Simple, multicomponent, ecofriendly, microwave-mediated route for the synthesis of antimicrobial 2-amino-6-aryl-4-(3 h)-pyrimidinones

Article abstract of DOI:10.1080/00397911.2013.807517

In this work, we describe a multicomponent microwave-mediated synthesis of 10 2-amino-6-aryl-4-oxo-1,6-dihydro-pyrimidine-5-carbonitriles in good chemical yields (44-67%), four of them not related in earlier literature. All pyrimidinones synthesized herein had their antimicrobial activity evaluated against the following microorganisms: Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Two of the synthesized substances displayed good antimicrobial activity against P. aeruginosa and S. aureus, two bacteria responsible for nosocomial infections. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.]

Full text of DOI:10.1080/00397911.2013.807517

This article was downloaded by: [Moskow State Univ Bibliote]
On: 22 November 2013, At: 09:06
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Simple, Multicomponent, Ecofriendly,
Microwave-Mediated Route for the
Synthesis of Antimicrobial 2-Amino-6-
aryl-4-(3H)-pyrimidinones
Ivangela E. A. da Silva a , Vanildo M. L. Braga a , Mychely S. Melo b ,
Maria Tereza dos S. Correia b & Janaína V. dos Anjos a
a Departamento de Química Fundamental , Universidade Federal de
Pernambuco , Recife , Brazil
b Departamento de Bioquímica , Universidade Federal de
Pernambuco , Recife , Brazil
Published online: 20 Nov 2013.
To cite this article: Ivangela E. A. da Silva , Vanildo M. L. Braga , Mychely S. Melo , Maria Tereza
dos S. Correia & Janaína V. dos Anjos (2014) Simple, Multicomponent, Ecofriendly, Microwave-
Mediated Route for the Synthesis of Antimicrobial 2-Amino-6-aryl-4-(3H)-pyrimidinones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
44:3, 374-380, DOI: 10.1080/00397911.2013.807517
To link to this article: http://dx.doi.org/10.1080/00397911.2013.807517
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Synthetic Communications1, 44: 374–380, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.807517
SIMPLE, MULTICOMPONENT, ECOFRIENDLY,
MICROWAVE-MEDIATED ROUTE FOR THE
SYNTHESIS OF ANTIMICROBIAL 2-AMINO-6-ARYL-
4-(3H)-PYRIMIDINONES
Ivangela E. A. da Silva,1 Vanildo M. L. Braga,1
Mychely S. Melo, Maria Tereza dos S. Correia, and Janaına
2
2
´
V. dos Anjos1
1
´
Departamento de Quımica Fundamental, Universidade Federal de
Pernambuco, Recife, Brazil
2
´
Departamento de Bioquımica, Universidade Federal de Pernambuco, Recife,
Brazil
GRAPHICAL ABSTRACT
Abstract In this work, we describe a multicomponent microwave-mediated synthesis of 10
2-amino-6-aryl-4-oxo-1,6-dihydro-pyrimidine-5-carbonitriles in good chemical yields (44–
67%), four of them not related in earlier literature. All pyrimidinones synthesized herein
had their antimicrobial activity evaluated against the following microorganisms: Bacillus
subtilis, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Two of
the synthesized substances displayed good antimicrobial activity against P. aeruginosa
and S. aureus, two bacteria responsible for nosocomial infections.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource(s):
Full experimental and spectral details.]
Keywords Antimicrobial activity; microwaves; multicomponent synthesis; 4-(3H)-
pyrimidinones
INTRODUCTION
Pyrimidinones are described in the literature as presenting a wide array of
biological activities such as antihypertensive,[1] potassium channel antagonism,[2]
anti-HIV,[3] antitumoral,[4] antiepileptic,[5] antimalarial,[6] antimicrobial,[7]
Received April 15, 2013.
Address correspondence to Janaına V. dos Anjos, Departamento de Quımica Fundamental,
´
Universidade Federal de Pernambuco, 50670 910, Recife, PE, Brazil. E-mail: janaina.anjos@ufpe.br
´
374

