Azido-neonicotinoids as candidate photoaffinity probes for insect nicotinic acetylcholine receptors [1]

Article abstract of DOI:10.2533/000942903777678605

The neonicotinoids are the most successful chemical class of insecticides reaching sales of more than 630 Mio $ in 2001, mainly due to the excellent market performance of imidacloprid and thiamethoxam. The insect nicotinic acetylcholine receptors (nAChRs) are the targets for these compounds, which are highly effective against a variety of sucking and chewing insects. Compared with the other neonicotinoid sales products, thiamethoxam binds in a different way, possibly to a different site of nAChRs in aphids. To gain further insight into the different modes of binding, a research program applying the photoaffinity labeling technique was started. A series of novel candidate photoaffinity probes containing a 5-azido-6-chloropyridin-3-ylmethyl group were prepared from 5-azido-6-chloropyridin-3-ylmethyl chloride, which was obtained in three steps from 6-chloropyridin-3-ylmethyl chloride. These probes showed good to excellent contact/feeding and systemic activity against Myzus persicae, however, they were at least 4- to 16-fold less effective against Aphis craccivora, Nilaparvata lugens, Spodoptera littoralis, and Diabrotica balteata than the neonicotinoid sales products. In general, the introduction of an azide group at C(5) of the 6-chloropyridin-3-ylmethyl substituent resulted in reduced potency as well as in a narrower pest spectrum. In competition binding assays with [³H]imidacloprid, analogues of imidacloprid, clothianidin, thiacloprid and thiamethoxam containing a 5-azido-6-chloropyridin- 3-ylmethyl group showed high displacing potency with nAChRs from Aphis and Myzus (K_i values: 2 to 27 nM) suggesting that these compounds are valuable candidate photoaffinity probes. Taking into account the biological screening activity as well as the receptor binding potency, 1-(5-azido-6- chloropyridin-3-ylmethyl)-2-nitroimino-imidazolidine N-(5-azido-6-chloropyridin- 3-ylmethyl)-N′-methyl-N″-nitroguanidine and 3-(5-azido-6- chloropyridin-3-ylmethyl)-2-cyanoimino-thiazolidine were identified as the preferred candidate neonicotinoid photoaffinity probes to study the imidacloprid binding site.

Full text of DOI:10.2533/000942903777678605

CROP PROTECTION RESEARCH
710
CHIMIA 2003, 57, No.11
Chimia 57 (2003) 710–714
© Schweizerische Chemische Gesellschaft
ISSN 0009–4293
Azido-Neonicotinoids as Candidate
Photoaffinity Probes for Insect Nicotinic
Acetylcholine Receptors [1]
Peter Maienfischa*, Joerg Haettenschwilera, Alfred Rindlisbacherb, Arnaud Decockc,
Henning Wellmannc, and Hartmut Kayserc
Abstract: The neonicotinoids are the most successful chemical class of insecticides reaching sales of more
than 630 Mio $ in 2001, mainly due to the excellent market performance of imidacloprid and thiamethoxam.
