Synthesis of potential chemotherapic quinoxalinone derivatives by biocatalysis or microwave-assisted Hinsberg reaction

Article abstract of DOI:10.1016/j.tetlet.2007.11.204

In recent years, great efforts have been dedicated to the design of compounds acting as selective inhibitors of the HIV-1 reverse transcriptase (RT). Due to the promissory results previously attained with some quinoxaline derivatives, we aimed to improve the specific standard Hinsberg synthetic pathway by means of biocatalysis or microwave (MW) irradiation. Both techniques rendered the products in very good yields. However, employing the microwave-assisted organic synthesis (MAOS), in the absence of solvent, the same reactions may be completed in minutes. Some of these quinoxalinone derivatives exhibited good inhibitor activity against some human tumoral cells and the lymphoma related to HIV-1.

Full text of DOI:10.1016/j.tetlet.2007.11.204

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 1053–1056
Synthesis of potential chemotherapic quinoxalinone derivatives
by biocatalysis or microwave-assisted Hinsberg reaction
*
´
Javier Gris, Romina Glisoni, Lucas Fabian, Beatriz Fernandez, Albertina G. Moglioni
Quı´mica Medicinal, Departamento de Farmacologı´a, Facultad de Farmacia y Bioquı´mica, Universidad de Buenos Aires (1113),
Junı´n 956, Buenos Aires, Argentina
Received 22 October 2007; revised 27 November 2007; accepted 30 November 2007
Available online 4 December 2007
Abstract
In recent years, great efforts have been dedicated to the design of compounds acting as selective inhibitors of the HIV-1 reverse trans-
criptase (RT). Due to the promissory results previously attained with some quinoxaline derivatives, we aimed to improve the specific
standard Hinsberg synthetic pathway by means of biocatalysis or microwave (MW) irradiation. Both techniques rendered the products
in very good yields. However, employing the microwave-assisted organic synthesis (MAOS), in the absence of solvent, the same reactions
may be completed in minutes. Some of these quinoxalinone derivatives exhibited good inhibitor activity against some human tumoral
cells and the lymphoma related to HIV-1.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Quinoxaline derivatives; Biocatalysis; Microwave irradiation; Hinsberg reaction; AIDS
Since of 2005, the World Health Organization (WHO)
estimated that worldwide more than 40 million people
were infected with the human immunodeficiency virus
(HIV). In particular South America is facing a rapidly
growing number of HIV infections which require an effec-
tive antiviral therapy. Ideally, anti-HIV drugs should be
highly selective, have good oral availability, and favorable
pharmacokinetics.
preparation of such type of compounds. By heating
ortho-phenylenediamines with a-ketoacids, quinoxali-
nones were obtained, though yields were never above
50–65%. Furthermore, it was necessary to vary the condi-
tions of the reactions (e.g., temperature, reaction solvent,
catalysis) for each particular synthesis.4
Computational studies indicated that this reaction loses
efficiency due to several factors.5 Among them, when many
intermediates coexisted, the reaction reached the equilib-
rium. These findings were in agreement with the experimen-
tal observations (e.g., chromatography),5 and were
characterized by very low yields and required a laborious
work to isolate the quinoxaline. Consequently, this complex
reaction displays a pronounced yield decrease as the
amount of reactants increases, leading to even lower perfor-
mances in larger scales. Even though a few reports describ-
ing the microwave-assisted synthesis of quinoxalines are
available in the literature,6,7 this is the first work presenting
the preparation of benzoquinoxalines using this technology.
Herein, six quinoxalinones (3a–i) and three benzo-
quinoxalinones (4a–c) were obtained in good yields, by
Moreover, large-scale production, at low costs to make
them accessible for patients in developing countries would
constitute a crucial advantageous feature.
Several derivatives of quinoxaline (e.g., HBY-097 and
S-2720) display interesting activity against HIV as non-
nucleosidic inhibitors of the reverse transcriptase (RT).1,2
The present study describes the synthesis and characteriza-
tion of a family of quinoxalinone derivatives.
The Hinsberg reaction,3 although known for more
than a century, is still the most useful method for the
*
Corresponding author. Tel.: +54 11 4964 8233; fax: +54 11 4964 8252.
E-mail address: amoglio@ffyb.uba.ar (A.G. Moglioni).
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.11.204

