Macrolides from the scent glands of the tropical butterflies Heliconius cydno and Heliconius pachinus

Article abstract of DOI:10.1039/b710284d

The four major components present in scent gland extracts of the male Costa Rica longwing butterflies Heliconius cydno and Heliconius pachinus were identified as 12- and 14-membered macrolides containing a C₁₈-carbon skeleton. By use of micro-reactions and spectrometric examinations, structural proposals were made and subsequently proven by synthesis, using ring-closing-metathesis as the key steps. These macrolides, (9Z,11E,13S)- octadeca-9,11-dien-13-olide (5, S-coriolide), (9Z,11E,13S,15Z)-octadeca-9,11,15- trien-13-olide (6), (9Z,13S)-octadec-9-en-13-olide (13), and (9Z,11S)-octadec-9-en-11-olide (25), are biosynthetically obviously derived from oleic, linoleic, and linolenic acids. Their absolute configurations were determined by gas chromatographic investigations on chiral phases, showing all to possess (S)-configuration. The Royal Society of Chemistry.

Full text of DOI:10.1039/b710284d

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Macrolides from the scent glands of the tropical butterflies Heliconius cydno
and Heliconius pachinus†
Stefan Schulz,*a Selma Yildizhan,a Katja Stritzke,a Catalina Estradab and Lawrence E. Gilbertb
Received 5th July 2007, Accepted 7th September 2007
First published as an Advance Article on the web 18th September 2007
DOI: 10.1039/b710284d
The four major components present in scent gland extracts of the male Costa Rica longwing butterflies
Heliconius cydno and Heliconius pachinus were identified as 12- and 14-membered macrolides
containing a C18-carbon skeleton. By use of micro-reactions and spectrometric examinations, structural
proposals were made and subsequently proven by synthesis, using ring-closing-metathesis as the key
steps. These macrolides, (9Z,11E,13S)-octadeca-9,11-dien-13-olide (5, S-coriolide),
(9Z,11E,13S,15Z)-octadeca-9,11,15-trien-13-olide (6), (9Z,13S)-octadec-9-en-13-olide (13), and
(9Z,11S)-octadec-9-en-11-olide (25), are biosynthetically obviously derived from oleic, linoleic, and
linolenic acids. Their absolute configurations were determined by gas chromatographic investigations
on chiral phases, showing all to possess (S)-configuration.
occurring in the scent glands of male and female H. cydno and H.
pachinus are reported, and their function is discussed in relation
to the behaviour of the butterflies.
Introduction
The Costa Rica longwing butterflies Heliconius cydno and H.
pachinus (Lepidoptera, Nymphalidae) are members of the Central-
and South-American Heliconiinae subfamily. These butterflies are
Results and discussion
known for their complex mimicry rings and interesting behaviour.1
Gilbert postulated that males of a related species, H. erato, trans-
fer a pheromone, a so-called antiaphrodisiac, during copulation to
the female which deters other males from this female.2 Chemical
investigations of another heliconiid, Agraulis vanillae, showed that
both males and females contain the same compounds in their scent
bouquet. Ross et al.3 identified 6-methyl-5-hepten-2-one and fatty
acid esters of the corresponding alcohol as well as 1,15- and 1,16-
hexadecanediyl diacetates in their secretion. They postulated that
the secretion functions as a deterrent against predators, but no
experimental proof was given. Meinwald and coworkers isolated a
fatty acid derived macrolide, (R)-coriolide (R-5), from both sexes
of H. pachinus, a species closely related to H. cydno,4 and suggested
a pheromonal role of this compound.5
Abdominal scent glands of male Heliconius cydno and H. pachinus
raised in a greenhouse were cut and extracted with pentane. The
extracts were analysed by GC-MS revealing the presence of four
major compounds A–D (Fig. 1). The mass spectrum of compound
C (Fig. 2) was almost identical to that reported for (9Z,11E)-
octadeca-9,11-dien-13-olide (coriolide, 5).5,9
Recently these butterflies have received considerable attention
in terms of the molecular genetics of wing colour pattern, genetics
of mate preference and speciation,6 so additional details of the
chemistry of pheromonal secretions adds to an important model
system in evolutionary biology. Both H. pachinus and H. cydno
hybridise with an exchange of genes with H. melpomene,7 a species
distinct in both colour pattern and pheromonal chemistry.8 Thus
this system presents mysteries only understood when chemistry,
ecology, and behaviour are unravelled in concert.
In the present work the synthesis, identification, and enantiomer
determination of coriolide and three additional major macrolides
aInstitut fu¨r Organische Chemie, Technische Universita¨t Braunschweig,
Hagenring 30 38106, Braunschweig, Germany. E-mail: stefan.schulz@tu-
bs.de.
bSection of Integrative Biology, The University of Texas, Austin, TX, 78712,
USA
† Electronic supplementary information (ESI) available: Mass spec-
tra; GC-MS analyses; further experimental details. See DOI:
10.1039/b710284d
Fig. 1 Total ion chromatogram of an extract of male abdominal scent
glands of Heliconius cydno. The chromatogram of H. pachinus is very
similar.
