Synthesis and antifungal activity evaluation of new heterocycle containing amide derivatives

Article abstract of DOI:10.1080/14786419.2015.1041137

A series of heterocycle containing amide derivatives (1-28) were synthesised by the combination of acyl chlorides (1a, 2a) and heterocyclic/homocyclic ring containing amines, and their in vitro antifungal activity was evaluated against five plant pathogenic fungi, namely Gibberella zeae, Helminthosporium maydis, Rhizoctonia solani, Botrytis cinerea and Sclerotinia sclerotiorum. Results of antifungal activity analysis indicated that some of the products showed good to excellent antifungal activity, as compound 2 showed excellent activity against G. zeae and R. solani and potent activity against H. maydi, B. cinerea and S. sclerotiorum, and compounds 1, 8 and 10 also displayed excellent antifungal potential against H. maydi, B. cinerea and S. sclerotiorum and good activity against R. solani when compared with the standard carbendazim.

Full text of DOI:10.1080/14786419.2015.1041137

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Synthesis and antifungal activity
evaluation of new heterocycle
containing amide derivatives
Xuesong Wanga, Sumei Gaoa, Jian Yanga, Yang Gaoa, Ling Wanga &
Xiaorong Tanga
a School of Physics and Chemistry, Xihua University,
Chengdu610039, P.R. China
Published online: 03 Jul 2015.
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To cite this article: Xuesong Wang, Sumei Gao, Jian Yang, Yang Gao, Ling Wang & Xiaorong
Tang (2015): Synthesis and antifungal activity evaluation of new heterocycle containing
amide derivatives, Natural Product Research: Formerly Natural Product Letters, DOI:
10.1080/14786419.2015.1041137
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Natural Product Research, 2015
http://dx.doi.org/10.1080/14786419.2015.1041137
Synthesis and antifungal activity evaluation of new heterocycle containing
amide derivatives
Xuesong Wang, Sumei Gao, Jian Yang, Yang Gao, Ling Wang and Xiaorong Tang*
School of Physics and Chemistry, Xihua University, Chengdu 610039, P.R. China
(Received 9 January 2015; final version received 3 April 2015)
A series of heterocycle containing amide derivatives (1–28) were synthesised by the
combination of acyl chlorides (1a, 2a) and heterocyclic/homocyclic ring containing
amines, and their in vitro antifungal activity was evaluated against five plant pathogenic
fungi, namely Gibberella zeae, Helminthosporium maydis, Rhizoctonia solani, Botrytis
cinerea and Sclerotinia sclerotiorum. Results of antifungal activity analysis indicated
that some of the products showed good to excellent antifungal activity, as compound 2
showed excellent activity against G. zeae and R. solani and potent activity against
H. maydi, B. cinerea and S. sclerotiorum, and compounds 1, 8 and 10 also displayed
excellent antifungal potential against H. maydi, B. cinerea and S. sclerotiorum and good
activity against R. solani when compared with the standard carbendazim.
Keywords: synthesis; amide derivatives; plant pathogenic fungi; antifungal activity
1. Introduction
Amide fungicides have played an important role in the history of pesticide science. The first
amide fungicide, carboxin, was discovered in 1966 (Schmeling & Kulka 1966). After this,
numerous amide fungicides with novel structures have successively emerged such as benodanil,
furcarbanil and mebenil (Yang et al. 2008). Presently, amide fungicides are extensively used to
control diseases caused by plant pathogenic fungi and bacteria (Raffa et al. 2002; Narayana et al.
2004; Wen et al. 2005; Priya et al. 2006; Ertan et al. 2007). Fungicides inhibit the growth of
pathogens and cause their eventual death by interfering in pathogen’s respiration (Leroux 1996;
Huang 2004). Furthermore, amide fungicides are usually efficient, safe and environmental
friendly (Smiley et al. 1990; Kataria et al. 1993).
Heterocycle compounds are very important for the development of fungicides. They have
various bioactivities including antifungal and antibacterial (Raffa et al. 1999; El-masry et al.
*Corresponding author. Email: tangxiaorong0901@163.com
q 2015 Taylor & Francis

