Synthesis and biological activity of methyl 2,6,10-trimethyldodecanoate and methyl 2,6,10-trimethyltridecanoate: Male-produced sexual pheromones of stink bugs Euschistus heros and Piezodorus guildinii

Article abstract of DOI:10.1023/A:1026433608967

Methyl 2,6,10-trimethyltridecanoate (1) and methyl 2,6,10-trimethyldodecanoate (2) have been identified as male-produced sex pheromones of the Brazilian soybean stink bugs Euschistus heros (F.) and Piezodorus guildinii (Westwood). In order to establish a defined attractive blend for both species, compounds 1 and 2 were synthesized as mixtures of stereoisomers to be employed in behavior bioassays. (±)-Citronellol (3) was utilized as starting material, and the syntheses was carried out in six steps with good overall yield. When tested alone, synthetic compounds 1 and 2 proved to be active in a two-choice olfactometer; however, a 20: 1 mixture of 1 and 2 was much more attractive to E. heros females. A similar blend had been found among the headspace volatiles of males.

Full text of DOI:10.1023/A:1026433608967

Journal of Chemical Ecology, Vol. 26, No. 12, 2000
SYNTHESIS AND BIOLOGICAL ACTIVITY OF
METHYL 2,6,10-TRIMETHYLDODECANOATE AND
METHYL 2,6,10-TRIMETHYLTRIDECANOATE:
MALE-PRODUCED SEXUAL PHEROMONES OF
STINK BUGS Euschistus heros AND Piezodorus guildinii
1,
2
2
´
PAULO H. G. ZARBIN, * AURELIA RECKZIEGEL, ERNST PLASS,
MIGUEL BORGES,3 and WITTKO FRANCKE2
1Departamento de Qu
UFPR, Laboratorio de Ecologia Qu
C.P. 19081 CEP 81531-990 Curitiba-PR, Brazil
´
ımica, Universidade Federal do Parana
´
´
´
ımica e Sıntese Organica
´
ˆ
2Institute of Organic Chemistry, University of Hamburg
Martin-Luther-King-Platz-6, D-20146, Hamburg-Germany
3EMBRAPA CENARGEN, SAIN
/
Parque Rural 70849-970, Bras
´
ılia-DF, Brazil
(Received May 10, 2000; accepted July 30, 2000)
Abstract—Methyl 2,6,10-trimethyltridecanoate (1) and methyl 2,6,10-tri-
methyldodecanoate (2) have been identified as male-produced sex pheromones
of the Brazilian soybean stink bugs Euschistus heros (F.) and Piezodorus
guildinii (Westwood). In order to establish a defined attractive blend for both
species, compounds 1 and 2 were synthesized as mixtures of stereoisomers to
be employed in behavior bioassays. ( )-Citronellol (3) was utilized as starting
material, and the syntheses was carried out in six steps with good overall
yield. When tested alone, synthetic compounds 1 and 2 proved to be active
in a two-choice olfactometer; however, a 20 : 1 mixture of 1 and 2 was much
more attractive to E. heros females. A similar blend had been found among
the headspace volatiles of males.
Key Words—Methyl 2,6,10-trimethyltridecanoate, methyl 2,6,10-trimethyl-
dodecanoate, Euschistus heros, Piezodorus guildinii, pheromone, synthesis,
Heteroptera, Pentatomidae, biological activity, stink bugs.
*To whom correspondence should be addressed; e-mail: pzarbin@quimica.ufpr.br
2737
0098-0331 00 1200-2737$18.00 0  2000 Plenum Publishing Corporation
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/
/

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ZARBIN ET AL.
INTRODUCTION
Soybean, Glycine max (L.) Merryl, is intensely attacked by complexes of
stink bugs around the world. In Brazil, the most important members are
Nezara viridula (L.), Euschistus heros (F.), and Piezodorus guildinii (Westwood)
(Panizzi and Rossi, 1991), which lead to the use of more than four million liters
of chemical insecticides annually (Correa-Ferreira and Moscardi, 1996). There-
fore, efforts have been made to develop alternative methods in pest management,
such as application of pheromones.
The first attractant pheromone identified for a member of this complex
was that of the southern green stink bug, N. viridula (Baker et al., 1987). The
chemical communication system of E. heros was elucidated by Aldrich et al.
