Synthesis of Gallic-Acid-1-Phenyl-1H-[1,2,3]Triazol-4-yl Methyl Esters as Effective Antioxidants

Article abstract of DOI:10.1055/s-0042-118860

Using a click chemistry approach, a series of gallic-acid-1-phenyl-1H-[1,2,3]triazol-4-ylmethyl esters was synthesized to develop more effective antioxidants. The results of DPPH screening indicate that few of the synthesized analogs display better antioxidant effect compared to the standards. Among all, compounds, 9 and 20 displayed highest DPPH radical scavenging effect with IC₅₀ values as low as 6.4±0.2 and 7.9±0.4 μM respectively, compared to the standard ascorbic acid (IC₅₀=12±0.8 μM) and gallic acid (IC₅₀=9.0±0.6 μM). Compound 10 also displayed a potent antioxidant effect with IC₅₀ of 10.80±0.4 μM. This study provides an important aspect with regard to the use of these gallic-acid based synthetic antioxidants in food industry as dietary supplements.

Full text of DOI:10.1055/s-0042-118860

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
Synthesis of Gallic-Acid-1-Phenyl-1H-[1,2,3]Triazol-4-yl
Methyl Esters as Effective Antioxidants
Authors
S. H. Lone, Shakeel-U-Rehman, K. A. Bhat
Affiliation
Bioorganic Chemistry Division, Indian Institute of Integrative Medicine (CSIR), Srinagar, Jammu and Kashmir, India
Key words
values as low as 6.4±0.2 and 7.9±0.4µM respec-
tively, compared to the standard ascorbic acid
(IC50=12±0.8µM) and gallic acid (IC50=9.0±0.6µM).
Compound 10 also displayed a potent antioxidant
effect with IC50 of 10.80±0.4µM. This study pro-
vides an important aspect with regard to the use of
these gallic-acid based synthetic antioxidants in
food industry as dietary supplements.
Abstract
▶
gallic acid
ascorbic acid
triazoles
antioxidants
food-industry
●
▼
▶
●
Using a click chemistry approach, a series of gal-
lic-acid-1-phenyl-1H-[1,2,3]triazol-4-ylmethyl
esters was synthesized to develop more effective
antioxidants. The results of DPPH screening indi-
cate that few of the synthesized analogs display
better antioxidant effect compared to the stand-
ards. Among all, compounds, 9 and 20 displayed
highest DPPH radical scavenging effect with IC50
▶
●
▶
●
▶
●
Supporting Information for this article is available
online at http://www.thieme-connect.de/products
abundant source of antioxidants and include
anthocyanins, aprons, chalcones, flavanones
(naringenin), flavanols (procyanidin), flavan-3-ol
(epicatechin, catechin), flavones (apigenin, luteo-
lin etc.), flavonols (kaempferol, quercetin, rutin
etc.) and isoflavonoids (genistein, daidzein etc.),
hydroxybenzoic acid (gallic acid), hydroxycin-
namic acid (caffeic acid, ferulic acid etc.), pro-
Introduction
▼
During the past few years there has been an
upsurge in the newer developments in the areas
of disease prevention, especially in the role of
free radicals in causing the disease and antioxi-
dants in the prevention of disease [1,2]. In nor-
mal human body the occurrence of prooxidants
particularly in the form of reactive oxygen spe-
cies and reactive nitrogen species are effectively
kept under check by some degree of antioxidant
defense. Nature has rendered each cell with its
own protective mechanism against any kind of
harmful effects whatsoever, be it free radicals,
sodium glutathione peroxide, glutathione reduc-
tase or thiols [3]. However exposure to adverse
physiological, environmental, or pathological
agents such as pollutants, cigarette smoking, UV-
rays, toxic chemicals, over-nutrition etc. results
in the shift of this delicately maintained balance
leading to the lipid peroxidation, oxidative
damage to DNA, proteins etc. and under such
conditions the dietary intake of antioxidants
is warranted to exert promising therapeutic
potential to combat the radicals and prevent
them from causing the oxidative stress which
otherwise may lead to chronic disorders like car-
diovascular diseases, cancers and neurodegener-
ation [4]. Plant natural-products constitute an
anthocyanidins, vitamin
C and vitamin E
received 05.06.2016
accepted 10.10.2016
(α-Tocopherols, Tocotreinols) [5]. Gallic acid (GA,
3,4,5-trihydroxybenzoic acid) along with its
derivatives which occur widely within the plant
kingdom represent a large family of plant sec-
ondary polyphenolic metabolites with known
antioxidant properties. GA along with its deriva-
tives are considered the main polyphenolic com-
pounds in grapes, different berries, mango, areca
nut, walnut, green tea and other fruits as well as
in wine [6]. Gallic acid shows different biological
activities such as induction of apoptosis in
tumour cells in higher proportions than normal
cells and is an excellent free radical scavenger [7].
