Insect antifeedant activity of flavones and chromones against Spodoptera litura

Article abstract of DOI:10.1021/jf025627a

The antifeedant polymethylated flavones 5-hydroxy-3,6,7,8,4′-heptamethoxyflavone, 5-hydroxy-3,6,7,8-tetramethoxyflavone, and 5,6-dihydroxy-3,7-dimethoxyflavone have been isolated from the cudweed, Gnaphalium affine D. Don (Compositae). These flavonoids and authentic analogues showed insect antifeedant activity against the common cutworm (Spodoptera litura F.). In a previous paper, it was suggested that there was no substituent on the B-ring of the flavonoid for the beneficial antifeedant activity against the common cutworm. These flavonoids having a phenyl group as the B-ring and the chromone as elimination of the B-ring from the flavonoids were used to test the hypothesis of the previously described B-ring effect. The known fact is that Sculletaria baicarensis (Rutaceae) produced the 2-phenyl flavone. Test compounds and their methylated derivatives were prepared from this material for the structure-activity relationship (SAR) study of insect antifeedant activity. In spite of the 2-phenyl flavonoids, some tested compounds did not show any insect antifeedant activity against the common cutworm, although these inactive flavonoids were deficient in the 6-substituent group on the A-ring of the flavonoid. This 6-position-substituted derivative almost showed strong insect antifeedant activity against common cutworm. Moreover, the tested flavonoids having a hydroxyl group as a substituent on any of the positions tended to increase the activity. These results suggested the importance of the 6-position substitution on the flavonoid; however, hydrophilic substituents decreased the activity. Baicalein (5,6,7-trihydroxyflavone) derivatives did not show any activity despite having the 6-substituent derivative. Although the activity of some chromones increased the activity of the flavone, the bulky B-ring was a disadvantage for the antifeedant activity. It was suggested that the charge on C(3) and C(5) of the flavonoid was important for the biological activity. Additionally, an adequate hydrogen bonding property, which is different from lipophilicity, was an advantage for the activity on the basis of a QSAR analysis.

Full text of DOI:10.1021/jf025627a

J. Agric. Food Chem. 2003, 51, 389−393 389
Insect Antifeedant Activity of Flavones and Chromones against
Spodoptera litura
MASANORI MORIMOTO,* KUMIKO TANIMOTO, SACHIKO NAKANO,
TAKAYOSHI OZAKI, AYAKO NAKANO, AND KOICHIRO KOMAI
Department of Agricultural Chemistry, Kinki University, Nakamachi, Nara 3327-204, Japan
The antifeedant polymethylated flavones 5-hydroxy-3,6,7,8,4′-heptamethoxyflavone, 5-hydroxy-3,6,7,8-
tetramethoxyflavone, and 5,6-dihydroxy-3,7-dimethoxyflavone have been isolated from the cudweed,
Gnaphalium affine D. Don (Compositae). These flavonoids and authentic analogues showed insect
antifeedant activity against the common cutworm (Spodoptera litura F.). In a previous paper, it was
suggested that there was no substituent on the B-ring of the flavonoid for the beneficial antifeedant
activity against the common cutworm. These flavonoids having a phenyl group as the B-ring and the
chromone as elimination of the B-ring from the flavonoids were used to test the hypothesis of the
previously described B-ring effect. The known fact is that Sculletaria baicarensis (Rutaceae) produced
the 2-phenyl flavone. Test compounds and their methylated derivatives were prepared from this
material for the structure-activity relationship (SAR) study of insect antifeedant activity. In spite of
the 2-phenyl flavonoids, some tested compounds did not show any insect antifeedant activity against
the common cutworm, although these inactive flavonoids were deficient in the 6-substituent group
on the A-ring of the flavonoid. This 6-position-substituted derivative almost showed strong insect
antifeedant activity against common cutworm. Moreover, the tested flavonoids having a hydroxyl
group as a substituent on any of the positions tended to increase the activity. These results suggested
the importance of the 6-position substitution on the flavonoid; however, hydrophilic substituents
decreased the activity. Baicalein (5,6,7-trihydroxyflavone) derivatives did not show any activity despite
having the 6-substituent derivative. Although the activity of some chromones increased the activity
of the flavone, the bulky B-ring was a disadvantage for the antifeedant activity. It was suggested that
the charge on C(3) and C(5) of the flavonoid was important for the biological activity. Additionally, an
adequate hydrogen bonding property, which is different from lipophilicity, was an advantage for the
activity on the basis of a QSAR analysis.
