Mechanochemical Synthesis and Antioxidant Activity of Curcumin-Templated Azoles

Article abstract of DOI:10.1002/ardp.201500305

A solvent-free, mechanochemical method for the synthesis of curcumin (1) derived 3,5-bis(styryl)pyrazoles and 3,5-bis(styryl)isoxazole (2a-g) at room temperature, with very short reaction time, is reported. Such earlier structural modifications of curcumin, at its β-diketone unit by transforming it into an isosteric pyrazole or isoxazole unit, required prolonged heating. The evaluation of the antioxidant activity of these compounds, based on DPPH, FRAP, and β-carotene bleaching assays, showed that several of these azoles are better antioxidants than curcumin, with the isoxazole derivative 2g being overall the best. Typically, the inhibition of 2,2-diphenyl-1-picrylhydrazyl (10^-2 mmol), expressed as EC₅₀ values, by curcumin (1), 3,5-bis(4-hydroxy-3-methoxystyryl)pyrazole (2a), and 3,5-bis(4-hydroxy-3-methoxystyryl)isoxazole (2g) are 40 ± 0.06, 14 ± 0.18, and 8 ± 0.11 μmol, respectively. Moreover, the reported method is useful in accessing 3,5-bis(4-hydroxy-3-methoxystyryl)-1-phenylpyrazole (2b), which is important in studies related to neuroprotection and Alzheimer's disease, and 2a and 2g, which are inhibitors of protein kinases involved in neuronal excitotoxicity.

Full text of DOI:10.1002/ardp.201500305

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Arch. Pharm. Chem. Life Sci. 2015, 348, 908–914
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Full Paper
Mechanochemical Synthesis and Antioxidant Activity of
Curcumin-Templated Azoles
Daisy R. Sherin and Kallikat N. Rajasekharan
Department of Chemistry, University of Kerala, Kariavattom, Thiruvananthapuram, Kerala, India
A solvent-free, mechanochemical method for the synthesis of curcumin (1) derived 3,5-bis(styryl)-
pyrazoles and 3,5-bis(styryl)isoxazole (2a–g) at room temperature, with very short reaction time, is
reported. Such earlier structural modifications of curcumin, at its b-diketone unit by transforming it
into an isosteric pyrazole or isoxazole unit, required prolonged heating. The evaluation of the
antioxidant activity of these compounds, based on DPPH, FRAP, and b-carotene bleaching assays,
showed that several of these azoles are better antioxidants than curcumin, with the isoxazole
derivative 2g being overall the best. Typically, the inhibition of 2,2-diphenyl-1-picrylhydrazyl
ꢀ
2
(
(
10 mmol), expressed as EC50 values, by curcumin (1), 3,5-bis(4-hydroxy-3-methoxystyryl)pyrazole
2a), and 3,5-bis(4-hydroxy-3-methoxystyryl)isoxazole (2g) are 40 ꢁ 0.06, 14 ꢁ 0.18, and 8 ꢁ 0.11 mmol,
respectively. Moreover, the reported method is useful in accessing 3,5-bis(4-hydroxy-3-methoxy-
styryl)-1-phenylpyrazole (2b), which is important in studies related to neuroprotection and
Alzheimer’s disease, and 2a and 2g, which are inhibitors of protein kinases involved in neuronal
excitotoxicity.
Keywords: 3,5-Bis(styryl)pyrazole/isoxazole / Antioxidant / Curcumin / Mechanochemical
Received: September 3, 2015; Revised: October 21, 2015; Accepted: October 21, 2015
DOI 10.1002/ardp.201500305
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
:
Introduction
curcumin with hydrazines and hydroxylamine, hetero-
cyclization has led to bis(styryl)pyrazoles and bis(styryl)-
isoxazoles in which the central b-diketone unit has been
masked and rigidized [2] resulting in molecules with
interesting bioactivity such as antiangiogenic, antimalarial,
antimycobacterial, and cytotoxic activities [3–8]. Some of
these are reported to be neuroprotective to inhibit
b-amyloid secretion and to bind to protein kinase
C [9–12]. The reported methods for synthesizing these
curcumin-templated azoles generally involve long reaction
times. With our interest in the synthesis and bioactivity
studies on curcumin, its analogs and derivatives [13–18], we
continue to investigate the structural modification of
curcumin at its b-diketone unit by transforming this central
part of the molecule into an isosteric heterocycle. Thus, we
now report a rapid, solvent-free mechanochemical route
to these bis(styryl)pyrazoles and isoxazole. We have also
evaluated the antioxidant activity of these compounds,
keeping in mind the current interest in curcumin, its
derivatives and analogs as antioxidants [19–24].