Due to this antioxidant effect, GA-containing
plants have shown various possible bioactivities
which mainly include antiangiogenic, antidia-
betic and antimelanogenic effects along with
reduced heart infarction incidence and oxidative
kidney and liver damage [8–10]. GA has also been
used in cosmetics, food industry and in pharma-
ceuticals as an effective antioxidant [11]. It is
non-toxic to mammalian organisms at pharma-
Bibliography
DOI http://dx.doi.org/
10.1055/s-0042-118860
Published online: 2016
Drug Res
© Georg Thieme Verlag KG
Stuttgart · New York
ISSN 2194-9379
Correspondence
K. A. Bhat
Scientist
Indian Institute of Integrative
Medicine Sanat Nagar
Srinagar 190005
Jammu and Kashmir
P/O Sanat Nagar Srinagar
India
Tel.: +911/942/431 253
Extn: 123
Fax: +91/194/2441 331
kabhat@iiim.ac.in
*Both the authors contributed equally
Lone SH et al. Gallic Acid Triazoles… Drug Res

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
cological doses. LD50 dose for GA has been found to be 5g/kg
body weight in rats [12]. Gallic acid has been subjected to a
number of structural modifications to access its structure-activ-
ity relationships. Alkyl esters of gallic acid have been found to
exhibit potential antioxidant as well as anticancer properties
[13]. Novel galloyl-pyrrolidine derivatives have been used as
potential anti-tumor agents [14]. Till date there has not been any
attempt towards the synthesis of azole containing analogs of
gallic acid and evaluate their antioxidant potential. Triazoles, a
versatile bunch of heterocycles are known chemotherapeutic
agents. 1,2,3-triazoles, as clinical drug candidates have been fre-
quently employed for the treatment of various diseases, which
have shown their large developmental value and wide potential
as medicinal agents exhibiting diverse array of biological func-
tions which include anticancer, antifungal, antitubercular, anti-
inflammatory, antiviral, antibacterial and anticonvulsant,
analgesic, antidiabetic, antiparasitic, antihistaminic, obesitic,
antihypertensive, antineuropathic, as well as other biological
activities [15–27]. But a very little or no study documents the
antioxidant potential of the triazolyl compounds. Since gallic
acid (1) is reported to possess effective antioxidant potential and
triazoles are also reported to possess versatile biological proper-
ties with the triazole ring being used as an attractive linker to
combine different pharmacophore fragments to produce innova-
tive bifunctional drug molecules, in a convenient and efficient
pathway. Therefore it is expected from combination principle that
if we link triazoles with gallic acid, the resulting compounds with
triazole scaffold should be better antioxidants. Keeping in view
this fact that the whole is always greater than the sum as well
as our previous work to carry out structural diversification of
natural products for synthesizing medicinally important leads
[28–30], we designed a click chemistry based approach to synthe-
size the triazolyl gallic acid analogs for better antioxidant activity.
conditions followed by displacement with sodium azide in
quantitative yields. 1,3-dipolar cycloaddition reaction of 3 with
aromatic azides in presence of CuSO4.5H2O and sodium ascor-
bate in t-BuOH:H2O (2:1) resulted in regioselective formation of
1,4-disubstituted-triazolyl derivatives (4–20) in excellent yields
▶ꢀ
(
Fig. 2). All the reactions were carried out at room tempera-
●
ture under ultra-sonication and completed within 4h. The prod-
1
ucts were confirmed by H and 13C NMR spectral data analysis.
In 1H NMR cyclization of azides to form triazoles was confirmed
by H-5 resonance of triazole ring in aromatic region as well as by
▶ꢀ
other proton absorptions in the same region ( Fig. 1e). The
●
structure was further supported by 13C NMR and DEPT, which
showed all the expected carbon signals corresponding to acid
triazolyl derivatives. ESI-MS of all the derivatives was in good
agreement with the desired structures. By employing the above
reaction conditions, a series of such triazolyl gallic acid-deriva-
tives that vary at substitutions on aromatic ring were synthe-
sized from a range of aromatic azides. It was observed that all
the reactions worked smooth under ultra-sonication conditions
▶ꢀ
(● Table 1). Gallic acid along with its triazolyl analogs were then
studied for the possible antioxidant activity using a well-known
DPPH scavenging assay system. Preliminary screening of all the
analogs was done at 10 and 5µM concentrations. Almost all the
analogs displayed an appreciable scavenging effect. The analogs
were then screened at different concentrations to evaluate their
DPPH scavenging effect in terms of the IC50 values depicted
▶ꢀ
in ● Table 2. Both parent gallic acid (1) as well as ascorbic acid
(21) served as positive controls in this assay. In general a dose-
dependent antioxidant potential of the analogs was observed.
