Insect antifeedant flavonoids from Gnaphalium affine D. Don

Article abstract of DOI:10.1021/jf990282q

The antifeedant flavonoids, 5-hydroxy-3,6,7,8,4'-pentamethoxyflavone (1), 5-hydroxy-3,6,7,8-tetramethoxyflavone (2), 5,6-dihydroxy-3,7- dimethoxyflavone (3), and 4,4',6'-trihydroxy-2'-methoxychalcone (4), have been isolated from cudweed Gnaphalium affine D. Don (Compositae). Four natural flavonoids showed insect antifeedant activity against the common cutworm (Spodoptera litura F.). These flavonoids were detected in small amounts in the plant by HPLC analysis, but these natural compounds had strong antifeedant activity against the common cutworm. On the other hand, 4 was detected in a large amount in the plant, but this compound had only a slight activity. Therefore, these natural compounds were regarded as one of the plant's defensive systems against phytophagous insects along with the woolly plant surface. As for the structure-activity relationship, it is an advantage for antifeedant activity to have no oxy-substituents on the B-ring of the flavonoid but have an ether linkage such as a pyran in the chemical structure.

Full text of DOI:10.1021/jf990282q

1888
J. Agric. Food Chem. 2000, 48, 1888−1891
In sect An tifeed a n t F la von oid s fr om Gn a ph a liu m a ffin e D. Don
Masanori Morimoto,* Sumiko Kumeda, and Koichiro Komai
Department of Agricultural Chemistry, Kinki University, Nakamachi, Nara 3327-204, J apan
The antifeedant flavonoids, 5-hydroxy-3,6,7,8,4′-pentamethoxyflavone (1), 5-hydroxy-3,6,7,8-tet-
ramethoxyflavone (2), 5,6-dihydroxy-3,7-dimethoxyflavone (3), and 4,4′,6′-trihydroxy-2′-methoxy-
chalcone (4), have been isolated from cudweed Gnaphalium affine D. Don (Compositae). Four natural
flavonoids showed insect antifeedant activity against the common cutworm (Spodoptera litura F.).
These flavonoids were detected in small amounts in the plant by HPLC analysis, but these natural
compounds had strong antifeedant activity against the common cutworm. On the other hand, 4
was detected in a large amount in the plant, but this compound had only a slight activity. Therefore,
these natural compounds were regarded as one of the plant’s defensive systems against phytophagous
insects along with the woolly plant surface. As for the structure-activity relationship, it is an
advantage for antifeedant activity to have no oxy-substituents on the B-ring of the flavonoid but
have an ether linkage such as a pyran in the chemical structure.
Keyw or d s: Gnaphalium affine; 5-hydroxy-3,6,7,8,4′-pentamethoxyflavone; 4,4′,6′-trihydroxy-2′-
methoxychalcone; antifeedant; Spodoptera litura
INTRODUCTION
silica gel, Fuji silysia chemicals BW-127ZH and BW-300 (Fuji
Silysia Chemical, Ltd., J apan), and gel filtration, Sephadex
HL-20 (Amersham Pharmacia Biotech Inc., Sweden). TLC
silica gel plates with a fluorescent indicator (Merck Silica Gel
60 F254, 0.25 mm thick) were used. HPLC for the quantitative
analysis of the flavonoids was carried out using a Shimadzu
LC-9A system. The column used was an Inertsil ODS, 4.6 mm
i.d. × 250 mm (GL Science Inc., J apan).
A part of the screening of natural products from wild
plants in J apan is the potential application for the
control of phytophagous pests. Additionally, there is the
chance of finding compounds for the development of
agrochemicals. As a result of a screening test, we
recognized that the hexane and ether extracts of Gnapha-
lium affine have potential antifeedant activity against
a polyphagous insect, the common cutworm, Spodoptera
litura. This plant species is used as a medicinal plant
in the Asian region, for astringent and vulnerary
purposes. As a plant physiological feature, this plant
and related species belong to the winter annual weeds
in J apan and have many short hairs on the plant
surface. Recently, some constituents in this plant have
been investigated as inhibitory agents of bovine LAR
and platelet aggregation (Tachibana et al., 1995). One
of the constituents of G. affine, 5-hydroxy-3,6,7,8,4′-
pentamethoxyflavone (1), showed anticancer activity
In sect Bioa ssa ys. Common cutworms (S. litura) were
reared on an artificial diet (Insecta LF, Nihon Nosan Kogyo
Co., J apan) in a controlled room environment at 26.5 °C and
6
0% humidity.