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ring closure. A similar mechanism starting with linolenic acid
would lead to (9Z,11E,15Z)-octadeca-9,11,15-trien-13-olide, the
putative structure of compound D. Compounds A and B are
most likely derived from oleic acid, but a different precursor like
vaccenic acid seemed also to be plausible.
We therefore tried to elucidate the position of the double bond
in both octadecenolides by addition of dimethyldisulfide (DMDS)
to the extract, followed by GC-MS analysis.10,11 Surprisingly, the
adducts showed largely different mass spectra (Fig. 3). The adduct
of A exhibited an intensive cluster of peaks around m/z 171. This
can be explained by elimination of the ester group from the chain
and additional loss or transfer of hydrogen. When the double bond
is located at C-9, cleavage between the two thiomethyl groups leads
to such ions carrying the alkyl end of the molecule. The other
cleavage product carrying the carboxyl end is also present at m/z
203. Ions at m/z 171 and 203 can be found in the spectrum of the
second adduct, too, but only of relatively low abundance. Instead,
ions at m/z 122 and 136 dominate. They can be explained by
additional losses of CH3SH, H2O, and H from m/z 171 or 203, as
shown in Fig. 3. These results pointed towards the location of the
double bond at C-9 in both compounds, but other positions could
not be completely ruled out by the derivatisation results.
The macrolides A–D were then synthesised to prove our
structural assignments, to elucidate their absolute configuration,
and provide material for biotests. (S)-Coriolide (5) has been syn-
thesised before using the enzymatic oxidation of linoleic acid (2)
with soy bean lipoxygenase, reduction and macrolactonisation,12,13
while a similar reaction with linolenic acid (1) leading to
octadeca-9,11,15-trien-13-olide (6) was described in a patent.14
We followed this route using both 2 and 1 as starting materials.
The oxidation with soy bean lipoxygenase at C-13 proceeds
with concomitant double bond migration and is known to
furnish the S-configured hydroperoxide.15,16 Reductive work-up
15
with NaBH4 delivers the corresponding acids (9Z,11E,13S)-
Fig.
2
Mass spectra of compounds A ((Z)-octadec-9-en-11-olide,
13-hydroxyoctadeca-9,11-dienoic acid (coriolic acid, 3) and
(9Z,11E,13S,15Z)-13-hydroxyoctadeca-9,11,15-trienoic acid (4).
Cyclisation worked best in our hands using Corey/Nicolaou
conditions13 to furnish S-5 and S-6 (Fig. 4). Both macrolides
were generated in high ee (>95%), but only moderate yield.
Nevertheless, the target molecules are obtained in two steps only,
making this route very attractive for this class of compounds.
The two macrolides were identical to the natural compounds,
thus confirming our structural assignments for C and D. Non-
racemic mixtures of their enantiomers were then needed for
the determination of the absolute configuration of the natural
compounds. They were synthesised by inversion of S-3 and S-4 by
the Mitsunobu procedure, followed by macrolactonisation.
Gas chromatographic analysis of the synthetic macrolides 5 and
6 and a crude scent gland extracts of Heliconius cydno and Helico-
nius pachinus on a chiral Hydrodex (2,3-di-O-methyl-6-TBDMS-
b-cyclodextrin) phase showed that both natural macrolides are
enantiomerically pure and possess S-configuration (Fig. 5).
Therefore, compound C is (9Z,11E,13S)-octadeca-9,11-dien-13-
olide (S-5, coriolide), while the structure of compound D is
(9Z,11E,13S,15Z)-octadeca-9,11,15-trien-13-olide (S-6).
Z-25), B ((Z)-octadec-9-en-13-olide, 13), C ((9Z,11E)-octadeca-9,11-
dien-13-olide, coriolide, 5), and D ((9Z,11E,15Z)-octadeca-9,11,15-trien-
13-olide, 6).
The other three compounds exhibited similar mass spectra,
but with different molecular ions. Compounds A and B had a
molecular mass 2 amu higher than that of C, suggesting these
to be two octadecenolides, while compound D had a molecular
mass 2 amu less than that of C and was therefore believed to
be an octadecatrienolide. The mass spectrum of 5 showed a
characteristic ion at m/z 207 (M − 71), which can be attributed to
the loss of the pentyl side chain. This ion occurs also prominently
in the spectrum of compound D, in which case it corresponds to
the loss of a pentenyl side chain (M − 69). Compound B showed
a small ion at m/z 209, which could be interpreted as a loss of a
pentyl side chain. In contrast, the mass spectrum of compound A
contained an intense ion at m/z 181 (M − 99) pointing to a heptyl
side chain. Hydrogenation of an extract with Pd/C furnished two
saturated macrolides E and F (for mass spectra see ESI†). The main
one E was identified as 13-octadecanolide by its characteristic ion
at m/z 211 (M − 71), while the minor one showed a peak at m/z
183 (M − 99), consistent with 11-octadecanolide. Biosynthetically,
coriolide is certainly derived from linoleic acid by oxidation
at C-13 with concomitant double bond migration, followed by
Our attention then turned towards the synthesis of the two
octadecenolides A and B. Attempts to apply the soy bean
lipoxygenase reaction to oleic acid for synthesis of the two com-
pounds failed. Therefore we switched to a synthetic route using
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Fig. 4 Synthesis of coriolide ((S)-5) and (S)-6: a) soybean lipoxygenase,
O2, b) NaBH4, c) PPh3, (C5H5NS)2.
