Synthesis and herbicidal activity of O,O-diethyl N-{4-Methyl-[1,2,3] thiadiazole-5-carbonyl}- 1-amino-1-substitutedbenzyl phosphonates

Article abstract of DOI:10.1080/10426500903453326

Target compounds 3 were synthesized by the condensation of O,O-diethyl α-amino substitutedbenzyl phosphonates 1 and 4-methyl-[1,2,3]thiadiazole- 5-carboxylic acid 2 in the presence of dicyclohexylcarbodiimide (DCC) as a dehydration reagent. Their structures were confirmed by spectroscopic data (IR, 1H NMR, 31P NMR, MS) and elemental analysis. The results of a preliminary bioassay (in vitro) indicated that some of the title compounds 3 possessed moderate to good herbicidal activities against dicotyledonous plants (Brassica campestris L) at the concentration of 100 mg/L, and most of these compounds exhibited higher herbicidal activities against dicotyledonous plants (Brassica campestris L) than monocotyledonous plants (Echinochloa crus-galli). Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

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Synthesis and Herbicidal Activity of O,O-
Diethyl N-{4-Methyl-[1,2,3]thiadiazole-5-
carbonyl}- 1-amino-1-substitutedbenzyl
Phosphonates
Wu Tang a , Zhi-Hua Yu a & De-Qing Shi a
a Key Laboratory of Pesticide and Chemical Biology, Ministry of
Education, College of Chemistry, Central China Normal University,
Wuhan, Hubei, People's Republic of China
Published online: 24 Sep 2010.
To cite this article: Wu Tang , Zhi-Hua Yu & De-Qing Shi (2010) Synthesis and Herbicidal
Activity of O,O-Diethyl N-{4-Methyl-[1,2,3]thiadiazole-5-carbonyl}- 1-amino-1-substitutedbenzyl
Phosphonates, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:10, 2024-2029, DOI:
10.1080/10426500903453326
To link to this article: http://dx.doi.org/10.1080/10426500903453326
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Phosphorus, Sulfur, and Silicon, 185:2024–2029, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903453326
SYNTHESIS AND HERBICIDAL ACTIVITY OF O,O-DIETHYL
N-{4-METHYL-[1,2,3]THIADIAZOLE-5-CARBONYL}-
1-AMINO-1-SUBSTITUTEDBENZYL PHOSPHONATES
Wu Tang, Zhi-Hua Yu, and De-Qing Shi
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College
of Chemistry, Central China Normal University, Wuhan, Hubei, People’s Republic
of China
Target compounds 3 were synthesized by the condensation of O,O-diethyl α-amino sub-
stitutedbenzyl phosphonates 1 and 4-methyl-[1,2,3]thiadiazole-5-carboxylic acid 2 in the
presence of dicyclohexylcarbodiimide (DCC) as a dehydration reagent. Their structures
were confirmed by spectroscopic data (IR, 1H NMR, 31P NMR, MS) and elemental analysis.
The results of a preliminary bioassay (in vitro) indicated that some of the title compounds
3 possessed moderate to good herbicidal activities against dicotyledonous plants (Brassica
campestris L) at the concentration of 100 mg/L, and most of these compounds exhibited
higher herbicidal activities against dicotyledonous plants (Brassica campestris L) than
monocotyledonous plants (Echinochloa crus-galli).
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Amide; α-amino substitutedbenzyl phosphonate; herbicidal activity; [1,2,3]thiadi-
azole
INTRODUCTION
α-Amino phosphonic acids and their ester derivatives, as bioisosteres of natural amino
acids, are receiving increasing attention in medicinal chemistry and pesticide science be-
cause some derivatives have been found to exhibit a wide range of biological activities such
as enzyme inhibition, antibiotics, and haptens of catalytic antibodies, fungicides, herbi-
cides, plant regulators, and plant virucides [for example, as antiviral agents against tobacco
mosaic virus (TMV)].1–8 Elictor is a kind of environment-benign novel agrochemical that
protects crops against pathogen attack by promoting their immune system. [1,2,3]Thiadia-
zole chemistry has attracted more and more attention9; some thiadiazole derivatives have
Received 20 September 2009; accepted 28 October 2009.
