Synthesis, characterization and antimicrobial activity of three gallates containing imidazole, benzimidazole and triclosan units

Article abstract of DOI:10.14233/ajchem.2014.15600

Three new gallates containing the antimicrobial units of imidazole, benzimidazole and triclosan, respectively, were designed and synthesized. Firstly, the direct esterification method, in which p-toluenesulfonic acid was used as the catalyst, was adopted

Full text of DOI:10.14233/ajchem.2014.15600

Asian Journal of Chemistry; Vol. 26, No. 2 (2014), 513-520
http://dx.doi.org/10.14233/ajchem.2014.15600
Synthesis, Characterization and Antimicrobial Activity of Three
Gallates Containing Imidazole, Benzimidazole and Triclosan Units
1,2
1,2
ZHIYUAN WANG , HAIBIN GU1,2,* and WUYONG CHEN
1Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, P.R. China
2National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan University, Chengdu 610065, P.R. China
*Corresponding author: Fax: +86 28 85405237; Tel: +86 28 85404462; E-mail: guhaibing@scu.edu.cn
Received: 8 April 2013;
Accepted: 10 May 2013;
Published online: 15 January 2014;
AJC-14578
Three new gallates containing the antimicrobial units of imidazole, benzimidazole and triclosan, respectively, were designed and synthesized.
Firstly, the direct esterification method, in which p-toluenesulfonic acid was used as the catalyst, was adopted to synthesize the three
gallates. Results show that it is infeasible to obtain the target products, especially for the direct esterification reaction of 5-methyl-2-nitro-
imidazole-1-ethanol and gallic acid, the synthesized product is just a complex composed by equimolar 5-methyl-2-nitro-imidazole-1-
ethanol and gallic acid and stabilized by a lot of intramolecular and intermolecular hydrogen bonds, which was proved by the single-
crystal X-ray diffraction analysis. Another, the indirect esterification method, in which the phenolic hydroxyl groups of gallic acid were
first protected by acetyls as shown in Scheme-I, was employed. The obtained compounds were proved to be the expected products by
elemental analysis, IR, 1H NMR, 13C NMR and X-ray single-crystal diffraction. Finally, the inhibition zone method was used to determine
the antimicrobial effect of the synthesized gallates and their initial compounds. Results indicate that the introduction of the three antimicrobial
units has obvious synergistic or additive effect on the antimicrobial activities of gallates. The gallates shows different inhibitory effect
against different tested microbes, which is mainly decided by the introduced antimicrobial units.
Keywords: Gallates, Imidazole, Benzimidazole, Triclosan, Antimicrobial activity, Crystal structure.
the period of processing, storage and wear, which not only
lower the grades of leather but also endanger the health of
consumers24. Therefore, there is an utmost need to develop
antimicrobial compounds with broad-spectrum, high efficiency
and less toxicity. In the leather industry, natural tannin conta-
ining gallates such as Chinese gallnut, valonia, chestnut and
myrobalan, are mainly used as tanning agents25.Although these
natural gallates show certain antimicrobial activities, their
performance can not be comparable with the commercial leather
fungicides such as 2-(thiocyanomethylthio)benzothiazole
(TCMTB)24. The purpose of our research program is to improve
the antimicrobial activities of gallates by introducing different
antimicrobial units into the molecular structure of gallates and
estimate the potential of the synthesized compounds as leather
antimicrobial agents. In this study, based on the combination
principle of active structures, we designed three new gallates
containing the antimicrobial units of imidazole, benzimidazole
and triclosan, respectively. It is well known that imidazole and
benzimidazole derivatives have good antimicrobial activities
and they have been widely used as antimicrobial agents in
many fields such as medicine and farm chemical26,27. Triclosan
is also an efficient and safe antimicrobial agent and because
INTRODUCTION
Gallic acid is an important decomposition product of
hydrolyzable tannin and shows good biological activities,
usually reacts with alcohols to prepare its esterification products
because of its poor lipid-solubility1,2. The synthesized gallates
can effectively eliminate superoxide anion radicals and hydroxyl
radicals, so they are generally used as antioxidants for food
such as fat and cream1-6. Because of its bactericidal action and
bactriostasis, gallates are often applied as preservatives for
fruits, vegetable and wood7-12. Furthermore, in the area of
pharmaceuticals, cosmetic and photosensitive heat-sensitive
materials, gallates also finds extensively application1,2,13. For
example, as a medicine, gallates exhibit some actions to combat
platelet aggregation, facilitate fibrinolysis and thrombolysis,
dilate the blood vessel and increase blood flow to the coronary
artery and have certain curative effect on cardiovascular and
cerebrovascular diseases, viral disease, bacterial infections and
stomach ulcer1,14-23. Consequently, more and more studies have
been focused on the synthesis and application of gallates1, 2.
