Synthesis and field test of a pheromone analog of chilecomadia valdiviana

Article abstract of DOI:10.4067/s0717-97072018000204019

The main pheromone component of Chilecomadia valdiviana has recently been reported to be (7Z,10Z)-7,10-hexadecadienal. The synthesis of a structural analog, (5Z,8Z)-5,8-tetradecadienyl formate is reported. The pheromone analog was not attractive to male C

Full text of DOI:10.4067/s0717-97072018000204019

J. Chil. Chem. Soc., 63, Nº 2 (2018)
SYNTHESIS AND FIELD TEST OF A PHEROMONE ANALOG OF CHILECOMADIA VALDIVIANA
HEIDY HERRERAa, WILSON BARROS-PARADAb,c, M. FERNANDA FLORESa,
EDUARDO FUENTES-CONTRERASb, JAN BERGMANNa,*
aInstituto de Química, Facultad de Ciencias, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile
bMillennium Nucleus Center in Molecular Ecology and Evolutionary Applications in the Agroecosystems (CEM),
Facultad de Ciencias Agrarias, Universidad de Talca, Talca, Chile
cEscuela de Agronomía, Pontificia Universidad Católica de Valparaíso, Casilla 4-D, Quillota, Chile
ABSTRACT
The main pheromone component of Chilecomadia valdiviana has recently been reported to be (7Z,10Z)-7,10-hexadecadienal. The synthesis of a structural
analog, (5Z,8Z)-5,8-tetradecadienyl formate is reported. The pheromone analog was not attractive to male C. valdiviana in the field, nor did it antagonize attraction
of males to the pheromone compound.
Keywords: Chilecomadia valdiviana, formate, pheromone analog.
Cossidae), is a native moth from Chile and Argentina whose larval stages have
long been known to feed on the wood of native species of trees and bushes [5-
8]. Over the last two decades, the insect has also been detected in economically
important forest and fruit tree crops such as eucalyptus, avocado, apple, cherry,
olive, pear and others [9-13]. Besides direct and indirect damage to the tree,
the presence of C. valdiviana also affects export of wood products because
of quarantine restrictions in destination countries [14]. The main pheromone
component produced by females is the unsaturated aldehyde (7Z,10Z)-7,10-
hexadecadienal (Z7,Z10-16:Ald), together with small amounts of structurally
related compounds [15], and it was shown that the Z7,Z10-16:Ald alone is
responsible for the long-range attraction of males to the pheromone source
[16].
Because aldehydes are susceptible to degradation, particularly under field
conditions, and the degradation products are usually not biologically active,
we synthesized an analog, (5Z,8Z)-5,8-tetradecadienyl formate (Z5,Z8-14:Fo),
in which the α-methylene group is formally replaced by an oxygen atom
(Fig. 1), and studied its biological activity in field tests. We have chosen this
modification because formates have shown to successfully mimic aldehyde
pheromones [17-19], and because it has been suggested that this functional
group is more stable than the formyl group of an unsaturated aldehyde [19].
1. INTRODUCTION
Pheromones are natural compounds released by an individual, which
elicit a response, either behavioral or physiological, in another individual of
the same species. Since the first identification of a pheromone in 1959 [1],
the structures of over 1,500 insect pheromones have been elucidated [2], and
in many cases pheromone-based methods have been successfully integrated
in pest management programs [3]. Research in insect olfaction and the
development of pest control strategies include the study of the biological
activity of anthropogenic compounds that are structurally similar to the
naturally occurring pheromones. In this context, some of the most common
structural modifications of the natural pheromone compounds are alterations of
the carbon chain (elongation, shortening, alteration of multiple bonds), changes
of the polar functional group, and the introduction of isosteric atoms or isotopes
[4]. The biological activity of the modified compounds varies greatly, and the
analogs may be attractants, antagonists, or show no biological activity at all.