The authors are grateful to the Natural Science Foundation of China (Grant No. 20872046) and the Natural
Science Foundation of Hubei Province (Grant No. 2008CDB086) for the financial support.
Address correspondence to De-Qing Shi, Key Laboratory of Pesticide and Chemical Biology, Ministry of
Education, College of Chemistry, Central China Normal University, Wuhan 430079, Hubei, People’s Republic of
China. E-mail: chshidq@mail.ccnu.edu.cn
2024

α-AMINO PHOSPHONATES WITH [1,2,3]THIADIAZOLE RING
2025
Cl
O
SCH
S
3
H CO
CH
3
S
3
O
H
S
N
CH
3
N
N
N
N
S
P
NHCONH
N
N
OCH
3
N
S
S
O
N
OCH
3
methidathion
tiadinil
thidiazuron
acibenzolar-S-menthyl
Figure 1 Structures of some commercial thiadiazole pesticides.
played a major role in modern pesticidal industry and have been commercialized as plant
activators, fungicides, plant growth regulators, and insecticides in plant protection10,11 (see
Figure 1). For example, acibenzolar-S-methyl was developed by Syngenta and used as
plant activator; tiadinil was discovered by Nihon Nohyaku and acted as a plant activator,
which induces fungicide resistance in rice plants; thidiazuron was used as plant growth
regulator; methidathion was developed and used cholinesterase inhibitor, which acts as a
nonsystemic insecticide and acaricide with contact and stomach action. In an attempt to find
novel agrochemical lead compounds, we have synthesized a series of title compounds 3 by
the condensation of O,O-diethyl α-amino substitutedbenzyl phosphonate 1 and 4-methyl-
[1,2,3]thiadiazole-5-carboxylic acid 2 in the presence of dicyclohexylcarbodiimide (DCC)
as a dehydration reagent, as shown in Scheme 1. The target compounds 3 were evaluated
for herbicidal activities (see the Supplemental Materials, available online) in vitro against a
dicotyledonous plant (Brassica campestris L) and a monocotyledonous plant (Echinochloa
crus-galli).
O
P
O
1) NH3.H2O
Ar
2) HPO(OC2H5)2
O
P
p-TsOH H2O
NH4OH(aq)
H
C
Ar
OC2H5
OC2H5
H
C
H
OC2H5
OC2H5
C
H
N
ArCHO
Ar
P(OEt)2
Ar
C
NH2
NH3 OTs
O
O
1
HN COOMe
NH2NH2.H2O
Me
SOCl2
Me
OEt
N
O
O
N
O
N
r.t.
S
H3CO
NHNH2
COOEt
H3CO
OCH3
Me
OEt
r.t.
Me
N
1
Me
O
P
N
S
NaOH/MeOH
H
N
OC2H5
OC2H5
N
N
S
DCC/CHCl3
COOH
O
3
Ar
2
Ar = C6H5(3a); 2-ClC6H4(3b); 4-ClC6H4(3c); 4-BrC6H4(3d); 4-CH3C6H4(3e);
4-CH3OC6H4(3f); 4-NO2C6H4(3g); 2,4-Cl2C6H3(3h)
Scheme 1 Synthesis route of the title compounds 3.
RESULTS AND DISCUSSION
Synthesis and Structure Determination of Title Compounds 3
A series of novel O,O-diethyl N-{4-methyl-[1,2,3]thiadiazole-5-carbonyl}-1-amino-
1-substitutedbenzyl phosphonates 3 was synthesized by the condensation of O,O-diethyl
α-amino substitutedbenzyl phosphonate 1 with 4-methyl-[1,2,3]thiadiazole-5-carboxylic
acid 2 in good yields in the presence of DCC as a dehydration reagent under mild conditions.