KEYWORDS: Flavone; chromone; Sculletaria baicarensis; antifeedant; Spodoptera litura
INTRODUCTION
property. The known fact is that Sculletaria baicarensis (Ru-
taceae) produced the 2-phenyl chromone (7). We prepared the
test compounds from this source and synthesized some chromones
for the evaluation of this hypothesis.
The widespread flavonoids act as various functional secondary
metabolites in plants. These functions have been reported as
the constituents for the ultraviolet defense system against
sunlight, as an antioxidant in the plant body (1), and as an
attractant for pollinators as flower pigments (2). On the other
hand, we know some flavonoids have a repellency property
against some phytophagous insects and a termite acting as an
antifeedant (3, 4). These various properties of the flavonoids
can be applied to the development of functional food, medicinal,
and agrochemical agents. The phytophagous insect overcoming
the plant defense system can use the flavonoids for their host
selection (5). In a previous paper, we isolated four antifeedants
from the Japanese annual weed, Gnaphalium affine, and
described their derivatives for insect antifeedant activity (6). In
this study, we have further examined the role of the chemical
structures of the flavonoid in a structure-activity relationsip
(SAR) study of insect antifeedants. We regard the lack of
substituents on the B-ring as benefitical to the insect antifeedant
MATERIALS AND METHODS
General. 1H and 13C NMR spectra were measured on a JEOL 270EX
(270 MHz) spectrometer. Mass spectra were taken at 70 eV (probe)
using a Shimadzu GCMS 9100-MK. The compounds were separated
by column chromatography on silica gel, Fuji silysia chemical BW-
127ZH and BW-300 (Fuji Silysia Chemical, Ltd.). TLC used silica
gel plates with a fluorescent indicator (Merck silica gel 60 F254, 0.25
mm thick).
Insect Rearing. Common cutworms (Spodoptera litura F.) were
reared on an artificial diet (Insecta LF, Nihon Nosan Kogyo Co.) in a
controlled room environment at 26.5 °C and 60% humidity.
Evaluation of Test Compounds with Choice Leaf Disk Bioassay.
The experimental setup was described in a previous report (6).
Evaluation of the test compounds used the ED50 value of the antifeedant
value calculated from the rate of consumption (8). A straight line was
fitted to the points obtained from the bioassay, and the ED50 was
10.1021/jf025627a CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/04/2002

390 J. Agric. Food Chem., Vol. 51, No. 2, 2003
Morimoto et al.
calculated as the dose corresponding to the midpoint between complete
inhibition and no effect by a computer program.
7.57 (3H, m, Ar-H), 6.69 (1H, s, Ar-H), 6.58 [1H, s, CdC(3)H], 3.98
(3H s, Ar-OCH3), 3.93 (3H s, Ar-OCH3).
Nobiletin (5,6,7,8,3′,4′-hexamethoxyflavone, 11): yellow powder
Preparation of Test Compounds. The commercial folk drug
(Scuretallia baicarensis; Japanese name, Oogon) was extracted with
methanol. The concentrated yellowish oil was separated by silica gel
(Fuji Silysia Chemical, BW-127ZH) column chromatography with
hexane/ethyl acetate 3:1. The fraction including the flavones was
rechromatographed on the silica gel with the same solvent system. The
final purification of the flavones was performed by recrystallization.
Two flavones, norwogonin (6) and oloxylin A (9), were isolated from
this extract. These natural compounds were characterized by spectrum
analyses. For the preparation of the flavonoid methyl ethers of
appropriate molar concentration of methyl iodide corresponding to the
number of phenols in the chemical structure of the parent compound,
we used the reactions with acetone containing potassium carbonate.
