Is the herbicidal activity of 3-cyanopyridin-2-yl phosphates related to phosphatase?

Article abstract of DOI:10.1080/10426500802514442

The herbicidal activity of 3-cyanopyridin-2-yl phosphates, which were designed according to the idea of a mechanism-based inactivator, is probably related to a phosphatase. Taylor & Francis Group, LLC.

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Is the Herbicidal Activity of 3-
Cyanopyridin-2-yl Phosphates
Related to Phosphatase?
Ping Wei a , Qi Hui a , Xin-Ying Zhang a , Li-Min Yu a ,
Miao Wang a & Yi-Xiang Ding a
a Shanghai Institute of Organic Chemistry, Chinese
Academic of Science, Shanghai, China
Published online: 21 Sep 2009.
To cite this article: Ping Wei , Qi Hui , Xin-Ying Zhang , Li-Min Yu , Miao Wang & Yi-
Xiang Ding (2009): Is the Herbicidal Activity of 3-Cyanopyridin-2-yl Phosphates Related
to Phosphatase?, Phosphorus, Sulfur, and Silicon and the Related Elements, 184:10,
2545-2552
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Phosphorus, Sulfur, and Silicon, 184:2545–2552, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802514442
Is the Herbicidal Activity of 3-Cyanopyridin-2-yl
Phosphates Related to Phosphatase?
Ping Wei, Qi Hui, Xin-Ying Zhang, Li-Min Yu, Miao Wang,
and Yi-Xiang Ding
Shanghai Institute of Organic Chemistry, Chinese Academic of Science,
Shanghai, China
The herbicidal activity of 3-cyanopyridin-2-yl phosphates, which were designed
according to the idea of a mechanism-based inactivator, is probably related to a
phosphatase.
Keywords Atherton–Todd reaction; 3-cyanopyridin-2-yl phosphates; herbicidal activi-
ties; mechanism-based inactivator
INTRODUCTION
Enzyme inhibitors are widely used in the treatment of human dis-
eases. Some important structural subunits for irreversible inactivators
have been discovered. Widlanski and colleagues1–4 designed and syn-
thesized 4-(fluoromethyl)phenyl phosphate as a mechanism-based in-
activator, which is likely to function as a phosphotyrosine phosphatase.
4-(Fluoromethyl)phenyl phosphate undergoes a phosphatase-catalyzed
hydrolytic reaction to give a reactive intermediate quinone methide,
which can irreversibly inactivate the phosphatase by forming a cova-
lent bond to an active site residue.
We recently reported the synthesis and activity of o- or p-
trifluoromethylphenyl phosphate,5 which would also be a mechanism-
based inactivator as an analog of 4-(fluoromethyl)phenyl phosphate.
It is very interesting that trifluoromethylphenyl phosphates exhibit
herbicidal activities related to a phosphoryl group. To further confirm
the result, we investigated the herbicidal activity of 3-cyanopyridin-
Received 13 August 2008; accepted 26 September 2008.
We thank the National Natural Science Foundation of China (Grant No. 29772047,
20572123) for financial support and the State Key Laboratory of Elemento-organic Chem-
istry, NanKai University for their testing of the herbicidal activity.
Address correspondence to Yi-Xiang Ding, Shanghai Institute of Organic Chemistry,
Chinese Academic of Science, 200032 Shanghai, China. E-mail: dingyx@mail.sioc.ac.cn
2545

2546
P. Wei et al.
2-yl phosphates. 3-Cyanopyridin-2-yl phosphates could also undergo
a phosphatase-catalyzed hydrolytic reaction to give a ketene imine
as electrophlic intermediate, which could inactivate the phosphatase
by forming a covalent bond to a nucleophilic site residue (Scheme 1).
In this article, we report the study on the herbicidal activities of 3-
cyanopyridin-2-yl phosphates.
SCHEME 1
RESULTS AND DISCUSSION
The 3-cyano-2-hydroxypyridines (1) were readily prepared by literature
known procedures6 using piperidine as a catalyst via the cyclization of
cyanoacetamide with sodium formylacetone, which was obtained by
the reaction of acetone with ethyl formate in the presence of sodium
methoxide.
3-Cyanopyridin-2-yl phosphates (2) were prepared by phosphoryla-
tion of the corresponding 3-cyano-2-hydroxypyridine. By use of phos-
phoryl chloride as phosphorylating reagent,7 only moderate yields were
achieved. The yields of 3-cyanopyridin-2-yl phosphates were improved
by the Atherton–Todd procedure.8 When 1.2 equiv. of diethyl phos-
phite were used, the isolated yields of the products increased to more
than 90%. All the compounds are stable; soluble in DMSO, DMF, and
trichloromethane; but are insoluble in water (Scheme 2).
SCHEME 2