The structures of target compounds 3 were deduced from their spectroscopic data (IR, 1H
NMR, 31P NMR, MS) and elemental analysis. In the 1H NMR spectra of 3, the CH proton

2026
W. TANG ET AL.
linking with the phosphonyl group displayed as a doublet of doublet due to coupling with
P atom and nitrogen proton with chemical shifts in δ 5.6–6.2. The methyl protons linking
with [1,2,3]thiadiazole ring presented as a singlet, giving chemical shifts in δ 2.8–2.9. Two
methyl groups in the phosphonate moiety exhibited as two triplets and two methylene group
as three multiple peaks due to their different chemical environments. For 31P NMR spectra,
the phosphorus atom of all compounds displayed as a singlet with chemical shifts in δ 17–21.
The IR spectra of compounds 3 showed normal stretching absorption bands, indicating the
existence of the NH (∼3200 cm−1), C O (∼1680 cm−1), P O (∼1225 cm−1), P O C
(∼1025 cm−1) moieties. The EI-MS or ESI-MS of compounds 3 revealed the existence of
their molecular ion peaks, which were in accordance with the given structures of products
3.
Herbicidal Activities
The herbicidal activity values of the title compounds 3 against Brassica campestris
L (oil rape) and Echinochloa crus-galli (barnyard grass) have been investigated at the con-
centrations of 100 mg/L and 10 mg/L compared with the commercially available herbicide,
glyphosate, according to the method described in the Supplemental Materials.
EXPERIMENTAL
Instruments
The melting points of the products were determined on an XT-4 binocular microscope
(Beijing Tech Instrument Co., Beijing, China) and were uncorrected. The IR spectra were
recorded on a Nicolet NEXUS470 spectrometer as KBr pellets with absorption given
1
in cm−1. H and 31P NMR spectra were performed on a Varian Mercury Plus-600 (600
MHz) spectrometer at room temperature in CDCl3 with TMS and 85% H3PO4 as the internal
and external standards, respectively. Mass spectra were measured on a Finnigan TraceMS
2000 spectrometer at 70 eV using EI method or Applied Biosystems API 2000 LC/MS/MS
(ESI-MS) spectrometer. Elemental analysis was taken on a Vario EL III elemental analysis
instrument. Analytical TLC was performed on silica gel GF254. Unless otherwise noted, all
materials were commercially available and were used directly without further purification.
All solvents were dried and redistilled before use. α-Amino substitutedbenzyl phosphonates
1 were synthesized from aromatic aldehyde, ammonia, and diethyl phosphite according to
the reported procedure.12,13 4-Methyl-[1,2,3]thiadiazole-5-carboxylic acid 2 was obatined
in 78% yield using diethyl carbonate as the starting material, followed by nucleophilic
substitution with 85% hydrazine hydrate, condensation with acetyl acetate, cyclization
with SOCl2, and then saponification according to the reported synthetic protocols.14 Mp
174–176◦C, lit. mp 173–175◦C.
General Synthetic Procedures for O,O-Diethyl N-{4-Methyl-[1,2,3]-
thiadiazole-5-carbonyl}-1-amino-1-substitutedbenzyl Phosphonates 3
To a solution of α-amino substitutedbenzyl phosphonate 1 (1.0 mmol) and 4-methyl-
[1,2,3]thiadiazole-5-carboxylic acid 2 (0.14 g, 1.0 mmol) in anhydrous chloroform (5 mL),
was added dropwise dicyclohexylcarbodiimide (DCC, 0.23 g, 1.1 mmol) in anhydrous

α-AMINO PHOSPHONATES WITH [1,2,3]THIADIAZOLE RING
2027
chloroform (2 mL) at 0–5◦C was added dropwise under stirring for 30 min. The mixture
was allowed to stir at room temperature for 3–5 h (monitored by TLC). The solvent was
removed under reduced pressure, acetone (2 mL) was added to the crude product, and the
solid that formed was filtered off. Anhydrous ethyl ether (3 mL) was added to the filtrate,
the product 3 was collected by filtration as colorless crystals in 71–94% yields.
