Sonochemical synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines catalyzed by [HNMP] + [HSO4]- A nd their antimicrobial activity studies

Article abstract of DOI:10.1038/ja.2017.47

In this study, the one-pot four-component reaction of aromatic aldehyde, 2-thiobarbituric acid, ammonium acetate in the presence of a catalytic amount of [H-NMP] + [HSO₄]-under ultrasonic irradiation in water is reported. In the present procedu

Full text of DOI:10.1038/ja.2017.47

The Journal of Antibiotics (2017), 1–8
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ORIGINAL ARTICLE
Sonochemical synthesis of pyrido[2,3-d:6,5-d′]-
dipyrimidines catalyzed by [HNMP]+[HSO4]−
and their antimicrobial activity studies
Hossein Naeimi1, Asieh Didar1, Zahra Rashid2 and Zohreh Zahraie3
In this study, the one-pot four-component reaction of aromatic aldehyde, 2-thiobarbituric acid, ammonium acetate in the
presence of a catalytic amount of [H-NMP]+[HSO4]− under ultrasonic irradiation in water is reported. In the present procedure,
the pyrido[2,3-d:6,5-d′]dipyrimidine derivatives were purely produced as valuable products. The process proved to be simple,
environmentally friendly, efficient and high to excellent yielding. Moreover, some of the synthetic compounds were investigated
and revealed important antimicrobial activity of prepared products.
The Journal of Antibiotics advance online publication, 26 April 2017; doi:10.1038/ja.2017.47
INTRODUCTION
The pyridopyrimidine scaffold is extensively described as heterocycles toward the preparation of these fused molecules.
or antitumor activity.5,23–25 Therefore, great efforts have been directed
in many natural and synthetic biologically active compounds,
In the last few years, ultrasonic-assisted organic synthesis has been
as well as in different drug discovery programs. The properties of an important eco-friendly synthetic approach that is widely used in
pyridopyrimidine depend on the position of the nitrogen atom in the organic synthesis and has a profound impact on the chemical methods
fused ring scaffold.1,2 Pyrido[2,3-d:6,5-d′]pyrimidines occupy a special for the synthesis of complicated synthesis.26 Ultra-sonication is based
place in four possible isomeric structures and their structure has been on generating the phenomenon of cavitation, nucleation, growth and
the subject of medical research, because this scaffold is associated with implosive collapse that generates high pressures and temperatures
a wide range of pharmacological properties and biological activities, in their surroundings. This performance leads to mass transfer
such as dihydrofolate reductase inhibitory activity,3 antimicrobial improvement and performing chemical reactions.27 Ultrasonic-
activity,4 antitumor activity,5 anti-inflammatory,6 tyrosine kinase assisted organic synthesis can be extremely applicable, to synthesize
inhibition,7,8 calcium channel antagonists9 and fibroblast growth a wide range of practical synthesis. The notable features of the
factor receptor 3 inhibition.10–12 Some of the pharmaceutically ultrasound approach are increase of reaction rate, facile manipulation
important compounds containing pyrido[2,3-d]pyrimidine nucleus and mild reaction conditions compared with traditional methods; this
such as adenosine kinase inhibitor (I) and cyclin-dependent technique is more efficient and easily controlled, and is along with the
kinase inhibitors (II)13 are presented in Figure 1. Moreover, it is goals of green chemistry.28,29 However, the effect of using ultrasonic
also reported that some heterocycles of this class have been irradiation in the heterocyclic system is not fully explored.