Choice Leaf-Disk Bioassay. The experimental setting was
based on that described by Escoubas et al. (Escoubas et al.,
993). Leaf-disks, 2 cm diameter, were prepared with a cork
1
borer from fresh sweet potato (Ipomoea batatas) leaves that
had been cultivated in the Kinki University farm without
agrochemicals.
Two disks were treated with a specific amount of plant
extracts or test compounds in an acetone solution, and two
other disks with acetone only were used as the control. The
four disks were set in alternating positions in the same Petri
dish. After complete removal of the solvent, 15 larvae (third
instar) were released into the dish. The dishes were then kept
in an insect rearing room at 26.5 °C in the dark for 2-5 h.
Partially consumed leaf-disks were taped onto photocopier
paper for monotone data conversion. The monotone data were
photocopied, determined to contain no errors, and then con-
verted to digital data files using a digital scanner. Digital data
analyses were performed on a Macintosh computer using the
public-domain NIH Image program (developed by the U.S.
National Institutes of Health and available from the Internet
by anonymous FTP from zippy.nimh.nih.gov, or on a floppy
disk from the National Technical Information Service, Spring-
field, Virginia, part number PB95-500195GEI). For each
experiment, the data file of an intact disk was measured and
compared to that of the treated disk. For evaluation of the
antifeedant activity of the extracts and test compounds, we
adopted the antifeedant index (AFI): AFI ) % of treated disks
consumed/(% of treated disks consumed + % of control disks
consumed) × 100. The control disks were set at an AFI value
of 50. The data were evaluated by probit analysis. A straight
line was fitted to the points obtained by bioassay, and the ED50
(
Kingston et al., 1979). There were reports of the
isolation of the polymethylated flavonoids from the
plant, including Gnaphalium spp. (Torrenegra et al.,
1
980; Guerreiro et al., 1982). Antifeedants occurring in
the Compositae, sesquiterpenes in Senecio spp., poly-
acetylenes in Rudbeckia spp., and chromenes in Encelia
spp. have been previously reported (Gonz a´ lez-Coloma
et al., 1995; Guillet et al., 1997; Isman and Proksch,
1
985). We have isolated four antifeedants from G. affine
and have described their related compounds for the
investigation of insect antifeedant activity.
MATERIALS AND METHODS
Gen er a l. The 1H and 13C NMR spectra were measured
using a J EOL 270EX (270 MHz) spectrometer. Mass spectra
were taken at 70 eV (probe) using a Shimadzu GCMS 9100-
MK. FT-IR were recorded using a Shimadzu FT-IR 8020D. The
compounds were separated by column chromatography on
*
Author to whom correspondence should be addressed.
0.1021/jf990282q CCC: $19.00 © 2000 American Chemical Society
1
Published on Web 04/26/2000

Insect Antifeedant Flavonoids
J. Agric. Food Chem., Vol. 48, No. 5, 2000 1889
was calculated as the dose corresponding to midpoint between
complete inhibition and no effect by the computer program.
TLC Bioassay. The TLC plates were cut into 4 × 10 cm
pieces. The samples containing carrier solvent were applied
to the plate as a band, and the plate was developed in the
appropriate solvent system for good separation. Distilled water
was added to the artificial diet to make a paste, which was
then applied to the surface of the developed TLC plate. This
TLC plate was then placed in a plastic cup with 50 larvae
) 9.0 Hz, Ar-H), 6.69 (1H, s, H -3), 4.18 (3H, s, -OCH
3
),
), 4.03 (6H, s, -OCH
); EIMS m/z (relative intensity) 372
, 100%).
4.10 (3H, s, -OCH
3
), 4.06 (3H, s, -OCH
3
3
× 2), 3.97 (3H, s, -OCH
3
+
(M , 31.6%), 357 (M-CH
3
Qu a n tita tive An a lysis of F la von oid s in th e P la n ts. For
measurement of the amount in the plants, the flavonoids were
analyzed by HPLC. The analysis was carried out using a
Shimadzu LC-9A system. The column used was an Inertsil
ODS,. 4.6 mm i.d. × 250 mm (GL Sciences Inc., J apan). One
of the flavonoids, quercetin, was used as the internal standard
for the quantitative analysis by HPLC. We investigated
methylated flavonoids for six extracts from Gnaphalium spp.
in J apan at 285 nm by a UV detector.
(fourth instar) for 1 d at 26.5 °C. The uneaten area was
compared with the Rf values of the compounds detected on
the reference TLC plate developed under the same conditions.
