Light-triggered release of insecticidally active spirotetramat-enol

Article abstract of DOI:10.1016/j.cclet.2018.01.025

Spirotetramat metabolizes to its active enol form in the plant. We described here a photocaged pesticide delivery system that can release insecticidal spirotetramat enol form upon light irradiation. Covalently linking spirotetramat-enol with photoresponsive coumarin generated the caged insecticide. The photophysical and photochemical properties, deprotection photolysis and insecticidal activities of the caged spirotetramat enol were studied. This light-triggered system can undergo cleavage to release free spirotetramat enol form at the presence of blue light (420 nm) or sunlight. Bioassays indicated that the triggered molecule has no obvious insecticidal activity against Aphis craccivora Koch at dark and could be activated by light to release the insecticidal ingredients, which provides precise control over insecticide delivery.

Full text of DOI:10.1016/j.cclet.2018.01.025

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CCLET 4415 No. of Pages 3
Chinese Chemical Letters xxx (2018) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Communication
Light-triggered release of insecticidally active spirotetramat-enol
Zhiping Xu *, Zhenhong Gao , Xusheng Shaoa,b,*
a,
a
a
Shanghai Key Laboratory of Chemical Biology, School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China
State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237, China
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 19 October 2017
Received in revised form 9 January 2018
Accepted 12 January 2018
Available online xxx
Spirotetramat metabolizes to its active enol form in the plant. We described here a photocaged pesticide
delivery system that can release insecticidal spirotetramat enol form upon light irradiation. Covalently
linking spirotetramat-enol with photoresponsive coumarin generated the caged insecticide. The
photophysical and photochemical properties, deprotection photolysis and insecticidal activities of the
caged spirotetramat enol were studied. This light-triggered system can undergo cleavage to release free
spirotetramat enol form at the presence of blue light (420 nm) or sunlight. Bioassays indicated that the
triggered molecule has no obvious insecticidal activity against Aphis craccivora Koch at dark and could be
activated by light to release the insecticidal ingredients, which provides precise control over insecticide
delivery.
Keywords:
Photocage
Spirotetramat enol
Coumarin
Insecticide
Light
©
2018 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
Uncontrollable delivery method causes the low utilization rates
of pesticide, which in turn led to many adverse effects such as
increased dosage, high toxicity and environmental pollution [1].
Therefore, new technologies are needed for controlled release of
pesticide molecules. Controlled release system can enhance
bioavailability, prolong length of activity and reduce the usage
amount of pesticides [1]. Microencapsulation and nanotechnology
are previously developed for slow-release of pesticides [2,3].
Recently, the photo-triggered technology provides an alternative
strategy for better controlled release in which the release process
can be remotely, temporally and spatially regulated [4].
The light-dependent release technology takes advantage of a
kind of molecules called photocage that can undergo cleavage at
the presence of certain wavelength of light [4,5]. This technology
has broad applications in controlled release of pharmaceuticals as
well as agrichemicals [4–6]. This process is triggered by light which
can provide invasive, clean and spatiotemporal control over the
release. A photocaged release system is composed of a photocage
and a bioactive fragment [4,5]. The well-studied photocages
include o-nitrobenzyl, coumarin-4-ylmethyl and p-hydroxylphe-
nacyl. Coumarin (Cou) derivatives are the mostly-used photocages
because of their easy preparation, adjustable irradiation wave-
length, fast release rates and low intrinsic toxicity [6].
Spirotetramat is a keto-enol insecticide with excellent efficacy
against sucking insects [7]. It acts on insect acetyl-CoA carboxylase
that can interfere with lipid biosynthesis [8]. Spirotetramat has
good systematic properties with both phloem and xylem mobility
[7]. After administration on plant, spirotetramat can easily be
degraded to its active enol form named as spirotetramat-enol (SE)
[9–11]. Photorelease of agrochemicals mainly focuses on the
herbicides [12], sex pheromone [13] and plant growth regulators
[14], such as 2,4-D [15,16], salicylic acid [17] and trehalose-6-
phosphate [18]. Recently, we reported coumarin-caged fipronil
that enabled success release of insecticide fipronil both in vivo and
in vitro [19]. Inspired by above descriptions, we herein described a
photorelease system for conditionally releasing active spirotetra-
mat-enol by linking SE with coumarin photocage.
Spirotetramat is a proinsecticide. It can be hydrolyzed in plant
tissues to insecticidally active enol metabolite SE [10]. SE has the
similar mode of action with that of spirotetramat that can inhibit
acetyl-CoA carboxylases partially purified from Myzus persicae,
Spodoptera frugiperda and Tetranychus urticae [8]. Most important-
ly, SE has good physiochemical properties that permitting its
movement both upwards and downwards [10]. Therefore, we can
envision that designing a SE releasing system is feasible to
maintain high activity and excellent systematic properties of
spirotetramat. Taking absorption wavelength into account, 7-
diethylamino substituted coumarin was used here as a photo-
trigger as it has the biologically benign absorption region. The free
hydroxyl group in SE also provide a position for attachment of
phototriggered protection group.
*
Corresponding authors.
E-mail addresses: zhipingxu@ecust.edu.cn (Z. Xu), shaoxusheng@ecust.edu.cn
(
X. Shao).
https://doi.org/10.1016/j.cclet.2018.01.025
001-8417/© 2018 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
1
Please cite this article in press as: Z. Xu, et al., Light-triggered release of insecticidally active spirotetramat-enol, Chin. Chem. Lett. (2018),
https://doi.org/10.1016/j.cclet.2018.01.025

