Efficient synthesis and in vitro antifungal activity of 1H-benzimidazol-1-yl acetates/propionates containing 1H-1,2,4-triazole moiety

Article abstract of DOI:10.1016/j.cclet.2012.10.024

A series of novel 1H-benzimidazol-1-yl acetates and 1H-benzimidazol-1-yl propionates containing 1H-1,2,4-triazole moiety were synthesized under microwave irradiation by multi-step reactions, in yields of 87-94%. Their in vitro antifungal activities against Botrytis cinerea and Sclerotinia sclerotiorum were evaluated by mycelial growth rate method. All the target compounds exhibit high activities against B. cinerea with the EC₅₀ values of 7.96-21.74 μg/mL, higher than that of carbendazim.

Full text of DOI:10.1016/j.cclet.2012.10.024

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 1381–1384
www.elsevier.com/locate/cclet
Efficient synthesis and in vitro antifungal activity
of 1H-benzimidazol-1-yl acetates/propionates
containing 1H-1,2,4-triazole moiety
*
Pei Zhi Zhang, Shao Fang Zhou, Tian Ren Li, Lin Jiang
College of Chemistry and Material Science, Shandong Agricultural University, Tai’an 271018, China
Received 26 September 2012
Available online 16 November 2012
Abstract
A series of novel 1H-benzimidazol-1-yl acetates and 1H-benzimidazol-1-yl propionates containing 1H-1,2,4-triazole moiety
were synthesized under microwave irradiation by multi-step reactions, in yields of 87–94%. Their in vitro antifungal activities
against Botrytis cinerea and Sclerotinia sclerotiorum were evaluated by mycelial growth rate method. All the target compounds
exhibit high activities against B. cinerea with the EC50 values of 7.96–21.74 mg/mL, higher than that of carbendazim.
# 2012 Lin Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Benzoimidazole; 1,2,4-Triazole; Synthesis; Antifungal activity
Benzimidazole is an important heterocycle containing two nitrogen atoms, and its derivatives exhibit a broad
spectrum of biological activities, such as antifungal, antibacterial, antiviral, antitumor, and antiparasitic activities [1–
5]. Thus, benzimidazole derivatives are widely used in agriculture and pharmaceuticals. For example, approximately
twenty benzimidazole fungicides including carbendazim, benomyl and thiabendazole have been developed. Due to the
high efficiency, broad spectrum and good systemic property, many of this series are still used in the fungicide market
[6]. However, owing to the increased resistance of many fungal pathogens, their antifungal activities are significantly
reduced. Therefore, it is necessary to develop some novel benzimidazole compounds with low resistance and high
activity.
On the other hand, 1,2,4-triazole derivatives display antimicrobial, antifungal, antitumor, anti-inflammatory, and
plant growth-regulating activities [7–11], and therefore has been received considerable attention. Up to date, more
than thirty 1,2,4-triazole derivatives have been successfully developed commercial agricultural and medical
fungicides [12,13], e.g. tebuconazole, flusilazole and anastrozole (Fig. 1). Among these fungicide molecules, the
1,2,4-triazole ring and other groups are connected though a methylene or a methenyl, which suggests that the (1,2,4-
triazol-1-yl)methyl/methenyl moiety plays an important role in keeping antifungal activity. To the best of our
knowledge, the benzimidazole compounds containing the (1,2,4-triazol-1-yl)methyl moiety have not been reported.
Motivated by these findings, herein we introduced a (1,2,4-triazol-1-yl)methyl into the benzimidazole ring. Moreover,
* Corresponding author.
E-mail address: jiangl@sdau.edu.cn (L. Jiang).
1001-8417/$ – see front matter # 2012 Lin Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.10.024

