Synthesis and bioactivity of rotenone oxime o-ether derivatives

Article abstract of DOI:10.4314/bcse.v26i3.11

A series of rotenone oxime O-ether derivatives were synthesized and characterized. All compounds were tested for their insecticidal, miticidal and fungicidal activities against the selected pests and compared with those of rotenone. The results of biological tests show that the rotenone oxime O-ether derivatives have improved insecticidal but weak miticidal activities against M. eparate, N. cincticeps, T. urticae compared with rotenone. The disustituted oxime O-ethers showed novel fungicidal activity against R. solani with an inhibition of 80.7-95.2%.

Full text of DOI:10.4314/bcse.v26i3.11

Bull. Chem. Soc. Ethiop. 2012, 26(3), 421-428
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v26i3.11
ISSN 1011-3924
 2012 Chemical Society of Ethiopia
SYNTHESIS AND BIOACTIVITY OF ROTENONE OXIME O-ETHER DERIVATIVES
Gao Cao*, Zhen Zhou and Ying Wang
School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University,
Guangzhou 510006, P. R. China
(Received July 20, 2011; revised March 12, 2012)
ABSTRACT. A series of rotenone oxime O-ether derivatives were synthesized and characterized. All
compounds were tested for their insecticidal, miticidal and fungicidal activities against the selected pests and
compared with those of rotenone. The results of biological tests show that the rotenone oxime O-ether derivatives
have improved insecticidal but weak miticidal activities against M. eparate, N. cincticeps, T. urticae compared
with rotenone. The disustituted oxime O-ethers showed novel fungicidal activity against R. solani with an
inhibition of 80.7-95.2%.
KEY WORDS: Rotenone oxime O-ether, Synthesis, Insecticidal activity, Miticidal activity, Fungicidal activity
INTRODUCTION
Pesticides play an important role in our lives, not only for crop protection in agriculture, but also
for human health. However, the unrestricted use of highly toxic pesticides over several decades
has resulted in the accumulation of pesticides in the soil and their dispersion into the
environment [1]. Rotenone (Figure 1) is an abundant natural product occurring in the roots of
tropical plants belonging to the Leguminosae family [2]. It has been widely used as an
insecticide, acaricide and piscicide because of its broad spectrum of toxicity, and hence has
been a valuable alternative to synthetic pesticides [3, 4]. However, rotenone has a serious
limitation to its widespread usage due to its susceptibility towards ultraviolet rays or solar
irradiation. Owing to rotenone’s high photolability, either breaking down or isomerizing in the
presence of sunlight will decrease its bioactivities under field conditions, resulting in poor
persistence in the environment and inadequate field performance [5].
O
2
O
1
O
3
H
A
11
D
4
10
12a
6a
B
C
O
O
O
E
6
H
5'
4'
8'
7'
Figure 1. Structure of rotenone with the atoms labeling scheme used in the spectral elucidation.
Imitating and modifying the chemistry of biologically active natural products is an
alternative approach for developing more efficient and less toxic pesticides. Several
investigations of structure-activity relationships have been reported, using mainly natural
__________
*Corresponding author. E-mail: g.cao@mail.scut.edu.cn

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Gao Cao et al.
rotenoids and their derivatives [6-9]. The high inhibitory potency of rotenone is associated with
the compounds containing the A-B-C-D-E five rings system with the cis-6aβ, 12aβ-B/C ring
juncture, this arrangement result in an approximately V-shaped molecule with a certain angle;
Another important structural feature is that 2,3-dimethoxy substitution on the ring A and a
suitable substituent on the ring E [10, 11]. Modifications at the B and C rings of rotenone are
permissible as long as they do not seriously affect the preferred configuration of the B/C ring
juncture. In order to improve the biological activities and photostabilization of rotenone, we
designed and synthesized a series of rotenone oxime O-ether derivatives using natural rotenone
as a substrate. Furthermore, all the compounds prepared, along with the parent compound
rotenone, were tested for their insecticidal, miticidal and fungicidal activities against selected
pathogens.
RESULTS AND DISCUSSION
Scheme 1. Synthetic pathway to rotenone oxime O-ether derivatives (3a-3g and 4a-4c).
