Male-specific volatiles released by Homalinotus validus (Coleoptera: Curculionidae) include (1R,2S)-grandisyl acetate, a new natural product

Article abstract of DOI:10.1016/j.tetlet.2016.12.037

Homalinotus validus is an important pest of babassu palm (Attalea speciosa) cultures in North Brazil. Investigations on the chemical ecology of this species are essential for the development of an integrated pest management system, since attempts to control the pest by conventional insecticides failed. GC/MS and GC/FT-IR analyses of headspace volatiles obtained from males and females revealed the presence of two male specific compounds, which were identified to be (1R,2S)-grandisol and the new (1R,2S)-grandisyl acetate. Both compounds presumably act as an aggregation pheromone of the species.

Full text of DOI:10.1016/j.tetlet.2016.12.037

Tetrahedron Letters xxx (2016) xxx–xxx
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Male-specific volatiles released by Homalinotus validus (Coleoptera:
Curculionidae) include (1R,2S)-grandisyl acetate, a new natural product
Diogo M. Vidal a, Sandra M.S. Gomes a, Wittko Francke b, Olzeno Travisan c, Mauro A.C.M. Rodrigues c,
Paulo H.G. Zarbin a,
⇑
a Departament of Chemistry, Federal University of Parana, 81531-990 Curitiba, PR, Brazil
b Institute of Organic Chemistry, University of Hamburg, Hamburg, Germany
c Superintendência da Amazônia Oriental—CEPLAC, Belém 66635-110, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Homalinotus validus is an important pest of babassu palm (Attalea speciosa) cultures in North Brazil.
Investigations on the chemical ecology of this species are essential for the development of an integrated
pest management system, since attempts to control the pest by conventional insecticides failed. GC/MS
and GC/FT-IR analyses of headspace volatiles obtained from males and females revealed the presence of
two male specific compounds, which were identified to be (1R,2S)-grandisol and the new (1R,2S)-grandi-
syl acetate. Both compounds presumably act as an aggregation pheromone of the species.
Ó 2016 Elsevier Ltd. All rights reserved.
Received 6 October 2016
Revised 13 December 2016
Accepted 14 December 2016
Available online xxxx
Keywords:
Grandisol
Grandisyl acetate
GC-FTIR
Aggregation pheromone
Weevil volatiles
Homalinotus validus (Coleoptera: Curculionidae) occurs in trop-
ical areas of Latin America including the Brazilian northern region,
where it causes serious losses in babassu (Attalea speciosa) produc-
tion. The weevil also feeds on other palm species like A. maripa and
A. butyracea. Detection and control of the beetles are labor-inten-
sive and expensive, predominantly due to the height of the babassu
palms. Insecticides are not effective for the control of this pest, and
infestations are controlled by manual collection of adults or by
removing infested branches. Unfortunately, there is very little
information about biological and ecological aspects of the genus
Homalinotus that might help develop efficient integrated pest man-
agement systems.1 Therefore, the objective of our study was to
identify beetle-produced semiochemicals that could be related to
the aggregation behavior of H. validus.
methyl-2-prop-1-en-2yl)cyclobutylethanol6, which was confirmed
by co-injection with an analytical standard.7 The mass spectrum of
the minor compound 2 showed a fragmentation pattern closely
related to that of grandisol, again with m/z 68 as the base peak.
An abundant fragment of m/z 43 and a small but diagnostic signal
of m/z 61 (Fig. 2a) indicated an acetate substructure, which was
confirmed by its FT-IR spectrum, showing strong carboxyl bands
at 1737 cmÀ1 (C@O) and 1243 cmÀ1 (H3CC(@O)AO stretch). The
(x1,000,000)
3.0
(x1,000,000)
(x10,000)
2.5
2.0
1.5
1.0
0.5
0.0
2.5
2.0
1.5
1.0
0.5
0.0
1
2
1
5.0
2.5
0.0
Volatiles from live insects2 were obtained by dynamic head-
space collection.3 Chemical analyses started by comparison of GC
profiles of samples from males and females, revealing the existence
of two male-specific compounds in a ratio of 96:44 (Fig. 1). On a
DB-5 capillary column, the retention indices of these compounds
were found to be 1212 for compound 1, and 1415 for 2.5
11.5
12.0
12.5
14.2
14.3
14.4
2
The MS and FT-IR spectra along with retention index datasets
suggested the major compound
1 to be grandisol, cis-2-(1-
10.0
15.0
20.0
25.0
30.0
⇑
Corresponding author.
E-mail address: pzarbin@ufpr.br (P.H.G. Zarbin).
Fig. 1. Comparison of GC profiles from male and female aeration samples revealing
two male specific compounds, 1 and 2.
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2
D.M. Vidal et al. / Tetrahedron Letters xxx (2016) xxx–xxx
%
The absolute configuration of the natural compounds was
68
100
50
0
determined by enantioselective gas chromatography, using a mod-
ified b-cyclodextrin as the stationary phase,10 whereas racemic 1
and enantiopure (1R,2S)-1, and the respective acetates (2 and
(1R,2S)-2) served as references. Fig. 3A shows that grandisol (1)
is produced as a pure enantiomer, since its retention time coincides
with that of the synthetic (1R,2S)-enantiomer.11 The absolute
