3-(4-Methylfuran-3-yl)propan-1-ol: A White-Spotted stinkbug (Eysarcoris ventralis) repellent produced by an endophyte isolated from green foxtail

Article abstract of DOI:10.1021/jf904093y

Stinkbug is a major rice plant pest in Asia. The extract of the culture filtrate of a fungus isolated from a green foxtail, Setaria viridis (L.) Beauv., was found to have a repellent effect on the white-spotted stinkbug, Eysarcoris ventralis (Westwood). The active principle was purified and isolated, and identified as 3-(4-methylfuran-3-yl)propan-1-ol (1) on the basis of spectroscopic data. Four acyl derivatives were prepared from 1 and assessed for repellent effect on the stinkbug; the acetyl derivative 2 was most effective.

Full text of DOI:10.1021/jf904093y

2882 J. Agric. Food Chem. 2010, 58, 2882–2885
DOI:10.1021/jf904093y
3-(4-Methylfuran-3-yl)propan-1-ol: A White-Spotted Stinkbug
(Eysarcoris ventralis) Repellent Produced by an Endophyte
Isolated from Green Foxtail
HIROMITSU
N
AKAJIMA,* ATSUSHI
I
SHIHARA, YUJI
S
AWA
,
AND
E
MI
S
AKUNO
Department of Agricultural Chemistry, Faculty of Agriculture, Tottori University, Koyama,
Tottori 680-8553, Japan
Stinkbug is a major rice plant pest in Asia. The extract of the culture filtrate of a fungus isolated from
a green foxtail, Setaria viridis (L.) Beauv., was found to have a repellent effect on the white-spotted
stinkbug, Eysarcoris ventralis (Westwood). The active principle was purified and isolated, and
identified as 3-(4-methylfuran-3-yl)propan-1-ol (1) on the basis of spectroscopic data. Four acyl
derivatives were prepared from 1 and assessed for repellent effect on the stinkbug; the acetyl
derivative 2 was most effective.
KEYWORDS: Eysarcoris ventralis; Setaria viridis; repellent; endophyte; 3-(4-methylfuran-3-yl)propan-1-ol
INTRODUCTION
pests (10, 11). This suggests that the endophytic metabolites may
contain insect pest toxins or repellents. We used the stinkbug,
Eysarcoris ventralis (Westwood), as a test insect because it is
known to be a rice pest in paddy fields in Japan (1) as well as in
upland rice fields in Asia (12). In our screening search, the extract
of the culture filtrate of an endophyte isolated from a green foxtail
was found to have a repellent effect. The active principle was
isolated and identified as 3-(4-methylfuran-3-yl)propan-1-ol (1).
In this paper, we report the repellent activity of compound 1 and
its derivatives.
“Pecky rice” is the grain sucked by stinkbugs at the milky or
pasty stage of rice and is partially or wholly stained, probably by
bacteria or fungi that invade the grain at the sucking point. If a
rice samplecontains somepecky grains, both the quality and price
are lowered according to the degree of contamination. In Japan
there are about 10 species of stinkbugs that are regarded as major
pests of rice; the most notorious among them are the sorghum
plant bug, Stenotus rubrovittatus (Matsumura) (Heteroptera:
Miridae), and the rice bug, Leptocorisa chinensis (Dallas)
(Hemiptera: Alydidae) (1-3). The synthetic insecticides currently
used to control these pests in Japan include neonicotinoids
(dinotefuran, nitenpyram, and imidacloprid), organophosphates
(fenitrothion and phenthoate), and pyrethroids (silafluofen and
ethofenprox) (4). Applying insecticides too often not only pro-
duces insecticide-resistant insects, but disturbs the ecosystem.
Using attractant or repellent to control these pests in place
of insecticides is a promising alternative method of protecting
the rice plant. Although there have been some reports on stink-
bug attractant including a pheromone of the white-spotted
spined bug Eysarcoris parvus (Uhler) (5), an attractant phero-
mone for the male rice bug L. chinensis (Dallas) (6, 7), sex
attractant pheromones of the sorghum plant bug S. rubrovittatus
(Matsumura) (8), and an aggregation pheromone from Eysarcoris
lewisi (Distant) (9), there have been no reports on stinkbug
repellents.
MATERIALS AND METHODS
General Experimental Procedures. Solvents and reagents used in
this study were purchased from Wako Pure Chemical Industries, Ltd.,
Osaka, Japan, unless otherwise noted. UV spectra were recorded with a
Hitachi U-2001. NMR spectra were measured with a JEOL JNM-ECP
500 spectrometer. Chemical shifts were referenced to CDCl3 (δH 7.26, δC
77.0). Mass spectra were obtained with a JEOL AX505HA (direct probe).