MULTICOMPONENT SYNTHESIS OF 4-(3H)-PYRIMIDINONES
375
Figure 1. Bropirimine, a bioactive pyrimidinone.
anti-inflammatory,[8] anti-tubercular,[9] and antibacterial[10] activites, among
others.[11] Such diversity of activities, as well as relative amiable synthetic proce-
dures, have made them valuable targets worth pursuing and testing for more than
a century.
Bropirimine (Fig. 1) is a successful example of a drug that contains the
2-amino-6-aryl-4-(3H)-pyrimidinone scaffold.[12] It was first synthesized by
Stringfellow and coworkers and became known because of its anticancer and anti-
viral properties.[13] The most employed route of synthesis of this pyrimidinone
derivative is a Biginelli-like reaction.[13] The original Biginelli reaction is a multicom-
ponent reaction where an aldehyde, a b-keto ester, and an urea derivative can be
used to provide a vast array of synthetic derivatives.[14] A variation of this method-
ology for the synthesis of the title compounds employs a Michael adduct and an uro-
nium donor system, such as urea,[15] thiourea,[16] and guanidine[17] or their
derivatives.[18] This reaction results in an alicyclic compound that can be converted
to the pyrimidinone of interest by employing thermal cyclization.
Usually, for the synthesis of the pyrimidone scaffold, the first step is a
Knoevenagel reaction between an aldehyde and a species with an acid hydrogen
(such as ethyl cyanoacetate). The resulting Michael adduct can be reacted with uro-
nium donors species to produce the aimed heterocycle.[19] In most cases, this reaction
requires long refluxing periods. One of the alternatives for the improvement of this
process lies in the use of microwave in organic chemistry. This type of radiation can
be focused to the reaction medium and transfer energy directly to the species, super-
heating them and accelerating the process.[20] This transference of energy can be
particularly important in multicomponent reactions.
Multicomponent reactions (MCRs) are procedures in which three or more
reagents are mixed together to yield a product, in a cascade process.[21] The use of
microwave energy may accelerate this type of reaction, because the conductive heat-
ing could improve the rate-determining step for the overall process.[22]
Microwave-mediated MCRs have shown many advantages when compared to usual
synthetic routes, such as simplification of the experimental procedure, shortening of
the reaction time, better global yields, and duly noted water economy (because the
long reflux periods are drastically reduced).[23] As an example, Stadler and Kappe
made use of microwave radiation to synthesize 48 derivatives of dihydropyrimidine
through the use of Biginelli’s multicomponent reaction.[24] This way, microwave-
mediated MCRs are an outstanding strategy, not only because of their convergent

376
I. E. A. DA SILVA ET AL.
nature, atom economy, and simplification of experimental procedure but also
because of their value to the pharmaceutical industry regarding the construction
of low-molecular-weight libraries.[23]
Such positive impacts on MCRs by the use of microwave methodology have
prompted us to investigate and compare the methodologies (reflux and microwaves)
in the synthesis of pyrimidinones, as well as to test the synthesized compounds
against some bacteria including Staphylococcus aureus and Pseudomonas aeruginosa,
two of the main pathogens involved in nosocomial infections, affecting mainly
immunossupressed patients.[25]
RESULTS AND DISCUSSION
To optimize the conditions for this reaction some preliminary tests were con-
ducted to evaluate some effects, such as solvent, initial power, temperature, and
time. First, water was used as a solvent and temperature was set at 50 ꢀC, for a per-
iod of 30 min. These conditions were unsatisfactory, once the consumption of the
aldehyde was far from complete. Even when performed for longer periods, for
became clear that a second factor in the reaction methodology should be altered.
The next factor to be studied was the initial power, which was increased from
150 W to 300 W, changing the temperature of the vessel to 70 ꢀC, for 30 min. This
led to the decomposition of guanidine to ammonia. Initial power was then readjusted
to 200 W, keeping temperature and time at the same values as the previous reaction.
These conditions have shown some improvement when examined by thin-layer
chroamtography (TLC), even though the aldehyde was not completely consumed.
In fact, aldehyde consumption was only complete when the reaction was left to con-
tinue for two more 30-min cycles, totaling 90 min of reaction time. Although the
completion of the starting material was perceived, the yields were poor after workup
and crystallization (under 30%).
Aiming for better yields, changes on the solvent systems were proposed.
Besides water, acetonitrile and ethanol were also tested, revealing that ethanol was
a better fit. However, potassium carbonate and guanidine hydrochloride are not sol-
uble in ethanol. This problem was easily fixed using equal quantities of water and
ethanol in the reaction media. After the conditions were optimized, the condensation
was carried out in a sealed vessel at a monomode microwave reactor in a water–
ethanol mixture (1:1, v=v) at 70 ꢀC (initial power 200 W) for 90 min, with yields vary-
ing from 44 to 67%, after purification (Scheme 1, Table 1).
To evaluate the efficiency of microwave irradiation in the preparation of the
title compounds, we also performed the same reaction without microwave
Scheme 1. Multicomponent synthesis of pyrimidinones 4a–j.

