Design, synthesis and herbicidal activity study of aryl 2,6-disubstituted sulfonylureas as potent acetohydroxyacid synthase inhibitors

Article abstract of DOI:10.1016/j.bmcl.2017.06.007

A series of sulfonylurea derivatives containing a 2,6-disubstituted aryl moiety were designed, synthesized and evaluated for their herbicidal activities. Most of these compounds showed excellent inhibitory rates against both monocotyledonous and dicotyledonous weeds, especially 10a, 10h and 10i. They exhibited equivalent or superior herbicidal efficiency than commercial chlorsulfuron at the dosage of 15?g/ha and the preliminary SAR was summarized. In order to illuminate the molecular mechanism of several potent compounds, their apparent inhibition constant (K_i^app) of Arabidopsis thaliana acetohydroxyacid synthase (AHAS) were determined and the results confirmed that these compounds were all potent AHAS inhibitors. 10i have a K_i^app of 11.5?nM, which is about 4 times as potent as chlorsulfuron (52.4?nM).

Full text of DOI:10.1016/j.bmcl.2017.06.007

Accepted Manuscript
Design, synthesis and herbicidal activity study of aryl 2,6-disubstituted sulfo-
nylureas as potent acetohydroxyacid synthase inhibitors
Wei Wei, Shaa Zhou, Dandan Cheng, Yuxin Li, Jingbo Liu, Yongtao Xie,
Yonghong Li, Zhengming Li
PII:
S0960-894X(17)30609-1
DOI:
http://dx.doi.org/10.1016/j.bmcl.2017.06.007
BMCL 25041
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
26 March 2017
14 May 2017
2 June 2017
Please cite this article as: Wei, W., Zhou, S., Cheng, D., Li, Y., Liu, J., Xie, Y., Li, Y., Li, Z., Design, synthesis and
herbicidal activity study of aryl 2,6-disubstituted sulfonylureas as potent acetohydroxyacid synthase inhibitors,
Bioorganic & Medicinal Chemistry Letters (2017), doi: http://dx.doi.org/10.1016/j.bmcl.2017.06.007
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Design, synthesis and herbicidal activity study of aryl 2,6-disubstituted sulfonylureas as potent
acetohydroxyacid synthase inhibitors
Wei Wei, Shaa Zhou, Dandan Cheng, Yuxin Li, Jingbo Liu, Yongtao Xie, Yonghong Li, Zhengming Li*
State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and
Engineering (Tianjin), Nankai University, No. 94, Weijin Road, Nankai District, Tianjin 300071, China
Abstract
A series of sulfonylurea derivatives containing a 2,6-disubstituted aryl moiety were designed,
synthesized and evaluated for their herbicidal activities. Most of these compounds showed excellent
inhibitory rates against both monocotyledonous and dicotyledonous weeds, especially 10a, 10h and
10i. They exhibited equivalent or superior herbicidal efficiency than commercial chlorsulfuron at the
dosage of 15 g/ha and the preliminary SAR was summarized. In order to illuminate the molecular
mechanism of several potent compounds, their apparent inhibition constant (Kiapp) of Arabidopsis
thaliana acetohydroxyacid synthase (AHAS) were determined and the results confirmed that these
compounds were all potent AHAS inhibitors. 10i have a Kiapp of 11.5 nM, which is about 4 times as
potent as chlorsulfuron (52.4 nM).
Keywords: sulfonylureas; acetohydroxyacid synthase (AHAS); herbicidal activity; apparent inhibition
constant (Kiapp
)
Sulfonylurea herbicides are widely applied over the world owing to their ultra-low application
dosage and extremely low acute toxicity to mammals. They control the growth of weeds by
noncompetitively inhibiting their acetohydroxyacid synthase (AHAS, EC 2.2.1.6), the first key enzyme
in branched amino acids biosynthesis pathway.1-3 Previous studies on structure-activity relationships
(SAR) have shown that the presence of a sulfonyl-ortho substituent is critical for the bioactivity.4-5
Different substitution patterns on the aryl moiety could result in different species selectivity features.
Our group previously found that nitro group was an excellent sulfonyl-ortho group with especially high
security towards Millet (Setaria italica),6-7 a popular crop in Northern China. At the same time, it is
worth noting that there are totally two sulfonyl-ortho positions in the molecule, both of which could
be substituted, just like the pattern of Triflusulfuron-methyl, a sugar beet herbicide.8-9 However, there
are seldom reports about the 2,6-disubstituted sulfonylureas in addition to this.10-11 The halogens
were presumed as suitable substituents considering the electrostatic and hydrophobic characters. An
alkoxy group was introduced in order to fit the geometric configuration of the herbicide binding
site12-13 and enhance the hydrophobicity of the target molecule. In view of the above-mentioned basis,
a series of aryl 2,6-disubstituted sulfonylureas containing a nitro group was designed and synthesized
(Fig. 1), in the hope to find potent lead compounds with interesting selectivity characteristics.
Biological evaluation of these compounds was carried out.
*Corresponding author
Postal address: Bo-Ling building 518, Nankai University, No. 94, Weijin Road, Tianjin, China (300071)
E-mail address: nkzml@vip.163.com