In EIMS, the ionization voltage was 70 eV. In CIMS, the reaction gas was
isobutane. Merck Kieselgel 60 F254 was used for the TLC. The TLC
solvent was 30% (v/v) acetone in n-hexane.
Insects. The stinkbugs, E. ventralis (Westwood) (Heteroptera:
Pentatomidae), were collected from some unoccupied grounds on the
Koyama Campus of Tottori University from June to September 2008 and
kept at 24-26 °C under an ambient photoperiod in Petri dishes with
brown rice and distilled water.
Microorganism. The fungus used in this study was isolated, identified
as follows, and deposited as NITE AP-796 at NITE Patent Micro-
organisms Depositary of National Institute of Technology and Evaluation
(NITE), Japan. A green foxtail plant (Setaria viridis (L.) Beauv.) was
collected on the Koyama Campus of Tottori University, and the leaves
were treated with ethanol for 1 min and then 5% sodium hypochlorite for 1
or 3 min. The leaves were then rinsed with sterile water, cut into small
pieces with a sterilized razor, and placed onto malt medium containing
streptomycin (50 mg/L) in plastic Petri dishes (90 ꢀ 15 mm). The Petri
dishes were incubated at 24 °C in darkness, and the fungi growing close to
the leaves were transferred to malt slant medium. The secondary meta-
bolite of one of the fungi had a repellent effect on E. ventralis (Westwood),
In this study, we attempted to find a new and natural repellent
among secondary metabolites produced by fungal endophytes.
The endophytes live within plants and show no external sign of
the infection, and thus their metabolites must not be toxic to
plants. This symbiotic relationship is believed to provide a
competitive advantage for the host plant, increasing tolerance
to abiotic/biotic stresses such as drought, disease, and insect
*Corresponding author (telephone/fax þ81-857-31-5362; e-mail
nakajima@muses.tottori-u.ac.jp).
pubs.acs.org/JAFC
Published on Web 02/04/2010
© 2010 American Chemical Society

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2883
Figure 1. Repellentassay. (A) Structureoftheassayapparatus:a, Advantecno. 2filterpaper(5ꢀ 40mm);b, glassbottle(12 ꢀ 35 mm);c, polyvinylchloride
pipe (88 ꢀ 17 mm); d, Advantec no. 2 filter paper (90 mm) with two holes (12 mm); e, lid (90 ꢀ 9 mm) of plastic Petri dish with two holes (12 mm); f, polyvinyl
chloride pipe (88 ꢀ 42 mm); g, black paper (90 mm); h, lid (90 ꢀ 9 mm) of plastic Petri dish. (B) Assay apparatus. (C) Stinkbugs, Eysarcoris ventralis
(Westwood), in the assay apparatus.
and the fungus was foundto be similar to Biscogniauxia atropunctata in the
sequence of their 18S rRNA gene: for analysis of the 18S rRNA sequence,
the fungus was grown on PDA medium at 24 °C for 7 days. Mycelia were
collected and disrupted with a pestle in the buffer (150 mM NaCl, 10 mM
Tris-HCl, pH 8.0, 10 mM EDTA, 0.1% SDS). Genomic DNA was
obtained with a Dneasy Plant Mini Kit (Qiagen GmbH, Hilden,
Germany). The PCR used genomic DNA as the template and ITS2 and
ITS5 as the PCR primers. Amplification conditions were 95 °C for 5 min,
followed by 30 cycles of 95 °C for 15 s, 57 °C for 15 s, 72 °C for 30 s, and
finally 72 °C for 5 min. The PCR products were purified with a Wizard SV
Gel and PCR Clean-Up System (Promega) and directly sequenced. All of
the sequencing reactions were done with a BigDye Terminator ver. 3.1
Cycle Sequencing Kit (Applied Biosystems), and the sequence determina-
tion was performed with an ABI PRISM 3130 sequencer.
Repellent Assay. The test sample was dissolved in an appropriate
amount of acetone, and 50 μL of the solution was applied to a piece of filter
paper (5 ꢀ 40 mm, no. 2, Advantec MFS, Inc.). For the control, only
acetone (50 μL) was applied. These papers were dried and put into
respective glass bottles (12 ꢀ 35 mm), which were connected to the assay
apparatus (Figure 1A,B). Twenty stinkbugs, E. ventralis (Westwood), were
introduced in the assay apparatus and left at 10 °C under light (Figure 1C).
