Solvent-free, green and efficient synthesis of pyrano[4, 3-b]pyrans by grinding and their biological evaluation as antitumor and antioxidant agents

Article abstract of DOI:10.1007/s00044-013-0586-4

A facile, green, and efficient method has been developed for the synthesis of pyrano[4, 3-b]pyrans via a one-pot reaction of aromatic aldehydes, malononitrile, and 4-hydroxy-6-methyl-pyran-2-one in the presence of ammonium acetate under solvent-free condi

Full text of DOI:10.1007/s00044-013-0586-4

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-013-0586-4
ORIGINAL RESEARCH
Solvent-free, green and efficient synthesis of pyrano[4, 3-b]pyrans
by grinding and their biological evaluation as antitumor
and antioxidant agents
Deepika Rajguru
Shubha Jain
•
Balwant S. Keshwal
•
Received: 26 December 2012 / Accepted: 13 March 2013
Ó Springer Science+Business Media New York 2013
Abstract A facile, green, and efficient method has been
developed for the synthesis of pyrano[4, 3-b]pyrans via a
one-pot reaction of aromatic aldehydes, malononitrile, and
reaction conditions, and uses of chemicals that reduce the
risks to humans and the environment. Organic solvents are
high on the list of hazardous chemicals because they are
used in large amounts and are usually volatile liquids.
Therefore, in recent years, solventless organic reactions
have attracted great interest. They have many advantages
such as high efficiency and selectivity, operational sim-
plicity, low costs, mild reaction conditions, and reduced
pollution (Tanaka and Toda, 2000; Shirini et al., 2007;
Thirunarayanan and Vanangamudi, 2006). The grinding
method for the solid-state reactions has been reported for
Reformatsky reaction (Tanaka et al., 1991), Aldol con-
densation (Toda et al., 1990), Dieckmann condensation
(Toda et al., 1998), Knoevenagel condensation (Ren et al.,
2002), and other reactions (Ren et al., 2004, 2005;
Schmeyers et al., 1998).
4
-hydroxy-6-methyl-pyran-2-one in the presence of ammo-
nium acetate under solvent-free conditions using grinding
method. The experimental simplicity, short reaction time,
easy work-up, avoidance of organic solvents, and utilization
of an inexpensive and readily available catalyst make this
new methodology practical and economically attractive. The
antitumor activity of the compounds was tested against
human breast cancer cell line MCF-7. Compounds 4l, 4o, and
4
p showed good cytotoxic activity comparable with standard
drug Doxorubicin. On the other hand, compounds 4q and 4r
exhibited potent growth inhibitory activity. Furthermore, the
synthesized compounds were screened for in vitro antioxi-
dant activity by DPPH assay. All the compounds assayed
showed moderate to good free radical scavenging activity.