found to possess activities of anti-HIV,14 antifolate,15 potassium
sparing,16 antibacterial,17 analgesic,6,18 antihypertensive,19 antiallergic,20 considerable attention of synthetic organic chemists in recent years;
anticonvulsants21 and tuberculostatic.3
ionic liquids is an environmentally friendly solvent with unique
Organic reactions in acidic ionic liquids media have received the
Annulated pyrimidine derivatives have received great attention properties such as high ionic conductivity, non-volatility, high thermal
during the past years, because they exhibit useful biological activities. stability, non-flammability and miscibility with organic compounds,
Uracil and its fused derivatives, such as pyrano[2,3-d]pyrimidines, especially with the heterocyclic compounds. Because of these useful
pyrido[2,3-d]pyrimidines, pyrazo[3,4-d]pyrimidines or pyrimido[4,5-d] properties, numerous works have been published in the last decades
pyrimidines and annulated pyrido[2,3-d:6,5-d′]dipyrimidine deriva- reporting the possibility to perform several organic reactions and
tives based on diverse procedures such as Knoevenagel condensation, catalyzed processes in ILs.30,31
Michael addition followed by cyclodehydration strategy and finally
As a part of our continuing efforts on the development of
heterocyclization.22 These compounds have a wide range of biological new simple and eco-compatible approach for the synthesis of
activities such as antibacterial and antifungal activity, antiasthmatics, biologically active heterocyclic compounds,32,33 we wish to describe
antiallergic, antihypertensive, cardiotonic, bronchodilator, antibronchitic an efficient synthesis of novel pyrido[2,3-d]pyrimidines via a one-pot
1Faculty of Chemistry, Department of Organic Chemistry, University of Kashan, Kashan, Iran; 2Young Researchers and Elite Club, Central Branch, Islamic Azad University, Tehran,
Iran and 3Faculty of Chemistry, Department of Biotechnology, University of Kashan, Kashan, Iran
Correspondence: Professor H Naeimi, Faculty of Chemistry, Department of Organic Chemistry, University of Kashan, Kashan 87317, I.R. Iran.
E-mail: naeimi@kashanu.ac.ir
Received 21 March 2016; revised 24 January 2017; accepted 23 February 2017

Synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines
H Naeimi et al
2
four-component reaction by using catalytic amount of [H-NMP]+ yields in a shorter reaction time and mixture of EtOH and water was
[HSO4]− in water under ultrasonic irradiation at room temperature. also equally effective, but in longer time. The reaction in the
Furthermore, the antibacterial activity of some of the prepared other solvents gave the desired products in lower yields (Table 2,
products was studied.
entries 1–3).
In continuation of this research, the effect of various powers of
ultrasonic irradiation has been surveyed. Product 4f was synthesized as
a model reaction in order to optimize the best-suited reaction
conditions. It was observed that the reaction in the presence of
[H-NMP]+[HSO4]− as catalyst and ultrasonic irradiation with power
26.5 W cm− 2 provides the best result as obtained product with 98%
isolated yield during 10 min (Table 3, entry 3). In general, increase
of ultrasonic power means that higher intensity of ultrasound was
introduced into the reaction vessel, which would accelerate the
reactions. As it can be seen in this table, the increase of ultrasonic
RESULTS AND DISCUSSION
Development of new highly effective synthetic methods and
procedures with environmental friendly tools is one of the priority
goals of chemical research. In the present study, to help achieve this
goal, it should be considered the highly significant pharmacological
activities of pyrido[2,3-d]pyrimidine. In continuation of our research
on the efficient preparation of different heterocycles via a simple
and environmentally benign synthetic method, a four-component
synthesis was planned based on foreseeing a one-pot reaction among
benzaldehyde, 2-thiobarbituric acid and ammonium acetate with 1:2:1
molar ratio for the synthesis of pyrido[2,3-d]dipyrimidine under
ultrasonic irradiation. Some limited previously reported works were
found in the literature related to preparation of hexahydropyrido
[2,3-d:6,5-d′]dipyrimidine-4,6(1H,5H)-dione.34–36
Table 1 Different amounts of the [H-NMP]+[HSO4]− as catalyst in
model reactiona
Entry
Catalyst (mol%)
Time (min)
Yield (%)b
At the beginning, choosing a convenient and green reaction
medium is extremely important for successful synthesis. To this
1
2
3
0
12
15
20
12
5
30
80
98
aim, due to valuable properties of ionic liquids in recent times37,38
,
and our experience in the efficacy of the catalyst [HNMP]+[HSO4]− as
an acidic green catalyst, we examined its catalytic activity in a model
reaction between 4-chlorobenzaldehyde, 2-thiobarbituric acid and
ammonium acetate with 1:2:1 mole in water under ultrasonic
irradiation at power of 26.5 W cm− 2 (Scheme 1). When the model
reaction was carried out in the presence of 12 mol% of catalyst, the
product is obtained in low yield. However, it was found that increase
the catalyst loadings to 15 mol%, improved the product yield over the
98%. Thus, 15 mol% of catalyst amount was chosen as the maximum
quantity of the catalyst for this reaction (Table 1, entries 2 and 3).