After completion of the reaction by thin-layer chromatography (TLC),
water was added to the product. The solution was extracted with ethyl
acetate and dried over anhydrous sodium sulfate. The solvent was
removed by a rotary evaporator under reduced pressure. These
derivatives were characterized by spectrum analyses: worgonin (4),
isowogonin (5), and moslosooflavone (7), prepared from norwogonin
by methylation. Nobiletin (11) was separated from the folk drug made
from Japanese orange peel by silica gel column chromatography. The
chromones were synthesized by the coupling reaction of the phenol
and ketone. The phenol, cresol, 3,5-dimethoxyphenol, and 3,4,5-
trimethoxyphenol were coupled with acetoacetic ethylate under base
conditions. These coupling reactions produced 2,7-dimethylchromone
(19), 2-methyl-5,7-dimethoxychromone (20), and 2-methyl-5,6,7-tri-
methoxychromone (21), respectively. Chromone 18 and 7-methoxy-
chromone (23) were prepared by Claisen condensation from the phenol
and alkyl ester following dehydroxygenation with strong acid. Chrysin
(5,7-dihydroxyflavone, 1), apigenin (5,7,4′-trihydroxyflavone, 2), lu-
teolin (5,7,3′,4′-tetrahydroxyflavone, 3), baicarein (5,6,7-trihydroxy-
flavone, 8), flavone 12, 6-methylflavone (13), and 6-hydroxyflavone
(13) were purchased from Sigma Chemical Co., Ltd.
(hexane); mp 132-134 °C; EIMS, m/z (relative intensity) 402 (M+,
1
24.3%), 387 (100%); H NMR (CDCl3) δ 7.48 (1H, dd, J ) 2.5, 8.6
Hz, Ar-H), 7.34 (1H, d, J ) 2.5 Hz, Ar-H), 6.92 (1H, d, J ) 8.6 Hz,
Ar-H), 6.57 [1H, s, CdC(3)H], 4.03 (3H, s, Ar-OCH3), 3.96 (3H, s,
Ar-OCH3), 3.90 (3H, s, Ar-OCH3), 3.89 (3H, s, Ar-OCH3), 3.88 (6H,
s, Ar-OCH3 ×2); 13C NMR (CDCl3) δ 177.4, 161.1, 152.3, 151.9, 149.3,
148.3, 144.0, 130.8, 128.7, 123.9, 119.6, 114.7, 111.2, 108.6, 106.7,
62.2, 61.9, 61.7, 61.6, 56.0, 55.9.
6-Methoxyflavone (15): white needles (hexane); mp 162.7-164.3
°C; EIMS, m/z (relative intensity) 252 (M+, 100%), 222 (32.0%), 150
(67.3%), 135 (20.8%), 122 (16.9%), 107 (41.9%); 1H NMR (CDCl3) δ
7.82-7.89 (2H, m, Ar-H), 7.42-7.49 (2H, m, ar-H), 7.53 (1H, d, J )
2.97 Hz, Ar-H), 7.22 (1H, dd, J ) 9.23, 2.97 Hz, Ar-H), 6.72 [1H, s,
CdC(3)H], 3.84 (3H, s, Ar-OCH3); 13C NMR (CDCl3) δ 178.3, 163.2,
157.0, 151.1, 131.9, 131.5, 129.0, 126.2, 124.6, 123.8, 119.5, 106.8,
104.8.
7-Methoxyflavone (17): pearl pink solid (hexane); mp 103-105 °C;
EIMS, m/z (relative intensity) 252 (M+, 100%), 224 (49.6%), 209
(49.2%), 150 (36.4%), 122 (35.8%); 1H NMR (CDCl3) δ 8.14 (1H, d,
J ) 9.23 Hz, Ar-H), 7.89-7.97 (2H, m, Ar-H), 7.45-7.53 (3H, m,
Ar-H), 6.99 (1H, d, J ) 9.23 Hz, Ar-H), 6.97 (1H, s, Ar-H), 6.76 [1H,
s, CdC(3)H], 3.94 (3H, s, Ar-OCH3); 13C NMR (CDCl3) δ 177.9, 164.2,
163.0, 158.0, 131.9, 131.4, 129.0, 127.1, 126.2, 117.8, 114.4, 107.5,
100.4.
Chromone (18): white powder (hexane); mp 38.7-40.1 °C; EIMS,
m/z (relative intensity) 146 (M+, 100%), 118 (63%), 92 (46.4%), 63
(46.3%); 1H NMR (CDCl3) δ 8.20 (1H, dd, J ) 7.92, 1.65 Hz, Ar-H),
7.86 [1H, d, J ) 5.94 Hz, C(2)HdC], 7.67 (1H, ddd, J ) 7.92, 6.92,
1.65 Hz, Ar-H), 7.44 (1H, d, J ) 7.92 Hz, Ar-H), 7.38 (1H, ddd, J )
7.92, 6.92, 1.65 Hz, Ar-H), 6.33 [1H, d, J ) 5.94 Hz, CdC(3)H]; 13
C
NMR (CDCl3) δ 177.4, 156.4, 155.2, 133.6, 125.6, 125.1, 124.7, 118.0,
112.8.