It is well known that fused pyran derivatives possess a
variety of a pharmacological and biological properties, such
as fungicidal, insecticidal, and acaricidal activity (Uher
et al., 1994), antiviral and antileishmanial activity (Perez–
Perez et al., 1995; Fan et al., 2010), and anticonvulsant
activity (Aytemir et al., 2004). Moreover, they have been
introduced as non-peptide human immunodeficiency virus
(HIV) protease inhibitors (Wang et al., 1996; Pochet et al.,
Keywords Pyrano[4, 3-b]pyrans ꢀ Green chemistry ꢀ
One-pot synthesis ꢀ Grinding ꢀ Solvent-free ꢀ Cytotoxicity ꢀ
Antioxidant activity
Introduction
1996; Mazumder et al., 1996). Despite their wide range of
Over the past several years, chemists have been aware of
the environmental implications of their chemistry. Nowa-
days, they are trying to develop new synthetic methods,
pharmacological, industrial, and synthetic applications, the
synthesis of pyrano[4, 3-b]pyrans has received little atten-
tion. Recently, a one-pot, three-component reaction of
4-hydroxy-6-methyl-pyran-2-one with malononitrile and
aromatic aldehydes has enjoyed wider utilization in the
synthesis of these compounds. A variety of reagents, such as
piperidine (Piao and Imafuku, 1997; Stoyanov et al., 2000),
TEBAC (Da-Qing et al., 2008), KF/Al O (Wang et al.,
D. Rajguru ꢀ B. S. Keshwal (&) ꢀ S. Jain
School of Studies in Chemistry, Vikram University,
Ujjain, Madhya Pradesh 456010, India
e-mail: bskeshwal2@gmail.com
2
3
2006), magnesium oxide (Seifi, and Sheibani 2008), DBU
(Khurana et al., 2010), and ionic liquids (Shaabani et al.,
123

Med Chem Res
2
005) have been employed to accomplish this transforma-
The results are summarized in Table 2. It is evident that all
the aldehydes used, either bearing electron-donating or
electron-withdrawing groups, reacted smoothly with mal-
ononitrile and 4-hydroxy-6-methyl-pyran-2-one to produce
the corresponding pyrano[4, 3-b]pyran derivatives (4a–r)
in excellent yields. It should be noted that the methodology
worked well for heteroaromatic aldehydes (Table 2, entries
11–18).
tion. However, inspite of their potential utility, all of these
methods suffer from one or more disadvantages, such as
harsh reaction conditions, unsatisfactory yields, prolonged
reaction times, tedious work-up, and use of organic solvents.
As part of our current studies on the development of new
routes to the synthesis of biologically active heterocycles,
we wish to report, herein, a rapid and clean procedure for the
preparation of pyrano[4, 3-b]pyrans. The present study also
describes pyrano[4, 3-b]pyrans as potential cytotoxic and
antioxidant agents.
The possible mechanism of the reaction is depicted in
Scheme 1.
Cytotoxicity
Results and discussion
In vitro cytotoxic activity of the synthesized compounds
and Doxorubicin (Standard) was tested using the MTT
assay against human breast cancer cell line MCF-7. The
results are presented in Table 3 as IC50 (lM) values. The
data of Table 3 indicate that all the compounds tested
exhibited moderate to remarkable cytotoxicity. The struc-
ture–activity relationship (SAR) suggested that insertion of
halogens like Cl or Br into the aryl group of pyrano[4,
3-b]pyrans, as in 4e and 4f, induces an increase of the
cytotoxicity. Introduction of the electron-donating substit-
uents, such as Me and OMe, caused a decrease of the
cytotoxic activity. This is why compounds 4b and 4c
showed minimum inhibition with IC50 values of 54 and
57 lM, respectively. No significant effect on the antitumor
In an initial endeavor, equivalent amounts of benzaldehyde
1
3
a, malononitrile 2, and 4-hydroxy-6-methyl-pyran-2-one
, and ammonium acetate (10 mol %) were reacted in
ethanol under reflux. After 2 h, only 64 % of the desired
product 4a was obtained. In an attempt to improve the
reaction yield and acknowledging the benefits of grinding,
the same reaction was carried out by grinding under sol-
vent-free conditions. Grinding for 10 min led to a yellow
solid mass (the completion of the reaction was checked by
TLC). The solid mass was washed with water, dried, and
recrystallized from ethanol to give 2-Amino-7-methyl-5-
oxo-4-phenyl-4H, 5H-pyrano[4, 3-b]pyran-3-carbonitrile
4
a in 94 % yield. Other catalysts, such as basic alumina,
Na CO , NaHCO , K CO , and NH Cl were not found as
activity was observed for the insertion of NO group into
2
the aromatic ring of pyrano[4, 3-b]pyran, as in 4d, com-
pared to that of its H substituted analog 4a. It is noteworthy
to mention that replacement of aryl group of pyrano[4,
3-b]pyrans by heteroaromatic ring increased the cytotoxic
activity to a great extent. Comparison of the data of the
compounds 4l, 4m, and 4o indicates that insertion of Cl
into the thiophene ring produces an increase in the cyto-
toxicity, whereas insertion of electron-donor Me group
induces a decrease of the biological activity. Surprisingly,
compounds 4q (IC50 = 7 lM) and 4r (IC50 = 5 lM),
containing CN and Br substituted indole rings, respec-
tively, showed potent cytotoxic effects.