The insect nicotinic acetylcholine receptors (nAChRs) are the targets for these compounds, which are highly
effective against a variety of sucking and chewing insects. Compared with the other neonicotinoid sales prod-
ucts, thiamethoxam binds in a different way, possibly to a different site of nAChRs in aphids. To gain further
insight into the different modes of binding, a research program applying the photoaffinity labeling technique
was started. A series of novel candidate photoaffinity probes containing a 5-azido-6-chloropyridin-3-ylmethyl
group were prepared from 5-azido-6-chloropyridin-3-ylmethyl chloride, which was obtained in three steps
from 6-chloropyridin-3-ylmethyl chloride. These probes showed good to excellent contact/feeding and
systemic activity against Myzus persicae, however, they were at least 4- to 16-fold less effective against Aphis
craccivora, Nilaparvata lugens, Spodoptera littoralis, and Diabrotica balteata than the neonicotinoid sales
products. In general, the introduction of an azide group at C(5) of the 6-chloropyridin-3-ylmethyl substituent
resulted in reduced potency as well as in a narrower pest spectrum. In competition binding assays with
[3H]imidacloprid, analogues of imidacloprid, clothianidin, thiacloprid and thiamethoxam containing a 5-azi-
do-6-chloropyridin-3-ylmethyl group showed high displacing potency with nAChRs from Aphis and Myzus
(Ki values: 2 to 27 nM) suggesting that these compounds are valuable candidate photoaffinity probes. Taking
into account the biological screening activity as well as the receptor binding potency, 1-(5-azido-6-chloropy-
ridin-3-ylmethyl)-2-nitroimino-imidazolidine, N-(5-azido-6-chloropyridin-3-ylmethyl)-N´-methyl-N´´-nitrogua-
nidine and 3-(5-azido-6-chloropyridin-3-ylmethyl)-2-cyanoimino-thiazolidine were identified as the preferred
candidate neonicotinoid photoaffinity probes to study the imidacloprid binding site.
Keywords: Azido-neonicotinoids · Candidate photoaffinity probes · Imidacloprid · Insecticidal activity ·
Insecticides · Neonicotinoids · Nicotinic acetylcholine receptors · Thiamethoxam
1. Introduction
receptors (nAChRs) and are highly effec- subclass. It was first synthesized in 1991
tive against a variety of sucking and chew- and is now developed worldwide for use in
An important milestone in the history of ing insects. As the first representative of more than 100 crops. Thiamethoxam is
modern insect control is marked by the dis- this chemical class, imidacloprid (1) was marketed since 1998 under the trademarks
covery of the neonicotinoids [2]. These introduced to the market in 1991, and since Actara® for foliar and soil treatment and
compounds act on nicotinic acetylcholine then, a series of analogues (compounds 2 to Cruiser® for seed treatment. In all these us-
7) have been launched (Fig. 1) [3]. Today ages, thiamethoxam provides excellent
*Correspondence: Dr. P. Maienfischa
Tel.: + 41 61 323 66 47
Fax: + 41 61 323 85 29
the neonicotinoids are the fastest growing control of a broad range of commercially
chemical class of insecticides. This tremen- important pests, such as aphids, whiteflies,
dous success is based on their unique chem- thrips, rice hoppers, Colorado potato beetle,
ical and biological properties, such as flea beetles, wireworms, leaf miners as well
broad-spectrum insecticidal activity, low as some lepidopterous species [5]. Low use
application rates, excellent systemic char- rates, flexible application methods, excel-
acteristics, favourable safety profile, and a lent efficacy, and the favourable safety pro-
E-Mail: peter.maienfisch@syngenta.com
aSyngenta Crop Protection AG
Optimisation Chemistry
Schwarzwaldallee 215
CH–4002 Basel
bSyngenta Crop Protection AG
Research Biology, Insect Control
Schaffhauserstr. 101
new mode of action.
file make this new insecticide well suited
CH–4332 Stein
Our own research in this area resulted in for modern integrated pest management
the discovery of thiamethoxam (5) [4]. This programs in many cropping systems.
cSyngenta Crop Protection AG
Biochemistry
compound is a second-generation neoni-
All sales products 1 to 7 bind with high
Schwarzwaldallee 215
CH–4002 Basel
cotinoid and belongs to the thianicotinyl affinity to nicotinic acetylcholine receptors

CROP PROTECTION RESEARCH
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CHIMIA 2003, 57, No.11
[6][7]. To provide further evidence for our
recent findings that thiamethoxam binds,
compared to the other neonicotinoid sales
products, in a different way, possibly to a
different site of the receptor in aphids [7],
we have started a research program apply-
ing the photoaffinity labeling technique
to investigate neonicotinoid-receptor inter-
actions and to identify the amino acids
involved in neonicotinoid binding. This
article summarises the current status rela-
tive to neonicotinoid photoaffinity probes
and reports for the first time the synthesis,
binding potency and biological activity of
the novel candidate photoaffinity probes 13
to 16 (Fig. 5).