Fig. 1. Design strategy of compounds 10.
Scheme 1. Synthetic routes of intermediates 1a-d.
The synthetic routes are shown in Scheme 1 and 2. Intermediates 1a-d were prepared via a SNAr
reaction of o-chloronitrobenzene derivatives and benzyl mercaptan sodium in refluxing ethanol. The
intermediate 3 and 6 were synthesized through reactions with special region-selectivity reported by
the literature.14-15 4 and 5 were obtained from 3 via Sandmeyer reaction in good yield. Intermediates
1a-d were oxidized and chlorinated under the treatment of 1,3-Dichloro-5,5-dimethylhydantoin
(DCDMH) and concentrate HCl in THF under 0 °C,16-17 affording the corresponding sulfonyl chlorides
which were allowed to react immediately with excess ammonia hydroxide to give key intermediates
2a-d. 2e was prepared from 2a through a substitution of Cl atom by 2,2,2-trifluoroethoxy group. In
this reaction, the sulfonamide group of 2 was protected by N,N-Dimethylformamide dimethyl acetal
(DMF-DMA) to avoid the failure caused by the side reaction of sulfonamide’s deprotonation.18 The
protecting group was removed by stirring the intermediate 8 in excess hydrazine monohydrate in
ethanol for an hour to attain 2e in almost quantitative yield. The sulfonyl carbamates 9 were prepared
in excellent yields by treating sulfonamides 2a-e with ethyl chloroformate in the presence of fine
powdered potassium carbonate in refluxing acetone. The reaction of sulfonyl carbamate and
corresponding heterocyclic amine with continuous removal of the azeotrope of ethanol and toluene

