Design and syntheses of novel N -(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1 H -isoindole-1,3(2 H)-dione and N -(benzothiazol-5-yl)isoindoline-1,3-dione as potent protoporphyrinogen oxidase inhibitors

Article abstract of DOI:10.1021/jf200616y

Discovery of protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors has been one of the hottest research areas in the field of herbicide development for many years. As a continuation of our research work on the development of new PPO-inhibiting herbicides, a series of novel N-(benzothiazol-5-yl)-4,5,6,7- tetrahydro-1H-isoindole-1,3(2H)-diones (1a-p) and N-(benzothiazol-5-yl) isoindoline-1,3-diones (2a-h) were designed and synthesized according to the ring-closing strategy of two ortho-substituents. The bioassay results indicated that some newly synthesized compounds exhibited higher PPO inhibition activity than the control of sulfentrazone. Compound 1a, S-(5-(1,3-dioxo-4,5,6,7- tetrahydro-1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl) O-methyl carbonothioate, was identified as the most potent inhibitor with k_i value of 0.08 μM, about 9 times higher than that of sulfentrazone (k _i = 0.72 μM). Further green house assay showed that compound 1b, methyl 2-((5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-2(3H)-yl)-6- fluorobenzothiazol-2-yl)thio)acetate, exhibited herbicidal activity comparable to that of sulfentrazone even at a concentration of 37.5 g ai/ha. In addition, among six tested crops, wheat exhibited high tolerance to compound 1b even at a dosage of 300 g ai/ha. These results indicated that compound 1b might have the potential to be developed as a new herbicide for weed control of wheat field.

Full text of DOI:10.1021/jf200616y

ARTICLE
pubs.acs.org/JAFC
Design and Syntheses of Novel N-(Benzothiazol-5-yl)-4,5,6,7-
tetrahydro-1H-isoindole-1,3(2H)-dione and N-(Benzothiazol-5-
yl)isoindoline-1,3-dione as Potent Protoporphyrinogen
Oxidase Inhibitors
Li-Li Jiang,† Yang Zuo,† Zhi-Fang Wang,† Yin Tan,† Qiong-You Wu,† Zhen Xi,*,‡ and Guang-Fu Yang*,†
†Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University,
Wuhan 430079, P. R. China
‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P. R. China
ABSTRACT: Discovery of protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors has been one of the hottest research areas
in the field of herbicide development for many years. As a continuation of our research work on the development of new
PPO-inhibiting herbicides, a series of novel N-(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-diones (1aꢀp) and
N-(benzothiazol-5-yl)isoindoline-1,3-diones (2aꢀh) were designed and synthesized according to the ring-closing strategy of two
ortho-substituents. The bioassay results indicated that some newly synthesized compounds exhibited higher PPO inhibition activity
than the control of sulfentrazone. Compound 1a, S-(5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-
2-yl) O-methyl carbonothioate, was identified as the most potent inhibitor with ki value of 0.08 μM, about 9 times higher than that of
sulfentrazone (ki = 0.72 μM). Further green house assay showed that compound 1b, methyl 2-((5-(1,3-dioxo-4,5,6,7-tetrahydro-
1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl)thio)acetate, exhibited herbicidal activity comparable to that of sulfentrazone
even at a concentration of 37.5 g ai/ha. In addition, among six tested crops, wheat exhibited high tolerance to compound 1b even at a
dosage of 300 g ai/ha. These results indicated that compound 1b might have the potential to be developed as a new herbicide for
weed control of wheat field.
KEYWORDS: protoporphyrinogen oxidase, 4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione, isoindoline-1,3-dione, benzothiazole,
herbicide
’ INTRODUCTION
activity. We are very interested in the structure of flumioxazin, which
integrated its ortho-substituents at the 4- and 5-positions into a
heterocycle of 2H-benzo[1,4]oxazin-3(4H)-one.
Protoporphyrinogen oxidase (PPO, E.C. 1.3.3.4) is the last enz-
yme in the common tetrapyrrole biosynthesis pathway before the
pathway branches toward chlorophyll (in plant) and heme (in
animal) synthesis.1 PPO has been identified as one of the most
significant targets for several chemical families of herbicides such
as diphenylethers,2 phenylpyrazoles,3 oxadiazoles,4 triazolinones,5
thiadiazoles,6 pyrimidineones,7 oxazolidinediones,8 isoxazoles,9 and
N-phenyl phthalimides10 that have been introduced into market for
many years. These PPO-inhibiting herbicides can cause peroxidative
destruction of cellular membrane and bleaching of plant tissues in the
presence of light. In contrast to the other herbicides, PPO inhibitors
have many advantages such as low toxicity, low use-rate (10ꢀ50 g ai/
ha), broad herbicidal spectrum (active against both monocotyledon
and dicotyldon weeds), quick onset of action (necrosis within 24 h),
long lasting effect and other environmentally benign characteristics
(e.g., low toxicity).11
Among the existing PPO inhibitors, N-phenyl phthalimide has
been a very interesting and hot research area due to its broad
structural diversity.12ꢀ16 As shown in Figure 1, chlorphthalim is the
pioneering compound of the N-phenyl phthalimide family. Structural
optimization of chlorphthalim has resulted in the discovery of a lot of
structurally diverse commercial compounds, such as cinidon-ethyl,17
flumiclorac-pentyl,18,19 and flumioxazin.20,21 It has been established
that N-phenyl phthalimide has a common structural feature of
N-2,4,5-trisubstituted phenylnitrogen to obtain optimum herbicidal
It is well-known that the derivatives of benzothiazole always
possess a wide range of biological activities including antitumor,
antiviral, antimicrobial, and antiglutamate properties.22ꢀ25 Some
of benzothiazole derivatives have also been widely used in agricul-
ture. For example, bentaluron, chlobenthiazone and TCMTB
have been used as commercial fungicides for many years26,27
(Figure2). Inaddition, some2-benzothiazole thioether derivatives
also possess anticandious, antimicrobacterial, photosynthesis-
inhibiting, fungicidal, insecticidal and herbicidal properties.28ꢀ31
Previously, we have designed and discovered some benzothiazole-
type ring-closing analogues of oxadiargyl with high PPO-inhibiting
activity and green house herbicidal activity.32 Therefore, as a
continuation of our research work on the development of new
PPO inhibitors,13ꢀ15,32ꢀ36 we are very interested in the designand
synthesis of N-phenyl phthalimide bearing benzothiazole sub-
structure, N-(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-
1,3(2H)-dione 1aꢀp as shown in Figure 3. As a comparison, we
also synthesized some N-(benzothiazol-5-yl)- isoindoline-1,3-
dione derivatives 2aꢀh. Herein, we report the detailed syntheses,
Received: February 12, 2011
Accepted: April 25, 2011
Revised:
April 21, 2011
Published: April 25, 2011
r
2011 American Chemical Society
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ARTICLE
Figure 1. Chemical structures of some commercial N-phenyl phthalimides.