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Synthesis and bioactivity of rotenone oxime O-ether derivatives
423
Compound 2 was prepared by the reaction of rotenone and hydroxylamine in ethanol
(Scheme 1) by the procedure reported previously, and its melting point is in agreement with the
literature value (237-239 °C) [12]. Furthermore, X-ray diffraction results show that compound 2
exists in the form of E-isomer with the isopropenyl group in an equatorial position [13]. In the
process of preparing 3, the phase transfer catalyst plays an important role in improving the
yields and shortening the reaction time. Compounds 3a-3g were prepared in an alkaline
medium, and the addition of potassium iodide accelerated the reactions via the halogen-
exchange. Table 1 summarized the time of reactions, yield, and melting point of 3a-3g, 4a-4c
derivatives.
Table 2 shows the insecticidal and miticidal activities of rotenone and the oxime O-ethers
against the selected insects Mythimna separata (M. separate), Nephotettix cincticeps (N.
cincticeps), Aphis fabae (A. fabae) and mite Tetranychus urticae (T. urticae). Generally, most of
the rotenone oxime O-ether derivatives exhibited insecticidal and miticidal activities against M.
eparate, N. cincticeps and T. urticae, comparable to the parent compound rotenone. It is notable
that all compounds, including rotenone, have no insecticidal activity against A. fabae. Of the
test compounds, compounds 4a and 4c are the most active.
Table 1. Reaction time, yield and m.p. data in synthesis of rotenone oxime O-ethers.
Reaction
time (h)
36
Product
Yield (%)
M.p. (°C)
3a
3b
3c
3d
3e
3f
3g
4a
4b
4c
73.0
68.8
75.1
71.9
41.0
57.3
60.0
55.6
44.5
54.2
226-228
178-180
191-193
188-190
> 260
165-167
190-192
> 260
10
20
10
12
12
13
23
25
> 260
> 260
25
Table 2. Insecticidal and miticidal activities of rotenone oxime O-ether derivatives.
Compound
Mortality (%)
M. separata
43.2
N. cincticeps
T. urticae
20.3
13.3
14.2
12.9
32.6
16.7
15.6
15.2
A. fabae
Rotenone
21.5
25.4
30.5
23.5
4.8
18.4
20.5
19.0
22.7
21.4
22.1
0
0
0
0
0
0
0
0
0
0
0
3a
3b
3c
3d
3e
3f
3g
4a
4b
4c
35.2
40.8
34.6
5.0
31.5
30.4
45.3
46.7
27.1
20.8
30.2
42.1
43.5
For the structure-activity relationship analysis, compounds 3a-3g and 4a-4c were defined as
monosubstituted derivatives and disubstituted derivatives respectively. Comparing the
bioactivities of the monosubstituted derivatives (3a-3g), it was found that suitable substituents
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Gao Cao et al.
on the phenyl group are so important that a huge difference has been observed. For example, 3e
and 3f have moderate antifungal activity against Rhizoctonia solani (R. solani), but 3g lost
antifungal activity completely (Table 3). The oxime O-ethers, in which R is a disubstituted
group, showed a higher activity than those in which R is a monosubstituted group. For example,
4a, 4b and 4c have particularly excellent fungicidal activity against R. solani, with an inhibition
rate of 80.7-95.2%, while the monosubstituted oxime ethers 3a, 3c, 3g and rotenone have nearly
no inhibition effect on any fungicidal activity. This information can be useful for designing new
macrocyclic fungicides. From the different inhibition effects of 4a, 4b and 4c, the fungicidal
activity of disubstituted oxime ethers is also closely associated with R on the bridged chain. In
addition, the results show that the introduction of the thiazole ring (3d) provides little help but
is actually harmful in terms of improving the bioactivity. Further studies on the biological
activity and structure-activity relationships of this series of compounds are in progress.
Table 3. Fungicidal activity of the test compounds against the selected pathogen species (500 mg/L).
Compound
Inhibition (%)
G. zeae
P. capsici
P. oryzae
B. cinerea
R. solani S. sclerotiorum E. graminis
Rotenone
0
0
6.8
0
0
0
55.1
39.4
0
0
0
0
7.8
0
2.9
0
25.4
5.6
7.1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
7.5
5.6
1.2
9.3
3.7
5.4
10.0
3a
3b
3c
3d
3e
3f
3g
4a
4b
4c
0
10.0
0
0
0
0
0
0
0
40.1
0
8.5
60.2
60.5
0
90.6
95.2
80.7
0
3.4
6.4
2.6
0
0
0
0
3.1
6.0
0
9.1
6.4
3.1
3.5
6.2
0
CONCLUSIONS
The molecular design, synthesis, insecticidal, miticidal and fungicidal activities of a series of
rotenone oxime O-ether derivatives have been demonstrated. Some compounds were found to
display higher insecticidal and miticidal activities against M. separata, N. cincticeps and T.
urticae than rotenone. Derivatives 4a, 4b and 4c not only showed general insecticidal activity
but also have a novel fungicidal activity, especial against R. solani at a dosage of 500 mg/L.