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Fig. 1. Molecular design of photoresponsive coumarin-caged spirotetramat-enol and its synthetic route. Reagents and condition: (a) 1. SeO
2
, Ar, p-xylene, reflux, 53 h; 2.
NaBH , CH OH, r.t., 4 h, 26%. (b) p-nitrophenyl chloroformate, DIPEA, Ar, dry dichloromethane, r.t., 20 h, 50%. (c) NaOH, methanol, H O, r.t., 47%. (d) DIPEA, Ar, dry DMF (N,N-
4
3
2
dimethylformamide), r.t., 48 h, 32%.
The synthetic route for coumarin caged SE (denoted as CS) was
depicted in Fig. 1. Instruments, detailed procedure and analysis
data can be found in Supporting information. Coumarin derivative
3
was prepared according to previously-reported procedure [19].
SE was synthesized by hydrolysis of spirotetramat. Finally,
coupling of intermediate 3 with SE catalyzed by N,N-Diisopropy-
lethylamine (DIPEA) afforded the caged product CS.
With coumarin-triggered SE in hand, we firstly investigated its
photophysical properties. The maximum absorption and emission
wavelength of CS are 395 nm and 485 nm, respectively (Table S1 in
Supporting information). The Stokes shift is 90 nm and fluores-
cence quantum yield is around 0.11. CS has two obvious absorption
bands centered at 395 nm and 250 nm which corresponded to the
absorption of coumarin and SE, respectively (Fig. 2).
To investigate the phototriggered SE release ability, the solution
of CS was irradiated under blue light (420 nm, LED) and the UV-
visible spectra changes were recorded at time intervals. Obvious
spectra changes were observed, with the increase of absorption at
Fig. 3. Photo-controlled release of SE irradiated by blue light. (A) Time-dependent
release of SE upon blue light (420 nm) irradiation. (B) The release process can be
turned on and off by switching the light on and off.
here. Same trend were also observed when CS was exposed to
sunlight (Fig. S1).
The time-dependent release of SE upon blue light irradiation
was also studied by plotting UPLC peak area of SE versus different
irradiation times (Fig. 3). The photorelease approaches saturation
at about 20 min and 100% SE was regenerated. By switching the
light source on and off, the release process can be initiated or
stopped, indicating that release of SE can only be induced by light.
After successful identification of photorelease of SE, we then
studied its insecticidal effects against cowpea aphids (Aphis
craccivora) (Table 1). The bioassay against cowpea aphids was
carried out according to our previously reported procedure [20,21].
All compounds were dissolved in dimethyl sulfoxide (DMSO) as
stock solutions. Various concentrations of test compounds were
prepared by serial dilution of stock solutions with distilled water.
The plant leaves of horsebean with about 50 apterous adults were
dipped in corresponding chemical solutions containing Triton X-
100 (0.1 mg/L) for 5 s and the excess solutions were sucked out
with filter paper. Then the burgeons were positioned in the
250 nm corresponding to SE. The intensity of absorption at 395 nm
also increased along with the wavelength hypochromatically
shifting to 388 nm. The above observations indicate that photolysis
occurred when CS was subjected to irradiation.
To further identify the occurrence of photocleavage, the
photorelease process was monitored by ultra performance liquid
chromatography (UPLC) (Fig. S1 in Supporting information). The
sample was analyzed every 10 min of irradiation. The overlay
chromatogram indicated gradual decrease of peak at t
which is corresponding to caged compound CS, suggesting the
photolysis of CS. Appearance of two new peaks at t = 4.60 min and
.95 min related to cleaved product SE and coumarin derivative 2,
R
= 7.10 min
R
5
respectively. Trim amount of photolysis byproducts also generated
upon irradiation whose chemical structures were not identified
Fig. 2. (A) UV–vis absorption of CS at regular intervals of irradiation in MeOH/H
2
O (50/50) (5.6 Â10À5 mol/L). (B) UV–vis absorption of SE. (C) UV–vis absorption of Cou.
Please cite this article in press as: Z. Xu, et al., Light-triggered release of insecticidally active spirotetramat-enol, Chin. Chem. Lett. (2018),
https://doi.org/10.1016/j.cclet.2018.01.025