2
3
3
2
3
4
effective as ammonium acetate. The results are listed in
Table 1. The effect of catalyst amount on the yield and rate
was also investigated by using different amounts of
ammonium acetate. Reaction with 5 mol % of the catalyst
required longer reaction time and only 40 % yield of the
product 4a was obtained. Excessive amount of catalyst
(
20 mol %) did not increase the yield remarkably.
The above optimized reaction condition was extended to
a variety of aromatic aldehydes with different substituents.
Table 1 Synthesis of 4a under solvent-free conditions in the pres-
ence of different catalysts using grinding method
Antioxidant activity
a
Yield (%)
Entry
Catalyst (mol%)
Time (min)
The synthesized compounds were screened for in vitro
antioxidant activity by DPPH assay. The results obtained are
depicted in Table 4 as IC50 (lM) values and compared with
those of ascorbic acid as standard. Increased absorbance of
the compounds with concentration (data not shown) reveals
that compounds possess radical scavenging activity. Anal-
ysis of the data in Table 4 indicates that insertion of elec-
tron-donating Me and OMe groups, as in 4b and 4c, and
halogens like Cl and Br, as in 4e and 4f, in the aryl group of
pyrano[4, 3-b]pyrans induces an increase in the antioxidant
1
2
3
4
5
6
7
8
a
Basic Al
Na CO
NaHCO
CO (10)
2
O
3
(10)
15
15
20
15
20
10
20
10
76
82
79
85
40
94
65
95
2
3
(10)
(10)
3
K
2
3
NH
NH
NH
NH
4
4
4
4
Cl (10)
OAc (10)
OAc (5)
OAc (20)
Isolated yield
1
23

Med Chem Res
Table 2 Synthesis of 2-Amino-4-aryl-3-cyano-5-oxo-4H, 5H-pyrano[4, 3-b]pyrans in the presence of ammonium acetate under solvent-free
conditions by grinding
NH2
CN
OH
O
CN
CN
Ar
NH OAc (10 mol%)
4
ArCHO
Grinding, r.t., solvent-free
O
O
O
O
1
(a-r)
2
4(a-r)
3
°
Entry
Ar
Product
Time (min)
Yield (%)
m.p. ( C) found (reported)
1
2
3
4
5
6
7
8
9
C
6
H
5
4a
4b
4c
4d
4e
4f
10
12
12
15
14
15
15
15
18
15
12
12
12
14
15
15
14
18
94
95
92
96
93
91
90
95
88
91
95
97
94
93
92
90
86
91
234–236 (236–238)
224–225 (223–225)
202–205 (205–207)
215–218 (216–218)
228–230 (230–231)
226–227 (223–224)
266–268 (267–268)
232–233 (234–235)
232–235 (230–231)
202–204 (205–207)
223–224
4-CH
3
C
6
H
4
4-CH OC
3
6
H
4
4-O
4-ClC
4-BrC
2-ClC
3-O NC
2, 4-Cl
2
NC
6
H
4
6 4
H
6 4
H
6
H
4
4g
4h
4i
2
6 4
H
2
C
6
H
3
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
3, 4-(CH
3
O)
2
C
H
6 3
4j
2-Furanyl
2-Thienyl
4k
4l
242–244
5-Me-2-Thienyl
3-Me-2-Thienyl
5-Cl-2-Thienyl
3-indolyl
4m
4n
4o
4p
4q
4r
175–177
174–175
228–229
206–208
5-CN-3-indolyl
5-Br-3-indolyl
214–216
196–198
OH
N
C
CN
Ar
HO
CN
CN
CN
NH OAc
4
O
4
O
ArCHO
ArCH
NH OAc
CN
O
O
NH2
NH
CN
Ar
CN
Ar
O
O
O
O
O
O
Scheme 1 Plausible reaction pathway for the formation of pyrano[4, 3-b]pyrans
123

Med Chem Res
Table 3 Cytotoxicity of the synthesized compounds against human
breast cancer cell line MCF-7 using the MTT assay
linked to heteroaromatic rings were more active than those
containing aromatic rings. More studies are needed to be
carried out to find the correlation between IC50 of the eval-
uated pyrano[4, 3-b]pyrans and their molecular descriptors,
such as electronic, lipophilic, and steric parameters.
