Synthesis and biological activity of α-oxo-2-pyridyl methyl phosphinates

Article abstract of DOI:10.1080/10426500701792974

In an attempt to discover novel compounds with high activity and low toxicity, a series of new O,O-dimethyl-α-(substituted phenoxyacetoxy)-2- pyridyl methyl phosphinates, 5a-5h, have been designed and synthesized by the reaction of substituted phenoxyacetic chloride with 1-hydroxy-2-pyridyl methyl phosphinate, The structures of all new compounds were characterized by elementary analysis, IR, 1H NMR, and MS spectroscopies. The results of preliminary bioassay indicate that most of the target compounds have excellent inhibitory activities on barnyard grass and rape. Copyright Taylor & Francis Group, LLC.

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Synthesis and Biological
Activity of α -Oxo-2-Pyridyl
Methyl Phosphinates
Tao Wang a b & Hong Wu He b
a College of Chemistry and Chemical Engineering ,
Jiangxi Normal University , Nanchang, P. R. China
b Key Laboratory of Pesticide and Chemical
Biology, Ministry of Education , Institute of Organic
Synthesis, Central China Normal University , Wuhan,
P. R. China
Published online: 28 Jul 2008.
To cite this article: Tao Wang & Hong Wu He (2008) Synthesis and Biological Activity
of α -Oxo-2-Pyridyl Methyl Phosphinates, Phosphorus, Sulfur, and Silicon and the
Related Elements, 183:8, 1884-1891, DOI: 10.1080/10426500701792974
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Phosphorus, Sulfur, and Silicon, 183:1884–1891, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701792974
Synthesis and Biological Activity of α-Oxo-2-Pyridyl
Methyl Phosphinates
Tao Wang1,2 and Hong Wu He2
1College of Chemistry and Chemical Engineering, Jiangxi Normal
University, Nanchang, P. R. China
2Key Laboratory of Pesticide and Chemical Biology, Ministry of
Education, Institute of Organic Synthesis, Central China Normal
University, Wuhan, P. R. China
In an attempt to discover novel compounds with high activity and low toxicity, a
series of new O,O-dimethyl-α-(substituted phenoxyacetoxy)-2-pyridyl methyl phos-
phinates, 5a–5h, have been designed and synthesized by the reaction of substituted
phenoxyacetic chloride with 1-hydroxy-2-pyridyl methyl phosphinate, The struc-
tures of all new compounds were characterized by elementary analysis, IR, 1H NMR,
and MS spectroscopies. The results of preliminary bioassay indicate that most of
the target compounds have excellent inhibitory activities on barnyard grass and
rape.
Keywords α-Oxo-2-pyridyl methyl phosphinates; herbicidal activities; synthesis
INTRODUCTION
Pyruvate dehydrogenase complex (PDHc) is already known to be a site
of pesticide action, because it plays a pivotal role in cellular metabolism
catalyzing the oxidative decarboxylation of pyruvate and the subse-
quent acetylation of coenzyme A (CoA) to acety-CoA.1−4 An attempt
to design inhibitors of PDHC as herbicides using biochemical rea-
soning was reported by Baillie et al.5 Series of acetylphosphinates
and acetylphosphonates have been prepared as mechanism- based in-
hibitors of PDHc because their lowest homologues are regarded as
bioisosters of pyruvate (acetyl formate).6 A. C. Baillie et al.5 reported
Received 20 August 2007; accepted 30 August 2007.
We gratefully acknowledge financial support of this work by National Natural Science
Foundation of China (Project, No: 29572045) and National Key Basic Research Develop-
ment Program of China (“973” Project, No: 2003 C B114400).