Curcumin, a diarylheptanoid [1, 2] with a bisphenolic moiety
and extracted from the rhizomes of Curcuma longa L., is a
widely investigated bioactive molecule. In spite of its
efficacy and safety, the poor bioavailability hampers its
clinical use as a therapeutic agent. In order to circumvent
this, several strategies have been adopted for improving its
bioavailability. These include the modification of the route
and the medium, of administration, encapsulated delivery,
metabolic blockade, and structural modifications [1]. By
exploiting the reactivity of the b-diketone moiety in
Correspondence: Dr. Kallikat N. Rajasekharan, Department of
Chemistry, University of Kerala, Kariavattom, Thiruvanantha-
puram 695581, Kerala, India.
E-mail: rajkn_1951@yahoo.com, kn.rajasekharan@gmail.com
Fax: 91 4712307158
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Antioxidant Activity of Curcumin-Templated Azoles
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Results and discussion
p-chloro, p-nitro, and p-carboxyphenylhydrazines gave the
bis(styryl)pyrazoles (2b–f) in good yields. Similarly, hydroxyl-
amine afforded the bis(styryl)isoxzole 2g. These azole
derivatives have been characterized by spectral data. It is
noteworthy that despite the mild conditions now used, the
initially formed hydrazone derivatives of curcumin proceeded
rapidly to cyclize, affording the azole derivatives.
Synthesis
Curcumin (1) on reaction with hydrazine, hydrazine deriva-
tives, or with hydroxylamine affords pyrazole and isoxazole
derivatives, respectively. A perusal of the reaction conditions
that have recently been reported shows that these reactions
would generally take 2–24 h for the completion under
conventional heating. Typically, the curcumin-templated
pyrazole (2a) or its N-aryl derivatives have been prepared
from curcumioids and hydrazine or arylhydrazines by reflux in
ethanol for 40 h [8]. Such pyrazoles have also been obtained
by refluxing in toluene for 18–24 h [11]. Refluxing curcumin
Antioxidant studies
Antioxidant capacity was evaluated by DPPH, FRAP, and
b-carotene assays. Curcumin (1) was taken as the standard in
all these assays. The AO capacity by the DPPH assay was
determined by monitoring the decrease in the absorbance
value of a 0.01 mmol solution of DPPH and the result was
interpreted in terms of EC50 values, the amount of AO
necessary to decrease the initial concentration of DPPH by
50%. The percentage inhibition of DPPH by the curcuminoid
azoles was plotted against various test concentrations (Fig. 1).
From the plots, EC50 values were calculated (Table 2). From
Fig. 1, the values for the percentage inhibition of DPPH by
curcumin (1) and its azole derivates 2a–g, and hence the AO
capacity, are seen to be in the order 2g > 2a > 2c > 2b > 2e
> 1 > 2f > 2d. Typical EC50 values of curcumin (1), 3,5-bis-
(4-hydroxy-3-methoxystyryl)pyrazole (2a), and 3,5-bis(4-hy-
droxy-3-methoxystyryl)isoxazole (2g) are 40 ꢁ 0.06, 14 ꢁ 0.18,
and 8 ꢁ 0.11 mmol, respectively.
(
1) and hydrazine in glacial acetic acid has been reported to
shorten the reflux time to 6–8 h [5, 12] or to 2 h [3]. Room
temperature reactions have also been reported but these
required long duration [11]. The reaction of curcumin with
hydroxylamine to yield curcumin-derived isoxazole also
required prolonged heating, either in acetic acid for
6–24 h [5, 6, 12, 25] or in ethanol for 18–40 h [8, 11].
We have now investigated whether the curcumin-tem-
plated pyrazoles and isoxazole (2a–g) could be synthesized
rapidly by mechanochemical grinding and found that the
room temperature grinding of curcumin (1) with hydrazine
hydrate in the presence of catalytic amount of acetic acid for
about a minute rapidly gave the 3,5-bis(styryl)pyrazole (2a)
(
Scheme 1; Table 1). The advantages of this method appear to
The FRAP values were obtained by comparing the absor-
bance change at 593 nm in a test reaction mixture with those
in the standard ferrous sulfate solution and the experimental
be a much reduced reaction time, an improved yield, and a
better purity. The above reaction was found to be general
in that the reaction of phenylhydrazine and p-methoxy,
2
þ
results were expressed as micromolar Fe equivalents. The
Scheme 1. Synthesis of 2a–g.