Among all the synthesized analogs, compound 2, prop-2-ynyl-
3,5-dihydroxy-4-(prop-2-ynyloxy) benzoate formed as a side
product in the propargylation reaction of gallic acid and propar-
gyl bromide, was found to be least active of all. Since in com-
pound 2 the free para-OH moiety as well as the OH of acid
moiety are in esterified state, it lead to a loss in antioxidant
action, suggesting that the OH groups in gallic acid molecule are
very important for exhibiting the DPPH scavenging effect. This
fact is in strong conformity with the previously documented fact
that OH-group para to the acid group in gallic acid [31], its deriv-
atives is necessary for exhibiting a potential DPPH scavenging
effect. Therefore no efforts to modify compound 2 were invested.
It was also noted that to produce analogs with better activity
than the parent gallic acid molecule only acid group accepts any
sort of modification. Since the desired product, prop-2-ynyl-3,4,
5-trihydroxy benzoate (3), with all the 3 phenolic OH groups in
free state and that of the carboxylic acid moiety in esterified
state, was formed in excellent yields and exhibited an appre-
ciable scavenging effect displaying IC50 value of 25.67±0.5µM,
less than that of standard gallic acid and ascorbic acid with IC50
of 9.01±0.6 and 12.07±0.8µM respectively. This observation
was in strong concurrence with the previous reports that the
various long chain esters of gallic acid possess a lower scav-
enging effect compared to gallic acid and follow the order as
gallic acid (IC50 =6.0 ± 0.1µM), methyl gallate (IC50 =7.2±0.1µM),
Results and Discussion
▼
Taking cue from above literature that more potent antioxidants
can be synthesized, while modifying the carboxylic acid moiety
of gallic acid, we designed a click approach to carry out the syn-
thetic modications at this moiety to obtain more potent and
effective antioxidant derivatives of gallic acid. Gallic acid (1) was
thus subjected to propargylation in dry DMF using NaH as base.
The propargylation reaction delivered the required alkyne at the
desired position which could easily be confirmed from its 1H and
13
▶ꢀ
●
C NMR spectra ( Fig. 1a, b). However a very little amount of
side-product with one alkyne moiety tethered to the acid group
and the other alkyne moiety to one of the 3 hydroxyl function-
alities of the benzene nucleus was also formed (2). To localize as
which of the 3 hydroxyl moieties underwent propargylation, we
1
13
▶ꢀ
resorted to close analysis of its H and C NMR spectra ( Fig.
●
1
1c, d). As can be seen in the H NMR of compound 2, a singlet
integrating for 2 equivalent aromatic protons corresponding to
positions 2 and 6 in the aromatic ring is a clear indication of the
2 OH groups (position 3 and 5) in the aromatic ring being intact
and that the para-hydroxyl might have been propargylated. This
was further supplemented by the 13C NMR of compound 2. Pres-
ence of only 11 signals for 13 carbon atoms suggested a sym-
metrical nature of aromatic ring and hence evidencing the
propargylation at para-hydroxyl moiety. After propargylation
various aromatic azides were prepared from their respective
aromatic amines by diazotization with sodium nitrite in acidic
>n-propyl gallate (IC50 =8.2±0.1µM),
>n-octyl gallate
(IC50 =11.8±0.2µM)>n-dodecyl gallate (IC50 =13.2±0.2µM)
against DPPH (190µM) in ethanolic solution [31]. Compound 3
was further subjected to Huisgen’s cycloaddition reaction at its
well poised alkyne moiety to afford a range of triazolyl analogs
(4–20). Among all the synthesized analogs, a notable difference
in the antioxidant potential was observed which may be attrib-
uted to the position of substituents depending upon the type of
Lone SH et al. Gallic Acid Triazoles… Drug Res

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
Fig. 1 (a and b) 1H and 13C NMR spectra of
compound 3. (c and d) 1H and 13C NMR spectra of
compound 2. (e and f) 1H and 13C NMR spectra of
compound 4.
aromatic azide used. The highest DPPH scavenging effect was
observed in case of [1-(2-methoxyphenyl)-1H-1,2,3-triazol-
4-yl]methyl-3,4,5–trihydroxy benzoate (9) displaying IC50 of
6.41±0.2µM compared to standard gallic acid and ascorbic acid
with IC50 of 9.01±0.6 and 12.07±0.8µM respectively. However
its
congener,
[1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl]
methyl-3,4,5-trihydroxybenzoate (10) with OCH3 at para-posi-
tion was less active than standard gallic acid but more active
than ascorbic acid displaying IC50 of 12.07±0.8µM. The trimeth-
oxy analog (11) displayed a lower antioxidant effect with IC50 of
20.8±1.1µM, depicting the effect of number and position of
methoxy groups in exhibiting the desired scavenging effect.
