Synthesis and insecticidal activity of new deoxypodophyllotoxin derivatives modified in the D-ring

Article abstract of DOI:10.1016/j.bmcl.2014.07.076

In continuation of our program aimed at the discovery of new natural-product-based insecticidal agents, twenty-six deoxypodophyllotoxin derivatives modified in the D-ring were synthesized and evaluated as insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at 1 mg/mL. The configuration of three compounds 3, 4, and IIIi was unambiguously determined by single-crystal X-ray diffraction. It demonstrated that aminolysis of deoxypodophyllotoxin in the presence of pyrrolidine and piperidine could result in complete inversion of the configuration of the carbonyl group at its C-2 position. Five compounds IIa, IIi-k, and IIIh showed the equal or higher insecticidal activity than toosendanin. Especially IIj displayed the most potent insecticidal activity with the final mortality rate of 65.5%.

Full text of DOI:10.1016/j.bmcl.2014.07.076

Bioorganic & Medicinal Chemistry Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and insecticidal activity of new deoxypodophyllotoxin
derivatives modified in the D-ring
⇑
Juanjuan Wang, Xiang Yu, Xiaoyan Zhi, Hui Xu
Research Institute of Pesticidal Design & Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, Shaanxi Province, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
In continuation of our program aimed at the discovery of new natural-product-based insecticidal agents,
twenty-six deoxypodophyllotoxin derivatives modified in the D-ring were synthesized and evaluated as
insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker)
in vivo at 1 mg/mL. The configuration of three compounds 3, 4, and IIIi was unambiguously determined
by single-crystal X-ray diffraction. It demonstrated that aminolysis of deoxypodophyllotoxin in the pres-
ence of pyrrolidine and piperidine could result in complete inversion of the configuration of the carbonyl
group at its C-2 position. Five compounds IIa, IIi–k, and IIIh showed the equal or higher insecticidal activ-
ity than toosendanin. Especially IIj displayed the most potent insecticidal activity with the final mortality
rate of 65.5%.
Received 12 April 2014
Revised 18 July 2014
Accepted 29 July 2014
Available online xxxx
Keywords:
Deoxypodophyllotoxin
Insecticidal activity
Natural-product-based insecticide
Structural modification
Mythimna separata Walker
Ó 2014 Elsevier Ltd. All rights reserved.
The naturally occurring aryltetralin lignan podophyllotoxin
(compound 1, Fig. 1) is isolated from the roots and rhizomes of
Podophyllum hexandrum such as P. hexandrum and Podophyllum
peltatum. Compound 1 has been used as the lead compound for
the preparation of potent anticancer drugs such as etoposide,
teniposide and etopophos,1–3 and the insecticidal agents.4–8
deoxypodophyllotoxin II (Fig. 1) with an opened D ring as insecti-
cidal agents by introduction of Part A of compounds I into com-
pound 2. Meanwhile, deoxypodophyllotoxin derivatives III
(Fig. 1), where the piperidine moiety was substituted for the pyr-
rolidine one in the Part A of II, were prepared as the control.
As shown in Scheme 1, firstly, 4-deoxypodophyllotoxin (2) was
prepared from podophyllotoxin (1) mediated by 10% palladium/
carbon.21 Then 2 reacted with pyrrolidine and piperidine to give
two D-ring opened intermediates 3 and 4, respectively. Finally, in
the presence of N,N0-diisopropylcarbodiimide (DIC) and 4-dimeth-
ylaminopyridine (DMAP), the target products IIa–n and IIIa–i,l–n
were obtained by the reaction of carboxylic acids with 3 and 4,
respectively. Moreover, the configuration of 3, 4, and IIIi was fur-
ther unambiguously identified by single-crystal X-ray diffraction.22
As shown in Figures 2–4, the substituents at the C-2 and C-3 posi-
tions of 3, 4, and IIIi were all in b configuration. It clearly demon-
strated that aminolysis of 2 in the presence of pyrrolidine and
piperidine could result in complete inversion of the configuration
of the carbonyl group at its C-2 position.
As shown in Table 1, the insecticidal activity of compounds
IIa–n and IIIa–i,l–n was evaluated against the pre-third-instar lar-
vae of oriental armyworm, Mythimna separata (Walker) at the con-
centration of 1 mg/mL.23 Toosendanin was used as the positive
control at 1 mg/mL. Leaves treated with acetone alone were used
as a blank control group. It was found that for the corresponding
mortality rates of tested compounds after 35 days were usually
higher than those after 10 and 20 days, these compounds exhibited
the delayed insecticidal activity. Additionally, the symptoms of the
Recently, we have investigated the insecticidal activity of 2a/b-
bromo- or 2b-chloropodophyllotoxin derivatives modified in the
C ring and 4-deoxypodophyllotoxin (compound 2, Fig. 1) deriva-
tives modified in the E ring, and found some compounds showed
the equal or higher insecticidal activity than toosendanin, a com-
mercial botanical insecticide isolated from Melia azedarach.9–13
On the other hand, as the pesticides originated from plant second-
ary metabolites may result in less or slower resistance develop-
ment and lower pollution, so the discovery of new pesticidal
agents from plant secondary metabolites, or by using them as
the lead compounds for further structural modification, have
recently been one of the important routes for research and devel-
opment of new insecticides.14–19 Recently, Xiao et al. found that
introduction of pyrrolidine at the D-ring of 1 could lead to the
potent compounds I (Fig. 1), which exhibited the good antitumor
activity.20 Encouraged by the above-mentioned results, and in
continuation of our program aimed at the discovery and develop-
ment of novel natural-product-based pesticides, in this Letters
we designed and prepared
a series of novel derivatives of
⇑
Corresponding author. Tel./fax: +86 (0)29 87091952.
E-mail address: orgxuhui@nwsuaf.edu.cn (H. Xu).
http://dx.doi.org/10.1016/j.bmcl.2014.07.076
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wang, J.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.07.076