To achieve suitable conditions, a model reaction performed in
various solvents in the presence of a catalytic amount of [HNMP]+
[HSO4]− ionic liquid at room temperature. Among the different
solvents screened, using water gave the products in high to excellent
aReaction conditions: 4-cholorobenzaldehyde (0.25 mmol), 2-thiobarbituric acid (0.5 mmol),
ammonium acetate (0.3 mmol), H2O (10 ml), 26.5 W cm− 2
bIsolated yields.
.
Table 2 Screening of solvents for the synthesis of 4fa
Entry
Solvent
Time (min)
Yieldb (%)
1
2
3
4
5
EtOH
Acetone
10
15
15
10
5
70
40
40
99
98
Acetonitrile
H2O/EtOH (4:1)
H2O
aReaction conditions: 4-cholorobenzaldehyde (0.25 mmol), 2-thiobarbituric acid (0.5 mmol),
ammonium acetate (0.3 mmol), Solvent (5 ml), catalyst (15 mol%), 26.5 W W cm− 2
bIsolated yields.
.
Table 3 Power optimization for the synthesis of 4fa
Entry
Power (W cm− 2
)
Time (min)
Yield (%)b
1
2
3
4
20
10
5
85
98
98
80
26.5
33
10
15
39.5
Figure 1 Representative compounds containing pyrido[2,3-d]pyrimidine.
A full color version of this figure is available at The Journal of Antibiotics
journal online.
aReaction conditions: 4-cholorobenzaldehyde (0.25 mmol), 2-thiobarbituric acid (0.5 mmol),
ammonium acetate (0.3 mmol), H2O (10 ml), catalyst(15 mol%).
bIsolated yields
Scheme 1 Model reaction for the synthesis of 5-(4-chlorophenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]dipyrimidine-4,6(1H,5H)-dione (4f).
The Journal of Antibiotics

Synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines
H Naeimi et al
3
power led to relatively higher yield until the ultrasound power Knoevenagel condensation reaction of the activated aldehyde and
intensity to reach 39.5 W and then the yield slightly decreased with 2-thiobarbituric acid. Subsequently, Michael-type addition of com-
pound 2 to the intermediate 3 and tautomerization produce the
In order to survey the recyclability and reusability of the catalyst, the intermediate 3. Then, the amine group in intermediate 3 attacked to
increasing ultrasound power intensity (Table 3, entry 4).
activated carbonyl group and the corresponding products were
obtained by intramolecular cyclization and dehydration. Brønsted
acidic ionic liquid ([H-NMP]+[HSO4]−) can activate carbonyl groups
via hydrogen bonding to decrease the energy of transition state.
The results of antimicrobial activity of compounds are summarized
in Tables 6 and 7. Our results indicated that none of synthesized
compounds had antimicrobial activity against gram negative bacteria
(Table 6). Compounds 4i and 4m were active against gram positive
bacteria. Although compound 4i had the highest inhibition zone
against S. epidermidis in comparison with compound 4m, it did not
have strongest MIC value.
As displayed in Tables 6 and 7, compounds 4c, 4f and 4h had
activity against Gram-positive bacteria and fungi. Compound 4h
revealed better effects against Gram-positive bacteria and fungi in
comparison with compounds 4c and 4f. In addition, as indicated in
Table 7, MIC values of the compounds 4c, 4f, 4m and 4h
(o31.2 μg ml− 1) were evaluated.
reaction mixture filtered to separate the solid product. Then, diethyl
ether was added to the filtrate for removing the remained organic
compounds. The remained [H-NMP]+[HSO4]− catalyst in water easily
extracted from mentioned mixture. After that, the water was
evaporated under vacuum, to separate the [H-NMP]+[HSO4]−. The
recovered catalyst was reused for subsequent reactions. As indicated in
Figure 2, it was shown no major loss of efficiency with regard to the
reaction yield after four successive runs.
To show the merit of this method, a comparison of the present
work with very few previously reported methods was provided for the
formation of pyrido[2,3-d:6,5-d′]pyrimidine is presented in Table 4.
These methods suffer from one or more disadvantages such as; long
reaction times, low yields and harsh and unclean reaction conditions.
To explore the scope and limitation of this reaction, we have
extended the reaction with a range of aromatic aldehydes (Scheme 2).
