Journal of Agricultural and Food Chemistry
Article
displayed >90% inhibition against A. juncea and E. prostrata;
compound I-16 with a nitrogen group on the ortho position of
the benzene ring showed 75% inhibition against E. prostrata.
This promising result indicated that the introduction of an
electron-withdrawing group at the ortho position of the
benzene ring appears to favor herbicidal activity. For
compounds (I-19−I-24) with two chlorine substituents on
the benzene ring, compound I-20 with a chlorine atom at 2,4-
positions displayed higher herbicidal activity than those with
substituents on the other positions. When different substituents
were introduced to the 1,3-cyclohexanedione ring, it was found
that the addition of two methyl groups at position C4 of the
ring favors herbicidal activity. Among the 2,4-disubstituted
analogues, compounds with 2,4-dichloro, 2-CH3-4-chloro, and
2,4-dibromo substituents on the benzene ring displayed higher
herbicidal activity than those with other types of substituents at
the same positions. It was interesting that the more powerful
electron-withdrawing groups on the benzene ring were
detrimental to herbicidal activity. The possible reason for this
observation is that when more electron-withdrawing groups
were introduced in the benzene ring, the pKa values of
compounds decreased. The instability of these compounds
increased as well. The electron-deficient benzene rings made
the ether bonds in these compounds very weak, indicating an
easy metabolism of the compounds when absorbed by plants.
To study the herbicidal activity of other ring systems, we
synthesized compounds II. As shown in Table 2, compared to
their benzene-substituted analogues, compounds II-2 and II-7
with naphthalene rings displayed more enhanced herbicidal
activity than compound I-2. To our surprise, compound II-13
with a 1-bromonaphthalen-2-yl group displayed significantly
higher herbicidal activity than the phenyl-substituted analogues.
At the dosage of 150 g ai/ha, II-13 displayed complete control
against the tested broadleaf weeds (E. prostrata, A. retroflexus,
and A. juncea), 80% inhibition against D. sanguinalis, and 70%
inhibition against S. faberii.
Herbicidal Spectrum and Crop Safety of II-13. The
herbicidal spectrum experiments indicated that compound II-
13 displayed >70% inhibition against 11 of the 13 tested weeds
at the dasage of 150 g ai/ha (Table 3). It is worth noting that,
at the rate of 150 g ai/ha, II-13 displayed 70% inhibition ratio
against S. faberii, whereas mesotrione was almost inactive to it
at the same rate. Even at a rate of 37.5 g ai/ha, II-13 still
displayed 100% control of E. prostrata, A. retroflexus, and
A. juncea, >80% inhibition of C. serotinum and S. media, and
60% control of D. sanguinalis, which were nearly as potent as
mesotrione against these six weeds. To evaluate whether II-13
has the potential to be developed as a herbicide or not, we
tested its crop safety (Table 4). The results indicated that
canola and maize displayed high tolerance to II-13 at the rate of
150 g ai/ha, whereas mesotrione was not selective for canola
(100% injury), indicating that II-13 has the potential to be
developed as a postemergence herbicide for weed control in
maize and canola fields.
herbicide mesotrione. Compound II-13 displayed a strong and
broad spectrum of weed control at dosages of 37.5−150 g ai/ha
by postemergence application, which was similar to the potency
of mesotrione in controlling the growth of some weeds.
Furthermore, II-13 was selective for canola and maize at the
dosage of 150 g ai/ha, showing that II-13 could be developed
as a herbicide for canola and maize fields. II-13 is the first
HPPD inhibitor showing crop safety to canola. The promising
finding will provide a new insight for the future design of
selective HPPD inhibitors for canola fields. Further structural
optimization and field trial experiments of II-13 are ongoing.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
■
S
Detailed analytical 1H NMR, 13C NMR, and HRMS data
for triketone series I and II compounds (PDF)
AUTHOR INFORMATION
Corresponding Authors
*(W.-C.Y.) Phone: +86-27-67867800. Fax: +86-27-67867141.
■
ORCID
Funding
We are grateful to the National Natural Science Foundation of
China (No. 21332004, 21372094, and 21672079).
Notes
The authors declare no competing financial interest.
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