Compound 20 with ortho-hydroxymethyl moiety also exhibited
potent DPPH scavenging effect only after compound 9 and dis-
played IC50 of 7.9±0.4µM. However compounds with simple
phenyl (4) and napthyl (5) moieties were found to be moderately
active displaying IC50 of 17.12±1.3 and 14.20±0.9µM respec-
tively. Similarly compound 18 having 5-Iodo-2-methyl phenyl
moiety exhibited a moderate DPPH scavenging effect with IC50
of 19.90±0.8µM. All the remaining compounds exhibited lower
DPPH scavenging effect as compared to both the standard: gallic
Fig. 2 Synthesis of triazole analogs of Gallic acid.
(1) and ascorbic acid (21). All the results have been summed up
▶ꢀ
in Table 2.
●
Lone SH et al. Gallic Acid Triazoles… Drug Res

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
Table 1 Preparation of various analogs of gallic acid.
a
a
S.No.
S. No.
R
Product
Yield%
R
Product Yield%
10
13
14
70
86
1
2
4
5
69
71
NO2
11
Br
NO2
3
4
6
65
62
12
13
15
16
68
79
7
F
Br
5
8
88
F
Br
14
17
83
OCH3
6
7
9
71
CN
CH3
15
16
17
18
19
20
72
80
10
90
I
OCH3
OCH3
8
11
12
84
H3CO
OCH3
NO2
75
OH
9
63
‘R’ refers to any substituted aryl moiety
‘a’ refers to the product yield after isolation/purification process
Lone SH et al. Gallic Acid Triazoles… Drug Res

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
with saturated sodium bicarbonate solution twice, dried over
anhydrous sodium sulphate and concentrated to a minimum
volume under reduced pressure on rotary evaporator without
making use of heating from water bath.
Table 2 DPPH scavenging potential of various analogs of gallic acid.
Compound
aIC50 (µM)
Compound
aIC50 (µM)
2
nd
13
25.67±2.0
28.24±1.6
nd
3
25.67±0.5
17.12±1.3
14.20±0.9
77.00±2.0
nd
14
4
15
General procedure for the synthesis of triazole analogs
of compound 3 (4–20)
5
16
61.66±2.2
24.24±1.0
19.19±0.8
29.88±1.5
07.92±0.4
12.07±0.8
09.01±0.6
6
17
To a solution of compound 3 (25mg, 0.083mmol) in t-BuOH:H2O
(2:1, 3ml), sodium ascorbate (2.0mg, 0.012mmol) and
CuSO4.5H2O (2mg, 0.0075mmol) were added at room tempera-
ture. To this mixture, aryl azide (0.12mmol) was added and the
reaction mixture sonicated till its completion. The crude mix-
ture was extracted with ethylacetate (3×20ml) and the com-
bined organic layers dried over sodium sulphate and purified
through column chromatography to give pure 4–20 in 62-90%
yield.
7
18
8
41.40±1.0
6.41±0.2
10.80±0.4
20.87±1.1
nd
19
9
20
10
11
12
21 (AA)
1 (GA)
a refers to the mean value of 3 independent readings±SD
GA and AA refer to standard gallic and ascorbic acids
Conclusion
▼
Spectral analysis of the representative compounds
Prop-2-ynyl-3,5-dihydroxy-4-(prop-2-ynyloxy)benzoate (2)
1H NMR (400MHz, MeOD) δ 7.00 (s, 2H), 4.78–4.82 (m, 4H), 2.93
(s, 1H), 2.77 (s, 1H). 13C NMR (101MHz, MeOD) δ 167.08, 152.31,
138.7, 126.6, 11.23, 80.15, 78.98, 76.85, 76.21, 61.69, 53.35. ESI-
MS at m/z=247 for [M+H]+ calculated for C13H10O5.
In conclusion, a range of galloyl triazole analogs were synthe-
sized using click chemistry approach and studied for the possi-
ble antioxidant potential. Compound 9, 10, 20 displayed potent
scavenging effect with IC50 values of 6.41±0.2, 10.80±0.4 and
07.92±0.4, µM respectively as compared to the standard gallic
acid and ascorbic acid with IC50 of 12.07±0.8 and 9.01±0.6µM
respectively. Since gallic acid derivatives find their use as food
antioxidant additives, this study provides an important aspect
with regard to the use of these gallic acid based synthetic anti-
oxidants in food industry as dietary supplements and are more
potent than their natural precursor-gallic acid.
Prop-2-ynyl-3,4,5-trihydroxybenzoate (3)
1H NMR (400MHz, MeOD) δ 7.06 (s, 2H), 4.84 (s, 2H), 2.92 (s,
1H). 13C NMR (101MHz, MeOD) δ 167.60, 146.71, 140.25, 121.02,
110.35, 79.21, 76.17, 53.05. ESI-MS at m/z=209 for [M+H]+.
[1-(Phenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (4)
1H NMR (400MHz, MeOD) δ 8.53 (s, 1H), 7.80 (m, 2H), 7.4–7.6
(m, 3H), 7.02 (s, 2H), 5.41 (s, 2H).13C NMR (101MHz, MeOD) δ
168.11, 146.69, 145.34, 140.19, 138.44, 131.11, 130.35, 124.21,
121.82, 121.18, 110.37, 58.48. ESI-MS at m/z=328 [M+H]+ (cal-
culated for C16H13N3O5, 327).