These derivatives were identified as being the most promising candidates for further study.
Further structural optimization and fungicidal activities studies on these rotenoid analogues are
ongoing in our laboratories.
EXPERIMENTAL
General
Rotenone (purity = 95-98%) was purchased from Sigma Aldrich (Steinheim, Germany). Other
reagents were analytical grade. Melting points were determined using a RY-1 melting point
apparatus and were given uncorrected. Infrared spectra were recorded on an Avatar-360FT
1
infrared spectrometer using potassium bromide discs. H NMR spectra were recorded on a
Bruker Avance-400 superconductor nuclear magnetic resonance instrument, with chemical shift
(δ) values reported in ppm relative to tetramethylsilane (TMS) as an internal standard. Elemental
analysis was performed with an Elemental Vario EL apparatus.
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Synthetic procedures for compound 3a-3g, 4a-4c
A solution of chloroalkane (RCl or RCl2, 0.01 mol) in anhydrous pyridine (5 mL) was added
dropwise to a stirred solution of compound 2 (0.01 mol, 0.02 mol for 4a-4c) in acetone (20 mL)
at room temperature (20 °C). Then the mixture was stirred and heated to reflux. All reactions
were performed under an atmosphere of nitrogen. After the reaction finished, the reaction
mixture was concentrated. The residual solution was purified by column chromatography (2×22
inch silica column) using petroleum ether and ethyl acetate (3:1 by volume) as eluent. The main
peak was concentrated to afford 3a-3g, 4a-4c.
Characterization data of the rotenone oxime O-ether derivatives
Compound 3a. Orange solid. 1H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 3H, 8’-CH3), 2.91 (dd, J =
8.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.27 (dd, J = 10.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.50 (s, 3H,
OCH3), 3.78 (s, 3H, OCH3), 4.21 (d, J = 12.0 Hz, 1H, 6-H), 4.48 (t, J = 2.8 Hz, 1H, 12a-H),
4.55 (dd, J = 12.0 Hz, J = 2.4 Hz, 1H, 6-H), 4.80 (d, J = 2.4 Hz, 1H, 6a-H), 4.90 (s, 1H, 7’-H),
5.06 (s, 1H, 7’-H), 5.14 (t, J = 8.8 Hz, 1H, 5’-H), 5.28 (dd, J = 12.0 Hz, J = 12.0 Hz, 2H,
NOCH2), 6.39 (s, 1H, 4-H), 6.44 (d, J = 8.4 Hz, 1H, 10-H), 6.77 (s, 1H, 1-H), 7.38 (m, 3H,
C6H5 3,4,5-H), 7.47 (d, J = 6.4 Hz, 2H, C6H5 2,6-H), 7.79 (d, J = 8.4 Hz, 1H, 11-H). Anal. calcd
for C30H29NO6: C, 72.13%, H, 5.85%, N, 2.80%. Found: C, 71.80%, H, 5.49%, N, 2.80%. IR
(KBr) ν/cm-1: 3062, 2929, 2982, 2852, 1620, 1509, 1198, 741.