(1994), and evidence was presented that methyl 2,6,10-trimethyltridecanoate
(1) is a component of the male-produced pheromone of the species (Borges et
al., 1998a). Recently, we identified methyl 2,6,10-trimethyltridecanoate (1) and
methyl 2,6,10-trimethyldodecanoate (2) as two male-specific compounds of P.
guildinii, and reported the sharing of pheromone components between P. guil-
dinii and E. heros (Borges et al., 1999).
To date, no bioassays have been conducted to check the biological activity
of mixtures of stereoisomers of methyl 2,6,10-trimethyldodecanoate (2), nor has
the reaction of the stink bugs to different blends of compounds 1 and 2 been
described. It was previously observed that the activity of pure isomers of 1 in
E. heros does not significantly differ from that of the racemic mixture (Costa et
al., 1999).
Here we describe a straightforward synthesis of compounds 1 and 2 as mix-
tures of stereoisomers and the biological activity of the synthetic compounds
against females of E. heros. The material will also be used to monitor the
response of P. guildinii for the first time in the field.
METHODS AND MATERIALS
Analytical Procedures. The IR spectra refer to films and were measured on
1
a Bomem M-102 spectrometer. The H NMR spectra were recorded with TMS
as an internal standard at 400 MHz on a Bruker ARX 400 spectrometer. The 13
C
NMR spectra were recorded with TMS as an internal standard at 100 MHz on
a Bruker ARX 400. GC-MS. Analysis was carried out on a Shimadzu QP-5000
GC-MS spectrometer in a split injector mode. A DB-5 capillary column (30 m ×
0.53 mm × 0.25 mm) used in GC and GC-MS analogs was operated at 70 C for
1 min, increased to 270 C at a rate of 70 C min, and held at this temperature
/
for 10 min.
Synthesis. All reagents and solvents used in the syntheses were of the high-

STINK BUG PHEROMONES
2739
est commercially available standard. Chromatographic purification were carried
out on silica gel 60, Merck, 230–400 mesh.
(3R S)-3,7-Dimethyl-6-octenyl-4-methyl-l-benzenesulfonate (4). (R S)-Cit-
/
/
ronellol (3) (2.0 g, 12.8 mmol) was dissolved in chloroform (10 ml) and cooled
in an ice bath (0 C). Pyridine (2.0 ml, 25.6 mmol) was added, followed by addi-
tion of p-toluenesulfonylchloride (3.65 g, 19.2 mmol) in small portions with con-
stant stirring. The reaction was completed after 3.5 hr. Ether (50 ml) and water
(10 ml) were added, and the organic layer was washed successively with 10%
HCl, sat. NaHCO3 and water and then dried (MgSO4). The solvent was removed
under reduced pressure, and the crude tosylate was column chromatographed
(hexane–ethyl acetate 8 : 2) on silica gel yielding 3.0 g (9.66 mmol, 75%) of
1
1
(R S)-4. IR (nmax film cm ): 3032, 2930, 1597, 1360, 1179, 948; H NMR
/
(400 MHz, CDCl3) d: 0.81 (d, J 6.4 Hz, 3H); 1.10–1.30 (m, 2H); 1.40–1.55
(m, 2H); 1.57 (s, 3H); 1.67 (d, J 1.2 Hz, 3H); 1.82–1.96 (m, 2H); 2.45 (s, 3H);
4.01–4.10 (m, 2H); 5.02 (tq, J 1.2, 7.2 Hz, 1H); 7.34 (d, J 8 Hz, 2H); 7.79
(d, J 8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d: 17.5; 18.9; 21.5; 25.1; 25.6;
28.7; 35.5; 36.5; 68.9; 124.2; 127.7; 129.7; 131.3; 133.0; 144.6.