a
Compound
IC50 (lM)
4
4
4
4
4
4
4
4
4
4
4
4
4
a
b
c
46
54
57
42
32
35
27
15
22
12
10
7
d
e
Conclusion
f
In summary, we have described a green and efficient
method for the synthesis of pyrano[4, 3-b]pyran derivatives
under solvent-free grinding conditions. The experimental
simplicity, short reaction times, high yields, easy work-up
procedure, avoidance of organic solvents, and utilization
of an inexpensive and readily available catalyst make
this novel protocol practical and economically attractive
to prepare these derivatives. The synthesized com-
pounds showed moderate to good in vitro cytotoxic activity
against human breast cancer cell line MCF-7 when com-
pared with standard drug Doxorubicin. Compounds 4q
and 4r exhibited potent growth inhibitory activity. This
study also describes pyrano[4, 3-b]pyrans as potential
antioxidants.
k
l
m
o
p
q
r
5
Doxorubicin
19
a
IC50: the compound concentration for which the growth of treated
was only 50 %
cells from time
0
Table 4 Free radical scavenging activity of the synthesized com-
pounds using DPPH assay
a
Compound
IC50 ± SE (lM)
4
4
4
4
4
4
4
4
4
4
4
4
4
a
b
c
769.35 ± 5.4
634.06 ± 7.52
519.67 ± 6.73
815.71 ± 2.9
486.82 ± 4.78
512.17 ± 3.96
227.56 – 5.47
739.44 – 5.11
943.06 – 7.96
616.2 – 4.09
338.96 – 4.87
566.53 – 3.90
440.22 – 5.73
106.4 – 9.8
Experimental section
General
d
e
All the chemicals were purchased from Merck and Sigma-
Aldrich and used without further purification. Melting
points were determined in open glass capillaries and are
uncorrected. IR spectra were recorded on Perkin Elmer-
f
k
l
m
o
p
q
r
1
430 spectrophotometer using potassium bromide pellets.
1
13
H and C NMR spectra were obtained at 400 MHz with a
Bruker (AVANCE) spectrometer using DMSO-d as sol-
6
vent and TMS as an internal standard. MS spectra were
measured at Micromass ZMD ESI (70 eV) system.
Ascorbic acid
a
Standard error
General procedure for the synthesis of 2-Amino-4-aryl-
5-oxo-4H, 5H-pyrano[4, 3-b]pyran-3-carbonitriles
(4a–r)
property. On the contrary, introduction of Me in the thio-
phene ring and insertion of Br in the indole ring of pyrano[4,
3
-b]pyrans, as in 4m and 4r, respectively, decreased the
Aromatic aldehyde 1 (2 mmol), malononitrile 2 (2.5 mmol),
4-hydroxy-6-methyl-pyran-2-one 3 (2 mmol), and ammo-
nium acetate (10 mol %) were taken in a mortar and mixed
thoroughly. The mixture was ground with a pestle at room
temperature. The mixture becomes a sticky paste during the
course of reaction which finally solidifies on completion of
the reaction (monitored by TLC). The solid mass was washed
with water, dried, and recrystallized from ethanol to obtain
the pure product.
radical scavenging activity. The data of Table 4 indicate that
insertion of electron-withdrawing substituents, such as NO2
and CN, as in 4d and 4q, produces a decrease in the anti-
oxidant activity. Among the compounds tested, 4k and 4p
exhibited potent free radical scavenging activity with IC50
values of 227.56 and 338.96 lM, respectively.