1
Compound 3b. White solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 3H, 8’-CH3), 2.91 (dd, J =
8.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.27 (dd, J = 9.6 Hz, J = 16.0 Hz, 1H, 4’-H), 3.50 (s, 3H,
OCH3), 3.78 (s, 3H, OCH3), 4.21 (d, J = 12.0 Hz, 1H, 6-H), 4.49 (d, J = 2.4 Hz, 1H, 12a-H),
4.57 (dd, J = 12.0 Hz, J = 2.4 Hz, 1H, 6-H), 4.79 (d, J = 3.2 Hz, 1H, 6a-H), 4.90 (s, 1H, 7’-H),
5.06 (s, 1H, 7’-H), 5.15 (t, J = 9.2 Hz, 1H, 5’-H ), 5.20~5.33 (m, 3H, =CH2, OCH2 ), 5.75 (d, J
= 17.6 Hz, 1H, =CH2), 6.39 (s, 1H, 4-H), 6.45 (m, 2H, 1-H, 10-H), 6.71 (dd, J = 10.8 Hz, J =
21.6 Hz, =CH), 7.42 (q, J = 8.0 Hz, 4H, C6H4), 7.79 (d, J = 8.8 Hz, 1H, 11-H). Anal. calcd for
C32H31NO6: C, 73.13%, H, 5.94%, N, 2.66%. Found: C, 73.65%, H, 6.13%, N, 2.58%. IR (KBr)
ν/cm-1: 3081, 3063, 2976, 2935, 2877, 2853, 1620, 1511, 1198, 900, 742.
1
Compound 3c. White solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 3H, 8’-CH3), 2.91 (dd, J =
8.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.27 (dd, J = 10.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.58 (s, 3H,
OCH3), 3.79 (s, 3H, OCH3), 4.23 (d, J = 12.0 Hz, 1H, 6-H), 4.49 (s, 1H, 12a-H), 4.58 (d, J =
12.0 Hz, 1H, 6H), 4.74 (s, 1H, 6a-H), 4.90 (s, 1H, 7’-H), 5.05 (s, 1H, 7’-H), 5.15 (t, J = 8.8 Hz,
1H, 5’-H), 5.26 (s, 2H, OCH2 ), 6.39 (s, 1H, 4-H), 6.41 (s, 1H, 1-H), 6.44 (d, J = 8.8 Hz, 1H, 10-
H), 7.37 (d, J = 8.0 Hz, 1H, C5H3N 5-H), 7.72 (d, J = 8.8 Hz, 1H, 11-H), 7.82 (d, J = 8.0 Hz,
1H, C5H3N 4-H), 8.52 (s, 1H, C5H3N 2-H). Anal. calcd for C29H27N2ClO6: C, 65.11%, H,
5.09%, N, 5.24%. Found: C, 64.92%, H, 5.21%, N, 5.28%. IR (KBr) ν/cm-1: 3063, 2963, 2930,
2879, 2856, 1780, 1621, 1514, 1199, 739.
1
Compound 3d. White solid. H NMR (CDCl3, 400 MHz) δ: 1.76 (s, 3H, CH3), 2.89-2.95 (m,
1H, 4’-CH2), 3.25-3.32 (m, 1H, 4’-CH2), 3.47 (s, 3H, OCH3), 3.78 (s, 3H, OCH3), 4.22 (d, J =
12.0 Hz, 1H, 6-H), 4.51 (bs, 1H, 12a-H), 4.59 (dd, J = 3.0 Hz, J = 12.0 Hz, 1H, 6-H), 4.72 (d, J
= 3.0 Hz, 1H, 6a-H), 4.91 (s, 1H, 7’-H), 5.06 (s, 1H, 7’-H), 5.15 (t, 1H, J = 8.4 Hz, 5’-H), 5.33
(s, 2H, OCH2), 6.31 (s, 1H, thiazole ring H), 6.40 (s, 1H, 4-H), 6.50 (d, J = 8.4 Hz, 1H, 10-H),
7.56 (s, 1H, 1-H), 7.80 (d, J = 8.4 Hz, 1H, 11-H). Anal. calcd for C28H27ClN2O6S: C, 60.59%,
H, 4.90%, N, 5.05%. Found: C, 60.72%, H, 5.02%, N, 4.96%. IR (KBr) ν/cm-1: 3016, 2971,
2936, 2876, 2850, 1617, 1485, 1201, 982, 738.
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Gao Cao et al.
1
Compound 3e. White solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 3H, 8’-CH3), 2.92 (dd, J =
8.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.28 (dd, J = 9.6 Hz, J = 16.0 Hz, 1H, 4’-H), 3.52 (s, 3H,
OCH3), 3.78 (s, 3H, OCH3), 4.23 (d, J = 12.0 Hz, 1H, 6-H), 4.50 (d, J = 2.8 Hz, 1H, 12a-H),
4.58 (dd, 1H, J = 2.4 Hz, J = 12.4 Hz, CH2Cl), 4.64 (s, 2H, 6H, CH2Cl), 4.81 (d, J = 3.2 Hz, 1H,
6a-H), 4.90 (s, 1H, 7’-H), 5.06 (s, 1H, 7’-H), 5.15 (t, J = 8.8 Hz, 1H, 5’-H ), 5.23 (d, J = 12.4
Hz, 1H, NOCH2), 5.32 (d, J = 12.4 Hz, 1H, NOCH2), 6.40 (s, 1H, 4-H), 6.45 (d, J = 8.8 Hz, 1H,
10-H), 6.48 (s, 1H, 1-H), 7.46~7.58 (m, 8H, C6H4C6H4), 7.80 (d, J = 8.8 Hz, 1H, 11-H). Anal.