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J. Gris et al. / Tetrahedron Letters 49 (2008) 1053–1056
H
N
NH2
NH2
O
R
HO
R
O
O
a)
S. cereviciae 20 °C
+
b) MW irradiation
N
2 a-f
3 a-f
1 a
R= -CH3 (a); -C2H5 (b); -(CH2)2-CO2H (c); -CH2-CO2H (d); -CH2-C6H5 (e); -OH (f)
H
NH2
N
O
R
HO
R
O
a)
S. cereviciae 20 °C
+
b) MW irradiation
NH2
N
O
1 b
2 a-c
4 a-c
R= -CH3 (a); -C2H5 (b); -(CH2)2-CO2H (c)
Scheme 1. Synthesis of quinoxalinone and benzoquinoxalinone derivatives by biocatalysis or microwave-assisted Hinsberg reaction.
reacting ortho-phenylenediamine or 2,3-diaminenaphtha-
lene with a variety of a-ketoacids (Scheme 1) through enzy-
matic catalysis or microwave irradiation. Data are reported
in Table 1.
wave units are suitable in many cases for the development
of the reaction.
Microwave-assisted synthesis was carried out in one-pot
reaction, where ortho-phenylenediamine or 2,3-diamine-
naphthalene was mixed with the a-ketoacid without sol-
vent, and irradiated with a domestic oven applying a
potency of 650–750 W.11 These solvent free reactions prove
that it is possible to prepare easily isolable compounds in
acceptably good yield, and in a short time reaction. Fur-
thermore, the method could be efficiently applied to greater
scales with a minimal risk of by-products generation.
Reaction times and yields of compounds 3a–f prepared
by microwave irradiation are presented in Table 1.
Finally, comparing the findings obtained by both metho-
dologies, it could be stated that even though the biocata-
lytic reaction presents an interesting and broad field of
application, and that the yields are slightly higher, it
demands a more tedious work-up to purify the products.
However, biocatalysis is a method to be taken into consid-
eration in the case of more complex reactions. On the other
hand, the use of microwaves as the heating source results in
an easier and cleaner technique, leading to very good yields
in relatively short reaction times. So, having into account
the facility and versatility of the MW chemistry applied
to the synthesis of quinoxalinones and benzoquinoxalinon-
es, as well as the good yields achieved and the easy work-up
of the reactions, this technique is preferable with respect to
the use of enzymatic catalysis.
Synthesis via enzymatic catalysis involves enormously
complex biochemical reactions compared to the classical
organic synthesis. Reactions depicted in this Letter will
have probably a strong empirical aspect. Nevertheless,
enzymes were used due to their usefulness as efficient cata-
lysts to synthesize some quinoxalinone derivatives (see
Table 1). Microorganism-mediated processes, are being
used as means for oxidative–reductive reactions, condensa-
tions, acylations, and cyclizations. Reaction rates were
enhanced by a factor of 108–1010 when compared to regular
organic synthetic pathways. Moreover, since enzymes per-
form at pH 7 at room temperature and are completely
degradable, the biocatalysis is more environmentally
friendly. These facts minimize undesired decompositions,
isomerizations, racemizations, or rearrangements. Also,
the manipulation of the bacterial activity to increase the
expression of the desired enzymes, as well as the inhibition
of other enzymes related to undesired secondary reaction
products constitutes a very important additional tool. In
the context of the synthesis of these heterocycles by using
enzymatic means, our group had previously published pre-
liminary assays.8
Compounds 3a–f and 4a–c were prepared by mixing the
starting materials in a sucrose solution. Saccharomyces
cereviciae was added and the mixture was stirred.9 Products
were crystallized from the appropriate solvent. Melting
points were compared with those reported in the literature,
The studies against HIV were developed for compound
3e and the methyl ester of 4c, and no activity was observed,
as compared to efavirenz, though it is worth mentioning
that the assayed concentrations up to the order 10À6 M
were not cytotoxic.
1
and the structures were confirmed by IR and H NMR
spectroscopy.10
The other technique employed was the microwave irra-
diation. Microwave radiation is converted into heat with
high efficiency, so that superheating becomes possible at
ambient pressure. Great acceleration in the reaction time
can be achieved, and the assay that takes several hours
under conventional conditions, can be completed over the
course of minutes. In addition, unmodified home micro-
On the other hand, potential antitumoral activity of
compounds 4a and 4b has been investigated in the National
Cancer Institute (USA). Compound 4a displayed in vitro
activity against a non-small lung cell line (EKVX) and
human kidney cells (CL A498), while 4b displayed
in vitro activity against central nervous system (CNS)
human cells.12 However, the cytotoxicity shown in both

