Novel synthetic methods for N-cyano-1H-imidazole-4-carboxamides and their fungicidal activity

Article abstract of DOI:10.1016/j.bmcl.2011.11.115

A novel synthetic method of N-cyanocarboxamides has been developed with advantages of mild reaction condition, simpler procedure and easy reactant-product isolation compared with the existing methods. Using this novel method, 16 new N-cyano-1H-imidazole-4

Full text of DOI:10.1016/j.bmcl.2011.11.115

Bioorganic & Medicinal Chemistry Letters 22 (2012) 1455–1458
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel synthetic methods for N-cyano-1H-imidazole-4-carboxamides
and their fungicidal activity
⇑
Wen-Chao Yang, Jing Li, Jun Li, Qiong Chen, Guang-Fu Yang
Key Laboratory of Pesticide & Chemical Biology, College of Chemistry, Ministry of Education, Central China Normal University, Wuhan 430079, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel synthetic method of N-cyanocarboxamides has been developed with advantages of mild reaction
condition, simpler procedure and easy reactant-product isolation compared with the existing methods.
Using this novel method, 16 new N-cyano-1H-imidazole-4-carboxamide derivatives were synthesized
and their structures were characterized by spectrum analysis. Further antifungal activity study showed
that most of the newly synthesized compounds have good antifungal activity selectively against Rhizoc-
tonia solani among the six fungi tested. Particularly, compound 12h was identified as the most promising
Received 25 August 2011
Revised 10 November 2011
Accepted 28 November 2011
Available online 4 December 2011
Keywords:
N-Cyanocarboxamide
Imidazole
candidate with an EC50 of 2.63 lg/mL against R. solani.
Ó 2011 Elsevier Ltd. All rights reserved.
Imidazo[1,5-d][1,2,4]triazin-1(2H)-one
Antifungal activity
Heterocyclic compounds are of particular interest in pharma-
ceutical and agrochemical industries. Imidazole and its derivatives
are one of the most important families in the field of heterocyclic
chemistry. In last several decades, many publications showed the
widespread biological activity of imidazole derivatives, such as
anti-convulsant,1,2 anticancer,3,4 and antimicrobial activities.5
Especially for antifungal activity, dozens of imidazole derivatives
have been developed as commercial fungicides6 and some repre-
sentatives molecules (compounds 1–6) were showed in Figure
1A, which made such a research field extremely attractive.
N-Cyanocarboxamide derivatives, which exhibit significant bio-
logical activities in agrochemical field, have also attracted much
attention from the researchers working in the field of drug and
pesticide discovery. As shown in Figure 1B, for instance, compound
7, a cyanamide containing halogenated aryloxyacetyl, showed her-
bicidal activity when it was used before germination.7 In addition,
compounds 88 was reported to show good antifungal activity, and
a patent from BASF reported compounds 9 as potential fungicide.9
However, the synthesis of N-cyanocarboxamides is a remaining
challenge. Two synthetic methods have been established to yield
the N-cyanocarboxamides. One is the direct N-cyanation of amide
by using cyanogen bromide or p-toluenesulfonyl cyanide as cyana-
tion reagent.10–13 The other is 1,3-dipolar cycloaddition of nitrile
oxides with 4,5-dihydrooxazole and 4,5-dihydrothiazole.14–16
These existing methods suffered from some drawbacks, such as
very strict reaction condition, highly toxic reagents, and expensive
starting materials.
As a part of our extensive research program to discover novel
bioactive heterocycles,17–23 we tried to synthesize 2-substituted-
8-dimethylimidazo[1,5-d][1,2,4]triazin-1(2H)-one 11 by the alkyl-
ation reaction of 8-methylimidazo[1,5-d][1,2,4]triazin-1(2H)-one
10 in the DMF solution with NaH as base. The general procedure
for synthesis of 8-methylimidazo[1,5-d][1,2,4]triazin-1(2H)-one
10 was described in Supplementary data. As shown in Scheme 1,
very interestingly, we isolated a small amount of minor product,
which was identified to be N-cyano-1,5-dimethyl-1H-imidazole-
4-carboxamide 12 by the X-ray diffraction analysis. This unex-
pected finding led us to develop a new synthetic method for
N-cyanocarboxamide derivatives. After optimizing the reaction
protocol, the ring-opening rearrangement of 8-methylimi-
dazo[1,5-d][1,2,4]triazin-1(2H)-one 10 provide an effective alterna-
tive for the synthesis of N-cyanocarboxamide derivatives. The
newly developed method has some advantages compared with
the existing methods, such as mild reaction condition, without
using highly toxic reagents, much simper reaction procedure and
easy to isolate product. In addition, using this novel synthetic meth-
od, a series of N-cyano-1H-imidazole-4-carboxamide derivatives
were synthesized and characterized. Furthermore, most of the
new compounds showed excellent antifungal activity against Rhi-
zoctonia solani.
As depicted in Scheme 2, with 8-methyl-2H-imidazo[1,5-
d][1,2,4]triazin-1-one derivatives 11 as the key intermediate, a ser-
ies of N-cyano-N,1,5-trisubstituted-1H-imidazole-4-carboxamides
were successfully synthesized in yields of 11–76%. Actually, we have
tried two different routes to synthesize the title compounds. First of
all, we used the DMF solution of 2-alkyl-8-methylimidazo[1,5-
d][1,2,4]triazin-1(2H)-one to react with various alkylation reagents
⇑
Corresponding author.
E-mail address: gfyang@mail.ccnu.edu.cn (G.-F. Yang).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.11.115