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Arch. Pharm. Chem. Life Sci. 2015, 348, 908–914
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Table 1. M.p. and yield of 3,5-bis(styryl)pyrazoles (2a–f) and isoxazole (2g).
Entry
M.p. (°C)
Lit. m.p. (°C)
Yield (%)
Lit. yield (%)
2
2
2
2
2
2
2
a
b
c
d
e
f
208
89
126
168
171
135
146
214 [5]
89 [5]
106 [5]
84
82
81
77
79
79
82
71 [5]
65 [5]
35 [5]
35 [11]
55 [4]
–
–
–
–
g
162 [5]
76 [5]
plots of FeSO
4
equivalents (mmol) of all the compounds and
very recently by Jha et al. [25] based on their extensive
electrochemical cyclic voltammetric studies in that the azole
derivatives of curcumin show better antioxidant properties
than curcumin. Our results based on the DPPH, FRAP, and
b-carotene bleaching assays provide further support to the
recent observation by Puneeth and Chandrashekariah [26]
that among curcumin-derived N-arylpyrazoles, the presence
of electron releasing substituents on the aryl ring confers
improved antioxidant activity.
the standard are presented in Fig. 2. A higher value of
absorbance gives a higher ferrous sulfate equivalent and thus
indicates a better antioxidant activity. The absorbance
observed for the compounds and the standard curcumin
are presented in Fig. 3. The AO capacity of compounds, as
measured by the FRAP method, showed a similar trend as that
seen in the case of DPPH assay.
In the b-carotene bleaching assay, the oxidative destruction
of b-carotene by the degradation products of linoleic acid was
measured spectrophotometrically. The AO activity data,
calculated as a percentage, are presented in Fig. 4. The results
showed a similar trend as in the case of DPPH and FRAP assays.
The heterocyclization of curcumin thus seems to result in
improved AO activity. The isoxazole derivative of curcumin
Conclusion
In summary, we have succeeded in the rapid, solventless
synthesis of curcumin-templated bis(styryl)pyrazoles (2a–f)
and isoxazole (2g) by mechanochemical grinding at room
temperature. We now observe that some of these azole
derivatives of curcumin are better antioxidants than parent
curcumin (1), and among these azoles (2a–g), the isoxazole
derivative of curcumin (2g) is superior. The above route allows
an easy preparative access to 2b, an intensively studied
neuroprotector [9–11], and 2a and 2g which are inhibitors of
protein kinases involved in neuronal excitotoxicity [18].
(
2g) exhibits better AO capacity than the parent curcumin and
the pyrazole derivatives. Among the compounds now studied,
the compounds 2g, 2a, 2c, 2b, and 2e have better AO capacity
than curcumin (1). The presence of electron releasing groups
in the N-phenyl group of the pyrazole derivative, as in 2c,
leads to
a better activity than that in the parent
N-phenylpyrazole curcumin (2b) and the presence of electron
withdrawing group, as in 2d, leads to a lower activity. The
present results are in good agreement with those reported
Experimental
Chemistry
Reagents and solvents used were of analytical grade. The
thin layer chromatography (TLC) and preparative thin layer
chromatography (PTLC) were performed on glass plates
(
20 ꢂ 75 mm and 20 ꢂ 20 cm, respectively) coated with TLC
grade silica gel-G (E. Merck, India). The spots or bands were
visualized directly or under UV light. The C, H, N analyses
1
were carried out on Vario EL Elementar analyzer. H and
1
3
C NMR were recorded on Bruker Topspin and Bruker AV,
1
13
5
00 MHz (500 MHz for H and 125 MHz for C NMR), Bruker
1
Avance III, 400 MHz (400 MHz for H and 100 MHz for
1
3
C NMR) at room temperature. Chemical shifts are given
in ppm relative to TMS as an internal standard. HRMS were
recorded on JEOL JMS 600H mass spectrometer. The
ꢀ2
Figure 1. Percentage inhibition of DPPH (10 mmol) at various
concentrations of curcumin (1) and its heterocyclic derivatives
absorbance values were recorded on
spectrophotometer.
a
Jasco V-550
(2a–g).