After 30 min, the number of bugs in each bottle was determined. The
experiment was repeated four times. The repellent activity was computed
from the formula
further purified by silica gel flash chromatography (Wakogel FC-40, 30 ꢀ
390 mm) with 200 mL (10 mL ꢀ 20) each of 10, 20, and 30% ethyl acetate
in n-hexane saturated with water. Fractions 1-9 eluted with 20% ethyl
acetate in n-hexane saturated with water were combined and concentrated in
vacuo to afford the active compound (1, 59 mg) as colorless oil. When
necessary, further purification by HPLC was carried out with a Cosmosil
5C18-AR column (Nacalai Tesque, 10 ꢀ 250 mm), 60% MeOH in water as
the solvent, a flow rate of 1.0 mL/min, and monitoring at 250 and 280 nm
1
(tR 29 min): UV (MeOH) λmax (log ε) 218 (3.93) nm; H NMR and 13C
NMR data, see Table 1; EIMS, m/z (%) 140 (Mþ, 14), 109 (8), 96 (100), 95
(55), 81 (8), 79 (8), 77 (6); HREIMS, m/z 140.08447 (calcd for C8H12O2,
140.08373).
Esterification of Compound 1. Compound 1 (10 mg) was dissolved in
pyridine (500 μL) and treated with acetic anhydride (500 μL) overnight at
room temperature. The reaction mixture was poured into acidic water
(pH 2.0) and the product extracted with ethyl acetate. The ethyl acetate
solution was washed with 1 M sodium bicarbonate and brine, dried over
anhydrous sodium sulfate, and concentrated. TLC purification of the ethyl
acetate extract afforded compound 2 (8.9 mg): UV (MeOH) λmax (log ε)
219 (3.40), 206 (3.57) nm; 1H NMR and 13C NMR data, see Table 1;
EIMS, m/z (%) 182 (Mþ, 9), 139 (2), 122 (100), 109 (14), 107 (9), 96 (62), 95
(100), 93 (38), 79 (38), 77 (13).
Compound 1 (9.5 mg) was dissolved in acetone (1 mL) and treated with
pyridine (12 μL) and propionyl chloride (12 μL) overnight at room
temperature. The workup procedure was the same as in the preparation
of compound 2. TLC purificationgave compound3 (7.6 mg): UV (MeOH)
repellent activity ¼ ½100C=ðC þ TÞ -50ꢁ ꢀ 2
λ
max (log ε) 218 (3.69), 205 (3.61) nm; 1H NMR and 13C NMR data, see
where C is the number of bugs in the control glass bottle and T is the
number of bugs in the glass bottle containing the test compound. The
average value and the standard error were obtained.
Table 1; CIMS, m/z (%) 197 (100).
Compound 1 (9.7 mg) was dissolved in acetone (1 mL) and treated with
pyridine (23 μL) and butyryl chloride (29 μL) overnight at room
temperature. The workup procedure was the same as in the preparation
of compound 2. TLC purificationgave compound4 (4.0 mg): UV (MeOH)
Isolation and Identification of Compound 1. The isolate of
Biscogniauxia sp. was grown without shaking at 24 °C for 14 days in the
dark in 500 mL conical flasks (50) containing liquid medium (200 mL/flask)
composed of glucose (30 g/L), peptone (3 g/L), the extract from 50 g/L of
malt, and water. Metabolites were extracted from the culture filtrate with
10 L of ethyl acetate three times after adjustment of the pH to 2.0 with HCl.
The ethyl acetate solution was dehydrated over anhydrous sodium sulfate
and concentrated to dryness to afford the extract (7.7 g). The extract was
subjected to silica gel column chromatography (Daisogel IR-60, 62 ꢀ
720 mm), with 8 L each of 0, 5, 10, and 20% acetone in n-hexane. The
fraction eluted with 10% acetone in n-hexane was concentrated to dryness
to afford the active residue (660 mg). A portion (100 mg) of the residue was
λ
max (log ε) 215 (3.67), 205 (3.65) nm; 1H NMR and 13C NMR data, see
Table 1; CIMS, m/z (%) 211 (100%).
Compound 1 (11.5 mg) was dissolved in acetone (1 mL) and treated
with pyridine (19 μL) and benzoyl chloride (28 μL) overnight at room
temperature. The workup procedure was the same as in the preparation of
compound 2. TLC purification gave compound 5 (7.4 mg): UV (MeOH)
λ
max (log ε) 276 (3.31), 235 (4.21), 205 (4.05) nm; 1H NMR and 13C NMR
data, see Table 1; EIMS, m/z (%) 244 (1), 139 (2), 122 (100), 105 (37),
104 (10), 96 (11), 95 (23), 93 (26), 79 (21), 77 (32).