The overview of the results presented in Table 3 and
Table 4 revealed that, in general, pyrano[4, 3-b]pyrans
1
23

Med Chem Res
Spectroscopic and analytical data of selected
compounds
6.15 (s, 1H, =CH), 6.73 (d, 1H, J = 5.0 Hz, thiophene),
7.03 (s, 2H, NH ), 7.15 (d, 1H, J = 2.5 Hz, thiophene) ppm.
2
1
3
C NMR (400 MHz, DMSO-d ): d = 13.37, 19.39, 29.40,
6
2
3
-Amino-4-(furan-2-yl)-7-methyl-5-oxo-4H, 5H-pyrano[4,
-b]pyran-3-carbonitrile (4k, C H N O )
58.40, 97.82, 100.93, 119.07, 122.69, 131.27, 133.46,
1
4 10 2 4
136.52, 157.64, 157.75, 161.09, 162.39 ppm. MS (70 eV):
?
m/z = 301.1 (M ?1).
Pink crystals (from EtOH); m.p. 223–224 °C. IR (KBr):
3458, 3260, 3088, 2293, 1649, 1555, 1342, 1253,
=
2-Amino-4-(5-chlorothiophen-2-yl)-7-methyl-5-oxo-4H,
5H-pyrano[4, 3-b]pyran-3-carbonitrile (4o,
C H ClN O S)
-
1 1
1
091, 790 cm . H NMR (400 MHz, DMSO-d ): d = 2.25
6
(
s, 3H, CH ), 4.47 (s, 1H, CH), 6.10 (s, 1H, =CH), 6.16 (d,
3
14
9
2 3
1
H, J = 3.1 Hz, furan), 6.30 (dd, 1H, J = 1.8, J = 1.2 Hz,
a b
furan), 6.97 (s, 2H, NH ), 7.37 (d, 1H, J = 1.0 Hz, furan)
2
Yellow crystals (from EtOH); m.p. 228–229 °C. IR
(KBr): = 3463, 3358, 2952, 2216, 1632, 1546, 1306,
1
3
ppm. C NMR (400 MHz, DMSO-d ): d = 19.43, 29.88,
6
-
1 1
5
5.36, 97.95, 98.40, 105.90, 110.17, 118.89, 141.55,
1028, 838, 767 cm . H NMR (400 MHz, DMSO-d ): d =
6
1
54.12, 158.58, 158.75, 161.13, 162.36 ppm. MS (70 eV):
2.22 (s, 3H, CH ), 4.24 (s, 1H, CH), 6.13 (s, 1H, =CH),
3
?
m/z = 270.0 (M ).
6.84 (d, 1H, J = 2.7 Hz, thiophene), 6.93 (s, 2H, NH ), 7.11
2
1
3
d, 1H, J = 1.5 Hz, thiophene) ppm. C NMR (400 MHz,
(
2-Amino-7-methyl-5-oxo-4-(thiophen-2-yl)-4H, 5H-
pyrano[4, 3-b]pyran-3-carbonitrile (4l, C H N O S)
DMSO-d ): d = 19.35, 35.47, 58.28, 97.89, 101.18, 119.19,
6
1
4 10 2 3
123.95, 128.44, 133.26, 135.34, 159.97, 161.28, 162.07,
?
64.28 ppm. MS (70 eV): m/z = 320.0 (M ).