The results are indicated in Table 5.
As shown in Scheme 3, hexahydropyrido[2,3-d:6,5-d′]dipyrimidine
could be synthesized via sequential condensation, addition, hydrolysis,
cyclization and tautomerization. The reaction may proceed in a
stepwise manner, in which the intermediate 3 was formed by fast
CONCLUSION
In this study, we have described a successful strategy for the
efficient and convenient synthesis of pyrido[2,3-d:6,5-d′]dipyrimidine
derivatives in the one-pot, four-component condensation reaction of
2-thiobarbituric acid, ammonium acetate and aromatic aldehydes
using the inexpensive, nontoxic and easily available [H-NMP]+
[HSO4]− as a catalyst under ultrasonic irradiation. The advantages
of this protocol are such as the economically reaction procedure, easy
workup, high product yields and short reaction times. In addition,
antimicrobial activities of different compounds were investigated.
EXPERIMENTAL PROCEDURE
Chemistry
Materials. All commercially available reagents were used without further
purification and purchased from the Merck Chemical Company (Darmstadt,
Germany) in high purity.
Figure 2 Catalyst recyclability on the synthesis of pyridopyrimidine.
Table 4 Comparison condition used for the synthesis of pyrido[2,3-d:6,5-d']dipyrimidine
Entry
Catalyst
Condition
Time
Yield (%)a
1
2
3
[H-NMP]+[HSO4]−b
Al2O3(solid phase)c
Al2O3(liquid phase)c
us
MW
Δ
5 min
6 h
89
86 (Kidwai et al.40
98 (Kidwai et al.40 and Vafaeezadeh et al.43
)
)
48 h
aIsolated yields.
bReaction conditions: 4-cholorobenzaldehyde (0.25 mmol), 2-thiobarbituric acid (0.5 mmol), ammonium acetate (0.3 mmol), H2O (10 ml), catalyst (15 mol%), 26.5 W cm− 2
cReaction conditions: benzaldehyde, 2-thiobarbituric acid, ammonium acetate 1:2:1, Al2O3 (acid).
.
Scheme 2 The reaction leading to the synthesis of novel pyrido[2,3-d]dipyrimidine derivatives.
The Journal of Antibiotics

Synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines
H Naeimi et al
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Table 5 Synthesis of pyrido[2,3-d:6,5-d']dipyrimidine derivatives
under ultrasonic irradiationa
Table 5 (Continued )
Entry
Aldehyde
Product
Time (min)
Yield (%)b
Entry
Aldehyde
Product
Time (min)
Yield (%)b
aReaction conditions: aldehyde (0.25 mmol), 2-thiobarbituric acid (0.5 mmol), ammonium
acetate (0.3 mmol), H2O (10 ml), catalyst (15 mol%), 26.5 W cm− 2
bIsolated yields.
.
The Journal of Antibiotics

Synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines
H Naeimi et al
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Scheme 3 Proposed reaction mechanism for the formation of 4a.
Table 6 In vitro antimicrobial activity of the prepared compounds 4c, 4f, 4i, 4m and 4h by agar diffusion assayAbbreviation: NT, not tested.
Diameter of zone of inhibition in mm
Test microorganisms
4c
4f
4i
4m
4h
Tetracycline
Nystatin
a
P. aeruginosa
E. coli
−
−
−
−
−
−
−
−
−
−
−
8
0.0
19.5 0.5
19
NT
NT
NT
NT
NT
NT
−
−
−
P. vulgaris
B. subtilis
S. aureus
−
−
−
1
10 0.0
−
13.5 0.5
19.5 1.5
26.5 0.5
23.5 0.5
17.5 0.5
18.5 0.5
18 0.0
17
14
1
11
1
18.5 0.5
11 0.0
24.5 0.5
S. epidermidis
C. albicans
A. niger
2
15.5 0.5
14 0.0
22.5 0.5
13.5 0.5
38
NT
1
−
−
−
−
−
−
−
26 1
10 0.0
12.5 1.5
NT
NT
31.5 0.5
31.5 1.5
A. brasiliensis
−
14 1
aA dash (–) indicates no antimicrobial activity.
Table 7 Minimum inhibitory concentration (MIC in μg ml− 1) values of the effective synthesized compounds 4c, 4f, 4i, 4m and 4h.