gives the desired products 10a-q.
R1
1
R1
2a
: R =Cl
DCDMH
HCl (conc.)
THF,0 oC
2h
NH3/H2O
1
SO2NH2
NO2
SBn
NO2
2b
: R =Br
THF, 0 o
C
2c: R1=I
rt overnight
65%, 2 steps
1
2d
: R =F
1a-d
2a-d
CF3
CF3
Cl
Cl
O
O
O
O
O
O
Na
N2H4·H2O
EtOH, rt
1h, 99%
DMF-DMA
SO2NH2
NO2
S
S
SO2NH2
N
N
N
N
HOCH2CF3
THF, reflux
6h, 61%
DCM, rt
1h, 95%
NO2
NO2
R2
NO2
2a
7
8
2e
R2
R1
R1
O
N
X
R1
O
O
N
X
O
O
ClCOOEt
K2CO3
O
SO2NH2
NO2
S
H2N
N
R3
S
N
H
OCH2CH3
N
H
N
H
N
R3
acetone, reflux
8h, 90-100%
toluene
reflux, 4h
NO2
NO2
2a-e
9a-e
10a-q
10a-q:
a R1=Cl,R2/R3=CH3/CH3,X=CH;
b R1=Cl,R2/R3=OCH3/OCH3,X=CH; c R1=Cl,R2/R3=H/CH3,X=CH;
1
2
3
1
2
3
1
2
3
d
g
e
f
R =Cl,R /R =Cl/OCH3,X=CH;
R =OCH2CF3,R /R =CH3/CH3,X=CH; R =Cl,R /R =CH3/OCH3,X=CH;
1
2
3
1
2
3
1
2
3
h
i
R =F,R /R =CH3/OCH3,X=CH;
R =Cl,R /R =CH3/OCH3,X=N;
R =F,R /R =OCH3/OCH3,X=CH;
1
2
3
1
2
3
1
2
3
j
k
l
R =F,R /R =CH3/H,X=CH;
R =F,R /R =CH3/OCH3,X=N;
R =I,R /R =CH3/OCH3,X=CH;
1
2
3
1
2
3
1
2
3
m
n
o
R =I,R /R =OCH3/OCH3,X=CH;
R =I,R /R =CH3/H,X=CH;
R =Br, R /R =CH3/OCH3,X=CH;
p R1=Br, R2/R3=OCH3/OCH3,X=CH; q R1=Br, R2/R3=CH3/OCH3,X=N;
Scheme 2. Synthetic route of compounds 10a-q.
As shown in table 1, derivatives 10a-q were evaluated for their herbicidal activities based on the
rape (Brassica napus) root test19 at concentration of 0.1, 1 and 10 mg/L for an initial screening.
Chlorsulfuron was selected as the positive control. Some compounds showed comparable herbicidal
activity with chlorsulfuron under testing condition. The structure of the heterocycle moiety make a
critical contribution to the herbicidal activities. The most effective substructure is 4,6-disubstituted
pyrimidine and the best substituents include methyl and methoxy group. The presence of a Cl atom at
4 position of pyrimidine is slightly unfavorable (10f). When the heterocycle is 1,3,5-triazine system
(10g, 10k and 10q), the activity decreased compared to chlorsulfuron. If the heterocycle is 4-methyl
pyrimidine (10c, 10j and 10n), title compounds exhibit relatively high inhibitory rates at 10 mg/L, but
the activity decreased rapidly as lower dosage was used. Conventional structure-activity relationship
(SAR) of herbicidal sulfonylureas requires an electron-withdrawing group (EWG) at sulfonyl-ortho
position.4 However, with the existence of a nitro group already at aryl-2 position, the additional
introduction of an electron releasing 2,2,2-trifluoroethoxy group at aryl-6 position (10d) could
successfully maintain the herbicidal activity at a high level.
Table 1
Initial herbicidal activity screening of compounds 10a-q based on rape root test.
Inhibitory rates (%)
Compds
0.1 mg/L
48.8
64.1
18.7
57.9
25.8
42.6
10.1
45.9
46.4
1 mg/L
55.3
68.4
37.3
62.2
52.2
51.2
40.2
57.7
66.5
10 mg/L
68.2
69.9
67.7
65.1
62.2
62.2
64.1
68.4
67.9
10a
10b
10c
10d
10e
10f
10g
10h
10i