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P.Z. Zhang et al. / Chinese Chemical Letters 23 (2012) 1381–1384
Fig. 1. Chemical structures of some commercial triazole fungicides.
in order to improve the penetrability to pathogen cells, we linked an acetate or a propionate group to the 1-position of
the benzimidazole ring. Thus, we designed and synthesized eight novel 2-((1H-1,2,4-triazol-1-yl)methyl)-1H-
benzimidazol-1-yl acetates (4a–d) and 3-(2-((1H-1,2,4-triazol-1-yl)methyl)-1H-benzimidazol-1-yl)propinonates
(5a–d) under microwave irradiation, and evaluated their antifungal activities against two selected funguses.
The target compounds were synthesized following the described procedure in Scheme 1. The key intermediate 1H-
1,2,4-triazol-1-yl acetic acid (1), was prepared from 1H-1,2,4-triazole and methyl chloroacetate referring to the
literature [14]. Compound 1 was treated with o-phenylenediamine (2) in polyphosphoric acid (PPA) under microwave
radiation, followed by adjusting the pH to 9.0 with concentrated NH3ÁH2O, to afford 2-((1H-1,2,4-triazol-1-
yl)methyl)benzimidazole (3) in 87% yield. Finally, 3 was reacted with chloroacetate to yield the target compound 4, or
3 was reacted with acrylate to give the target compound 5. Both the two kinds of reactions were performed in CH3CN
under microwave radiation, using anhydrous K2CO3 as a base and dibenzo-18-crown-6 as a phase transfer catalyst.
Currently, microwave-assisted synthesis as an effective technique is widely used in chemical reactions. Compared
with conventional methods, this technique exhibits many advantages such as higher yield and shorter reaction time
[15,16]. Thus, the reactions were carried out by microwave irradiation, which could smoothly afford the target
compounds 4 and 5 in yields of 87–94%, whereas the products were obtained in yields of 53–85% under the
conventional reflux condition in 4 h. In addition, two ways were employed in the syntheses of the target compounds: 4
was obtained by nucleophilic substitution reaction of 3 with chloroacetate, while 5 was obtained by Michael addition
reaction of 3 with acrylate. However, if 5 was synthesized by the substitution reaction of 3 with 3-chloropropionate, the
yield was fairly low (30–50%). The reason was that 3-chloropropionate displays a lower reaction activity to the N atom
of benzimidazole ring when compared with chloroacetate.
The structures of the target compounds were characterized by IR, NMR, MS and elemental analyses, as shown in
Ref. [17].
In vitro antifungal activity of the target compounds 4 and 5 was evaluated by mycelial growth rate method
according to the literature [18]. Two kinds of funguses, peas Botrytis cinerea and tomato Sclerotinia sclerotiorum,
were used to the test. Carbendazim, a commercial fungicide, was used as the positive control (CK), and sterile water
was used as the blank. The inhibition rate was expressed as the mean of values obtained in three independent
experiments, and the effective concentration (EC50) that inhibited mycelium growth by 50% was obtained. As seen
from Table 1, satisfactory toxicity regression equations were given with the correlation coefficients (r) of
Scheme 1. Reagents and conditions: (i) methyl chloroacetate, anhydrous K2CO3, CH3CN, reflux 6 h; (ii) H2O, reflux 12 h; (iii) PPA, MW. 180 W,
10 min; NH3ÁH2O; (iv) chloroacetate, anhydrous K2CO3, dibenzo-18-crown-6, CH3CN, MW. 180 W, 10 min, (v) acrylate, anhydrous K2CO3,
dibenzo-18-crown-6, CH3CN, MW. 180 W, 10 min.