configuration of grandisol in H. validus proved to be the same as
in several other weevil species, where it acts as an aggregation
pheromone.12 As expected, GC analyses showed that the acetate
2 is produced with the same (1R,2S)-configuration as grandisol
(1) (Fig. 3B).13
a
43
93
95
100.0
107
105
121
125.0
53
50.0
79
40
136
O
73
75.0
61
83
0,05
0,04
0,03
0,02
0,01
0,00
-0,01
b
c
O
To the best of our knowledge, this is the first time that grandisyl
acetate has been identified as
a natural product, while its
trans-stereoisomer (fragranyl acetate) has been described as a
component of the essential oils in plants of the genus Achillea
(Asterales: Asteraceae).14
Bioassays for both compounds are currently in progress in the
laboratory and in the field. However, according to general experi-
ence on the chemical ecology of Curculionidae,12 it can be pre-
dicted that they will act as aggregation pheromone of H. validus.
(2)
4000
3500
3000
2500
2000
1500
1000
Wavenumber (cm-1)
Fig. 2. Mass (a) and infrared (b) spectra and the proposed structure of the natural
compound 2 (c).
Acknowledgments
The authors are grateful to CNPq (Special Visiting Professor
Grant: 407245/2013-8) and INCT Semioquímicos na Agricultura
for financial support, and to Professor Kenji Mori for sharing a
(1R,2S)-grandisol sample.
References
1. (a) Barbosa MLL, Ferreira IA, Fonseca CRVD, Gouveia FBP. Acta Amaz.
2011;41:401;
(b) Zarbin PHG, Rodrigues MACM, Lima ER. Quim Nova. 2009;32:722.
2. H. validus were collected in Ouro Preto do Oeste, Rondonia
- Brazil
(10o43’54.6”S 62o15’07.5”W) and maintained at 28 °C and a 12:12 h (L:D)
photoperiod in the Laboratory of Semiochemicals at the Federal University of
Paraná (UFPR).
3. Three insects of each sex were placed in aeration chambers (37 Â 4 cm i.d.),
containing banana as food source, with
a continuous flow of 1 L/min of
humidified, charcoal-filtered air. Volatiles released by banana were collected
for comparison of GC profiles. Volatiles were trapped in glass traps (11 Â 0.5 cm
i.d.) containing 20 mg of HayeSep-D adsorbent polymer (Analytical Research
systems, Inc., Gainesville, FL, USA). The adsorbed volatiles were eluted with
doubly distilled hexane (300 lL), and the resulting extracts were stored at 20 °C
until analyses and bioassays. Extractions were performed every 24 h.
4. GC/MS: QP2010 Plus (Shimadzu) coupled to a GC2010 (Shimadzu). GC/FTIR:
DiscovIR-GC (DANI Instruments) coupled to
a
GC2010 (Shimadzu). DB-5
lm film thickness), used in
(Agilent Technologies, 30 m  0.25 mm id  0.25
both instruments. Conditions: splitless, 1 min at 50 °C, then increased to 250 at
7 °C/min and kept at this temperature for 10 min.
5. Retention indices were calculated based on the retention times of the target
compounds and a series of n-alkanes (C10–C26) in a GC2010 – FID (Shimadzu)
equipped with
a
DB-5 column (Agilent Technologies, 30 m  0.25 mm
id  0.25 film thickness). Conditions: splitless, starting at 50 °C, then
lm
increased to 280 °C at 3 °C/min and kept at this temperature for 10 min.
6. NIST 2008 MS Library: NIST MS Search 2.0 f, 9th ed. Wiley.
7. Bedoukian Research, Danbury, CT, US.
8. An excess of acetic anhydride (125 lL, 1.25 mmol) and pyridine (125 lL) were
added to grandisol (154 mg, 1.0 mmol) in CH2Cl2 (4 mL). The solution was
stirred for 12 h, diluted with CH2Cl2 (20 mL), washed with aqueous HCl (10%)
and with saturated NaHCO3. The organic layer was separated, dried over
Na2SO4, and concentrated. After flash chromatography (hexane/ethyl acetate:
9/1), grandisyl acetate was obtained in 92% yield (180 mg). 1H NMR (200 MHz,
CDCl3): d 1.19 (s, 3H), 1.32–2.30 (m, 12H), 2.46–2.67 (m, 1H), 3.97–4.19 (m,
2H), 4.60–4.68 (m, 1H), 4.81–4.88 (m, 1H). 13C NMR (50 MHz, CDCl3): d 19.0,
20.8, 20.9, 23.1, 28.0, 28.9, 32.3, 41.1, 52.3, 61.9, 109.8, 144.8, 171.1.
Fig. 3. Determination of the absolute configuration of grandisol (A) and grandisyl
acetate (B) released by males of H. validus.
presence of a terminal double bond in 2 was obvious because of the
band at 3082 cmÀ1 (out-of-phase C@CH2 stretch) (Fig. 2b). Conse-
quently, 2 was suggested to be the acetate of grandisol (1)
(Fig. 2c). This was supported by an increase of 200 units in the
retention index of 2 as compared to grandisol (1). A reference sam-
ple was synthesized by acetylation of grandisol,8,9 and the assign-
ment of grandisyl acetate for compound 2 was confirmed by
comparison of the spectral data of natural and synthetic products,
as well as by co-injection.
9. Vidal DM, Fonseca MG, Zarbin PHG. Tetrahedron Lett. 2010;51:6704.
10. Enantioselective GC: GC2010 – FID (Shimadzu) equipped with a b-DEX 325
(Supelco Analytical, 30 m  0.25 mm id  0.25
lm film thickness) column.
Conditions: splitless, 135 min at 70 °C, then increased to 230 °C at 7 °C/min.
Also see: Leal WS, Oehlschlager AC, Zarbin PHG, et al. J. Chem. Ecol.. 2003;29:15.
11. Mori K, Fukamatsu K. Liebigs Ann Chem. 1992;1992:489.
12. (a) Ambrogi BG, Vidal DM, Zarbin PHG, Rosado-Neto GH. Quím Nova.
2009;32:2151;
(b) Francke W, Dettner K. Top Curr Chem. 2005;240:85;
Please cite this article in press as: Vidal D.M., et al. Tetrahedron Lett. (2016), http://dx.doi.org/10.1016/j.tetlet.2016.12.037