Figure 2. Chemical structures of some typical benzothiazole derivatives.
resulted solid was collected by filtration and washed with water (2 L),
then dried to give the desired solid products.
Data for 4a. Yield: 46%; mp 102.3ꢀ104.5 °C; 1H NMR (600 MHz,
CDCl3) δ 4.26 (bs, 2H), 7.41 (d, J = 10.2 Hz, 1H), 7.43 (d, J = 6.6 Hz,
1H); EI-MS 233.9 (M)þ.
Data for 4b. Yield: 42%; mp 101.3ꢀ103.9 °C; 1H NMR (400 MHz,
CDCl3) δ 4.38 (bs, 2H), 7.32 (s, 1H), 7.44 (s, 1H); EI-MS 206.8 (M)þ.
Preparation of 6-Fluoro-2-mercapto-5-nitrobenzothia-
zole (5a) and 6-Chloro-2-mercapto-5-nitrobenzothiazole
(5b). Potassium O-ethyl carbonodithioate (90 mmol, 14.43 g) was
dissolved in 300 mL of DMF, and then, compound 4a,b was added. The
resulted mixture was heated to a temperature of 80ꢀ85 °C. After the
reaction completed according to the TLC detection, the solution was
slowly poured into 500 mL of water and acidified with concentrated
hydrogen chloride to pH = 1ꢀ2. The resulted solid was filtered off,
dried, and recrystallized to afford compound 5a or 5b.
Figure 3. Design strategy of the title compounds.
PPO inhibition activity and herbicidal activities of compounds
1aꢀp and 2aꢀh, and the results indicate that these compounds
display good PPO inhibition activity and promising herbicidal
activity.
Data for 5a. Yield: 66%; mp 190.1ꢀ191.3 °C; 1H NMR (600 MHz,
DMSO) δ 7.85 (d, J = 6.6 Hz, 1H), 8.02 (d, J = 11.4 Hz, 1H), 14.11(bs,
1H); ESI-MS 229.0 (M ꢀ H)ꢀ.
Data for 5b. Yield: 87%; mp 230.3ꢀ232.1 °C; 1H NMR (600 MHz,
DMSO) δ 7.84 (s, 1H), 8.17 (s, 1H), 14.24 (bs, 1H); ESI-MS 245.0
(M ꢀ H)ꢀ.
’ MATERIALS AND METHODS
Preparation of 6-Fluoro-2-mercapto-5-aminobenzothia-
zole (6a) and 6-Chloro-2-mercapto-5-aminobenzothiazole
(6b). Fe powder was added portionwise to a stirred solution of NH4Cl
(0.83 g) and 5a,b (10.4 mmol) in a mixture of EtOH/H2O (v/v: 10:1,
220 mL) at reflux temperature. After TLC detection showing that
reaction was finished, the reaction mixture was filtered and concentrated
to dryness. The residue was dissolved in water (200 mL) and extracted
with EtOAc (200 mL), and the organic phase was washed with brine
(150 mL), dried, filtered, and then concentrated to give the desired solid
products.
All chemical reagents were commercially available and treated with
standard methods before use. Solvents were dried in a routine way and
1
redistilled before use. H NMR spectra were recorded on a VARIAN
Mercury-Plus 600 or 400 spectrometer in CDCl3 or DMSO-d6 with
TMS as the internal reference. Mass spectral data were obtained on a
ThermoFisher Mass platform DSQII by electrospray ionization (ESI-
MS). Elemental analyses were performed on a Vario EL III elementary
analysis instrument. Melting points were taken on a Buchi B-545 melting
point apparatus and are uncorrected.
Preparation of 2,4-Disubstituted 5-Nitroanilines (4a and
4b). A solution of HNO3 (2.77 g, 44 mmol) in concentrated H2SO4
(43.1 g, 440 mmol) was added dropwise to a stirred mixture of 3a,b (40
mmol) and concentrated H2SO4 (200 mL) in an ice bath (ꢀ20 °C). The
complete addition took about 15 min. After stirring for 3 h, the solution
was slowly poured into a mixture of ice and water (1000 mL). The
Data for 6a. Yield: 31%; mp 250.1ꢀ252.3 °C; 1H NMR (600 MHz,
DMSO) δ 5.54 (s, 2H), 6.73 (d, J = 9.0 Hz, 1H), 7.39(d, J = 10.2 Hz,
1H), 13.43(bs, 1H); ESI-MS 199.0 (M ꢀ H)ꢀ.
Data for 6b. Yield: 76%; mp 256.7ꢀ258.4 °C; 1H NMR (600 MHz,
DMSO) δ 5.69 (s, 2H), 6.77 (s, 1H), 7.56 (s, 1H), 13.47 (bs, 1H); ESI-
MS 216.9 (M þ H)þ.
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Preparation of 2-(6-Fluoro-2-mercaptobenzothiazol-5-
yl)-4,5,6,7-tetrahydro-1H- isoindole-1,3(2H)-dione (7a) and
2-(6-Chloro-2-mercaptobenzothiazol-5-yl)-4,5,6,7- tetrahy-
dro-1H-isoindole-1,3(2H)-dione (7b). A solution of compound 6a
(or 6b) (13.7 mmol) and 4,5,6,7-tetrahydroisobenzofuran-1,3-dione
(2.31 g, 15.2 mmol) in glacial acetic acid (160 mL) was refluxed for
about 3 h. After the reaction was complete according to the TLC
detection, the solution was slowly poured into 500 mL of water. The
resulting mixture was stirred until the solid appeared. Then, after
filtration, the obtained solid was dried and recrystallized to afford
compound 7a or 7b.
1H), 7.72 (d, J = 6.0 Hz, 1H); ESI-MS 435.1 (M þ H)þ. Anal. Calcd for
C20H19FN2O4S2: C, 55.28; H, 4.41; N, 6.45. Found: C, 55.24; H, 4.71;
N, 6.33.
1
Data for 1i. Yield: 48%; mp 176ꢀ178 °C; H NMR (600 MHz,
CDCl3) δ 1.86 (s, 4H), 2.47 (s, 4H), 4.01 (s, 3H), 7.87 (s, 1H), 8.04 (s,
1H); ESI-MS 408.9 (M þ H)þ. Anal. Calcd for C17H13ClN2O4S2: C,
49.94; H, 3.20; N, 6.85. Found: C, 50.00; H, 3.31; N, 6.75.
1
Data for 1j. Yield: 49%; mp 166ꢀ167 °C; H NMR (600 MHz,
CDCl3) δ 1.40 (t, J = 7.2 Hz, 3H), 1.86 (s, 4H), 2.47 (s, 4H), 4.45 (q, J =
7.2 Hz, 2H), 7.87 (s, 1H), 8.04 (s, 1H); ESI-MS 421.3 (M ꢀ H)ꢀ. Anal.
Calcd for C18H15ClN2O4S2: C, 51.12; H, 3.58; N, 6.62. Found: C, 51.26;
H, 3.67; N, 6.36.
