Graphite catalyzed solvent free synthesis of dihydropyrimidin-2(1H)-ones/ thiones and their antidiabetic activity

Article abstract of DOI:10.1016/j.bmcl.2014.04.099

A solvent free three component condensation reaction between an aldehyde, ethyl acetoacetate and urea catalyzed by graphite, a green catalyst is described for the synthesis of dihydropyrimidin-2(1H)-ones. This protocol is scalable and the catalyst is reus

Full text of DOI:10.1016/j.bmcl.2014.04.099

Accepted Manuscript
Graphite catalyzed solvent free synthesis of dihydropyrimidin-2(1H)-ones/thi-
ones and their antidiabetic activity
Kashinath L. Dhumaskar, Surya NandanMeena, Sanjeev C. Ghadi, Santosh G.
Tilve
PII:
S0960-894X(14)00456-9
DOI:
http://dx.doi.org/10.1016/j.bmcl.2014.04.099
BMCL 21592
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
17 January 2014
7 April 2014
23 April 2014
Please cite this article as: Dhumaskar, K.L., NandanMeena, S., Ghadi, S.C., Tilve, S.G., Graphite catalyzed solvent
free synthesis of dihydropyrimidin-2(1H)-ones/thiones and their antidiabetic activity, Bioorganic & Medicinal
Chemistry Letters (2014), doi: http://dx.doi.org/10.1016/j.bmcl.2014.04.099
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Graphical Abstract
Graphite catalyzed solvent free synthesis of
dihydropyrimidin-2(1H)-ones/thiones and
their anti diabetic activity
Kashinath L. Dhumaskara, Surya NandanMeenab, Sanjeev C. Ghadib, *,Santosh G. Tilvea,*
1
1
R
O
R
O
CHO
O
NH
Graphite
o
NH2
O
+
70
C
N
H
X
H2N
X
O

Bioorganic & Medicinal Chemistry Letters
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m
Graphite catalyzed solvent free synthesis of dihydropyrimidin-2(1H)-
ones/thiones and their antidiabetic activity
Kashinath L. Dhumaskara, Surya NandanMeenab, Sanjeev C. Ghadib,*, Santosh G. Tilvea,*
aDepartment of Chemistry, Goa University,Taleigao Plateau
Goa-403206 India.
*Email: stilve@unigoa.ac.in, phone: +91 832 6519317
bDepartment of Biotechnology, Goa University,Taleigao Plateau
Goa-403206 India.
*saga@unigoa.ac.in
ARTICLE INFO
ABSTRACT
Article history:
Received
A solvent free three component condensation reaction between an aldehyde, ethyl acetoacetate
and urea catalyzed by graphite,
a green catalyst is described for the synthesis of
Revised
dihydropyrimidin-2(1H)-ones. This protocol is scalable and the catalyst is reusable. This method
is also applied for the synthesis of dihropyrimidin-2(1H)-thiones. α-amylase, a key enzyme in
carbohydrate metabolism is generally targeted for management of type 2 diabetes. The
therapeutic potential of the dihydropyrimidinones and dihropyrimidinthiones to inhibit α-
amylase activity was evaluated by in vitro assay. Of the synthesized compounds 3,4-
dihropyrimidin-2(1H)-thione (1k) demonstrated highest inhibition of α-amylase activity.
Accepted
Available online
Keywords:
Biginelli reaction
Multicomponent reaction
Solvent less
2009 Elsevier Ltd. All rights reserved.
Graphite catalysis
Dihydropyrimidinones
α-amylase inhibition
anti diabetic.
Type 2 diabetes is the most predominant form of diabetes
mellitus resulting from insulin resistance and relative insulin
deficiency.1 α-Amylase, a key carbohydrate digestive enzyme
hydrolyses dietary starch and is responsible for augmentation of
postprandial glucose. The failure to control the postprandial
glucose levels leads to long term health complications such as
heart disease, diabetic retinopathy and strokes. Modulation of α-
amylase activity using synthetic inhibitors is considered a
promising and effective therapeutic for management of
hyperglycemia.2 The stabilization of glucose level would
preclude hyperglycemia and ward off type-2 diabetes associated
health complications.3 Thus efforts are being pursued to test the
natural and non-natural compounds for antidiabetic activity.
as building blocks for the synthesis of various heterocycles.7 The
three component reaction between an aldehyde, β-keto ester and
urea or thiourea to give 3,4-dihydropyrimidin-2(1H)-ones and
3,4-dihropyrimidin-2(1H)-thiones is known as Biginelli reaction.8
Recently, syntheses of these heterocycles have been
comprehensively reviewed.9 Several catalysts have been
successfully employed for this reaction. Recent reports include
sulfated
tungstate,10
periodic
mesoporous organosilica,11 silica gel supported polyphosphoric
acid (PPA-SiO2),12 titanium silicate,13Iron(III) tosylate,14 BF3,15
FeCl3,16 InCl3,17 Yb(OTf)3,18 ionic liquid,19 t-(CH3)3COK,20 Ph3P,21
and L-proline.22
Graphite, an allotrope of carbon, though much known as
support for organic reagents is less used as a reagent itself. The
very few applications of graphite as catalyst are Friedel-Craft
alkylation,23 acylation reaction,24 Diels Alder reaction,25 and for
conversion of aldehydes into nitriles.26 To further its use, recently
we used it successfully for the synthesis of quinoxalines.27
Continuation of these studies herein we report graphite as an
inexpensive heterogeneous, nontoxic, recyclable green catalyst
under solvent free conditions for the synthesis of DHPMs.
Acarbose
a natural antidiabetic drug that demonstrates
inhibition of pancreatic α-amylase activity is being marketed
successfully to control postprandial glucose.4 Additionally,
during in vitro evaluation and testing of candidate drugs with
plausible α-amylase inhibitory activity, acarbose has been
frequently used as a positive reference standard.5
Dihydropyrimidinones (DHPMs) are known for their broad
spectrum of biological activities such as antifungal, antibacterial,
anti-tubercular, anti-inflammatory antioxidant, anti HIV,
anticancer, anti-malarial, anti-filarial,6 and are additionally used
In our efforts, initially we tried the reaction of benzaldehyde,
ethyl acetoacetate and urea in ethanol on 1mmol scale. Checking