Fig. 5 GC investigation of coriolide 5 (A, ion trace 278) and of
octadecatrienolide (6, ◦B, ion trace m/z 276) o◦n a chiral stationary phase
(Hydrodex, 15 m, 150 C, 0.2 ◦C min−1 to 200 C). The following samples
were analysed (from top to bottom): crude scent gland extract of H. cydno,
co-injection scent gland extract and synthetic (R/S) mixture, synthetic
(S) compounds, and (R/S) mixture. The analysis of H. pachinus showed
identical results.
yield, surprisingly showing a 9 : 1 Z : E ratio in contrast to the
E-preference often found in RCM.17 The preference for the Z-
isomer, identical to compound B, was verified by NMR analysis
using NOESY spectra.
The configuration of B was then clarified by synthesis of pure
enantiomers. Alkyne RCM18 allowed a simple entry towards
diastereomerically and enantiomerically pure products (Fig. 7),
starting with 5-hexynoic acid (14). This acid was isomerised into 4-
hexynoic acid19 and transformed into the aldehyde 15. Dipentylz-
inc was then used in an enantioselective alkylation accord-
ing to Kobayashi et al.20 using (1R,2R)-1,2-N,Nꢀ-bis(p-toluene-
sulfonylamino)cyclohexane as ligand for the chiral titanium cata-
lyst. The zinc reagent always attacks from the Re-side when this
Fig. 3 Mass spectra and fragmentation pattern of DMDS-adducts
derived from A and from B.
ring-closing-metathesis (RCM) as the key step. The Grignard
reaction of hexanal (7) and 1-bromo-3-butene furnished dec-1-
en-5-ol 9, which was acylated with 9-decenoic acid (11), generated
from 9-decen-1-ol (10). The resulting ester rac-12 was then sub-
mitted to RCM using the Grubbsꢀ catalyst of the first generation
(Fig. 6). rac-Octadec-9-en-13-olide (13) was obtained in good
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Fig. 6 Synthesis of rac-octadec-9-en-13-olide (13): a) PDC, DMF, b) SOCl2, c) bis(tricyclohexylphosphane)benzylidene ruthenium(IV) dichloride,
CH2Cl2.
Fig. 7 Synthesis of (9S)-octadec-9-en-13-olide (S-13): a) KOtBu, b) DIBAL, c) Zn(C5H11)2, (1R,2R)-(TsNH)2C6H10, Ti(OiPr)4, d) SOCl2, e) Mo(CO)6,
4-Cl-Ph-OH, f) Lindlar cat., H2, g) [Cp*Ru(MeCN)3]PF6, HSi(OEt)3, CH2Cl2, P(CH2OH)3, h) AgF, MeOH.
ligand is used, producing the alcohol (S)-undec-2-yn-6-ol (16) in
moderate yield, but excellent ee (98%). Esterification with undec-9-
ynoic acid (18), which was obtained by isomerisation from undec-
10-ynoic acid (17),19 gave the diynoate 19. This precursor was
submitted to alkyne RCM with Mo(CO)6 and p-chlorophenol in
chlorobenzene,18 furnishing octadec-9-yn-13-olide (S-20) in good
yield. The cyclic alkyne was finally hydrogenated under Lindlar
catalysis to deliver the pure Z,S-configured macrolide Z,S-13 with
an ee of 98%. The opposite (R)-enantiomer was obtained by a
similar sequence using the (S,S)-cyclohexanediamine derivative as
ligand in the asymmetric alkylation reaction. Attempts to obtain
pure (E)-13 from 20 by hydrosilylation according to Fu¨rstner
et al.21 were only partly successful, leading to a 44 : 56 E :
Z mixture under non-optimised conditions. Nevertheless, this
mixture proved to be very useful in the determination of the double
bond geometry of the natural product.
Finally, the enantiomers of 13 were separated on a chiral
cyclodextrin phase, showing that the natural compound possesses
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exclusively S-configuration (see ESI†). It follows that B is
(9Z,13S)-octadec-9-en-13-olide (S,Z-7).
H. pachinus and H. cydno investigated by us are S-configured.
This assignment is unambiguous, because the optical rotation
of the synthesised pure compound exhibits the same sense of
rotation as reported9,12 and the soy bean lipoxygenase is known
to produce S-configured hydroperoxides. The agreement between
natural and synthesised compounds was proven by chiral GC-
MS. One explanation of the discrepancy in the results obtained by
Meinwald et al. and ours may be that the butterflies, originating
from different sources, produced different enantiomers, or that the
sample isolated by Meinwald et al. was not pure.
All natural macrolides are obviously derived from oleic, linoleic,
and linolenic acids, formed by oxidation at different positions
and ring closure. They all exhibit the same S-configuration. A
minor component in the secretion is ricinollactone ((Z)-octadec-
9-en-12-olide), showing that oxidation occurs in case of the
octadecenolides at the a-, b-, and c-positions relative to the double
bond of oleic acid.
