Solvent-free one-pot synthesis of polysubstituted tetrahydropyrimidines and their antioxidant and antimicrobial properties

Article abstract of DOI:10.1007/s11164-015-2063-9

A versatile and highly efficient one-pot multicomponent approach for the synthesis of novel multisubstituted tetrahydropyrimidine (dimethyl/diethyl-1,3-disubstituted-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate) derivatives catalyzed by Bromo(dimethylsulfonium) bromide under solvent-free conditions has been developed. The protocol is eco-friendly, operationally simple, and proceeds in short reaction time, providing high-yield, high-purity (90-95 %) stable target compounds without any side products. Further, the scope of this protocol extended to aliphatic substrates, thus establishing the versatility of the catalyst. The lead compounds were screened for antioxidant and antimicrobial activities. Among them, compounds 4a, 4d, 4e, 4j exhibited excellent antibacterial activity when compared with the standard gentamycin. Compounds 4e and 4k exhibited excellent antifungal activity in comparison with the standard itraconazole. The results of this study revealed that all synthesized compounds were significantly scavenged DPPH free radicals in a concentration-dependent manner. The IC₅₀ values of the compounds is between 13.28 and 23.16 μM when compared with the standard ascorbic acid. Compound 4f was found to be a good antioxidant. Graphical abstract: [Figure not available: see fulltext.]The synthesis of polysubstituted tetrahydropyrimidines (dimethyl/diethyl-1,3-disubstituted-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate) derivatives from but-2-ynedioates, amines, and formaldehyde via a one-pot multicomponent reaction is reported. The reactions were performed under solvent-free and mild conditions with shorter reaction times, high purity, and high yield. The obtained products are interesting heterocyclic compounds containing ester functional groups and exhibited excellent antibacterial activity and moderate-to-good antioxidant properties.

Full text of DOI:10.1007/s11164-015-2063-9

Res Chem Intermed
DOI 10.1007/s11164-015-2063-9
Solvent-free one-pot synthesis of polysubstituted
tetrahydropyrimidines and their antioxidant
and antimicrobial properties
Shailaja Myadaraboina1 Manjula Alla1
•
•
Arunadevi Parlapalli1 Sarangapani Manda2
•
Received: 3 February 2015 / Accepted: 16 April 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A versatile and highly efficient one-pot multicomponent approach for the
synthesis of novel multisubstituted tetrahydropyrimidine (dimethyl/diethyl-1,3-disub-
stituted-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate) derivatives catalyzed by Bro-
mo(dimethylsulfonium) bromide under solvent-free conditions has been developed. The
protocol is eco-friendly, operationally simple, and proceeds in short reaction time,
providing high-yield, high-purity (90–95 %) stable target compounds without any side
products. Further, the scope of this protocol extended to aliphatic substrates, thus
establishing the versatility of the catalyst. The lead compounds were screened for an-
tioxidant and antimicrobial activities. Among them, compounds 4a, 4d, 4e, 4j exhibited
excellent antibacterial activity when compared with the standard gentamycin. Com-
pounds 4e and 4k exhibited excellent antifungal activity in comparison with the standard
itraconazole. The results of this study revealed that all synthesized compounds were
significantly scavenged DPPH free radicals in a concentration-dependent manner. The
IC50 values of the compounds is between 13.28 and 23.16 lM when compared with the
standard ascorbic acid. Compound 4f was found to be a good antioxidant.
&
Shailaja Myadaraboina
shailaja2603@gmail.com
1
2
Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology,
Hyderabad 500607, India
Department of Medicinal Chemistry, UCPSc, Kakatiya University, Warangal, India
123