10j
10k
10l
10m
10n
10o
10p
10q
6.7
0
40.7
33.5
0
43.9
20.6
7.9
47.8
29.2
67.9
45.0
31.6
65.0
53.0
40.5
64.1
72.6
44.5
68.9
65.1
65.1
68.5
64.8
67.5
68.9
chlorsulfuron 49.3
To further investigate the SAR of series 10 and their weed control spectra, 10 high-active
compounds were selected to perform more detailed herbicidal activity assay20-21 and the results are
shown in table 2 and Fig. 2. Compounds 10 exhibited significant inhibitory activities against both
monocotyledonous (Echinochloa Crusgalli and Digitaria adscendens) and dicotyledonous (Brassica
napus and Amaranthus retroflexus) weeds. chlorsulfuron and monosulfuron were used as positive
control. 7 compounds (10a, 10d, 10h, 10i, 10l, 10m and 10o) could completely control the growth of
Brassica napus at 15 g/ha dosage when applied in pre-emergence manner. For Amaranthus
retroflexus, a malignant latifoliate weed, 5 compounds (10a, 10h, 10i, 10m and 10o) achieved more
than 90% inhibitory rates (15 g/ha, pre-emergence). Generally, the herbicidal activity of these
compounds reached the potency of commercial herbicide chlorsulfuron and monosulfuron.
Pre-emergence application showed better effects than post-emergence application.
As for monocotyledonous weeds, the control effect of chlorsulfuron and monosulfuron is
somewhat unsatisfactory at 15 g/ha dosage. However, the inhibitory rates of 10h (81.5%) and 10i
(92.5%) against Echinochloa Crusgalli were higher than chlorsulfuron (66.4%) and monosulfuron
(3.0%). Digitaria adscendens is a tough weed in dry farmland and its growth cannot be controlled
effectively by chlorsulfuron and monosulfuron even the dosage increased to 150 g/ha, whereas 10a
and 10i could achieve a inhibition of 89.4% and 67.0% respectively at 15 g/ha (post-emergence). In
pre-emergence manner, the activities of 5 compounds (10a, 10b, 10h, 10l and 10o) are 76.9%, 53.5%,
62.8%, 68.1% and 57.2% respectively, which are better than chlorsulfuron (23.3%) and monosulfuron
(40.6%). Interestingly, 10a exhibited a special inhibiting ability towards Digitaria adscendens. Generally,
the most active compounds are 10a, 10h and 10i.
To study the SAR of compounds 10 at aryl moiety, we noticed that the general activity sequences
of compounds who shared the same heterocycle structure were 10h (F) ≥ 10m (I) > 10b (Cl) > 10p (Br),
10i (F) > 10l (I) = 10o (Br) > 10e (Cl) and 10a (Cl) ≥ 10d (OCH2CF3). This result indicated that a F atom
was the most favorable substituent at 2-position of the aryl moiety, but the other substituents did not
show any obvious priority. The introduction of a 2,2,2-trifluoroethoxy group did not result in drastic
decrease of the herbicidal activity.
Table 2
Herbicidal assay of 10 high-active compounds at multiple dosage against four kinds of weeds.
Amaranthus
retroflexus
Echinochloa
Crusgalli
Digitaria
adscendens
Brassica napus
dosage
(g/ha)
compds.
10a
pre
post
77.5
86.7
99.8
35.7
47.9
94.1
72.6
pre
post
pre
post
pre
post
15
100
100
100
73.3
84.8
100
92.9
97.3
100
100
61.1
99.3
100
84.0
100
100
100
64
67.3
81.1
98.8
38.7
77.9
82.5
78.6
100
100
100
25.8
79.4
88.3
96
76.9
87.5
100
89.4
89.9
98.7
0
30
150
15
53.5
59.8
90.3
38.5
10b
10d
30
96.9
97.3
43.5
18.7
42.8
5.2
150
15