Data for 7a. Yield: 58%; mp 283.4ꢀ285.2 °C; 1H NMR (600 MHz,
DMSO) δ 1.75 (s, 4H), 2.35 (s, 4H), 7.34 (d, J = 6.6 Hz, 1H), 7.87 (d, J =
9.0 Hz, 1H), 14.00 (bs, 1H); ESI-MS 333.0 (M ꢀ H)ꢀ.
Data for 1k. Yield: 76%; oil; 1H NMR (600 MHz, CDCl3) δ 1.28 (t,
J = 7.2 Hz, 3H), 1.86 (s, 4H), 2.47 (s, 4H), 4.16 (s, 2H), 4.23 (q, J = 7.2
Hz, 2H), 7.72 (s, 1H), 7.89 (s, 1H); ESI-MS 437.2 (M þ H)þ. Anal.
Calcd for C19H17ClN2O4S2: C, 52.23; H, 3.92; N, 6.41. Found: C, 52.19;
H, 4.12; N, 6.31.
Data for 7b. Yield: 77%; mp 296.3ꢀ298.4 °C; 1H NMR (600 MHz,
DMSO) δ 1.75 (s, 4H), 2.36 (s, 4H), 7.40 (s, 1H), 8.07 (s, 1H), 14.09
(bs, 1H); ESI-MS 348.9 (M ꢀ H)ꢀ.
1
Data for 1l. Yield: 54%; mp 151ꢀ152 °C; H NMR (600 MHz,
General Procedure for the Preparation of the Title Com-
pounds 1aꢀp. K2CO3 powder (0.33 g, 2.4 mmol) was added to a
solution of 7a (or 7b) (1.2 mmol) in acetone (20 mL). After stirring for
10 min at room temperature, halogen derivative (RX, 1.8 mmol) in
acetone solution was added dropwise to the mixture. The resulted
mixture reacted for about 30 min and then was filtered and concentrated.
The residue was purified via flash chromatography to give the pure
products 1aꢀp in yields of 43ꢀ76%.
CDCl3) δ 1.26 (t, J = 7.2 Hz, 3H), 1.70 (d, J = 7.2 Hz, 3H), 1.86 (s, 4H),
2.47 (s, 4H), 4.20 (q, J = 7.2 Hz, 2H), 4.67 (q, J = 7.2 Hz, 1H), 7.73 (s,
1H), 7.90 (s, 1H); ESI-MS 451.0 (M þ H)þ. Anal. Calcd for
C20H19ClN2O4S2: C, 53.27; H, 4.25; N, 6.21. Found: C, 53.44; H,
3.97; N, 6.41.
1
Data for 1m. Yield: 48%; mp 115ꢀ116 °C; H NMR (600 MHz,
CDCl3) δ 1.21 (t, J = 7.2 Hz, 3H), 1.76 (s, 6H), 1.85 (s, 4H), 2.46 (s,
4H), 4.18 (q, J = 7.2 Hz, 2H), 7.77 (s, 1H), 7.91 (s, 1H); ESI-MS 465.0
(M þ H)þ. Anal. Calcd for C21H21ClN2O4S2: C, 54.24; H, 4.55; N,
6.02. Found: C, 54.46; H, 4.67; N, 6.26.
1
Data for 1a. Yield: 55%; mp 176ꢀ178 °C; H NMR (600 MHz,
CDCl3) δ 1.85 (s, 4H), 2.47 (s, 4H), 4.00 (s, 3H), 7.72 (d, J = 9.0 Hz,
1H), 7.88 (d, J = 6.0 Hz, 1H); ESI-MS 393.0 (M þ H)þ. Anal. Calcd for
C17H13FN2O4S2: C, 52.03; H, 3.34; N, 7.14. Found: C, 51.82; H, 3.30;
N, 6.93.
Data for 1n. Yield: 48%; mp 88ꢀ89 °C; 1H NMR (600 MHz,
CDCl3) δ 1.26 (t, J = 7.2 Hz, 3H), 1.86 (s, 4H), 2.47 (s, 4H), 2.90 (t, J =
7.2 Hz, 2H), 3.59 (t, J = 7.2 Hz, 2H), 4.17 (q, J = 7.2 Hz, 2H), 7.73 (s,
1H), 7.88 (s, 1H); ESI-MS 451.0 (M þ H)þ. Anal. Calcd for
C20H19ClN2O4S2: C, 53.27; H, 4.25; N, 6.21. Found: C, 53.26; H,
4.69; N, 6.17.
Data for 1b. Yield: 43%; mp 86ꢀ87 °C; 1H NMR (600 MHz,
CDCl3) δ 1.85 (s, 4H), 2.46 (s, 4H), 3.79 (s, 3H), 4.17 (s, 2H), 7.58 (d,
J = 9.0 Hz, 1H), 7.72 (d, J = 6.0 Hz, 1H); ESI-MS 407.1 (M þ H)þ. Anal.
Calcd for C18H15FN2O4S2: C, 53.19; H, 3.72; N, 6.89. Found: C, 53.34;
H, 3.90; N, 6.71.
Data for 1o. Yield: 55%; oil; 1H NMR (600 MHz, CDCl3) δ 1.25 (t,
J = 7.2 Hz, 3H), 1.85 (s, 4H), 2.15ꢀ2.17 (m, 2H), 2.47 (s, 4H), 2.49
(t, J = 7.2 Hz, 2H), 3.40 (t, J = 7.2 Hz, 2H), 4.13 (q, J = 7.2 Hz, 2H), 7.72
(s, 1H), 7.88 (s, 1H); ESI-MS 465.0 (M þ H)þ. Anal. Calcd for
C21H21ClN2O4S2: C, 54.24; H, 4.55; N, 6.02. Found: C, 54.49; H, 4.58;
N, 5.83.
Data for 1c. Yield: 48%; mp 98ꢀ99 °C; 1H NMR (600 MHz, CDCl3)
δ 1.28 (t, J = 7.2 Hz, 3H), 1.85 (s, 4H), 2.46 (s, 4H), 4.15 (s, 2H), 4.23
(q, J = 7.2 Hz, 2H), 7.58 (d, J = 9.0 Hz, 1H), 7.71 (d, J = 6.6 Hz, 1H); ESI-
MS 421.1 (M þ H)þ. Anal. Calcd for C19H17FN2O4S2: C, 54.27; H,
4.08; N, 6.66. Found: C, 54.47; H, 4.36; N, 6.65.