Bacteria
Fungus
A. niger
Compound
S. epidermidis
S. aureus
B. subtilis
C. albicans
A. brasiliensis
a
4c
3.9
1.95
62.5
3.9
250
500
1000
2000
62.5
250
NT
−
−
42000
−
500
42000
−
−
42000
−
4f
−
42000
−
4i
4m
−
−
−
4h
1.95
250
NTb
1000
7.8
42000
NT
1000
NT
1000
NT
Tetracycline
Nystatin
NT
100
12.5
25
Abbreviation: NT, not tested.
aA dash (–) indicates no antimicrobial activity.
The Journal of Antibiotics

Synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines
H Naeimi et al
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Apparatus
5-(2-Nitrophenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione (4d). Yellow powder; m.p.: 230 °C decom-
pose. IR (KBr) (νmax/cm–1): 3437 (NH), 3137 (C–H, sp2 stretch), 1610 (C= O),
IR spectra were obtained as KBr pellets on a Perkin–Elmer 781 spectro-
photometer (Waltham, MA, USA) and on an impact 400 Nicolet FT–IR
spectrophotometer (Thermofisher, Waltham, MA, USA). 1H NMR and 13C 1535, 1445, (C= C, Ar). 1H NMR (DMSO-d6, 400 MHz) δ (p.p.m.): 11.57–1.99
NMR were recorded in dimethul sulfoxide (DMSO)-d6 solvents on a Bruker
DRX-400 spectrometer (Karlsruhe, Germany) with tetramethylsilane as internal
reference. UV–Vis spectra were obtained with a Perkin–Elmer 550 spectro-
photometer recorded in EtOH solvent. Melting points were obtained with a
Yanagimoto micro melting point apparatus and are uncorrected. Mass spectra
were recorded on an Agilent Technology HP 5973 Network Mass Selective
Detector Mass spectrometer (Agilent Technology, Santa Clara, CA, USA)
operating at an ionization potential of 70 eV (EI). The BANDELIN ultrasonic
HD 3200 (BANDELIN electronic GmbH & Co. KG, Berlin, Germany) with
probe model KE 76, 6 mm diameter was used to produce ultrasonic irradiation.
(5H, s, NH), 7.45 (1H, m, H-Ar), 7.30–7.32 (1H, m, H-Ar),
7.19 (1H, s, H-Ar), 7.06 (1H, s, H-Ar), 6.09–6.21 (1H, s, CH). 13C NMR
(DMSO-d6, 100 MHz) δ (p.p.m.): 173.4, 163.1, 150.1, 136.0, 131.5, 129.7,
127.1, 124.0, 95.2, 29.1; Anal. Calcd for C15H10N6O4S2: C, 44.77; H, 2.50;
N, 20.88,%; Found C, 44.81; H, 2.53; N, 20.91%.
5-(3-Methoxyphenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione (4e). Yellow powder; m.p.: 242 ˚C decom-
pose. IR (KBr) (νmax/cm–1): 3591, 3447 (NH), 3166 (C–H, sp2 stretch), 2922
(C–H, sp3), 1632 (C= O), 1437, 1536 (C= C, Ar). 1H NMR (DMSO-d6,
The purity determination of the substrates and reaction monitoring were 400 MHz) δ (p.p.m.): 11.56–11.73 (4H, m, NH), 7.19–7.23 (1H, s, NH),
accomplished by TLC on silica-gel poly gram SILG/UV 254 plates (from Merck
Company). All the newly synthesized compounds were screened for anti-
microbial activity. The microorganisms used in this research were: Pseudomonas
aeruginosa (ATCC 27853), Escherichia coli (ATCC 10536) and Proteus vulgaris
(PTCC 1182) as examples of Gram-negative bacteria, Bacillus subtilis (ATCC
6633), Staphylococcus aureus (ATCC 29737) and Staphylococcus epidermidis
(ATCC 12228) as examples of Gram-positive bacteria, Candida albicans (ATCC
10231), Aspergilluasniger (ATCC 16404) and Aspergilluasbrasiliensis (ATCC
16404) as examples of fungal strains.