2,7-Dimethylchromone (19): white solid (hexane); mp 95.7-98 °C;
EIMS, m/z (relative intensity) 174 (M+, 100%), 146 (45.1%), 134
(33.7%), 106 (22.3%); 1H NMR (CDCl3) δ 7.96 (1H, d, J ) 8.25 Hz,
Ar-H), 7.01 (1H, s, Ar-H), 7.09 (1H, d, J ) 8.25 Hz, Ar-H), 6.04 [1H,
s, CdC(3)H], 2.37 (3H, s, Ar-CH3), 2.27 [3H, s, CdC(2)-CH3]; 13C
NMR (CDCl3) δ 178.2, 165.8, 156.5, 144.6, 126.3, 125.2, 121.1, 117.4,
110.3, 21.7, 20.5.
2-Methyl-5,7-dimethoxychromone (20): pearl pink solid (hexane);
mp 168.3-171.3 °C; EIMS, m/z (relative intensity) 220 (M+, 87.8%),
192 (100%), 177 (87.3%), 149 (21.2%); 1H NMR (CDCl3) δ 6.43 (1H,
d, J ) 2.31 Hz, Ar-H), 6.29 (1H, d, J ) 2.31 Hz, Ar-H), 5.95 [1H, s,
CdC(3)H], 3.86 (3H, s, Ar-OCH3), 3.85 (3H, s, Ar-OCH3), 2.53 [3H,
s, CdC(2)-CH3]; 13C NMR (CDCl3) δ 162.7, 161.1, 159.1, 156.9, 154.5,
111.3, 104.8, 95.4, 93.3, 55.8, 55.7.
2-Methyl-5,6,7-trimethoxychromone (21): yellow powder (hexane);
mp 107.3-110.7 °C; EIMS, m/z (relative intensity) 250 (M+, 100%),
235 (91.0%), 207 (56.3%), 179 (18.7%), 164 (23.2%), 149 (23.6%);
1H NMR (CDCl3) δ 6.65 (1H, s, Ar-H), 6.04 [1H, s, CdC(3)H], 3.96
(3H, s, Ar-OCH3), 3.92 (3H, s, Ar-OCH3), 3.86 (3H, s, Ar-OCH3), 2.56
[3H, s, CdC(2)-CH3]; 13C NMR (CDCl3) δ 160.9, 156.2, 153.5, 151.6,
151.3, 139.2, 113.0, 108.0, 96.2, 61.3, 60.9, 56.2, 22.9.
2-Methyl-7-methoxychromone (22): pearl pink powder (hexane);
mp 158-160.7 °C; EIMS, m/z (relative intensity) 190 (M+, 100%),
162 (74.7%), 147 (94.5%), 91 (25.5%); 1H NMR (CDCl3) δ 7.50 (1H,
d, J ) 8.91 Hz, Ar-H), 6.86 (1H, dd, J ) 8.58, 2.31 Hz, Ar-H), 6.82
(1H, d, J ) 2.31 Hz, Ar-H), 6.14 (1H, s, Ar-H), 6.04 [1H, s, CdC(3)H],
3.87 (3H, s, Ar-OCH3), 2.40 [3H, s, C(2)-CH3]; 13C NMR (CDCl3) δ
162.7, 161.3, 155.3, 152.5, 125.5, 113.6, 112.3, 112.0, 100.9, 55.7,
18.6.
Worgonin (5,7-dihydroxy-8-methoxyflavone, 4): yellow powder
(hexane); mp 190-193 °C (lit. 203 °C); UV (MeOH) λmax 300 (sh),
260 nm; EIMS, m/z (relative intensity) 284 (M+, 45.4%), 269 (97.0%),
241 (37.0%), 140 (100%), 69 (73.9%); 1H NMR (CDCl3) δ 12.50 (1H,
s, Ar-OH), 7.89-7.95 (2H, m, Ar-H), 7.54-7.60 (3H, m, Ar-H), 6.69
(1H, s, Ar-H), 6.45, [1H, s, CdC(3)H], 4.04 (3H, s, Ar-OCH3).