Data for 3a: Yield 72%, colorless crystals, mp 127–129◦C; IR (KBr): υ 3209 (N H),
1
1674 (C O), 1546 (C N), 1228 (P O), 1028 (P O C) cm−1; H NMR (CDCl3, 600
MHz): δ 1.05 (t, J = 7.2 Hz, 3H, CH2CH3), 1.34 (t, J = 7.2 Hz, 3H, CH2CH3), 2.80 (s, 3H,
CH3), 3.54–3.57 (m, 1H, OCH2), 3.73–3.78 (m, 1H, OCH2), 4.08–4.17 (m, 2H, OCH2),
5.69 (dd, J = 20.7 Hz, J = 9.6 Hz, 1H, PCH), 7.34–7.36 (m, 3H, ArH), 7.54–7.56 (m, 2H,
1
ArH), 9.00 (d, J = 7.2 Hz, 1H, NH);31P { H} NMR (CDCl3, 243 MHz): δ 18.76; EI-MS
(70 eV): m/z 371 (17.6), 370 (19.4), 369 (M+, 19.6), 368 (17.6), 226.5 (15.9), 225.5 (23.2),
177 (35.6), 173 (91.0), 171 (100), 169 (90.1), 142 (19.9), 105 (21.3), 104 (19.3), 91 (48.2),
90 (69.3), 77 (24.0). Anal. Calcd for C15H20N3O4PS: C 48.77, H 5.46, N 11.38; found C
48.35, H 5.10, N 11.53.
Data for 3b: Yield 94%, colorless solid, mp 135–137◦C; IR (KBr): υ 3214 (N H),
1
1680 (C O), 1541 (C N), 1235 (P O), 1022 (P O C) cm−1; H NMR (CDCl3, 600
MHz): δ 1.06 (t, J = 7.8 Hz, 3H, CH2CH3), 1.37 (t, J = 7.2 Hz, 3H, CH2CH3), 2.88 (s, 3H,
CH3), 3.62–3.65 (m, 1H, OCH2), 3.83–3.86 (m, 1H, OCH2), 4.17–4.22 (m, 2H, OCH2),
6.24 (dd, J = 21.3 Hz, J = 9.0 Hz, 1H, PCH), 7.27–7.31 (m, 2H, ArH), 7.45 (t, J = 7.2
1
Hz, 1H, ArH), 7.68 (t, J = 6.8 Hz, 1H, ArH), 8.07 (s, 1H, NH);31P { H} NMR (CDCl3,
243 MHz): δ 17.52; ESI-MS: m/z 441.5 (M++K-1, 8%), 425.6 (M++Na-1, 22%), 403.5
(M+, 100%). Anal. Calcd for C15H19ClN3O4PS: C 44.61, H 4.74, N 10.41; found C 44.50,
H 4.47, N 10.36.
Data for 3c: Yield 77%, colorless crystals, mp 153–155◦C; IR (KBr): υ 3226 (N H),
1
1667 (C O), 1538 (C N), 1234 (P O), 1025 (P O C) cm−1; H NMR (CDCl3, 600
MHz): δ 1.11 (t, J = 7.2 Hz, 3H, CH2CH3), 1.34 (t, J = 7.2 Hz, 3H, CH2CH3), 2.86 (s, 3H,
CH3), 3.68–3.71 (m, 1H, OCH2), 3.87–3.90 (m, 1H, OCH2), 4.09–4.18 (m, 2H, OCH2),
5.60 (dd, J = 21.3 Hz, J = 8.4 Hz, 1H, PCH), 7.34 (d, J = 7.8 Hz, 2H, ArH), 7.45 (d, J =
1
8.4 Hz, 2H, ArH), 8.38 (sb, 1H, NH);31P { H} NMR (CDCl3, 243 MHz): δ 19.47; ESI-MS:
m/z 425.5 (M++Na-1), 403.5 (M+, 100%). Anal. Calcd for C15H19ClN3O4PS: C 44.61, H
4.74, N 10.41; found C 44.80, H 4.97, N 10.73.