As the processed products of natural animal hides and
skins, leathers are easy to be eroded by bacteria and fungi in

514 Wang et al.
Asian J. Chem.
of its good compatibility with skin, it has been extensively
applied in all kinds of daily chemicals containing hand-
washing, soap, washing powder and mouthwash28,29. Accor-
dingly, the new designed gallates may exhibit good antimi-
crobial properties if the combination of these antimicrobial
units and gallic structure shows a significant synergistic inhibi-
tion effect against microbes. So, to efficiently synthesize these
gallates, we tested two synthetic routes-direct and indirect
esterification method (Scheme-I). Elemental analysis, IR, 1H
NMR, 13C NMR and X-ray single-crystal diffraction were used
to characterize their structures. Furthermore, the antimicrobial
activities of the new gallates and their original compounds
were compared by determining the diameters of inhibition zones.
m.p. 65-67 ºC. Anal. calcd. (%) for C14H11O3Cl3: C, 50.37; H,
3.30. Found (%): C, 51.03; H, 3.30. Slected IR data (KBr, cm-1):
3367.403258.46 (νCH -OH), 2930.26, 2867.28 ((νCH ), 1597.85,
2
2
1583.31, 1493.68 (νbenzene C=C), 1468.77 (δCH ), 1232.02 (nAr-O-C),
2
1050.08 (nCH -O), 1115.86, 796.64 (νAr-Cl), 850.53, 833.79 (δAr-H).
2
1H NMR (600 MHz, CDCl3), δppm: 1.84 (s, 1H, OH), 3.82 (t,
2H, -CH2O-), 4.07 (t, 2H, -OCH2-), 6.72 (d, 1H, Ph), 6.97
(d+s, 2H, Ph), 7.01 (s, 1H, Ph), 7.13 (d, 1H, Ph), 7.47 (d, 1H,
Ph). 13C NMR (600 MHz, CDCl3), δppm: 61.10 (-CH2O-), 70.89
(-OCH2-), 115.43 (Ph), 118.34 (Ph), 121.76 (Ph), 121.89 (Ph),
124.61 (Ph), 127.84 (Ph), 128.37 (Ph), 130.33 (Ph), 130.56
(Ph), 143.50 (Ph), 150.44 (Ph), 152.23 (Ph).
Synthesis of gallates by direct esterification method:
The reaction between 5-methyl-2-nitro-imidazole-1-ethanol
and gallic acid was taken as an example. The catalyst of p-
toluenesulfonic acid (6.0 g, 0.035 mol) and water-carrying
agent of benzene (30 mL) were added to a solution of gallic
acid (10.23 g, 0.06 mol) and 5-methyl-2-nitro-imidazole-1-
ethanol (21 g, 0.12 mol) in 1,4-dioxane (300 mL). The mixture
was held under Dean-Stark conditions for 8.0 h before the
solvent as well as water-carrying agent were removed under
vacuum. The residue was washed by distilled water for three
times to remove the catalyst. Then, the crude product was
purified by recrystallization with distilled water.A green crystal
was obtained and the yield is 62.5 %. m.p. 188-190 ºC. Anal.
calcd. (%) for C13H16N3O8: C, 45.61; H, 4.68; N, 12.28. Found
(%): C, 45.72; H, 5.08; N, 12.45. Slected IR data (KBr, cm-1):
EXPERIMENTAL
Triclosan and 5-methyl-2-nitro-imidazole-1-ethanol were
purchased from Kelong Chemicals Co., Ltd, Chengdu, China.
Trisacetyl-galloyl chloride (TAGC) was synthesized from
gallic acid by the route shown in Scheme-I and its melting
point is 107-108 ºC (106-107 ºC)9. 2-Methylol benzimidazole
was synthesized by the reaction of o-diaminobenzene and
glycolic acid and its melting point is 168-170 ºC (169-171 ºC)30
All the other reagents used in this experimental were research
grade.
Elemental analyses (C, H, N) were performed on a Carlo-
Erba 1106 analyser. Infrared spectra were obtained on a
FT-IR spectrophotometer (MAGNA.IR506, Nicolet Ltd., USA)
by using KBr disk in the range 4000-400 cm-1. Measurement
of the crystal was carried out on a CCD X-ray single crystal
diffractometer (Xcalibur, Eos, Britain). 1H and 13C NMR spectra
were recorded on a Bruker Avance 600 (or 400) instrument.
Chemical shifts were reported as δ (ppm) relative to TMS as
internal standard.
Synthesis of 2,4,4’-trichloro-2’-hydroxy ethyoxyl diphenyl
ether: Triclosan (14.475 g, 0.05 mol) and potassium iodide
(0.5 g, 0.03mol) were dissolved in 50 mL distilled water with
NaOH (4.0 g, 0.1 mol) at room temperature. Then, the tempe-
rature was raised to 80 ºC and 2-chloroethanol (20.13 g, 0.25
mol) was added dropwise over 0.5 h under mechanical stirring.
The mixture was stirred for 3 h at 80 ºC. During this period,
the pH of the mixture is kept at 9-10 by adding 50 % (w/w)
NaOH solution. Then, the mixture was cooled to room tempe-
rature and 300 mL distilled water was added. An oily crude
product separated out when hydrochloric acid was added to
adjust the pH of the solution to 2-3. After washed by 50 % (w/w)
NaOH solution and then distilled water for three times, the
product was purified by recrystallization with ethanol-water
(6:4, v/v) mixed solvent. 7.5 g of pure product, which is white
needle-like crystal, was obtained and the total yield is 49.9 %.