(2R S)-2Methyl-l-bromobutane (5a). To a stirred solution of Ph3P (38.51
/
g, 147 mmol) in CH2Cl2 (300 ml) at 0 C, Br2 (23.46 g, 147 mmol, 7.52 ml)
was added dropwise until the reaction mixture turned orange. A few crystals of
Ph3P were added until the mixture was decolorized again. The alcohol 5 (12.96
g, 147 mmol) was added dropwise, and the solution was stirred at room temper-
ature for 4 hr. Subsequently, 500 ml of sat. NaHCO3 was added cautiously, and
the organic layer was diluted with 800 ml pentane. The layers were separated,
and the aqueous layer was extracted with pentane (2 × 150 ml). The combined
organic layers were dried (MgSO4), the solvent was removed cautiously by dis-
tillation, and 150 ml of pentane was added. The flask was kept in a freezer for
3 hr, and the mixture was separated from precipitated Ph3PO by rapid filtration
through a Buchner funnel. Pentane was removed, and the residue was distilled
to give 10.90 g (72 mmol, 49%) of 5a, bp 95 C 506 mbar. 1H NMR (400 MHz,
/
CDCl3) d: 0.91 (t, J 7.6 Hz, 3H); 1.01 (d, J 6.6 Hz, 3H); 1.22–1.57 (m, 2H);
1.73 (oct, J 6.6 Hz, 1H); 3.34 (dd, J 9.6, J 6.6 Hz, 1H); 3.40 (dd, J 9.6,
J
6.6 Hz, 1H).
(2R S)-2-Methyl-l-bromopentane (6a). As described above, the alcohol 6
/
(10.0 g, 97.9 mmol) was converted into the bromide 6a (9.71 g, 70.9 mmol,
73%; bp 122 C 540 mbar) by using 25.67 g (97.9 mmol) PPh3 and 15.64 g
/
1
(97.9 mmol, 5.01 ml) Br2 in 200 ml CH2Cl2. H NMR (400 MHz, CDCl3) d:
0.91 (t, J 7.4 Hz, 3H); 1.01 (d, J 6.6 Hz, 3H); 1.16–1.48 (m, 4H); 1.81 (oct,
J
6.6 Hz, 1H); 3.32 (dd, J 9.7, J 6.6 Hz, 1H); 3.40 (dd, J 9.7, J 6.6 Hz,
1H); 13C NMR (100 MHz, CDCl3) d: 14.14; 18.75; 20.02; 34.95; 37.10; 41.61.
6R S,10R S)-2,6,10-Trimethyl-2-dodecene (7). The Grignard reagent was
/
/
prepared from bromide 5a (4.40 g, 32.0 mmol) and magnesium (0.78 g, 32.0

2740
ZARBIN ET AL.
mmol) in dry THF (12 ml). This slurry was added dropwise to a solution of 4
(2.0 g, 6.4 mmol) in dry THF (12 ml) with stirring and cooling below 60 C.
A solution of Li2CuCl4 in THF (0.1 M, 0.37 ml) was added to the mixture, and
the temperature was gradually raised to room temp. After stirring overnight,
the mixture was poured into ice and ammonium chloride solution and subse-
quently extracted with ether. The extract was washed with saturated NaHCO3
solution and brine, dried with MgSO4, and concentrated in vacuo. The residue
was chromatographed on silica gel (hexane–ether 9.5 : 0.5) to give the alkene
1
7 in 85% yield (1.15 g, 5.47 mmol). IR (nmax film cm ): 2920, 1600, 1455,
1
1376, 1069; H NMR (400 MHz, CDCl3) d: 0.85 (d, J 6.4 Hz, 3H); 0.85 (t, J
6.4 Hz, 3H); 0.86 (d, J 6.8 Hz, 3H); 1.00–1.16 (m, 4H); 1.26–1.44 (m, 8H);
1.60 (s, 3H); 1.68 (s, 3H); 1.88–2.04 (m, 2H); 5.11 (bt, J 6.4 Hz, 1H); 13C
NMR (100 MHz, CDCl3) d: [11.4, 11.43]; 17.63; [19.23, 19.28]; [19.61, 19.67];
24.46; 25.62; 25.74; [29.50, 29.58]; [32.44, 32.47]; 34.44; [36.95, 36.99]; [37.14,
37.22]; [37.31, 37.34]; 125.14; 130.94; GC-MS (70 eV) m z %: 210 (M+, 16.17),
/
140 (5.68), 125 (16.63), 111 (25.59), 97 (16.46), 83 (35.42), 70 (100), 56 (92.00).