1
Colorless crystals (from EtOH); m.p. 242–244 °C. IR
(
KBr): = 3475, 3376, 2926, 2212, 1654, 1540, 1301,
1 1
In vitro cytotoxic activity
-
1
2
6
1
032, 862, 754 cm . H NMR (400 MHz, DMSO-d ): d =
6
.23 (s, 3H, CH ), 4.66 (s, 1H, CH), 6.13 (s, 1H, =CH),
3
The cytotoxicity of the synthesized compounds was tested
by MTT assay. MTT [(3-(4, 5-dimethylthiazol-2-yl)-2,
5-diphenyl tetrasodium bromide)] is a pale yellow substrate
that is cleaved by living cells to yield a dark blue formazan
product. This process requires active mitochondria, and
even freshly dead cells do not cleave significant amount of
MTT. Thus the amount of MTT cleaved is directly pro-
portional to the number of viable cells present, which is
quantified by colorimetric methods. This assay was per-
formed at Deshpande Laboratories, Bhopal using the
standard operating procedures. Briefly, the compounds
were dissolved in DMSO and serially diluted with com-
plete medium to get the concentrations a range of test
concentration. DMSO concentration was kept\0.1 % in all
the samples. Cell lines maintained in appropriate condi-
tions were seeded in 96 well plates and treated with dif-
ferent concentrations of the test samples and incubated at
.91 (dd, 1H, J = 3.5 Hz, J = 1.5 Hz, thiophene); 6.97 (d,
a
b
H, J = 2.9 Hz, thiophene); 7.13 (s, 2H, NH ), 7.25 (d, 1H,
2
1
3
J = 3.9 Hz, thiophene) ppm. C NMR (400 MHz, DMSO-
d6): d = 19.40, 31.26, 57.81, 97.94, 100.89, 119.03, 124.44,
1
24.63, 126.61, 147.78, 157.72, 158.44, 161.22,
?
62.57 ppm. MS (70 eV): m/z = 286.1 (M ).
1
2
5
-Amino-7-methyl-4-(5-methylthiophen-2-yl)-5-oxo-4H,
H-pyrano[4, 3-b]pyran-3-carbonitrile (4m,
C H N O S)
15 12 2 3
Brown crystals (from EtOH); m.p. 175–177 °C. IR
(
KBr): = 3476, 3358, 2965, 2226, 1643, 1548, 1352,
-
1 1
272, 1082, 768 cm . H NMR (400 MHz, DMSO-d ): d
1
6
=
2.24 (s, 3H, CH ), 2.39 (s, 3H, CH ), 4.57 (s, 1H, CH),
3 3
6
.04 (s, 1H, =CH), 6.55 (d, 1H, J = 1.6 Hz, thiophene),
.74 (d, 1H, J = 3.3 Hz, thiophene), 6.84 (s, 2H, NH ) ppm.
6
37 °C, 5 % CO for 96 h. MTT reagent was added to the
2
2
1
3
C NMR (400 MHz, DMSO-d ): d = 14.97, 19.44, 31.30,
wells and incubated for 4 h; the dark blue formazan
product formed by the cells was dissolved in DMSO under
a safety cabinet and read at 550 nm. Percentage inhibitions
were calculated and plotted with the concentrations used to
calculate the IC50 values.
6
5
1
8.19, 97.89, 101.02, 118.97, 124.29, 124.47, 138.17,
40.64, 157.51, 158.28, 161.30, 162.10 ppm. MS (70 eV):
?
m/z = 301.1 (M ?1).