3299.86 (νOH), 3098.87(νCH ), 1682.59 (νC=O), 1533.47,
3
1367.65, 1352.11 (νNO ), 1068.76 (νCH -OH), 1606.00 (νC=N),
2
2
1
1488.23, 1465.55, 1423.63 (νAr). H NMR (600 MHz,
(CD3)2SO), δppm: 2.46 (s, 3H, CH3), 3.69 (m, 2H, -CH2O-),
4.36 (t, 2H, -NCH2-), 5.03 (t, 1H, C-OH), 6.93 (s, 2H, Ph),
8.03(s, 1H, =CH of imidazole), 8.86 (s, 1H, Ph-OH), 9.20 (s,
2H, Ph-OH), 12.24 (s, 1H, COOH). 13C NMR (600 MHz,
(CD3)2SO), δppm: 14.70 (CH3), 48.72 (-NCH2-), 60.21 (-CH2O-),
109.17 (Ph), 120.89 (=CH of imidazole), 133.43 (Ph), 138.44
(N=C of imidazole), 138.86 (Ph-OH), 145.86 (Ph-OH), 152.41
(C-NO2), 167.93 (COOH).
Similar procedure was applied for the other two direct
esterification reactions. The product of the direct esterification
between 2-methylol benzimidazole and gallic acid is a grey-
red powder whose IR spectrum is similar to that of 2-methylol
benzimidazole. And for the reaction between 2,4,4’-trichloro-
2’-hydroxy ethyoxyl diphenyl ether and gallic acid, the product
is also a grey-red powder whose IR spectrum is similar to that
of 2,4,4’-trichloro-2’-hydroxy ethyoxyl diphenyl ether, too.
So, this method did not work in the two reactions.
Synthesis of gallates by indirect esterification method:
The 2-methylol benzimidazole was taken as an example to
OH
OAc
OAc
OAc
OAc
OH
O
C
Ac2O
SOCl2
hydrazine hydrate
R
OH
HOOC
OH
OH
HOOC
OAc
OAc
NO2
Cl
ROOC
OAc
OAc
OCH2CH2
ROOC
OH
OH
triethylamine
OAc
N
Cl
N
O
N
CH3
1
CH2CH2
R =
,
,
CH2
N
H
Cl
Cl
2
3
Scheme-I: Synthetic route of the designed gallates by indirect esterification method

Vol. 26, No. 2 (2014) Synthesis andAntimicrobialActivity of Three Gallates Containing Imidazole, Benzimidazole and Triclosan Units 515
indicate the general procedure of the indirect esterification
method. To a stirred solution of TAGC (6.29 g, 0.02 mol) and
2-methylol benzimidazole (2.96 g, 0.02 mol) in anhydrous
CH2Cl2 (250 mL) was added triethylamine (10.12 g, 0.1 mol)
at 3 ºC. The temperature of 3 ºC was kept for 0.5 h, then, the
reaction mixture was allowed to stir for 12 h at room tempe-
rature and a light-rufous solution was obtained. The CH2Cl2
layer was first washed with 200 mL of diluted hydrochloric
acid (10 %, v/v) to remove the unreacted triethylamine and
then was washed with distilled water (100 mL × 3). After
removal of the water layer, the CH2Cl2 layer was added to a
round flask containing 80% hydrazine monohydrate (3.7545 g,
0.06 mol) and the mixture was stirred for 0.5 h at room tempe-
rature. Next, glacial acetic acid (3.603 g, 0.06 mol) in 100 mL
distilled water was added and the mixture was then stirred for
3 min. After filtration, the solid product was washed with
distilled water (50 mL × 3) and the CH2Cl2 layer of the filtrate
was also washed with distilled water (50 mL × 3), dried over
anhydrous Na2SO4 and evaporated to dryness. The residue and
solid product after filtration was added together and recrysta-
llized with the mixed solvent of ethanol and distilled water
(3:7, v/v). The separated white product (compound 1) was
vacuum dried and the yield is 83.3 %. m.p. 238-240 ºC. Anal.
calcd. (%) for C15H12N2O5: C, 60.00; H, 4.03; N, 9.33. Found
(%): C, 60.23; H, 4.24; N, 8.95. Slected IR data (KBr, cm-1):
3509.29 (νNH), 3455.79, 3409.16 (νOH), 1689.40 (νC=O), 1631.02
(νC=N), 1604.95, 1590.63, 1455.64 (νAr), 1434.59 (δCH ), 1345.68,
1239.06 (νC-N), 1207.30 (νasC-O-C), 1032.54 (νsC-O-2C), 859.95,
750.39 (νAr-H). 1H NMR (600 MHz, (CD3)2SO), δppm: 3.45 (m,
CH2 of C2H5OH), 5.44 (s, 2H, -CH2O-), 7.05 (d, 2H, Ph), 7.21
(m, 2H, Ph), 7.58 (s, 2H, Ph), 9.09 (s, 1H, Ph-OH), 9.36 (s,
2H, Ph-OH), 12.65 (s, 1H, NH). 13C NMR (600 MHz,
(CD3)2SO), δppm: 60.13 (-CH2O-), 109.35 (Ph), 119.15 (Ph),
122.48 (Ph), 122.53 (Ph), 122.59 (Ph), 139.32 (Ph), 146.11
(Ph), 149.90 (Ph), 165.91(-COO-).