Address correspondence to Tao Wang, College of Chemistry and Chemical Engineer-
ing, Jiangxi Normal University, Nanchang, 330022, P. R. China. E-mail: wangtao1962@
sohu.com
1884

α-Oxo-2-pyridyl Methyl Phosphinates
1885
that some acetylphosphinates and acetyl phosphonates showed mod-
est herbicidal activity due to their inhibition against PDHc. However,
the activity of them was not sufficiently high for full development as
herbicides. In the course of our research for new phosphinate deriva-
tives with good biological activities, it has been shown that certain
substituted phenoxy acetoxy alkyl phosphinates possess good herbi-
cide activities. In order to find new phosphinates with better pesticide
activity, the pyridine structural unit is introduced into their molecules,
so O,O-Dimethyl-(substituted phenoxyacetoxy)-2-pyridyl methyl phos-
phonates were synthesized by the reaction of substituted phenoxyacetic
chloride 4 with 1-hydroxy-2-pyridyl methyl phosphinate 3 under mild
conditions. The synthetic route is shown in Scheme 1.
SCHEME 1
RESULTS AND DISCUSSION
Preparation of Compounds 3 and 5
The reaction of dialkyl phosphates with aldehydes is a convenient
method used to synthesize α-hydroxyphosphonates. There are some
reports on the synthesis of α-hydroxyphosphinates. However, there
are few reports on the reaction of dimethylphosphinate 2 with
2-pyridinecarbox-aldehyde. Herein, we report the reaction of 2 with
2-pyridinecarbox-aldehyde to produce α-hydroxyphosphinate 3. The
reaction under mild conditions (room temperature) resulted in high
yields of the products 5a–5h (Table I) as shown in Scheme 1. However,
the addition of a base (triethylamine) was essential to the addition

1886
T. Wang and H. W. He
TABLE I Preparation of α-Oxophosphinates
Compd.
X Y
Formula
Color
nD20
r.t. (h) Yield (%)
5a
5b
5c
5d
5e
5f
2-Cl, 4-Cl
2-F, H
3-CF3, H
4-Cl, H
C16H16Cl2NO5P Light yellow 1.5412
16H17FNO5P Light yellow 1.5216
C17H17F3NO5P Light yellow 1.5248
C16H17ClNO5P Light yellow 1.5198
4
4
4
4
4
4
4
4
73
68
62
76
70
70
64
61
C
2-Cl, 5-CH3 C17H19ClNO5P Light yellow 1.5131
4-Cl, 5-CH3 C17H19ClNO5P Light yellow 1.5275
2-Cl, 6-Cl
2-Cl, 3-Cl
5g
5h
C
16H16Cl2NO5P Light yellow 1.5026
C16H16Cl2NO5P Light yellow 1.5162
reaction. Without the use of the triethylamine as a catalyst, the
reaction was greatly slowed and the yields were very low too. We
try to synthesize compound 3 by the addition reaction of 2 with
2-pyridinecarboxaldehyde in the presence of KF/Al2O3, but only
corresponding α-hydroxyphosphonates were found. The compounds 5
were prepared from the compound 3 and substituted phenoxyacetic
chlorides 4 in the presence of triethylamine.
The Structures of the Title Compounds 5
The molecular structures of all new compounds 5 obtained were con-
firmed by 1H NMR, IR spectra, MS and elemental analyses. In the
1H NMR spectra of 5: both the proton in the P-OCH3 and the P-CH3
moiety displayed a doublet of doublets, which was due to couplings to
the phosphorus. The proton in the OCH2CO moiety exhibited doublets,
while the proton in the P-CH moiety displayed doublet of doublets,
which was due to couplings to the phosphorus. Also, 5 showed other
Ar-H at 6.86–8.64 ppm as multiple absorptions. For 31P NMR spec-
tra, the phosphorus atom of 5a showed double peaks, giving chemical
shifts at 47.1–48.4 ppm. The IR spectra of all compounds showed nor-
mal stretching absorption bands indicating the existence of the Ph-H
(∼2950 cm−1), C=O (∼1760 cm−1), C=C (∼1620, ∼1450 cm−1), P=O
(∼1250 cm−1), P-O-C (∼1050 cm−1) and P-C (∼750 cm−1). The EI mass
spectra of compound 5 gave the anticipated molecular ion peaks. All
the fragmentation ions of 5 were consistent with the structure and can
be assigned clearly.