3-Cyanopyridin-2-yl Phosphates
2547
To find out a relationship between the herbicidal activities and
the phosphate substructure, we also synthesized 3-cyanopyridin-
2-yl acetate (3a), p-toluenesulfonate (3b), 2-(3-chlorophenoxy)-
3-cyano-6-phenylpyridine
(4a),
and
2-(2,4-dichlorophenoxy)-3-
cyano -6-phenylpyridine (4b). 3-Cyanopyridin-2-yl acetate and
its p-toluenesulfonate analog were prepared from 3-cyano-2-
hydroxypyridine and acetyl chloride or p-toluenesulfonyl chloride
in the presence of a base. The phenoxyderivatives 4a and 4b were
obtained by the reaction of sodium phenolate with 2-bromo-3-
cyanopyridine.9,10
We have determined the herbicidal activity of the compounds with
respect to the growth inhibition of rape roots under the condition of
darkness. The results of the tests proved that some of the compounds
exhibited herbicidal activities. The rape roots growth inhibition rates
(%) of these compounds at concentrations of 10 µg/mL and 1 µg/mL are
listed in Table I. They have no or only low activity against Echinochloa
crusgalli.
The comparison of 2a with 2c, 2b with 2d, and 2h with 2i indi-
cated that the activities of the isopropyl phosphates were obviously
much lower as compared with the corresponding methyl and ethyl phos-
phates. The results are similar to the o- and p-trifluoromethylphenyl
phosphates.5 The possible reason is that the hydrolysis of phosphate
influences the herbicidal activity. Isopropyl phosphates are more diffi-
cult to be hydrolyzed to form the postulated electrophilic ketene imine
intermediates. Isopropyl thiophosphates are as inactive as isopropyl
phosphates. The 3-cyano-2-pyridin-2-yl ethers (4) exhibit rarely herbi-
cidal activities. Although 3-cyanopyridin-2-yl acetate (3a) or tosylate
(3b) could also be hydrolyzed to give reactive ketene imines, they do
not show any herbicidal potential. Therefore, a phosphoryl group is
necessary for the herbicidal activity. We presume that the herbicidal
activity of 3-cyanopyridin-2-yl phosphates is related to a phosphatase.
The result puts an interesting question to us as to whether some phos-
phatases can be a target for herbicides.
EXPERIMENTAL
All reagents and solvents were dried before use. The reactions were per-
1
formed under a nitrogen atmosphere. H NMR spectra were recorded
on a Varian EM-360A (300 Hz) spectrometer using TMS as internal
standard and CDCl3 as solvent. Elemental analyses were performed
by a Rapid CHN-O-S elemental analysis instrument. Mass and HRMS
spectra were taken on a Finnigan 4021 spectrometer. The IR spec-
tra (KBr pellets, ν in cm−1) were obtained with a Y-Zoom CUROR