795.63, 749.15 (δAr-H). 1H NMR (600 MHz, (CD3)2SO), δppm
:
4.34 (t, 4H, OCH2CH2O-), 6.79 (d, 1H, Ph), 6.91 (s, 2H, Ph),
7.06 (d, 1H, Ph), 7.08 (d, 1H, Ph), 7.18 (d, 1H, Ph), 7.37(s,
1H, Ph), 8.97 (s, 1H, Ph-OH), 9.24(s, 2H, Ph-OH). 13C NMR
(600 MHz, (CD3)2SO), δppm: 62.84 (-CH2O-), 67.59 (-OCH2-),
109.13 (Ph), 115.57 (Ph), 119.17 (Ph), 119.45 (Ph), 121.78
(Ph), 122.65 (Ph), 124.05 (Ph), 127.62 (Ph), 128.70 (Ph),
130.07 (Ph), 130.12 (Ph), 139.01 (Ph), 143.24 (Ph), 145.96
(Ph), 150.78 (Ph), 152.25 (Ph), 166.12 (-COO-).
Crystal structure determination: A single crystal of a
compound was mounted on a glass fiber. X-Ray diffraction
intensity data were collected on an Xcalibur, Eos diffractometer
equipped with a graphite-monochromated MoKα radiation by
using the ω-2θ scan technique. The Multi-scan/CrysAlisPro31,
Oxford Diffraction Ltd., was applied for the data reduction
and absorption correction. All the structures were solved by
direct methods and refined by full matrix least squares methods
using SHELX-97 program32. The hydrogen atoms of hydroxyl
groups that were located in a difference Fourier map were
limitedly refined with isotropic temperature factors and the
other hydrogen atoms that were added in their calculated
position were refined using a riding model32.
Antimicrobial activity determination: The evaluation
of the inhibitory effect of the synthesized gallates and their
original compounds was carried out by the inhibition zone
method33. The diameters of filter-paper discs are 22 mm and
the concentration of the tested compounds is 50 mg/mL. The
tested microbes contained Escherichia coli, Staphylococcus
aureus, Viscous red round yeast, Aspergillus niger and Peni-
cillium citrinum, which were all isolated from mildewed
leather33,34.Test inoculum of 5 × 104 bacteria/mL and 103 yeasts
or spores/mL was applied. Nutrient Agar and Potato medium
were employed as culture media for bacteria and fungi,
respectively. The diameters of inhibition zones were tested by
a vernier caliper after an incubation period of 24 h at 37 ºC for
bacteria or of 48 h at 30 ºC for fungi. All experiments were
made in duplicate and the results were confirmed in three
independent experiments.
Compound 2, the product of indirect esterification between
5-methyl-2-nitro-imidazole-1-ethanol and gallic acid, is a
white solid and the total yield is 87.5 %. m.p. 216-217ºC.Anal.
calcd. (%) for C13H13N3O7: C, 48.30; H, 4.05; N, 13.00. Found
(%): C, 47.35; H, 4.78; N, 12.59. Slected IR data (KBr, cm-1):
3373.00 (νOH), 1693.44 (νC=O), 1608.05 (νC=N), 1539.33,
1458.73 (νAr), 1429.91 (δCH ), 1333.70 (νNO ), 1236.18 (νasC-O-C),
RESULTS AND DISCUSSION
Structure of 2,4,4’-trichloro-2’-hydroxy ethyoxyl diphe-
nyl ether: To obtain the gallate containing the antimicrobial
unit of Triclosan, the hydroxyl group was attached to triclosan.
The etherification product of triclosan, 2,4,4’-trichloro-2’-
hydroxy ethyoxyl diphenyl ether (THEDE), was character-
ized by X-ray single-crystal diffraction. Table-1 is a summary
of the crystal data and structure refinement parameters. Its
crystal structure and crystal packing diagram are shown in
Fig. 1. The selected bond lengths and bond angles are listed in
Table-2. The hydrogen bonds are listed in Table-3.
3
2
1
1046.62 (νsC-O-C), 856.30 (δAr-H). H NMR (600 MHz,
(CD3)2SO), δppm: 2.46(s, 3H, CH3), 4.56 (t, 2H, -NCH2-), 4.67(t,
2H, -CH2O-), 6.85(s, 2H, Ph), 8.05(s, 1H, =CH of imidazole),
9.33 (s, 2H, Ph-OH) 9.04 (s, 1H, Ph-OH). 13C NMR (600 MHz,
(CD3)2SO), δppm: 14.45 (CH3), 45.53 (-NCH2-), 62.70 (-CH2O-),
108.98 (Ph), 119.04 (Ph), 133.62 (=CH of imidazole), 138.95
(Ph), 139.25 (=CH of imidazole), 146.04 (Ph), 151.93 (N=C
of imidazole)), 165.87 (COO).
As shown in Fig. 1, the molecular structure of the synthe-
sized product is different from that of triclosan. The hydrogen
atom of phenolic hydroxyl group of triclosan has been
successfully substituted by the hydroxyethyl group, which
proves that our synthesis procedure is feasible. It can be seen
from Table-2 that the bond length of O2-C13 is 1.4324(17) Å,
the bond angle of C3-O2-C13 is 117.33(11)º. Furthermore,
there is intermolecular hydrogen bonding between the oxygen
Compound 3, the product of indirect esterification between
2,4,4’-trichloro-2’-hydroxy ethyoxyl diphenyl ether and gallic
acid, is a white solid and the total yield is 84.9 %. m.p. 124-
126 ºC. Anal. calcd. (%) for C21H15O7 Cl3: C, 51.93; H, 3.11.