2
J. Wang et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
R
OH
5
6
4
11
3
O
O
O
O
O
O
10
A
B
8
O
9
C
O
D
O
7
2
1
N
Part A
O
1'
O
2'
3'
O
6'
E
5'
O
O
O
O
4'
O
O
O
O
O
I
1
2
R
R
O
O
O
O
O
O
O
O
O
O
N
N
Part A
O
O
O
O
O
II
O
III
Figure 1. Chemical structures of podophyllotoxin (1), deoxypodophyllotoxin (2) and their derivatives (I–III).
R
O
O
O
O
O
N
5a-n
DIC/DMAP
OH
O
O
3
O
O
11
9
O
r.t./1-22 h
77-92%
14 examples
N
IIa-n
2
OH
O
O
O
O
pyrrolidine
reflux, 2 h
O
O
O
O
O
H2, 10% Pd/C
95 oC, 2 atm
O
91%
O
O
3
OH
66%
3
73%
O
O
O
piperidine
O
O
11
9
O
reflux, 18 h
O
2
N
O
2
1
O
5a-i,l-n
R
N
DIC/DMAP
O
O
O
O
r.t./1-28 h
65-93%
12 examples
O
4
O
O
O
O
O
O
IIIa-i,l-n
R=
a: Et; b: n-heptyl; c: (CH2)10CH3; d: (CH2)13CH3; e: Ph; f: 3-pyridyl;
g: h: i: j: k:
O
PhCH2;
1-naphthylmethylene; (m-Me)Ph; (p-Me)Ph; (p-OMe)Ph;
l: (m-F)Ph; m: (m-Cl)Ph; n: (m-Br)Ph.
R
OH
5a-n
Scheme 1. Synthetic route for preparation of deoxypodophyllotoxin derivatives IIa–n and IIIa–i,l–n.
Please cite this article in press as: Wang, J.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.07.076

