011
Available online 27 April 2011
Keywords:
Anti-tuberculosis agents
Quinoxaline 1,4-di-N-oxide derivatives
Isoniazid
Ó 2011 Elsevier Ltd. All rights reserved.
Microwave assisted synthesis
Druglikeness
Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. Tb),
is a major infectious disease suffered by mankind in mostly low and
middle income countries, although no region in the world remains
untouched. According to World Health Organization (WHO) data,
every second a newly infection by tuberculosis bacillus occurs
somewhere in the world; the number of infections is constantly ris-
ing and will soon affect a third of the world’s population. The statis-
tics indicate that 1.3 million people throughout the world died from
Therefore, the challenge of chemotherapy development in the
future is to discover drugs with new targets and new mechanisms
of action for treating patients infected by strains of MDR-TB and
XDR-TB, as well as to demonstrate lower levels of toxicity and to
1
0,11
shorten treatment periods.
Despite the efforts and resources
involved in anti-TB therapy, no new TB drugs have been introduced
in therapy during the past 40 years. Many classes of organic com-
pounds have been tested to achieve this aim, with special attention
being paid to nitrogen heterocycles, five and six membered
1
TB in 2008.
7
,12–14
The control of this disease is seriously threatened mainly due to
the explosive spread of the HIV epidemic, especially in Africa
where two–thirds of HIV patients also carry TB. It is also due to
the recent influx of immigrants from countries where TB is ende-
mic, and to the increasing emergence of multidrug-resistant tuber-
culosis (MDR-TB) and extensively drug-resistant tuberculosis
rings.
With this idea, our group has been working for several
years in the synthesis and biological evaluation of new structures
derived from quinoxaline heterocycle (Fig. 1), with promising re-
sults. Quinoxaline derivatives show interesting biological proper-
ties such as antibacterial, antiviral, anticancer, antifungal,
antihelminthic, and insecticidal.
(
XDR-TB). Recent reports from WHO and the International Union
As a result of our anti-tuberculosis research project, several pa-
pers have been published, in which both synthesis and biological
activity assessments have been described for a large number of
Against Tuberculosis and Lung Disease show that the drug-resis-
tant tuberculosis emergent epidemic is at a global-level and that
the problem is most likely underestimated by many.2 The in-
creased incidence of MDR-TB, which is defined as resistance to
the first-line drugs isoniazid and rifampicin, and XDR-TB, defined
as resistance not only to rifampicin and isoniazid but also fluoro-
quinolones and to at least one of the injectable second-line drugs
demonstrates the need for further research.8
–7
,9
⇑
Corresponding author. Tel.: +34 948 425653; fax: +34 948 425652.
E-mail address: sperez@unav.es (S. Pérez-Silanes).
Figure 1. General structure of quinoxaline-1,4-di-N-oxide.
0
960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.04.072

3
700
E. Torres et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3699–3703
quinoxaline and quinoxaline 1,4-di-N-oxide derivatives with a
variety of substituents in positions 2, 3, 6, and 7 (Fig. 1) of the quin-
oxaline ring. Some of them have shown growth inhibition values of
9
9% and 100%. In addition, we observed that the absence of the two
N-oxide groups generally led to the loss of the antimycobacterial
activity.1
5–23
Also, different papers indicate that many isonicotinic acid
hydrazide (Isoniazid, INH) derivatives have shown interesting
2
4–33
anti-TB activities.
INH possesing the highest activity
(
MIC = 0.21
l
M) against actively dividing M. tuberculosis.34,35 INH
is a pro-drug activated by catalase-peroxidase hemoprotein, KatG,
once inside M. tuberculosis. In the activation reaction the hydrazine
group is removed and two different active intracellular bacterial
active metabolites have been proposed,36 a isonicotinyl radical
form that is added to Nicotinamide Adenine Dinucleotide
3
7
36
(
NAD) or isonicotinic acid, a stable oxidative end product. The
mechanism of action is not well known yet.
The new compounds were designed based on the fusion between
the INH and a quinoxaline 1,4-di-N-oxide as shown in Figure 2. This
design is based on the molecular hybridization, defined by Viegas-
Junior et al. as a strategy of rational design based on the combina-
tion of pharmacophoric moieties of different bioactive substances
to produce a new hybrid compound with improved affinity and effi-
cacy when compared to the parent drugs.38 In addition, this strategy
can result in compounds presenting a modified selectivity profile,
different and/or dual modes of action and reduced undesired side
3
9–41
effects.