Herbicidal Activities
The data for the bioassays are listed in Table II. The preliminary
biological tests showed that some of the compounds 5a–h, such as 5a,

α-Oxo-2-pyridyl Methyl Phosphinates
1887
TABLE II The Inhibition Percentage of Compounds 5 to Barnyard
Grass and Rapea
Barnyard grass
Stalk Root
Rape
Stalk
Root
Compd.
X Y
10 100 (ppm) 10 100 (ppm) 10 100 (ppm) 10 100 (ppm)
5a
5b
5c
5d
5e
5f
2-Cl, 4-Cl
2-F, H
3-CF3, H
4-Cl, H
2-Cl,5-CH3 35.1
4-Cl,5-CH3 60.7
2-Cl, 6-Cl
2-Cl, 3-Cl
55.5
33.3
37.0
40.7
66.6
40.7
46.3
51.8
27.8
78.6
57.1
67.8
94.8
46.1
94.8
92.3
48.7
97.8
42.2
62.2
97.4
7.70
91.6
94.4 98.8
98.8
50.0
97.7
98.8
96.6
98.8
89.5
94.2
2.80 0.00 20.0
83.3
94.8
97.4
79.5
97.8
82.2
91.1
94.4 90.0
94.4 96.6
88.8 95.5
94.8 97.6
71.8 46.5
84.6 29.1
91.6
66.6
94.8
20.5
5.1
5g
5h
57.1
67.8
aNegative inhibition percentage shows promotive action for plant growth.
5c, 5d, 5e, 5f, etc., have excellent herbicidal activities for the root of
barnyard grass and rape. It is found that most of the target compounds
5a–h, such as 5a, 5c, 5d, 5f, etc., have excellent inhibitory activities
against stalk of rape. The property of substituting groups (X, Y) on
benzene ring has a great effect on the herbicidal activity of the com-
pounds 5a–h. Especially, compounds 5a, 5d, and 5f showed 96.6–98.8%
inhibitory effect on the root of rape at a dose of 10 ppm. According to
the results of herbicidal assays, there is a need for testing further the
herbicidal activity of compounds 5a, 5d, and 5f at lower concentrations.
CONCLUSION
In summary, we have synthesized a series of new O,O-dimethyl-
α-(substituted phenoxyacetoxy)-2-pyridyl methyl phosphinates under
mild reaction conditions. This method has the potential in the synthe-
sis of many biologically active phosphinates. The results of preliminary
bioassay indicate that most of the target compounds 5a–h have excel-
lent inhibitory activities on barnyard grass and rape.
EXPERIMENTAL
General Remarks
Melting points are uncorrected. MS were measured with a Finnigan
Trace MS spectrometer. IR were recorded with a PE-983 infrared spec-
trometer as KBr pellets. NMR were recorded in CDCl3 with a Varian
Mercury 400 spectrometer and resonances relative to TMS. Elementary

1888
T. Wang and H. W. He
TABLE III 1H NMR Chemical Shifts (TMS, CDCl3) of 5 and Coupling
Constants J (Hz)
Compd.
δ/ppm, TMS, 400 MHz
5a
1.51–1.61 (dd, 3H, P-CH3, J = 14.4 Hz), 3.69–3.73 (dd, 3H, P-OCH3, J =
12.4 Hz), 4.90–4.92 (d, 2H, -OCH2CO-, J = 10.0 Hz), 6.21–6.31 (dd, 1H,
-OCHP, J = 1 0.4 Hz), 6.81–8.62 (m, 7H, -C5H4N, -C6H3), 31P NMR, 47.1–
48.4, J = 518 Hz.