2548

3-Cyanopyridin-2-yl Phosphates
2549
instrument. Melting points were determined in Thiele melting point
tubes and are uncorrected.
The herbicidal activity of the synthesized compounds was tested by
the Research Institute of Elemento-organic Chemistry, NanKai Uni-
versity, with rape disc bioassay experiments under the condition of
darkness for 48 h at 28◦C.11
The 6-aryl-3-cyano-2-hydroxypyridines (1)6 and 2-bromo-3-cyano-6-
phenylpyridine were prepared according to the literature.9
General Procedure for the Preparation of 6-Aryl-3-
cyanopyridin-2-yl Phosphates (2)
To an ice-cooled solution of the 6-aryl-3-cyano-2-hydroxypyridine (1)
(1.0 mmol) and triethylamine (3.0 mmol) in acetonitrile (15 mL), a mix-
ture of CCl4 (4.0 mmol) and dialkyl phosphite (1.2 mmol) was slowly
added. Then the reaction was kept for 6–24 h at r.t. The reaction mix-
ture was neutralized with AcOH, extracted with ether, washed with
water, dried over Na2SO4, filtrated, and evaporated in vacuo. The re-
sulting residue was purified by flash column chromatograghy using
hexane/ethyl acetate as eluent. Physical and spectroscopic data are as
follows:
3-Cyano-6-phenylpyridin-2-yl Diethyl Phosphate (2a)
Mp 86–87 ◦C (lit.12 88 ◦C).
3-Cyano-6-(4-methoxyphenyl)pyridin-2-yl Diethyl Phosphate
(2b)
1H NMR: δ 1.43 (t, 6 H, J = 7.0 Hz, 2 CH3), 3.87 (s, 3 H, CH3), 4.43
(m, 4 H, 2 CH2), 6.93∼8.07 (m, 6 H, C6H4, C5H2N). IR: 3070, 2837,
2225, 1594, 1459, 1252, 1172, 1030, 950. m/z (%) 362 (100) [M+], 226
(67), 363 (52), 236 (40), 237 (17), 253 (11), 183 (10), 238 (8). Anal. Calcd.
for C17H19N2O5P: C, 56.36; H, 5.29; N, 7.73; Found: C, 56.41; H, 5.32;
N, 7.69.
3-Cyano-6-phenylpyridin-2-yl Diisopropyl Phosphate (2c)
1H NMR: δ 7.92–8.02 (m, 1 H), 7.58–7.67 (m, 2 H), 7.50–7.58 (m, 2
H), 7.26–7.32 (m, 2 H), 4.53–4.67 (m, 2 H), 1.37 (dd, 12 H, J1 = 15.7 Hz,
J2 = 5.7 Hz). IR: 3450, 2333, 1595, 1391, 1285, 1034, 950, 841, 784. MS
(EI): m/z (%): 360 (8) [M+], 277 (73), 220 (23), 197 (24), 196 (100), 168