As a continuation of our research in quinoxalines 1,4-di-N-
oxide, and with the aim of identifying new antitubercular drug
candidates, we have synthesized and evaluated seven new
1
,4-di-N-oxide-quinoxaline-2-ylmethylene
isonicotinic
acid
hydrazide derivatives possessing different substituents in positions
6
7
R
and/or R (Compound 3a–3g, Scheme 1). Moreover, we calcu-
lated a number of physicochemical parameters for quantifying
drug-likeness and in order to assure that the compounds obey
the Lipinsky rule, which provides a method for assessing the like-
lihood that a given molecule could be orally bioavailable based on
a series of physicochemical requirements.
The seven new 1,4-di-N-oxide-quinoxaline-2-ylmethylene
isonicotinic acid hydrazide derivatives presented in this paper
were prepared through the synthetic route illustrated in Scheme 1.
Scheme 1. General synthesis of 1,4-di-N-oxide-quinoxaline-2-ylmethylene isoni-
cotinic acid hydrazide derivatives. Reagents and conditions: (i) triethylamine,
pyrrolidine, 59%; (ii) ethyl acetate, reflux; (iiia) ethanol, water, rt, 41%; (iiib)
tetrahydrofuran, sodium metabisulfite, microwave assisted synthesis, 44%.
The synthesis sequence was carried out in three stages; first,
using a variation of the Beirut reaction, the 2,3-dimethylquinoxa-
line 1,4-di-N-oxide intermediates 1a–1g were synthesized, in
which the appropriate benzofuroxane react with butanone in pres-
ence of triethylamine and pyrrolidine. The starting compounds,
5
-substituted benzofuroxane or 5,6-disubstituted benzofuroxane
1
6,18,23,42–48
were obtained by previously described methods.
We
then proceeded to the oxidation of methyl group in position 2 of
quinoxaline ring, using SeO as the oxidant agent, in order to obtain
2
the carboxaldehyde derivatives 2a–2g. The oxidation was carried
out by microwave assisted synthesis. Finally, by carrying out a var-
2
6,33
iation of a previously described method,
the new 1,4-di-N-
oxide-quinoxaline-2-ylmethylene hydrazide isonicotinic acid
derivatives 3a–3g were obtained through the reaction of the corre-
sponding aldehyde derivative 2a–2g with INH. Two different meth-
ods were used to obtain the 3a–3g derivatives. One being
conventional method with water and ethanol as solvents at room
temperature and the other being, a microwave assisted method
2 2 5
using tetrahydrofuran as solvent and Na S O as catalyst.
This synthesis strategy used allowed us to conduct a compara-
tive study between the conventional method and the microwave
Figure 2. Design concept of the new synthesized compounds using molecular
hybridization approach.

E. Torres et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3699–3703
3701
assisted method. The most significant observations made when
comparing the two methods were that the optimized microwave-
assisted method dramatically shortened reaction times and that
the yields obtained were similar to when the conventional method
was used. Furthermore, the amount of solvent used with the
microwave-assisted method was less than that used with the con-
ventional method. As a result, a minimum of solvent waste is gen-
erated, making this
a more efficient and environmentally
sustainable chemical process.
Figure 3. General structure of 2-carboxamide-1,4-di-N-oxide quinoxaline deriva-
tives P1–P7.
New derivatives were unsubstituted or substituted in positions
6
7
R and R by methyl or methoxy moiety as electron-releasing groups
and by chloro, fluoro or trifluoromethyl moiety as electron-with-
drawing groups. Formation of isomeric quinoxaline 1,4-di-N-oxides
ondary screening. Four out of six compounds (3a, 3b, 3d, and 3g)
passed the cut-off established by the TAACF, showing SI >10.
Compounds 3a, 3b, and 3d showed the higher selective indexes,
identifying the 3a compound as the one with most promising
results.
was observed in the case of monosubstituted benzofuroxanes.
According to the previous reports,4
9,50
we have observed that
7
-substituted quinoxaline 1,4-di-N-oxides prevailed over the 6-iso-
mer, or only the 7-isomer formed in the case of methoxy substituent.
In practice, the workup and purification allow isolation of the major
isomer.
Some interesting structure–activity relationships can be ob-
served from these results. Comparing the new series with parent
compounds we observed that the new hybrids presented similar
activity results against M. tuberculosis H37Rv strain. However, the
In vitro anti-tuberculosis activity evaluation of compounds
6
7
3
a–3g was carried out within the Tuberculosis Antimicrobial
electronic profile of substituents in R and/or R of quinoxaline ring
does not have the same influence in the antimycobacterial activity.