MULTICOMPONENT SYNTHESIS OF 4-(3H)-PYRIMIDINONES
Table 1. Melting points and yields of the synthesized pyrimidinones
377
Compound
Ar
Yield (%)
Mp (ꢀC)
4a
4b
4c
4d
4e
4f
C6H5
4-Cl-C6H4
62
46
61
47
47
55
67
46
44
54
172–174
233–235
249–251
210–212
197–199
131–133
194–197
207–210
317–319
153–155
4-F-C6H4
4-Br-C6H4
4-CH3-C6H4
3-CH3-C6H4
2-CH3-C6H4
4-OCH3-C6H4
3-NO2-C6H4
3,4-diCl-C6H3
4g
4h
4i
4j
irradiation, using the same solvent (water–ethanol) and the same quantities for the
reagents 2 and 3 and benzaldehyde (1a), in reflux. Twenty-four hours after the
beginning of the reaction, there still was a huge quantity of benzaldehyde, evidenced
by TLC. This experiment shows that conventional heating has not the same effect
that microwave-induced heating for the synthesis of the pyrimidinone scaffold.
The formation of products 4a–j can be explained by the occurrence of two sub-
sequent reactions in reaction media: the first one is the Knoevenagel reaction,[19]
where an aromatic aldehyde reacts with ethyl cyanoacetate, producing Michael’s
intermediate. Once formed, the Knoevenagel adduct can react with guanidine:
Michael’s adduct is attacked by the lone electron pair of a nitrogen atom in the uro-
nium portion of guanidine. There is a sequence of additions with a subsequent ring
closure to form the pyrimidinone nucleus. The last step in this mechanistic expla-
nation is quite intriguing. According to Mendonc¸a and coworkers,[26] atmospheric
oxygen is responsible for this oxidation and loss of a H2 molecule, leading to the het-
erocycle (Scheme 2).
The synthesized pyrimidinones had their minimum inhibitory concentration
(MIC) and minimum bactericidal concentration (MBC) determined using previously
related protocols.[27] The results are depicted in Table 2.
Scheme 2. Proposed mechanism of formation of 4a via multicomponent reaction of 1a, 2, and 3.

378
I. E. A. DA SILVA ET AL.
Table 2. Antimicrobial activity for 4a–j
Bacillus subtilis
Escherichia coli
Pseudomonas aeruginosa
Staphylococcus aureus
Pyrimidinone MICa
MBCa MICa MBCa
MICa
MBCa
MICa
MBCa
4a
4b
10
2.5
2.5
2.5
1.25
5
>10
5
1.25
2.5
2.5
2.5
2.5
5
5
5
0.625
5
2.5
5
4c
4d
>10
5
2.5
2.5
2.5
0.625
2.5
10
5
2.5
2.5
2.5
5
>10
5
1.25
1.25
2.5
1.25
2.5
5
4e
1.25
5
5
5
4f
4g
2.5
2.5
>10
5
>10
5
10
>10
5
1.25
2.5
2.5
1.25
2.5
5
5
4h
4i
2.5
5
2.5
2.5
1.25
5
1.25
5
1.25
5
5
10
2.5
2.5
4j
5
0.039
>10
0.039
>10
0.039
2.5
0.019
5
0.078
Clindamycinb
0.039
0.019
0.019
aMIC, minimum inhibitory concentration; MBC, minimum bactericidal concentration.
bPositive control.
It can be observed that the values for MIC and MBC are lower for
P. aeruginosa and S. aureus. More specifically, the best results are related to pyrimi-
dinones 4a (for S. aureus) and 4d (for P. aeruginosa), the latter presenting a MIC
value of 0.625 mg=mL. These results indicate that these substances have a bacterio-
static profile, decreasing the multiplication of microbial cells. These results are
encouraging, because these microorganisms are often cited as responsible for
nosocomial infections and antibiotic resistance.[25]
Another interesting feature is that the synthesized substances show results for
both Gram-positive (S. aureus) and Gram-negative microorganisms (P. aeruginosa).
Gram-positive and Gram-negative bacteria differ in cell wall composition, with
Gram-negative organisms more difficult to eliminate once they have an extra lipopoly-
saccharide outer membrane. These preliminary results may indicate that the synthe-
sized pyrimidine derivatives are potential broad-spectrum antimicrobial agents.[28]
In summary, we have developed a multicomponent microwave-mediated
strategy for the synthesis of 10 2-amino-6-aryl-4-oxo-1,6-dihydro-pyrimidine-5-
carbonitriles in good chemical yields (44–67%). These substances were tested against
four microorganisms and two of the synthesized pyrimidinones were active against
S. aureus and P. aeruginosa.
EXPERIMENTAL
General Experimental Procedures
All reagents were obtained from commercial sources and used without further
purification. Infrared (IR) spectra of the compounds were recorded on a Perkin-
Elmer model 283 spectrometer employing KBr pellets. 1H NMR spectra were
obtained with a Varian 400-MHz instrument using tetramethylsilane (TMS) as
the internal standard. 13C NMR spectra were recorded on a Varian 100-MHz
spectrometer. Exact mass measurements of the molecular ions were obtained on
a Shimadzu Eletrospray LC=MS-IT-TOF instrument. Thin-layer chromatography