2
X. Wang et al.
2000; Charris et al. 2002; Mahran et al. 2003; Sundari & Valliappan 2004). When they are used
as fungicides, they usually possess the following advantages: good selectivity (Xu et al. 2007),
excellent activity (Nakib et al. 1991; Laldhar et al. 1996; Ganesabaskaran et al. 2006), low
toxicity (Huang et al. 2003) and special mode of action (Kuhn 1989). Therefore, cyclic
compounds have huge potential in the agricultural chemistry field.
In this study, a series of heterocycle containing amides have been designed in accordance
with the principle of connecting bioactive substructures together. Their syntheses were based on
amine derivatives and furan-2-carboxylic acid or thiophene-2-carboxylic acid to find new
fungicides or lead compounds with high efficacy and low toxicity as well as safety to non-target
organisms. So, amides 1–28 were synthesised, and their antifungal activities against Gibberella
zeae, Helminthosporium maydis, Rhizoctonia solani, Botrytis cinerea and Sclerotinia
sclerotiorum were also evaluated.
2. Results and discussion
2.1. Chemistry
The acyl chlorides 1a and 2a used in the synthesis of amide derivatives were synthesised by the
reaction described in Figure 1. They were used without further purification in the subsequent
amides synthesis reactions, which are shown in Figure 2.
In the synthesis of compounds 1–22, the ratio of the acyl chlorides and amine derivatives
was 1:1, while in the synthesis of compounds 23–28, the ratio was 2:1. Compounds 9, 15 and 17
were obtained as liquid, whereas the rest were obtained as solid. Compounds 23–28 were re-
crystallised with the mixture of dimethyl sulphoxide (DMSO) and water (15:1), and the rest
solids were re-crystallised with anhydrous ethanol. The products are listed in Table 1. To date,
compounds 3, 6, 21–22 and 24–28 have not been reported.
2.2. Antifungal activity
Compared with the efficient fungicide carbendazim, the synthesised compounds 1–28 were
evaluated for their antifungal potential against G. zeae, H. maydis, R. solani, B. cinerea and S.
sclerotiorum fungi, and the activity results are shown in Table 2. Compounds 1–4, 6, 8 and 10
showed good to excellent anti-fungal activity. Among them, compound 2 showed the best
antifungal activity against all the five under examine fungi such as it showed potent activity
against H. maydis, B. cinerea and S. sclerotiorum whereas moderate activity against G. zeae and
R. solani when compared with the standard carbendazim. Compound 1 exhibited potent activity
against H. maydis and excellent activity against G. zeae, R. solani, B. cinerea and
S. sclerotiorum as compared to the standard carbendazim. Compounds 8 and 10 displayed
remarkable activity against H. maydis and B. cinerea, whereas they displayed good activity
against G. zeae and S. sclerotiorum as compared to carbendazim.
The activity results indicated that thiazole, benzothiazole, benzyl and 2-phenylethyl ring in
products possibly contributed to the anti-fungal activity because the compounds containing such
ring structures indicated better activity. Results further showed that when the benzothiazole
Figure 1. Preparation of acyl chlorides (1a, 2a).

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3
Table 1. Synthesised heterocycle containing amide derivatives.
Compound
X
S
R1
R2 Compound
X
O
R1
R2
1
15
2
O
O
S
16
17
18
19
20
21
22
23
24
25
26
27
28
S
3
O
S
4
5
O
S
O
S
6
7
O
S
O
S
8
9
O
S
O
S
10
11
12
13
14
O
S
O
S
O
S
O
S
rings have a substituent at position-6, their antifungal activity decreased remarkably irrespective
of whether the substituent was electron denoting or electron withdrawing. This possibly implies
that when the benzothiazole ring has an appropriate electronic density, the compound could have
good activity. The activity results further showed that the products having sulphur atom in the
five-membered ring had better activity than those having oxygen atom in the five-membered
ring. The comparison of activity results of compounds 7–10 indicated that the methylene added
to the carbon chains did not have a great influence on the activity.