Moreover, residual silica gel was found on the plate after the
TLC plate assay was removed and extracted with ethyl acetate.
The extract of residual silica gel after the TLC plate assay
was developed in the same solvent system, detected with UV
light (254 nm) and 50% sulfuric acid heated to 150 °C to
confirm the compounds with antifeedant properties contained
in the silica gel residue (Escoubas et al., 1992).
Extr a ction a n d Isola tion . Plant material of cudweed (G.
affine) was collected at the flowering stage from March to J uly
in Nara and Kyoto Prefecture, J apan. The fresh whole body
of the cudweed (3.7 kg) was extracted with hexane. The
concentrated extract had any paraffins removed with metha-
nol. The yellow oil (11.9 g) was separated by silica gel (Fuji
Silysia Chemical, BW-127ZH) column chromatography with
SYNTHESIS OF DERIVATIVES
Selective Dem eth yla tion of Meth yl Eth er F la von es. A
solution of a methylated flavone in acetonitrile was mixed with
a solution of anhydrous aluminum bromide in acetonitrile
under reflux conditions in a nitrogen atmosphere. Water was
added to the mixture 10 min later. The mixture was then
extracted with ethyl acetate and dried over anhydrous sodium
sulfate. The solvent was removed by a rotary evaporator under
reduced pressure. The resulting demethyl derivative was
separated (Horie et al., 1993, 1995).
F la von oid Meth yl Eth er s. The appropriate molarity of
methyliodide corresponds to the number of phenols in the
chemical structure of the parent compound used for the
reactions with acetone containing potassium carbonate. The
methylation was performed through the night at room tem-
perature, and the liquid turned brown with formation of iodine.
After completion of the reaction, water was added, and the
solution was extracted with ethyl acetate and dried over
anhydrous sodium sulfate. The solvent was removed by a
rotary evaporator under reduced pressure and purified in an
ordinary manner. These derivatives were characterized by
spectral analyses.
5
:1 hexane/ethyl acetate. The fraction including the antifeed-
ants was rechromatographed on the silica gel (Fuji Silysia
Chemical, BW-300) with the same solvent system. The final
purification of the antifeedants was performed by gel filtration
chromatography (Pharmacia, Shepadex LH-20) with methanol.
Three antifeedant flavonoids, 5-hydroxy-3,6,7,8,4′-penta-
methoxyflavone (1), 5-hydroxy-3,6,7,8-tetramethoxyflavone (2),
and 5,6-dihydroxy-3,7-dimethoxyflavone (3) were isolated from
this extract (Imre et al., 1984; Bohlmann et al., 1979, 1980).
After extraction with hexane, the plant residue was extracted
with ether and treated in the same manner. Thus we separated
out a constituent, 4,4′,6′-trihydroxy-2′-methoxychalcone (4)
5
-Dem eth ylta n ger etin (6): white powder (hexane); mp 175
(Bohlmann et al., 1979). For evaluation of the structure-
1
°
9
C; H NMR (CDCl
.0 Hz, Ar-H), 7.04 (2H, d, J ) 9.0 Hz, Ar-H), 6.60 (1H, s,
Ar-H), 4.11 (3H, s, OCH ), 3.97 (3H, s, OCH ), 3.95 (3H, s,
OCH ), 3.90 (3H, s, OCH ); EIMS m/z (relative intensity) 358
M , 56.8%), 343 (M-CH , 100%).
′,4′-Dih yd r oxy-4,6′-d im eth oxych a lcon e (7): pale orange
needles (CHCl ); mp 194-195 °C; UV (MeOH) λmax 208, 366
nm; H NMR (hexane) δ 14.43 (1H, s, Ar-OH), 7.79 (2H, s,
CHdCH-), 7.55 (2H, d, J ) 8.0 Hz, Ar-H), 6.92 (2H, d, J )
.0 Hz, Ar-H), 6.10 (1H, d, J ) 2.5 Hz, Ar-H), 5.96 (1H, d, J
2.5 Hz, Ar-H), 5.23 (1H, s, Ar-OH), 3.91 (3H, s, OCH ),
3
) δ 12.57 (1H, s, Ar-OH), 7.90 (2H, d, J )
activity relationship, one of the methylated flavonoids, tan-
geretin (5), was isolated from the hexane extract of Citrus
auranetium. The peel of this citrus contains the known
3
3
3
3
5
1
-hydroxy-3,6,7,8,4′-pentamethoxyflavone (1) (Sarin et al.,
960). However, we did not detect this compound in the hexane
+
(
3
2
extract of C. auranetium. These natural compounds were
characterized by spectral analyses.