1
Data for 1d. Yield: 66%; oil; 1H NMR (600 MHz, CDCl3) δ 1.26 (t,
J = 7.2 Hz, 3H), 1.70 (d, J = 7.8 Hz, 3H), 1.85 (s, 4H), 2.46 (s, 4H), 4.21
(q, J = 7.2 Hz, 2H), 4.66 (q, J = 7.2 Hz, 1H), 7.59 (d, J = 9.0 Hz, 1H), 7.73
(d, J = 6.0 Hz, 1H); ESI-MS 435.1 (M þ H)þ. Anal. Calcd for
C20H19FN2O4S2: C, 55.28; H, 4.41; N, 6.45. Found: C, 55.27; H,
4.59; N, 6.27.
Data for 1p. Yield: 69%; mp 114ꢀ117 °C; H NMR (600 MHz,
CDCl3) δ 1.85 (s, 4H), 2.47 (s, 4H), 3.79 (s, 3H), 4.18 (s, 2H), 7.73 (s,
1H), 7.89 (s, 1H); ESI-MS 421.3 (M ꢀ H)ꢀ. Anal. Calcd for
C18H15ClN2O4S2: C, 51.12; H, 3.58; N, 6.62. Found: C, 51.29; H,
3.84; N, 6.43.
Preparation of 2-(2,4-Disubstituted phenyl)isoindoline-
1,3-dione (8a and 8b). A solution of 2,4-disubstituted aniline (100
mmol) and phthalic anhydride (15.5 g, 105 mmol) in 150 mL of glacial
acetic acid was refluxed for about 2 h. Then, the solution was slowly
poured into 1000 mL of water (1000 mL). After stirring for about
30 min, the resulting solid was collected by filtration, washed with water
(3 ꢁ 100 mL), and then dried to give to the desired solid products.
Data for 8a. Yield: 96%; mp 163.5ꢀ164.2 °C; 1H NMR (600 MHz,
CDCl3) δ 7.22 (d, J = 9.0 Hz, 1H), 7.56 (dd, J1 = 1.8 Hz, J2 = 9.0 Hz,
1H), 7.75 (d, J = 1.8 Hz, 1H), 7.82 (dd, J1 = 3.0 Hz, J2 = 5.4 Hz, 2H), 7.97
(dd, J1 = 3.0 Hz, J2 = 5.4 Hz, 2H); EI-MS 358.8 (M þ Na)þ.
Data for 8b. Yield: 81%; mp 133.0ꢀ134.8 °C; 1H NMR (600 MHz,
CDCl3) δ 7.26 (d, J = 15.2 Hz, 2H), 7.31 (d, J = 6.4 Hz, 1H), 7.81 (dd,
J1 = 2.4 Hz, J2 = 5.4 Hz, 2H), 7.97 (dd, J1 = 2.4 Hz, J2 = 5.4 Hz, 2H); ESI-
MS: 274.2 (M ꢀ H)ꢀ.
Data for 1e. Yield: 49%; oil; 1H NMR (600 MHz, CDCl3) δ 1.27 (d,
J = 6.6 Hz, 6H), 1.85 (s, 4H), 2.46 (s, 4H), 4.11 (s, 2H), 5.08ꢀ5.10 (m,
1H), 7.58 (d, J = 8.4 Hz, 1H), 7.70 (d, J = 6.6 Hz, 1H); ESI-MS 435.0 (M
þ H)þ. Anal. Calcd for C20H19FN2O4S2: C, 55.28; H, 4.41; N, 6.45.
Found: C, 55.50; H, 4.70; N, 6.28.
1
Data for 1f. Yield: 60%; mp 124ꢀ125 °C; H NMR (600 MHz,
CDCl3) δ 1.47 (s, 9H), 1.85 (s, 4H), 2.46 (s, 4H), 4.06 (s, 2H), 7.58 (d,
J = 9.0 Hz, 1H), 7.70 (d, J = 6.0 Hz, 1H); ESI-MS 435.0 (M þ H)þ. Anal.
Calcd for C20H19FN2O4S2: C, 55.28; H, 4.41; N, 6.45. Found: C, 55.46;
H, 4.60; N, 6.34.
Data for 1g. Yield: 66%; oil; 1H NMR (600 MHz, CDCl3) δ 0.93 (t,
J = 7.2 Hz, 3H), 1.66ꢀ1.68 (m, 2H), 1.85 (s, 4H), 2.46 (s, 4H), 4.13 (t,
J = 7.2 Hz, 2H), 4.16 (s, 2H), 7.58 (d, J = 8.4 Hz, 1H), 7.72 (d, J = 6.0 Hz,
1H); ESI-MS 435.1 (M þ H)þ. Anal. Calcd for C20H19FN2O4S2: C,
55.28; H, 4.41; N, 6.45. Found: C, 55.01; H, 4.60; N, 6.41.
Preparation of 2-(2,4-Disubstituted phenyl)-5-nitroisoin-
doline-1,3-dione (9a and 9b). A solution of HNO3 (3.52 g, 55
mmol) in concentrated H2SO4 (48.5 g, 495 mmol) was added dropwise
to a stirred mixture of 8a (or 8b) (50 mmol) and concentrated H2SO4
1
Data for 1h. Yield: 60%; oil; H NMR (600 MHz, CDCl3) δ 1.27
(t, J = 7.2 Hz, 3H), 1.85 (s, 4H), 2.46 (s, 4H), 2.90 (t, J = 7.2 Hz,
2H),3.58 (t, J = 7.2 Hz, 2H), 4.17 (q, J = 7.2 Hz, 2H), 7.58 (d, J = 9.0 Hz,
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(180 mL) in an ice bath (ꢀ15 °C). The complete addition took about 15
min. After stirring for 3 h, the solution was slowly poured into a mixture
of ice and water (1000 mL). The resulting solid was collected by
filtration, washed with water (3 ꢁ 500 mL), and then dried to give to
the desired solid products.
(dd, J1 = 3.0 Hz, J2 = 5.4 Hz, 2H); EI-MS 430.6 (M)þ. Anal. Calcd for
C20H15FN2O4S2: C, 55.80; H, 3.51; N, 6.51. Found: C, 55.50; H, 3.71;
N, 6.70.
1
Data for 2d. Yield: 59%; mp 137ꢀ139 °C; H NMR (600 MHz,
CDCl3) δ 1.27 (d, J = 6.0 Hz, 6H), 4.13 (s, 2H), 5.09ꢀ5.11 (m, 1H),
7.65 (d, J = 9.0 Hz, 1H), 7.81ꢀ7.84 (m, 3H), 7.99ꢀ8.00 (m, 2H); EI-MS
452.7 (M þ Na)þ. Anal. Calcd for C20H15FN2O4S2: C, 55.80; H, 3.51;
N, 6.51. Found: C, 55.76; H, 3.30; N, 6.27.
Data for 9a. Yield: 90%; oil; 1H NMR (600 MHz, CDCl3) δ 7.86 (dd,
J1 = 3.6 Hz, J2 = 5.4 Hz, 2H), 7.98ꢀ8.01 (m, 4H); EI-MS 380.4 (M)þ.