1456
W.-C. Yang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1455–1458
H
O
N
A
H
N
H
N
S
N
NHCOOCH3
N
O
N
N
N
1
2
Fuberidazole ( )
Benomyl ( )
Thiabendazole (3)
N
Cl
H
N
N
O
N
NHCOOCH3
N
N
CN
O
(H3C)2NO2S
Climbazole (4)
5
Cyamidazosulfamid ( )
Carbendazim (6)
B
OR1
CN
O
CN
N
R1
N
O
R3
R2
N
R1
N
N
R2 CN
O
O
N
7
8
9
R1= chlorophenyl, bromophenyl, iodophenyl
R2= hydrogen, short chain alkyl
R1= phenyl, benzyl, heteroaromatics
R2= phenyl, benzyl, heteroaromatics
R1= chlorophenyl
R3= hydrogen, short chain alkyl, aryl
Figure 1. (A) Chemical structures of some commercial fungicides with imidazole moiety highlighted in blue. (B) Chemical structures of some representative N-
alkylcyanamides with pesticidal activity.
(2H)-one, alkylation reagent and NaH is 1:1:1, 2-alkyl-8-methy-
O
O
O
limidazo[1,5-d][1,2,4]triazin-1(2H)-one is the major product with
yields of 11–71%. If the corresponding stoichiometry changes to
1:2:2, N-cyano-N,1-dialkyl-5-methyl-1H-imidazole-4-carboxam-
ide become the major product with yields of 5–38% based on one
pot synthesis using 8-methylimidazo[1,5-d][1,2,4]triazin-1(2H)-
one as starting material.
R1
R1
NaH, DMF
R1X (1eq.), r.t.
N
N
N
+
N
R1
N
NH
N
N
N
N
CN
N
12 (minor)
10
11 (major)
Scheme 1. The reaction of 8-dimethylimidazo[1,5-d][1,2,4]triazin-1(2H)-one with
In general, the yields of N-cyano-N,1-dialkyl-5-methyl-1H-
imidazole-4-carboxamides are relatively low. The property of
alkylation reagents has significant effect on the yields of the prod-
uct. As shown in Table 1, if both R1 and R2 are substituted benzyl,
the yields of the target compounds are relatively good; if both R1
and R2 are alkyl substitutions, the yield of target compound
decreased significantly. All the newly synthesized compounds
were characterized using 1H NMR, EI-MS and elemental analysis.
In addition, the crystal structure (CCDC 836164) of compound
12g was determined by X-ray diffraction analyses as shown in Fig-
ure 2.24 (see Supplementary data).
According to the above reaction results, we proposed the
reaction mechanism for the formation of the title compounds as
shown in Scheme 3. First of all, NaH attacked the hydrogen on C4
of the starting material 11 to generate carbanion M-1. Subsequently,
the carbanion M-1 underwent a ring-opening reaction via N2–N3
bond cleavage to produce a more stable amide anion M-2. Then,
the amide anion M-2 carried out an intramolecular attack to result
in a more stable imidazole anion M-3, which tautomerized to imid-
azole anion M-4. Finally, imidazole anion M-4 reacted with various
various alkylating reagents.
in the presence of NaH. This two-step reaction procedure can result
in N-cyano-5-methyl-1H-imidazole-4-carboxamide bearing differ-
ent groups at R1 and R2 positions. The second route is to carry out
one-pot reaction of 8-methylimidazo[1,5-d][1,2,4]triazin-1(2H)-
one with two equivalent alkylation reagents in the presence of
NaH, which afforded N-cyano-5-methyl-1H-imidazole-4-carbox-
amide bearing the same groups at R1 and R2 positions. Compared
with the former procedure, the one-pot reaction always resulted in
very low yields of products. For example, 71% of compound 12a
can be obtained by the two-step reaction procedure; whereas only
38% of compound 12a was afforded if one-pot reaction procedure
was applied.
In fact, the reaction between 8-methylimidazo[1,5-d][1,2,4]
triazin-1(2H)-one and alkylation reagent can produce two
products, 2-alkyl-8-methylimidazo[1,5-d][1,2,4]triazin-1(2H)-one
and N-cyano-N,1-dialkyl-5-methyl-1H-imidazole-4-carboxamide.
If the stoichiometry of 8-methylimidazo[1,5-d][1,2,4]triazin-1
Route 1
O
O
O
R1
R1
NH
N
NaH, DMF
N
N
N
NaH, DMF
R2X, r.t.
N
N
R2
N
N
R1X(1eq.), r.t.
N
N
C
N
11
10
12
Route 2
NaH, DMF
R1X(2eq.), r.t. (R1=R2)
Scheme 2. New synthetic routes for N-cyano-N,1,5-trisubstituted-1H-imidazole-4-carboxamides. Where, R1 = C6H5CH2, substituted C6H5CH2, CH3CH2CH2CH2. R2 = C6H5CH2,
substituted benzyl, CH3CH2CH2CH2, C6H5CH2CH2CH2, CH3CH2CH2.

