Insect Control: Biological and Synthetic Agents - Index of
Insect Control: Biological and Synthetic Agents - Index of
Insect Control: Biological and Synthetic Agents - Index of
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70 3: Neonicotinoid <strong>Insect</strong>icides<br />
3.3.2. Neonicotinoids Having Noncyclic<br />
Structures<br />
From the new chemical class <strong>of</strong> ring system containing<br />
neonicotinoids noncyclic structures having the<br />
same mode <strong>of</strong> action can also be deduced. These<br />
noncyclic type neonicotinoids can have as separate<br />
substituents [R 1 ,R 2 ] (i), e.g., for R 1 hydrogen or<br />
alkyl like methyl (acetamiprid) <strong>and</strong> ethyl (nitenpyram)<br />
<strong>and</strong> in the case <strong>of</strong> E ¼ NH for the substituent<br />
R 2 alkyl like methyl (clothianidin <strong>and</strong> dinotefuran),<br />
respectively.<br />
3.3.2.1. N-[(6-chloro-3-pyridinyl)methyl]-N-ethyl-<br />
N 0 -methyl-2-nitro-1,1,-ethenediamine (nitenpyram,<br />
TI-304) Starting from the cyclic nithiazine<br />
(Soloway et al., 1978), the acyclic nitenpyram (Bestguard<br />
TM ) was discovered during optimization <strong>of</strong><br />
substituents <strong>of</strong> an acyclic nitroethene (Minamida<br />
et al., 1993). The insecticidal activity <strong>of</strong> 1-(3-pyridylamino)-2-nitroethene<br />
compounds against the<br />
brown planthopper <strong>and</strong> the green leafhopper were<br />
studied. It was found that the 1-methylamino-1-<br />
(pyrid-3-ylmethylamino)-2-nitroethene was more<br />
active than the corresponding 1-ethyl, 1-methoxy,<br />
or 1-thiomethoxy derivatives. Introduction <strong>of</strong><br />
sterically large amino groups like ethylamino,<br />
isopropylamino, hydrazino, N-pyrrolidino, or Nmorpholino<br />
decreased the activity against the<br />
green rice leafhopper. Furthermore, the methylene<br />
bridge between the pyrid-3-yl <strong>and</strong> nitrogen was<br />
replaced with other linkages. However, all attempts<br />
at shortening <strong>and</strong> lengthening the linkage failed<br />
to increase the insecticidal activities against the<br />
brown planthopper <strong>and</strong> the green rice leafhopper<br />
(Akayama <strong>and</strong> Minamida, 1999). Heterocyclic<br />
aromatic substituents, different from pyrid-3-yl,<br />
were incorporated into the nitroethen structure.<br />
The replacement <strong>of</strong> pyrid-3-yl with 6-fluoro-pyrid-<br />
3-yl, 6-chloro-pyrid-3-yl, 6-bromo-pyrid-3-yl, <strong>and</strong><br />
2-chloro-1,3-thiazol-5-yl enhanced the activity<br />
against the brown planthopper.<br />
3.3.2.2. (E)-N-[(6-chloro-3-pyridinyl)methyl]-<br />
N 0 -cyano-N-methyl-ethanimidamide (acetamiprid,<br />
NI-25) Acetamiprid (Takahashi et al., 1992;<br />
Matsuda <strong>and</strong> Takahashi, 1996) has an N-cyanoamidine<br />
structure, which contains in analogy to imidacloprid<br />
<strong>and</strong> thiacloprid the CPM moiety. This<br />
neonicotinoid was invented during a search for<br />
nitromethylene derivatives by Nippon Soda Co.<br />
Ltd. in 1989 <strong>and</strong> was registered in 1995 in Japan.<br />
The insecticide is marketed under the trade name<br />
Mospilan Õ for crop protection. The noncyclic acetamiprid<br />
was discovered by optimization studies<br />
<strong>of</strong> special 2-N-cyanoimino compounds with an<br />
imidazolidine 5-ring obtained from Nihon Bayer<br />
(Yamada et al., 1999). The noncyclic 2-nitromethylene<br />
<strong>and</strong> 2-N-nitroimine derivatives are less active<br />
than the corresponding ring structures, but numerous<br />
noncyclic derivatives show excellent activities<br />
against the armyworm <strong>and</strong> aphid as well as the<br />
cockroach. Regarding the substituent on the amino<br />
group, the N-methyl group exhibited the highest<br />
activity against the diamondback moth, while<br />
derivatives with hydrogen, N-methyl, <strong>and</strong> N-ethyl<br />
showed potent activity against the cotton aphid<br />
(Yamada et al., 1999).<br />
3.3.2.3. [C(E)]-N-[(2-chloro-5-thiazolyl)methyl]-N 0 -<br />
methyl-N 00 -nitroguanidine (clothianidin, TI-435) As<br />
a result <strong>of</strong> continuous investigations <strong>of</strong> noncyclic<br />
neonicotinoids, researchers from Nihon Bayer Agrochem<br />
<strong>and</strong> Takeda in Japan found that these noncyclic<br />
neonicotinoids showed high activities against<br />
sucking insects. In the optimization process, Takeda<br />
researchers were able to demonstrate that compounds<br />
containing the nitroguanidine moiety, coupled<br />
with the thiazol-5-ylmethyl residue, have<br />
increased activity against some lepidopteran pests<br />
(Uneme et al., 1999). This is in accordance with the<br />
general pharmacophore [ w N w C(E)›X w Y], where ›<br />
X w Y is an electron-withdrawing group such as ›<br />
N w NO2, <strong>and</strong> E represents the NH w Me unit. After<br />
further optimization in this subclass, clothianidin<br />
(TI-435) emerged as the most promising derivative<br />
from this program (Ohkawara et al., 2002; Jeschke<br />
et al., 2003). Clothianidin has already been<br />
registered in Japan for foliar <strong>and</strong> soil applications<br />
under the trade names Dantotsu TM <strong>and</strong> Fullswing TM<br />
(Sumitomo Chemical Takeda Agro), <strong>and</strong> also in<br />
Korea, Taiwan, <strong>and</strong> other countries. Registrations<br />
have also been granted in North America <strong>and</strong><br />
Europe for seed treatment under the br<strong>and</strong> name<br />
Poncho Õ (Bayer CropScience).<br />
In the novel noncyclic structure <strong>of</strong> clothianidin<br />
(TI-435) (i.e., R ¼ H; E ¼ NHMe), the Nnitroguanidine<br />
pharmacophore [ w N w C(N)›N w NO2]<br />
is similar to that <strong>of</strong> imidacloprid, but the CPM group<br />
has been replaced by the CTM moiety (Ohkawara<br />
et al., 2002) (Figure 2). Clothianidin crystallizes<br />
under normal laboratory conditions using common<br />
solvents as needlelike crystals containing no additional<br />
solvent or water molecules. The best-quality<br />
crystals for X-ray structure analysis were obtained<br />
by slow evaporation <strong>of</strong> a methanol/H2O (1 : 1) solution<br />
at room temperature. Figure 8 shows a photograph<br />
using polarized light <strong>of</strong> the crystal needle with<br />
the dimensions 0.90 0.30 0.07 mm 3 used for<br />
X-ray structure analysis (Jeschke et al., 2003). Clothianidin<br />
(TI-435) was subjected to conformational