30
100
100
25.0
59.5
83.8
77.1
86.2
100
100
100
100
100
100
100
99.5
100
100
87.0
100
100
100
100
100
100
100
100
100
100
100
77.8
92.1
24.4
42.1
52.9
39.5
56.9
100
100
100
100
88
91.0
94.4
0
48.1
81.1
0
91.4
96.4
0
99.2
100.0
0
59.3
97.2
0
49.6
61.4
0
150
15
10e
30
6.9
5.3
5.5
10.7
22.1
83.1
84.6
90.0
100
100
100
92.2
100
100
70.8
83.4
95.9
89.7
100
100
87.7
100
100
100
100
100
42.2
85.1
86.5
26.0
44.0
0
14.5
20.7
0
150
15
36.8
59
26.1
41.3
49.9
80.4
98.8
100
100
56.6
82.6
89.6
74.6
83.5
89.0
50.5
70.4
87.8
85.0
88.9
90.6
100
100
100
38.6
71.0
99.7
14.8
0
10f
30
85.4
99.8
97.6
100
100
100
100
100
74.3
99.3
100
99.8
100
100
90.6
100
100
100
100
100
91.0
98.6
100
14.1
92.2
81.5
90.4
96.1
92.5
94.7
100
49.0
61.5
90.0
26.9
61.1
80.0
48.8
72.0
96.3
66.4
94.6
99.5
3.0
35.9
78.7
62.8
63.6
89.5
25.5
75.5
100
25.8
37.4
49.2
67.2
88.0
67.0
71.9
75.4
45.6
56.1
80.3
25.0
37.4
38.5
43.2
65.0
73.5
28.1
51.7
68.5
0
150
15
10h
30
150
15
10i
30
93.9
100
86.1
95.0
95.8
93.6
100
100
91.6
95.6
100
89.8
100
100
62.6
69.3
91.6
150
15
68.1
97.8
100
10l
30
150
15
30.9
58.0
64.7
57.2
80.3
100
10m
10o
30
150
15
30
150
15
23.3
56.5
62.4
40.6
57.6
94.4
controla
controlb
30
150
15
30
60.8
91.4
37.6
69.1
150
controla: chlorsulfuron
controlb: monosulfuron
pre: pre-emergence
post: post-emergence
Fig 2. Overall herbicidal activity of 10 compounds at 15 g/ha.
To investigate the herbicidal mechanism of compounds 10, the assay of acetohydroxyacid
synthase (AHAS) was carried out using the catalytic subunit of AHAS from Arabidopsis thaliana.22 The
corresponding apparent inhibition constant (Kiapp) was determined with chlorsulfuron as positive
control. As shown in table 3, 10h, 10i, 10l and 10o were confirmed as potent AHAS inhibitors with Kiapp

values in the 10-30 nM range, approximately 2-4 times as potent as observed for chlorsulfuron (52.4
nM), while the other compounds were less potent inhibitors of the enzyme. A plot of the inhibition
data for compounds 10 is given in Fig. 3. Compounds 10i, 10l and 10o all have
a
4-methoxy-6-methyl-pyrimidine moiety and show an increased affinity to AHAS. The attachment of a
2,2,2-trifluoroethoxy group to aryl moiety slightly decrease the affinity to the enzyme (10d), which
may result from the electron-releasing character of the group. In addition, F-containing molecules
(10h and 10i) are good inhibitors with Kiapp values of 28.3 and 11.5 nM, respectively, which is
consistent to the results of herbicidal activity assay.
Table 3
Apparent inhibition constant (Kiapp) of compounds 10.
compds.
10a
10d
10h
10i
10l
10m
10o
Kiapp (nM) Std. Err. (nM)
172.9
165.8
28.3
5.80
6.21
1.16
1.19
1.17
3.45
1.51
2.42
11.5
22.9
112.7
15.3
chlorsulfuron 52.4
Fig 3. AHAS inhibition curves of compounds 10.
In summary, a series of nitro-containing aryl 2,6-disubstituted sulfonylureas was synthesized and
their chemical structures were identified. All the compounds were evaluated for their herbicidal
activities and most of them exhibited significant inhibitory activities against 4 kinds of weeds at 15
g/ha dosage. The herbicidal activities of 10a, 10h, 10i, 10m and 10o are almost equivalent to
commercial herbicides for Brassica napus and Amaranthus retroflexus. As for monocotyledonous
weeds, 10a, 10h and 10i exhibited much higher herbicidal activities than chlorsulfuron and
monosulfuron. Additionally, 10a showed a special inhibiting ability towards Digitaria adscendens, a
kind of famous tough weed in dry farmland. Preliminary SAR of compounds 10 is summarized.
Heterocycle moiety make a great contribution to the herbicidal activity. 4,6-disubsitituted pyrimidine
is favored, whereas the 1,3,5-triazine system and 4-mono substituted pyrimidine will cause the rapid
decrease of the activity. The superior group on the aryl moiety is a F atom and the introduction of a