(TLC) that no reaction takes place by stirring the reaction
mixture we added 100 mg of graphite (flakes, Aldrich chemicals)
and continued stirring the reaction mixture further. However after
prolonged stirring we could not notice (TLC) any product
formation. Next, we tried the reaction in other solvents like
dioxane, chloroform, toluene, THF and methanol in presence of
graphite. In none of these cases we could observe (TLC) any
product formation. Further, we attempted the reaction neat
without any success. Next we heated the reaction mixture
containing graphite on an oil bath at three different temperatures
(50, 60 & 70 °C). Although no product formation was observed
for the reactions at 50 and 60 °C, we could see solid product
separating out and reaction completing in one hour for the
reaction at 70 °C. The product was obtained in 90% yield. In a
recent report using TiO2 as a catalyst, it is mentioned that the
reaction does not work at 70°C without the use of catalyst.28 In
another report, sulfonated carbon29 is used as a catalyst at 140 °C
under solvent free conditions. Having confirmed that product
DHPM can be obtained at 70°C using graphite we further studied
the optimization of catalyst loading. After several experiments
with diminishing quantities of graphite, 10% w/w was found to
be sufficient to complete the reaction in a reasonable amount of
time. With optimized reaction conditions, we further extended
this method for a wide variety of aryl aldehydes carrying electron
withdrawing or electron donating groups, at ortho, meta or para
position 1a-1j (Table 1). In general it was observed that aryl
aldehydes having electron donating group reacts slower
compared to aryl aldehydes having electron withdrawing groups.
any inhibition of α-amylase activity. Also with electron donating
groups on the benzene ring of DHPMs showed no inhibition of α-
amylase activity. However, presence of electron withdrawing
groups on benzene ring demonstrated α-amylase inhibition, e.g.
nitro group at meta position (1f) displayed 26.49 % inhibition.
Further, two compounds from the synthesized series with sulfur
in the pyrimidinone ring demonstratedα amylase inhibition.
Compound (1n) having para-methoxy group in the benzene ring
displayed 66.5
dihropyrimidin-2(1H)-thione (1k) demonstrated
%
inhibition, whereas the parent 3,4-
dose
a
dependent inhibition with maximum inhibition of α amylase
activity of 97.2 % at 300µg/mL (Fig. 2).
Fig 1. Inhibition of α amylase activity by acarbose at various
concentrations
Thiourea also reacted in
a similar manner to give the
corresponding 3,4-dihropyrimidin-2(1H)-thiones 1k-1n (Table
1). However in this case we had to heat the reaction mixture at
120 °C. Having successfully obtained the DHPMs, we then
investigated the recyclability of our catalyst. For this purpose, the
reaction mass was dissolved in ethanol, filtered and recovered
catalyst was used for further trials. We could successfully use the
recycled graphite for 10 cycles without any appreciable decrease
in yield or increase in reaction time. The reaction was also
studied for scale up studies up to 10 grams without any problem.
The mechanism by which graphite acts as a catalyst is not clearly
understood. It may act as a supporting material for adsorption of
the of the substrate and delivers the heat rapidly and also acts as a
Lewis base (supplementary information).
Fig 2. Dose dependent inhibition of α-amylase activity by various
The dihydropyrimidinones and dihydropyrimidinthiones
synthesized during present studies were tested for their in vitro
inhibition of α amylase activity. They were compared to acarbose
which demonstrated 100 % inhibition at 100 mg/mL (Fig.1). The
parent DHPM with unsubstituted benzene ring did not display
dihydropyrimidinones derivatives