5b
5c
5d
5e
5f
1.50–1.59 (dd, 3H, P-CH3, J = 14.8Hz), 3.68–3.72 (dd, 3H, P-OCH3, J =
12.4 Hz), 4.91–4.93 (d, 2H, -OCH2CO-, J = 9.6 Hz), 6.22–6.34 (dd, 1H,
-OCHP, J = 12.4 Hz), 6.94–8.63 (m, 8H, -C5H4N, -C6H4).
1.51∼1.59 (dd, 3H, P-CH3, J = 14.8 Hz), 3.68–3.73 (dd, 3H, P-OCH3, J = 12.4
Hz), 4.89–4.92 (d, 2H, -OCH2CO-, J = 11.6 Hz), 6.22–6.34 (dd, 1H, -OCHP,
J = 12.8 Hz), 7.11–8.64 (m, 8H, -C5H4N, -C6H4).
1.50∼1.60 (dd, 3H, P-CH3, J = 14.8Hz), 3.68∼3.73 (dd, 3H, P-OCH3, J = 12.4
Hz), 4.82∼4.84 (d, 2H, -OCH2CO-, J = 10.4 Hz), 6.21∼6.32 (dd, 1H, -OCHP,
J = 12.4 Hz), 6.84∼8.63 (m, 8H, -C5H4N, -C6H4).
1.50–1.58 (dd, 3H, P-CH3, J = 13.7 Hz), 2.28 (s, 3H, PhCH3), 3.69–3.73
(dd, 3H, P-OCH3, J = 12.4 Hz), 4.90–4.92 (d, 2H, -OCH2CO-, J = 9.6 Hz),
6.23–6.35 (dd, 1H, -OCHP, J = 12.4 Hz), 6.67–8.63 (m, 7H, -C5H4N, -C6H3).
1.50–1.60 (dd, 3H, P-CH3, J = 14.8 Hz), 2.27 (s, 3H, PhCH3), 3.68–3.72 (dd,
3H, P-OCH3, J = 12.4 Hz), 4.83–4.86 (d, 2H, -OCH2CO-, J = 10.4 Hz), 6.21–
6.32 (dd, 1H, -OCHP, J = 12.4 Hz), 6.62–8.63 (m, 7H, -C5H4N, -C6H3).
1.58–1.66 (dd, 3H, P-CH3, J = 14.8 Hz), 3.72–3.79 (dd, 3H, P-OCH3, J = 12.4
Hz), 4.83–4.86 (d, 2H, -OCH2CO-, J = 10.4 Hz), 6.30∼6.42 (dd, 1H, -OCHP,
J = 12.4 Hz), 7.04–8.63 (m, 7H, -C5H4N, -C6H3).
5g
5h
1.50–1.61 (dd, 3H, P-CH3, J = 14.4 Hz), 3.69–3.73 (dd, 3H, P-OCH3, J = 12.4
Hz), 4.93–4.95 (d, 2H, -OCH2CO-, J = 10.0 Hz), 6.22–6.32 (dd, 1H, -OCHP,
J = 12.4 Hz), 6.79–8.62 (m, 7H, -C5H4N, -C6H3).
analyses were taken with a Vario EL III elementary analysis instru-
ment. The reagents solvents were available commercially and purified
according to conventional methods before use.
Dichloromethylphosphine 1 was prepared according to the literature
procedure, 7∼121: b p 80–82◦C, n2D0 1.4952, Yield, 40–45%.
General Procedure for Preparation of 213
To a solution of dichloromethylphosphine 1 (5.85 g, 50.0 mmol) in dry
benzene (40 mL) was added dropwise with stirring to a cooled solution
of methanol (3.84 g, 120 mmol) and triethylamine (5.05 g, 50.0 mmol)
under nitrogen at 0∼5◦C. After the reaction mixture was standing for
1 h and then filtered, the filtrate was condensed to give dimethylphos-
phinate 2, which was used directly without further purification.