S. Myadaraboina et al.
Graphical abstract
R
COO
2
-
O
O
R1 NH2
R1
R
R
N
2O
2O
H
C
H
O
R
COO
N
2
R1
BDMS
olvent ree
S
f
The synthesis of polysubstituted tetrahydropyrimidines (dimethyl/diethyl-1,3-
disubstituted-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate) derivatives from but-
2-ynedioates, amines, and formaldehyde via a one-pot multicomponent reaction is
reported. The reactions were performed under solvent-free and mild conditions with
shorter reaction times, high purity, and high yield. The obtained products are
interesting heterocyclic compounds containing ester functional groups and exhibited
excellent antibacterial activity and moderate-to-good antioxidant properties.
Keywords Multicomponent reaction (MCR) Á Acetylene dicarboxylates Á
Amines Á Bromo(dimethylsulfonium) bromide (BDMS) Á Polysubstituted
tetrahydropyrimidines Á Antioxidant Á Antimicrobial
Introduction
In recent times, one-pot multicomponent reactions (MCRs) have emerged as a
powerful tool in synthetic organic chemistry because of their significant advantage
[1] in construction of complex molecules [2] from readily available raw materials,
such as operation simplicity, reduction of isolation and purification steps, and
minimization of cost, time, and waste production [3–5]. MCRs are environmentally
benign and often proceed with excellent chemoselectivity. Over the past several
years, numerous MCRs for construction of C–N bonds [6] have been reported and
popular protocols for synthesis of different nitrogen-containing heterocycles.
There are numerous MCR approaches [1, 7–9] in the literature for the synthesis
of tetrahydropyrimidine derivatives; most of them have limitations, such as expense,
excess amounts of catalyst, long reaction times, and drastic reaction conditions, etc.
Due to increasing concerns over hazardous effect of organic solvents on
environment and human health, the stress on solvent-free protocols in organic
synthesis has received much attention. In this context, herein we report an efficient,
three-component, one-pot, solvent-free MCR for the synthesis of polysubstituted
tetrahydropyrimidines (dimethyl/diethyl-1,3-disubstituted-1,2,3,6-tetrahydropyrim-
idine-4,5-dicarboxylate) derivatives starting from readily available substituted but-
2-ynedioate, substituted amines, and formaldehyde in the presence of BDMS as a
catalyst at ambient temperature. BDMS [10] is an inexpensive, highly efficient
acidic catalyst that generates dry HBr in situ [11]. It can be easily prepared in a
laboratory (DMS and Br2) and is used for various organic transformations as well as
in synthesis of a variety of heterocyclic compounds [12–14]. The usefulness of this
123

Solvent-free one-pot synthesis of polysubstituted…
catalyst has been demonstrated by the authors for Michael addition, Mannich
reaction, and protection of amines, etc. [15–17].
Among nitrogen-containing heterocyclic pharmacophores, pyrimidine and its
analogues exhibit diverse medicinal chemistry properties such as antiviral [18],
anti–inflammatory [19], and protein-nucleic acid interactions [20] for the treatment
of Alzheimer’s disease [21]. A number of pyrimidine antagonists such as
5-fluorouracil, gemcitabin, capecitabine and fluoxuridine are currently in use as
anticancer drugs [22]. Tetrahydropyrimidines (THPs) are responsible for salt and
heat sensitivity of protein–DNA interactions. Amino acid attached tetrahydropy-
rimidines have shown unique muscarinic agonist activity [23]. Development of
green synthetic methodologies and evaluation of novel class of N-containing
heterocyclic molecules has been our area of focus.
The discovery of the role of free radicals in cancer, diabetes, cardiovascular
diseases, autoimmune diseases, neurodegenerative disorders, aging, and other
diseases has led to new medical investigations. Minimizing oxidative damage may
be an important approach to primary prevention or treatment of these diseases, since
antioxidants may block free radical formation or interrupt an oxidizing chain
reaction [24]. Based on the antimicrobial and antioxidant properties of tetrahy-
dropyrimidines, it is considered worthwhile to synthesize di-methyl/ethyl-1,3-
disubstituted-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate derivatives in the
presence of Bromo(dimethylsulfonium) bromide (BDMS) under solvent-free
conditions and to develop these as new antioxidant and antimicrobial agents.
Results and discussion
Chemistry
Preliminary study to establish suitable conditions for a three-component, one-pot
reaction was attempted by reacting dimethyl acetylene dicarboxylates (1),
benzylamine (2), and formaldehyde (3) using BDMS as catalyst (Scheme 1). The
reaction proceeds smoothly within a short time and the product was isolated in good
yield.
An investigation of the model reaction protocol for the ideal catalyst load was
carried by varying the catalyst from 2 to 10 mol% and the yields were found to vary
from 50 to 90 % (Table 1). No further increase in yield or change in reaction time
was observed with an increase in catalyst load above 10 mol%.
O
NH2
CO2CH3
H3C
H3C
O
O
N
BDMS
soventfree
rt
HCHO
N
CO2CH3
1
O
3
2
4d
Scheme 1 Model reaction for the optimization of reaction conditions
123