In cases where the pheromone analog exhibits adequate biological activity and
is less costly to prepare and/or more stable than the natural pheromone, it may
replace the pheromone in pest control methods.
The carpenterworm, Chilecomadia valdiviana (Philippi) (Lepidoptera:
Figure 1: Structures of (7Z,10Z)-7,10-hexadecadienal (Z7,Z10-16:Ald) and (5Z,8Z)-5,8-
tetradecadienyl formate (Z5,Z8-14:Fo)
e-mail: jan.bergmann@pucv.cl
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J. Chil. Chem. Soc., 63, Nº 2 (2018)
combined organic phases were washed with water and brine, dried over MgSO
and concentrated. The white precipitate was filtered and washed with ether4.
The filtrate was again concentrated and the residue was purified by column
chromatography (hexane-ethyl acetate 7:1) on silver nitrate-impregnated silica.
2. EXPERIMENTAL
2.1. General synthetic procedures
All reagents were purchased from Merck (Darmstadt, Germany) or Sigma-
Aldrich (St. Louis, MO, USA) and used as received. Solvents were purchased
from Merck and dried according to standard procedures if necessary. Syntheses
involving air- or moisture-sensitive materials were carried out under inert
atmosphere in dried glassware. Silica gel 60 (0.063–0.200 mm, Merck) was
used for column chromatography. Nuclear magnetic resonance (NMR) data
1
Yield: 0.45 g (1.53 mmol, 39 %). H NMR (CDCl3): δ 0.91 (t, 3H, J = 6.7),
1.23-1.45 (m, 14H), 1.48-1.66 (m, 6H), 2.00-2.12 (m, 4H), 2.75-2.84 (m, 2H),
3.40 (dt, 1H, J = 6.6, 9.6), 3.47-3.56 (m, 1H), 3.75 (dt, 1H, J = 6.8, 9.5), 3.83-
3.94 (m, 1H), 4.56-4.62 (m, 1H), 5.28-5.47 (m, 2H). 13C NMR (CDCl3): 14.1,
19.7, 22.6, 25.5, 25.6, 26.3, 27.0, 27.2, 29.3, 29.4, 30.8, 31.5, 62.3, 67.5, 98.8,
127.9, 128.8, 129.8, 130.3
1
were acquired on a Bruker Fourier 300 spectrometer (300 MHz for H and
75 MHz for 13C), and chemical shifts (δ) are reported in ppm relative to the
Synthesis of (5Z,8Z)-5,8-tetradecadien-1-ol (8)
internal standard tetramethylsilane. Coupling constants J are given in Hz.
To a solution of 7 (0.45 g, 1.53 mmol) in 20 mL methanol was added
a catalytic amount of p-toluenesulfonic acid. After 2 h stirring at room
temperature, the solvent was removed and the residue was dissolved in
dichloromethane. The solution was washed with sat. NaHCO3, dried over
MgSO4, and concentrated. The residue was purified by column chromatography
(hexane-ethyl acetate 5:1). Yield 300 mg (1.43 mmol, 93%). 1H NMR (CDCl3):
δ = 0.90 (t, 3H, J = 7.1), 1.23-1.47 (m, 8H), 1.52-1.65 (m, 2H), 1.98-2.16
(m, 4H), 2.74-2.84 (m, 2H), 3.61-3.71 (m, 2H), 5.28-5.47 (m, 4H). 13C NMR
(CDCl ): 14.1, 22.6, 25.6, 25.8, 26.9, 27.2, 29.3, 31.5, 32.4, 62.9, 127.8, 128.5,
129.6, 3130.3
2.2. Synthesis of (5Z,8Z)-5,8-tetradecadienyl formate (Fig. 2)
Synthesis of 5-(2’-tetrahydropyranyloxy)pentan-1-ol (2)
To a solution of 5.00 g (48.1 mmol) 1,5-pentanediol (1) and 110 mg
p-toluenesulfonic acid in 80 mL dry dichloromethane was added 4.04 g