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ꢀ
2
Table 2. Percentage inhibition of DPPH (10 mmol) by curcumin (1) and its heterocyclic derivatives (2a–g).
Inhibition by curcuminoids at various concentrations (mmol)
0.01 0.025 0.05 0.075
%
Entry
1
0.005
0.1
EC50 (mmol)
20.92 ꢁ 0.05 33.23 ꢁ 0.12 41.38 ꢁ 0.08 57.36 ꢁ 0.23 75.28 ꢁ 0.17 83.79 ꢁ 0.31
29.82 ꢁ 0.16 43.28 ꢁ 0.56 62.23 ꢁ 0.22 71.45 ꢁ 0.17 84.99 ꢁ 0.26 95.12 ꢁ 0.11
22.43 ꢁ 0.08 36.44 ꢁ 0.15 46.35 ꢁ 0.32 62.23 ꢁ 0.38 79.35 ꢁ 0.09 85.87 ꢁ 0.24
26.42 ꢁ 0.25 40.89 ꢁ 0.19 54.38 ꢁ 0.47 65.61 ꢁ 0.52 82.32 ꢁ 0.13 93.11 ꢁ 0.38
14.93 ꢁ 0.19 17.91 ꢁ 0.07 23.22 ꢁ 0.21 27.02 ꢁ 0.44 33.52 ꢁ 0.36 46.91 ꢁ 0.23
21.47 ꢁ 0.35 35.08 ꢁ 0.29 43.29 ꢁ 0.07 59.15 ꢁ 0.09 77.69 ꢁ 0.16 84.92 ꢁ 0.27
16.27 ꢁ 0.41 20.12 ꢁ 0.33 25.36 ꢁ 0.47 29.43 ꢁ 0.25 35.68 ꢁ 0.05 49.17 ꢁ 0.35
32.49 ꢁ 0.26 57.25 ꢁ 0.14 70.98 ꢁ 0.53 81.43 ꢁ 0.32 91.33 ꢁ 0.36 98.22 ꢁ 0.09
40 ꢁ 0.06
14 ꢁ 0.18
28 ꢁ 0.22
18 ꢁ 0.19
102 ꢁ 0.57
36 ꢁ 0.04
100 ꢁ 0.49
8 ꢁ 0.11
2
2
2
2
2
2
2
a
b
c
d
e
f
g
Synthesis of 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-
heptadiene-3,5-dione (1)
found: 369.13379; (MþNa): 391.11576; found: 391.11569.
Anal. calcd. for C21
20 6
H O : C, 68.47; H, 5.47; found: C, 68.34; H,
To a mixture of 4-hydroxy-3-methoxybenzaldehyde (0.304 g,
5.33.
2
mmol), acetylacetone (0.1 mL, 1 mmol), and boric acid
(
0.2 g), a minimum amount of DMF (2 mL) was added. The
General procedure for the synthesis of curcuminoid 3,5-
bis(styryl)pyrazoles and isoxazole
mixture was then heated for 10 min at 90–95°C. To the clear
mixture thus obtained, glacial acetic acid (60 mL) and 1,2,3,4-
tetrahydroquinoline (20 mL) in DMF (0.5 mL) were added and
heating was continued for 6 h. After the reaction, the deeply
colored reaction mixture was added very slowly to 20%
aqueous acetic acid (10 mL) with vigorous stirring for half an
hour until the precipitation was complete. The separated
yellow precipitate was then filtered and dried. The crude
A mixture of 1 (0.037 g, 0.1 mmol) and hydrazine hydrate,
phenylhydrazine, 4-substituted phenylhydrazine, or hydrox-
ylamine hydrochloride (0.1 mmol) in the presence of acetic
acid (0.5 mL) was subjected to vigorous grinding using an
agate mortar and pestle for 1–2 min. The crude product
3
obtained in powdery form was purified by PTLC (CHCl /EtOAc,
3:2 or 4:1).
product was purified by preparative TLC (CHCl
3
/MeOH, 95:5).