1st Generation Neonicotinoids
Subclass: Chloronicotinyl compounds
NO2
NO2
NH
CN
CN
N
N
N
N
NH
N
CH3
N
N
S
C2H5 CH3
CH3
Cl
N
Cl
N
Cl
N
Cl
N
1
2
3
4
Imidacloprid
Nitenpyram
Acetamiprid
Thiacloprid
2nd Generation Neonicotinoids
Other Neonicotinoids
Subclass: Thianicotinyl compounds
NO2
N
NO2
NO2
N
N
CH3
S
S
N
N
N
NH
N
NH
Cl
Cl
H
H
CH3
CH3
N
N
O
O
5
6
7
Thiamethoxam
Clothianidin
Dinotefuran
2. Photoaffinity Labeling Technique
Comp.
Common Name Brand Name
Company
Year of Market Sales 2001a
Introduction
Mio $
Three major approaches are mainly
used to study molecular recognition in re-
ceptor–ligand interactions [8a]:
1) Spectroscopic methods: X-ray crystallo-
graphy, high-resolution NMR, etc.
1
Imidacloprid
Admire, Confidor, Gaucho,
Provado
Bayer
1991
544
2
3
Nitenpyram
Acetamiprid
Bestguard
Takeda
1995
1996
<30
32
Mospilan, Assail, Adjust,
Epik, Gazelle, Profil,
Rescate
Nippon Soda
2) Chemical methods: photoaffinity label-
ing, chemical affinity labeling, etc.
3) Genetic methods: site-directed muta-
genesis, molecular chimera, etc.
4
5
6
7
Thiacloprid
Calypso, Alanto, Barygard
Actara, Cruiser
Bayer
2000
1998
2001
2002
<30
45 / 141b
Thiamethoxam
Clothianidin
Dinotefuran
Syngenta
Takeda, Bayer
Dantotsu, Pocho, Clutch
Starkle, Alubarin
-
-
Mitsui
Chemicals
Among these methods photoaffinity la-
beling is a very powerful tool for the iden-
tification of ligand-binding proteins in
crude protein mixtures [8]. This approach
uses photolabile derivatives of ligands
(photoaffinity probes; see Fig. 2) for the co-
valent labeling of target proteins, for exam-
ple enzymes or receptors. Upon absorption
of UV-light, photoaffinity probes are con-
verted into highly reactive intermediates,
which can covalently bind to amino acid
residues at the binding site of target pro-
teins. Subsequently, the radiolabeled pro-
tein can be isolated, the labeled amino acids
identified and thus the binding domain
characterised.
a
Data from Phillips McDougall
Sales 2002; Syngenta data
b
Fig 1. Neonicotinoid sales products
Radiolabel
Photoaffinity probe
Candidate photoaffinity probe
3H; 125
I
Ligand
Photoreactive
group
Ligand
Photoreactive
group
Photoreactive groups
Currently, aryl/heteroaryl azides and
aryldiazirines are the photoreactive groups
mainly used in photoaffinity labeling gen-
erating aryl/heteroaryl nitrenes and aryl
carbenes, respectively, as reactive interme-
diates that can insert directly into most car-
bon-, nitrogen-, oxygen-, and sulfur-con-
taining covalent bonds (Fig. 2).
Protein
hν, 280 nm
..
Aryl or
Hetaryl
H
Aryl or
Hetaryl
Aryl or
Hetaryl
N3
N
N
..
Direct insertion
- N2
Protein
Protein
Azides
..