Found (%): C, 52.88; H, 3.91. Slected IR data (KBr, cm-1):
3363.37(νAr-OH), 1694.27(νC=O), 1533.03, 1494.89 (νAr),
1471.23 (δCH ), 1306.28 (νasAr-O-C), 1220.36 (νasC-O-C), 1116.28,
767.06 (νAr-C2l), 1097.59 (νsC-O-C), 1029.28 (νsAr-O-C), 868.42,

516 Wang et al.
Asian J. Chem.
TABLE-1
CRYSTAL DATA AND STRUCTURE REFINEMENT DETAILS FOR THEDE
Empirical formula
Temperature (K)
Space group
C14H11O3Cl3
145.0
Formula weight
Crystal system
a (Å),b (Å),c (Å)
Volume /Å3
333.58
Monoclinic
10.9914(3),4.71693(10),27.4699(7)
1398.38(6)
P21/c
90.00, 100.927(2), 90.00
4, 1.584
α (º), β (º),γ(º)
µ (mm-1), F(000)
0.658, 680
Z, ρcalc(mgmm-3)
Crystal size (mm3)
Index ranges
0.40 × 0.35 × 0.35
-13 ≤ h ≤ 6, -3 ≤ k ≤ 5, -31 ≤ l ≤ 34
2846 (0.0142)
2θ range for data collection
Reflections collected
Data/restraints/parameters
Absorption correction
6.04-52.78º
5562
2846/0/182
Independent reflections (Rint)
Observed reflections
Max. and min. transmission
Goodness-of-fit on F2
Final R indexes [all data]
2561
1.0 and 0.96383
multi-scan
Refinement method
Full-matrix least-squares on F2
R1 = 0.0267, wR2 = 0.0626
0.264/-0.217
1.047
Final R indexes [I>2σ(I)]
R1 = 0.0308, wR2 = 0.0651
Largest diff. peak/hole (eÅ-3)
TABLE-2
SELECTED BOND LENGTHS (Å) AND ANGLES (°) FOR THEDE
Bond
Bond
Bond
Length (Å)
1.7412(15)
1.7343(15)
Length (Å)
1.3926(17)
1.3726(17)
Length (Å)
1.4324(17)
1.4219(17)
Cl1-C1
Cl2-C8
O1-C1
O1-C7
O2-C13
O3-C14
Cl3-C10
1.7461(16)
O2-C3
1.3653(17)
–
–
Angle
Angle
Angle
(º)
118.06(11)
124.78(13)
(º)
116.50(12)
107.53(11)
(º)
110.20(12)
117.33(11)
C7-O1-C4
O2-C3-C2
O2-C3-C4
O2-C13-C14
O3-C14-C13
C3-O2-C13
TABLE-3
atoms of different two THEDE molecules. From Table-3, the
hydrogen bond length of H3···O31 is 1.91 Å and the bond angle
of O3-H3···O31 is 163.0º.
HYDROGEN BOND LENGTHS (Å)
AND BOND ANGLES (º) FOR THEDE
D-H (Å)
D-H···A
H···A (Å) D···A (Å) <(DHA)(º)
1.91 2.7217(10) 163.0
Direct esterification method: p-Toluenesulfonic acid,
which is a frequently-used catalyst for the esterification reaction
between gallic acid and lower alcohols1, was used for the
synthesis of the three gallates. Unfortunately, no expected
product was obtained. 2-Methylol benzimidazole and THEDE
did not react with gallic acid under our conditions. But, it is
interesting that we got a product from the direct esterification
reaction between 5-methyl-2-nitro-imidazole-1-ethanol and
gallic acid. The X-ray single-crystal diffraction was used to
characterize its structure. A summary of the crystal data and
structure refinement parameters for the compound of 5-methyl-
2-nitro-imidazole-1-ethanol and gallic acid (CMG) are given
in Table-4. The crystal structure and crystal packing diagram
are shown in Fig. 2. The selected bond lengths and bond angles
are listed in Table-5. The data in Table-6 are the intermolecular
and intramolecular hydrogen bonds and Fig. 3 shows the three-
dimension network constructed by hydrogen bonds.
O3-H3···O31
0.84
Symmetry code:1-X,-1/2+Y, 1/2-Z.
It can be seen from Fig. 2 that the obtained product is not
an ester formed by 5-methyl-2-nitro-imidazole-1-ethanol and
gallic acid, but an equimolar complex of them. It should be
noticed that the complex is not a simple mixture of 5-methyl-
2-nitro-imidazole-1-ethanol and gallic acid.As shown in Fig. 2,
the hydrogen atom of carboxyl group of gallic acid has moved
to the imidazole ring of 5-methyl-2-nitro-imidazole-1-ethanol
and a N2-H bond was formed.
However, this move did not significantly change the prop-
erties of the carboxyl group of gallic acid and the imidazole.