α-Oxo-2-pyridyl Methyl Phosphinates
1889
TABLE IV IR Data of Compounds 5
υ
υ
υ
υ
υ
υ
υ
υ
Compd. ph-H
C-H
C=O
Ph
P=O C-O-C
P-O-C
P-C
6a
6b
6c
6d
6e
6f
3070 2955, 2851 1770 1590,1487,1436 1229 1167 1040,900 756
3070 2955, 2852 1771 1590,1506,1436 1236 1175 1040,900 753
3076 2932, 2857 1784 1593,1495,1457 1175 1127 1040,894 762
3070 2955, 2851 1770 1593,1492,1437 1218 1142 1042,901 749
3057 2954, 2852 1771 1590,1491,1436 1225 1169 1041,900 749
3217 2956, 2857 1761 1592,1492,1436 1218 1183 1043,895 750
3068 2954, 2851 1774 1590,1456,1437 1232 1178 1043,900 786
3076 2955, 2851 1769 1578,1457,1436 1224 1147 1041,894 771
6g
6h
General Procedure for Preparation of 314−20
To a solution of 2 (1.88 g, 20.0 mmol) prepared above in dry benzene (20
mL) was added with stirring to a solution of 2-pyridine- carboxaldehyde
(2.57 g, 24.0 mmol) and catalyst triethylamine (1.01 g, 10.0 mmol) under
nitrogen at 0–5◦C. After the reaction mixture was stirred for 6–8 h at
50–60◦C, the solvent was removed under reduced pressure. The residue
was chromatographed on silica with 20% acetone in petroleum ether as
eluent to give the compound 3.
White crystal, Yield: 86.6%. m.p. 89–90◦C. IR (KBr)υ: 3258(s, OH),
3055 (w, Ph-H), 2921, 2822 (m, C-H), 1221 (s, P=O), 1132(s, C-OH),
1032, 891 (s, P-O-C), 792 (s, P-C) cm−1; 1H NMR (CHCl3,300Hz)δ: 1.40–
1.64 (dd, 3H, -CH3, J = 15.2 Hz), 3.48–3.68(dd, 3H, -OCH3, J = 12.4 Hz),
4.48(s, br, 1H,OH), 4.76–4.94 (d, 1H, -OCHP, J = 10.4 Hz), 6.76–7.22
(m, 4H, -C5H4N). MS(70ev) m/z(%):201(M+), 94 (84.83), 79 (100); Anal.
calcd. (%) for C8H12NO3P: C, 47.77; H, 6.01; N, 6.96. Found (%): C, 47.64;
H, 6.26; N, 7.08.
General Procedure for Preparation of Substituted
Phenoxyacetyl Chlorides 4
Substituted phenoxyacetic acids were prepared according to the liter-
21
ature procedure, substituted phenoxyacetic acids: X,Y = 2-Cl, 4-Cl,
m.p. 137–139◦C, Yield, 89.8%; X,Y = 2-F, H, m.p. 140–140.5◦C, Yield,
90.5%; X,Y = 3-CF3, H, m.p. 97.0–98.0◦C, Yield, 72.6%; X,Y = 4-Cl, H,
m.p. 159–61◦C, Yield, 87.7%; X,Y = 2-Cl,5-CH3, m.p. 136–138◦C, Yield,
78.5%; X,Y = 4-Cl,5-CH3, m.p. 181–183◦C, Yield, 86.0%; X,Y = 2-Cl,
6-Cl, m.p. 138–139◦C, Yield, 70.5%; X,Y = 2-Cl, 3-Cl, m.p. 171–173◦C,
Yield, 87.2%.

1890
T. Wang and H. W. He
TABLE V Elemental Analysis and MS Data of Compound 5
Calcd.(found)
Compd.