W.-C. Yang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1455–1458
1457
Table 1
alkylation reagents to afford the N-cyano-N,1-dialkyl-5-methyl-1
H-imidazole-4-carboxamides 12. The optimization of R2 substitu-
tion is sort of evidence to our proposed reaction mechanism. For
same R2 substitution of 4-methyl benzyl, the yield order for title
compounds at R1 substitution is thus: 2-fluoro benzyl > 4-fluoro
benzyl > 2-chloro benzyl. For same R2 substitution of 4-fluoro ben-
zyl, the yields of title compounds with electron-donating group on
benzyl at R1 substitution are a little bit higher than moderate.
The fungicidal activities of all the title compounds were
screened against six kinds of fungi, Fusarium oxysporium,
Rhizoctonia solani, Botrytis cinereapers, Gibberella zeae, Dothiorella
Characterization of N-cyano-N,1-disubstituted-5-methyl-1H-imidazole-4-carboxa-
mide
O
R1
N
R2
N
N
R2
CN
Compound
R1
Mp (°C)
Yielda (%)
12a
12b
12c
12d
12e
12f
12g
12h
12i
12j
12k
12l
12m
12n
12o
12p
C6H5CH2
C6H5CH2
125–127
104–106
125–127
165–167
133–135
93–95
141–143
150–152
116–118
128–130
119–121
124–126
50–52
71
42
76
28
56
31
35
54
66
5b
gregaria and Colletotrichum gossypii, at a concentration of 50 lg/
2-F-C6H5CH2
2-F-C6H5CH2
2-F-C6H5CH2
4-F-C6H5CH2
C6H5CH2CH2CH2
2-Cl-C6H5CH2
2,4-F2-C6H5CH2
2-COOMe-C6H5CH2
4-F-C6H5CH2
4-CH3-C6H5CH2
C6H5CH2
CH3CH2CH2CH2
4-CH3-C6H5CH2
3-NO2-C6H5CH2
4-CH3-C6H5CH2
4-CH3-C6H5CH2
4-CH3-C6H5CH2
4-F-C6H5CH2
mL according to the reported method.25 Triadimefon, a commercial
fungicide, was used here as a positive control. All the compounds
did not show significant fungicidal activity (data not shown)
against F. oxysporium, B. cinereapers, G. zeae, D. gregaria and
C. gossypii, at a dosage of 50 lg/mL. However, most of the title com-
4-F-C6H5CH2
4-F-C6H5CH2
pounds showed significant fungicidal activity against R. solani at the
same dosage. Therefore, the EC50 values against R. solani of all the
title compounds and triadimefon were determined (see Supple-
mentary data).
4-CH3-C6H5CH2
4-F-C6H5CH2
CH3CH2CH2CH2
CH3CH2CH2CH2
4-CH3-C6H5CH2
3-NO2-C6H5CH2
5b
15
16b
40
11
59
CH3CH2CH2CH2
C6H5CH2
C6H5CH2
78–80
101–103
185–187
As listed in Table 2, all the EC50 values range from 2.63
31.32
g/mL, among which the compound 12h (R1 = 2,4-difluorob-
enzyl, R2 = 4-fluorobenzyl) displayed the highest activity with EC50
of 2.63 g/mL, about 5.6-folds higher than triadimefon. Based on
lg/mL to
l
4-F-C6H5CH2
a
Yields after silica gel chromatography purification.
Yields by one-pot reaction using 8-methyl-2H-imidazo[1,5-d][1,2,4]triazin-1-
l
b
the antifungal activity screening and EC50 quantification, the follow-
one as starting material.
ing structure–activity relationships could be concluded. If the R2 is
Figure 2. Crystal structure of compound 12g. The dotted line shows the intramolecular H-bond.
O
O
O
1
R1
R1
R1
N
N
N
N
N
2
N
7
N
N
N
N
5
N
N
3
4
C
δ+ δ-
NaH
M-1
11
M-2
O
O
O
R2X
R1
R1
R1
N
C
N
N
C
N
N
C
N
N
R2
N
N
N
N
N
M-4
12
M-3
Scheme 3. Proposed mechanism for the formation of the title compounds.