(6R S,10R S)-2,6,10-Trimethyl-2-tridecene (7a). As described above, com-
/
/
pound 4 (2.0 g, 6.4 mmol) was converted into the alkene 7a (1.13 g, 5.04 mmol,
79%) by using 4.78 g of bromide 6a (31.7 mmol). 1H NMR (400 MHz, CDCl3)
d: 0.82–0.89 (m, 9H); 1.00–1.17 (m, 4H); 1.20–1.40 (m, 10H); 1.60 (bs, 3H);
1.68 (bs, 3H); 1.88–2.05 (m, 2H); 5.10 (bt, J 6.6 Hz, 1H); 13C NMR (100 MHz,
CDCl3 d: 14.43; 17.63; [19.61, 19.65]; [19.66, 19.73]; 20.18; 24.43; [25.62,
25.73]; [32.44, 32.47]; [32.50, 32.54]; [34.38, 34.44]; [37.15, 37.23]; [37.31,
37.34, 37.39, 37.45]; [39.35, 39.43]; [39.51, 39.58]; 125.14; 130.94.
(6R S,10R S)-2,6,10-Trimethyl-(E)-2-dodecen-1-ol (8). To a solution of
/
/
SeO2 (27.5 mg, 0.25 mmol) and salicylic acid (0.17 g, 1.23 mmol) in CH2Cl2
(7.5 ml) at 0 C, t-BuOOH (80%, 5.50 ml, 47.6 mmol) was added in one pot.
Compounds 7 (2.5 g, 11.9 mmol) in CH2Cl2 (7.5 ml) was added over 30 min. The
solution was stirred at room temperature for 24 hr, diluted in benzene (10.0 ml),
and concentrated in vacuo. Ether was added (25.0 ml), and the organic layer was
washed with a 10% solution of KOH and again concentrated. The residue was
dissolved in cold acetic acid (5.0 ml) and kept in an ice bath during the addition
of dimethylsulfide (5.5 ml). The reaction was stirred for 5 hr at room tempera-
ture, and a 20% aqueous solution of K2CO3 was added. The organic layer was
separated, washed with brine, dried over anhydrous MgSO4, and concentrated
furnishing the crude product as a yellow oil. This was dissolved in cold ethanol
(10.0 ml), and NaBH4 (0.45 g, 11.9 mmol) was added over 30 min, and the solu-
tion stirred for 15 min. After addition of a 1 N solution of HCl (15.0 ml) and
water (15.0 ml), the mixture was extracted with ether (3 × 60 ml). The organic
layer was washed with sat. NaHCO3 solution and brine, dried over MgSO4, and
concentrated in vacuo. The crude product was purified by column chromatogra-
phy on silica get (hexane–ethyl ether 7 : 3), and the alcohol 8 was obtained in

STINK BUG PHEROMONES
2741
1
37% yield (1.0 g, 4.42 mmol). IR (nmax film cm ): 3332, 2960, 1459, 1371,
1
1008; H NMR (400 MHz, CDCl3) d: 0.83–0.89 (m, 9H); 1.07–1.20 (m, 4H);
1.24–1.46 (m, 8H); 1.61 (bs, 1H); 1.67 (bs, 3H); 1.98–207 (m, 2H); 4.00 (s,
2H); 5.4 (bt, J 7.2 Hz, 1H); 13C NMR (100 MHz, CDCl3) d: 11.40; 13.62;
[19.17, 19.22]; [19.52, 19.57]; 24.44; 25.18; [29.47, 29.57]; [32.47, 32.50];
34.43; [36.74, 36.8]; [36.94, 36.98]; [37.26; 37.30]; 69.16, 126.92; 134.38; GC-
MS (70 eV) m z %: 208 (M-18, 0.6), 140 (0.8), 123 (7.2), 109 (18.0), 83 (13.8),
/
71 (57.2), 57 (50.7), 43 (100), 41 (60.8).
(6R S,10R S)-2,6,10-Trimethyl-(E)-2-tridecen-1-ol (8a). As described
/
/
above, compound 7a (2.66 g, 11.9 mmol) was converted into alcohol 8a (1.30
g, 5.41 mmol, 45%). 1H NMR (400 MHz, CDCl3) d: 0.80–0.90 (m, 9H);
1.03–1.12 (m, 4H); 1.15–1.46 (m, 11H); 1.67 (bs, 3H); 1.96–2.10 (m, 2H); 3.99
(s, 2H); 5.41 (bt, J 7.1 Hz, 1H); 13C NMR (100 MHz, CDCl3) d: 13.67;
14.42; [19.57, 19.63]; [19.65, 19.72]; 20.16; 24.41; 25.19; [32.50, 32.51]; [36.74,
36.82]; [37.26, 37.44]; [39.40, 39.49]; 69.12, 126.94; 134.37.