S. Myadaraboina et al.
Table 1 Effect of amount of BDMS on the synthesis dimethyl-1,3-dibenzyl-1,2,3,6-tetrahydropyrim-
idine-4,5-dicarboxylate
Entry
BDMS (mol%)
Timea (min)
Yieldb (%)
1
2
3
4
5
6
a
0
2
720
10
8
40
50
73
84
90
90
6
8
5
10
20
5
5
Reaction conditions: Dimethyl acetylenedicarboxylate (1.0 mmol), benzyl amine (2.0 mmol), HCHO
(3.0 mmol), and catalyst at room temperature
b
Yield of pure compound after column chromatography
In order to elucidate the role of BDMS, a control reaction was carried out without
catalyst. The reaction was extremely sluggish and goes to about 40 % completion
even after 12 h, thus establishing the role of catalyst is increasing the momentum of
the MCR. Further, the optimum concentration of the catalyst required for the
protocol was established by performing the model reaction with varying concen-
trations of BDMS (2–10 mol% Table 1). The results indicated that 10 mol% of
BDMS was sufficient, and any excess of the catalyst did not increase the yields
significantly.
Inspired by these interesting results, we evaluate the influence of solvents on the
BDMS catalyzed conversion. The reaction was carried out in three different
solvents, namely non-polar (DCM), polar aprotic (acetonitrile), and polar protic
(methanol) (Scheme 1; Table 2). When the reaction was carried out in MeOH, in
30 min the yield was 88 %, in DCM and CH3CN afforded the product the product in
15 and 10 min with yield 90 and 92 %, respectively. Following the same protocol
under solvent-free conditions, 95 % yield of THPs was obtained almost instanta-
neously. As is evident from the above investigations, the reaction ideally proceeds
in solvent-free conditions with 10 mol% of BDMS (Scheme 2; Table 3).
Table 2 Screening of reaction condition with respect to solvent for the synthesis of dimethyl-1,3-
dibenzyl-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate
S. no
Catalyst
Solvent
Timea (min)
Yieldb (%)
1
2
3
4
a
BDMS
BDMS
BDMS
BDMS
DCM
15
10
30
5
90
92
88
95
CH3CN
MeOH
No solvent
Reaction conditions: Dimethyl acetylenedicarboxylate (1.0 mmol), benzyl amine (2.0 mmol), HCHO
(3.0 mmol), and catalyst (10 mol%) at room temperature
b
Isolated yield
123

Solvent-free one-pot synthesis of polysubstituted…
O
O
NH2
CO2CH3
Catalyst
H3C
H3C
O
O
N
(10 mol%)
HCHO
sovent free
rt
N
CO2CH3
1
3
2
4d
Scheme 2 Model reaction for the optimization of reaction conditions
Table 3 Synthesis of tetrahydropyrimidine (4d) in the presence of different catalysts under solvent-free
conditions
Entry
Catalyst
Solvent
Timea
Yieldb (%)
1
2
3
5
a
FeCl3
ZrCl4
I2
–
–
–
–
7 h
68
72
50
95
10 h
9 h
BDMS
5 min
Reaction conditions: dimethyl acetylenedicarboxylate (1.0 mmol), benzyl amine (2.0 mmol), HCHO
(3.0 mmol), and catalyst (10 mol%) at room temperature
b
Isolated yield
O
CO2R1
R1
R1
R2
10 mol% BDMS
O
O
N
R2
NH2
n
HCHO
( )
Solvent free
rt
N
R2
3
CO2R1
2(a-i)
O
1
2a: R2 =2-FC6H4; n=0
2b: R2 =4-BrC6H4; n=0
4(a-l)
4a: R1=CH3;R2=2-FC6H4
2c: R2 =4-CH3C6H4; n=0
2d: R2 =C6H5; n=1
2e: R2 =4-ClC6H5CH2; n=1
2f: R2 =C6H5; n=2
2g:
2h:
2i:
4b: R1=CH3;R2=2-BrC6H4
4c: R1=CH3;R2=4-CH3C6H4
4d: R1=CH3;R2=C6H5CH2
4e: R1=CH3;R2=4-ClC6H5CH2
4f: R1=CH3;R2=C6H5CH2CH2
4g: R1=CH3;R2=C6H5(CH)CH3
4h: R1=CH3;R2=CH2)3CH3
4i: R1=CH3;R2=(CH2)2OCH3
4j: R1=C2H5;R2=2-FC6H4
R
R
R
2 =C6H5(CH)CH3
2 =CH3; n=3
2 =OCH3; n=2
4k: R1=C2H5;R2=C6H5(CH)CH3
CH2
4l: R1=C2H5;R2=C6H5
Scheme 3 Synthesis of tetrahydropyrimidines
Among these catalysts, FeCl3 afforded the product in 68 % yield in 7 h. In case
of ZrCl4 and iodine, the products were obtained in 72 % yield in 10 h and 50 %
yield in 9 h. However, BDMS proved to be the most ideal catalyst with the shortest
reaction time, i.e., almost instantaneous and with excellent yield (95 %). The
123