D.M. Vidal et al. / Tetrahedron Letters xxx (2016) xxx–xxx
3
(c) Szczerbowski D, Torrens GG, Rodrigues MACM, et al. Tetrahedron Lett.
2016;57:2842;
(1R,2S)-1 (100
l
L; 1000 ng/
l
L in hexane) in dichloromethane. The resulting
solution was stirred for 12 h at 25 °C, diluted with hexane (400 lL), washed
(d) Zarbin PHG, Moreira MAB, Haftmann J, Francke W, Oliveira ARM. J Braz
Chem Soc. 2007;18:1048.
13. Synthetic (1R,2S)-grandisyl acetate was obtained starting from (1R,2S)-1 in a
with aqueous HCl (10%), and with saturated NaHCO3. The organic layer was
separated, dried over Na2SO4 in a tip of a Pasteur pipette, and used for GC
analyses without further purification.
l
g scale following a similar approach used to obtain the racemate. An excess of
14. El-Shazly A, Hafez S, Wink M. Pharmazie. 2004;59:226.
acetic anhydride (10 L) and pyridine (10 L) were added to a solution of
l
l
Please cite this article in press as: Vidal D.M., et al. Tetrahedron Lett. (2016), http://dx.doi.org/10.1016/j.tetlet.2016.12.037