2
5
-Amino-7-methyl-4-(3-methylthiophen-2-yl)-5-oxo-4H,
H-pyrano[4, 3-b]pyran-3-carbonitrile (4n, C H N O S)
1
5
12
2
3
Free radical scavenging activity
Brown crystals (from EtOH); m.p. 174–175 °C. IR
The free radical scavenging activity of the synthesized
compounds was tested by DPPH assay. DPPH is a free
radical and accepts one electron or hydrogen radical to
become a stable diamagnetic molecule. DPPH in methanol
(
KBr): = 3472, 3375, 2962, 2223, 1648, 1552, 1332,
-
1 1
275, 1076, 763 cm . H NMR (400 MHz, DMSO-d ): d
1
6
=
2.24 (s, 3H, CH ), 2.28 (s, 3H, CH ), 4.68 (s, 1H, CH),
3 3
123

Med Chem Res
shows a strong absorption band at 517 nm (independent of
pH from 5.0 to 6.5) and the solution appears to be deep
violet in color. As the DPPH radical is scavenged by the
donated hydrogen from the antioxidant, the absorbance is
diminished according to the stoichiometry. The degree of
discoloration indicates the scavenging potential of the
antioxidant compounds. Briefly, solutions of different
Perez–Perez M, Balzarini J, Rozenski J, De-Clercq E, Herdewijn P
(
1995) Synthesis and antiviral activity of phosphonate deriva-
tives of enantiomeric dihydro-2H-pyranyl nucleosides. Bioorg
Med Chem Lett 5:1115
Piao MZ, Imafuku K (1997) Convenient synthesis of amino-substi-
tuted pyranopyranones. Tetrahedron Lett 38:5301
Pochet L, Doucet C, Schynts M, Thierry N, Boggetto N, Pirotte B,
Jiang KY, Masereel B, de Tullio P, Delarge J, Reboud-Ravaux
M (1996) Esters and amides of 6-(chloromethyl)-2-oxo-2H-1-
benzopyran-3-carboxylic acid as inhibitors of a-chymotrypsin:
significance of the ‘‘aromatic’’ nature of the novel ester-type
coumarin for strong inhibitory activity. J Med Chem 39:2579
Ren ZJ, Cao WG, Tong WQ (2002) The Knoevenagel condensation
reaction of aromatic aldehydes with malononitrile by grinding in
the absence of solvents and catalysts. Synth Commun 32:3475
Ren ZJ, Cao WG, Ding WY, Shi W (2004) Solvent-free stereoselective
synthesis of cis-1-carbomethoxy-2-Aryl-3,3-dicyanocyclopro-
panes by grinding. Synth Commun 34:4395
-
1
concentrations (100, 200, 300, 400, 500 lg mL ) of the
test compounds and ascorbic acid (standard) were prepared
in methanol and added (1.5 mL) to the methanolic solution
of DPPH (1.5 mL, 200 lM). The mixture was shaken
vigorously and allowed to stand for 30 min in dark. After
this, the absorbance was measured at 517 nm. Methanol
(1.5 mL) was mixed with DPPH solution (1.5 mL, 200 lM)
and used as a control.
Ren ZJ, Cao W, Tong W, Jin Z (2005) Solvent-free, one-pot synthesis
of pyrano[2,3-c]pyrazole derivatives in the presence of KFꢀ2H O
The percentage of scavenging activity was calculated by
using the formula:
2
by grinding. Synth Commun 35:2509
Schmeyers T, Toda F, Boy J, Kaupp G (1998) Quantitative solid–
solid synthesis of azomethines. J Chem Soc Perkin Trans 2:989
Seifi M, Sheibani H (2008) High surface area MgO as a highly effective
heterogeneous base catalyst for three-component synthesis of
tetrahydrobenzopyran and 3,4-dihydropyrano[c]chromene deriv-
atives in aqueous media. Catal Lett 126:275
%
Inhibition ¼ ðAc ꢁ At = AcÞ x 100
Where, Ac = absorbance of control (1.5 mL of each of
methanol and 200 lM DPPH solution), At = absorbance of
test compound/ascorbic acid.
Shaabani A, Samadi S, Badri Z, Rahmati A (2005) Ionic liquid
promoted efficient and rapid one-pot synthesis of pyran annu-
lated heterocyclic systems. Catal Lett 104:39
Shirini F, Marjani K, Nahzomi HT (2007) Silica triflate as an efficient
catalyst for the solvent-free synthesis of 3,4-dihydropyrimidin-
2(1H)-ones. Arkivoc 1:51
Stoyanov EV, Ivanova IC, Heber D (2000) General method for the
preparation of substituted 2-amino-4H,5H-pyrano[4,3-b]pyran-
The percentage (%) inhibition curves for ascorbic acid
and samples were plotted against concentration, from
which IC50 values of percentage inhibition of DPPH by
ascorbic acid and samples were calculated using regression
equation.