In the parent compounds, the most active structures are those with
Acquisition & Coordinating Facility (TAACF) screening program
5
1
for the discovery of novel drugs for the treatment of tuberculosis.
7
The results of the in vitro evaluation of anti-tuberculosis
activity are reported in Table 1. Table 1 shows IC50 and IC90 data
against M. tuberculosis H37Rv strain, CC50 values in VERO cells
and SI values obtained for the seven new 1,4-di-N-oxide-quinox-
aline-2-ylmethylene hydrazide isonicotinic acid derivatives and
the reported 2-carboxamide-1,4-di-N-oxide quinoxaline deriva-
tives as parent compounds (Fig. 3).16 We have used these parent
compounds to carry out a structure–activity comparative study.
These compounds were chosen due to their structural closeness
with the new compounds (3a–3g) and their interesting anti-M.
tuberculosis activities.
an electron-withdrawing group in R of quinoxaline ring (P7, P2, and
P6) but in the new series, the type of the substituents in these posi-
tions appears to have less influence on the antimycobacterial activ-
ity. This is because unsubstituted derivative (3a) and substituted by
electron-withdrawing group (3b) or electron-releasing group (3e)
showed a high activity.
The structure–activity relationships observed for the new syn-
thesized compounds suggest the possibility that these compounds
could be acting through a new mechanism of action in comparison
with the parent compounds. According to Scior et al.,36 the isoni-
cotinyl hydrazide derivatives, like those presented in this work,
could be considered INH pro-drugs because hydrazide is cleaved
into isonicotinic acid, the bioactive form of INH. The new hybrids
could act via a dual mechanism of action in which, by means of a
hydrolysis reaction, the INH would be released and could act with
its mechanism of action; at the same time, the quinoxaline would
be released, which could synergically contribute to the antimyco-
bacterial action of the INH.
Six out of seven new compounds (3a–3b, 3d–3g) were con-
sidered active in the primary screening (Concentration-Re-
sponse), with IC90 values ranging between 1.16 and 23.05
The compounds which passed the primary screening with IC90
values lower than 10 g/mL were considered for the cytotoxicity
lM.
l
assay in VERO cells. Only compound 3c, with a methoxy group
7
in R of the quinoxaline ring, failed to pass and go onto the sec-
Table 1
Biological results of the first and second anti-tuberculous screening
Compound
R6
R7
Anti-tubercular activity (H37Rv)
Cytotoxicity
IC50a
(
lM)
IC90b
(l
M)
CC50c
(lM)
SId (CC50/IC90
)
P1
P2
P3
P4
P5
P6
P7
H
H
H
H
CH
H
H
H
Cl
OCH
CH
CH
F
4.91
1.10
18.87
8.35
90.84
2.83
<0.81
8.42
1.25
36.38
13.01
296.41
4.65
1.07
>323.28
>290.90
N.T.
>38.39
>230.94
N.T.e
e
3
3
>309.26
>23.77
e
N.T.e
3
3
N.T.
>305.52
>265.02
>65.70
>246.30
CF
3
3
3
3
3
3
3
3
a
b
c
d
e
f
H
H
H
H
CH
H
H
H
Cl
OCH
CH
CH
F
1.17
1.04
<0.59
1.33
1.22
<0.58
1.50
1.32
1.16
>123.72
55.81
N.T.
52.06
>123.72
76.46
>93.02
48.10
N.T.e
2.86
>43.47
3.31
e
3
50.60
18.18
2.57
23.05
3.50
3
3
3
g
CF
3
70.01
19.99
INH
—
0.21
>500
>20,000
a
b
c
IC50 against M. tuberculosis H37Rv.
IC90 against M. tuberculosis H37Rv.
Cytotoxicity in VERO cells.
Selectivity index.
d
e
Not tested.

3
702
E. Torres et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3699–3703
Table 2
Supplementary data
c log P, molecular weight (MW), number of H bond donors, H bond acceptors and
drug-likeness value for compounds (3a–3g)
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.04.072.
Compound c log Pa H bond
H bond
acceptors
Molecular
weight
Drug-
likeness
a
donors
3
3
3
3
3
3
3
a
b
c
d
e
f
1.66
2.27
1.56
2.28
1.98
1.72
2.42
1
1
1
1
1
1
1
6
6
6
6
6
6
6
323.31
353.33
337.33
351.36
357.75
341.30
391.30
4.41
3.34
4.84
4.46
4.54
3.13
À2.29
References and notes
1.