As shown in Table-5, the bond lengths of O7-C13 and O8-
C13 is 1.210(3) Å and 1.317(3) Å, respectively, which shows
that the former still keep the property of C=O double bond
and the latter is still a C-O single bond. That means that,
Fig. 1. Molecular structure and crystal packing diagram of THEDE

Vol. 26, No. 2 (2014) Synthesis andAntimicrobialActivity of Three Gallates Containing Imidazole, Benzimidazole and Triclosan Units 517
TABLE-4
CRYSTAL DATA AND STRUCTURE REFINEMENT DETAILS FOR CMG
Empirical formula
Temperature (K)
C13H16N3O8
293.15
Formula weight
Crystal system
342.29
Monoclinic
Space group
α (º), β (º), γ (º)
Z, ρcalc (mg mm-3)
Crystal size (mm3)
Index ranges
P21/c
a (Å), b (Å), c (Å)
14.8163(7), 7.1017(4), 14.6837(7)
1495.15(13)
90.00, 104.599(5), 90.00
4, 1.521
Volume (Å3)
µ (mm-1), F(000)
0.128, 716
5.74-52.74º
6336
3057/0/234
0.40 × 0.40 × 0.35
2θ range for data collection
Reflections collected
Data/restraints/parameters
Final R indexes [I > 2σ(I)]
Largest diff. peak/hole (e Å-3)
-18 ≤ h ≤ 12, -7 ≤ k ≤ 8, -17 ≤ l ≤ 18
3057[R(int) = 0.0179]
1.037
Independent reflections
Goodness-of-fit on F2
Final R indexes [all data]
R1 = 0.0639, wR2 = 0.1769
0.515/-0.691
R1 = 0.0836, wR2 = 0.1956
TABLE-5
SELECTED BOND LENGTHS (Å) AND ANGLES (º) FOR CMG
Bond
O3-C6
O4-C7
O5-C8
O6-C9
Length (Å)
1.417(4)
1.358(3)
1.361(3)
1.367(3)
Bond
O8-C13
N1-C1
N1-C2
N2-C1
Length (Å)
1.317(3)
1.379(4)
1.352(4)
1.359(4)
Bond
N2-C3
C2-C3
N3-C1
C11-C13
Length (Å)
1.344(4)
1.320(4)
1.419(4)
1.487(4)
O7-C13
1.210(3)
–
Angle
–
(º)
–
Angle
–
(º)
Angle
(º)
C2-N1-C1
C3-N2-C1
O1-N3-C1
O2-N3-O1
O2-N3-C1
105.1(2)
108.7(3)
118.9(3)
123.4(3)
117.6(3)
C3-C2-N1
C2-C3-N2
O3-C6-C5
O4-C7-C8
O5-C8-C7
111.5(2)
107.1(2)
111.6(2)
114.8(2)
121.1(2)
O5-C8-C9
O6-C9-C8
O7-C13-O8
O7-C13-C11
O8-C13-C11
118.6(2)
116.3(2)
122.2(3)
123.2(3)
114.6(2)
N2-C1-N1
107.6(2)
–
–
–
–
Fig. 3. Three-dimension network constructed by hydrogen bonds for CMG
although the carboxyl group of gallic acid lost its hydrogen
atom, it did not change into a carboxylate. Similarly, in the
imidazole ring, the bond lengths of N2-C1 and N2-C3 are
1.359(4) and 1.344(4), respectively, which shows that the
N2-C1 still be a double bond.
The crystal structure analysis (Table-6) shows intramo-
lecular and intermolecular hydrogen bonds in the unit cell.
There is intramolecular hydrogen bonding between the
hydroxy-oxygen atoms (O4, O5) of gallic acid and nitro-oxygen
atoms of 5-methyl-2-nitro-imidazole-1-ethanol. Thereinto, the
hydrogen bond lengths of H5···O1 and H5···O4 are 2.12(4)
and 2.27(3) Å, respectively and the bond angles of O5-H5···O1
and O5-H5···O4 are 157(4) and 116(3)º, respectively. Besides,
there exist intermolecular bonding between the hydroxy-oxygen
atoms (O6, O4, O53, O63) and (O71) carboxy-oxygen atom of
gallic acid and hydroxy-oxygen atoms (O3, O32) of 5-methyl-
2-nitro-imidazole-1-ethanol. The bond lengths of H6···O71,
H4···O32, H3···O53 and H3···O63 are 1.79(5), 1.65(5), 1.98(4)
Fig. 2. Molecular structure and crystal packing diagram of CMG

518 Wang et al.
Asian J. Chem.
TABLE-6
HYDROGEN BOND LENGTHS (Å)
AND BOND ANGLES (º) FOR CMG
in Table-8. The data in Table-9 are the intermolecular and in-
tramolecular hydrogen bonds.
D-H (Å)
D-H···A
H···A (Å) D···A (Å) <(DHA) (º)
O6-H6···O71
O5-H5...O1
O5-H5...O4
O4-H4...O32
O3-H3...O53
O3-H3...O63
0.93(5)
0.73(4)
0.73(4)
1.00(4)
0.86(4)
0.86(4)
1.79(5)
2.12(4)
2.27(3)
1.65(5)
1.98(4)
2.45(4)
2.705(3)
2.808(3)
2.668(3)
2.640(3)
2.813(3)
3.009(3)
166(4)
157(4)
116(3)
174(4)
162(4)
123(3)
Symmetry code: 1-X, 1-Y,-Z; 21-X, 1-Y, 1-Z; 31-X, 1/2+Y, 1/2-Z.
and 2.45(4) Å, respectively; the bond angles of O6-H6···O71,
O4-H4···O32,O3-H3···O53 andO3-H3···O63 are 166(4), 174(4),
162(4) and 123(3)º, respectively. As shown in Fig. 3, a three-
dimension network is formed because of the existence of a lot
of intramolecular and intermolecular hydrogen bonds in the
complex, which are also the reason that we can get the
complex. On the contrary, the fact that there is no complex
between the other two alcohols (2-methylol benzimidazole and
THEDE) and gallic acid is perhaps due to the lack of enough
intramolecular and intermolecular hydrogen bonds.