3
1
5
-H yd r oxy-3,6,7,8,4′-p en t a m et h oxyfla von e (1): yellow
-
8
)
3
1
powder (hexane); mp 122-123 °C; UV (MeOH) λmax 275, 325
1
nm; H NMR (CDCl
3
) δ 12.20 (1H, s, Ar-OH), 8.09 (2H, d, J
3
+
)
9.0 Hz, Ar-H), 6.97 (2H, d, J ) 9.0, Ar-H), 4.03 (3H, s,
.82 (3H, s, OCH
00%), 285 (M-CH
2
3
); EIMS m/z (relative intensity) 300 (M ,
, 15.6%).
OCH
3
), 3.88 (6H, s, OCH
3
× 2), 3.83 (3H, s, OCH
3
), 3.80 (3H,
3
+
s, OCH
M-CH
-Hyd r oxy-3,6,7,8-tetr a m eth oxyfla von e (2): yellow pow-
der (hexane); mp 98-100 °C; UV (MeOH) λmax 278, 352 nm;
H NMR (CDCl
H), 7.54 (2H, m, Ar-H), 4.10 (3H, s, OCH
.91 (3H, s, OCH ), 3.97 (3H, s, OCH ); EIMS m/z (relative
intensity) 358 (M , 66.9%), 343 (M-CH , 100%).
,6-Dih yd r oxy-3,7-d im eth oxyfla von e (3): yellow crystals
3
); EIMS m/z (relative intensity) 388 (M , 66.6%), 373
′-Hydr oxy-4,4′,6′-tr im eth oxych alcon e (8): yellow needles
(
3
, 100%).
1
(
(
(
hexane); mp 113 °C; UV (MeOH) λmax 208, 362 nm; H NMR
CDCl ) δ 13.93 (1H, s, Ar-OH), 7.79 (2H, s, -CHdCH-), 7.55
2H, d, J ) 8.0 Hz, Ar-H), 6.92 (2H, d, J ) 8.0 Hz, Ar-H),
.10 (1H, d, J ) 2.5 Hz, Ar-H), 5.96 (1H, d, J ) 2.5 Hz, Ar-
H), 3.91 (3H, s, OCH ), 3.85 (3H, s, OCH ), 3.82 (3H, s, OCH );
EIMS m/z (relative intensity) 314 (M , 100%), 299 (M-CH
2.2%).
,2′,4′,6′-Tetr a m eth oxych a lcon e (9): yellow needles (hex-
5
3
1
3
) δ 12.62 (1H, s, Ar-OH), 8.13 (3H, m, Ar-
6
3
), 3.92 (3H, s, OCH ),
3
3
3
3
3
3
+
3
+
3
,
3
1
5
4
1
(
hexane); mp 178 °C; UV (MeOH) λmax 274, 346 nm; H NMR
CDCl ) δ 12.37 (1H, s, Ar-OH), 8.11 (3H, m, Ar-H), 7.54 (2H,
1
ane); mp 119-121 °C; UV (MeOH) λmax 245, 366 nm; H NMR
(
3
(
1
6
CDCl
3
) δ 7.46 (2H, d, J ) 8.0 Hz, Ar-H), 7.32 (1H, d, J )
3.0 Hz, CHdC(R)H), 6.86 (1H, d, J ) 13.0 Hz, CHdC(â)H),
.78 (2H, d, J ) 8.0 Hz, Ar-H), 6.14 (2H, s, Ar-H), 3.85 (3H,
), 3.82 (3H, s, OCH ), 3.75 (6H, s, OCH
m, Ar-H), 6.44 (1H, s, Ar-H), 6.34 (1H, s, Ar-OH), 4.00 (3H,
s, OCH ), 3.88 (3H, s, OCH ); EIMS m/z (relative intensity)
14 (M , 66.9%), 299 (M-CH , 100%).
,4′,6′-Tr ih yd r oxy-2′-m eth oxych a lcon e (4): yellow pow-
3
3
+
3
3
s, OCH
3
3
3
× 2); EIMS
, 100%).