N
N
Protein
hν, 340 nm
Aryl
Aryl
Aryl
CH
Direct insertion
- N2
CF3
CF3
CF3
Diazirines
3. Design of Neonicotinoid
Photoaffinity Probes
Fig 2. Photoaffinity probes and examples of photoreactive groups used in photoaffinity labeling
As the first neonicotinoid photoaffinity
probe, the 2-azido-5-125iodobenzoyloxy- tive with receptor proteins from the fly This is also the major disadvantage of the
ethyl derivative 8 of an imidacloprid ana- Drosophila, but not with those from other two recently published candidate photo-
logue (Fig. 3) has been described [9]. How- insects. Furthermore, the photoreactive affinity probes 9 and 10, which behaved as
ever, this probe is not ideal, because it is of group is in quite some distance from that typical nicotinic agonists in cockroach
limited hydrolytic stability and only effec- part of the molecule essential for binding. nerve cord preparations [10].

CROP PROTECTION RESEARCH
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CHIMIA 2003, 57, No.11
overall yield of this four-step synthesis
18→19→20→21→17 was only 7.5% [12].
Therefore, an alternative synthetic route
was developed at Syngenta. The key step
involved the introduction of the azido
group by a metalation reaction employing
the strong ortho-directing effect of the 6-
chloro group. Thus, starting from readily
125
I
O2N
N
O
N
O
N3
N
Cl
N
N
8
accessible
6-chloropyridin-3-ylmethyl
chloride (22), the chloromethyl group was
first protected as the morpholin-4-ylmethyl
group. The resulting pyridine derivative 23
NO2
N
NO2
N
N
CF3
N
N
o
CF3
was lithiated at –78 C with 2.0 equiv. of
Cl
N
Cl
N
lithium diisopropylamide (LDA), and the
resulting solution quenched at –100oC with
2.0 equiv. of tosyl azide to afford the azido
pyridine 24 in 45% yield. Treatment of 24
with ethyl chloroformate yielded the de-
sired key intermediate 17. By this synthetic
approach 17 was obtained in only three
steps and in an overall yield of 35%.
The candidate photoaffinity probes 11
to 16 were prepared following methodolo-
gy, which we have already published previ-
ously [4b][12–14]. The 5-azido-6-chloro-
pyridin-3-ylmethyl substituent was intro-
duced by alkylation of the nitroimino- or
cyanoimino-heterocycles 26, 27, 29, 31, 33
and 34 with the chloride 17 (Scheme 2).
N
N
10
9
Fig 3. Structures of first neonicotinoid photoaffinity probe 8 and of recent candidate probes
9 and 10
SAR for 6-chloropyridin-3-yl methyl substituent
Candidate neonicotinoid photoaffinity probes
4
α
N3
Neonicotinoid
pharmacophore
Neonicotinoid
pharmacophore
5
2
Cl
N
Cl
N
A
Insecticidal activity against aphids:
5-Azido-6-chloropyridin-3-ylmethyl substituent
as key element for effective receptor binding
and covalent labeling of neonicotinoid binding
sites
2-Position: H >> other substituents
4-Position: H best substituent
5-Position: H = Cl
α-Position: H > Me > other substituents
Fig. 4. Structure-activity relationships of 6-chloropyridin-3-ylmethyl substituted neonicotinoids
and design of candidate photoaffinity probes of type A
5. Biological Activity
The biological activity of the candidate
photoaffinity probes 11 to 16 was evaluated
against five insect species for contact/feed-
ing activity and against Aphis craccivora
(A.c.) and Myzus persicae (M.p.) for sys-
temic activity in direct comparison with the
neonicotinoid standards imidacloprid (1),
thiacloprid (4), thiamethoxam (5), and
clothianidin (6). The biological results are
shown in Table 1.