(48,1 mmol) 3,4-dihydro-2H-pyran at 0 ºC. After 30 min stirring at room
temperature, 100 mL hexane and 30 mL sat. NaHCO3 were added and stirring
was continued for another 10 min. The phases were separated and the aqueous
phase was extracted three times with 50 mL hexane-ethyl acetate (1:1). The
combined organic phases were dried with MgSO4 and concentrated. The crude
product was purified by column chromatography (hexane-ethyl acetate 4:1) to
yield 3.80 g (20.2 mmol, 42%) of a colorless oil. 1H NMR (CDCl3): δ = 1.21-
1.90 (m, 12H), 3.32-3.90 (m, 6H), 4.60 (t, 1H, J = 3.5 Hz). 13C NMR (CDCl3):
19.7, 22.5, 25.5, 29.4, 30.7, 32.5, 62.4, 62.8, 67.5, 98.9
Synthesis of (5Z,8Z)-5,8-tetradecadienyl formate
Dicyclohexylcarbodiimide (0.38 g, 1.84 mmol) and a catalytic amount
of 4-(dimethylamino)pyridine were added to a solution of formic acid (85
mg, 1.85 mmol) in 6 mL dry dichloromethane. After addition of 300 mg
(1.43 mmol) 8, the reaction mixture was stirred 4 h at room temperature.
Dichloromethane (15 mL) was added, the solution was filtered, and the filtrate
was washed with brine, dried over MgSO4, and concentrated. The residue was
purified by column chromatography (hexane-ethyl acetate 9:1). Yield 330 mg
(1.39 mmol, 97%). 1H NMR (CDCl3): δ = 0.90 (t, 3H, J = 6.8), 1.24-1.53 (m,
8H), 1. 46-1.76 (m, 2H), 2.00-2.20 (m, 4H), 2.71-2.85 (m, 2H), 4.19 (t, 2H, J =
6.6), 5.27-5.47 (m, 4H), 8.07 (s, 1H). 13C NMR (CDCl ): 14.1, 22.6, 25.6, 25.8,
26.7, 27.2, 28.1, 29.3, 31.5, 63.9, 127.7, 128.8, 129.2,3130.3, 161.1
Synthesis of 5-(2’-tetrahydropyranyloxy)pentanal (3)
Pyridinium dichromate (5.60 g, 14.9 mmol) and MgSO4 (0.5 g) were added
to a solution of 2 (2.80 g, 14.9 mmol) in 100 mL dry dichloromethane, and
the mixture was stirred overnight at room temperature. Hexane (30 mL) was
added and the mixture was filtered. The filtrate was concentrated, water (50
mL) was added, and the mixture was extracted with diethyl ether (3 x 50 mL).
The combined organic phases were dried with MgSO4 and concentrated. The
crude product was purified by column chromatography (hexane-ethyl acetate
7:1) to yield 2.50 g (13.4 mmol, 93%) of a colorless oil. 1H NMR (CDCl3): δ =
1.51-1.70 (m, 10H), 2.50 (m, 2H), 3.41-3.70 (m, 2H), 3.72-3.80 (m, 2H), 4.60
(t, 1H, J = 3.5 Hz), 9.80 (t, 1H, J = 1.8). 13C NMR (CDCl3): 19.0, 19.7, 25.4,
29.1, 31.6, 43.6, 62.4, 67.0, 98.9, 202.5
2.3. Field test
The field test was carried out from September 28 until October 12, 2016,
in an apple orchard in Colbún Poniente (35° 43′ 12.99″S, 71° 27′ 33.59″W).
Traps consisted of 20 L-buckets filled with a saline solution as described earlier
[15]. Lures containing synthetic compounds were prepared by loading white
rubber septa (Sigma-Aldrich, catalog #Z553905) with 100 μL of an appropriate
solution of Z7,Z10-16:Ald (synthesized as described in [15]) and/or Z5,Z8-
14:Fo in hexane. Septa treated with 100 μL of hexane were used as controls.