Yellow solid: yield, 78%; m.p. 183°C (Lit. m.p., 182–184°C [13];
Synthesis of 3,5-bis(4-hydroxy-3-methoxystyryl)pyrazole
(2a)
Grinding of 1 and hydrazine hydrate in the presence of acetic
1
1
84–186°C [27]; 178–180°C [28]); H NMR (500 MHz, acetone-
): d 3.77 (s, 6H, OCH ), 5.47 (s, 1H, 4-H), 5.82 (s, 2H, ArOH),
d
6
3
6
7
.54 (d, 2H, 2,6-H, J ¼ 16.0 Hz), 6.73 (d, 2H, ArH, J ¼ 8.0 Hz),
.02–7.04 (dd, 2H, ArH), 7.18 (s, 2H, ArH), 7.43 (d, 2H, 1,7-H,
acid (0.1 mL) gave 3,5-bis(4-hydroxy-3-methoxystyryl)pyrazole
(2a) as yellow powder. Yield 84%; m.p. 208°C (Lit. yield:
13
1
J ¼ 15.5 Hz), 8.05 (s, 1H, OH); C NMR (125 MHz, acetone-d
6
): d
50.0, 148.8, 141.4, 128.1, 123.8, 122.3, 116.2, 111.5, 101.6,
6.3, 54.9; HRMS (ESI): calcd. for C21
, (MþH): 369.13382;
71%; m.p. 214°C [5]). H NMR (500 MHz, acetone-d
6
): d 3.82 (s,
1
5
3
6H, OCH ), 5.47 (s, 1H, 4-H), 5.83 (s, 2H, ArOH), 6.54 (d, 2H, 2,6-
H, J ¼ 16.5 Hz), 6.72 (d, 2H, ArH, J ¼ 8.0 Hz), 7.02–7.04 (dd, 2H,
H
O
20 6
Figure 2. The FeSO
heterocyclic derivatives (2a–g).
4
equivalents (mmol) of curcumin (1) and its
Figure 3. The absorbance values of curcumin (1) and its
heterocyclic derivatives (2a–g) in the presence of FRAP reagent.
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Arch. Pharm. Chem. Life Sci. 2015, 348, 908–914
D. R. Sherin and K. N. Rajasekharan
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4
26 2 5
71.19245. Anal. calcd. for C28H N O : C, 71.47; H, 5.57; N,
5
.95; found: C, 71.54; H, 5.59; N, 6.02.
Synthesis of 3,5-bis(4-hydroxy-3-methoxystyryl)-1-(4-
nitrophenyl)pyrazole (2d)
Mechanochemical grinding of 1 (0.1 mmol) and 4-nitro-
phenylhydrazine (0.015 g, 0.1 mmol) together in the presence
of acetic acid (1.0 mL) led to 3,5-bis(4-hydroxy-3-methoxy-
styryl)-1-(4-nitrophenyl)pyrazole (2d) as yellow powder in
1
7
7% yield; m.p. 168°C (Lit. yield: 35% [11]). H NMR (500 MHz,
6 3
acetone-d ): d 3.77 (s, 6H, OCH ), 5.43 (s, 1H, 4-H), 5.84 (s, 2H,
ArOH), 6.53 (d, 2H, 2,6-H, J ¼ 16.0 Hz), 6.72 (d, 4H, ArH,
J ¼ 8.0 Hz), 7.01–7.04 (dd, 4H, ArH), 7.16 (s, 2H, ArH), 7.41
1
3
(
d, 2H, 1,7-H, J ¼ 16.0 Hz); C NMR (125 MHz, acetone-d
6
): d
Figure 4. The antioxidant activity (%) of curcumin (1) and its
heterocyclic derivatives (2a–g) in b-carotene assay.
149.8, 145.0, 140.4, 130.3, 128.2, 123.8, 122.3, 116.2, 111.8,
1
4
6
07.5, 56.3, 54.9; HRMS (ESI): calcd. for C27
86.16651; found: 486.16650. Anal. calcd. for C27
6.80; H, 4.78; N, 8.66; found: C, 66.86; H, 4.83; N, 8.65.
H
23
N
3
O
6
, (MþH):
23 3 6
H N O : C,
ArH), 7.16 (s, 2H, ArH), 7.43 (d, 2H, 1,7-H, J ¼ 15.5 Hz), 9.03 (s,
Synthesis of 1-(4-chlorophenyl)-3,5-bis(4-hydroxy-3-
methoxystyryl)pyrazole (2e)
13
13
1
H, NH); C NMR (125 MHz, acetone-d
6
): d C NMR (125 MHz,
acetone-d
6
): d 150.1, 148.6, 141.8, 130.5, 128.6, 123.8, 122.4,
The grinding of 1 (0.1 mmol) with 4-chlorophenylhydrazine
(0.1mmol) as above afforded 1-(4-chlorophenyl)-3,5-bis(4-
hydroxy-3-methoxystyryl)pyrazole (2e) as yellow powder in
79% yield; m.p. 171°C (Lit. yield: 55% [4]). H NMR (500 MHz,
6 3
acetone-d ): d 3.68 (s, 6H, OCH ), 5.42 (s, 1H, 4-H), 5.81 (s, 2H,
1
16.2, 111.5, 101.6, 56.3, 54.9; HRMS (ESI): calcd. for
, (MþNa): 387.13206; found: 387.13208. Anal.