4
X. Wang et al.
Table 2. Anti-fungal activity results of compounds 1–28 at 100 mg/L.
Inhibition of growtha (%)
Compound
G. zeae
H. maydis
R. solani
B. cinerea
S. sclerotiorum
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
93.1 ^ 2.3
100.0 ^ 0
35.1 ^ 1.9
47.2 ^ 2.4
33.3 ^ 1.2
56.1 ^ 2.7
35.5 ^ 1.8
71.4 ^ 1.5
37.0 ^ 1.2
73.1 ^ 1.9
43.2 ^ 2.3
36.2 ^ 1.0
44.1 ^ 1.5
38.6 ^ 1.3
41.2 ^ 1.1
39.3 ^ 1.4
37.3 ^ 2.1
36.2 ^ 1.7
44.2 ^ 2.3
38.4 ^ 1.5
40.0 ^ 2.0
35.5 ^ 2.2
31.8 ^ 2.3
29.3 ^ 1.8
32.5 ^ 1.2
26.9 ^ 1.9
29.2 ^ 1.8
31.3 ^ 2.3
100.0 ^ 0
93.2 ^ 1.8
100.0 ^ 0
75.3 ^ 1.4
78.6 ^ 2.3
45.5 ^ 1.9
80.6 ^ 1.3
48.6 ^ 2.2
91.8 ^ 2.1
48.4 ^ 1.3
92.7 ^ 1.5
43.3 ^ 2.7
44.6 ^ 2.5
43.1 ^ 1.3
41.5 ^ 2.2
42.4 ^ 1.7
34.6 ^ 2.3
25.4 ^ 2.3
43.5 ^ 3.2
37.5 ^ 1.6
41.2 ^ 1.9
38.8 ^ 1.2
29.6 ^ 1.3
31.3 ^ 1.6
43.9 ^ 1.1
34.5 ^ 1.9
37.3 ^ 2.5
40.8 ^ 1.2
43.2 ^ 1.7
87.5 ^ 1.6
83.4 ^ 1.7
100.0 ^ 0
32.5 ^ 2.5
48.1 ^ 1.8
38.6 ^ 1.1
49.7 ^ 2.5
32.6 ^ 2.5
57.5 ^ 2.9
33.3 ^ 2.0
59.6 ^ 2.1
21.0 ^ 1.3
26.4 ^ 1.3
28.5 ^ 2.4
23.4 ^ 1.7
30.3 ^ 2.3
25.0 ^ 1.5
23.6 ^ 1.9
24.6 ^ 3.0
22.1 ^ 2.1
28.0 ^ 1.4
23.4 ^ 1.5
29.1 ^ 2.4
26.6 ^ 2.8
27.7 ^ 1.5
26.8 ^ 2.3
22.0 ^ 2.3
31.2 ^ 1.6
29.2 ^ 3.1
100.0 ^ 0
90.6 ^ 1.4
100.0 ^ 0
56.0 ^ 1.6
57.3 ^ 2.2
44.4 ^ 2.1
58.9 ^ 1.1
56.0 ^ 1.2
93.7 ^ 2.4
56.4 ^ 3.1
94.5 ^ 1.8
43.5 ^ 2.1
41.2 ^ 2.6
39.4 ^ 2.3
44.6 ^ 2.4
36.5 ^ 2.0
41.2 ^ 2.4
39.0 ^ 3.1
41.1 ^ 1.4
38.8 ^ 2.5
32.1 ^ 2.3
39.3 ^ 2.5
39.7 ^ 1.9
34.3 ^ 1.4
29.6 ^ 2.5
28.6 ^ 1.4
36.2 ^ 2.8
24.4 ^ 2.0
33.3 ^ 2.9
91.3 ^ 1.9
91.5 ^ 2.1
100.0 ^ 0
60.6 ^ 2.3
65.5 ^ 3.1
51.6 ^ 3.0
58.3 ^ 1.5
52.3 ^ 2.7
91.9 ^ 2.2
51.6 ^ 1.6
91.4 ^ 1.4
41.4 ^ 1.9
39.1 ^ 1.7
40.3 ^ 1.9
37.2 ^ 1.8
39.3 ^ 2.5
43.1 ^ 2.9
36.2 ^ 1.2
36.4 ^ 1.6
35.3 ^ 1.7
32.3 ^ 2.7
30.4 ^ 1.3
28.5 ^ 1.2
29.3 ^ 2.6
30.3 ^ 1.7
27.4 ^ 2.6
31.5 ^ 1.3
32.6 ^ 2.3
34.4 ^ 1.4
95.0 ^ 1.7
25
26
27
28
Carbendazim
a Data are given as mean of triplicates ^ SD.
Although a definite structure–activity relationship could not be found by means of the
synthesised compounds, the interesting results obtained can be used for further designing and
synthesising more similar compounds to study their quantitative structure–activity relationship,
so that more bioactive compounds or bioactive lead compounds may be discovered.
3. Experimental
3.1. General
Allthechemicalsandsolventswerepurchasedfromcommercialsourcesandusedassuch. Thefungi
G. zeae, H. maydis, R. solani, B. cinerea and S. sclerotiorum were obtained from the Chinese
Academy of Agricultural Sciences and they were preserved at 48C. NMR (1H and 13C) spectra were
taken on a Bruker 300 MHz spectrometer in deuterated-dimethyl sulphoxide (DMSO-d6). Melting
points were determined using an X-4B micro-melting point apparatus (Shanghai Precision
Instruments Co., Ltd., Shanghai, China) and were not corrected.
3.2. Preparation of carboxylic acid chlorides (1a and 2a)
Thionyl chloride (15 mL) was added to 0.01 mol corresponding acids. The mixture was refluxed
at 808C for 2 h in a tube filled with anhydrous calcium chloride. The reaction was monitored by