The following treatments were used: (1) 300 mg Z5,Z8-14:Fo, (2) 300 mg
Z7,Z10-16:Ald, (3) 300 mg Z7,Z10-16:Ald + 300 mg Z5,Z8-14:Fo, (4) control.
For each treatment, 6 replicates were used, spatially arranged as a complete
randomized block design. Traps were placed at 3.0–3.5 m height from the tree
branches, evenly distributed on different orchard rows with a distance of 20–22
m between the traps. The captured moths were counted, sexed and removed
from the traps at intervals of 7 days. Total male trap catches, expressed as
individuals per trap and per day, were compared among treatments using a
non-parametric Kruskal-Wallis test.
Synthesis of (Z)-1-bromo-3-nonene (5)
A solution of 3.68 g (14.0 mmol) triphenylphosphine in 100 dry
dichloromethane was cooled to 0 ºC and 0.71 mL (14.0 mmol) bromine was
added dropwise. After addition of 1.99 g (14.0 mmol) (Z)-3-nonen-1-ol (4), the
mixture was warmed to room temperature and stirred for 2 h. Hexane (100 mL)
and sat. NaHCO3 (100 mL) were added, the phases were separated, and the
aqueous phase was extracted twice with hexane. The combined organic phases
were washed with water and brine, dried over MgSO4, and concentrated. The
precipitate was filtered off, washed with hexane, and the filtrate was again
concentrated. The residue was purified by column chromatography (hexane).
Yield 2.58 g (12.6 mmol, 90 %).
1H NMR (CDCl3): δ = 0.90 (t, 3H, J = 6.7), 1.22-1.45 (m, 6H), 1.99- 2.11
(m, 2H), 2.58-2.68 (m, 2H), 3.18 (t, 2H, J = 7.3), 5.31-5.42 (m, 1H), 5.49-5.60
(m, 1H). 13C NMR (CDCl3): δ = 14.0, 22.6, 27.4, 29.2, 30.9, 31.5, 32.5, 125.7,
133.2
3. RESULTS AND DISCUSSION
3.1. Synthesis of (5Z,8Z)-5,8-tetradecadienyl formate
Synthesis of (Z)-3-nonenyl triphenylphosphonium bromide (6)
A solution of 1.80 g (8.78 mmol) 5 and 2.30 g (8.78 mmol)
triphenylphosphine in 60 mL acetonitrile was refluxed for 72 h. After
cooling, the solvent was removed and the residue was purified by column
chromatography (dichloromethane-methanol 2:1). Yield: 3.05 g (74%).
1H NMR (CD3OD): δ = 0.88 (t, 3H, J = 6.6), 1.15-1.37 (m, 6H), 1.85-1.95
(m, 2H), 2.39-2.53 (m, 2H), 3.50-3.62 (m, 2H), 5.44-5.59 (m, 2H), 7.76-7.97
(m, 15H). 13C NMR (75 MHz, CD3OD): δ 13.0, 19.9, 21.2, 21.9, 22.1, 26.8,
28.7, 31.2, 117.9, 119.0, 125.7, 125.9, 132.5, 130.3, 130.1, 133.4, 133.6, 134.9,
135.0
The synthesis of Z5,Z8-14:Fo is outlined in Fig. 2. 1,5-Pentanediol (1)
was transformed to the mono-tetrahydropyranyl (THP) ether 2 by reaction with
3,4-dihydro-2H-pyran (DHP) in dichloromethane (DCM) [20], which was
subsequently oxidized using pyridinium dichromate (PDC) to furnish aldehyde
3. This oxidation reagent was chosen because of its experimental simplicity and
good yields [21]. In parallel, (Z)-3-nonen-1-ol (4) was brominated using the
bromine-triphenylphosphine complex (PPh -Br2). Use of this reagent prevents
undesired elimination and rearrangements,3 as well as undesired bromination
of the double bond [22]. The resulting bromide 5 was transformed to the
corresponding Wittig salt 6 in good yield by heating with triphenylphospine
(PPh3) in acetonitrile (MeCN). Generation of the ylide from 6 using sodium
bis(trimethylsilyl)amide (NaN(SiMe3) ) in tetrahydrofuran (THF) and reaction
with aldehyde 3 at -78 ºC resulted in th2e formation of the protected (Z,Z)-dienol
7 [23]. Traces of the (E,Z)-isomer were separated by column chromatography
on silver nitrate-impregnated silica gel. Acid-catalyzed deprotection in
methanol (MeOH) and subsequent esterification of alcohol 8 with formic acid
catalyzed by dicyclohexylcarbodiimide (DCC) furnished the desired product
Z5,Z8-14:Fo in good overall yield.