WHO, Global Tuberculosis Report 2009, http://www.who.int/tb/publications/
global_report/2009/pdf/full_report.pdf.
2.
3.
4.
http://www.theunion.org/tuberculosis/tuberculosis.html.
http://www.who.int/topics/tuberculosis/en/.
Lonnroth, K.; Castro, K. G.; Chakaya, J. M.; Chauhan, L. S.; Floyd, K.; Glaziou, P.;
Raviglione, M. C. Lancet 2010, 375, 1814.
g
a
Theoretical calculated values using Osiris program.
5.
6.
7.
Dye, C.; Williams, B. G.; Espinal, M. A.; Raviglione, M. C. Science 2002, 295, 2042.
Caminero, J. A. Int. J. Tuberc. Lung. Dis. 2010, 14, 382.
Lluis Ballell, R. A. F.; Duncan, K.; Young, R. J. Antimicrob. Agents Chemother. 2005,
4
9, 2153.
8
9
.
Gandhi, N. R.; Nunn, P.; Dheda, K. H.; Schaaf, S.; Zignol, M.; Van Soolingen, D.;
Jensen, P.; Bayona, J. Lancet 2010, 375, 1830.
Ahmad, S.; Mokaddas, E. Respir. Med. 2009, 103, 1777.
Currently, there are many approaches that assess a compound’s
drug-likeness partially based on topological descriptors, finger-
prints of molecular drug-likeness structure keys or other proper-
ties as c log P and molecular weights. In this work we calculated
various physicochemical parameters using Osiris Property
.
10. Ginsberg, A. M. Tuberculosis (Edinb) 2010, 90, 162.
1
1
1. Barry, C. E., 3rd; Blanchard, J. S. Curr. Opin. Chem. Biol. 2010, 14, 456.
2. Mantu, D.; Luca, M. C.; Moldoveanu, C.; Zbancioc, G.; Mangalagiu, I. I. Eur. J.
Med. Chem. 2010, 45, 5164.
5
2,53
Explorer.
13. Singh, R.; Manjunatha, U.; Boshoff, H. I.; Ha, Y. H.; Niyomrattanakit, P.;
Ledwidge, R.; Dowd, C. S.; Lee, I. Y.; Kim, P.; Zhang, L.; Kang, S.; Keller, T. H.;
Jiricek, J.; Barry, C. E., 3rd Science 2008, 322, 1392.
We subjected the seven new derivatives 3a–3g to the analysis of
Lipinski’s rule which indicates if a chemical compound could be an
orally active drug in humans.54 We calculated theoretical c log P
using Osiris Property Explorer, molecular weight (MW) and number
of hydrogen bond donors and acceptors. Observing the results in
Table 2 it can be said that compounds 3a–3g satisfied the physico-
chemical parameters range established by the Lipinski’s rule.
Fragment based drug-likeness was predicted for the new deriv-
atives 3a–3g. This drug property indicates if the compound predom-
inantly contains fragments which are frequently present in
commercial drugs. As can be observed in Table 2, our theoretical
data showed that compounds 3a–3f presented positive values and
only compound 3g presented a negative drug-likeness. The majority
of marketed drugs show values between 0 and 4. This indicates that
1
4. Janin, Y. L. Bioorg. Med. Chem. 2007, 15, 2479.
15. Carta, A.; Loriga, M.; Paglietti, G.; Mattana, A.; Fiori, P. L. P. Eur. J. Med. Chem.
004, 39, 195.
2
16. Ancizu, S.; Moreno, E.; Solano, B.; Villar, R.; Burguete, A.; Torres, E.; Pérez-
Silanes, S.; Aldana, I.; Monge, A. Bioorg. Med. Chem. 2010, 18, 2713.
17. Vicente, E.; Villar, R.; Solano, B.; Burguete, A.; Ancizu, S.; Pérez-Silanes, S.;
Aldana, I.; Monge, A. An. R. Acad. Nac. Farm. 2007, 73, 927.
1
1
8. Jaso, A.; Zarranz, B.; Aldana, I.; Monge, A. Eur. J. Med. Chem. 2003, 38, 791.
9. Moreno, E.; Ancizu, S.; Pérez-Silanes, S.; Torres, E.; Aldana, I.; Monge, A. Eur. J.
Med. Chem. 2010, 45, 4418.
20. Vicente, E.; Pérez-Silanes, S.; Lima, L. M.; Ancizu, S.; Burguete, A.; Solano, B.;
Villar, R.; Aldana, I.; Monge, A. Bioorg. Med. Chem. 2009, 17, 385.