Isowogonin (5,8-dihydroxy-7-methoxyflavone, 5): yellow needles
(hexane); mp 162-164.7 °C; EIMS, m/z (relative intensity) 284 (M+,
100%), 266 (31.3%), 255 (20.8%), 238 (54.8%), 153 (18.0%); 1H NMR
(CDCl3) δ 12.49 (1H, s, Ar-OH), 7.87-7.92 (2H, m, Ar-H), 7.48-
7.56 (3H, m, Ar-H), 6.68, (1H, s, Ar-H), 6.62 [1H, s, CdC(3)H], 4.01
(3H, s, Ar-OCH3).
Norwogonin (5,7,8-trihydroxyflavone, 6): yellow powder (MeOH);
mp 267-269.3 °C; EIMS, m/z (relative intensity) 270 (M+, 100%),
1
168 (46.6%), 140 (17.9%), 69 (53.7%); H NMR (acetone) δ 12.30
(1H, s, Ar-OH), 8.04-8.10 (2H, m, Ar-H), 7.56-7.64 (3H, m Ar-H),
6.78 (1H, s, Ar-H), 6.70 [1H, s, CdC(3)H]; 13C NMR (CDCl3) δ 186.9,
168.1, 157.3, 155.0, 151.4, 136.0, 135.9, 133.4, 133.3, 130.6, 108.9,
98.3.
Moslosooflavone (5-hydroxy-7,8-dimethoxyflavone, 7): yellow
needles (hexane); mp 181-183 °C; EIMS, m/z (relative intensity) 298
(M+, 100%), 283 (92.4%), 269 (24.9%), 255 (62.4%), 153 (67.4%);
1H NMR (CDCl3) δ 12.68 (1H, s, Ar-OH), 7.89-7.92 (2H, m, Ar-H),
7.50-7.58 (3H, m, Ar-H), 6.69 (1H, s, Ar-H), 6.58 [1H, s, CdC(3)H],
3.98 (3H s, Ar-OCH3), 3.93 (3H s, Ar-OCH3).
Oloxylin A (5,7-dihydroxy-6-methoxyflavone, 9): yellow powder
(hexane); mp 184-186 °C (lit. 200-201, 231-232°C); UV (MeOH)
λmax 300 (sh), 256, 232 nm; EIMS, m/z (relative intensity) 284 (M+,
1
85.5%), 269 (58.6%), 266 (42.4%), 69 (100%); H NMR (CDCl3) δ
7-Methoxychromone (23): white powder (isopropyl alcohol); mp
107-109 °C; EIMS, m/z (relative intensity) 176 (M+, 100%), 148
(29.5%), 133 (40.4%), 122 (23.4%); 1H NMR (CDCl3) δ 8.09 (1H, d,
J ) 8.91 Hz, Ar-H), 7.78 [1H, d, J ) 5.94 Hz, HC(2)dC], 6.96 (1H,
dd, J ) 2.31, 8.91 Hz, Ar-H), 6.82 (1H, d, J ) 2.31 Hz, Ar-H), 6.27
[1H, d, J ) 5.94 Hz, CdC(3)H], 3.89 (3H, s, Ar-OCH3); 13C NMR
(CDCl3) δ 176.9, 164.0, 158.1, 154.8, 127.0, 118.6, 114.4, 112.8, 100.2,
55.7.
13.10 (1H, s, Ar-OH), 7.85-7.92 (2H, m, Ar-H), 7.48-7.58 (3H, m,
Ar-H), 6.78 (1H, s, Ar-H), 6.72 [1H, s, CdC(3)H], 4.15 (3H, s, Ar-
OCH3).
Mosloflavone (5-hydroxy-6,7-dimethoxyflavone, 10): white needle
(hexane); mp 146-148.7 °C; EIMS, m/z (relative intensity) 298 (M+,
87.3%), 283 (86.6%), 269 (30.8%), 255 (79.5%), 153 (100%); 1H NMR
(CDCl3) δ 12.68 (1H, s, Ar-OH), 7.86-7.93 (2H, m, Ar-H), 7.49-

Insect Antifeedant Activity of Flavones and Chromones
J. Agric. Food Chem., Vol. 51, No. 2, 2003 391
Figure 4. Chromones tested for antifeedant bioassay against S. litura.