NO2
NO2
NO2
N
N
N
N3
Cl
N3
Cl
N3
Cl
N
NH
N
H
NH
N
H
NH
CH3
CT3
N
N
N
[3H]-12
11
12
CN
S
NO2
NO2
NH
NO2
N
N
N
O
N
O
N3
Cl
N3
CH3
N3
Cl
N3
Cl
CH3
N
N
N
N
N
N
N
Cl
N
N
N
Candidate photoaffinity probes 11 to 16
showed good to excellent contact/feeding
and systemic activity against Myzus persi-
cae. Against all other insects, however,
these compounds were at least 4- to 16-fold
13
14
16
15
Fig. 5. Structures of candidate photoaffinity probes 11 to 16 and [3H]-12
The preferred neonicotinoid photoaffin- synthesis targets [12]. To explore further less effective than the neonicotinoid stan-
ity probe would show nanomolar affinity to candidate photoaffinity probes of type A we dards. The broadest spectrum of activity
nAChRs from insects (e.g. from aphids), have selected and synthesised the novel 5- was seen for the azides 11 and 13. In gener-
possess reasonable insecticidal activity, azido-6-chloropyridin-3-ylmethyl deriva- al, the introduction of an azide group at
have the photoreactive group in close prox- tives 13 to 16.
imity to the binding-relevant part of the
molecule and be easy to synthesise.
The structure–activity relationships 4. Synthesis of Candidate
(SAR) developed at Syngenta [11] for the Neonicotinoid Photoaffinity Probes
6-chloropyridin-3-ylmethyl substituent led
C(5) of the 6-chloropyridin-3-ylmethyl
substituent (1→11; 4→13) resulted in re-
duced potency as well as in a narrower pest
spectrum.
to the design of candidate neonicotinoid
5-Azido-6-chloropyridin-3-ylmethyl
6. Receptor Binding Potency
photoaffinity probes of type A (Fig. 4). In chloride (17) is a key intermediate for the
collaboration with the group of John E. synthesis of the candidate neonicotinoid
Binding potencies to nAChRs were
Casida, compounds 11 and 12 (Fig. 5), both photoaffinity probes 11 to 16. It was first measured using membrane preparations
containing 5-azido-6-chloropyridin-3- prepared starting from 6-chloro-5-nitroni- from Aphis craccivora and Myzus persicae.
ylmethyl substituent, were chosen as first cotinic acid 18 (Scheme 1). However, the Data for the azido compounds 11 to 16 and
a

CROP PROTECTION RESEARCH
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CHIMIA 2003, 57, No.11
neonicotinoids as candidate photoaffinity
probes. This study demonstrated that 5-azi-
do-6-chloropyridin-3-ylmethyl derivatives
are clearly more potent than the corres-
ponding 4-azido analogues. Compounds 35
and 38 and especially the 2-nitroimino-thi-
azoline 36 and the 2-nitroimino-imidazoli-
dine 37 were found to be very potent in dis-
placing [3H]imidacloprid from Drosophila
nAChRs (Table 2, Fig. 6).
COOH
.
O2N
Cl
O2N
Cl
H2N
Cl
Fe, AcOH, 90 o
C
BH3 SMe2, THF
OH
OH
N
N
N
59%
22%
18
19
20
1) NaNO2, HCl
2) NH2OH
N3
Cl
N3
Cl
SOCl2
OH
Cl
N
N
68%
85%
21
17
ClCO2Et
THF, 60 o
C
88%
N3
7. Conclusion
morpholine,
toluene; 74%
1) LDA, THF, -78 o
C
Candidate photoaffinity probes 11 to 16,
all containing a 5-azido-6-chloropyridin
3-ylmethyl group, were successfully
prepared from 5-azido-6-chloropyridin-
3-ylmethyl chloride, which was obtained
in three steps from 6-chloropyridin-
3-ylmethyl chloride. Taking into account
the biological screening activity (Table 1)
as well as the receptor binding potency
(Table 2) we conclude that compounds 11,
12, and 13 are the preferred candidate neon-
icotinoid photoaffinity probes to investi-
gate neonicotinoid-receptor interactions
and to identify the amino acids involved in
imidacloprid binding. Although only limit-
ed data are available compounds 36 and 37
may also be considered as valuable candi-
dates.