Data for 9b. Yield: 88%; mp 191.5ꢀ193.7 °C; 1H NMR (600 MHz,
CDCl3) δ 7.52 (d, J = 9.0 Hz, 1H), 7.86 (dd, J1 = 3.6 Hz, J2 = 5.4 Hz,
2H), 8.00 (dd, J1 = 2.4 Hz, J2 = 5.4 Hz, 2H), 7.52 (d, J = 7.2 Hz, 1H); EI-
MS 320.4 (M)þ.
1
Data for 2e. Yield: 71%; mp 119ꢀ121 °C; H NMR (600 MHz,
CDCl3) δ 0.93 (t, J = 7.2 Hz, 3H), 1.65ꢀ1.71 (m, 2H), 4.14 (t, J = 6.6
Hz, 2H), 4.18 (s, 2H), 7.64 (d, J = 9.0 Hz, 1H), 7.83ꢀ7.84 (m, 3H), 7.99
(m, 2H); EI-MS 453.4 (M þ Na)þ. Anal. Calcd for C20H15FN2O4S2: C,
55.80; H, 3.51; N, 6.51. Found: C, 55.92; H, 3.34; N, 6.72.
Preparation of 2-(2,4-Disubstituted phenyl)-5-aminoi-
soindoline-1,3-dione (10a and 10b). Fe powder (5.6 g, 99 mmol)
was added portionwise to a stirred solution of NH4Cl (4 g, 74 mmol), 9a
(or 9b) (49.7 mmol) in a mixture of EtOH/H2O (v/v: 10:1, 220 mL) at
refluxing temperature. After TLC detection showed that reaction was
finished, the reaction mixture was filtered and concentrated to dryness.
The residue was dissolved in water (200 mL) and extracted with EtOAc
(200 mL), and the organic phase was washed with brine (150 mL), dried,
filtered, and then concentrated to give the desired solid products.
Data for 10a. Yield: 37%; mp 180.2ꢀ182.5 °C; 1H NMR (600 MHz,
CDCl3) δ 4.25 (bs, 2H), 6.73 (s, 1H), 7.61 (s, 1H), 7.80 (dd, J1 = 3.0 Hz,
J2 = 5.4 Hz, 2H), 7.96 (dd, J1 =3.0 Hz, J2 = 5.4 Hz, 2H); EI-MS 349.4 (M)þ.
Data for 10b. Yield: 44%; mp 165.2ꢀ167.3 °C; 1H NMR(600 MHz,
CDCl3) δ 4.05 (bs, 2H), 6.73 (d, J = 6.6 Hz, 1H), 7.21 (d, J = 9.0 Hz,
1H), 7.80 (dd, J1 = 3.0 Hz, J2 = 5.4 Hz, 2H), 7.96 (dd, J1 = 3.0 Hz, J2 = 5.4
Hz, 2H); ESI-MS 290.7 (M þ H)þ.
Data for 2f. Yield: 45%; oil; 1H NMR (600 MHz, CDCl3) δ 1.27 (t,
J = 6.9 Hz, 3H), 2.91 (t, J = 6.9 Hz, 2H), 3.60 (t, J = 6.9 Hz, 2H), 4.17
(q, J = 6.9 Hz, 2H), 7.63 (d, J = 8.4 Hz, 1H), 7.82ꢀ7.85 (m, 3H), 7.99
(dd, J1 = 3.0 Hz, J2 = 5.4 Hz, 2H); EI-MS 430.4 (M)þ. Anal. Calcd for
C20H15FN2O4S2: C, 55.80; H, 3.51; N, 6.51. Found: C, 55.66; H, 3.13;
N, 6.72.
Data for 2g. Yield: 48%; oil; 1H NMR (600 MHz, CDCl3) δ 1.26 (t,
J = 7.2 Hz, 3H), 1.72 (d, J = 7.2 Hz, 3H), 4.22 (q, J = 7.2 Hz, 2H), 4.69 (q,
J = 7.2 Hz, 1H), 7.83ꢀ7.84 (m, 3H), 7.95 (s, 1H), 7.99ꢀ8.00 (m, 2H);
EI-MS 446.0 (M)þ. Anal. Calcd for C20H15ClN2O4S2: C, 53.75; H,
3.38; N, 6.27. Found: C, 53.80; H, 2.98; N, 6.33.
Data for 2h. Yield: 42%; oil; 1H NMR (600 MHz, CDCl3) δ 1.27 (t,
J = 7.2 Hz, 3H), 2.91 (t, J = 6.9 Hz, 2H), 3.60 (t, J = 6.9 Hz, 2H), 4.17
(q, J = 7.2 Hz, 2H), 7.83ꢀ7.84 (m, 3H), 7.94 (s, 1H), 7.99ꢀ8.01
(m, 2H); ESI-MS 446.8 (M þ H)þ. Anal. Calcd for C20H15ClN2O4S2:
C, 53.75; H, 3.38; N, 6.27. Found: C, 53.49; H, 3.87; N, 6.37.
Enzyme Expression, Purification and Inhibition Kinetic
Analysis. The expression of the recombinant human PPO enzyme was
performed according to the reported methods,37ꢀ39 which have been
described in detail previously.32 Because the product of the enzymatic
reaction has a maximum excitation wavelength at 410 nm and a
maximum emission wavelength at 630 nm, the PPO activity can be
assayed by fluorescence as described previously.40ꢀ43 The concentration
of protoporphyrinogen IX was determined by the difference of the
absorption of protoporphyrin IX before and after the complete enzyme
oxidation of the substrate monitored by UVꢀvis spectrophotometer at a
wavelength of 410 nm. The concentration of protoporphyrin IX was
calculated from the calibration graph. In assays, the inhibitors were
dissolved in dimethyl sulfoxide (DMSO). The final concentration ranged
from 0.005 μM to 250 μM. The enzymatic reaction rate was measured in
100 mM potassium phosphate (pH = 7.5), 5 mM DTT, 1 mM EDTA,
Tween 80 (0.03%, v/v), 200 mM imidazole, 5 μM FAD, and approxi-
mately 0ꢀ40 μg of protein. The reaction was initiated by adding the
substrate (0ꢀ6.5 μM) to the assay mixture, and the formation of
protoporphyrin IX was monitored at room temperature using a fluo-
rescence detector with the excitation and emission wavelengths set to
410 and 631 nm, respectively. The kinetic parameters were evaluated
by Sigma Plot software 10.0 (SPSS, Chicago, IL, USA). IC50 was
determined by measuring PPO activity over a range of inhibitor
concentrations at a single substrate concentration. IC50 values were
calculated by fitting v versus [I] data to a single binding site model
described by eq 1,
Preparation of 2-(2-Mercapto-6-chlorobenzothiazol-5-
yl)isoindoline-1,3-dione (11a) and 2-(2-Mercapto-6-fluoro-
benzothiazol-5-yl)isoindoline-1,3-dione (11b). Potassium O-
ethyl carbonodithioate (50 mmol, 8.0 g) was dissolved in 160 mL of
DMF, and then, compound 10a (or 10b (25 mmol) was added. The
resulting mixture was heated to refluxing temperature. After the reaction
was complete according to the TLC detection, the solution was slowly
poured into 500 mL of water and acidified with concentrated hydrogen
chloride to pH = 1ꢀ2. The resulted solid was filtered off, dried, and
recrystallized to afford compound 11a or 11b.