Synthesis of 2-((5Z,8Z)-5,8-tetradecadienyloxy)tetrahydropyran (7)
A 1.0 M solution of sodium bis(trimethylsilyl)amide in THF (4.0 mL, 4.0
mmol) was added dropwise to a suspension of 1.50 g (mmol) 6 in 80 mL dry
tetrahydrofuran at -20 ºC. After 30 min, the resulting red solution was cooled
to -78 ºC and 0.85 g (3.90 mmol) 3 were added. After 30 min, the mixture was
allowed to warm to room temperature and was stirred for another 1.5 h, after
which it was poured on an ice-water mixture. Diethyl ether was added, the
phases separated, and the aqueous phase was extracted twice with ether. The
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J. Chil. Chem. Soc., 63, Nº 2 (2018)
Figure 2: Synthesis of (5Z,8Z)-5,8-tetradecadienyl formate (Z5,Z8-14:Fo). Reagents and conditions: (a) DHP, DCM, 0 ºC; (b) PDC, DCM; (c) PPh3-Br2,
DCM; (d) PPh3, MeCN, reflux; (e) NaN(SiMe3)2, THF, 3, -78 ºC; (f) H+, MeOH; (g) HCOOH, DCC. Abbreviations are explained in the text.
3.2. Field test
length and the position and geometry of the double bonds were maintained
in the formate analog, these results suggest a predominant importance of the
formyl group of the natural aldehyde in the interaction of the pheromone with
the respective antennal receptor. Due to the lack of biological activity found
in the present field test, it appears that it will not be possible to replace the
aldehyde pheromone by its formate analog in pest control methods.
No males were attracted to traps baited with the pheromone analog Z5,Z8-
14:Fo alone (Table 1, entry 1). Furthermore, the number of males caught in
traps baited with a 1:1 mixture of Z7,Z10-16:Ald and Z5,Z8-14:Fo did not
differ from traps containing Z7,Z10-16:Ald only (Table 1, entries 2 and 3).
These results indicate that Z5,Z8-14:Fo is not attractive to males, nor does it
inhibit or synergize the attraction of males to the pheromone.
4. CONCLUSIONS
Table 1: Captures of male C. valdiviana in traps baited with synthetic
compounds.
The pheromone analog (5Z,8Z)-5,8-tetradecadienyl formate was
synthesized by using standard organic chemistry reactions. In field tests
with this compound, no biological activity towards males of Chilecomadia
valdiviana was observed.
Males per trap per day
Entry
Treatmenta
(mean ± S.E.)b
1
Z5,Z8-14:Fo (300 mg)
0 b
5. ACKNOWLEDGEMENTS
2
Z7,Z10-16:Ald (300 mg)
7.5 ± 1.0 a
Financial support from Fondo Nacional de Desarrollo Científico y
Tecnológico (grant 1140779 to JB) is gratefully acknowledged. HH thanks
Comisión Nacional de Investigación Científica y Tecnológica for a doctoral
fellowship (21130375).
Z7,Z10-16:Ald (300 mg) + Z5,Z8-
14:Fo (300 mg)
3
9.1 ± 2.3 a
4
Control
0 b
H(3,24) = 19.7
P ≤ 0.001
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