6.93 (1H, s, H-Ar), 6.62–6.64 (1H, m, H-Ar), 6.56–6.57 (m, 1H), 6.49–6.52
(1H, s, H-Ar), 5.91–5.97 (1H, s, CH), 3.63 (3H, s, CH3). 13C NMR (DMSO-d6,
100 MHz) δ (p.p.m.): 173.2, 159.4, 145.2, 129.0, 119.6, 113.6, 109.8, 96.2, 55.2,
30.8; Anal. Calcd for C16H15N5O3S2: C, 49.34; H, 3.88; N, 17.98,%; Found C,
49.38; H, 3.90; N, 18.02%.
5-(4-Chlorophenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione (4f). Yellow powder; m.p.: 257 °C decom-
pose. IR (KBr) (νmax/cm–1): 3433 (NH), 3130 (C–H, sp2 stretch), 1626 (C= O),
1434, 1534 (C= C, Ar). 1H NMR (DMSO-d6, 400 MHz) δ (p.p.m.): 11.67 (5H,
s, NH), 7.19 (1H, s, H-Ar), 7.06 (1H, s, H-Ar), 6.94 (2H, d, H-Ar), 5.91 (1H, s,
CH). 13C NMR (DMSO-d6, 100 MHz) δ (p.p.m.): 175.5, 165.2, 162.9, 144.0,
136.5, 133.8, 130.1, 122.0, 119.4, 93.1,31.2.
Typical procedure for the synthesis of [H-NMP]+[HSO4]−
[H-NMP]+[HSO4]− was synthesized by following procedure. The N-methyl-2-
pyrrolidone (9.9 g, 0.1 mol, 9.71 ml) was charged into a 250 ml three necked
flask with magnetic stirrer, then sulfuric acid (9.6 g, 0.1 mol, 5.5 ml) was slowly
added dropwise into the flask at 0–5 °C. After stirring for 4 h at room
temperature, the reaction mixture was washed with ethyl acetate (3 × 10 ml)
and dried at 80 °C in vacuum.39 The ionic liquid was prepared in quantitative
yield and characterized by 1H NMR data before using in the reaction as
followed: 1H NMR (DMSO-d6, 400 MHz): δ (p.p.m.) 3.28–3.31 (t, 2H,
J = 7.2 Hz), 2.75 (s, 3H), 2.15–2.19 (t, 2H, J = 8.1 Hz), 1.88–1.96 (q, 2H,
J = 7.6 Hz).
5-(2-Fluorophenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione (4g). White powder; m.p.: 240 °C decom-
pose. IR (KBr) (νmax/cm–1): 3432 (NH), 3108 (C–H, sp2 stretch), 1623, 1687
(C = O), 1433, 1544 (C=C, Ar); 1H NMR (DMSO-d6, 400 MHz) δ (p.p.m.):
17.00 (1H, s, NH), 11.49–11.75 (4H, m, NH), 7.08–7.12 (2H, m, H-Ar),
6.91–7.00 (2H, m, H-Ar), 6.01 (1H, s, CH); 13C NMR (DMSO-d6, 100 MHz)
δ (p.p.m.): 173.2, 163.3 (m, 1C), 162.0, 159.6, 130.4–130.5, 130.0 (d, 1C),
127.5, 115.2, 95.4, 26.8, 23.6; Anal. Calcd for C15H12FN5O2S2: C, 47.74; H,
3.20; N, 18.56,%; Found C, 47.76; H, 3.24; N, 18.60%.
General procedure for synthesis of pyrido[2,3-d:6,5-d′]dipyrimidine
derivatives
5-(2-Hydroxynaphthalen-1-yl)2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:
6,5-d′]dipyrimidine-4,6(1H,5H)-dione (4h). Light brown powder; m.p.:
308 ˚C decompose. IR (KBr) (νmax/cm–1): 3530 (NH), 3069 (C–H, sp2 stretch),
2892 (C–H, sp3), 1680 (C=O), 1450, 1562 (C = C, Ar); 1H NMR(DMSO-d6,
400 MHz) δ (p.p.m.): 17.1 (1H, s, NH), 11.56 (2H, s, NH), 11.40 (2H, s, NH),
7.96 (1H, d, H-Ar), 7.77 (2H, m, H-Ar), 7.39-7.41 (2H, m, H-Ar),
7.19–7.22 (1H, m, H-Ar), 5.39–5.41 (1H, m, CH); 13C NMR (DMSO-d6,
100 MHz) δ (p.p.m.): 173.7, 161.6, 154.5, 147.8, 131.2, 129.2, 127.6, 125.4,
123.4, 116.8, 115.4, 97.5, 91.6, 24.8. Anal. Calcd for C19H13FN5O3S2: C, 53.89;
H, 3.09; N, 16.54,%; Found C, 53.92; H, 3.12; N, 16.56%.