J. Gris et al. / Tetrahedron Letters 49 (2008) 1053–1056
1055
Table 1
Synthesis of quinoxalinone derivatives by biocatalysis and MW irradiation
Entry
Substrate
1
Substrate 2
Products 3, 4
Mp (°C) (lit.)
Biocatalysis
MW irradiationa
HO
Time
(h)
Yieldb
(%)
Time
(min)
Yieldb
(%)
R
O
O
N
CH3
O
1
2
3
4
5
6
7
8
9
1a
1a
1a
1a
1a
–CH3 2a
243–245 (244–245)13
72
72
72
72
72
72
72
72
72
95
8.5
3.5
5
88
90
91
90
86
90
80
70
90
N
H
3a
N
C2H5
O
–C2H5 2b
263–264
95
N
H
3b
N
COOH
–(CH2)2COOH
2c
256–258 (257–258)14
95
N
H
O
3c
N
COOH
–CH2COOH
2d
211–213
95
11
13
6
N
H
O
O
3d
N
C6H5
–CH2C6H5 2e
198–200 (199–200)5
95
N
H
3e
N
OH
O
1a
–OH 2f
>320 (410)15
92
N
H
3f
N
CH3
O
1b
1b
1b
–CH3 2a
291–292 (293–295)16
93
5
N
H
4a
4b
N
C2H5
O
–C2H5 2b
263–264
93
5
N
H
COOH
N
–(CH2)2COOH
2c
262–263 (261–263)16
90–95
3
N
H
4c
O
Comparison of reaction times and yields between both methods.
a
Using household microwave.
Yields refer to pure products.
b
cases was higher than the minimal required to continue the
screening. 4c was evaluated by the Biological Evaluation
Committee (BEC). Findings indicated a higher activity
against AIDS-related lymphoma than the reference