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Z. Xu et al. / Chinese Chemical Letters xxx (2018) xxx–xxx
3
Table 1
new strategy for controlled release of SE, which would enable
precise and spatiotemporal control over insecticidal activity.
Insecticidal activity of CS, SE, Cou against cowpea aphids (Aphis craccivora).
Treatment
LC50 (mmol/L)
Acknowledgments
Aphis craccivora
CS-blue light
CS-dark
SE-blue light
SE-dark
0.11
This work was financially supported by the National Natural
Science Foundation of China (Nos. 21472046, 21372079), Science
and Technology Commission of Shanghai Municipality (No.
>0.87
a
n.t.
0.08
Cou-blue light
Cou-sunlight
No activity
No activity
No activity
No activity
16391902300) and the Fundamental Research Funds for the
b
Central Universities (No. 222201718004).
CK -blue light
CK-dark
Appendix A. Supplementary data
a
n.t. denotes not tested.
CK denotes control check.
b
Supplementary data associated with this article can be found, in
the online version, at https://doi.org/10.1016/j.cclet.2018.01.025.
ꢀ
conditioned room ((25 Æ1) C). Water with Triton X-100 (0.1 mg/L)
was used as control. Three sets of experiments were performed for
each compound. The first group was held in the dark throughout
the trials. The second group was irradiated for 1 h with a LED lamp
420 nm), and then returned to darkness for 24 h incubation. The
third group was irradiated by sunlight (September, Shanghai) for
h, and also returned to darkness for 24 h incubation. Controls
were treated similarly. The mortality rates were calculated 24 h
after treatment. Each treatment had three repetitions and the data
were subjected to probit analysis.
CS alone in the dark has low insecticidal activity with LC50 value
more than 1 mmol/L. Upon irradiation, the activity increased
significantly with LC50 approaching 0.11 mmol/L. No significant
activity difference was observed for SE before and after irradiation.
SE has higher activity than CS plus blue light. Light alone do not
have any obvious activity to aphids. The above results indicated
that efficient light-triggered release of SE was achieved using
coumarin as a cage.
References
[
[
[
1] M. Kah, T. Hofmann, Environ. Int. 63 (2014) 224–235.
2] D. Yang, G. Li, X. Yan, H. Yuan, J. Agric. Food Chem. 62 (2014) 10632–10637.
3] D. Wibowo, C. Zhao, B.C. Peters, A.P.J. Middelberg, J. Agric. Food Chem. 62
(2014) 12504–12511.
(
[
[
4] P. Klan, T. Šolomek, C.G. Bochet, et al., Chem. Rev. 113 (2013) 119–191.
5] C. Brieke, F. Rohrbach, A. Gottschalk, et al., Angew. Chem. Int. Ed. 51 (2012)
1
8
446–8476.
[6] C. Bao, L. Zhu, Q. Lin, H. Tian, Adv. Mater. 27 (2015) 1647–1662.
[
[
7] P. Lümmen, J. Khajehali, K. Luther, et al., Insect Biochem. Mol. Biol. 55 (2014) 1–
8
.
8] T. Peng, Y. Pan, C. Yang, et al., Pestic. Biochem. Physiol. 126 (2016) 64–69.
[9] X. Chen, Z. Meng, Y. Zhang, et al., Environ. Sci. Pollut. Res. 23 (2016) 1–10.
10] J. Cheng, X. He, Z. Wang, et al., Pest Manag. Sci. 69 (2013) 1121–1130.
[
[11] P. Jeschke, Pest Manag. Sci. 72 (2016) 210–225.
[12] P. Stloukal, P. Kucharczyk, V. Sedlarik, et al., J. Agric. Food Chem. 60 (2012)
4111–4119.
[13] S. Atta, M. Ikbal, N. Boda, et al., Photoch. Photobio. Sci. 12 (2013) 393–403.
[14] S. Atta, M. Ikbal, A. Kumar, et al., J. Photoch. Photobio. B 111 (2012) 39–49.
[15] S. Atta, M. Bera, T. Chattopadhyay, et al., RSC Adv. 5 (2015) 86990–86996.
[16] S. Atta, A. Paul, R. Banerjee, et al., RSC Adv. 5 (2015) 99968–99975.
In summary, a photo-triggered release system was synthesized
by covalently linking of coumarin photocage with spirotetramat-
enol. The system can efficiently release insecticidal SE upon
irradiation of sunlight or blue light. The compound has the light-
triggered insecticidal activity again cowpea aphid. This provides a
[17] S. Barman, S.K. Mukhopadhyay, K.K. Behara, et al., ACS Appl. Mater. Inter. 6
(
2014) 7045–7054.
[
[
18] C.A. Griffiths, R. Sagar, Y. Geng, et al., Nature 540 (2016) 574–592.
19] Z. Gao, P. Yuan, D. Wang, et al., Bioorg. Med. Chem. Lett. 27 (2017) 2528–2535.
[20] Y. Zhang, Y. Feng, Z. Li, et al., Chin. Chem. Lett. 28 (2017) 1228–1231.
[21] Q. Hou, Y. Jing, X. Shao, Chin. Chem. Lett. 28 (2017) 1723–1726.
Please cite this article in press as: Z. Xu, et al., Light-triggered release of insecticidally active spirotetramat-enol, Chin. Chem. Lett. (2018),
https://doi.org/10.1016/j.cclet.2018.01.025