(2R S,6R S,10R S)-2,6,10-Trimethyldodecan-1-ol (9). Compound 8 (1.0
/
/
/
g, 4.4 mmol) in 15 ml of hexane was hydrogenated over PtO2 (5.0 mg) at room
temperature and 25 psi in a Parr apparatus for 4.0 hr. The mixture was filtered
through Celite, and the filtrate was evaporated at reduced pressure to afford 0.9 g
1
(3.9 mmol) of alcohol 9, 88% yield. H NMR (400 MHz, CDCl3) d: 0.84–0.91
(m, 9H); 0.92 (d, J 6.8 Hz, 3H), 1.10–1.17 (m, 4H); 1.24–1.42 (m, 12H);
1.60–1.67 (m, 2H); 3.42 (dd, J 10.4, J 6.4 Hz, 1H); 3.50–3.54 (m, 1H); 13C
NMR (100 MHz, CDCl3) d: 11.4; 16.6; [19.2, 19.3]; 19.7; 24.4; 24.5; [29.4,
29.6]; 32.7; 33.4; 34.4; 35.8; 37.0; 37.3; 37.5; 68.5.
(2R S,6R S,10R S)-2,6,10-Trimethyltridecan-1-ol (9a). As described
/
/
/
above, compound 8a (1.1 g, 4.6 mmol) was converted into alcohol 9a (1.1 g,
1
4.5 mmol, 99%). H NMR (400 MHz, CDCl3) d: 0.80–0.90 (m, 9H); 0.93 (d,
J
7.2 Hz, 3H), 1.00–1.15 (m, 4H); 1.20–1.42 (m, 14H); 1.58–1.68 (m, 2H);
3.42 (dd, J 10.4, J 6.6 Hz, 1H); 3.48–3.54 (m, 1H); 13C NMR (100 MHz,
CDCl3) d: 14.42; [16.57, 16.64]; [19.65, 19.70]; [19.72, 19.78]; 20.16; [24.40,
24.43]; [24.45, 24.48]; [32.49, 32.52]; 32.77; [33.45, 33.50]; 35.81; [37.29,
37.34]; 37.39; [37.44, 37.50]; [39.41, 39.49]; [68.41, 68.47].
(2R S,6R S,10R S)-Methyl-2,6,10-trimethyldodecanoate (2). Jones CrO3
/
/
/
(∼20.0 ml) was added to a solution of the alcohol 9 (0.65 g, 2.85 mmol) in ace-
tone (85.0 ml), and the mixture was stirred for 30 min at 5 C. The excess CrO3
was destroyed with i-PrOH, and the mixture was concentrated in vacuo, diluted
with water, and extracted with ether. The ether extract was washed with H2O and
sat. NaCl solution, dried with MgSO4, and concentrated. The residue obtained was
diluted in ether (20 ml) and treated with ethereal CH2N2 at 0 C, until the reac-
tion mixture turned yellow. The solution was stirred for 30 min, concentrated, and
the residual oil was chromatographed on silica gel (hexane–ethyl acetate 9.5 : 0.5),
yielding 0.55 g of 2 (2.14 mmol, 75%). 1H NMR (400 MHz, CDCl3) d: 0.83–0.87

2742
ZARBIN ET AL.
(m, 9H); 1.01–1.10 (m, 3H); 1.14 (d, J 6.8 Hz, 3H); 1.18–1.45 (m, 11H); 2.45
(sext, J 6.8 Hz, 3H); 3.67 (s, 3H); 13C NMR (100 MHz, CDCl3) d: [11.42, 11.43];
[17.03, 17.14]; [19.21, 19.27]; [19.60, 19.65]; 24.47; 24.71; [29.47, 29.58]; 32.65;
[34.12, 34.16]; 34.43; 36.84; [36.93, 36.97]; [37.31, 37.35, 37.36, 37.39]; [39.47,
39.50]; 51.44; 177.43; GC-MS (70 eV) m z %: 256 (M+, 0.6); 232 (0.6); 203 (1.3);
/
152 (0.5); 119 (9.6); 101 (29.8); 88 (100); 69 (18.3); 55 (29.8).