calcd for C37H34ClNO6: C, 71.20%, H, 5.49%, N, 2.24%. Found: C, 71.31%, H, 5.45%, N,
2.32%. IR (KBr) ν/cm-1: 3017, 2975, 2938, 2912, 2852, 1675, 1620, 1511, 1197, 780, 731.
1
Compound 3f. White solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 3H, 8’-CH3), 2.91 (dd, J =
8.0 Hz, J = 16.0 Hz, 1H, 4’-H), 3.27 (dd, J = 9.6 Hz, J = 16.0 Hz, 1H, 4’-H), 3.52 (s, 3H,
OCH3), 3.78 (s, 3H, OCH3), 4.22 (d, J = 12.0 Hz, 1H, 6-H), 4.49 (d, J = 2.4 Hz, 1H, 12a-H),
4.58 (m, 3H, 6-H, C6H4CH2Cl), 4.78 (d, J = 3.6 Hz, 1H, 6a-H), 4.90 (s, 1H, 7’-H), 5.06 (s, 1H,
7’-H), 5.15 (t, J = 8.8 Hz, 1H, 5’-H ), 5.23 (d, J = 12.0 Hz, 1H, NOCH2), 5.32 (d, J = 12.0 Hz,
1H, NOCH2), 6.40 (s, 1H, 4-H), 6.45 (s, 1H, 1-H), 6.45 (d, J = 8.4 Hz, 1H, 10-H), 7.39 (d, J =
8.0 Hz, 2H, C6H4 2-H, C6 H4 6-H), 7.48 (d, J = 8.0 Hz, 2H, C6H4 3-H, C6 H4 5-H), 7.79 (d, J =
8.4 Hz, 1H, 11-H). Anal. calcd for C31H30ClNO6: C, 67.94%, H, 5.52%, N, 2.56%. Found: C,
67.90%, H, 5.63%, N, 2.59%. IR (KBr) ν/cm-1: 3062, 2965, 2933, 2878, 2855, 1777, 1619,
1513, 1199, 776, 738.
1
Compound 3g. White solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 3H, 8’-CH3), 2.25 (s, 6H,
2×CH3), 2.41 (s, 3H, CH3), 2.91 (dd, J = 8.4 Hz, J = 16.0 Hz, 1H, 4’-H), 3.27 (dd, J = 10.0 Hz,
J = 16.0 Hz, 1H, 4’-H), 3.55 (s, 3H, OCH3), 3.78 (s, 3H, OCH3), 4.20 (d, J = 12.0 Hz, 1H, 6-H),
4.48 (t, J = 2.4 Hz, 1H, 12a-H), 4.56 (dd, J = 2.0 Hz, J = 12.0 Hz, 1H, 6-H), 4.78 (m, 3H, 6a-H,
CH2Cl), 4.90 (s, 1H, 7’-H), 5.05 (s, 1H, 7’-H), 5.14 (t, J = 8.8 Hz, 1H, 5’-H ), 5.33 (d, J = 11.6
Hz, 1H, NOCH2), 5.40 (d, J = 11.6 Hz, 1H, NOCH2), 6.39 (s, 1H, 4-H), 6.42 (s, 1H, 1-H), 6.45
(d, J = 8.8 Hz, 1H, 10-H), 7.18 (s, 3H, C6H4 3-H), 7.25 (d, J = 10.8 Hz, 1H, C6H4 6-H), 7.75 (d,
J = 8.8 Hz, 1H, 11-H). Anal. calcd for C33H34ClNO6: C, 68.80%, H, 5.95%, N, 2.43%. Found:
C, 68.63%, H, 6.03%, N, 2.40%. IR (KBr) ν/cm-1: 3082, 2974, 2966, 2937, 2835, 1619, 1507,
1184, 964, 743.