The identified macrolides might play a role in the chemical
communication system of H. cydno and H. pachinus. Females
contain a similar bouquet as the males, albeit in markedly
lower concentration. Investigation of females before and after
copulation showed that these lactones are produced by the
males and transferred during copulation. Gilbert postulated that
the transferred compounds generally act as antiaphrodisiacs in
Heliconius, protecting the fertilised female from additional male
courtship attempts.2 This mechanism was recently investigated by
us in more detail in H. melpomene.8 In this case (E)-b-ocimene is
transferred together with a matrix consisting of fatty acid esters.
While the esters modulate the evaporation rate, ocimene, the
major component of the scent glands, inhibits additional courtship
attempts of males on fertilised females. It may well be that the
macrolides, so far not found in other Heliconius sp. investigated
by us or others,3,5,8 serve this function, especially because no major
component other than the macrolides was present in the glands. A
defensive role, proposed for the compounds identified in the same
Compound A was proposed to be octadec-9-en-11-olide (25)
and synthesised via alkene RCM starting from octanal and
vinylmagnesium bromide. The resulting dec-1-en-3-ol (23) was
acylated with 9-decenoic acid and the resulting ester 24 submitted
to RCM. In this case an 88 : 12 E : Z mixture of 25 was
obtained and the structure of A confirmed to correspond to
the Z-isomer. An enantioselective synthesis of 25 was then
accomplished (Fig. 8). Reaction of octanoyl chloride (21) with
ethynyltrimethylsilane gave dec-1-yn-3-one 22. This ketone was
enantioselectively reduced with LiAlH4 in the presence of N-
methyl ephedrine22 to yield (S)-dec-1-yn-3-ol with moderate ee
(67%). Reduction with LiAlH4 furnished the decenol S-23, which
was acylated as described to form S-24. Finally, RCM gave an
88 : 12-mixture of (9E,11S)-octadec-9-en-11-olide (E,S-25) and
(9Z,11S)-octadec-9-en-11-olide (Z,S-25) with an ee of 67% in both
cases, showing the expected E preference.
Attempts to synthesise pure Z-25 by alkyne metathesis using
the Mo(CO)6 and p-chlorophenol system resulted in complete
product decomposition. The failure may be explained by the close
proximity of the ester group and the triple bond in the precursor
which may lead to interaction with the catalyst with an undesired
outcome.
Comparison with the natural compound A using gas chro-
matography with a 2,6-di-O-methyl-3-O-pentyl-b-cyclodextrin
phase23 revealed that the (9Z,11S)-25 enantiomer occurs naturally.
The three macrolides 6, 13, and 25 are new natural products,
while S-coriolide 5 has been found previously in the seed oil of
Monnina emarginata9 and the fungus Stagonospora.24 In a previous
investigation5 Meinwald et al. isolated 5 from male H. pachinus
and determined its absolute configuration by optical rotatory
dispersion and comparison with an authentic sample of the S-
enantiomer obtained from M. emarginata as R-5. No specific
rotation was reported. In contrast, the coriolides produced by both
Fig. 8 Synthesis of (S)-octadec-9-en-11-olide (S-25): a) ethynyltrimethylsilane, AlCl3, b) LiAlH4, N-methyl ephedrine, c) LiAlH4, d) dec-9-enoyl chloride,
e) bis(tricyclohexylphosphane)benzylidene ruthenium(IV) dichloride.
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glands of another heliconid, Agraulis vanillae, without mentioning
the transfer mechanism,3 might be a secondary function of these
glands. Different species of Heliconius show largely different,
species specific compositions of their scent glands, sometimes with
up to 100 components of different volatility. Further work on the
chemical ecology of these compounds is needed to clarify their
function in the life of these impressive butterflies.
DMDS adducts were formed by addition of 50 ll DMDS and
5 ll of iodine solution (60 mg iodine in 1 ml diethyl ether) to a
sample of crude natural extract. The reaction vessel was sealed and
kept at 50 ◦C for 24 h. Then the reaction mixture was washed with
saturated Na2S2O3 solution, extracted three times with hexane,
and the combined organic phases dried with NaCl. Finally, the
solution was concentrated under a gentle N2 stream and analysed
by GC-MS.
Experimental
General procedure A for macrolactonisation
A mixture of 2,2ꢀ-dithiopyridine (100 mg, 0.5 mmol) and triph-
enylphosphane (130 mg, 0.5 mmol) was dissolved in dry toluene
(1 ml) under a N2 atmosphere. Then the appropriate hydroxyacid
(0.3 mmol) was added. The reaction mixture was stirred for 5 h at
room temperature and then diluted with dry toluene to a 0.1 M
solution. This solution was added with a syringe pump to 100 ml
boiling dry toluene over a period of 15 h and heated under reflux
for another 10 h. Finally, the solvent was removed in vacuo and the
crude product purified by flash chromatography (pentane–diethyl
ether, 19 : 1).