(2R S,6R S,10R S)-Methyl-2,6,10-trimethyltridecanoate (1). As described
/
/
1
/
above, compounds 9a (0.68 g, 2.81 mmol) was converted into 1 (0.62 g, 2.30
mmol, 82%). H NMR (400 MHz, CDCl3) d: 0.80–0.90 (m, 9H); 1.00–1.11
(m, 3H); 1.14 (d, J 7.2 Hz, 3H); 1.19–1.45 (m, 13H); 2.44 (sext, J 7.2 Hz,
3H); 3.67 (s, 3H); 13C NMR (100 MHz, CDCl3) d: 14.43; [17.03, 17.13]; [19.60,
19.64]; [19.66, 19.71]; 20.15; 24.44; 24.71; [32.49, 32.51]; 32.63; [34.12, 34.16];
36.84; 36.93; [37.31, 37.37]; 37.42; 39.47; 51.45; 177.44; GC-MS (70 eV)
m z %: 270 (M+, 0.8); 227 (0.4); 199 (0.5); 180 (2.2); 157 (6.0); 101 (33.4);
/
88 (100); 69 (26.0); 55 (52.0).
Insects. Euschistus heros were collected near Brasilia and raised contin-
uously on soybean seeds (Glycine max), green beans (Phaseolus vulgaris),
peanuts (Arachis hypogaea), and sunflower seeds (Helianthus annuus) at 26
2 C, 70% relative humidity, and a 14L : 10D photo period.
Bioassay. The two-choice olfactometer was constructed from one large
(27.5 × 22.0 cm) and two small (13.5 × 7.5 cm) clear plastic containers and two
glass tubes (3.1 cm ID), each 20 cm long. The large container was the release
chamber, while one of the small chambers was used for the treatment and the
other for the control. An air current through the small chambers was produced
and regulated by a single-phase fan controlled by double “variac” voltage regula-
tors. The air current speed at the center of the olfactometer was 17.0 cm sec. The
/
upwind end of the treatment and the control chambers and the downwind end
of the release chamber were pierced with small holes (Borges, 1995). Treatment
and control chemicals were each applied to pieces of filter paper (4 × 1 cm) that
were placed inside the treatment chamber. The activity of synthetic pheromones
was monitored by using 10 E. heros females per experiment that were observed
for 20 min. Samples were used at 10 mg (Borges et al., 1998a) per treatment
(dissolved in hexane), and n-hexane was applied as a control. Bioassays were
performed for three days during the periods of 08:00–12:00 and 14:00–18:00 hr.
Numbers of replications varied between three and six. Behavior data were sta-
tistically analyzed with SigmaStat software (Kuo et al., 1992), and differences
between means were tested for significance by t test.
RESULTS AND DISCUSSION
Mori and Murata (1994a) synthesized ( )-1 by employing the Julia cyclo-
propane cleavage as the key reaction. Later, the same authors described the syn-

STINK BUG PHEROMONES
2743
SCHEME 1. Synthesis of methyl 2,6,10-trimethyltridecanoate (1) and methyl 2,6,10-
trimethyldodecanoate (2). Reagents: (a) TsCl, Py, 75%; (b) Ph3P Br2, CH2Cl2, 49 73%;
/
/
2
(c) (5a) Mg, Et O, Li CuCl , 85%; (c ) (6a) Mg, Et O, Li CuCl , 79%; (d) 1: SeO t-
′
2
2
4
2
2
4
/
/
/
BuOOH, 2: NaBH4 MeOH, 37 45%; (e) H2 Pt2O, 88 99%; (f) [O] Jones acetone; and
/
/
/
/
/
(g) CH2N2, Et2O, 75 82%.
/
thesis of all eight stereoisomers of this compound (Mori and Murata, 1994b).
We previously described the synthesis of the (2R,6S,10S) and (2S,6S,10S) iomers
of methyl 2,6,10-trimethyldodecanoate (2) over 15 steps (Ferreira and Zarbin,
1996). We have now developed a synthesis of a mixture of stereoisomers of
pheromones 1 and 2 in a total yield of 8% and 16%, respectively, over six
steps. The examples given here show that these pheromones can be obtained
by a flexible and operationally simple strategy.
Our route to compounds 1 and 2 is shown in Scheme 1. Citronellol 3 was
transformed into the known tosylate 4 (Kabalka et al., 1986) in 75% yield.