1
Compound 4a. n(2):n(RCl2) = 2:1, white solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 6H,
2×8’-CH3), 2.91 (dd, J = 8.0 Hz, J = 16.0 Hz, 2H, 2×4’-H), 3.27 (dd, J = 9.6 Hz, J = 16.0 Hz,
2H, 2×4’-H), 3.57 (s, 6H, 2×OCH3), 3.78 (s, 6H, 2×OCH3), 4.22 (d, J = 12.0 Hz, 2H, 2×6-H),
4.49 (d, J = 2.4 Hz, 2H, 2×12a-H), 4.57 (dd, J = 2.4 Hz, J =12.0 Hz, 2H, 2×6-H), 4.78 (d, J =
3.2 Hz, 2H, 2×6a-H), 4.90 (s, 2H, 2×7’-H), 5.05 (s, 2H, 2×7’-H), 5.15 (t, J = 8.8 Hz, 2H, 2×5’-
H), 5.25 (d, J = 12.0 Hz, 2H, 2×OCH2 -H), 5.30 (d, J = 12.0 Hz, 1H, 2×OCH2 -H), 6.40 (s, 2H,
2×4-H), 6.45 (d, J = 8.4 Hz, 2H, 2×10-H), 6.50 (s, 2H, 2×1-H), 7.45 (s, 4H, 2×C6H4-H), 7.78 (d,
J = 8.4 Hz, 2H, 2×11-H). Anal. calcd for C54H52N2O12: C, 70.42%, H, 5.69%, N, 3.04%. Found:
C, 70.23%, H, 5.64%, N, 2.99%. IR (KBr) ν/cm-1: 3061, 3017, 2929, 2983, 2870, 1675, 1620,
1510, 1201, 1092, 982, 740.
1
Compound 4b. n(2):n(RCl2) = 2:1, white solid. H NMR (CDCl3, 400 MHz) δ: 1.76 (s, 6H,
2×8’-CH3), 2.92 (dd, J = 8.0 Hz, J = 16.0 Hz, 2H, 2×4’-H), 3.24 (dd, J = 9.6 Hz, J = 16.0 Hz,
2H, 2×4’-H), 3.52 (s, 6H, 2×OCH3), 3.78 (s, 6H, 2×OCH3), 4.22 (d, J = 12.0 Hz, 2H, 2×6-H),
4.51 (s, 2H, 2×12a-H), 4.58 (dd, 2H, J = 2.4 Hz, J = 12.0 Hz, 2×6-H), 4.82 (d, J = 2.8 Hz, 2H,
2×6a-H), 4.90 (s, 2H, 2×7’-H), 5.06 (s, 2H, 2×7’-H), 5.13 (t, J = 8.8 Hz, 2H, 2×5’-H ), 5.28 (d,
J = 12.0 Hz, 2H, OCH2), 5.36 (d, J = 12.0 Hz, 2H, OCH2), 6.40 (s, 2H, 2×4-H), 6.45 (d, J = 8.4
Hz, 2H, 2×10-H), 6.49 (s, 2H, 2×1-H), 7.58 (m, 8H, 2×C6H4),7.81 (d, J = 8.4 Hz, 2H, 11-H).
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Synthesis and bioactivity of rotenone oxime O-ether derivatives
427
Anal. calcd for C60H56N2O12: C, 72.27%, H, 5.66%, N, 2.81%. Found: C, 73.05%, H, 5.62%, N,
2.72%. IR (KBr) ν/cm-1: 3018, 2972, 2935, 2912, 2860, 1677, 1621, 1513, 1202, 780, 741.