J. Wang et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
3
a
Table 1
Insecticidal activity of IIa–n and IIIa–i,l–n against M. separata on leaves at
concentration of 1 mg/mL
Compound
Corrected mortality rate (%)
20 days
10 days
35 days
1
2
3
4
IIa
IIb
IIc
IId
IIe
IIf
IIg
IIh
IIi
IIj
IIk
IIl
IIm
IIn
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
IIIg
IIIh
IIIi
IIIl
IIIm
IIIn
16.7 4.7
30.0 8.2
20.0 8.2
16.7 9.4
6.7 9.4
24.1 9.4
34.5 4.7
17.2 8.2
24.1 9.4
41.4 4.7
13.8 4.7
34.5 4.7
48.3 8.2
31.0 4.7
27.6 8.2
58.6 8.2
37.9 8.2
37.9 8.2
37.9 8.2
44.8 4.7
44.8 4.7
48.3 8.2
44.8 4.7
51.7 9.4
65.5 4.7
51.7 4.7
41.4 9.4
41.4 4.7
37.9 8.2
44.8 4.7
41.4 4.7
24.1 4.7
31.0 4.7
37.9 8.2
10.0 8.2
3.3 4.7
27.6
24.1 4.7
37.9
0
13.3 9.4
23.3 4.7
10.0 8.2
13.3 9.4
10.0 8.2
13.3 9.4
13.3 4.7
16.7 4.7
10.0 8.2
16.7 4.7
13.3 4.7
13.3 4.7
0
24.1 4.7
34.5 9.4
27.6 8.2
34.5 4.7
48.3 8.2
44.8 9.4
17.2 8.2
31.0 4.7
27.6 8.2
34.5 9.4
34.5 9.4
17.2 8.2
24.1 4.7
27.6 8.2
37.9 8.2
27.6 8.2
41.4 9.4
34.5 9.4
Figure 2. The X-ray crystal structure of 3.
10.0
0
3.3 4.7
6.7 9.4
6.7 4.7
13.3 9.4
13.3 12.5
6.7 4.7
13.3 4.7
10.0 8.2
13.3 9.4
3.3 4.7
48.3
0
41.4 4.7
55.2 9.4
48.3 8.2
44.8 4.7
37.9 8.2
27.6 8.2
51.7 4.7
3.3 4.7
37.9
0
31.0 4.7
24.1 4.7
44.8 4.7
3.3 4.7
Toosendanina
Blank control
33.3 4.7
0
0
a
Toosendanin was used as a positive control at 1 mg/mL.
activity with the final mortality rate of 65.5%, whereas the final
mortality rate of the precursor 1 was only 34.5%. In general, to
alkylacyloxy series, the proper length of the side chain at the
C-11 position of IIa–d and IIIa–d was important for their insecti-
cidal activity. For example, the final mortality rates of IIb
(R = (CH2)6CH3), IIc (R = (CH2)10CH3), IId (R = (CH2)13CH3), IIIb
(R = (CH2)6CH3), IIIc (R = (CH2)10CH3) and IIId (R = (CH2)13CH3)
were only 37.9%, 37.9%, 37.9%, 41.4%, 24.1% and 31%, respectively;
whereas the final mortality rates of IIa (R = CH3CH2) and IIIa
(R = CH3CH2) were 58.6% and 44.8%, respectively. Meanwhile,
introduction of 3-pyridylacyloxy group at the C-11 position of 3
and 4 did not result in the more potent compounds. To arylacyloxy
series, the electron effect on the phenyl ring of IIi–n to their insec-
ticidal activity was obvious. For example, introduction of the elec-
tron-donating groups such as methyl and methoxy on the phenyl
ring at the C-11 position of IIe led to the more potential com-
pounds IIi–k, and the final mortality rates of IIi–k were 51.7%,
65.5% and 51.7%, respectively; whereas introduction of the elec-
tron-withdrawing groups such as fluorine, chlorine and bromine
atoms on the phenyl ring at the C-11 position of IIe gave the less
active compounds IIl–n, and the final mortality rates of IIl–n were
41.4%, 41.4% and 37.9%, respectively;
Figure 3. The X-ray crystal structure of 4.
In summary, we have prepared twenty-six deoxypodophyllo-
toxin-based derivatives modified in the D-ring and evaluated their
insecticidal activity against the pre-third-instar larvae of M. separa-
ta in vivo at 1 mg/mL. It suggested that aminolysis of deoxypodo-
phyllotoxin in the presence of pyrrolidine and piperidine could
lead to complete inversion of the configuration of the carbonyl
group at its C-2 position. Among all derivatives, five compounds
IIa, IIi–k, and IIIh showed the equal or higher insecticidal activity
Figure 4. The X-ray crystal structure of IIIi.
tested M. separata were characterized by the same way as our pre-
vious reports.9–13 Among all derivatives, five compounds IIa, IIi–k,
and IIIh showed the equal or higher insecticidal activity than
toosendanin. Especially IIj displayed the most potent insecticidal
Please cite this article in press as: Wang, J.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.07.076

4
J. Wang et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
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than toosendanin. Especially IIj displayed the most potent insecti-
cidal activity with the final mortality rate of 65.5%. To arylacyloxy
series, the electron effect on the phenyl ring of IIi–n to their insec-
ticidal activity was observed. It demonstrated that, to alkylacyloxy
series, the proper length of the side chain at the C-11 position of
IIa–d and IIIa–d was important for their insecticidal activity.
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Acknowledgments
17. Dayan, F. E.; Cantrell, C. L.; Duke, S. O. Bioorg. Med. Chem. 2009, 17, 4022.
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The present research was supported by National Natural Sci-
ence Foundation of China (No. 31071737), and Special Funds of
Central Colleges Basic Scientific Research Operating Expenses
(YQ2013008).
21. Gensler, W. J.; Judge, J. F. X.; Leeding, M. V. J. Org. Chem. 1972, 1062, 37.
22. Crystallographic data (excluding structure factors) for the structure of 3, 4 and
IIIi have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication number CCDC 995275, 995273 and 995274,
respectively. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44
(0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk].
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2014.07.
076.
23. Biological assay: The insecticidal activity of compounds IIa–n and IIIa–i,l–n
against the pre-third-instar larvae of Mythimna separata Walker was assessed
by leaf-dipping method. Toosendanin, a commercial insecticide isolated from
Melia azedarach, was used as a positive control and supplied by Research &
Development Center of Biorational Pesticide, Northwest A&F University,
Shaanxi province, China. For each compound, 30 larvae (10 larvae per group)
were used. Acetone solutions of all the above tested compounds, and
toosendanin were prepared at the concentration of 1 mg/mL. Fresh wheat
leaves were dipped into the corresponding solution for 3 s, then taken out, and
dried in a room. Leaves treated with acetone alone were used as a blank control
group. Several treated leaves were kept in each dish, where every 10 larvae
were raised. If the treated leaves were consumed, additional treated leaves
were added to the dish. After 48 h, untreated fresh leaves were added to all
dishes until adult emergence. The experiment was carried out at 25 2 °C and
on 12 h/12 h (light/dark) photoperiod. The insecticidal activity of the tested
compounds was calculated by the following formula: corrected mortality rate
(%) = (T ꢀ C) ꢁ 100/(100% ꢀ C), where T is the mortality rate in the treated
group expressed as a percentage and C is the mortality rate in the untreated
group expressed as a percentage.
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