4
+
m/z (relative intensity) 328 (M , 66.9%), 313 (M-CH
3
1
der (CHCl
NMR (CDCl
2), 7.91 (1H, d, J ) 13.0 Hz, CHdC(â)H), 7.91 (1H, d, J )
3.0 Hz, CHdC(R)H), 7.58 (2H, d, J ) 8.0 Hz, Ar-H), 6.85
2H, d, J ) 8.0 Ar-H), 6.00 (1H, s, Ar-H), 5.91 (1H, s, Ar-
H), 3.87 (3H, s, OCH
2.1%), 271 (M-CH
Ta n ger etin (5): white needles (hexane); mp 152 °C; 1
NMR(CDCl ) δ 7.96 (2H, d, J ) 9.0 Hz, Ar-H), 7.10 (2H, d, J
3
); mp 248 °C; UV (MeOH) λmax 245, 366 nm; H
3
) δ 13.93 (1H, s, Ar-OH), 10.30 (2H, s, Ar-OH
RESULTS AND DISCUSSION
×
1
In sect An tifeed a n t Activities of Na tu r a l F la -
von oid s a n d Th eir Der iva tives. During the choice
leaf-disk bioassay for evaluation of insect antifeedants,
we initially recognized the insect antifeedant activities
of the hexane and ether extracts from G. affine. Active
(
+
3
); EIMS m/z (relative intensity) 286 (M ,
8
3
, 41.5%), 167 (100%).
H
3

1890 J. Agric. Food Chem., Vol. 48, No. 5, 2000
Morimoto et al.
F igu r e 1. Structures of test flavonoids.
Ta ble 1. An tifeed a n t Activity of th e F la von oid s fr om G.
a ffin e a n d Au th en tic F la von oid s a ga in st S. litu r a La r va e
in a Ch oice Lea f-Disk Bioa ssa y
compounds were present in the TLC bioassay of these
extracts; these natural compounds have been isolated
by column chromatography and other procedures. Based
on the spectral analyses, the antifeedants have the
features of polymethylated flavonoids. We have evalu-
ated the antifeedant activity of methylated flavonoids
by methylation. Therefore, we evaluated not only these
natural flavonoids from G. affine, but also the authentic
flavonoids, tangeretin, quercetin, and rotenone. The
flavonol quercetin is well-known to be widespread in
plants and acts as a plant defense system toward some
insect species. However, this compound was recognized
to have no effect on the common cutworm in our
bioassay. Quercetin was then altered to the methylated
derivatives because the antifeedants in G. affine are
polymethylated flavonoids. However, the methylated
quercetin did not increase the inhibition of the common
cutworm to feeding. This fact suggested that not all of
the methylated flavonoids have insect antifeedant activ-
ity. There are significant relationships between insect
antifeedant activity and the chemical structures of the
flavonoids. The 5-hydroxy-3,6,7,8-tetramethoxyflavone
antifeedant activity
ED50 2
pED50
2
test flavonoid
(mol/cm ) (mol/cm )
-
-
-
7
8
8
5
5
5
-hydroxy-3,6,7,8,4′-pentamethoxyflavone (1) 1.1 × 10
6.96
7.70
7.60
6.55
6.74
6.82
-hydroxy-3,6,7,8-tetramethoxyflavone (2)
,6-dihydroxy-3,7-dimethoxyflavone (3)
2.0 × 10
2.5 × 10
2.8 × 10
1.8 × 10
1.5 × 10
inactive
inactive
-7
tangeretin (5)
5-demethyltangeretin (6)
rotenone
quercetin
tetramethoxyquercetin
-
-
7
7
Ta ble 2. An tifeed a n t Activity of th e Ch a lcon e fr om G.