results suggested that the insect antifeedant activity decreased
due to the 2-position bulky substituents. In this study, the
flavones had a phenyl group as the B-ring, and the chromones
as derivatives of the elimination of the B-ring were used for
the evaluation of the previous hypothesis; some of them inhibited
common cutworm feeding. On the other hand, there were some
compounds that showed decreased insect antifeedant activity
in spite of haivng the phenyl group as the B-ring. These results
suggested that the biological activity required not only the
important 2-position substituent but also the substituted pattern
on the A-ring of these insect antifeedants, flavonoids, and
chromones. Most of the test compounds having a hydroxyl group
did not show the antifeedant activity. Additionally, there was
no active compound having a substituent on the 6-position of
the benzopyranone in the oxygenated derivatives.
Figure 1. 6-Unsubstituted flavone tested for antifeedant bioassay against
S. litura.
Figure 2. 6-Methoxyflavones tested for antifeedant bioassay against S.
litura.
There were some reports that the insect taste sensitivity was
dominated by GABAA receptors and active compounds against
one of the receptors acted as the insect antifeedant (10). There
were some reports about antifeedants having effective GABAA
receptors of pictotoxinin and strychnine (11). Originally, these
compounds were used in the insecticidal studies. Recently, there
was a report that some of our tested flavones bind to the
benzodiazepine receptor (12), and insecticidal natural com-
pounds having the same target site (13) were reported. Ai et al.
reported that the most active compound was 6-methylflavone
(12), but the flavones have hydroxyl groups with high binding
activity against the benzodiazepine receptor. In our case, the
flavones having a hydroxyl group did not show any insect
antifeedant activity, because there was a difference between the
receptor assay and topical application. Commonly, the receptor
assay canceled the biological barrier, for example, penetrability
or transition. We believe the data did not correlate with the
benzodiazepine receptor binding data because the penetrability
was significantly related.
These results showed an unclear correlation between the
chemical structures and biological activity. In the QSAR analysis
of the benzodiazepine binding activity, the activity was impor-
tant for the molecule refractivity (MR) and lipophilicity (π) in
the 6-position of the flavone (14). On the basis of our results
of the computational analysis with electric charge on the
benzopyranone and HB parameter, we concluded that the formal
charge on the benzopyranone calculated at the AM1 level was
more important than the values of HOMO (-0.129), LUMO
(0.07), and ∆H-L (0.121) (correlation coefficient toward pED50)
(9). The best relation to the biological activity was the melting
point parameter (-0.575) (correlation coefficient toward pED50).
None of the compounds having a melting point >250 °C showed
any insect antifeedant activity in this test. The parameters most
related with biological activity were the electric charges at C(3)
and C(5). We adopted four descriptors: the dipole moment, the
electric charges of both the 3- and 5-carbons (δ3, 5), and a
parameter relating the hydrogen bond on the Si-OH TLC (HB).
The HB parameter is defined by an adequate solvent system;
Figure 3. Monosubstituted flavones tested for antifeedant bioassay against
S. litura.
Computational Methods. The antifeedant flavonoids including those
in the previous paper were compared with respect to formal charge on
the benzopyranone and the biological activity by computational analysis
and other physicochemical parameters. The geometry of the structures
has been optimized on minimum energy using the AM1 model
Hamiltonian including WinMopac software. We had a training set of
the 19 antifeedant flavonoids and chromones by QREG software (9).
As a result, the biological activity was not related to the HOMO and
LUMO parameters. On the other hand, the formal charge on the
structure and hydrogen bonding parameter (HB) calculated from the
Rf value on the Si-OH TLC related to the biological activity. We
suggested a primitive formula for the expected value of the insect
antifeedant activity against the common cutworm.
RESULTS AND DISCUSSION
We evaluated the 6-unsubstituted flavones (Figure 1), the
6-substituted flavones (Figure 2), the monosubstituted in the
A-ring the flavones (Figure 3), and chromones (Figure 4) for
insect antifeedant activities against the common cutworm. From
the choice leaf-disk bioassay, we recognized the B-ring of the
flavonoid effect based on the data from the previous paper and
nobiletin (11) and the chromones (20) in this study. Nobiletin
(11) showed decreased activity by 1 order or magnitude toward
tangeretin (0.28) and 5-hydroxyauranetin (0.11) (Table 1). These

392 J. Agric. Food Chem., Vol. 51, No. 2, 2003
Morimoto et al.
antifeedant activity,
Table 1. Structural Features and Evaluation of Insect Antifeedant Activity for Flavones and Chromones Tested against S. litura F.