P.Z. Zhang et al. / Chinese Chemical Letters 23 (2012) 1381–1384
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Table 1
The in vitro antifungal activity of the target compounds 3 and 4.
Entry
R
Botrytis cinerea
Sclerotinia sclerotiorum
Regression equations
r
EC50 (mg/mL)
Regression equations
r
EC50 (mg/mL)
4a
4b
4c
CH3
y = 4.0885x + 0.7168
y = 3.8902x + 0.8483
y = 4.0806x + 0.7926
y = 4.0421x + 0.7163
y = 4.2795x + 0.6036
y = 4.2795x + 0.6036
y = 3.6630x + 1.0806
y = 3.7482x + 1.0928
y = 3.8794x + 1.9462
0.9689
0.9823
0.9611
0.9709
0.9943
0.9669
0.9809
0.9738
0.9746
18.69 Æ 1.27
20.33 Æ 1.31
14.45 Æ 1.16
21.74 Æ 1.34
15.62 Æ 1.19
7.96 Æ 0.90
17.27 Æ 1.24
13.98 Æ 1.14
30.15 Æ 1.60
y = 4.4775x + 0.3502
y = 4.6581x + 0.2264
y = 4.1568x + 0.5610
y = 4.1257x + 0.6825
y = 3.8573x + 0.6522
y = 4.0346x + 0.7849
y = 4.1708x + 0.5371
y = 4.5170x + 0.4133
y = 4.3606x + 0.9256
0.9890
0.9807
0.9916
0.9833
0.9935
0.9919
0.9907
0.9749
0.9875
31.04 Æ 1.49
32.37 Æ 1.51
31.84 Æ 1.50
19.10 Æ 1.28
46.51 Æ 1.75
16.98 Æ 1.23
34.99 Æ 1.54
14.74 Æ 1.67
4.91 Æ 0.69
C2H5
n-C4H9
CH2C6H5
CH3
4d
5a
5b
5c
C2H5
n-C4H9
CH2C6H5
5d
CK
0.9611–0.9943. On the other hand, the EC50 values of the target compounds against B. cinerea were ranged from 7.96
to 21.74 mg/mL, less than that of carbendazim, which means compounds 4 and 5 possess high antifungal activities to
this kind of pathogen; among them, 5b exhibits the highest activity. Compared with carbendazim, however, the target
compounds showed larger EC50 values (14.74–46.51 mg/mL) against S. sclerotiorum, suggesting that their activities
are lower than that of carbendazim. In addition, it was also found from Table 1, to the same pathogen, there was no
significant difference in EC50 values between compounds 4 and 5, indicating that 1H-benzimidazol-1-yl acetate and
propionate analogue display the similar antifungal activity.
Acknowledgment
This project was supported by Shandong Province Natural Science Foundation (No. ZR2009BM044).
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[17] Analytic data for target compounds. 4a: white solid, yield: 91%; mp: 173.4–175.2 8C; 1H NMR (400 Hz, CDCl3): d 3.74 (s, 3H), 5.18 (s, 2H),
5.68 (s, 2H), 7.27–7.78 (m, 4H), 7.93 (s, 1H), 8.28 (s, 1H); IR (KBr): y 1736, 1229 cmÀ1; ESI-MS m/z: 272.5 (M+H)+. Anal. Calcd. for
C13H13N5O2: C 57.56, H 4.83, N 25.82; found: C 57.84, H 5.07, N25.49. 4b: white solid, yield: 94%; mp: 177.8–179.1 8C; 1H NMR (400 Hz,
CDCl3): d 1.26 (t, 3H, J = 7.2 Hz), 4.20 (q, 2H, J = 7.2 Hz), 5.15 (s, 2H), 5.68 (s, 2H), 7.27–7.34 (m, 4H), 7.93 (s, 1H), 8.28 (s, 1H); IR (KBr): y
1735, 1220 cmÀ1; ESI-MS m/z: 286.4 (M+H)+. Anal. Calcd. for C14H15N5O2: C 58.94, H 5.30, N 24.55; found: C 59.22, H 5.08, N 24.35. 4c:
white solid, yield: 93%; mp: 125.4.4–126.1 8C; 1H NMR (400 Hz, CDCl3): d 0.88 (t, 3H, J = 7.2 Hz), 1.24–1.33 (m, 2H), 1.54–1.69 (m, 2H),
4.13 (t, 2H, J = 7.2 Hz), 5.15 (s, 2H), 5.68 (s, 2H), 7.26–7.79 (m, 4H), 7.93 (s, 1H), 8.27 (s, 1H); IR (KBr): y 1731, 1217 cmÀ1; ESI-MS m/z:
314.6 (M+H)+. Anal. Calcd. for C16H19N5O2: C 61.33, H 6.11, N 22.35; found: C 61.65, H 6.04, N 22.63. 4d: white solid, yield: 94%; mp:
152.4–153.6 8C; 1H NMR (400 Hz, CDCl3): d 5.17 (s, 2H), 5.20 (s, 2H), 5.64 (s, 2H), 7.26–7.79 (m, 9H), 7.83 (s, 1H), 8.23 (s, 1H); IR (KBr): y
1725, 1203 cmÀ1; ESI-MS m/z: 348.4 (M+H)+. Anal. Calcd. for C19H17N5O2: C 65.69, H 4.93, N 20.16; found: C 65.41, H 4.75, N 20.48. 5a:
pale yellow oil, yield: 89%; 1H NMR (400 Hz, CDCl3): d 2.84 (t, 2H, J = 7.2 Hz), 3.60 (s, 3H), 4.63 (t, 2H, J = 7.2 Hz), 5.88 (s, 2H), 7.18–7.61