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W.-C. Yang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1455–1458
Table 2
Acknowledgments
EC50 values of compounds 12 against R. solani
Compound
Equation
r2
EC50
(
lg/mL)
The research was supported in part by the National Basic
Research Program of China (No. 2010CB126103) and the NSFC
(Nos. 21102052, 20925206, 20932005 and 20872045).
12a
12b
12c
12d
12e
12f
12g
12h
12i
12j
12k
12l
12m
12n
12o
y = 4.1270 + 0.9822x
y = 2.7617 + 1.9926x
y = 3.4112 + 1.6858x
y = 3.6420 + 1.6483x
y = 4.5155 + 1.0030x
y = 4.0757 + 1.3860x
y = 4.4349 + 1.0313x
y = 4.5394 + 1.0989x
y = 1.5922 + 3.0357x
y = 1.9163 + 2.3390x
y = 3.4199 + 1.3178x
y = 2.5536 + 1.6355x
y = 3.6584 + 1.4055x
y = 3.8151 + 1.3139x
y = 4.5872 + 0.8552x
y = 4.3603 + 1.1463x
y = 1.0926 + 3.3487x
0.9849
0.9899
0.9775
0.9699
0.9884
0.9812
0.9543
0.9831
0.9919
0.9977
0.9401
0.9725
0.9708
0.9958
0.9610
0.9926
0.9421
7.74
13.28
8.76
6.67
3.04
4.64
3.53
2.63
13.26
20.82
15.81
31.32
9.01
7.98
3.04
3.61
14.68
Supplementary data
Supplementary data (synthetic and biological methods) associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.bmcl.2011.11.115.
References and notes
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substituted benzyl, the order of the biological activity for title com-
pounds at R1 substitution is thus: electron-withdrawing group on
benzyl > benzyl > electron-donating group on benzyl; If the R2 is
butyl, the order of the biological activity for title compounds at R1
substitution is thus: benzyl > electron-withdrawing group on ben-
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group on ortho position to benzyl is more favorable than on the para
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position to benzyl of R1 substitution. For same R1 substitution, the
order of the antifungal activity for title compounds at R2 substitu-
tion is probably thus: electron-withdrawing group on benzyl > ben-
zyl > electron-donating group on benzyl > alkyl.
In conclusion, a series of N-cyano-N,1,5-trisubstituted-1H-imid-
azole-4-carboxamides were synthesized by using a novel synthesis
method with 8-methylimidazo[1,5-d][1,2,4]triazin-1(2H)-one as
starting material. These new compounds were characterized by
1H NMR, EI-MS and elemental analysis. Particularly, the crystal
structure of the compound 12g was determined by X-ray
diffraction analyses. In addition, the possible mechanism of the
new synthetic method of N-cyano-N,1,5-trisubstituted-1H-imidaz-
ole-4-carboxamides was proposed here. Furthermore, all title
compounds were screened for antifungal activity and showed very
good biological activity against R. solani compared to the control.
Among those new compounds, compound 12h was identified as
the most promising fungicide candidate, displayed best antifungal
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activity against R. solani with EC50 of 2.63 lg/mL.