Natural Product Research
5
O
X
X
CH2Cl2
H-R1
+
COCl
C
R1
Et3N or pyridine
1-22
1a, 2a
O
O
X
X
CH2Cl2
Et3N or pyridine
R2
X
NH -R -NH
+
COCl
2
2
2
N
N
H
H
1a, 2a
Figure 2. Synthesis of amides derivatives 1–28.
23-28
periodic thin layer chromatography (TLC). When the reaction was completed, excess thionyl
chloride was removed under reduced pressure. The crude products were used in the subsequent
reaction (Figure 1).
3.3. General procedure for target compounds 1–28
Compounds H-R1 (0.01 mol) or NH2–R2–NH2 (0.005 mol) were completely dissolved in
CH2Cl2.Triethylamine (Et3N) or pyridine (3 mL) was added to the solution (Figure 2). Under
stirring, the carboxylic acid chloride (1a or 2a) was added drop by drop to the mixture at room
temperature. Afterwards, the reaction mixture was further stirred for 5 h at 20–708C. The
reaction was monitored by periodic TLC. After the completion of the reaction, the reaction
mixture was washed with HCl (10%) and NaOH (10%) in turn. The solvent was removed under
reduced pressure. Compounds 9, 15 and 17 were obtained pure directly by this method. The
crude products of compounds 23–28 were re-crystallised with the mixture of DMSO and water
(15:1), and the rest were re-crystallised with anhydrous ethanol. The purity of the synthesised
compounds was checked by TLC.
3.4. Assay of antifungal activity
The antifungal activity of compounds 1–28 against G. zeae, H. maydis, R. solani, B. cinerea and
S. sclerotiorum was determined using the plate growth rate method (Huang & Yang 2006).
Each synthesised compound was dissolved in DMSO. The solution was then diluted with
0.1% Tween-80 solution and then added to the sterile culture medium (PDA) at 458C. The
mixture was homogenised and transferred to a sterile Petri dish to solidify. For primary
screening, compounds were used at a concentration of 100 mg/L. At the same time, carbendazim
(standard fungicide, purity 90%) and 1 equiv. of DMSO were used as positive and negative
controls, respectively. Afterwards, a mycelium agar disc (5 mm diameter) of the target fungi was
placed in the centre of the PDA plates, and then the plates were incubated at 288C in the dark
until the target fungi used as the negative control covered the plate’s surface. Then the diameters
of all fungi in the cultures were measured and the results were reported as the inhibition of the
growth following Abbott’s formula. Each compound was tested three times.
4. Conclusion
A series of new heterocycle containing amide derivatives have been synthesised and their
antifungal activity was evaluated against G. zeae, H. maydis, R. solani, B. cinerea and S.
sclerotiorum. The results showed that compound 2 had remarkable antifungal activity and its
activity against H. maydis, B. cinerea and S. sclerotiorum surpassed the standard carbendazim.

6
X. Wang et al.
Compounds 1, 8 and 10 also exhibited excellent antifungal activity against the above-mentioned
five fungi. The results acquired in this study are promising and beneficial for further developing
and making researches on novel and more effective fungicides in the agricultural chemistry field.
Supplementary material
Supplementary material relating to this paper is available online, alongside Figures S1–S56.
http://dx.doi.org/10.1080/14786419.2015.1041137
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This project was supported by the Scientific Research Fund of Sichuan Provincial Education Department
[grant number 13ZA0206]; the Key Scientific Research Fund of Xihua University [grant number
Z1013314]; the Innovation Fund of Postgraduate of Xihua University [grant number YCJJ 2014130]; the
Research Center for Advanced Computation, Xihua University.
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