a ffin e a n d Its Der iva tives a ga in st S. litu r a La r va e in a
Ch oice Lea f-Disk Bioa ssa y
antifeedant activity
ED50
pED50
2
2
test chalcone
(mol/cm ) (mol/cm )
-7
4
,4′,6′-trihydroxy-2′-methoxychalcone (4)
3.8 × 10
6.42
4.68
5.05
6.28
2.1 × 10-5
2′,4′-dihydroxy-4,6′-dimethoxychalcone (7)
-6
2′-trihydroxy-4,4′,6′-trimethoxychalcone (8) 9.0 × 10
4
,2′,4′,6′-tetramethoxychalcone (9)
5.2 × 10-
7
(2) and 5,6-dihydroxy-3,7-dimethoxyflavone (3) were
shown to have the strongest insect antifeedant activi-
ties. On the other hand, 5-hydroxy-3,6,7,8,4′-penta-
methoxyflavone (1) was found to have less activity than
the previous two flavonoids. These flavonoids were
polymethylated, excluding the phenol by hydrogen
bonding with the carbonyl group at the 5-position of the
flavones; 2 and 3, especially, have only a hydrogen
substituent on the B-ring (Figure 1). Based on the
bioassay evaluation, introduction of a methyl ether on
the B-ring of the flavonoid decreases the insect anti-
feedant activity. This hypothesis is supported by the
comparison of the test compounds, the methylated
quercetin and methylated flavonoids in G. affine, which
have a number of diverse substituents on the B-ring
A comparison of flavones and chalcones for insect
antifeedant activity showed the importance of the
chemical structure. The important structural feature
was the ether linkage system consisting of the pyran
ring in the chemical structure. This fact was supported
by the difference in antifeedant activity for the two
categories of flavonoids (Tables 1 and 2). Some of
antifeedants occurring in the other plant species also
have ether linkages in their chemical structures. For
instance, the furan moiety is contained in the aza-
dirachtins and clerodan diterpenes, and the pyran
moiety is contained in the precocens and rotenoids
Klocke et al., 1989; Kato et al., 1972; Bowers et al.,
976). The isoflavones also have strong antifeedant
activity against some phytophagous insect species, and
rotenoids are included in this category (Lane et al.,
985). Harborne discussed the flavonoid insect relation-
ships in his book (Harborne and Grayer, 1993). These
relationships include both allomones and kairomones.
(
1
(Table 1).
With respect to the antifeedant activities of the
chalcones, all the methylated derivatives have less
activity than the parent compound. The natural com-
pound 4 had the strongest antifeedant activity of these
chalcones (Table 2). It was important for feeding inhibi-
tion of the common cutworm that the correct number
of methyl ethers be introduced on the aromatic moiety.
In comparison, the chalcone 4 had a weaker activity
than the three flavonoids in G. affine, but the amount
of chalcone was larger than these flavonoids in the
plant. This fact suggested that both acted as one
defensive system for the plant against phytophagous
insects.
1
Qu a n t it a t ive An a lysis of t h e F la von oid s in
P la n ts. It was shown by HPLC that these flavonoids
(
1-3) as antifeedants were present at levels of 4.5 ×
-4 -4 -3
10 %, 8.7 × 10 %, and 1.8 × 10 % on a fresh weight
basis, respectively. Although we have analyzed other
Gnaphalium spp. in J apan, i.e., G. japonicum Thumb.,
G. pensylvanicum Willd., G. spicatum Lam., G. pur-

Insect Antifeedant Flavonoids
J. Agric. Food Chem., Vol. 48, No. 5, 2000 1891
pureum L., and G. calviceps Ferm., these flavonoids
were not detected in these plant species by the HPLC
analysis.
Horie, T.; Tominaga, H.; Yoshida, I.; Kawamura, Y. Studies
of the selective O-alkylation and dealkylation of flavonoids.
XIV. A convenient method for synthesizing 5,6,7-trihydroxu-
3
-methoxyflavones from 6-hydroxy-3,5,7-trimethoxyfla-
In summary, three polymethylated flavonoids and one
chalcone, which were isolated from G. affine, were
shown to be antifeedants. Two flavonoids (2, 3) showed
the highest antifeedant activity, while 1 and the chal-
cone showed less feeding inhibition. A comparison of
their chemical structures showed that the introduction
of a methyl ether excluding the B-ring in the flavonoid
structure increased the antifeedant activity. However,
the introduction of a methyl ether at the 3- and 5-
position on the flavonoid was not relative to the rate of
antifeedant activity. Moreover, it was advantageous for
the effect of insect feeding inhibition that an agent had
an ether moiety linkage in the chemical structure.
vones. Bull. Chem. Soc. J pn. 1993, 66, 877-811.
Horie, T.; Kobayashi, T.; Kawamura, Y.; Yoshida, I.; Tominaga,
H.; Yamashita, K. Studies of the selective O-alkylation and
dealkylation of flavonoids. XVIII. A convenient method for
synthesizing 3,5,6,7-tetrahydroxyflavones. Bull. Chem. Soc.
J pn. 1995, 68, 2033-2041.
Imre, S.; Islimyeli, S.; O¨ ztunc, A.; B u¨ y u¨ ktimkin, M. Flavonoid
aglycones in some Digitalis species. Planta. Med. 1984, 50,
360.
Isman, M. B.; Proksch, P. Deterrent and insecticidal chromenes
and benzofurans from Encelia (Asteraceae). Phytochemistry
1985, 24, 1949-1951.
Kato, N.; Takahashi, M.; Shibayama, M.; Munakata, K.
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