General remarks and starting materials
Dry CH2Cl2 was distilled from CaH2, diethyl ether from LiAlH4,
toluene from Na, and THF from K and Na. All other chemicals
were commercially available (Fluka, Aldrich, Strem) and used
without further treatment. All reactions were monitored by
thin layer chromatography (TLC), carried out on Macherey-
Nagel Polygram SIL G/UV254 silica plates, visualised with heat
gun treatment with 10% molybdato phosphoric acid in ethanol.
Column chromatography was performed with Merck silica gel
60 (70–200 mesh). GC analyses were performed with a CE
instruments GC 8000 gas chromatograph equipped with a flame
ionisation detector and split/splitless injection using hydrogen
as carrier gas. GC-MS experiments were carried out with a
Hewlett-Packard model 5973 mass selective detector connected to
a Hewlett-Packard model 6890 gas chromatograph using a BPX5
fused silica capillary column (SGE, 30 m × 0.25 mm, 0.25 lm
film thickness). Chiral GC and GC-MS analyses were performed
with the same instruments. Chiral GC was performed on different
phases: 15 m or 35 m Hydrodex-6-TBDMS (2,3-di-O-methyl-6-
TBDMS-b-cyclodextrin, Machery & Nagel), 0.25 mm diameter,
(+)-(9Z,11E,13S)-Octadeca-9,11-dien-13-olide S-5
Pure S-5 (15 mg, 21%) was prepared from S-3 with an ee of
97% according to general procedure A. In an identical manner
R-enriched 3, obtained by Mitsunobu inversion, was transformed
into R-enriched 5.
20
[a]D +17.2 (c 0.8 in diethyl ether); dH (400 MHz, CDCl3) 0.81
(3H, t, J 6.9, CH3), 1.19–1.31 (14H, m, CH2), 1.48–1.54 (2H, m,
CH2), 1.79–1.85 (2H, m, CH2), 2.32–2.54 (4H, m, CH2), 5.35–5.39
(1H, m, CH), 5.45 (1H, dt, J 6.7 and 10.3, CH), 5.66 (1H, dd, J
3.7 and 15.4, CH), 5.96 (1H, t, J 10.8, CH), 6.43 (1H, dd, J 11.2
and 14.2, CH); dC (100 MHz, CDCl3) 14.0 (q), 22.5 (t), 24.76 (t),
24.84 (t), 25.1 (t), 25.4 (t), 26.3 (t), 26.7 (t), 27.0 (t), 31.6 (t), 33.0
(t), 35.1 (t), 72.3 (d), 123.8 (d), 128.3 (d), 131.2 (d), 132.0 (d), 172.9
(s); EI-MS m/z (%) 43 (35), 53 (10), 55 (42), 65 (11), 67 (47), 68
(11), 69 (13), 71 (35), 77 (28), 78 (10), 79 (57), 80 (35), 81 (38), 82
(13), 83 (14), 91 (31), 93 (36), 94 (19), 95 (25), 98 (16), 99 (100), 107
(16), 108 (10), 121 (13), 135 (12), 136 (15), 151 (26), 164 (10), 179
(18), 278 (31); HR-MS C18H30O2: calcd 278.2246, found 278.2241;
chiral GC (Hydrodex, 15 m, 150 ◦C, 0.2 ◦C min−1 to 200 ◦C): rtR =
65.74, rtS = 71.24 min.
GC temperature program 150 ◦C, then with 0.2 C min−1 to
◦
200 ◦C if not stated otherwise and 15 m 2,6-di-O-methyl-3-O-
pentyl-b-cyclodextrin in 50% OV 1701 phase, 0.32 mm diameter,23
GC temperature program 120 ◦C, then with 1 C min−1 to
◦
200 ◦C. 1H NMR and 13C NMR spectra were obtained with
Bruker AC-200 and AMX-400 instruments with CDCl3 as solvent.
Tetramethylsilane was used as internal standard. J values are
given in Hz. The optical rotary power was measured using a
20
Dr. Kernchen Propol Digital Automatic polarimeter. The [a]D
values are given in 10−1deg cm2 g−1.
Biological samples
(+)-(9Z,11E,13S,15Z)-Octadeca-9,11,15-trien-13-olide S-6
Butterflies originating from Costa Rica were kept in a greenhouse
in which Passiflora caerulea and Lantana were maintained. The
butterflies had access to sugar water, and sources of pollen from
Psiguria and Lantana flowers. Abdominal glands were manually
exposed and directly dissected into 100 ll pentane. The samples
were shipped to Braunschweig and stored at −70 ◦C until analysis.
Acid S-4 was transformed into S-6 (6 mg, 16%) according
to general procedure A. In an identical manner R-enriched
4, obtained by Mitsunobu inversion, was transformed into R-
enriched 6.