Experimental
▼
General
1H and 13C NMR spectra were recorded on Bruker 400, 100MHz
Bruker spectrometers using TMS as internal standard. Chemical
shifts (δ) are expressed as ppm. Mass spectra were recorded on
Shimadzo lab solutions, Chromatography was carried out using
ordinary phase column chromatography silica gel 60–120 mesh
(Merck grade) and precoated TLC plates with silica gel 60 F254
(Merck, 0.25mm). Detection was done by using cerric-sulfate
solution and para-anisaldehyde followed by heating.
[1-(Napthalen-1-yl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (5)
1H NMR (400MHz, MeOD) δ 8.40 (s, 1H), 7.9–8.1 (s, 2H), 7.45–
7.62 (m, 5H), 7.05 (s, 2H), 5.46 (s, 2H). 13C NMR (101MHz, MeOD)
δ 168.17, 163.97, 146.74, 144.89, 141.10, 135.84, 132.02, 130.03,
129.65, 129.29, 128.70, 128.44, 126.40, 125.18, 123.14, 121.24,
110.39, 58.57. ESI-MS at m/z=378 [M+H]+ (calculated for
C20H15N3O5, 377).
Synthesis
Synthesis of prop-2-ynyl-3,4,5-trihydroxybenzoate (3)
A solution of compound 1 (1000mg, 5.88mmol) in dimethyl for-
mamide (DMF) (5ml) and propargyl bromide (0.151mmol) was
heated under reflux for 12h in presence of base DBU. After cool-
ing, the reaction mixture was evaporated under vaccuo on a
rotary evaporator and the residue obtained was subjected to
normal silica-gel column chromatography using Hexane-EtOAc
(60:40) as eluent to furnsh 2 products 2 and 3.
[1-(2-bromophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (6)
1H NMR (400MHz, MeOD) δ 8.32 (s, 1H), 7.83 (m, 1H), 7.4–7.6
(m, 3H), 7.0 (s, 2H), 5.40 (s, 2H).13C NMR (101MHz, MeOD) δ
168.09, 146.70, 144.48, 140.19, 137.91, 135.19, 133.18, 130.05,
129.75, 128.24, 121.20, 120.38, 110.36, 58.43. ESI-MS at
m/z=406 [M+2]+ (calculated for C16H12BrN3O5, 404).
General procedure for synthesis of azides
[1-(3-bromophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (7)
To a solution of particular aromatic amine in 1,4-dioxane at
−15°C, 5 equivalents of 2M Sulphuric acid was added in small
installments while stirring. After 5min 2 equivalents of 3M
sodium nitrite was added drop wise and after 30min 3 equiva-
lents of 3M sodium azide was added drop wise carefully. Reac-
tion was brought to room temperature and extracted with
diethyl ether for at least 3 times. Organic layers were washed
1H NMR (400MHz, MeOD) δ 8.30 (s, 1H), 7.70 (s, 1H), 7.75–7.33
(m, 3H), 7.01 (s, 2H), 5.47 (s, 2H). 13C NMR (101MHz, MeOD) δ
168.26, 145.99, 144.31, 140.01, 135.13, 132.16, 130.05, 129.75,
128.24, 124.31, 121.20, 119.98, 109.36, 58.43. ESI-MS at
m/z=406 [M+2]+ (calculated for C16H12BrN3O5, 404).
Lone SH et al. Gallic Acid Triazoles… Drug Res

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
[1-(4-bromophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (8)
145.51, 140.17, 132.80, 124.23, 121.15, 117.34, 117.01, 116.80,
110.38, 58.42. ESI-MS at m/z=346. [M+H]+ (calculated for
C16H12FN3O5, 345).
1H NMR (400MHz, MeOD) δ 8.23 (s, 1H), 7.65 (d, J=7.8Hz, 1H),
7.53 (d, J=8.0Hz, 2H), 7.11 (s, 2H), 5.42 (s, 2H). 13C NMR
(101MHz, MeOD) δ 168.23, 146.12, 144.21, 140.24, 136.76,
133.07, 129.15, 124.34, 121.24, 120.30, 109.00, 58.01. ESI-MS at
m/z=406 [M+2]+ (calculated for C16H12BrN3O5, 404).
[1-(4-flurophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (16)
1H NMR (400MHz, MeOD+DMSO) δ 8.721 (s, 1H), 8.03 (d,
J=8Hz, 2H), 7.46 (d, J=8Hz, 2H), 7.18 (s, 2H), 5.546 (s, 2H). 13C
NMR (101MHz, MeOD+DMSO) δ 167.78, 165.27, 146.80, 140.11,
134.85, 124.19, 121.21, 118.04, 117.80, 110.37, 58.22. ESI-MS at
m/z=346 [M+H]+ (calculated for C16H12FN3O5, 345).