2884 J. Agric. Food Chem., Vol. 58, No. 5, 2010
Nakajima et al.
Table 1. NMR Spectroscopic Data for Compounds 1-5 (CDCl3)
1
2
3
4
5
a
a
δH
a
δH
a
a
δH
δC
δH
δC
δC
δC
δH
δC
1
2
3
4
5
6
7
8
139.0
124.8
119.9
139.6
19.7
7.16 (1H, s)
139.1
124.2
119.8
139.6
19.9
7.15 (1H, s)
139.1
124.3
119.8
139.6
19.9
7.15 (1H, s)
139.1
124.3
119.8
139.6
19.9
7.14 (1H, s)
139.1
124.2
119.8
139.6
20.0
7.17b (1H, s)
7.16 (1H, s)
7.15 (1H, s)
7.15 (1H, s)
7.14 (1H, s)
7.19b (1H, s)
2.53 (2H, t, 7.6)
2.03 (2H, m)
4.37 (2H, t, 6.4)
1.98 (3H, s)
2.45 (2H, t, 7.8)
1.82 (2H, m)
3.71 (2H, t, 6.4)
1.97 (3H, s)
2.42 (2H, t, 7.7)
1.88 (2H, m)
4.11 (2H, t, 6.5)
1.96 (3H, s)
2.42 (2H, t, 7.6)
1.88 (2H, m)
4.11 (2H, t, 6.7)
1.95 (3H, s)
2.41 (2H, t, 7.8)
1.87 (2H, m)
4.10 (2H, t, 6.4)
1.95 (3H, s)
32.1
62.4
28.2
63.9
28.3
63.7
28.3
63.6
28.4
64.3
8.0
8.0
8.0
8.0
8.1
R
171.2
21.0
174.5
27.6
9.2
173.7
36.2
18.5
13.7
166.6
130.3
129.5c
128.3c
132.9
2.06 (3H, s)
2.33 (2H, q, 7.4)
1.15 (3H, t, 7.4)
2.28 (2H, t, 7.3)
1.66 (2H, m)
0.95 (3H, t, 7.3)
8.05 (2H, d, 7.4)
7.45 (2H, t, 7.4)
7.56 (1H, t, 7.4)
a Intensities, multiplicities, and J values (hertz) shown in parentheses. b,c Interchangeable.
RESULTS AND DISCUSSION
E. ventralis (Westwood) collected at our campus was used as
the test insect. Through the course of our research we found that
the most advantageous property of the insect is that when left
under cool condition, they aggregate in a dark place. On the basis
of this property the assay apparatus shown in Figure 1A,B was
devised and used. The apparatus has two dark holes composed of
glass bottles: a piece of filter paper (a) containing a test sample in
one bottle (b) and a piece of filter paper (a) containing no sample
in the other (b). Twenty stinkbugs were introduced onto the filter
paper (d) on the lid of a Petri dish (e) as shown in Figure 1C and
left at 10 °C under light for 30 min. During this time, each insect
chose and entered a dark hole. Almost >70% of the insects were
found in the bottles; the remainder stayed out of the holes. By
comparing the respective number of insects found in the two
holes, we could ascertain the repellent activity of the sample
applied. By this assay, we screened secondary metabolites of the
endophytes isolated from many grass weeds. In our screening
search, the extract of the culture filtrate of an endophyte isolated
from a green foxtail was found to have a repellent effect on
the insect. The endophyte did not form spores in many trials,
making identification difficult, but was found to be close to
B. atropunctata (Schwein.) Pouzar (92% similarity) by a BLAST
similarity search based on the sequence of its 18S rRNA gene.
The fungus was grown on malt extract medium without
shaking at 24 °C for 14 days in the dark. The metabolites were
extracted from the culture filtrate with ethyl acetate and purified
by bioassay-guided chromatography to afford an active com-
pound (1) in the yield of 39 mg/L. Compound 1 had the molecular
formula C8H12O2 from its HREIMS and NMR data, requiring
three degrees of unsaturation. The 13C NMR spectrum of 1
(Table 1) in CDCl3 displayed eight carbon resonances: one owing
to methyl, three to methylenes (one of which was oxygenated),
two to sp2 methines, and two to sp2 quaternary carbons. Acetyl-
ation of 1 gave monoacetate 2, confirming the presence of one
hydroxyl in the molecule. The 1H NMR spectrum of 1 (Table 1)
indicated the presence of partial structures, C-C(8)H3 and
C-C(5)H2-C(6)H2-C(7)H2OH. Taking the remaining carbons
and protons, and their chemical shifts (δC 139.0 and 139.6; δH
7.16 and 7.16 for sp2 methines, δC 119.9 and 139.0 for sp2
quaternary carbons) into account, the 3,4-disubstituted furan
ring in the molecule was suggested. The furan ring was also
supported by its UV spectrum. Connecting these structural
parts gave a structure, 3-(4-methylfuran-3-yl)propan-1-ol, for 1.