20
[a]D +6.7 (c 2.0 in diethyl ether); dH (400 MHz, CDCl3) 0.96
(3H, t, J 7.5, CH3, H-18), 1.25–1.62 (8H, m, CH2), 1.86–1.92 (2H,
m, CH2, H-3), 1.99–2.13 (4H, m, CH2, H-8 and H-17), 2.36–2.38
(2H, m, CH2, H-14), 2.44–2.61 (2H, m, CH2, H-2), 5.31–5.41 (1H,
m, CH, H-15), 5.45–5.53 (3H, m, CH, H-13, H-16 and H-9), 5.72
(1H, dd, J 3.6 and 15.4, CH, H-12), 6.03 (1H, t, J 10.9, CH, H-
10), 6.51–6.60 (1H, dd, J 11.3 and 15. 4, CH, H-11); dC (100 MHz,
CDCl3) 14.1 (q, C-18), 20.7 (t, C-17), 24.8 (t, C-3), 24.8 (t), 25.4
(t), 26.3 (t), 26.6 (t), 27.0 (t, C-8), 32.9 (t, C-14), 33.0 (t, C-2), 71.8
(d, C-13), 123.2 (d, C-15), 124.1 (d, C-11), 128.2 (d, C-10), 130.5
Microreactions
Hydrogenation of crude scent gland extracts was carried out under
Pd/C catalysis (0.5 mg) using methanol as solvent. A suspension
of Pd/C in methanol was first activated by stirring for 30 min
under a H2 atmosphere. Then the scent gland extract was added
and again stirred for 30 min under a H2 atmosphere. Finally, Pd/C
was removed by microfiltration over a short silica plug.
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(d, C-12), 132.3 (d, C-9), 134.7 (d, C-16), 172.8 (s, C-1); EI-MS
m/z (%) 43 (12), 55 (38), 57 (11), 65 (11), 67 (47), 69 (22), 77 (18),
79 (48), 80 (10), 81 (43), 83 (23), 91 (36), 93 (39), 95 (28), 97 (12),
105 (24),107 (19), 109 (10), 119 (16), 133 (11), 147 (33), 161 (16),
171 (23), 207 (100), 208 (16), 276 (16). HR-MS C18H28O2: calcd
276.2089, found 276.2099; ee = 96%, chiral GC (Hydrodex, 15 m,
150 ◦C, 0.2 ◦C min−1 to 200 ◦C): rtR 64.23, rtS 71.05 min.
2.6, CH3), 2.22–2.33 (2H, m, CH2), 3.68–3.79 (1H, m, CH); dC
(100 MHz, CDCl3) 3.4 (q), 14.0 (q), 15.4 (t), 22.6 (t), 25.3 (t), 31.9
(t), 36.1 (t), 37.3 (t), 71.3 (d), 76.3 (s), 78.8 (s); MS m/z (%) 41 (93),
43 (62), 53 (38), 55 (68), 57 (13), 66 (36), 67 (52), 68 (19), 69 (38), 71
(12), 79 (38), 81 (12), 83 (23), 91 (10), 93 (26), 95 (11), 97 (100), 107
(17), 121 (18), 135 (10), 150 (7), 168 (3); HR-MS C11H20O: calcd
168.1514, found 168.1590; ee 98% (GC, 35 m Hydrodex, 100 ◦C,
1 ◦C min−1 to 220 ◦C).
rac-(Z)-Octadec-9-en-13-olide rac-Z-13
(+)-(S)-Octadec-9-yn-13-olide S-20
A solution of 12 (28 mg, 85 lmol) in dry CH2Cl2 (25 ml)
was treated with
a
catalytic amount of bis(tricyclohexyl-
A solution of 19 (140 mg, 0.43 mmol), p-chlorophenol (55 mg,
0.43 mmol), and Mo(CO)6 (6 mg, 0.023 mmol) in dry 4-
chlorobenzene (85 ml) was heated to reflux for 2 days under a N2
atmosphere. The solvent was evaporated and the residue purified
by flash chromatography using pentane–diethyl ether (19 : 1) to
give pure 20 (74 mg, 88%).
phosphane)benzylidene ruthenium(IV) dichloride (Grubbs’ cata-
lyst) under a N2 atmosphere. The solution was heated under reflux
for 36 h. Then the solvent was removed and the crude product
purified by flash chromatography (pentane–diethyl ether, 19 : 1) to
obtain pure Z-13 (15 mg, 63%).
20
dH (400 MHz, CDCl3) 0.88 (3H, t, J 6.9, CH3), 1.12–1.42 (13H,
m, CH2), 1.42–1.50 (2H, m, CH2), 1.53–1.64 (4H, m, CH2), 1.73–
1.86 (2H, m, CH2), 1.97–2.06 (1H, m, CH2), 2.13–2.24 (2H, m,
CH2), 2.30–2.36 (1H, m, CH2), 2.41–2.49 (1H, m, CH2), 4.98–5.04
(1H, m, CH), 5.31–5.45 (2H, m, CH); dC (100 MHz, CDCl3) 14.0
(q), 22.0 (t), 22.5 (t), 24.72 (t), 24.74 (t), 25.27 (t), 25.3 (t), 26.2 (t),
26.5 (t), 27.0 (t), 31.7 (t), 33.3 (t), 33.6 (t), 34.3 (t), 73.4 (d), 129.2
(d), 130.0 (d), 173.5 (s); EI-MS m/z (%) 43 (33), 53 (16), 54 (42), 55
(92), 56 (13), 57 (11), 67 (100), 68 (65), 69 (37), 79 (31), 80 (20), 81
(98), 82 (74), 83 (29), 93 (16), 94 (19), 95 (74), 96 (61), 97 (19), 107
(12), 108 (13), 109 (37), 110 (34), 121 (12), 122 (22), 123 (22), 124
(20), 135 (12), 136 (22), 137 (13), 138 (12), 149 (10), 150 (13), 182
(22), 196 (15), 280 (50); HR-MS C18H32O2: calcd 280.2402, found
280.2391.