2
1. Vicente, E.; Villar, R.; Burguete, A.; Solano, B.; Pérez-Silanes, S.; Aldana, I.;
Maddry, J. A.; Lenaerts, A. J.; Franzblau, S. G.; Cho, S.; Monge, A.; Goldman, R. C.
Antimicrob. Agents Chemother. 2008, 52, 3321.
2
2. Villar, R.; Vicente, E.; Solano, B.; Pèrez-Silanes, S.; Aldana, I.; Maddry, J. A.;
Lenaerts, A. J.; Franzblau, S. G.; Cho, S.; Monge, A.; Goldman, R. C. J. Antimicrob.
Chemother. 2008, 62, 547.
drug-likeness values of our new compounds were comparable to
those of the majority of the commercial drugs.5
5–58
Moreover, we
23. Zarranz, B.; Jaso, A.; Aldana, I.; Monge, A. Bioorg. Med. Chem. 2003, 11, 2149.
24. Manetti, F.; Corelli, F.; Biava, M.; Fioravanti, R.; Porretta, G. C.; Botta, M.
Farmaco 2000, 55, 484.
used the Osiris program to predict the overall toxicity of the deriv-
atives 3a–3g and indicated a low toxicity risk profile.
25. Bacelar, A. H.; Carvalho, M. A.; Proenca, M. F. Eur. J. Med. Chem. 2010, 45, 3234.
In conclusion, a new class of quinoxaline 1,4-di-N-oxide deriva-
tives containing isonicotinic acid hydrazide pharmacophore has
been synthesized using a new optimized microwave-assisted
method. The microwave method allowed us to greatly reduce reac-
tion times, maintaining or even improving reaction yields. The new
compounds were evaluated against M. tuberculosis H37Rv strain;
six were active in the primary screening, showing an
26. Lourenço, M. C.; Ferreira, L.; Nora de Souza, M. V.; Peralta, M. A.; Vasconcelos, T.
R.; Henriques, M. G. Eur. J. Med. Chem. 2008, 43, 1344.
2
2
7. Abdel-Aziz, M.; Abdel-Rahman, H. M. Eur. J. Med. Chem. 2010, 45, 3384.
8. Maccari, R.; Ottana, R.; Vigorita, M. G. Bioorg. Med. Chem. Lett. 2005, 15, 2509.
29. Silva, F. P.; Ellena, J.; Ferreira, M.; Mascarenhas, Y. P.; de Souza, M. V. N.;
Wardell, J. L.; Wardell, S. M. S. V. J. molstruc. 2006, 788, 63.
3
3
0. Carvalho, S. A.; da Silva, E. F.; de Souza, M. V.; Lourenco, M. C.; Vicente, F. R.
Bioorg. Med. Chem. Lett. 2008, 18, 538.
1. Gilani, S. J.; Khan, S. A.; Siddiqui, N. Bioorg. Med. Chem. Lett. 2010, 20, 4762.
IC90 610
lg/mL, and then they moved on to the secondary screen-
32. Sriram, D.; Yogeeswari, P.; Madhu, K. Bioorg. Med. Chem. Lett. 2005, 15, 4502.
3
3. Navarrete-Vazquez, G.; Molina-Salinas, G. M.; Duarte-Fajardo, Z. V.; Vargas-
Villarreal, J.; Estrada-Soto, S.; González-Salazar, F.; Hernández-Nùñez, E.; Said-
Fernández, S. Bioorg. Med. Chem. 2007, 15, 5502.
ing level. Four of the compounds were active at this level, showing
a SI P10. The promising biological results obtained, along with the
good drug-likeness predictors that were calculated, make these
compounds valid leads for further studies in anti-TB therapies
and for synthesizing new compounds that possess better activity.
The suggested hypothesis of a dual mechanism of action needs to
be refined with the aid of additional in vivo evaluations, degrada-
tion kinetics measurements and stability studies of the synthesized
compounds. These new structures cold offer further inspiration for
future applications involving hybridization.
34. Tuberculosis, 2008, 88, 112.
35. Slayden, R. A.; Barry, C. E., 3rd Microbes Infect. 2000, 2, 659.
36. Scior, T.; Garcés-Eisele, S. J. Curr. Med. Chem. 2006, 13, 2205.
37. Ben Wiseman, X. C.; Feliz, M.; Donald, L. J.; Pons, M.; Fita, I.; Loewen, P. C. J. biol.
chem. 2010, 285, 26662.