S. Myadaraboina et al.
method was established with dimethyl/diethyl acetylene dicarboxylates (1.0 equiv),
various substituted aromatic and aliphatic amines (2.0 equiv), and formaldehyde
(3.0 equiv) in the presence of 10 mol% of BDMS at ambient temperature. The
reaction was instantaneous and afforded dimethyl/diethyl-1,2,3,6-tetrahydropyrim-
idine-4,5-dicarboxylate in excellent isolated yields.
Having successfully established the ideal reaction conditions, the general
applicability of this method was evaluated by using different substituted amines and
acetylene dicarboxylates (Scheme 3; Table 4). The protocol was facile with both
aromatic and aliphatic amines and products were obtained in good yield. However,
the reaction time for the aliphatic amines was shorter compared to those of the
aromatic primary amines. No significant effect of the amine ring substitutions on the
reaction yields was observed. The reaction was not clean when heterocyclic amines
were used and isolation of the product was laborious. No decipherable alteration in
reactivity was observed when the acetylene dicarboxylate esters were either
dimethyl or diethyl and both gave equally good yield (90–98 %) in short reaction
times.
The structure of the compound dimethyl 1,3-dibutyl-1,2,3,6-tetrahydropyrim-
idine-4,5-dicarboxylate 4h was characterized by 1HNMR, mass and IR spectral, and
elemental analysis. In IR spectrum, characteristic stretching frequencies at 1740 and
1
1700 cm-1 correspond to C=O functional groups. The H NMR spectrum showed
that broad singlet at d 3.97 ppm and 3.50 ppm integrating for two protons each
corresponds to N attached CH2 of pyrimidine ring, singlet at d 3.90 and 3.64 ppm
integrating for three protons each corresponds to methyl protons of ester groups, two
Table 4 Synthesis of polysubstituted tetrahydropyrimidines
Entry
R1
R2
Producta,b
Time (min)
Yield (%)c
1
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
C2H5
C2H5
C2H5
2-FC6H4
4a
4b
4c
4d
4e
4f
4
7
5
5
6
5
6
2
3
8
5
8
93
96
95
98
92
96
94
92
93
90
93
95
2
4-BrC6H4
3
4-MeC6H4
C6H5CH2
4
5
4-ClC6H4CH2
C6H5CH2CH2
C6H5CH(CH3)
n-C4H10
6
7
4g
4h
4i
8
9
CH3OC2H5
4-FC6H4CH2
C6H5CH(CH3)
C6H5CH2
10
11
12
a
4j
4k
4l
Reaction conditions: alkynoate (1.0 mmol), amine (2.0 mmol), HCHO (3.0 mmol), and BDMS
(10 mol%) at room temperature
b
All products were fully characterized by usual spectroscopic techniques
c
Yield of pure isolated product after CC
123

Solvent-free one-pot synthesis of polysubstituted…
triplets at d 3.02 and 2.52 ppm integrating for two protons each corresponds to N
attached CH2 of butyl group. The mass spectrum of compound 4h shows a sharp
peak m/z at 313 [M?H]?. Similarly all the compounds were synthesized and
characterized.
The reaction proceed via a cascade of elementary reactions, namely enamine,
hydroamination, and was followed by cyclization. In order to understand the
mechanism of the reaction and role of the catalyst in the reaction, a series of
experiments were carried out in a step-wise manner. The reaction was performed by
segregating enamine formation and hydroamination steps and then mixing the
contents to cyclize to THPs, both with and without BDMS under solvent-free
conditions. Both the enamine formation and hydroamination steps were extremely
slow without BDMS. They were instantaneous with BDMS, which established the
role of BDMS in catalysis of both the steps unequivocally.
A plausible mechanism for the formation of THPs from the experimental
observation is given in Scheme 4. Initially, amine reacts with the formaldehyde to
form an N-methyleneamine derivative catalyzed by BDMS. BDMS also catalyses
the hydroamination of the amine, formaldehyde, and the dicarboxylate yields
aminomaleate. Finally, the aminomaleate derivative undergoes cycloaddition with
H
H
-
R NH2
r
B
O
H
H
S
r
B
O
r
HB
R
r
B
BDM
S
S
N
H
O
+
r
HB
DM
H
SO
r
HB
R
N
r
B
+
BDM
H H
C
S
O
S
H
2C
H
S
H
R
O
N
R
r
B
O
R
N
r
B
O2C
R
CO2
R
R
N
RHN
R
CO2
O2C
R
+
r
HB
O2C
R
CO2
DM
SO
r
HB
BDM
S
+
RNH2
R
R
CO2
O2C
Scheme 4 Plausible mechanism
123