Data for 11a. Yield: 95%; mp 303.2ꢀ305.6 °C; 1H NMR (600 MHz,
DMSO) δ 7.63 (s, 1H), 7.96 (s, 2H), 8.02 (s, 2H), 8.12 (s, 1H), 14.14
(bs, 1H); EI-MS 346.5 (M)þ.
Data for 11b. Yield: 85%; mp 335.1ꢀ337.2 °C; 1H NMR (600 MHz,
DMSO) δ 7.54 (d, J = 6.0 Hz, 1H), 7.21ꢀ7.96 (m, 3H), 8.01ꢀ8.03 (m,
2H), 14.04 (bs, 1H); EI-MS 330.0 (M)þ.
General Procedure for the Preparation of the Title Com-
pounds 2aꢀh. K2CO3 powder (0.33 g, 2.4 mmol) was added to a
solution of 11a (or 11b) (1.2 mmol) in acetone (20 mL). After stirring
for 10 min at room temperature, halogen derivative (RX, 1.8 mmol) in
acetone solution was added dropwise to the mixture. The resulting
mixture reacted for about 30 min and then was filtered and concentrated.
The residue was purified via flash chromatography to give the pure
products 2aꢀh in yields of 42ꢀ71%.
1
Data for 2a. Yield: 70%; mp 153ꢀ155 °C; H NMR (600 MHz,
CDCl3) δ 1.40 (t, J = 7.2 Hz, 3H), 4.45 (q, J = 7.2 Hz, 2H), 7.77 (d, J =
8.4 Hz, 1H), 7.83ꢀ7.84 (m, 2H), 8.00 (s, 3H); ESI-MS 403.2 (M þ
H)þ. Anal. Calcd for C18H11FN2O4S2: C, 53.72; H, 2.76; N, 6.96.
Found: C, 53.87; H, 2.49; N, 6.84.
max ꢀ min
1
y ¼ min þ
ð1Þ
Data for 2b. Yield: 67%; mp 140ꢀ142 °C; H NMR (600 MHz,
ꢀ x
1 þ 10logIC
50
CDCl3) δ 3.80 (s, 3H), 4.19 (s, 2H), 7.65 (d, J = 7.2 Hz, 1H), 7.84
(s, 3H), 8.00 (s, 2H); ESI-MS 403.4 (M þ H)þ. Anal. Calcd for
C18H11FN2O4S2: C, 53.72; H, 2.76; N, 6.96. Found: C, 53.51; H, 2.66;
N, 6.71.
where y is the percentage of maximal rate, max and min are the y val-
ues at which the curve levels off, x is the logarithm of inhibitor
concentration, and IC50 is the inhibitor concentration that elicits
50% of the total inhibition. As described before,44 calculated Ki value
is obtained by applying the following relationship, which exists for
competitive inhibition among Ki, Km, and IC50 at any saturating
1
Data for 2c. Yield: 62%; oil; H NMR (600 MHz, CDCl3) δ 1.26
(t, J = 7.2 Hz, 3H), 1.71 (d, J = 7.2 Hz, 3H), 4.24 (q, J = 7.2 Hz, 2H), 4.67
(q, J = 7.2 Hz, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.82ꢀ7.85 (m, 3H), 7.99
6175
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Journal of Agricultural and Food Chemistry
ARTICLE
Scheme 1. Synthetic Route for the Title Compounds 1aꢀpa
a Reagents and conditions: (a) HNO3/concd H2SO4, ꢀ20 °C; (b) CH3CH2OCS(S)K, DMF; HCl (6 N); (c) Fe, NH4Cl, EtOH/H2O, reflux; (d)
4,5,6,7-tetrahydroisobenzofuran-1,3-dione, reflux, HOAc; (e) RX, K2CO3, acetone, rt.
Scheme 2. Synthetic Route for the Title Compounds 2aꢀha
a Reagents and conditions: (a) isobenzofuran-1,3-dione, HOAc, reflux; (b) HNO3/concd H2SO4, 0 °C; (c) Fe, NH4Cl, EtOH/H2O, reflux; (d)
CH3CH2OCS(S)K, DMF; 6 N HCl; (e) RX, K2CO3, acetone, rt.
substrate concentration (S).
Ki ¼
area of the pot. Plastic pots with a diameter of 9.5 cm were filled with
soil to a depth of 8 cm. Approximately 20 seeds of the tested weeds
were sown in the soil at a depth of 1ꢀ3 cm and grown at a temperature
of 15ꢀ30 °C in a greenhouse. The air relative humidity is 50%. The
diluted formulation solutions were applied for postemergence treat-
ment, dicotyledon weeds were treated at the 2-leaf stage and mono-
cotyledon weeds were treated at the 1-leaf stage, respectively. The
postemergence application rate was 150 g ai/ha. Untreated seedlings
were used as the control group, and the solvent (DMF þ Tween-80)
treated seedlings were used as the solvent control group. Herbicidal
activity was evaluated visually 15 days post treatment. The results of
herbicidal activities are shown in Table 2, three replicates per
treatment.
IC50
ð2Þ
S=Km þ 1
Greenhouse Herbicidal Activities. The herbicidal activities of
compounds 1aꢀp, 2a, 2d, and 2e against monocotyledon weeds such as
Echinochloa crus-galli (EC), Digitaria sanguinalis (DS), and Setaria faberii
(SF), and dicotyldon weeds such as Amaranthus retroflexus (AR), Eclipta
prostrate (EP), Brassica juncea (BJ) and Abutilon theophrasti (AT) were
evaluated according to a previously reported procedure.32,45ꢀ47 Sulfen-
trazone was selected as a positive control. All test compounds were
formulated as a 100 g/L emulsified concentrates by using DMF as
solvent and Tween-80 as emulsification reagent. The concentrated
formulas were diluted with water to the required concentration and
applied to pot-grown plants in a greenhouse. The soil used was a clay
soil, pH 6.5, 1.6% organic matter, 37.3% clay particles, and CEC 12.1
mol/kg. The rate of application (g ai/ha) was calculated by the total
amount of active ingredient in the formulation divided by the surface
Crop Selectivity33,48. Conventional rice, soybean, cotton, wheat,
rape and maize were respectively planted in plots (diameter = 12 cm)
containing test soil and grown in a greenhouse at 20ꢀ25 °C. After the
plants had reached the 4-leaf stage, the spraying treatment was con-
ducted at different dosages by diluting the formulation of compound 1b
with water. The visual injury and growth state of the individual plant
6176
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Journal of Agricultural and Food Chemistry
ARTICLE
Table 1. PPO Inhibition Activity of the Title Compounds
1aꢀp and 2aꢀh
Table 2. Herbicidal Activity of Compounds 1aꢀp, 2a, 2d
and 2e
postemergence,150 g ai/ha
no.