Table 1.Synthesis of substituted 3,4-dihydropyrimidinones (1) and their anti diabetic activity.
R1
R1
O
O
CHO
O
NH
Graphite
NH2
O
+
N
H
X
H2N
X
O
1
1
a
b
c
d
e
f
R1
X
Temp.
Time
1h
yielda(%)
% inhibition of α-
amylase activity
M.P. ( °C )
(°C)
Ph
O
O
O
O
O
O
O
O
O
O
S
200-202 (203-205)30
212-213 (210-212)30
184-186 (184-186)31
238-239 (240-241)32
195-200 (207-208)30
225-226 (226-227)31,32
202-203 (202-203)30
206-208 (207-208)31
176-178 (176-178)33
188-190 (188-189)33
205-206 (205-207)30
183-185(184-186)33
150-153 (150-152)34
149-151 (150-152)30
70
70
97
97
98
97
91
96
96
96
95
96
96
94
98
97
0
0
p-ClC6H4
p-FC6H4
2h
70
2h
63.8
0
o-FC6H4
70
2h
p-NO2C6H4
m-NO2C6H4
p-OMeC6H4
m-OMeC6H4
3,4-OMeC6H3
70
2h
0
70
2h
26.5
0
g
h
i
70
2h
70
1.5h
1h
0
70
0
j
70
1h
0
O
O
k
l
Ph
120
120
120
120
10min
10min
10min
10min
97.2
0
m-HOC6H4
m-MeOC6H4
p-MeOC6H4
S
m
n
S
0
S
66.5
aIsolated yields.

24. Kodomari, M.; Suzuki,Y.; Yoshida, K. Chem. Commun. 1997,
1567.
In conclusion, we have developed a convenient metal free
graphite catalyzed green method for the synthesis of 3,4-
dihydropyrimidin-2(1H)-ones and 3,4-dihropyrimidin-2(1H)-
thiones. The synthesized compounds were tested for their
invitroantidiabetic activity with acarbose as standard. 3,4-
25. Besson, T.; Thiery, V.; Dubac, J. Microwaves in Organic
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Tetrahedron Lett. 54, 2013, 1003.
dihropyrimidin-2(1H)-thione displayed 97.2
300µg/mL.
% activity at
28. Kassaee, Z. M.; Masrouri, H.; Movahedi, F.; Mohammadi, R.
Helv. Chim. Acta 93, 2010, 261.
Acknowledgments
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We are thankful to the Council of Scientific and Industrial
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thankful to CSIR for awarding CSIR-NET (National Eligibility
Test) Senior Research fellowship.SNM acknowledges
Department of Biotechnology, New Delhi, for award of DBT-
SRF.
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35. Representative procedure for the graphite catalyzed synthesis of
3,4-dihydropyrimidinone/thiones: A mixture of benzaldehyde (106
mg, 1 mmol), urea (60 mg, 1 mmol), ethylacetoacetate (130 mg, 1
mmol) and (10 mg, 10% w/w) graphite was heated at 70°C (120
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6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-
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DMSO-d6) δ = 1.008 (t, 3H, J = 6.8 Hz, CH3), 2.182 (s, 3H, CH3),
3.898 (q, 2H, J = 6.8 Hz, CH2), 5.194 (d, 1H, CH), 6.633(s br.,
1H, NH), 7.184-7.081 (m, 5H, aromatic), 8.664 (s br., 1H, NH);
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55.15 (CH), 59.63 (CH2), 100.47 (Cq), 126.59 (2xCH), 127.47
(CH), 128.36(2xCH), 144.39(Cq), 147.37(Cq), 153.24(Cq)165.80
(Cq).νmax(KBr) 3244, 3115, 2980, 1726, 1701, 1649, 1222 cm-1
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SiscoPvt Ltd, India) was prepared by mixing 1.28 mg of enzyme
in 25 ml of phosphate buffer saline. Synthetic compounds (at a
concentration of 50, 150 or 300 µg/ml resuspended in methanol)
were added to 15 µl of α-amylase and incubated at 37°C for 30
minutes. After the pre-incubation, 0.5 ml of PBS containing 1% of
starch was added and incubated at 37°C for 10 minutes. The
reaction was terminated by adding 1 ml of DNSA (3,5-
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540 nm was determined using Shimadzu spectrometer. 0.2% (w/v)
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Supplementary Material
Supplementary material that may be helpful in the review
process should be prepared and provided as a separate electronic
file. That file can then be transformed into PDF format and
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