S. Myadaraboina et al.
imine to form poly-substituted pyrimidine derivatives in excellent yields.
Throughout the reaction, the DMSO and HBr liberated regenerate the BDMS
catalyst, which is recycled.
Conclusions
A novel and efficient protocol for solvent-free one-pot synthesis of polysubstituted
tetrahydropyrimidines via MCR using acetylene dicarboxylates, formaldehyde, and
various substituted amines catalyzed by BDMS has been achieved. The method has
many unique features and is an eco-friendly, solvent-free approach, avoiding
cumbersome work-up procedures. Excellent yields and shorter reaction times make
the method amenable for industrial applications. The versatility of catalyst (BDMS)
is an added advantage for extending protocol to aliphatic amines. The obtained
products are interesting heterocyclic compounds containing a, b acid functional
groups, which can serve as building blocks for synthesis of new chemical entities.
Among the synthesized compounds, compound 4e with 4-chloro substituted
derivative was considered a good antimicrobial agent and compound 4f with the
phenyl derivative with n = 2 as an antioxidant and compounds are stable at test
conditions.
Biological evaluation
Solvent-free synthesized tetrahydropyrimidines (4a–4l) were evaluated for antibac-
terial, antifungal, and antioxidant activities by agar diffusion method, spore
germination method, and DPPH method.
Antimicrobial activity
Compounds 4a–4l were evaluated for antibacterial activity against E. Coli and S.
aureus, by the Agar diffusion method [25] at the concentration of 50,100 lg/ml
using gentamycin as the standard drug (10 lg/ml) and the results are presented in
Table 5. Antifungal activity against A. niger and C. albicans by spore germination
method [26] at 100 lg/ml. Itraconazole was used as a reference drug (100 lg/ml).
From the antimicrobial activity data, all the synthesized compounds (4a–4l)
exhibited antibacterial activity with a zone of inhibition ranging from 13 to 24 mm
and antifungal activity with a percentage of spore germination ranging from 30 to
100 %. Among them, compounds 4a, 4d, 4e, 4j exhibited excellent antibacterial
activity when compared with the standard gentamycin. Compounds 4e and 4k
exhibited excellent antifungal activity in comparison with the standard itraconazole.
Structure–Activity Relationship: All the dimethyl/diethyl 1,3-dibutyl-1,2,3,6-
tetrahydropyrimidine-4,5-dicarboxylate derivatives carboxylates compounds have
shown moderate-to-good activity. The effect of substitutions of carboxylate and
amine were compared to study the SAR. Compounds 4a–4l have similar structure
except R2 position. Among the dimethyl-substituted series compounds with 2-fluoro
123

Solvent-free one-pot synthesis of polysubstituted…
Table 5 Antimicrobial activity of the polysubstituted tetrahydropyrimidines
Code
Antibacterial activity
Antifungal activity
A. niger C. albicans
S. aureus
E. coli
50 (lg/ml) 100 (lg/ml) 50 (lg/ml) 100 (lg/ml) 100 (lg/ml) 100 (lg/ml)
4a
13
12
16
22
15
14
12
13
16
18
13
14
21
24
13
12
17
22
15
14
15
15
21
12
15
21
14
12
14
14
15
21
18
12
13
12
22
13
22
15
14
14
18
10
14
16
12
12
15
14
14
22
61
72
45
54
100
30
35
92
56
58
95
78
96
56
58
42
98
78
93
92
56
48
98
97
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
Gentamycin
Itraconazole
100
100
phenyl, benzyl and 4-chloro benzyl amines have shown good zone of inhibition
against S. aureus at both 50 and 100 lg/ml. Similarly, in case of diethyl-substitution
compound with 2-fluoro phenyl amine has shown a good zone of inhibition against
S. aureus at both 50 and 100 lg/ml. On the other hand, compound 4k, which
contains diethyl dicarboxylate and phenylethyl amine, has shown very good
antifungal activity, almost equal to the standard against A. niger and C. albicans.
Compound 4e was the most active derivative in the series against fungal strains and
equal to the standard, i.e., itraconazole.
Antioxidant activity
Antioxidant studies were carried out by DPPH method [27]. The study reveals that
all the compounds exhibited antioxidant activity (Table 6) with IC50 values ranging
between 13.28 and 23.16 lM when compared with the standard ascorbic acid.
Compound 4f was found to be a better antioxidant, with an IC50 value of 13.28 lM
(Figs. 1, 2).
Experimental section
Melting points were determined in an open capillary tube with a cintex industrial
Corporation melting point apparatus. IR spectra were recorded on a Thermo Nicolet
NEXUS 670 spectrophotometer. 1H and 13C NMR spectra were recorded on Avance
300 spectrometer using TMS internal standard. Chemical shifts (d scale) are
1
reported in parts per million (ppm). H NMR spectra are reported in the order:
123

S. Myadaraboina et al.
123

Solvent-free one-pot synthesis of polysubstituted…
120
100
80
60
40
20
0
Fig. 1 Graphical representation
of the antibacterial and
antifungal activity of
tetrahydropyrimidines
Anꢀbacterial acꢀvity
S.aureus
Anꢀbacterial acꢀvity
S.aureus
Anꢀbacterial acꢀvity
E.coli
Anꢀbacterial acꢀvity
E.coli
Fig. 2 Graphical representation
of the antioxidant activity of
tetrahydropyrimidines
Anꢀoxidant acꢀvity IC 50 (μM)
25
20
15
10
5
0
multiplicity, coupling constant (J value) in Hertz (Hz), and number of protons.
Electron spray ionization mass spectra were recorded on Thermo Finnigan ESI ion
trap mass spectrometer. HRMS (ESI) was recorded on a QSTAR XL high-resolution
mass spectrometer.
General procedure for the synthesis of tetrahydropyrimidines derivatives
To the mixture of DMAD/DEAD (1 mmol), 37 % HCHO solution (3 mmol) and
amine (2 mmol) was stirred at room temperature followed by addition of the
catalyst (10 mol%) to the above reaction mixture. After completion of the reaction
(as monitored by TLC), ethyl acetate was added to the reaction mixture, the organic
layer was washed with brine solution, and then finally with water. The organic
solvent was dried over anhydrous Na2SO4, filtered, concentrated under reduced
pressure, and the crude product was purified by flash column chromatography to
obtain 100 % pure product.
123