ECa
DS
SF
AR
EP
BJb or ATc
d
1a
1b
1c
1d
1e
1f
ꢀ
ꢀ
þþ
þþ
þþ
þþ
þþ
þþ
þ
ꢀ
þþ
þþ
þþ
þ
þþþ
þþþ
þþþ
þþþ
þþþ
þþþ
þþþ
þþþ
þþ
þþþ
þþþ
þ
þþþ
þþþ
ꢀ
þþ
þþ
þþ
þþ
ꢀ
þþþ
þþþ
þþþ
þþþ
þþþ
þþ
þþþ
þþ
þþþ
þþ
þþþ
ꢀ
no.
Y
R
ki (μM)
ꢀ
1a
1b
1c
1d
1e
1f
F
COOCH3
0.08 ( 0.01
1.22 ( 0.15
0.25 ( 0.03
0.29 ( 0.07
0.21 ( 0.01
0.18 ( 0.01
0.28 ( 0.03
0.11 ( 0.01
0.52 ( 0.05
0.47 ( 0.07
1.66 ( 0.28
0.80 ( 0.15
1.66 ( 0.48
0.32 ( 0.01
0.75 ( 0.11
3.92 ( 0.54
0.51 ( 0.02
2.25 ( 0.21
132.0 ( 9.90
1.50 ( 0.06
1.24 ( 0.01
5.52 ( 1.49
85.90 ( 8.00
3.76 ( 0.10
0.72 ( 0.01
1g
1h
1i
þþ
þ
ꢀ
F
CH2COOCH3
ꢀ
F
CH2COOC2H5
ꢀ
ꢀ
ꢀ
F
CH(CH3)COOC2H5
CH2COOCH(CH3)2
CH2COOC(CH3)3
CH2COOCH2CH2CH3
CH2CH2COOC2H5
COOCH3
1j
ꢀ
ꢀ
ꢀ
þ
þ
ꢀ
F
1k
1l
ꢀ
ꢀ
ꢀ
þþþ
þþ
þþ
ꢀ
F
ꢀ
ꢀ
ꢀ
þþ
ꢀ
1g
1h
1i
F
1m
1n
1o
1p
2a
2d
2e
ꢀ
ꢀ
ꢀ
þþþ
þþ
þþ
ꢀ
F
ꢀ
ꢀ
ꢀ
þþ
þþ
ꢀ
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
F
ꢀ
ꢀ
ꢀ
þþþ
þþ
þþ
1j
COOC2H5
ꢀ
ꢀ
ꢀ
þþ
ꢀ
1k
1l
CH2COOC2H5
ꢀ
ꢀ
ꢀ
þþþ
þþþ
þþþ
þþþ
þþþ
þþ
þþþ
þþþ
þþþ
þþþ
CH(CH3)COOC2H5
C(CH3)2COOC2H5
CH2CH2COOC2H5
CH2CH2CH2COOC2H5
CH2COOCH3
ꢀ
ꢀ
ꢀ
1m
1n
1o
1p
2a
2b
2c
2d
2e
2f
ꢀ
ꢀ
þ
ꢀ
sulfentrazone
þþ
þþ
ꢀ
þþþ
a EC for E. crusgalli, DS for D. sanguinalis, SF for S. faberii, AR for A.
retroflexus, EP for E. prostrate, BJ for B. juncea and AT for A. theophrasti.
b Compounds 1aꢀp were tested against BJ. c Compounds 2a, 2d and 2e
were tested against AT. d Rating system for the growth inhibition
percentage: þþþ, 80%; þþ, 60ꢀ79%; þ, 50ꢀ59%; ꢀ, <50%
COOC2H5
F
CH2COOCH3
F
CH(CH3)COOC2H5
CH2COOCH(CH3)2
CH2COOCH2CH2CH3
CH2CH2COOC2H5
CH(CH3)COOC2H5
CH2CH2COOC2H5
F
F
subsequent reduction and final cyclization reactions to give
the key intermediates 2-(2-mercapto-6-chlorobenzothiazol-
5-yl)isoindoline-1,3-dione (11a) and 2-(2-mercapto-6- fluo-
robenzothiazol-5-yl)isoindoline-1,3-dione (11b). Then, these
two intermediates reacted with various alkylation reagents to
give the target compounds 2aꢀh in yields of 42ꢀ71%. The
structures of all intermediates and title compounds were
confirmed by elemental analyses, 1H NMR and ESI-MS
spectral data.
F
2g
2h
Cl
Cl
sulfentrazone
were observed at regular intervals. The final evaluation for crop safety of
compound 1b was conducted by visual observation in 30 days after
treatment on the 0ꢀ100 scale.
PPO Inhibition Activity. The ki values against human PPO of
the synthesized compounds 1aꢀp and 2aꢀh are listed in Table 1.
Sulfentrazone, a commercial PPO inhibitor, was used as a control.
As shown in Table 1, compounds 1aꢀh with a fluoro atom at the
6-positionalwaysdisplayedhigher PPO-inhibiting activitythan the
corresponding compounds 1iꢀp with a chloro atom at the
6-position. Except for compounds 1b, 1k, 1m, 1o and 1p, all
other compounds 1 displayed higher PPO-inhibiting activity than
sulfentrazone. The most promising one is compound 1a, whose ki
value against human PPO is 0.08 μM. This result indicates that
compound 1a shows 9 times higher PPO-inhibiting activity than
the control compound. In addition, from Table 1 we can also
conclude that compound 1 has higher PPO-inhibitingactivity than
the corresponding compound 2 bearing the same R and Y groups.