MULTICOMPONENT SYNTHESIS OF 4-(3H)-PYRIMIDINONES
379
(TLC) was performed on plates coated with silica gel containing GF254 as fluorescent
indicator. Microwave reactions were carried out in a Discover SP (CEM) microwave
instrument, equipped with a 35-mL vessel. Compounds 4a and h[29] and 4b, d, e, and i[30]
had their physical-chemical data compared to earlier literature for these substances.
Typical Experimental Procedure
To a sealed vessel suitable for reactions in microwave reactors (capacity: 35mL)
were added 0.94mmol of the aromatic aldehyde (1.0 eq) and 1.88mmol (0.2 mL, 2.0
eq) of ethyl cyanoacetate, dissolved in 4 mL of ethanol. To this solution were added
1.13mmol (108mg, 1.2 eq) of guanidine hydrochloride and 1.88mmol (250 mg, 2.0
eq) of potassium carbonate dissolved in 4 mL of water. The mixture was reacted under
the following conditions: temperature of 70ꢀC and 200 W of initial power for 90min.
The completion of the reaction was verified by TLC utilizing as eluting system
hexanes= ethyl acetate 7:3 (v=v). To the reaction medium was added HCl 37% until
its complete acidification. The mixture was then cooled to room temperature,
and ice was poured into it, causing the precipitation of the product. The precipitate
was then filtrated under vacuum, washed with water (50 mL), and subsequently
recrystallized from chloroform to yield the pure pyrimidinone derivatives.
2-Amino-6-oxo-4-phenyl-1,6-dihydropyrimidine-5-carbonitrile (4a)
White solid; yield: 62%; Rf (ethyl acetate–methanol, 7:3 v=v): 0.37; mp:
169–170 ꢀC. 1H NMR (DMSOd6, 400 MHz) d: 7.56–7.62 (m, 3H), 8.03 (d, 2H,
J ¼ 8.4 Hz), 8.34 (s, 2H, NH2), 13.95 (s, 1H, NH). 13C NMR (DMSOd6, 100 MHz)
d: 117.7, 128.6, 128.7, 131.4, 136.9, 155.6, 156.7, 162.1, 172.1. I. R. (KBr)
=
=
nmax=cmꢁ1: 1684 (C O); 2224 (CꢂN); 1600 (C N); 3138 (N-H).
Supporting Information
Full experimental details and spectroscopic data (1H and 13C NMR spectra)
for compounds 4a–j can be found in the Supplementary Content section of this
article’s Web page.
ACKNOWLEDGMENTS
Our thanks are due to the Brazilian National Research Council (CNPq) and
Pernambuco State’s Scientific and Research Foundation (FACEPE, PRONEX-
0788-1.06=08 CNPq, PRONEX=FACEPE=2008-0981-1.06=08, PPP=FACEPE=
APQ-1225-1.06=10) for providing financial assistance. V. M. L. B. is grateful to
INAMI (Nanotechnology for Nanomarkers Institute) for a technician’s fellowship.
REFERENCES
1. Alam, O.; Khan, S. A.; Siddiqui, N.; Ahsan, W.; Verma, S. P.; Gilani, S. J. Eur. J. Med.
Chem. 2010, 45, 5113–5119.
2. Lloyd, J.; Finlay, H. J.; Vacarro, W.; Hyunh, T.; Kover, A.; Bhandaru, R.; Yan, L.; Atwal,
K.; Conder, M. L.; Jenkins-West, T.; Shi, H.; Huang, C.; Li, D.; Sun, H.; Levesque, P.
Bioorg. Med. Chem. Lett. 2010, 20, 1436–1439.