38. Viegas-Junior, C.; Danuello, A.; da Silva Bolzani, V.; Barreiro, E. J.; Fraga, C. A.
Curr. Med. Chem. 2007, 14, 1829.
3
9. Nava-Zuazo, C.; Estrada-Soto, S.; Guerrero-Álvarez, J.; León-Rivera, I.; Molina-
Salinas, G. M.; Said-Fernández, S.; Chan-Bacab, M. J.; Cedillo-Rivera, R.; Moo-
Puc, R.; Mirón-López, G.; Navarrete-Vazquez, G. Bioorg. Med. Chem. 2010, 18,
6398.
4
0. Tributino, J. L.; Duarte, C. D.; Correa, R. S.; Doriguetto, A. C.; Ellena, J.; Romeiro,
Acknowledgments
N. C.; Castro, N. G.; Miranda, A. L.; Barreiro, E. J.; Fraga, C. A. Bioorg. Med. Chem.
2009, 17, 1125.
4
4
4
4
1. Lacerda, R. B.; de Lima, C. K.; da Silva, L. L.; Romeiro, N. C.; Miranda, A. L.;
Barreiro, E. J.; Fraga, C. A. Bioorg. Med. Chem. 2009, 17, 74.
2. Ortega, M. A.; Montoya, M. E.; Jaso, A.; Zarranz, B.; Tirapu, I.; Aldana, I.; Monge,
A. Pharmazie 2001, 56, 205.
3. Ortega, M. A.; Sainz, Y.; Montoya, M. E.; Jaso, A.; Zarranz, B.; Aldana, I.; Monge,
A. Arzneim.-Forsch 2002, 52, 113.
We wish to express our gratitude to the PIUNA project from the
University of Navarra and the Tuberculosis Antimicrobial Acquisi-
tion and Coordinating Facility (TAACF) for carrying out the biolog-
ical assays through research and development contracts. Enrique
Torres is indebted to the University of Navarra (Spain) for PhD
scholarship.
4. Jaso, A.; Zarranz, B.; Aldana, I.; Monge, A. J. Med. Chem. 2005, 48, 2019.
45. Jie Jack, Li. Name Reactions, third ed.; Springer: Berlin, Heidelberg, 2006. p. 43–44.

E. Torres et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3699–3703
3703
4
4
6. Stumm, G.; Niclas, H. J. J. Prakt. Chem. 1989, 331, 736.
7. González, M.; Cerecetto, H. In Topics in Heterocyclic Chemistry; Khan, M. T. H.,
Ed.; Springer: Berlin, 2007. Vol. 10, p. 265-303..
8. Cheeseman, G. W. H. In Condensed Pyrazines; Cookson, R. F., Ed.; J. Wiley & and
Sons: New York, 1979. vol. 35..
9. Zarranz, B.; Jaso, A.; Aldana, I.; Monge, A. Bioorg. Med. Chem. 2004, 12, 3711.
0. http://www.taacf.org/Process-text.htm.assays.
1. http://www.organic-chemistry.org/prog/peo/.
2. Tetko, I. V. Drug Discovery Today 2005, 10, 1497.
54. Lipinski, A. C.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. J. Adv. Drug Deliv. Rev.
2001, 46, 3.
55. Hajduk, P. J.; Greer, J. Nat. Rev. Drug. Disc. 2007, 6, 211.
56. Dias, L. R.; Santos, M. B.; Albuquerque, S.; Castro, H. C.; de Souza, A. M.; Freitas, A.
C.; DiVaio, M. A.; Cabral, L. M.; Rodrigues, C. R. Bioorg. Med. Chem. 2007, 15, 211.
57. El-Azab, A. S.; Al-Omar, M. A.; Abdel-Aziz, A. A.; Abdel-Aziz, N. I.; el-Sayed, M.
A.; Aleisa, A. M.; Sayed-Ahmed, M. M.; Abdel-Hamide, S. G. Eur. J. Med. Chem.
2010, 45, 4188.
58. Costa, M. S.; Boechat, N.; Rangel, E. A.; da Silva Fde, C.; de Souza, A. M.;
Rodrigues, C. R.; Castro, H. C.; Junior, I. N.; Lourenco, M. C.; Wardell, S. M.;
Ferreira, V. F. Bioorg. Med. Chem. 2006, 14, 8644.
4
4
5
5
5
5
3. Lipinski, A. C.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. Adv. Drug Deliv. Rev.
1
997, 23, 3.