calcd. for C21 : C, 69.22; H, 5.53; N, 7.69; found: C,
9.27; H, 5.55; N, 7.65.
21 20 2 4
C H N O
1
H N
20 2
O
4
6
ArOH), 6.51 (d, 2H, 2,6-H, J ¼ 14.5 Hz), 6.71 (d, 4H, ArH,
Synthesis of 3,5-bis(4-hydroxy-3-methoxystyryl)-1-
phenylpyrazole (2b)
By adopting the above procedure and by using 1 (0.1 mmol)
and phenylhydrazine (0.01 mL, 0.1 mmol) in the presence of
acetic acid (0.1 mL), 3,5-bis(4-hydroxy-3-methoxystyryl)-1-phe-
J ¼ 8.0s Hz), 7.01–7.04 (dd, 4H, ArH), 7.14 (s, 2H, ArH), 7.41
1
3
(d, 2H, 1,7-H, J ¼ 16.0 Hz); C NMR (125 MHz, acetone-d
6
): d
149.8, 140.4, 137.5, 130.6, 128.2, 123.8, 121.32, 116.6, 112.3,
107.5, 56.3, 54.8; HRMS (ESI): calcd. for C27 23ClN
, (MþH):
475.14246; found: 475.14349. Anal. calcd. for C27 23ClN : C,
H
2 4
O
H
2 4
O
nylpyrazole (2b) was obtained as yellow powder. Yield
68.28; H, 4.88; N, 5.90; found: C, 68.32; H, 4.85; N, 5.94.
1
8
2%; m.p. 89°C (Lit. yield: 65%; Lit. m.p. 89°C [5]). H NMR
(
500 MHz, acetone-d
6
): d 3.65 (s, 6H, OCH
3
), 5.47 (s, 1H, 4-H),
Synthesis of 1-(4-carboxyphenyl)-3,5-bis(4-hydroxy-3-
5
.83 (s, 2H, ArOH), 6.54 (d, 2H, 2,6-H, J ¼ 16.0 Hz), 6.87 (s, 2H,
methoxystyryl)pyrazole (2f)
ArH), 7.02–7.04 (dd, 4H, ArH), 7.16 (s, 5H, ArH), 7.42 (d, 2H, 1,7-
Following the procedure detailed above and starting from 1
and 4-hydrazinobenzoic acid (0.1 mmol each) in the presence
of acetic acid (1.0 mL) afforded 1-(4-carboxyphenyl)-3,5-bis(4-
13
H, J ¼ 15.5 Hz); C NMR (125 MHz, acetone-d
41.6, 128.1, 123.8, 122.3, 116.2, 111.6, 110.0, 56.3, 54.5; HRMS
ESI): calcd. for
(MþH): 441.18143; found:
: C, 73.62; H, 5.49; N,
6
): d 150.1, 148.6,
1
(
C
H N
27 24 2
O
4
,
hydroxy-3-methoxystyryl)pyrazole (2f) as yellow powder in
1
4
41.18124. Anal. calcd. for C27
24
H N
2
O
4
79% yield; m.p. 135°C; H NMR (500 MHz, acetone-d
6
): d 3.78
6
.36; found: C, 73.68; H, 5.54; N, 6.42.
(s, 6H, OCH
,6-H, J ¼ 16.0 Hz), 6.70 (d, 4H, ArH, J ¼ 7.5 Hz), 7.01–7.04 (dd,
4H, ArH), 7.14 (s, 2H, ArH), 7.41 (d, 2H, 1,7-H, J ¼ 16.0 Hz),
3
), 5.41 (s, 1H, 4-H), 5.82 (s, 2H, ArOH), 6.51 (d, 2H,
2
Synthesis of 3,5-bis(4-hydroxy-3-methoxystyryl)-1-(4-
methoxyphenyl)pyrazole (2c)
The reaction of 1 (0.1 mmol) with 4-methoxyphenylhydrazine
1
3
10.34 (s, 1H, COOH); C NMR (125 MHz, acetone-d
149.6, 144.8, 141.4, 130.3, 128.3, 124.1, 122.3, 116.2, 112.8,
107.4, 56.5, 54.2; HRMS (ESI): calcd. for C28
, (MþH):
485.17126; found: 485.16953. Anal. calcd. for C28 : C,
69.41; H, 4.99; N, 5.78; found: C, 69.45; H, 5.04; N, 5.83.