S. Myadaraboina et al.
Spectral data of synthesized compounds
4a: Dimethyl-1,3-bis(2-fluorophenyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
boxylate White solid: m.p. 104–106°C: IR: (KBr) vmax 2951, 2925, 1738, 1692,
1
1587, 1480, 1258, 730 cm-1: HNMR (300 MHz, CDCl3): d 7.18 (d, J = 8.0 Hz,
2H), 7.10 (d, J = 7.8 Hz, 2H), 6.85(m, 2H) 6.72 (m, 2H), 4.82 (s, 2H), 4.23 (s, 2H),
3.79 (s, 3H), 3.48 (s, 3H); 13C NMR (75 MHz, CDCl3): d 165.8, 163.9, 159.2,
157.1, 155.9, 153.8, 146.4, 136.3, 136.2, 128.5, 128.4, 123.8, 120.9, 116.5 100.1,
68.9, 52.5, 51.5, 51.47; MS (ESI): m/z 389[M?H]?; HRMS: C20H19O4N2F2
observed: 389.13153: calculated: 389.13074.
4b: Dimethyl-1,3-bis(4-bromophenyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
boxylate Viscous oil; IR: vmax 1741, 1700, 1587, 1480, 1262, 762 cm-1
;
1HNMR (300 MHz, CDCl3) d: 7.38 (d, J = 8.0 Hz, 2H),7.29 (d, J = 8.0 Hz,
2H), 6.82 (d, J = 8.0 Hz, 2H), 6.72 (d, J = 8.0 Hz, 2H), 4.70 (s, 2H), 4.15 (s, 2H),
3.72 (s, 3H), 3.59 (s, 3H); 13CNMR(75 MHz, CDCl3): d: 165.5, 164.2, 147.4, 146.0,
142.2, 132.7, 132.0, 126.2, 120.0, 119.5, 113.7, 101.6, 68.8, 52.9, 51.8, 47.2; MS
(ESI): m/z 380[M]?, 382[M?2]?.
4c:
Dimethyl-1,3-bis(p-tolylphenyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
boxylate Viscous oil; IR: vmax 1743, 1697, 1514, 1435, 1260 cm-1; HNMR
(300 MHz, CDCl3): d 7.22 (d, J=8.0 Hz, 2H); 7.13 (d, J=8.0 Hz, 2H), 6.88 (d,
J=8.0 Hz, 2H), 6.78 (d, J=8.0 Hz, 2H), 4.80 (s, 2H), 4.15 (s, 2H), 3.72 (s, 3H), 3.59
(s, 3H), 2.30 (s, 3H), 2.26(s, 3H); 13CNMR(75 MHz, CDCl3): d 166.1, 164.5, 146.8,
145.8, 140.7, 136.3, 130.5, 129.7, 128.6, 128.2, 127.9, 127.1, 124.9, 117.9, 98.7,
69.1, 52.3, 51.3, 47.5, 20.4, 20.8; MS (ESI): m/z 381[M?H]?: HRMS: C22H24O4-
N2Na observed: 403.16326: calculated: 403.16238.
1
4d: Dimethyl-1,3-dibenzyl-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate:
1
Viscous oil; IR: vmax 1735, 1720, 1565, 1478, 1250 cm-1; HNMR (300 MHz,
CDCl3): d 7.32–7.23(m, 10H), 4.16 (s, 2H), 3.91 (s, 3H), 3.83 (s, 2H), 3.65 (s, 3H),
3.60 (s, 2H), 3.54 (s, 2H); 13CNMR (75 MHz, CDCl3): d 166.8, 165.5,
148.1,137.8,136.0, 128.6,128.2, 127.9, 127.1, 92.1,65.9, 56.9, 54.2, 52.8, 51.0,
48.2; MS (ESI): m/z 381[M?H]?; HRMS: C22H24O4N2 observed: 381.1863;
calculated: 381.18163.
4e: Dimethyl-1,3-bis(4-chlorobenzyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
boxylate Viscous oil; IR: vmax 2951, 2925, 1738, 1692, 1587, 1480, 1258,
;
760 cm-1 1HNMR (300 MHz, CDCl3): d 7.29 (d, J = 8.3 Hz, 2H), 7.26 (d,
J = 8.3 Hz, 2H), 7.22 (d, J = 8.3 Hz, 2H), 7.08 (d, J = 8.3 Hz, 2H), 4.10 (s, 4 H),
3.92 (s, 3H), 3.66 (s, 3H), 3.55 (s, 2H), 3.52 (s, 2H); 13C NMR (75 MHz, CDCl3): d
166.6, 165.4, 147.7, 136.2, 134.5, 133.9, 130.26, 129.8, 129.4, 128.8, 128.4, 92.6,
65.6, 56.2, 29.6; MS (ESI): m/z 448[M?]; HRMS: C22H23O4N2Cl2 observed:
449.10379; calculated: 449.10294.
4f:
Dimethyl-1,3-diphenethyl-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxy-
late Viscous oil; IR: vmax 1741, 1700, 1587, 1480, 1262 cm-1;1HNMR(300 MHz,
CDCl3): d 7.30–7.11(m, 10H), 3.92 (s, 2H), 3.90 (s, 3H), 3.66 (s, 3H), 3.56(s, 2H),
123