[1-(2-methoxyphenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (9)
1H NMR (400MHz, MeOD) δ 8.34 (s, 1H), 7.61 (d, J=8.6Hz, 1H),
7.46–7.48 (m, 1H), 7.21 (d, J=8.2Hz, 1H), 7–7.07 (m, 1H), 6.99 (s,
2H), 5.39 (s, 2H), 3.85 (s, 3H). 13C NMR (101MHz, MeOD) δ
168.15, 153.45, 146.70, 144.07, 140.17, 132.22, 128.10, 127.35,
126.89, 122.24, 121.26, 115.95, 110.35, 58.52, 56.78. ESI-MS at
m/z=358 [M+H]+ (calculated for C17H15N3O6, 357).
[1-(4-cyanophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (17)
1H NMR (400MHz, MeOD) δ 8.68 (s, 1H), 8.06 (d, J=8.8Hz, 2H),
7.91 (d, J=8.6Hz, 2H), 7.00 (s, 2H), 5.43 (s, 2H). 13C NMR
(101MHz, MeOD) δ 168.07, 146.72, 145.97, 141.41, 135.38,
124.25, 122.19, 121.14, 118.94, 113.79, 110.37, 58.38. ESI-MS at
m/z=353 [M+H]+ (calculated for C17H12N4O5, 352).
[1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (10)
1H NMR (400MHz, CDCl3) δ 8.20 (s, 1H), 7.76 (d, J=8.0Hz, 2H),
7.00 (d, J=8.0Hz, 2H), 6.95 (s, 2H), 5.41 (s, 2H), 3.89 (s, 3H). 13
C
[1-(5-Iodo-2-methyl-phenyl)-1H-1,2,3-triazol-4-yl]methyl-
3,4,5-trihydroxybenzoate (18)
NMR (101MHz, MeOD) δ 168.25, 154.47, 146.43, 144.27, 140.17,
131.20, 124.12, 122.32, 119.70, 115.81, 110.08, 58.85, 57.12. ESI-
MS at m/z=358 [M+H]+ (calculated for C17H15N3O6, 357).
1H NMR (400MHz, MeOD) δ 8.32 (s, 1H), 7.78–77.82 (m, 2H),
7.23 (d, J=8Hz, 1H), 7.08 (s, 2H), 5.45 (s, 2H), 2.20 (s, 3H). 13C
NMR (101MHz, MeOD) δ 168.10, 146.69, 144.69, 140.50, 140.19,
138.78, 135.90, 135.11, 134.39, 127.63, 121.18, 110.36, 90.94,
58.46, 17.68. ESI-MS at m/z=468 [M+H]+ (calculated for
C17H14IN3O5, 467).
[1-(3,4,5-trimethoxyphenyl)-1H-1,2,3-triazol-4-yl]methyl-
3,4,5-trihydroxybenzoate (11)
1H NMR (400MHz, MeOD) δ 8.68 (s, 1H), 7.24 (s, 1H), 7.19 (s,
2H), 5.51 (s, 2H), 3.98 (s, 6H), 3.89 (s, 3H). 13C NMR (101MHz,
MeOD) δ 168.12, 155.51, 146.70, 145.22, 140.21, 139.78, 134.38,
124.52, 121.19, 110.37, 99.83, 61.39, 58.48, 57.13. ESI-MS at
m/z=418 [M+H]+ (calculated for C19H19N3O8, 419).
[1-benzyl}-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (19)
1H NMR (400MHz, MeOD) δ 7.96 (s, 1H), 7.28 (s, 5H), 6.95 (s.
2H), 5.53 (s, 2H), 5.26 (s, 2H). 13C NMR (101MHz, MeOD) δ
168.59, 146.66, 144.48, 139.74, 130.33, 129.73, 129.43, 125.66,
120.90, 110.23, 58.19, 55.32. ESI-MS at m/z=342 [M+H]+ (calcu-
lated for C17H15N3O5, 341).
[1-(2-nitrophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (12)
1H NMR (400MHz, MeOD) δ 8.57 (s, 1H), 8.31 (d, J=8.4Hz, 1H),
8.01–7.75 (m, 3H), 7.02 (s, 2H), 5.40 (s, 2H). 13C NMR (101MHz,
MeOD) δ 167.54, 150.43, 146.80, 144.31, 139.17, 132.59, 127.13,
126.36, 123.45, 121.20, 118.96, 110.39, 57.50. ESI-MS at
m/z=373 [M+H]+ (calculated for C16H12N4O7, 372).