Indirect esterification method: As shown in Scheme-I,
the indirect esterification method was used to synthesize the
three gallates. The three phenolic hydroxyl groups of gallic
acid were firstly protected by three acetyls, then, the obtained
trisacetyl gallic acid (TAGA) reacted with sulfoxide chloride
to synthesize the trisacetyl-galloyl chloride (TAGC) which can
easily react with alcohols to get the trisacetyl gallates. Finally,
hydrazine hydrate was used to remove the protecting groups
(acetyls) and the expected gallates were obtained successfully.
This route is suitable not only for lower alcohols but also for
higher or complicated alcohols, although there are many
reaction steps. The data of elemental analysis, IR, 1H and 13C
NMR for the obtained products in experimental part prove
that these compounds are exactly the gallates that we expected.
For the gallate of 2-methylol benzimidazole, compound
2, ethyl acetate was used as the solvent to prepare crystals for
the X-ray single-crystal diffraction analysis. The solution was
placed in room temperature. After two weeks of slow volatil-
ization, white crystals were obtained for the crystal structure
determination. A summary of the crystal data and structure
refinement parameters for the compound 2 are given in Table-
7. The crystal structure and crystal packing diagram are shown
in Fig. 4. The selected bond lengths and bond angles are listed
Fig. 4. Molecular structure and crystal packing diagram of the compound
2
As shown in Fig. 4, there is indeed a ester bond resulted
from the esterification reaction between gallic acid and 2-methylol
benzimidazole, which further prove that our indirect route is
feasible. It can be seen from Table-8 that, in the ester bond,
the bond lengths of O1-C9 and O2-C9 are 1.212(3) and
1.346(3) Å, respectively; the bond angles of O1-C9-O2, O1-
C9-C10, O2-C9-C10 and C9-O2-C8 are 121.9(2), 124.7(2),
113.4(2) and 114.88(18), respectively.
TABLE-7
CRYSTAL DATA AND STRUCTURE REFINEMENT DETAILS FOR THE COMPOUND 2
Empirical formula
Temperature (K), Wavelength (Å)
Space group
C19H20N2O8
293.15, 0.7107
P-1
Formula weight
Crystal system
a (Å), b (Å), c (Å)
Volume (Å3)
404.37
Triclinic
7.5420(3), 9.6464(5), 14.5325(7)
974.37(8)
73.316(4), 83.250(4), 74.361(4)
2, 1.378
0.38 × 0.15 × 0.10
-8 ≤ h ≤ 8, -11 ≤ k ≤ 10, -17 ≤ l ≤ 17
3432 (0.0179)
α (º), β (º), γ (º)
µ (mm-1, F(000)
0.109, 424
5.86-50
7347
3432/0/277
Z, ρcalc (mg mm-3)
Crystal size (mm3)
2θ range for data collection
Reflections collected
Data/restraints/parameters
Absorption correction
Refinement method
Final R indexes [I > 2σ (I)]
Largest diff. peak/hole (e Å-3)
Index ranges
Independent reflections (Rint)
Observed reflections
Max. and Min. transmission
Goodness-of-fit on F2
Final R indexes [all data]
2404
1.0 and 0.78813
1.035
multi-scan
Full-matrix least-squares on F2
R1 = 0.0589, wR2 = 0.1435
0.410/-0.299
R1 = 0.0878, wR2 = 0.1620

Vol. 26, No. 2 (2014) Synthesis andAntimicrobialActivity of Three Gallates Containing Imidazole, Benzimidazole and Triclosan Units 519
TABLE-8
SELECTED BOND LENGTHS (Å) AND ANGLES (º) FOR THE COMPOUND 2
Bond
O1-C9
O2-C8
O2-C9
O3-C12
Angle
Length (Å)
1.212(3)
1.436(3)
1.346(3)
1.364(3)
(º)
Bond
N1-C1
N1-C7
N2-C2
O4-C13
Angle
Length (Å)
1.392(3)
1.309(3)
1.379(4)
1.360(3)
(º)
Bond
N2-C7
C7-C8
C9-C10
O5-C14
Angle
Length (Å)
1.352(3)
1.483(4)
1.470(3)
1.369(3)
(º)
C9-O2-C8
C7-N1-C1
C7-N2-C2
N1-C7-N2
114.88(18)
105.1(2)
107.8(2)
112.4(2)
N1-C7-C8
N2-C7-C8
O2-C8-C7
–
123.0(2)
124.6(2)
107.65(19)
–
O1-C9-O2
O1-C9-C10
O2-C9-C10
–
121.9(2)
124.7(2)
113.4(2)
–
round yeast, there are significantly synergistic effects because
the inhibition zones of 1 are bigger than that of its two original
compounds.