Solvent-free one-pot synthesis of polysubstituted…
3.21 (t, J = 7.3 Hz, 4H), 2.80 (t, J = 6.0 Hz, 4 H); 13CNMR (75 MHz, CDCl3): d
166.1, 164.9, 147.2, 141.4, 139.7, 128.8, 128.2, 127.8, 125.2, 124.8, 92.9, 65.6,
56.1, 53.2, 52.6, 50.7; MS (ESI): m/z 409 [M?H]?; HRMS: C24H28O4N2 observed:
409.21259; calculated: 409.21218.
4g:
boxylate Viscous oil; IR: vmax 2977, 2949, 1740, 1689, 1584, 1480,
1286 cm-1 1HNMR(300 MHz, CDCl3): d 7.35–7.11 (m, 10H), 4.54–4.50 (m,
Dimethyl-1,3-bis(1-phenylethyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
;
2H); 3.96 (s, 2 H), 3.95 (s, 2H), 3.65 (s, 3H), 3.63 (s, 3H), 1.44 (d,, J=6.5 Hz,
3H),1.32(d, J = 6.4 Hz, 3H,); 13C NMR (75 MHz, CDCl3): d 166.6, 165.4, 147.7,
136.2, 134.5, 133.9, 130.26, 129.8, 129.4, 128.8, 128.4, 92.6, 65.6, 56.2, 29.6; MS
(ESI): m/z 409 [M?H]?; HRMS: C22H25O4N2 observed: 409.21259; calculated:
409.21218.
4h: Dimethyl-1,3-dibutyl-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate Vis-
cous oil; IR: vmax 1740, 1700, 1560, 1440, 1260 cm-1; 1HNMR (300 MHz, CDCl3):
d 3.99 (s, 2 H); 3.90 (s, 3 H); 3.65 (s, 3 H); 3.50 (s, 2H), 3.02(t, J = 7.5 Hz, 2H,),
2.52(t, J = 7.51 Hz, 2H,), 1.51–1.50 (m, 4H), 1.49–1.21 (m, 4H), 0.96–0.87 (q,
J = 7.3 Hz, 14.9 Hz, 6H); 13CNMR (75 MHz, CDCl3): d 165.3, 164.7, 162.8,
148.1, 67.4, 52.6, 52.3, 52.1, 50.8, 47.9, 42.4, 31.1, 30.1, 29.9, 29.4, 20.6, 20.4, 19.9,
19.7; MS (ESI): m/z 312[M]?; HRMS: C16H29O4N2 observed: 313.21254:calculat-
ed: 313.21218.
4i: Dimethyl-1,3-bis(2-methoxyethyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
boxylate Viscous oil; IR: vmax 1740, 1720, 1595, 1438, and 1209 cm-1
;
1HNMR (300 MHz, CDCl3): d 4.31 (s, 2H), 3.89 (s, 2H), 3.87 (s, 3H), 3.74 (s,
3H), 3.67 (s, 3H), 3.56 (t, J = 5.4 Hz, 4H), 3.38 (t, J = 5.4 Hz, 4H), 3.34 (s, 3H);
13CNMR (75 MHz, CDCl3): d 166.2, 165.0, 147.3, 135.8, 134.1, 133.5, 129.4,
128.4, 127.9, 65.2, 55.7, 53.0, 52.5, 50.7, 47.8, 29.2; MS (ESI): m/z 340[M?NH4]?.
4j:
Diethyl-1,3-bis(4-fluorophenyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicar-
boxylate Yellow oil; IR: vmax 2975, 1730, 1680, 1582, 761,722 cm-1; H NMR
(400 MHz, CDCl3): 6.92–6.90 (m, 8H), 4.78 (s, 2H), 4.18 (s, 2H), 4.17 (q,
J = 7.2 Hz, 2H), 3.99 (m, 2H,), 1.25 (t, J = 7.2 Hz, 3H,), 0.99 (t, J = 7.2 Hz, 3H);
MS (ESI): m/z 415 [M]?.
1
4k: Diethyl-1,2,3,6-tetrahydro-1,3-bis(1-phenylethyl)pyrimidine-4,5-dicarboxy-
late Yellow oil; IR: vmax 1741, 1700, 1587, 1480, 1262 cm-1
;
1HNMR
(300 MHz, CDCl3): d 7.30–7.2 (m, 10H), 4.41–4.32 (m, 4H),4.19 (s, 2H), 4.2 (s,
2H), 3.87 (s, 2H), 1.34–1.30 (m, 6H), 1.26–1.20 (m, 6H); MS (ESI): m/z
437[M?H]?; HRMS:C26H33N2O4 observed: 437.24428: calculated: 437.24348.
4l: Diethyl-1,3-dibenzyl-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate Orange
oil; IR : vmax 3058, 2980, 1740, 1692, 1597, 1493, 1457, 1372, 1258, 1227,1191, 107,
761, 722; 1H NMR (400 MHz, CDCl3): d 7.30–7.2 (m, 10H), 4.41–4.32 (m, 4H), 4.19
(s, 2H), 4.2 (s, 2H), 3.87 (s, 2H), 3.66 (s, 2H), 3.60 (s, 2H), 1.26–120 (m, 6H): 13C
NMR (100 MHz, CDCl3): d 165.9, 164.0, 148.3, 147.9, 141.5, 31.2, 130.9, 129.2,
123