[1-{2-(hydroxymethyl)phenyl}-1H-1,2,3-triazol-4-yl]
methyl-3,4,5-trihydroxybenzoate (20)
1H NMR (400MHz, MeOD) δ 8.33 (s, 1H), 7.67 (d, J=8.1Hz, 1H),
7.5–7.65 (m, 1H), 7.4–7.48 (m, 2H), 7.02 (s, 2H), 5.41 (s, 2H), 4.4
(s, 2H). 13C NMR (101MHz, MeOD) δ 168.11, 146.69, 144.62,
140.18, 137.97, 136.67, 131.50, 130.72, 129.78, 127.84, 126.94,
121.21, 110.36, 61.03, 58.48. ESI-MS at m/z=358 [M+H]+ (calcu-
lated for C17H15N3O6, 357).
[1-(3-nitrophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (13)
1H NMR (400MHz, MeOD) δ 8.70 (s, 1H), 7.8–8.5 (m, 4H), 7.12 (s,
2H), 5.51 (s, 2H). 13C NMR (101MHz, MeOD) δ 167.89, 150.81,
150.58, 146.80, 139.17, 139.16, 132.59, 127.23, 124.56, 122.67,
121.19, 116.66, 110.39, 56.59. ESI-MS at m/z=373 [M+H]+ (cal-
culated for C16H12N4O7, 372).
DPPH scavenging effect
DPPH free radical scavenging activity was evaluated by measur-
ing the scavenging activity of the samples on stable 2.2-diphe-
nyl-1-picryl hydrazyl radical (DPPH) [32]. A 0.5mM solution of
DPPH in methanol was prepared. Different concentrations of
each sample (5–50µM) were added to 1.0ml (0.5mM DPPH) and
final volume made up to 3.0ml with methanol. The mixture was
shaken vigorously and kept standing at room temperature for
15min. Then the absorbance of the mixture was measured at
517nm on UV spectrophotometer. The decrease in the absorb-
ance indicates an increase in DPPH-radical scavenging activity.
The percentage inhibition was calculated by the following equa-
tion:
[1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-tri-
hydroxybenzoate (14)
1H NMR (400MHz, MeOD) δ 8.72 (s, 1H), 8.40 (d, J=9.2Hz, 2H),
8.10 (d, J=8.8Hz, 2H), 7.02 (s, 2H), 5.43 (s, 2H). 13C NMR
(101MHz, MeOD) δ 168.07, 149.06, 146.72, 146.09, 142.66,
140.25, 126.66, 124.43, 122.20, 121.14, 110.39, 58.39. ESI-MS at
m/z=373 [M+H]+ (calculated for C16H12N4O7, 372).
[1-(3-flurophenyl)-1H-1,2,3-triazol-4-yl]methyl-3,4,5-
trihydroxybenzoate (15)
1H NMR (400MHz, MeOD) δ 8.55 (s, 1H), 7.62 (d, J=8.5Hz, 2H),
7.48–7.53 (m, 1H), 7.14–7.18 (m, 1H), 7.01 (s, 2H), 5.38 (s, 2H).
13C NMR (101MHz, MeOD) δ 168.06, 165.84, 163.39, 146.66,
DPPH radical scavenging (%)  AC  AS /AC 100
Lone SH et al. Gallic Acid Triazoles… Drug Res

DrugRes/2016-06-1205/28.10.2016/MPS
Original Article
14 Xun L, Yalin L, Wenfang Xu. Design synthesis and biological evaluation
of novel galloyl pyrollidine derivatives as potential antitumor agents.
Bioorganic & Medicinal Chemistry 2006; 14: 1287–1293
15 Wu J, Mi JL, Zhou CH. Chin Pharm J 2007; 42: 404–409
16 Meng JP, Lu YH, Halqam I et al. Ginseng compounds: an update on
their molecular mechanisms and medical applications. chin J Biochem
Pharm 2008; 29: 422–425
where AC is the absorbance of control and AS is absorbance of
sample. Ascorbic acid and gallic acid both were used as positive
control. The experiment was done in triplicate and mean values
were calculated. Standard deviation for the triplicate analysis
was also calculated. IC50 value was calculated as the concentra-
tion of sample required to scavenge 50% of DPPH free radicals.
17 Meng JP, Geng RX, Zhou CH et al. Advances in the research of benzimi-
dazole drugs. Chin J New Drugs 2009; 18: 1505–1514
18 Shi Y, Zhou CH. Synthesis and evaluation of a class of new coumarin
triazole derivatives as potential antimicrobial agents. Bioorg Med
Chem Lett 2011; 21: 956–960
19 Shi Y, Zhou CH, Zhou XD et al. Synthesis and antimicrobial evaluation
of coumarin-based benzotriazoles and their synergistic effects with
chloromycin and fluconazole. Acta Pharm Sinica 2011; 46: 798–810
20 Wan K, Zhang YY, Zhou YY et al. J Antibiot 2012; 37: 8
21 Pasqualotto AC, Thiele KO, Goldani LZ. Novel triazole antifungal drugs:
focus on isavuconazole, ravuconazole and albaconazole. Curr Opin
Invest Drugs 2010; 11: 165–174
Acknowledgement
▼
One of the authors Shabir H. Lone is grateful to CSIR (India) for
providing financial assistance in the form of Senior Research Fel-
lowship (Budget Head: P-81101).