[a]D +1.2 (c 3.1 in diethyl ether); dH (400 MHz, CDCl3) 0.88
(3H, t, J 6.9, CH3), 1.21–1.84 (22H, m, CH2), 2.10–2.50 (4H, m,
CH2), 4.91–4.98 (1H, m, CH); dC (100 MHz, CDCl3) 14.0 (q), 14.8
(t), 18.1 (t), 18.6 (t), 22.5 (t), 23.5 (t), 24.8 (t), 25.5 (t), 26.1 (t),
26.3 (t), 26.6 (t), 31.8 (2t), 33.7 (t), 34.0 (t), 73.6 (d), 80.0 (s), 80.7
(s), 174.1 (s); EI-MS m/z (%) 43 (42), 53 (20), 54 (13), 55 (84), 65
(18), 66 (14), 67 (57), 68 (13), 69 (20), 77 (30), 78 (22), 79 (100),
80 (69), 81 (48), 82 (11), 83 (14), 91 (38), 92 (9), 93 (56), 94 (35),
95 (32), 96 (13), 97 (10), 105 (14), 107 (31), 108 (12), 109 (13), 119
(11), 121 (28), 122 (7), 135 (18), 136 (11), 149 (9), 150 (44), 151 (8),
167 (10), 193 (5), 207 (6), 221 (4), 236 (3), 249 (2), 278 (1); HR-MS
C18H02O2: calcd 278.2246, found 278.2209.
(9E,13S)-Octadec-9-en-13-olide 9E,13S-13
According to Fu¨rstner et al.21 1 mol% of [Cp*Ru(MeCN)3]PF6
(0.34 mg) was added to a solution of 20 (19 mg, 0.068 mmol)
and triethoxysilane (13.3 mg, 0.081 mmol) in dry CH2Cl2 (2 ml)
and the mixture stirred for 15 min at room temperature. Then
tris(hydroxymethyl)phosphine (1.3 mg) was added and the result-
ing mixture was stirred for 30 min. Filtration through a short
pad of silica and evaporation of the organic solvent furnished the
hydrosilylated crude product. Then a solution of AgF (1 M in aq.
MeOH, 0.14 ml) was added and stirring commenced for 3 h in the
dark. The mixture was filtered and thoroughly washed with diethyl
ether. The combined organic filtrates were concentrated and the
crude product was purified by flash chromatography (pentane–
diethyl ether 20 : 1) to furnish 13 (7 mg, 35%). Chiral GC (15 m
Hydrodex) showed that the product was a 44 : 56 E : Z mixture
with an ee of 99% in both cases.
(9E,13S)-13: dH (400 MHz, CDCl3) 0.88 (3H, t, J 6.9, CH3),
1.22–1.39 (13H, m, CH2), 1.40–1.52 (2H, m, CH2), 1.57–1.66 (4H,
m, CH2), 1.70–1.74 (3H, m, CH2), 1.97–2.14 (2H, m, CH2), 2.25–
2.36 (1H, m, CH2), 2.42–2.49 (1H, m, CH2), 4.93–4.99 (1H, m,
CH), 5.24–5.31 (1H, dt, J 7.3 and 15.1, CH), 5.50–5.57 (1H, dt,
J 7.6 and 15.1, CH); dC (100 MHz, CDCl3) 14.0 (q), 23.5 (t), 24.2
(t), 25.2 (t), 26.2 (t), 26.5 (t), 27.0 (t), 28.3 (t), 30.3 (t), 32.7 (t), 32.7
(t), 32.8 (t), 32.9 (t), 74.4 (d), 77.2 (t), 129.5 (d), 131.4 (d), 173.7
(s); EI-MS m/z (%) 41 (83), 43 (34), 54 (45), 55 (93), 67 (100), 69
(36), 79 (27), 81 (89), 95 (67), 96 (50), 109 (33), 110 (28), 122 (17),
123 (18), 136 (16), 150 (9), 164 (6), 182 (16), 196 (12), 209 (4), 223
(2), 237 (1), 262 (2), 280 (35).