2) Tos-N3, -100 oC to 0 o
C
Cl
N
N
O
O
or
45%
N
N
N
Cl
Cl
Cl
morpholine,
THF; 88%
22
23
24
Scheme 1. Synthesis of the key intermediate 5-azido-6-chloropyridin-3-ylmethyl chloride (17)
NO2
NO2
N
N
NO2
H2NCH2CH2NHR
CHCl3, r.t.
Equiv.
K2CO3
N
17, 2.5
N3
Cl
R
N
R
N
N
HN
SCH3
DMF, 50 o
C
CH3S
N
25
26 (R = H; 95%)
27 (R = CH3; 78%)
11 (R = H; 44%)
16 (R = CH3; 65%)
CN
CN
N
N
N
H2NCH2CH2SH.HCl
17, 2.5 Equiv.K2CO3
DMF, 50 o
CN
NaHCO3, C2H5OH, 40 o
C
N3
C
N
S
HN
S
67%
93%
CH3S
SCH3
Cl
N
Among these azido-neonicotinoids, a
radiolabel is most easily introduced into the
acyclic nitroguanidine derivative 12 and
consequently [3H]-12 (Fig. 5) was radio-
synthesized with high specific activity as
first azido-neonicotinoid photoaffinity
probe. [3H]-12 was found to bind to a sin-
gle high-affinity site in Myzus that is com-
petitively inhibited by imidacloprid [16].
13
29
28
NO2
NO2
NO2
N
N
N
N
N
1 N HCl, CH3OH
80 o
17, 2.5 Equiv.K2CO3
CH3
CH3
N3
Cl
N3
Cl
C
HN
N
DMF, 50 o
C
N
N
N
H
NH
CH3
59%
83%
N
N
32
CH3
CH3
12
31
CH3NH2, HCHO
C2H5OH, 50 o
96%
C
NO2
NO2
Received: September 26, 2003
N
N
N
O
NO2
R
N
R
N3
Cl
N
17, 2.5 Equiv.K2CO3
HCHO, HCOOH
90 o
HN
N
R
DMF, 50 o
C
H2N
N
C
O
N
H
[1] Presented in part at the 10th IUPAC Inter-
national Congress of the Chemistry of
Crop Protection, Basel, Switzerland,
2002, Poster 3a.16 (book of abstracts
Vol.1, p 234).
33 (R = H; 52%)
34 (R = CH3; 71%)
14 (R = H; 17%)
15 (R = CH3; 46%)
30
Scheme 2. Synthesis of candidate photoaffinity probes of type A
[2] I. Yamamoto, J.E. Casida (Eds), ‘Nicoti-
noid Insecticides and the NicotinicAcetyl-
choline Receptor’, Springer-Verlag,
Tokyo, 1999, 1–300; and literature cited
therein.
[3] a) P. Maienfisch, F. Brandl, W. Kobel, A.
Rindlisbacher, R. Senn in: ‘Nicotinoid In-
secticides and the Nicotinic Acetylcholine
Receptor’, Eds. I. Yamamoto, J.E. Casida,
Springer-Verlag, Tokyo, 1999, 177–209;
and literature cited therein. b) T. Wakita,
K. Kinoshita, E. Yamada, N. Yasui, N.
Kawahara, A. Naoi, M. Nakaya, K. Ebi-
hara, H. Matsuno, H. Kodaka, Pest Man-
ag. Sci. 2003, 50, 1016–1022.
the neonicotinoid sales products 1, 4, 5 and [18]. The imidacloprid analogue 11, the
6 were obtained from competition binding clothianidin analogue 12, the thiacloprid
assays with [3H]imidacloprid as a ligand analogue 13 and the thiamethoxam ana-
that shares its binding characteristics with logue 14 possess high displacing potency
most other neonicotinoids, with the excep- with nAChRs from Aphis and Myzus (K
i
tion of thiamethoxam [6a][7][17]. Incu- values: 2 to 27 nM) suggesting that these
bations were performed with 100 µg of compounds are valuable candidate photo
membrane protein and 6 nM of the radio- affinity probes for the imidacloprid bind-
ligand for 2 h at 22 oC.