C
H
N
MS
5a
47.55 (47.33) 3.99 (3.95) 3.47 (3.09) 403 (M++1 41.51), 339 (30.70), 292
(12.06), 242 (48.69), 228 (61.41), 200
(40.40), 185 (44.19), 175 (50.37), 162
(12.87), 145 (42.49), 133 (26.31), 108
(71.68), 93 (100), 78 (51.42), 63 (46.56).
5b
5c
54.40 (54.56) 4.85 (4.69) 3.96 (3.65) 353 (M++1 42.72), 242 (29.96), 228
(62.18), 200 (33.88), 185 (46.72), 125
(74.42), 108 (75.93), 93 (100), 78 (66.08),
63 (53.09).
50.63 (51.11) 4.25 (4.44) 3.47 (3.25) 403 (M++1 45.23), 242 (32.62), 228
(48.81), 200 (41.62), 185 (36.89), 175
(54.40), 162 (10.91), 145 (75.99), 133
(17.27), 108 (78.95), 93 (97.45), 78 (100),
63 (53.85).
5d
5e
5f
51.98 (51.71) 4.63 (4.56) 3.79 (3.33) 369 (M++1 39.42), 242 (31.92), 228
(69.56), 200 (23.30), 185 (60.50), 141
(60.49), 108 (80.49), 93 (100), 78 (42.15),
63 (56.42).
53.21 (53.37) 4.99 (4.87) 3.65 (3.31) 383 (M++1 100), 242 (43.94), 228 (39.91),
200 (36.94), 185 (37.75), 155 (61.33), 125
(56.81), 108 (80.44), 93 (94.97), 78 (39.86),
63 (64.36).
53.21 (52.72) 4.99 (5.20) 3.65 (3.14) 383 (M++1 51.34), 242 (4.88), 228 (3.48),
200 (37.99), 185 (85.44), 155 (52.57), 125
(63.07), 108 (82.23), 93 (100), 78 (44.82),
63 (66.76).
5g
47.55 (47.08) 3.99 (3.95) 3.47 (2.98) 403 (M++1 28.68), 242 (31.28), 228
(26.85), 200 (20.37), 185 (8.62), 175
(34.59), 162 (4.30), 145 (27.69), 133
(22.93), 108 (46.35), 93 (100), 78 (33.72),
63 (69.37).
5h
47.55 (47.64) 3.99 (3.98) 3.47 (3.07) 403 (M++1 39.30), 242 (27.75), 228
(61.34), 200 (35.64), 185 (32.11), 175
(47.92), 162 (4.44), 145 (48.23), 133
(24.37), 108 (65.98), 93 (100), 78 (41.92),
63 (67.27).
A mixture of substituted phenoxyacetic acid (50.0 mmol) and thionyl
chloride (25 mL) was stirred and refluxed for 4 h. The thionyl chloride
was removed under reduced pressure to give substituted phenoxyacetyl
chlorides 4, which were used directly without further purification.

α-Oxo-2-pyridyl Methyl Phosphinates
1891
General Procedure for Synthesis of O,O-Dimethyl-α-
(Substituted Phenoxyacetoxy)-2-Pyridyl Methyl
Phosphinates 5
A solution of substituted phenoxyacetyl chloride 4 (22.0 mmols) in DCM
(10 mL) was added to stirred mixture of 1-hydroxyalkyl phosphinate 3
(4.02 g, 20.0 mmols) and triethylamine (2.22 g, 22.0 mmols) in DCM
(25 mL) at 20◦∼25◦C. The mixture was stirred at ambient temperature
for 4 hours, and then at 40◦C for 1 hour, washed with 0.1 M hydrochloric
acid, saturated sodium hydrogen carbonate solution, and brine respec-
tively. The resultant mixture was dried and evaporated. The residue
was chromatographed on silica with 20% acetone in petroleum ether as
eluent to give the title compounds 5. Yield: 61%∼76%. All results are
listed in Tables III, IV, and V.
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