Data for 3d: Yield 79%, colorless crystals, mp 156–157◦C; IR (KBr): υ 3218 (N H),
1
1672 (C O), 1535 (C N), 1239 (P O), 1021 (P O C) cm−1; H NMR (CDCl3, 600
MHz): δ 1.12 (t, J = 7.2 Hz, 3H, CH2CH3), 1.34 (t, J = 7.2 Hz, 3H, CH2CH3), 2.83 (s, 3H,
CH3), 3.66–3.68 (m, 1H, OCH2), 3.83–3.86 (m, 1H, OCH2), 4.08–4.15 (m, 2H, OCH2),
5.63 (dd, J = 21.0 Hz, J = 9.6 Hz, 1H, PCH), 7.40 (d, J = 7.8 Hz, 2H, ArH), 7.45 (d, J
1
= 8.4 Hz, 2H, ArH), 8.38 (d, J = 6.0 Hz, 1H, NH);31P { H} NMR (CDCl3, 243 MHz):
δ 19.75; ESI-MS: m/z 448 (M+, 100%), 225 (51%). Anal. Calcd for C15H19BrN3O4PS: C
40.19, H 4.27, N 9.37; found C 39.92, H 4.10, N 9.53.
Data for 3e: Yield 81%, colorless crystals, mp 148–149◦C; IR (KBr): υ 3225 (N H),
1
1666 (C O), 1531 (C N), 1230 (P O), 1025 (P O C) cm−1; H NMR (CDCl3, 600
MHz): δ 1.08 (t, J = 6.6 Hz, 3H, CH2CH3), 1.35 (t, J = 7.2 Hz, 3H, CH2CH3), 2.35
(s, 3H, CH3), 2.83 (s, 3H, CH3), 3.62–3.65 (m, 1H, OCH2), 3.85–3.88 (m, 1H, OCH2),
4.11–4.18 (m, 2H, OCH2), 5.60 (dd, J = 20.7 Hz, J = 9.0 Hz, 1H, PCH), 7.18 (d, J = 8.4
1
Hz, 2H, ArH), 7.41 (d, J = 8.4 Hz, 2H, ArH), 7.86 (sb, 1H, NH);31P { H} NMR (CDCl3,
243 MHz): δ 19.97; ESI-MS: m/z 405 (M++Na-1, 7%), 383 (M+, 100%). Anal. Calcd for
C16H22N3O4PS: C 50.12, H 5.78, N 10.97; found C 50.35, H 5.53, N 11.07.

2028
W. TANG ET AL.
Data for 3f: Yield 75%, colorless crystals, mp 141–142◦C; IR (KBr): υ 3193 (N H),
1
2982 (Ar-H), 1661 (C O), 1517 (C N), 1246 (P O), 1035 (P O C) cm−1; H NMR
(CDCl3, 600 MHz): δ 1.09 (t, J = 7.2 Hz, 3H, CH2CH3), 1.34 (t, J = 7.2 Hz, 3H, CH2CH3),
2.84 (s, 3H, CH3), 3.59–3.61 (m, 1H, OCH2), 3.79–3.83 (m, 1H, OCH2), 4.09–4.15 (m,
2H, OCH2), 5.62 (dd, J = 20.7 Hz, J = 9.0 Hz, 1H, PCH), 6.88 (d, J = 8.4 Hz, 2H, ArH),
1
7.46 (d, J = 7.8 Hz, 2H, ArH), 8.60 (sb, 1H, NH);31P { H} NMR (CDCl3, 243 MHz): δ
20.69; ESI-MS: m/z 437.9 (M++K-1, 12%), 422 (M++Na-1, 15%), 399.6 (M+, 100%),
257 (14%). Anal. Calcd for C16H22N3O5PS: C 48.11, H 5.55, N 10.52; found C 48.39, H
5.81, N 10.66.