ing site. On the other hand, compounds 15
Our results, together with some data and 16 may be more suitable to study the
from the literature, are compiled in Table 2 unusual binding of thiamethoxam 5.
as the inhibition constants K , which were
calculated from the measured IC50 values pared a series of further azidopyridinyl
In the meantime, Zhang et al. [15] pre-
i

CROP PROTECTION RESEARCH
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CHIMIA 2003, 57, No.11
Table 1. Biological activity of candidate photoaffinity probes 11 to 16 in comparison with the
neonicotinoid standards 1,4, 5, and 6
[4] a) P. Maienfisch, L. Gsell, A. Rindlisba-
cher, Pestic. Sci. 1999, 55, 351–355; b) P.
Maienfisch, H. Huerlimann, A. Rindlis-
bacher, L. Gsell, H. Dettwiler, J. Haetten-
schwiler, E. Sieger, M. Walti, Pest Manag.
Sci. 2001, 57, 165–176; c) P. Maienfisch,
A. Rindlisbacher, H. Huerlimann, J. Haet-
tenschwiler, A.K. Desai, V.S. Ekkundi,
V.D. Gangan, ACS Symposium Series,
2002, 800 (Synthesis and Chemistry of
Agrochemicals VI), 219–230.
[5] a) R. Senn, D. Hofer, T. Hoppe, M. Angst,
P. Wyss, F. Brandl, P. Maienfisch, L. Zang,
S. White, Brighton Crop Protection Con-
ference – Pests and Diseases, 1998, Vol. 1,
27–36; b) P. Maienfisch, M. Angst, F.
Brandl, W. Fischer, D. Hofer, H. Kayser,
W Kobel, A. Rindlisbacher, R. Senn, A.
Steinemann, H. Widmer, Pest Manag. Sci.
2001, 57, 906–913.
[6] a) P. Wiesner, H. Kayser, J. Biochem. Mol.
Toxicol. 2000, 14, 221–230; b) A. Zhang,
H. Kayser, P. Maienfisch, J.E. Casida, J.
Neurochem. 2000, 75, 1294–1303; and lit-
erature cited therein.
[7] H. Kayser, C. Lee, H. Wellmann, 10th
IUPAC International Congress of the
Chemistry of Crop Protection, Basel,
Switzerland, 2002, Poster 3c.23 (book of
abstracts Vol.1, p 305).
[8] For recent reviews on photoaffinity la-
belling see: a) Y. Hatanaka, Y. Kanaoka,
Heterocycles, 1998, 47, 625–632; b) F.
Kotzyba-Hilbert, I. Kapfer, M. Goeldner,
Angew. Chem. Int. Ed. Engl. 1995, 34,
1296–1312; c) H.J. Schafer, A. Schuhen,
Biol. Res. 1996, 29, 31–46; d) J.E. Casida,
G.B. Quistad, Special Publication - Royal
Society of Chemistry, 1999, 232 (Progress
in Neuropharmacology and Neurotoxicol-
ogy of Pesticides and Drugs), 34–45; e)
C.A. Gartner, Curr. Med. Chem. 2003, 10,
671–689.
[9] a) B. Latli, M. Tomizawa, J.E. Casida,
Bioconjug. Chem. 1997, 8, 7–14; b) M.
Tomizawa, J.E. Casida, Neurosci. Lett.
1997, 237, 61–4.
[10] K. Matsuda, M. Ihara, K. Nishimura, D.B.
Sattelle, K. Komai, Biosci. Biotechn.
Biochem. 2001, 65, 1534–1541.
Comp.