S. Myadaraboina et al.
128.0, 124.3, 121.4, 97.8, 69.4, 60.0, 48.8, 18.0, 14.3, 13.5; MS (ESI): m/z 409
[M?H]?; HRMS: C24H28O4N2 observed: 409.32259; calculated: 409.32218.
Biological evaluation
Antibacterial activity
Molten agar (27 ml) was added to sterile Petri dishes and allowed to solidify for 1 h.
Then 50 ll of the 24-h culture of a test organism was spread evenly onto the agar
plate with a sterile cotton swab. Six-millimeter-diameter-wide bores were made on
the agar using a sterile borer. The solutions of the compounds were added into each
of the bores using a sterile tip micropipette. A similar plate was prepared by
standard drugs by gentamycin (10 lg/ml). These dishes were then incubated at
37 °C for 24 h. Antibacterial activity of synthetic compounds was evaluated by
measuring the zone of growth inhibition against the test organisms with a zone
reader. The medium with DMSO as solvent was used as a negative control, whereas
media with gentamycin was used as a positive control. The test was carried out in
triplicate.
Antifungal activity
Monosporic cultures of Drechslera spicifera and Fusarium oxysporum isolated from
diseased fruits of tomato and maintained on Asthana and Hawkers medium A
(glucose 5 g, potassium nitrate 3.5 g, potassium dihydrogen phosphate 1.7 g,
magnesium sulphate 0.75 g, agar-agar 15 g, and distilled water 1 l) was employed
for these studies. The antifungal activity of the title compounds was assayed by
glass slide humid chamber technique as described by Horsfall using different
concentrations of (320, 640 lg/ml) prepared in dimethyl sulfoxide (DMSO) were
prepared by liquid dilution method. The spore suspension of different fungi was
prepared in different concentrations so as to show 30–40 spores in high power on
the sterilized glass slide and 100 % relative humidity blotter at the bottom of a Petri
dish and incubated at 28 2 °C for 8 h. At the end of incubation period, spores
germinated and non-germinated were scored in ten randomly selected microscopic
fields so as to cover 350–400 spores. Itraconazole (fungicide) was used as the
standard for comparison of the activity. The percentage of spore germination
inhibition was calculated with the help of the following formula. % Inhibi-
tion = 100 (C - T)/C, where C is the diameter of fungal growth on the control
plate, and T is the diameter of fungal growth on the test plate.
Antioxidant activity
DPPH method To 1 ml of 0.135 mM DPPH prepared in methanol, 1.0 ml of test
compounds was added, ranging from 20 to 100 lg/ml. The reaction mixture was
vortexed thoroughly and left in the dark at room temperature for 30 min. The
absorbance was measured spectrophotometrically at 517 nm. The scavenging ability
of the test compounds was calculated using the standard equation.
123

Solvent-free one-pot synthesis of polysubstituted…
The IC50 values were given in table. The amount of DPPH radical was calculated
following this equation:
% Inhibition of DPPH ¼ ½A0 À AsŠ=A0  100
where A0 is the absorbance of control and As is the absorbance of sample. The
standard drug is ascorbic acid.
Acknowledgments The authors are thankful to DST (SR/WOS-A/CS-66/2011), UGC (RGNF), New
Delhi, for financial support. MS is thankful to CSIR-IICT for providing laboratory facility, UCPSc,
Kakatiya university for biological evaluation.
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