1
Compound 4c. n(2):n(RCl2) = 2:1, white solid. H NMR (CDCl3, 400 MHz) δ: 1.75 (s, 6H,
2×8’-CH3), 2.41 (s, 6H, CH3), 2.90 (dd, J = 8.4 Hz, J = 16.0 Hz, 2H, 2×4’-H), 3.25 (dd, J = 9.6
Hz, J = 16.0 Hz, 2H, 2×4’-H), 3.58 (s, 6H, 2×OCH3), 3.78 (s, 6H, 2×OCH3), 4.22 (d, J = 12.0
Hz, 2H, 2×6-H), 4.46 (s, 2H, 2×12a-H), 4.52 (dd, 2H, J = 2.0 Hz, J = 12.0 Hz, 2×6-H), 4.70 (d,
J = 2.4 Hz, 2H, 2×6a-H), 4.90 (s, 2H, 2×7’-H), 5.05 (s, 2H, 2×7’-H), 5.14 (t, J = 8.8 Hz, 2H,
2×5’-H ), 5.23 (d, J = 10.8 Hz, 2H, OCH2), 5.32 (d, J = 10.8 Hz, 2H, OCH2), 6.36 (s, 2H, 2×4-
H), 6.44 (s, 2H, 2×1-H), 6.38 (d, J = 8.8 Hz, 2H, 2×10-H), 7.03 (s, 1H, C6H4 5''-H), 7.43 (s, 1H,
C6H4 2''-H), 7.79 (d, J = 8.8 Hz, 1H, 11-H). Anal. calcd for C56H56N2O12: C, 70.87%, H, 5.95%,
N, 2.95%. Found: C, 70.72%, H, 5.89%, N, 2.92%. IR (KBr) ν/cm-1: 3085, 2962, 2937, 2835,
1676, 1513, 1415, 1260, 1324, 1173, 910, 743.
Bioassay of insecticidal activity
Test pathogens: Stock colonies of rice green leafhopper N. cincticeps, bean aphid A. fabae, two-
spot red mite T. urticae and oriental armyworm M. separata were reared in a conditioned room
maintained at 25±5 °C, 65±5% relative humidity and 12:12 hour light:dark photoperiod [14].
Stock solutions of each test compound were prepared in acetone at a concentration of 1.000 g/L,
and then diluted to the required test concentrations for use with water containing an appropriate
amount of Tween-80.
Insecticidal activity against M. separata
Potter-spraying was used to measure the insecticidal activity of test compounds against M.
separata. Fifty third-instar M. separata and five corn fragments were placed in a Petri dish and
sprayed with test solutions (500 mg/L) using a Potter sprayer [15]. After air drying, they were
kept in a room for normal cultivation. After 24 hours, the number of live and dead insects was
recorded. The test was run three times, and the results were averaged.
Insecticidal and miticidal activities against N. cincticeps, A. fabae and T. urticae
To measure the activities of test compounds against N. cincticeps, A. fabae and T. urticae, a
leaf-dipping method was introduced. Rice seedlings (second semester) were dipped in the test
solution (500 mg/L) for 5 seconds, air-dried and then placed in a large test tube. Each test tube
contained 20 seedlings. Twenty leafhoppers (third instar lymph) were introduced into the tube,
and the mouth of the tube was covered with white cheesecloth. The tube was kept at room
temperature, and the number of live and dead insects counted after 24 hours. The test was run
three times, and the results were averaged. The mortality was determined by the number of live
and dead insects as follows:
N1
M =
×100%
N0
in which M is the mortality, N0 is the total number of live insects for the test, and
average number of dead insects.
is the
N1
Bioassay of fungicidal activity
Fungicidal activity of the title compounds against Gibberella zeae (G. zeae), Phytophthora
capsici (P. capsici), Pyricularia oryzae (P. oryzae), Botrytis cinerea (B. cinerea), Sclerotinia
sclerotiorum (S. sclerotiorum), Rhizoctonia solani (R. solani) and Erysiphe graminis (E.
Bull. Chem. Soc. Ethiop. 2012, 26(3)

428
Gao Cao et al.
graminis) were evaluated using the mycelium growth rate test [16]. The appropriate amount of
test compounds was weighed accurately, dissolved in the acetone and then diluted into 500
mg/L. The culture media, with a known concentration of the test compounds, were obtained by
mixing the solution of test compounds in acetone with potato dextrose agar (PDA), on which
fungus cakes were placed. The blank test was made using acetone. The culture was grown at
25±5 °C, 65±5% relative humidity and 12:12 hour light:dark photoperiod for 72 hours. Three
replicates were performed. After the mycelia grew completely, the diameter of the mycelia was
measured and the inhibition rate calculated according to the formula:
D1 − D0
I =
×100%
D1
In which I is the inhibition rate,
is the average diameter of mycelia in the blank test, and
D0
D1
is the average diameter of mycelia in the presence of the test compounds.
ACKNOWLEDGEMENTS
The authors gratefully thank the Natural Science Foundation of Guangdong Province (No.
10451022401005172) for their financial support for this project.
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