2,2,2-trifluoroethoxy group could maintain the herbicidal activity at a very high level. The assay of
AHAS elucidated the mechanism of action of compounds 10 and 10i have a Kiapp value of 11.5 nM,
about 4 times as potent as chlorsulfuron. The further studies on the crop species selectivity are in
progress and the results will be reported in future.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (no. 21272129),
the National Key Technologies Research and Development Program (no.2011BAE06B05) and the
Synergetic Innovation Center of Chemical Science and Engineering (Tianjin). We sincerely thank
Professor Xi Zhen and Niu Congwei from Nankai University for providing enzyme and helpful
instructions in the assay of AHAS.
References and notes
1. LaRossa, R. A.; Schloss, J. V. J. Biol. Chem., 1984, 259(14), 8753–8757.
2. Rost, T. L. J. Plant. Growth. Regul. 1984, 3(1), 51–63.
3. Krämer, W.; Schirmer, U.; Jeschke, P.; Witschel, M. Modern Crop Protection Compounds: Second
Edition. John Wiley & Sons: New York, 2012.
4. Levitt, G. American Chemical Society Symposium Series 443, Washington D.C., 1991, 16–31.
5. Li, Z. M.; Ma, Y.; Guddat, L. W.; Chen, P. Q.; Wang, J. G.; Pang, S. S.; Dong, Y. H.; Lai, C. M. Wang, L.
X., Jia, G. F.; Li, Y. H.; Wang, S. H.; Liu, J.; Zhao, W. G.; Wang, B. L. Pest. Manag. Sci. 2012, 68,
618–628.
6. Li, Z. M.; Jia, G. F.; Wang, L. X., Yang, Z. Q.; Lai, C. M. CN Patent 1 080 116, 1994.
7. Li, Y. H.; Gao, Y. B. J. Agro-Environ. Sci. 2004, 23 (4), 633–637.
8. Marcus, P. M. U.S. Patent 5 090 993, 1992.
9. Wittenbach, V. A.; Koeppe, M. K.; Lichtner, F. T.; Zimmerman, W. T.; Reiser, R. W. Pestic.
Biochem. Phys., 1994, 49, 72–81.
10. Chen, W.; Wei, W.; Wu, C. C.; Li, Y. X.; Li, Y. H.; Yu, S. J.; Li, Z. M. Chin. J. Org. Chem. 2015, 35,
1576–1581.
11. Dietrich, H.; Waldraff, C.; Willms, L.; Bieringer, H.; Rosinger, C.; Thurwachter, F.; Auler, T. U.S.
Patent 2 004 176 251, 2004
12. Pang, S. S.; Guddat, L. W.; Duggelby, R. G. J. Biol. Chem. 2003, 278(9), 7639–7644.
13. McCourt, J. A.; Pang, S. S.; King-Scott, J.; Guddat, L. W.; Duggleby, R. G. Proc. Natl. Acad. Sci. 2006,
103(3), 569–573.
14. Gan, Z. J.; Hu, B.; Song, Q.; Xu, Y. G. Synthesis. 2012, 44, 1074–1078.
15. Guilarte, V.; Castroviejo, M. P.; Garcia-Garcia, P.; Fernandez-Rodriguez, M. A.; Sanz, R. J. Org.
Chem. 2011, 76, 3416–3437
16. Pu, Y. M.; Christesen, A.; Ku, Y. Y. Tetrahedron Lett. 2010, 51, 418–421.
17. Zhang, J.; Wang, J.; Qiu, Z.; Wang, Y. Tetrahedron. 2011, 67, 6859–6867.
18. Gazvoda, M.; Kočevar, M.; Polanc, S. Eur. J. Org. Chem. 2013, 24, 5381–5386.
19. Wang B. L.; Duggleby, R. G.; Li, Z. M.; Wang, J. G.; Li, Y. H.; Wang, S. H.; Song, H. B. Pest. Manag.
Sci. 2005, 61, 407–412.
20. Pan, L.; Chen, Y. W.; Liu, Z.; Li, Y. H.; Li, Z. M. Chin. J. Org. Chem. 2013, 33(3), 542–550.
21. Liu, X. H.; Pan, L.; Ma, Y.; Weng, J. Q.; Tan, C. X.; Li, Y. H.; Shi, Y. X.; Li, B. J.; Li, Z. M.; Zhang, Y. G.
Chem. Biol. Drug Des. 2011, 78, 689–694.

22. Singh, B. K.; Stidham, M. A.; Shaner, D. L. Anal. Biochem. 1988, 171, 173–179.