380
I. E. A. DA SILVA ET AL.
3. Patil, A. D.; Kumar, N. V.; Kokke, W. C.; Bean, M. F.; Freger, A. J.; Debrossi, C.; Mai,
S.; Truneh, A.; Faulkner, D. J.; Carte, B.; Breen, A. L.; Hertzbery, R. P.; Johnson, R. K.;
Westley, J. W.; Potts, B. C. M. J. Org. Chem. 1995, 60, 1182–1188.
4. Agbaje, O. C.; Fadeyi, O. O.; Fadeyi, S. A.; Myles, L. E.; Okoro, C. O. Bioorg. Med.
Chem. Lett. 2011, 21, 989–992.
5. Lewis, R. W.; Mabry, J.; Polisar, J. G.; Eagen, K. P.; Ganem, B.; Hess, G. P. Biochemistry
2010, 49, 4841–4851.
6. Chiang, A. N.; Valderramos, J.-C.; Balachandran, R.; Chovatiya, R. J.; Mead, B. P.;
Schneider, C.; Bell, S. L.; Klein, M. G.; Huryn, D. M.; Chen, X. S.; Day, B. W.; Fidock,
D. A.; Wipf, P.; Brodsky, J. L. Bioorg. Med. Chem. 2009, 17, 1527–1533.
7. Rajanarendar, E.; Reddy, M. N.; Murthy, K. R.; Reddy, K. G.; Raju, S.; Srinivas, M.;
Praveen, B.; Rao, M. S. Bioorg. Med. Chem. Lett. 2010, 20, 6052–6055.
8. Mokale, S. N.; Shinde, S. S.; Elgire, R. D.; Sangshetti, J. N.; Shinde, D. B. Bioorg. Med.
Chem. Lett. 2010, 20, 4424–4426.
9. Trivedi, A. R.; Bhuva, V. R.; Dholariya, B. H.; Dodiya, D. K.; Kataria, V. B.; Shah, V. H.
Bioorg. Med. Chem. Lett. 2010, 20, 6100–6102.
10. Chitra, S.; Devanathan, D.; Pandiarajan, K. Eur. J. Med. Chem. 2010, 45, 367–371.
11. Stefani, H. A.; Oliveira, C. B.; Almeida, R. B.; Pereira, C. M. P.; Braga, R. C.; Cella, R.;
Borges, V. C.; Savegnago, L.; Nogueira, C. W. Eur. J. Med. Chem. 2006, 41, 513–518.
12. Shimizu, M.; Oh-Hashi, F.; Tsukagoshi, S.; Iwaguchi, T.; Kataoka, T. Anti-cancer Drugs
1995, 6, 158–162.
13. Stringfellow, D. A.; Eidson, E. E.; Wierenga, W.; Skulnick, H. I.; Renis, H. E.; Weed, S.
D. J. Med. Chem. 1980, 23, 237–239.
14. Biginelli, P. Ber. 1891, 24, 1317–1319.
15. Kappe, C. O. Eur. J. Med. Chem. 2000, 35, 1043–1052.
16. Melo, S. J.; Luu-Duc, C.; Thomasson, F.; Narcisse, G.; Gaultier, C. Ann. Pharm.
Franc¸aises 1992, 50, 39–51.
17. Wierenga, W. Pharmacol. Ther. 1985, 30, 67–89.
18. Sheibani, H.; Seifi, M.; Bazgir, A. Synth. Commun. 2009, 39, 1055–1064.
19. Mallouk, S.; Bougrin, K.; Laghzizil, A.; Benhida, R. Molecules 2010, 15, 813–823.
20. Collins, M. J. In Microwave synthesis: Chemistry at the speed of light; B. L. Hayes (Ed.);
CEM Publishing: Matthews, 2002; pp. 11–28.
21. Do¨mling, A.; Ugi, I. Angew. Chem. Int. Ed. 2000, 39, 3168–3210.
22. Hugel, H. M. Molecules 2009, 14, 4936–4972.
¨
23. Larhed, M.; Hallberg, A., Drug Disc. Today 2001, 6, 406–416.
24. Stadler, A.; Kappe, C. O. J. Comb. Chem. 2001, 3, 624–630.
25. Lyczak, J. B.; Cannon, C. L.; Pier, G. B. Microbes Infect. 2000, 2, 1051–1060.
26. Mendonc¸a Jr., F. J. B.; dos Anjos, J. V.; Falca˜o, E. P. S.; Yamamoto, A. P.; Melo, S. J.;
Srivastava, R. M. Heterocycl. Commun. 2005, 11, 479–484.
27. National Committee for Clinical Laboratory Standard. Methods for Dilution Antimicrobial
Susceptibility Tests for Bacteria That Grow Aerobically (Approved Standard M7-A6); NCCLS:
Wayne, PA, 2003, 6.
28. Woese, C. R. Microbiol. Rev. 1987, 51, 221–271.
29. Deshmukh, M. B.; Salunkhe, S. M.; Patil, D. R.; Anbhule, P. V. Eur. J. Med. Chem. 2009,
44, 2651–2654.
30. Bararjanian, M.; Balalaie, S.; Rominger, F.; Barouti, S. Helv. Chim. Acta 2010, 93, 777–784.