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P.Z. Zhang et al. / Chinese Chemical Letters 23 (2012) 1381–1384
(m, 4H), 7.95 (s, 1H), 8.69 (s, 1H); IR (CCl4) y: 1735, 1208 cmÀ1; ESI-MS m/z: 286.5 (M+H)+. Anal. Calcd. for C14H15N5O2: C 58.94, H 5.30,
1
N 24.55; found: C 58.64, H 5.62, N 24.26. 5b: yellow oil, yield: 91%; H NMR (400 Hz, CDCl3): d 1.20 (t, 3H, J = 7.2 Hz), 2.82 (t, 2H,
J = 6.4 Hz), 4.12 (q, 2H, J = 7.2 Hz), 4.64 (t, 2H, J = 6.4 Hz), 5.84 (s, 2H), 7.28–7.95 (m, 4H), 7.95 (s, 1H), 8.32 (s, 1H); IR (CCl4) y: 1732,
1206 cmÀ1; ESI-MS m/z: 300.5 (M+H)+. Anal. Calcd. for C15H17N5O2: C 60.19, H 5.72, N 23.40; found: C 60.39, H 5.96, N 23.72. 5c: yellow
oil, yield: 87%; 1H NMR (400 Hz, CDCl3): d 0.88 (t, 3H, J = 7.0 Hz), 1.24–1.33 (m, 2H), 1.50–1.57 (m, 2H), 2.83 (t, 2H, J = 7.2 Hz), 4.05 (t,
2H, J = 7.0 Hz), 4.64 (t, 2H, J = 7.2 Hz), 5.84 (s, 2H), 7.28–7.77 (m, 4H), 7.94 (s, 1H), 8.32 (s, 1H); IR (CCl4) y: 1731, 1191 cmÀ1; ESI-MS m/
z: 328.5 (M+H)+. Anal. Calcd. for C17H21N5O2: C 62.37, H 6.47, N 21.39; found: C 62.45, H 6.18, N 21.07. 5d: white solid, yield: 92%; mp:
152.4–153.6 8C; 1H NMR (400 Hz, CDCl3) d: 2.88 (t, 2H, J = 6.4 Hz), 4.65 (t, 2H, J = 6.4 Hz), 5.08 (s, 2H), 5.76 (s, 2H), 7.33–7.78 (m, 4H),
7.91 (s, 1H), 8.27 (s, 1H); IR (KBr) y: 1728, 1187 cmÀ1; ESI-MS m/z: 362.5 (M+H)+. Anal. Calcd. for C20H19N5O2: C 66.47, H 5.30, N 19.38;
found: C 66.28, H 5.49, N 19.13.
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