A-ring
B-ring
ED a (µmol/cm )
2
test compound
5
6
7
8
3′
4′
50
flavones
chrysin (1)
apigenin (2)
luteolin (3)
wogonin (4)
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OCH
H
H
H
H
H
H
H
OH
OCH
OCH
OCH
OH
OH
OH
OH
OCH
H
H
H
OCH
OH
OH
OCH
H
H
H
H
OH
H
H
H
H
H
H
H
H
2.50
OH
OH
H
H
H
inactive
inactive
2.00
inactive
1.52
1.30
0.96
inactive
inactive
5.60
3
isowogonin (5)
3
norwogonin (6)
moslosooflavone (7)
baicalein (8)
oloxylin A (9)
mosloflavone (10)
nobiletin (11)
OH
OCH
3
3
OH
OH
H
H
H
OCH
3
OCH
H
OCH
3
3
OCH
OCH
3
3
3
3
3
3
flavone (12)
H
H
H
H
H
H
H
CH
OH
OCH
H
H
H
H
H
H
OH
OCH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
0.11
6-methylflavone (13)
6-hydroxyflavone (14)
6-methoxyflavone (15)
7-hydroxyflavone (16)
7-methoxyflavone (17)
0.035
inactive
0.15
inactive
0.059
3
3
3
chromones
chromone (18)
2,7-dimethylchromone (19)
2-methyl-5,7-dimethoxychromone (20)
2-methyl5,6,7-trymethoxychromone (21)
2-methyl-7-metrhoxychromone (22)
7-methoxychromone (23)
H
H
OCH
OCH
H
H
H
H
H
OCH
H
H
H
CH
OCH
OCH
3
OCH
OCH
H
H
H
H
H
H
0.168
0.102
inactive
0.41
inactive
0.096
3
3
3
3
3
3
3
2
a ED50 value given >10 µmol/cm showed no activity in this table.
Figure 5. Conception of hydrogen bonding parameter (HB).
Rf values of most compounds strictly rely on the constitution
of the eluents developing the TLC analysis. The differential
condition of the TLC analysis defining the hexane/ethyl aceate
eluent system was able to normalize the coefficient (HB) by
the Rf value ) 0.12x + HB (x ) concentration of ethyl acetate,
%) (Figure 5). Improvement of the correlation was achieved
using this HB parameter (Figures 6 and 7).
Figure 6. Correlation between observed and calculated biological activities
of flavonoids and chromones.
The results suggested that the introduction of a bulky substituent
to the 2-position decreased this activity. On the other hand, the
introduction of a substituent to the 6- or 7-position increased
the activity. We suggested that our prediction of the antifeedant
activity requires a positive charge at the C(3) and a negative
charge at the C(5) nuclei and a high hydrogen bonding property.
In other words, increasing the insect antifeedant activity required
the introduction of an electron donor substituent to the 6- or
2-position of benzopyranone. We showed that there was a good
correlation between the insect antifeedant activity and Rf value
from the TLC analysis in the same eluent for the dihydroben-
zofurans (15). However, we are subsequently analyzing the
QSAR by considering the other parameters.
pED50 ) -0.195 dipole + 6.487 δ3 - 5.155 δ5 -
0.119 log P + 8.091
(n ) 19; r2 ) 0.73)
pED50 ) -0.129 dipole + 6.434 δ3 - 5.290 δ5 -
0.486 HB + 8.085
(Figure 7)
(Figure 6)
(n ) 19; r2 ) 0.79)
Although the decrease in the activity and number of hydroxyl
groups correlated, this was attributable to the penetrability
toward the receptor in the insect taste-sensitive organ. The reason
In summary, various flavones and chromones were evaluated
for the insect antifeedant activity against common cutworms.

Insect Antifeedant Activity of Flavones and Chromones
J. Agric. Food Chem., Vol. 51, No. 2, 2003 393
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Figure 7. Correlation between observed and calculated biological activities
of flavonoids and chromones.
for the reduction of the activity is the poor solubility of the
flavonoids as the hydroxyl groups increase, thus facilitating the
formation of crystals.
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Received for review April 25, 2002. Revised manuscript received
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