22 Fera MT, Camera EL, Sarro AD. New triazoles and echinocandins: mode
of action, invitro activity and mechanisms of resistance. Expert Rev
Anti-Infect Ther 2009; 7: 981–998
23 Sobue S, Tan K, Haug-Pihale G. The effects of hepatic impairment on
the pharmacokinetics of fosfluconazole and fluconazole following a
single intravenous bolus injection of fosfluconazole. Pharmocol 2005;
59: 160–166
24 Nam NH, Sardari S, Selecky M et al. Carboxylic acids and phosphate
ester derivatives of fluconazole: synthesis and antifungal activities.
Bioorg Med Chem 2004; 12: 6255–6269
25 Mora SJ, Cormick MP, Milanesio ME et al. The photodynamic activ-
ity of a novel porphyrin derivative bearing a fluconazole structure in
different media and against Candida albicans. Dyes Pigments 2010;
87: 234–240
26 Zhou CH, Meng KG, Fang JPB et al. CN Patent 2009; CN 101397276 (A)
27 Francavilla C, Low E, Nair S et al. Quaternary ammonium N,N-dichloro-
amines as topical, antimicrobial agents. Bioorg Med Chem Lett 2009;
19: 2731–2734
28 Lone SH, Bhat KA, Naseer S et al. Isolation, cytotoxicity evaluation
and HPLC-quantification of the chemical constituents from Artemisia
amygdalina. Decne Chromatogr B 2013; 940: 135–141
29 Lone SH, Bhat KA, Shakeel-u-Rehman et al. Synthesis and biological
evaluation of amino analogs of Ludartin: potent and selective cyto-
toxic agents. Bioorg Med Chem Lett 2013; 23: 4931–4934
30 Lone SH, Bhat KA, Majeed R et al. Click chemistry inspired facile synthe-
sis and bioevaluation of novel triazolyl analogs of Ludartin. A Bioorg
Med Chem Lett 2014; 24: 1047–1051
31 Lu Z, Nie G, Belton PS et al. Structure-activity relationship analysis of
antioxidant ability and neuroprotective effect of gallic acid deriva-
tives. Neurochemistry International 2006; 48: 263–274
32 Bozin B, Mimica-Dukic M, Simin N et al. Characterization of the vola-
tile composition of essential oils of some Lamiaceae spices and the
antimicrobial and antioxidant activities of the entire oils. J Agric Food
Chem 2006; 54: 1822–1828
Conflict of Interest
▼
The authors declare that there is no conflict of interest.
References
1 Harman D. Aging: a theory based on free radical and radiation chem-
istry. J Gerontol 1956; 11: 298–300
2 Halliwell B, Gutteridge JMC. Free radicals in biology and medicine.
Oxford: Oxford University Press; 1997
3 Sies H. Antioxidants in disease, mechanisms and therapy. New York:
Academic Press; 1996
4 Sies H. Biochemistry of oxidative stress. Angew Chem Internat Ed Eng
1986; 1058–1071
5 Devasagayam TPA, Tilak JC, Boloor KK et al. Free radicals and anti-
oxidants in human health: Current status and future prospscts. JAPI
2004; 52: 794
6 Singh J, Rai GK, Upadhyay AK et al. Indian Journal of agricultural Sci-
ences 2004; 74: 3–5
7 Isuzugawa K, Inoue MY. Ogihara, Catalase contents in cells determine
sensitivity to the apoptosis inducer gallic acid. Biological & Pharma-
ceutical Bulletin 2001; 24: 249–253
8 Constant J. Alcohol, ischemic heart disease, and the French paradox
Coronary Artery Disease 1997; 8: 645–649
9 Jadon A, Bhadauria M, Shukla S. Journal of Ethnopharmacology 2007;
109: 214–218
10 Kim YJ. Antimelanogenic and antioxidant properties of gallic acid.
Biological & Pharmaceutical Bulletin 2007; 30: 1052–1055
11 Zhao J, Khan IA, Fronczek FR. Gallic acid. Acta Crystallographica 2011;
67: 316–317
12 Shahrzad S, Aoyagi KA, Winter A et al. Pharmacokinetics of gallic acid
and its relative bioavailability from tea in healthy humans. The Journal
of Nutrition 2001; 131: 1207–1210
13 Locatellia C, Filippin-Monteirob FB, Creczynski-Pasab TB. Synthesis,
antimicrobial evaluation and QSAR studies of gallic acid derivatives.
http://dx.doi.org/10.1016/j.arabjc.2013.11.014
Lone SH et al. Gallic Acid Triazoles… Drug Res