For compound 2, it exhibits good antibacterial activity
that is better than that of its original compounds and has mode-
rate inhibitory effect against fungi which is between the gallic
acid and 2-methylol benzimidazole. These results indicate that
the two antimicrobial units in compound 2 have obviously
synergistic inhibitory effect against bacteria and additive effect
against fungi.
For compound 3, the two antimicrobial units (triclosan
and gallic structures) display obviously additive inhibitory
effect against all the tested microbes. But, compound 3 exhi-
bits the best antimicrobial activities because, compared with
1 and 2, its diameters of inhibition zones against all the tested
stains are the biggest.
To sum up, the introduction of antimicrobial units has
obvious effect on the antimicrobial activities of gallates. To
obtain desired gallates, it is the key to choose properly antimi-
crobial units.
TABLE-9
HYDROGEN BOND LENGTHS (Å) AND
BONDANGLES (º)FORTHE COMPOUND 2
D-H···A
D-H(Å)
H···A(Å)
D···A(Å)
∠(DHA)(º)
O3-H3···O8
O4-H4···O81
O5-H5···O4
O5-H5···N12
O8-H8C···O13
O8-H8D···O54
N2-H2···O6
0.82
0.93(4)
0.82
1.98
1.92(4)
2.31
2.781(3)
2.788(3)
2.743(3)
2.691(3)
2.815(3)
2.807(4)
2.857(4)
164.4
156(3)
113.2
0.82
1.97
146.2
0.87(4)
0.86(4)
0.86
1.95(4)
1.96(4)
2.09
173(4)
167(4)
147.4
Symmetry code: 12-X,-Y,-Z; 21+X,-1+Y,+Z; 31-X,1-Y,-Z; 41-X,-Y,-Z.
Furthermore, in the crystals of compound 2, there are a
water molecule and an ethyl acetate molecule. As shown in
Table-9, in the unit cell, there exist intermolecular hydrogen
bonds between the hydroxy-oxygen atoms (O3, O4, O5),
ester-oxygen atom (O13) and nitrogen atoms (N12, N2) of
imidazole ring in the compound 2 molecule, the water-oxgen
atom (O8) and ester-oxygen atom (O6) in ethyl acetate mole-
cule. There into, the hydrogen bond lengths of H3···O8,
H4···O81, H5···O4 and H5···N12 are 1.98 Å, 1.92(4) Å, 2.31 Å
and 1.97 Å, respectively and the bond angles of O3-H3···O8,
O4-H4···O81, O5-H5···O4 and O5-H5···N12 are 164.4, 156(3),
113.2 and 146.2º, respectively. The hydrogen bond lengths of
H8C···O13, H8D···O54 and H2···O6 are 1.95(4) Å, 1.96(4) Å
and 2.09 Å, respectively and the bond angles of O8-H8C···O13,
O8-H8D···O54 and N2-H2···O6 are 173(4), 167(4) and 147.4º,
respectively.
Antimicrobial activity: The in vitro antimicrobial prop-
erties of the new gallates and their original compounds were
evaluated against bacteria, yeast and moulds and the obtained
results are reported in Table-9. For compound 1, its inhibition
zones against bacteria is not as big as that of 5-methyl-2-
nitro-imidazole-1-ethanol but bigger than that of gallic acid,
which shows that the two units have an additive effect against
tested bacteria. However, for fungi, especially for Viscous red
Conclusion
In summary, for the synthesis of the three new gallates
containing the antimicrobial units of imidazole, benzimidazole
and triclosan, respectively, the direct esterification method,
where p-toluenesulfonic acid was chosen as the catalyst, is
not feasible. With regard to the direct esterification reaction
of 5-methyl-2-nitro-imidazole-1-ethanol and gallic acid, the
obtained product is just a special complex of them where the
existence of a lot of intramolecular and intermolecular hydrogen
bonds plays a key role for its stabilization. On the contrary,
the indirect esterification method shown in Scheme-I can
successfully prepare the designed gallates. The synthesized
gallates shows different inhibitory effect against different tested
microbes, which is mainly decided by the introduced antimi-
crobial units. Synergistic or additive inhibitory effects are found
TABLE-10
DIAMETERS OF INHIBITION ZONES OF THREE GALLATES AND THEIR ORIGINAL COMPOUNDS (mm)
Escherichia coli
Staphylococcus aureus
Viscous red round yeast
Aspergillus niger
Penicillium citrinum
GA
MNIE
1
MB
2
Triclosan
3
32.25
37.70
34.54
32.41
36.07
58.85
38.03
33.51
43.55
35.46
25.71
28.78
53.34
38.11
23.53
23.75
30.26
30.03
28.22
45.91
33.16
22.88
23.13
23.41
23.85
23.80
32.70
28.74
22.63
22.66
22.67
23.30
22.66
30.96
25.46
GA: gallic acid; MNIE: 5-methyl-2-nitro-imidazole-1-ethanol; MB: 2-methylol benzimidazole.

520 Wang et al.
Asian J. Chem.
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ACKNOWLEDGEMENTS
The project is financially supported by the National
Science Foundation of China (No. 21106088) and the Ph. D.
Programs Foundation of Ministry of Education of China (No.
20110181120079).
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