To a mixture of an aromatic aldehyde (0.25 mmol), 2-thiobarbituric acid
(0.5 mmol), ammonium acetate (0.3 mmol), [H-NMP]+[HSO4]− (12 mol%)
and water (2 ml) was added. Then, ultrasonic probe was directly immersed in
the resulting mixture. The progress of the reactions was monitored by TLC
until conversion of the starting materials was satisfactory. After completion of
the reaction, the solvent was evaporated and the precipitate was washed with
EtOH and hot water to afford the pure product. All products were identified by
physical and spectroscopic data. The synthesis of the compounds 4b and 4j was
investigated but unfortunately even after 24 h, only a trace amount of product
was observed by TLC, that is why we could not reported the spectroscopic data
of them.
5-(Pyridin-2-yl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione (4i). Red powder; m.p.: 280 °C decompose.
IR (KBr) (νmax/cm–1): 3398 (NH), 3210 (C–H, sp2 stretch), 2881 (C–H, sp3),
1605 (C = O), 1455, 1533 (C = C, Ar). 1H NMR (DMSO-d6, 400 MHz)
δ (p.p.m.): 14.00–16.00 (1H, s, NH), 11.84 (4H, s, NH), 8.60 (1H, m,
H-Ar), 8.42 (1H, m, H-Ar), 7.83 (2H, s, H-Ar), 6.20 (1H, s, CH); 13C NMR
(DMSO-d6, 100 MHz) δ (p.p.m.): 174.2, 163.4, 158.9, 146.8, 141.9, 126.2,
124.8, 92.9, 32.0. EI–MS (70 eV) m/z: 358 (0.06), 352 (3.91), 228 (100), 126
(4.96), 124 (37.53), 77 (23.27), 51 (8.31).
5-Phenyl-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]dipyrimidine-4,
6(1H,5H)-dione (4a). Cream powder; m.p.: 211 °C Lit40 (m.p.rep: 218 °C).
IR (KBr) (νmax/cm–1): 3452 (NH), 3054 (C–H, sp2 stretch), 2898 (C–H, sp3), 1637
(C =O), 1440, 1559 (C =C, Ar). 1H NMR (DMSO-d6, 400 MHz) δ (p.p.m.):
11.33–12.00 (3H, s, NH), 7.91 (1H, s, NH), 7.60 (1H, s, NH), 7.15 (2H, s, H-Ar),
7.05 (1H, s, H-Ar), 6.98-6.99 (2H, d, J=6.0, H-Ar), 5.93 (1H, s, CH).
5-(4-Nitrophenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine 4,6(1H,5H)-dione (4c). Light brown powder. m.p.: 330 °C
Lit41 (m.p.rep: 4300 °C decompose). IR (KBr) (νmax/cm–1): 3447 (NH),
3175 (C–H, .sp2 stretch), 1602 (C = O), 1432, 1509 (C = C, Ar). 1H NMR
(DMSO-d6, 400 MHz) δ (p.p.m.): 17.10 (1H, s, NH), 11.75–11.97 (2H, s,
NH), 11.62 (2H, s, NH), 8.04–8.28 (2H, d, J = 8.8 Hz, H-Ar), 7.23–7.25
(2H, d, J = 8.4 Hz, H-Ar), 6.04 (1H, s, CH), 13C NMR (DMSO-d6,
100 MHz) δ (p.p.m.): 173.5, 164.0, 163.1, 152.5, 145.7, 128.2, 123.5,
95.6, 31.6.
5,5'-(1,4-Phenylene)bis(2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione) (4k). Red powder; m.p.: 300 °C decompose.