2550
P. Wei et al.
(14); Anal. Calcd. for C18H21N2PO4: C, 60.00; H, 5.83; N, 7.78. Found:
C, 60.01; H, 5.84; N, 7.87.
3-Cyano-6-(4-methoxyphenyl)pyridin-2-yl Diisopropyl
Phosphate (2d)
1
Light yellow solid, H NMR: δ 7.92–8.01 (m, 1 H), 7.72 (d, 1 H, J =
3.7 Hz), 7.50–7.56 (m, 2 H), 7.13–7.17 (m, 2 H), 5.03–5.08 (m, 2 H), 4.20
(s, 3 H), 1.37 (dd, 12 H, J1 = 11.0 Hz, J2 = 6.0 Hz). IR: 2983, 2225, 1592,
1460, 1257, 1174, 1010, 948, 824, 608. MS (EI): m/z (%): 390 (23) [M+],
289 (17), 227 (18), 226 (100). Anal. Calcd. for C19H23N2PO5: C, 58.46;
H, 5.90; N, 7.18. Found: C, 58.30; H, 6.00; N, 6.96.
O-[6-(4-Chlorophenyl)-3-cyanopyridin-2-yl] O,O-Diisopropyl
Phosphorothioate (2e)
Light yellow solid, 1H NMR: δ 8.03–8.11 (m, 1 H), 7.71–7.78 (m, 1 H),
7.55–7.67 (m, 2 H), 7.13–7.20 (m, 1 H), 4.77–4.86 (m, 2 H), 1.37 (dd, 12
H, J1 = 14.7 Hz, J2 = 5.3 Hz); IR: 2924, 2231, 1592, 1454, 1261, 1093,
992, 830. MS (EI): m/z (%): 293 (11), 292 (20), 243 (10), 221 (21), 197
(38), 196 (100), 168 (12). Anal. Calcd. for C18H20ClN2PO3S: C, 52.55;
H, 4.87; N, 6.81. Found: C, 52.60; H, 4.97; N, 6.67.
5-Cyano-2,4ꢀ-bipyridin-6-yl Diisopropyl Phosphate (2f)
Light yellow solid, 1H NMR: δ 8.03–8.10 (m, 1 H), 7.80–7.88 (m, 1 H),
7.50–7.56 (m, 2 H), 7.16–7.23 (m, 2 H), 4.36–4.45 (m, 2 H), 1.37 (dd, 12
H, J1 = 13.0 Hz, J2 = 6.7 Hz). IR: 2983, 2937, 2233, 1596, 1458, 1398,
1289, 1007, 948, 828. MS (EI): m/z (%): 361 (6) [M+], 319 (16), 278 (53),
260 (45), 221 (19), 198 (33), 197 (100), 169 (17), 43 (24). Anal. Calcd. for
C17H20N3PO4: C, 56.51; H, 5.54; N, 11.63. Found: C, 55.81; H, 5.45; N,
11.44.
O-(5-Cyano-2,4ꢀ-bipyridinyl-6-yl) O,O-Diisopropyl
Phosphorothioate (2g)
Light yellow solid, 1H NMR: δ 8.04–8.13 (m, 1 H), 7.76–7.85 (m, 1 H),
7.50–7.58 (m, 2 H), 7.16–7.20 (m, 2 H), 4.37–4.50 (m, 2 H), 1.29 (dd, 12
H, J1 = 12.5 Hz, J2 = 7.0 Hz). IR: 2978, 2230, 1596, 1265, 1022, 986,
948, 843, 824, 792. MS (EI): m/z (%): 377 (2) [M+], 197 (100), 293 (43),
276 (12), 222 (16), 198 (54), 169 (16). Anal. Calcd for C17H20N3PO3S: C,
54.11; H, 5.31; N, 11.10. Found: C, 54.72; H, 5.53; N, 10.73.
3-Cyano-6-(thien-2-yl)pyridin-2-yl Diisopropyl Phosphate (2h)
1
Light yellow solid, H NMR: δ 7.92–7.96 (m, 1 H), 7.72 (d, 1 H, J =
3.7 Hz), 7.50–7.56 (m, 2 H), 7.13–7.17 (m, 1 H), 5.03–5.13 (m, 2 H), 1.37