Acknowledgments The authors are thankful to the authorities of
Deshpande Laboratories Pvt. Ltd., Bhopal (M.P.), India and Pinnacle
Biomedical Research Institute, Bhopal (M.P.), India for the studies of
biological activities. The authors also thank The Director, SAIF,
Panjab University, Chandigarh for NMR and MS spectral data.
5
cules 5:19
-ones and 2-amino-4H-pyrano[3,2-c]pyridine-5-ones. Mole-
Tanaka K, Toda F (2000) Solvent-free organic synthesis. Chem Rev
1
00:1025
Tanaka K, Kishigami S, Toda F (1991) Reformatsky and Luche
reaction in the absence of solvent. J Org Chem 56:4333
Thirunarayanan G, Vanangamudi G (2006) Synthesis of some
4-bromo-1-naphthyl chalcones using silica-sulfuric acid reagent
under solvent free conditions. Arkivoc 12:58
References
Toda F, Tanaka K, Hamai K (1990) Aldol condensations in the
absence of solvent: acceleration of the reaction and enhancement
of the stereoselectivity. J Chem Soc Perkin Trans 1:3207
Toda F, Suzuki T, Higa S (1998) Solvent-free Dieckmann conden-
sation reactions of diethyl adipate and pimelate. J Chem Soc
Perkin Trans 1:3521
Uher M, Konecny V, Rajniakove O (1994) Synthesis of 5-hydroxy-2-
hydroxymethyl-4H-pyran-4-one derivatives with pesticide activ-
ity. Chem Pap 48:282
Wang S, Milne GWA, Yang X, Posey IJ, Nicklaus MC, Graham L, Rice
WG (1996) Discovery of novel, non-peptide HIV-1 protease
inhibitors by pharmacophore searching. J Med Chem 39:2047
Wang XS, Zhou JX, Zeng ZS, Li YL, Da-Qing S, Tu SJ (2006) One-
pot synthesis of pyrano[3,2-c]pyran derivatives catalyzed by KF/
Aytemir MD, Calis U, Ozalp M (2004) Synthesis and evaluation of
anticonvulsant and antimicrobial activities of 3-hydroxy-6-
methyl-2-substituted 4H-pyran-4-one derivatives. Arch Pharm
3
37:281
Da-Qing S, Li-Hui N, Qi-Ya Z (2008) One-pot three-component
synthesis of pyrano[3,2-c]pyran-5-one derivatives in aqueous
medium. Chin J Org Chem 28:1633
Fan X, Feng D, Qu Y, Zhang X, Wang J, Loiseau PM, Andrei G,
Snoeck R, De-Clercq E (2010) Practical and efficient synthesis
of pyrano[3,2-c]pyridone, pyrano[4,3-b]pyran and their hybrids
with nucleoside as potential antiviral and antileishmanial agents.
Bioorg Med Chem Lett 20:809
Khurana JM, Nand B, Saluja P (2010) DBU: a highly efficient
catalyst for one-pot synthesis of substituted 3,4-dihydropyr-
ano[3,2-c]chromenes, dihydropyrano[4,3-b]pyranes, 2-amino-
2 3
Al O . Arkivoc 11:107
4Hbenzo[h]chromenes and 2-amino-4H benzo[g]chromenes in
aqueous medium. Tetrahedron 66:5637
Mazumder A, Wang S, Neamati N, Niclaus M, Sunder S, Chen J, Milne
GWA, Rice WG, Burke TR Jr, Pommier Y (1996) Antiretroviral
agents as inhibitors of both human immunodeficiency virus type 1
integrase and protease. J Med Chem 39:2472
1
23