IR (KBr) (νmax/cm–1): 3428 (NH), 3200 (C–H, sp2 stretch), 2923 (C–H, sp3),
1623 (C = O), 1434, 1535 (C = C, Ar); 1H NMR (DMSO-d6, 400 MHz)
δ (p.p.m.): 13.41 (2H, s, NH), 12.40 (2H, s, NH), 12.09 (1H, s, NH), 11.61
(1H, s, NH), 7.98 (2H, m, NH), 7.86-7.91 (4H, m, H-Ar), 7.51 (2H, m, NH),
5.59 (2H, s, CH); 13C NMR (DMSO-d6, 100 MHz) δ (p.p.m.): 173.4, 164.0,
The Journal of Antibiotics

Synthesis of pyrido[2,3-d:6,5-d′]-dipyrimidines
H Naeimi et al
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163.0, 126.2, 115.3, 96.4, 30.8. EI-MS (70 eV) m/z: 636 (0.55), 637 (1.06),
289 (27.58), 264 (35.19), 135 (55.28).
1
Mohsenimehr, M., Mamaghani, M., Shirini, F., Sheykhan, M. & Azimian Moghaddam, F.
One-pot synthesis of novel pyrido[2,3-d]pyrimidines using HAp-encapsulated-γ-Fe2O3
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(1H)-ones catalyzed by DBU in aqueous medium. Green Chem. 14, 945–951 (2012).
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kinase inhibitors. 7-amino-4-(phenylamino)- and 7-amino-(phenylmethyl)amino]pyrido
[4,3-d]pyrimidines: a new class of inhibitors of the tyrosine kinase activity of the
epidermal growth factor receptor. J. Med. Chem. 38, 3780–3788 (1995).
Kammasud, N. et al. 5-Substituted pyrido[2,3-d]pyrimidine, an inhibitor against three
receptor tyrosine kinases. Bioorg. Med. Chem. Lett. 19, 745–750 (2009).
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5-(4-Chloro-3-nitrophenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,
5-d′]dipyrimidine-4,6(1H,5H)-dione (4l). Yellow powder; m.p.: 249 °C
decompose. IR (KBr) (νmax/cm–1): 3450 (NH), 3090 (C–H, sp2 stretch), 1615
(C =O), 1542, 1434 (C =C, Ar); 1H NMR (DMSO-d6, 400 MHz) δ (p.p.m.):
11.63–11.70 (4H, m, NH), 7.53–7.56 (1H, m, NH), 7.28–7.30 (1H, m, H-Ar),
7.14–7.18 (1H, m, H-Ar), 7.05 (1H, s, H-Ar), 5.98 (1H, s, CH); 13C NMR
(DMSO-d6, 100 MHz) δ (p.p.m.): 173.5, 163.9, 163.1, 147.7, 145.2, 132.7, 131.4,
123.7, 121.9, 95.3, 30.8. EI–MS (70 eV) m/z: 436 (0.30), 431 (3.07), 311 (85.72),
144 (96.27), 116 (42.61), 69 (100), 43 (85.88); Anal. Calcd for C15H10ClN5O2S2:
C, 45.98; H, 2.57; N, 17.87,%; Found C, 46.01; H, 2.60; N, 17.92%.
2
3
4
5
6
7
5-(4-Methoxyphenyl)-2,8-dithioxo-2,3,7,8,9,10-hexahydropyrido[2,3-d:6,5-d′]
dipyrimidine-4,6(1H,5H)-dione (4m). Orange powder; m.p.: 280 °C decom-
pose; IR (KBr) (νmax/cm–1): 3432, 3090, 1629, 1542, 1442; 1H NMR
(DMSO-d6, 400 MHz) δ (p.p.m.): 11.62 (m, 2H, NH), 11.49 (m, 2H, NH),
7.11–7.09 (s, 1H, NH), 7.86–6.88 (m, 2H, H-Ar), 6.70–6.72 (m, 2H, H-Ar),
5.88 (s, 1H, CH), 3.66 (s, 3H, CH3); 13C NMR (DMSO-d6, 100 MHz)
δ (p.p.m.): 191.7, 164.6, 157.3, 132.2, 130.0, 121.2, 114.9, 107.8, 56.1, 16.5.
8
9
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CONFLICT OF INTEREST
The authors declare no conflict of interest.
ACKNOWLEDGEMENTS
We are grateful to University of Kashan for supporting this work by grant
number 159148/74.
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Supplementary Information accompanies the paper on The Journal of Antibiotics website (http://www.nature.com/ja)
The Journal of Antibiotics