3-Cyanopyridin-2-yl Phosphates
2551
(dd, 12 H, J1 = 11.0 Hz, J2 = 6.0 Hz); IR: 3100, 2230, 1595, 1459, 1287,
1021, 923, 821. MS (EI): m/z (%): 366 (11) [M+,], 265 (18), 203 (18),
202 (100), 174 (10), 41 (8). Anal. Calcd. for C16H19N2O4PS: C, 52.46; H,
5.19; N, 7.65; Found: C, 52.50; H, 5.23; N, 7.37.
3-Cyano-6-(thien-2-yl)pyridin-2-yl Dimethyl Phosphate (2i)
Light yellow acicular crystal, 1H NMR: δ 7.85–7.90 (m, 1 H),
7.65–7.70 (m, 1 H), 7.50–7.57 (m, 2 H), 7.10–7.16 (m, 1 H), 4.11 (d, 6
H, J = 15.0 Hz). IR: 3430, 2231, 1600, 1459, 1283, 1038, 933, 835,732;
MS (EI): m/z (%) 310 (100) [M+], 311 (15), 216 (24), 215 (85), 202 (40),
187 (13), 109 (35), 79 (13). Anal. Calcd. for C12H11N2O4PS: C, 46.45; H,
3.55; N, 9.03. Found: C, 46.42; H, 3.67; N, 9.08.
3-Cyano-6-phenylpyridin-2-yl Acetate (3a)
1H NMR: δ: 7.93–8.04 (m, 1 H), 7.48–7.67 (m, 2 H), 7.25–7.38 (m, 2
H), 6.96–7.12 (m, 2 H), 2.38 (s, 3 H). IR (film): 2923, 2227, 1664, 1605,
1563, 1500, 1333, 1233, 901, 756. MS (EI): m/z (%): 238 (1) [M+], 196
(100), 168 (30), 152 (1), 140 (9), 114 (4), 77 (4), 64 (5), 43 (24). Anal.
Calcd. for C14H10N2O2: C, 70.58; H, 4.23; N, 11.76. Found: C, 70.31; H,
4.49; N, 1152.
3-Cyano-6-phenylpyridin-2-yl Tosylate (3b)
To a solution of 3-cyano-2-hydroxy-6-phenylpyridine (196 mg, 1.0
mmol) in dichloromethane (10 mL), triethylamine (0.14 mL) and p-
toluenesulfonyl chloride (191 mg, 1.0 mmol) were added on an ice bath.
The mixture was stirred at room temperature for 1 h and washed three
times with brine. The organic layer was dried over Na2SO4, filtrated,
and concentrated. 297 mg of light yellow crystals were obtained after
recrystallization.
1H NMR: δ 7.81–8.19 (m, 5 H), 6.97–7.35 (m, 6 H), 2.35 (s, 3 H). IR:
3064, 2911, 2240, 1596, 1548, 1461, 1377, 1198, 1178, 1167, 1085, 780.
MS (EI): m/z (%): 286 (70) [M+—SO2], 258 (3), 194 (3), 166 (4), 155
(24), 140(9), 91 (100), 65 (20). Anal. Calcd for C19H14N2O3S: C, 65.13;
H, 4.03; N, 7.99. Found: C, 65.38; H, 3.89; N, 7.72.
General Procedure for the Preparation of 2-Aryloxy-3-cyano-
6-phenylpyridines (4)
To a mixture of 2-bromo-3-cyano-6-phenylpyridine, sodium hydride,
and anhydrous DMF a solution of 3-chloro- or 2,4-dichlorophenol in
DMF was slowly added under a dry nitrogen atmosphere at 100◦C for
3 h. The reaction solution was diluted with water, extracted with ether,

2552
P. Wei et al.
and dried over Na2SO4. The pure products were obtained by flash col-
umn chromatograghy.
2-(3-Chlorophenoxy)-3-cyano-6-phenylpyridine (4a)
1H NMR: δ 8.04–8.07 (m, 1 H), 7.82–7.87 (m, 1 H), 7.57–7.61 (m, 1
H), 7.33–7.47 (m, 3 H), 7.26–7.31 (m, 4 H), 7.17–7.22 (m, 1 H). 13C
NMR (75.4 MHz, CDCl3): δ 162.30, 158.89, 148.80, 143.94, 136.45,
130.65, 130.40, 129.36, 128.83 (2 C), 127.75 (2 C), 127.18, 126.81,
124.13, 121.66, 115.00, 114.16. IR: 2925, 2225, 1595, 1556, 1441, 1393,
1258, 1213, 934, 750. MS (ESI): m/z (%): 307.1 (100) [M+], 309.1 (30)
[M+]. HRMS (ESI): Calcd. for C18H11ClN2O (M+): 306.75073. Found:
306.75127.
3-Cyano-2-(2,4-dichlorophenoxy)-6-phenylpyridine (4b)
1H NMR: δ 8.07 (d, 1 H, J = 8.0 Hz), 7.75–7.78 (m, 1 H), 7.58 (d, 2
H, J = 8.1 Hz), 7.53 (d, 1 H, J = 2.6 Hz), 7.34–7.43 (m, 6 H). 13C NMR
(75.4 MHz, CDCl3): δ 162.04, 159.05, 147.58, 144.06, 136.35, 131.65,
130.85, 130.24, 128.97 (2 C), 127.98, 127.22 (2 C), 125.02, 124.54,
124.02, 114.81, 114.50. IR: 2924, 2233, 1596, 1480, 1381, 1264, 1124,
1104, 934, 838. MS (ESI): m/z (%): 341 (100) [M+], 342 [M+] (20), 343
[M+] (60), 345 [M+] (10). HRMS (ESI): Calcd. for C18H10Cl2N2O (M+):
341.19583. Found: 341.19497.
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