(+)-(S)-Undec-2-yn-6-ol 16
Pentyl bromide (10.90 ml, 13.31 g, 88 mmol) was added slowly
to a mixture of magnesium (2.33 g, 97 mmol) and dry diethyl
ether (100 ml) under a N2 atmosphere. After formation of the
Grignard reagent it was slowly added to a solution of anhydrous
zinc chloride (5 g, 37 mmol) in dry diethyl ether (35 ml). This
mixture was stirred overnight. After settling of a precipitate, the
liquid phase removed using a syringe. The residue was washed
three times with diethyl ether. The combined liquid phases were
transferred into an distillation appara◦tus and distilled under a
N2 atmosphere. Dipentyl zinc (bp 100 C, 0.1 Torr, 4.54 g, 59%)
was isolated under low pressure. A solution of (1R,2R)-1,2-N,N-
bis(p-toluolsulfonylamino)cyclohexane (31.41 mg, 0.083 mmol)
in dry toluol (4 ml) and titanium tetraisopropoxylate (1.48 ml,
1.42 g, 5 mmol) was stirred under a N2 atmosphere for 20 min
at 40 ◦C. The mixture was cooled to −78 ◦C and excess dipentyl
zinc (1.04 g, 5 mmol) in toluene (1 ml) and 4-hexynal (400 mg,
4.17 mmol) were added.20 Th◦is mixture was stirred for 3 h at
◦
−78 C and then heated to 0 C during 5 h. A solution of HCl
(2 N) was added, the mixture was washed with brine, and extracted
three times with diethyl ether. The combined organic layers were
dried with MgSO4 and the solvent was removed. The crude product
was purified by flash chromatography (pentane–diethyl ether 5 :
1) to furnish (+)-(S)-16 (301 mg, 43%).
20
[a]D +1.9 (c 4.2 in diethyl ether); dH (400 MHz, CDCl3) 0.88
(3H, t, J 6.5, CH3), 1.17–1.74 (10H, m, CH2), 1.78 (3H, t, J
3440 | Org. Biomol. Chem., 2007, 5, 3434–3441
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(E)-Octadec-9-en-11-olide E-25
Prof. M. Boppre´, Freiburg, for preparation of early samples of
Heliconius cydno. The insects were imported (1991–1992) to the
USA under permits to LEG from USDA APHIS and collected
and exported from Costa Rica under permits from MINAE to
LEG. We also thank officials of P. N. Corcovado and Fernando
Cortez, Jefe. Seccion de Investigaciones, SPN.
Alkene RCM was performed with 24 to furnish 25 as described
above for 13 (8 mg, 32%) in a E : Z ratio of 88 : 12.
dH (400 MHz, CDCl3) 0.88 (3H, t, J 6.2, CH3), 0.98–2.01 (22H,
m, CH2), 2.11–2.38 (4H, m, CH2), 5.26–5.55 (2H, m, CH), 5.65–
5.83 (1H, m, CH); dC (100 MHz, CDCl3) 14.1 (q), 22.6 (t), 24.4
(t), 25.4 (t), 25.7 (t), 26.0 (t), 26.3 (t), 28.1 (t), 29.2 (t), 29.3 (t),
31.8 (t), 32.8 (t), 33.8 (t), 35.4 (t), 74.5 (d), 130.4 (d), 137.0 (d),
174.3 (s); EI-MS m/z (%) E-25: 43 (47), 55 (98), 56 (15), 57 (35),
65 (10), 66 (10), 67 (100), 68 (39), 69 (42), 70 (11), 71 (10), 79
(36), 80 (21), 81 (81), 82 (56), 83 (39), 84 (28), 93 (21), 94 (15), 95
(54), 96 (32), 97 (35), 98 (96), 99 (10), 107 (11), 108 (15), 109 (34),
110 (37), 111 (25), 112 (11), 121 (12), 123 (14), 124 (11), 125 (17),
126 (16), 127 (29), 135 (24), 136 (15), 137 (10), 138 (15), 139 (11),
152 (15), 153 (23), 155 (12), 181 (30), 183 (10), 209 (11), 280 (15);
Z-25: 43 (41), 53 (15), 54 (31), 55 (88), 56 (11), 57 (38), 67 (100),
68 (39), 69 (38), 77 (11), 79 (42), 80 (16), 81 (80), 82 (51), 83 (32),
84 (19), 91 (10), 93 (25), 94 (14), 95 (61), 96 (30), 97 (30), 98 (60),
107 (13), 109 (31), 110 (42), 111 (20), 121 (16), 123 (16), 124 (12),
125 (13), 127 (23), 135 (35), 136 (16), 138 (15), 139 (11), 152 (12),
153 (21), 181 (31), 280 (13); HR-MS C18H32O2: calcd 280.2402,
found 280.2384; chiral GC (15 m Hydrodex): rtZ-25 50.20, rtE,R-25
51.04, rtE,S-25 51.50 min; chiral GC (2,6-di-O-methyl-3-O-pentyl-b-
cyclodextrin): rtZ,R-25 51.80, rtZ,S-25 52.15, rtE-25 52.65 min.
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Conclusion
The major constituents of the scent glands used by the tropical
longwing butterflies Heliconius cydno and H. pachinus were iden-
tified and synthesised for the first time. The synthetic compounds,
accessible by short and enantioselective routes, now allow biotests,
needed to understand the function of the macrolides for the
complex behaviour of Heliconius. Given that species lacking
macrolides readily hybridise with H. cydno and H. pachinus,25
perhaps courtship and mating signals are to be discovered
among the minor components of the abdominal glands and on
androconial scales of the wing while the major macrolides may
serve in as yet unsuspected functions such as protecting eggs from
fungal disease or in protecting adults from predators.
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Acknowledgements
Support by the Fonds der Chemischen Industrie is gratefully
acknowledged. Living stocks of H. pachinus and H. cydno were
maintained in greenhouse facilities at UT Austin made possible
by grants from the National Science Foundation. We thank
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3434–3441 | 3441
©