However, different from the series of compounds 1aꢀp, com-
pounds 2 bearing a fluoro substituent at the 6-position were found
to show lower PPO-inhibiting activity than the corresponding
compounds 2 bearing a chloro atom at the 6-position. For
’ RESULTS AND DISCUSSION
Synthesis of the Title Compounds. As shown in Scheme 1, the
target compound 1aꢀp was prepared by a five-step synthetic route
using 2,4-disubstituted aniline as starting materials. After nitration,
cyclization and reduction reactions, the 2,4-disubstituted aniline was
transformed into the key intermediate 2-mercapto-5-aminoben-
zothiazole (6a,b). Then, the key intermediates 6a,b reacted with
4,5,6,7-tetrahydroisobenzofuran-1,3-dione to afford 2-(2-mercapto-
benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione
(7a,b) in acceptable yields. Finally, intermediate 7aꢀc reacted with
various alkylation reagents to give the target compounds 1aꢀp in
yields of 43ꢀ76%. In addition, the synthetic route for compound
2aꢀh was as shown in Scheme 2, which also used 2,4-disubstituted
aniline as starting materials. 2,4-Disubstituted-aniline reacted with
phthalic anhydride to afford 2-(2,4-disubstituted phenyl)
isoindoline-1,3-diones (8a and 8b), which suffered nitration,
6177
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Journal of Agricultural and Food Chemistry
ARTICLE
Table 3. Further Herbicidal Testing of Compound 1b
(Postemergence)
ai/ha. Therefore, compound 1b was selected for further testing,
and the results are listed in Table 3, which indicate clearly that
compound 1b showed comparable herbicidal activity and spec-
trum as sulfentrazone. Even at a dosage as low as 37.5 g ai/ha,
compound 1b still exhibited high herbicidal activity against A.
retroflexus, E. prostrate, and A. theophrasti. In addition, we also
tested the crop selectivity of compound 1b as shown in Table 4.
Among six tested crops, only wheat exhibited high tolerance to
compound 1b by postemergence application at the dosages of
75ꢀ300 g ai/ha, whereas rice, cotton, soybean, maize, and rape
are susceptible at a dosage of 150 g ai/ha (Table 4). Even at a
dosage of 300 g ai/ha, wheat still exhibited tolerance to com-
pound 1b, which indicated that compound 1b might be devel-
oped as a potential herbicide used for weed control in wheat field.
In summary, a series of novel N-(benzothiazol-5-yl)-4,5,6,7-
tetrahydro-1H-isoindole-1,3(2H)-diones (1aꢀp) and N-(benzo-
thiazol-5-yl)isoindoline-1,3-diones (2aꢀh) were designed and
synthesized as potential PPO inhibitors. The results of in vitro
and greenhouse testing indicated that some newly synthesized
compounds had good PPO inhibition activity and herbicidal
activities at a concentration of 150 g ai/ha. Most interestingly,
compound 1a, S-(5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-
2(3H)-yl)-6-fluorobenzothiazol-2-yl) O-methyl carbonothioate,
showed the highest PPO-inhibiting activity with a ki value of
0.08 μM, about 9 times higher than that of sulfentrazone (ki =
0.72 μM). Further greenhouse testing indicated that com-
pound 1b, methyl 2-((5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-
isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl)thio)acetate, showed
comparable herbicidal activity even at a concentration of
37.5 g ai/ha. Additional crop selectivity testing showed that
wheat exhibited high tolerance to compound 1b even at a
dosage of 300 g ai/ha. These results indicate that compound
1b might have the potential to be developed as a new herbicide
for wheat field.
dosage (g ai/ha) ECa DS SF AR
EP
AT
BJ
b
1b
37.5
75
ꢀ
þ
ꢀ
þ
ꢀ
ꢀ
þþþ þþþ þþþ
þþþ þþþ þþþ
þ
þ
150
þþ þþ þþ þþþ þþþ þþþ þþþ
sulfentrazone
37.5
75
þ
þ
þ
þ
ꢀ
ꢀ
ꢀ
þþþ þþþ þþþ þþ
þþþ þþþ þþþ þþþ
þþþ þþþ þþþ þþþ
150
þþ þþ
b Rating system for the growth inhibition percentage: þþþ, 80%; þþ,
60ꢀ79%; þ, 50ꢀ59%; ꢀ, <50% a EC for E. crusgalli, DS for D.
sanguinalis, SF for S. faberii, AR for A. retroflexus, EP for E. prostrate,
AT for A. theophrasti, BJ for B. juncea.
Table 4. Crop Selectivity of Compound 1b
dosage (g ai/ha)
rice
cotton
soybean
maize
rape
wheat
75
150
300
/
60
/
/
80
/
/
50
/
/
40
/
/
50
/
0
0
0
example, the activities of compounds 2c (R = CH-
(CH3)COOC2H5, Y = F, ki = 132.0 μM) and 2f (R =
CH2CH2COOC2H5, Y = F, ki = 5.52 μM) are about 1.54
times and 1.47 times lower than those of compounds 2g (R =
CH(CH3)COOC2H5, Y = Cl, ki = 85.9 μM) and 2h (R =
CH2CH2COOC2H5, Y = Cl, ki = 3.76 μM), respectively. In
addition, Table 1 clearly indicates that the optimum R group
is COOCH3 or COOC2H5, while the optimum Y groups are F
for 4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione deriva-
tives (1aꢀp) and Cl for isoindoline-1,3-dione derivatives
(2aꢀh), respectively.
Greenhouse Herbicidal Activities. The postemergence her-
bicidal activities of compounds which displayed high PPO-
inhibition activity (ki < 2.0 μM) were tested in a greenhouse at
a concentration of 150 g ai/ha; sulfentrazone was also selected as
a control. As shown in Table 2, most of the compounds were not
found to display promising herbicidal activities at a concentration
of 150 g ai/ha against monocotyledon weeds such as E. crus-galli,
D. sanguinalis, and S. faberii. However, compounds 1b, 1c, and 1d
showed moderate herbicidal activity against these monocotyle-
don weeds at the same concentration. Fortunately, some com-
pounds bearing a fluoro atom at 6-position, such as 1a, 1b, 1d, 1e,
1f, 1g, and 1h, exhibited high and broad spectrum herbicidal
activity (>80% inhibition) at a concentration of 150 g ai/ha
against dicotyldon weeds such as A. retroflexus, E. prostrate, and B.
juncea. On the contrary, compounds 1i, 1j, 1k, and 1l, which
contained a chloro atom at the 6-position, showed much lower
herbicidal activity against the tested weeds. Besides, compound
2a showed high herbicidal activities (>80% inhibition) at a
concentration of 150 g ai/ha against dicotyldon weeds such as
A. retroflexus, E. prostrate, and A. theophrasti, and compounds 2d
and 2e exhibited high herbicidal activities (>80% inhibition)
against A. retroflexus and E. prostrate.
’ AUTHOR INFORMATION
Corresponding Author
*(G.-F.Y.) Tel: þ86-27-67867800. Fax: þ86-27-67867141. E-mail:
gfyang@mail.ccnu.edu.cn. (Z.X.) Tel: þ86-22-23504782. E-mail:
zhenxi@nankai.edu.cn.
Funding Sources
This research was supported in part by the National Basic
Research Program of China (No. 2010CB126103), the NSFC
(No. 20925206, 20932005 and 21002038), and the PCSIRT
(No. IRT0953).
’ ACKNOWLEDGMENT
We thank Dr. Jie Chen for the greenhouse testing of biological
activities.
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6178
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