6
): d 171.9,
(
0.014 g, 0.1 mmol) as above gave 3,5-bis(4-hydroxy-3-
24 2 6
H N O
methoxystyryl)-1-(4-methoxyphenyl)pyrazole (2c) as yellow
powder. Yield 81%; m.p. 126°C (Lit. yield: 35%; Lit. m.p.
24 2 6
H N O
1
1
3
2
06°C [5]). H NMR (500 MHz, acetone-d
6
): d 3.67 (s, 3H, OCH
), 5.47 (s, 1H, 4-H), 5.83 (s, 2H, ArOH), 6.53 (d,
H, 2,6-H, J ¼ 16.5 Hz), 6.72 (d, 4H, ArH, J ¼ 8.5 Hz), 7.02–7.04
3
),
.77 (s, 6H, OCH
3
Synthesis of 3,5-bis(4-hydroxy-3-methoxystyryl)isoxazole
(2g)
The mechanochemical grinding of 1 (0.01 mmol) and hydrox-
ylamine hydrochloride (0.007 g, 0.1 mmol) in the presence of
acetic acid (1.0 mL) gave 3,5-bis(4-hydroxy-3-methoxystyryl)-
isoxazole (2g) as yellow powder; yield 82%; m.p. 146°C (Lit.
(
dd, 4H, ArH), 7.18 (s, 2H, ArH), 7.43 (d, 2H, 1,7-H, J ¼ 16.0 Hz);
13
C NMR (125 MHz, acetone-d
28.2, 123.8, 122.1, 116.3, 111.6, 101.6, 56.9, 56.3, 54.9; HRMS
ESI): calcd. for
(MþH): 471.19200; found:
6
): d 159.4, 150.0, 148.8, 141.4,
1
(
28 26 2 5
C H N O ,
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912

Arch. Pharm. Chem. Life Sci. 2015, 348, 908–914
Antioxidant Activity of Curcumin-Templated Azoles
ARC HH PHARM
Archiv der Pharmazie
1
yield: 76%; Lit. m.p. 162°C [5]). H NMR (500 MHz, acetone-d
6
):
incubation for test sample and control, respectively. A
A
t
t
and
are the absorbance values of the sample and control after
incubation time.
o
d 3.82 (s, 6H, OCH
H, 2,6-H, J ¼ 16.0 Hz), 6.86 (d, 2H, ArH, J ¼ 8.0 Hz), 7.14–7.16
dd, 4H, ArH), 7.36 (s, 2H, ArH), 7.52 (d, 2H, 1,7-H, J ¼ 16.0 Hz);
3
), 5.61 (s, 1H, 4-H), 5.92 (s, 2H, ArOH), 6.64 (d,
2
(
1
3
C NMR (100 MHz, DMSO-d
6
): d 168.3, 162.1, 148.1, 147.9,
S.D.R. thanks UGC and MHRD, Govt. of India for fellowship.
K.N.R. thanks UGC for UGC-BSR Faculty Fellowship. The
authors also thank SAIF-STIC at CUSAT, Kochi, and NIIST
Trivandrum, for element analysis, NMR, and MS spectra.
1
1
47.9, 147.8, 136.3, 134.7, 127.3, 126.9, 121.6, 121.2, 115.6,
15.5, 112.6, 110.4, 110.3, 110.1, 97.8, 55.7, 55.6; HRMS (ESI):
calcd. for C21
Anal. calcd. for C21
8.98; H, 5.28; N, 3.96.
H
19NO
5
, (MþNa): 388.11609; found: 388.11603.
H
19NO : C, 69.03; H, 5.24; N, 3.93; found: C,
5
6
The authors have declared no conflicts of interest.
Antioxidant capacity assays
DPPH assay
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(
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ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com
913

Arch. Pharm. Chem. Life Sci. 2015, 348, 908–914
D. R. Sherin and K. N. Rajasekharan
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