Hydrocarbons 7 and 7a were obtained by coupling tosylate 4 with a Grignard
reagent prepared from bromides 5a and 6a, derived from 2-methyl-1-butanol (5)
and 2-methyl-1-pentanol (6), respectively (Ph3P and Br2, 49% and 73%), in 85%
and 79% yield (Fouquet and Schlosser, 1974; Zarbin et al., 1998). Oxidation of
7 and 7a was carried out by employing selenium dioxide (SeO2) and t-butyl
hydroperoxide (t-BuOOH) in CH2Cl2 (Tanis, 1988). To reduce the correspond-
ing aldehydes formed during the reactions, the crude residues were treated with
NaBH4 in methanol, affording the allylic alcohols 8 or 8a in 37% and 45% yield,
respectively. Hydrogenation over PtO2 catalyst in hexane afforded the saturated

2744
ZARBIN ET AL.
FIG. 1. Number (mean SE) of females Euschistus heros responding, in an olfactometer
bioassay, to different treatments. (A) Methyl 2,6,10-trimethyltridecanoate (1) vs. control
(t 5.060, P < 0.001); (B) methyl 2,6,10-trimethyldodecanoate (2) vs. control (t 0.894,
P
0.397); (C) methyl 2,6,10-trimethyltridecanoate (1) plus methyl 2,6,10-trimethyldo-
decanoate (2), in a 20 : 1 ratio, vs. control (t 4.330, P 0.003). Means followed by the
same letters are not significantly different, according to t test.
alcohols 9 and 9a in 88% and 99%, respectively (Leal et al., 1995). Finally,
the Jones oxidation furnished the carboxylic acids, which were directly treated
with diazomethane to give the desired pheromones, methyl 2,6,10-trimethyltride-
canoate (1) and methyl 2,6,10-trimethyldodecanoate (2) as mixtures of stereoiso-
mers in 75% and 82% yields, respectively (Ferreira and Zarbin, 1996). Mass
spectra and retention times of the synthetic products were identical with those
of the natural pheromones (Borges et al., 1999).
During laboratory bioassays, compounds 1 and 2 per se showed signifi-
cant behavior-releasing activities against E. heros females, such as elevating the
antennae, wing fanning, searching, walking towards the odor source and touch-
ing it, when compared with the solvent control. However, a 20 : 1 mixture of 1
and 2, which was previously found in a similar blend in the headspace of males
(Aldrich et al., 1994), showed a much higher micro-behavior-releasing capacity.
On one hand, the total number of E. heros females showing any micro-behavior
reactions increased significantly. On the other, the reaction of E. heros females
against this mixture, expressed by walking towards the pheromone loaden filter
paper and touching it, was more specific and similar to the reaction against a
natural odor source. The significant difference of this latter behavior-releasing
capacity of pure compounds 1 and 2, compared with a 20 : 1 mixture of 1 and
2, is demonstrated in Figure 1 (treatment A, t 5.060, P < 0.001; treatment B,
t
0.894, P 0.397; treatment C, t 4.330, P 0.003; t-test).

STINK BUG PHEROMONES
2745
In laboratory bioassays, methyl 2,6,10-trimethyltridecanoate (1) induced the
same level of behavior response in females of E. heros as males (Borges et
al., 1998a). During field tests, however, by using a similar pheromone blend, P.
guildinii was caught in baited traps in significantly larger numbers than E. heros
(Borges et al., 1998b). These observations support the idea that both compounds
1 and 2 are important to attract females of E. heros, and suggest that methyl
2,6,10-trimethyldodecanoate (2) is a decisive component of the distinct syner-
gistic communication system of this species. Specific studies on the chemical
ecology of P. guildinii remain to be carried out to better understand its behavior.
A complete set of data may enable the formulation of defined synthetic blends
attractive for P. guildinii and E. heros, which would be an extremely useful tool
in integrated pest management (IPM).
Acknowledgments—We thank the IFS (International Foundation for Science–Sweden, grant to
P.H.G.Z.), CNPq (Brazilian Consul for Scientific and Technological Development), Federal Univer-
sity of Parana, and E. Michelin Plantations, Rondono
gratefully acknowledges a grant from the DAAD (Deutscher Akademischer Austauschdienst). Dr.
Edison R. Sujii, from Embrapa Genetic Resources and Biotechnology, Brasılia, Brazil, helped with
statistical analysis, for which we are grateful.
´
polis-MT, Brazil, for financial support. A.R.
´
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