A.c.a
cf f
++
++
+
A.c.
syg
M.p.b
cf
M.p.
sy
N.l.c
S.l.d
D.b.e
cf
cf
cf
11
12
13
14
15
16
1
++++
+++
+++
-
+++
+++
++
+++++
+++++
+++
-
++
+++
+
-
-
+++
-
-
+
-
-
+++
++
+++++
+++++
+++++
+++++
+++++
+++++
+++++
-
+
+
+++
-
-
-
-
+
-
+
-
+++
+++
+++
++
+++++
++++
+++++
+++++
+++++
+++
+++++
++++
++++
+
++++
++
+++++
+++++
+++++
+++++
4
5
+++++
+++++
++++
++++
6
Test insects:
a Aphis craccivora, b Myzus persicae, c Nilaparvata lugens, d Spodoptera littoralis,
e Diabrotica balteata.
Type of activity: f Contact/feeding activity, g systemic activity.
Rating system: - denotes < 80% activity at 200 ppm; + denotes > 80% activity at 200 ppm;
++ denotes > 80% activity at 50 ppm; +++ denotes > 80% activity at 12 ppm;
++++ denotes > 80% activity at 3 ppm; +++++ denotes > 80% activity at 0.8 ppm
or below. See [4b] for details of the assays.
Table 2. Competition binding potency of candidate photoaffinity probes of type A with [3H]imi-
dacloprid ([3H]-1)
Comp.
11
K [nM]
M.p.b
4.5 d
1.0
-
Reference
i
A.c.a
4.5 d
-
-
D.m.c
e
-
This study
Kagabu et al. [12]
Zhang et al. [15]
15
24
12
22
27
4.5
5.0
-
13
161
This study
Kagabu et al. [12]
Tomizawa et al. [16]
-
-
13
14
15
16
1
2
2.5
-
This study
8
11
-
This study
125
160
-
-
This study
123
270
This study
6
3
-
This study
4
3
2
-
This study
5 f
2300
3200
-
Kayser et al. [17]
This study
[11] The work started at Ciba-Geigy, which be-
came Novartis in 1996, and then Syngen-
ta in 2000.
[12] S. Kagabu, P. Maienfisch, A. Zhang, J.
Granda-Minones, J. Haettenschwiler, H.
Kayser, T. Maetzke, J.E. Casida, J. Med.
Chem. 2000, 43, 5003–5009.
6
14
-
9
-
-
35
36
37
38
13
3.9
0.72
28
Zhang et al. [15]
Zhang et al. [15]
Zhang et al. [15]
Zhang et al. [15]
-
-
-
-
-
-
[13] P. Maienfisch, H. Huerlimann, J. Haetten-
schwiler, Tetrahedron Lett. 2000, 41,
7187–7191.
[14] A. Zhang, H. Kayser, P. Maienfisch,
J.E. Casida, J. Neurochem. 2000, 75,
1294–1303.
a Aphis craccivora, b Myzus persicae, c Drosophila melanogaster
d See [6a] for assay description, e not tested
f Thiamethoxam (5) binds in a mode different from that of the other neonicotinoid sales products, i.e. it
interferes in a non-competitive mode with [3H]imidacloprid (1) binding to receptor preparations
from A.c. and M.p., which explains the high Ki values. The intrinsic receptor affinity of
thiamethoxam, used as [3H]-5, is in the nanomolar range, comparable to that of imidacloprid (1).
[15] N. Zhang, M. Tomizawa, J.E. Casida, J.
Med. Chem. 2002, 45, 2832–2840.
[16] M. Tomizawa, Z. Wen, H.L. Chin, H. Mo-
rimoto, H. Kayser, J.E. Casida, J. Neu-
rochem. 2001, 78, 1359–1366.
[17] H. Kayser, C. Lee, A. Decock, M. Baur, J.
Haettenschwiler, P. Maienfisch (manu-
script in preparation).
NO2
NH
NO2
S
NO2
NH
CN
S
N
N
N
N3
Cl
N3
Cl
N3
Cl
N3
Cl
N
N
N
N
N
N
N
N
37
36
35
38
[18] Y.-C. Cheng, W.H. Prusoff, Biochem.
Pharmacol. 1973, 22, 3099–3108.
Fig. 6. Structures of candidate photoaffinity probes of type A recently published [15]