Data for 3g: Yield 71%, colorless solid, mp 132–134◦C; IR (KBr): υ 3226 (N H),
1
2990 (Ar-H), 1667 (C O), 1538 (C N), 1234 (P O), 1025 (P O C) cm−1; H NMR
(CDCl3, 600 MHz): δ 1.04 (t, J = 7.2 Hz, 3H, CH2CH3), 1.37 (t, J = 7.8 Hz, 3H, CH2CH3),
2.90 (s, 3H, CH3), 3.73–3.76 (m, 1H, OCH2), 3.91–3.96 (m, 1H, OCH2), 4.18–4.23 (m,
2H, OCH2), 6.11 (dd, J = 21.0 Hz, J = 9.0 Hz, 1H, PCH), 7.25 (d, J = 8.4 Hz, 2H, ArH),
1
7.55 (d, J = 9.0 Hz, 2H, ArH), 7.67 (sb, 1H, NH);31P { H} NMR (CDCl3, 243 MHz): δ
20.81; ESI-MS: m/z 414.2 (M+, 100%). Anal. Calcd for C15H19N4O6PS: C 43.48, H 4.62,
N 13.52; found C 43.10, H 4.34, N 13.69.
Data for 3h: Yield 82%, colorless crystals, mp 137–138◦C; IR (KBr): υ 3218 (N H),
1
2988 (Ar-H), 1664 (C O), 1543 (C N), 1236 (P O), 1031 (P O C) cm−1; H NMR
(CDCl3, 600 MHz): δ 1.11 (t, J = 7.2 Hz, 3H, CH2CH3), 1.37 (t, J = 7.2 Hz, 3H, CH2CH3),
2.87 (s, 3H, CH3), 3.67–3.71 (m, 1H, OCH2), 3.85–3.87 (m, 1H, OCH2), 4.14–4.22 (m, 2H,
OCH2), 6.19 (dd, J = 21.0 Hz, J = 8.4 Hz, 1H, PCH), 7.24 (d, J = 8.4 Hz, 1H, ArH), 7.47
1
(s, 1H, ArH), 7.67 (s, 1H, ArH), 8.46 (sb, 1H, NH);31P { H} NMR (CDCl3, 243 MHz):
δ 19.47; ESI-MS: m/z 437 (M+, 100%). Anal. Calcd for C15H18Cl2N3O4PS: C 41.11, H
4.14, N 9.59; found C 41.25, H 3.90, N 9.30.
Herbicidal Activity Methods
The herbicidal evaluation was carried out in the laboratory of biological activities
test, Nankai University, Tianjin, China. Compounds 3 were determined with Brassica
campestris L. and Radix Echinochloa crus-galli as samples of annual dicotyledonous and
monocotyledonous plants, respectively, using a previously reported procedure.15 For all of
the bioassay tests, each treatment was repeated twice.
CONCLUSION
In summary, a series of novel O,O-diethyl N-{4-methyl-[1,2,3]thiadiazole-
5-carbonyl}-1-amino-1-substitutedbenzyl phosphonates 3 were synthesized by the
condensation of O,O-diethyl α-amino substitutedbenzyl phosphonate 1 with 4-methyl-
[1,2,3]thiadiazole-5-carboxylic acid 2 under mild condition. The results of a preliminary
bioassay (in vitro) indicated that some of the title compounds 3 possessed moderate to
good herbicidal activities against dicotyledonous plants (Brassica campestris L) at the
concerntration of 100 mg/L, but weaker than that of the commercially available herbicide,
glyphosate, at both 100 mg/L and 10 mg/L.

α-AMINO PHOSPHONATES WITH [1,2,3]THIADIAZOLE RING
2029
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