Assignments of the carbon resonances to carbon atoms of the
Figure 2. Structures of compounds 1-5.
Table 2. Repellant Effect of Compounds 1-5 on White-Spotted Stinkbugs,
Eysarcoris ventralis (Westwood)
repellent activity (%) ( SE (n = 4)
compound
0.003 μmol
0.01 μmol
0.1 μmol
1 μmol
a
1
-
-
5.7 ( 4.6
90.2 ( 3.2
58.0 ( 5.4
51.8 ( 5.9
5.3 ( 3.6
89.3 ( 3.9
-
89.3 ( 3.0
96.4 ( 2.3
40.7 ( 6.8
80.4 ( 5.4
2
10.7 ( 3.2
-
19.5 ( 6.3
-
-
7.3 ( 3.0
20.5 ( 6.3
-19.4 ( 0.8
-
3
4
5
naphthalene
40.7 ( 4.5
44.6 ( 6.3
a -, not tested.
furan ring were based on HMQC and HMBC data. 3-(4-Methyl-
furan-3-yl)propan-1-ol has been reported as a synthetic inter-
mediate for alliacol A (13). On the basis of the spectroscopic and
spectrometric data in the literature, compound 1 was completely
identified as 3-(4-methylfuran-3-yl)propan-1-ol. It has never been
reported as a natural product, and this is the first report of its
production by a fungus.
Four acyl derivatives (2-5; Figure 2) were prepared from
compound 1, and the repellent effects of compounds 1-5 were
assessed by the assay using the white-spotted stinkbug (Table 2).
A dose of 0.1 μmol of acetyl derivative 2 produced 90.2%
repellency, which was more effective than the same dose of
naphthalene. Doses of 0.1 μmol of propionyl and butyryl deri-
vatives (3 and 4) produced moderate repellency comparable to the
same dose of naphthalene. At the same dose amount, compound
1 and its benzoyl derivative (5) showed almost no effect. At a dose
of 1 μmol, compound 1 and its propionyl and butyryl derivatives
(3 and 4) showed high repellency (89.3, 89.3, and 96.4%,
respectively), comparable to the same dose of naphthalene,

Article
J. Agric. Food Chem., Vol. 58, No. 5, 2010 2885
whereas benzoyl derivative (5) produced moderate repellency.
Accordingly, the order of these compounds in the repellent
activity was determined to be compound 2 > compound 3 =
compound 4 > compound 1 > compound 5. Interestingly, at a
dose of 0.01 μmol, butyryl derivative (4) showed weak attractant
activity, and this phenomenon was reproducible.
(4) Handbook of Pesticides, 10th ed. (Nouyaku-Binran); Yoneyama, S.,
Ando, K., Tsuzuki, T., Eds.; Rural Culture Association Japan
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By this study we demonstrated that a metabolite produced by
an endophyte showed repellent activity to a grass weed pest.
Recently, Shiba and Sugawara (14) reported that loline alkaloids
are generally observed in the highest concentrations in many
Neotyphodium-grass symbiotic associations and are known to be
toxic to insects; some Neotyphodium-infected grasses have en-
hanced resistance to the rice leaf bug, Trigonotylus caelestialium.
If compound 1 is produced by the endophyte and accumulates in
the foxtail plants, this symbiotic association enhances the resis-
tance of the foxtail plants to the stinkbugs through the repellent
effect by the compound. The role of this compound in the
symbiosis is still unknown and remains to be investigated. As
mentioned in the Introduction, “pecky rice” caused by stinkbugs
is a serious agricultural problem in Japan. Acetyl derivative 2
could be an effective alternative chemical for controlling these
pests, and experiments to assess its effect in pots and in fields are
now being arranged.
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Seasonal attraction of the rice bug, Leptocorisa chinensis Dallas
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ACKNOWLEDGMENT
We thank Shin Hikami and Takato Kukimoto for technical
assistantce.
(13) Wu, H.; Moeller, K. D. Anodic coupling reactions: a sequential cycliza-
tion route to the arteannuin ring skeleton. Org. Lett. 2007, 9, 4599–4602.
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associations confer resistance to the rice leaf bug, Trigonotylus
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