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J. Gris et al. / Tetrahedron Letters 49 (2008) 1053–1056
compound employed by the NCI.12 Nevertheless, it did not
reach the lower toxicity level to perform in vivo studies.
(methanol): kmax nm: 270, 285; Anal. Calcd for C10H10N2O: C, 68.95;
H, 5.78; N, 16.08; found: C, 68,86; H, 5.97; N, 16.30. 3-[3-Quinoxalin-
2(1H)-one] propanoic acid (entry 3, 3c): white crystals (ethanol);
spectra data agree again with those reported by Rodrigo.14 2-[3-
Quinozalin-2(1H)-one] acetic acid (entry 4, 3d): white crystals (etha-
nol); 1H NMR (DMSO-d6): d 2.39 (s, 2H, CH2), 7.82 (m, 2H,
aromatics), 7.48 (t, 1H, aromatics), 7.69 (d, 1H, aromatics), 12.4 (s,
1H, COOH); IR (cmÀ1): 166, 1608, 3167–3435; Anal. Calcd for
C10H8N2O3: C, 58.82; H, 3,95; N, 13,72; found: C, 58.91; H, 4.09; N,
13.88. 3-Benzylquinoxalin-2(1H)-one (entry 5, 3e): white needles
(ethanol); spectra data was previously reported by us5 and agree
again with the results obtained in this work. 3-Hydroxyquinoxalin-
2(1H)-one (entry 6, 3f): white powder (ethanol) in part volatile
without decomposition, reported by Motylevski.15 3-Methyl-
benzo[g]quinoxalin-2(1H)-one (entry 7, 4a): yellow crystals (methanol/
water) reported by Rodrigo.16 3-Ethylbenzo[g]quinoxalin-2(1H)-one
(entry 8, 4b): yellow crystals (methanol/water); 1H NMR (DMSO-d6):
d 1.45 (t, 3H, CH3), 3,04 (q, 2H, CH2), 7.63 (t, 1H, aromatics), 7.69
(t, 1H, aromatics), 7.72 (t, 1H, aromatics), 7.82 (s, 1H, aromatics),
8.11 (d, 1H, aromatics), 8.23 (d, 1H, aromatics), 8.54 (s, 1H,
aromatics), 12.47 (s, 1H, NH); IR (cmÀ1): 1640, 1670, 3405; UV
(methanol): kmax nm: 272, 282; Anal. Calcd for C14H12N2O: C, 74,98;
H, 5.39; N, 12.49; found: C, 75.05; H, 5,46, N, 12,60. 3-{3-
Benzo[g]quinoxalin-2(1H)-one} propanoic acid (entry 9, 4c): yellow
crystals (methanol/water) synthesized by Rodrigo.16 There was
agreement with spectroscopic data determined in this work.
11. Typical procedure for microwave irradiation: Reactions were per-
formed in the absence of solvent. In every case equimolecular
amounts of both reactants (2 mmol) were mixed and subjected to
microwave irradiation under the reaction conditions described in
Table 1 for each compound. After the completion of the reaction
(TLC), the mixture was diluted with MeOH, EtOH or CH2Cl2 (20 ml)
and concentrated under reduced pressure to give always a solid
substance. Compounds already known were crystallized from the
appropriate solvent. Melting points were compared with those
reported in the literature, and their structure was confirmed by IR
and 1H NMR spectroscopy.
Acknowledgment
We are grateful for the financial support from Univer-
sidad de Buenos Aires (UBACyT B-087 and B-016).
References and notes
1. Kleim, J. P.; Bender, R.; Kirsch, R.; Meichsner, C.; Paessens, A.;
Ro¨sner, M.; Rubsamen Waigmann, H.; Kaiser, R.; Wichers, M.;
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4. Abasolo, M. I.; Gaozza, C. H.; Fernandez, B. M. J. Heterocycl.
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8. Baez, M. V.; Robinsohn, A.; Legaspi, M.; Hedrera, M.; Fernandez, B.
M. J. Planar Chromatogr. 2003, 16, 28.
9. Typical procedure for the biocatalytic method (compounds 1–9):
Saccharose (10% P/V in distilled water) and Saccharomyces cereviciae
(10 g) were mixed in a 1-l flask and stirred for 1 h at room
temperature. Then, 100 mg of accurately measured (1 mmol) ortho-
phenylenediamine or 2,3-diaminonaphthalene, and different a-keto-
acids in excess (1.4 mmol) were added to the mixture. Stirring was
continued for 48 h at room temperature. After the reaction was
completed, the mixture was centrifuged and the acid pellet was
isolated and re-suspended in methanol. This mixture was stirred for
another 24 h and centrifuged. The upper layer was separated and the
solvent, evaporated. The solid obtained was washed to eliminate the
saccharose residue and render the final heterocyclic compound.
Products were crystallized from the appropriate solvent. Melting
points were compared with those reported in the literature, and their
structure was confirmed by IR and 1H NMR spectroscopy.
12. Pharmacological assays were made by the National Cancer Institute
(NCI, USA). Patent: Rodrigo, Gabriela A.; Ferna´ndez Beatriz M.
‘Cromo´foros tric´ıclicos dinitrogenados precursores de drogas anti-
HIV y compuestos farmace´uticos que las contienen’. INPI No. AR
030103167 (presented August 2004). Accepted April 2007.
13. Nishio, T. J. Org. Chem. 1984, 49, 827.
10. Spectra data for products: 3-Methylquinoxalin-2(1H)-one (entry 1,
3a): white needles (anhydrous ethanol); spectral properties agree with
those described by Nishio.13 3-Ethylquinoxalin-2(1H)-one (entry 2,
3b): white crystals (ethanol); 1H NMR (DMSO-d6): d 1.50 (t, 3H,
CH3), 3.06 (q, 2H, CH2), 7.60 (t, 1H, aromatics), 7.69 (t, 1H,
aromatics), 12.50 (s, 1H, NH); IR: (cmÀ1), 1640, 1670, 3405; UV
14. Rodrigo, G. A.; Piton, K. B.; Bekerman, D. G.; Abasolo, M.;
Ferna´ndez, B. M. Inf. Technol. 1999, 10, 29.
15. Motylevski, Z. Bull Intern. Acad. Sci. Cracovie. 1908, 32–34; Ber.
1908, 41, 800.
16. Rodrigo, G.; Bekerman, D.; Renou, S.; Abasolo, M.; Ferna´ndez, B.
M. J. Heterocycl. Chem. 1997, 34, 505.