Spiroacetal biosynthesis in insects from diptera to hymenoptera: The Giant Ichneumon wasp Megarhyssa nortoni nortoni Cresson

Article abstract of DOI:10.1021/ja8036433

The volatile components of the mandibular gland secretion generated by the Giant Ichneumon parasitoid wasp Megarhyssa nortoni nortoni Cresson are mainly spiroacetals and methyl ketones, and all have an odd number of carbon atoms. A biosynthetic scheme rationalizing the formation of these diverse components is presented. This scheme is based on the results of incorporation studies using ²H-labeled precursors and [¹⁸O]dioxygen. The key steps are postulated to be decarboxylation of β-ketoacid equivalents, β-oxidation (chain shortening), and monooxygenase-mediated hydroxylation leading to a putative ketodiol that cyclizes to spiroacetals. The generality of the role of monooxygenases in spiroacetal formation in insects is considered, and overall, a cohesive, internally consistent theory of spiroacetal generation by insects is presented, against which future hypotheses will have to be compared.

Full text of DOI:10.1021/ja8036433

Published on Web 10/09/2008
Spiroacetal Biosynthesis in Insects from Diptera to
Hymenoptera: The Giant Ichneumon Wasp Megarhyssa
nortoni nortoni Cresson
Brett D. Schwartz,† Christopher J. Moore,‡ Fredrik Rahm,† Patricia Y. Hayes,†
William Kitching,† and James J. De Voss*,†
Department of Chemistry, The UniVersity of Queensland, Brisbane, Australia, and Department of
Primary Industries and Fisheries, Yeerongpilly, 4105 Queensland, Australia
Received May 15, 2008; E-mail: j.devoss@uq.edu.au
Abstract: The volatile components of the mandibular gland secretion generated by the Giant Ichneumon
parasitoid wasp Megarhyssa nortoni nortoni Cresson are mainly spiroacetals and methyl ketones, and all
have an odd number of carbon atoms. A biosynthetic scheme rationalizing the formation of these diverse
components is presented. This scheme is based on the results of incorporation studies using 2H-labeled
precursors and [18O]dioxygen. The key steps are postulated to be decarboxylation of ꢀ-ketoacid equivalents,
ꢀ-oxidation (chain shortening), and monooxygenase-mediated hydroxylation leading to a putative ketodiol
that cyclizes to spiroacetals. The generality of the role of monooxygenases in spiroacetal formation in
insects is considered, and overall, a cohesive, internally consistent theory of spiroacetal generation by
insects is presented, against which future hypotheses will have to be compared.
Insect spiroacetals have thus attracted much synthetic4 attention
in their own right and have served as model target systems for
Introduction
The spiroacetal structural motif is widespread in a variety of
natural products isolated from prokaryotes and eukaryotes and
from marine and terrestrial organisms.1 In particular, simple
spiroacetals represent a novel class of insect-derived semio-
chemicals that have been employed for both intraspecific
(pheromonal) and interspecific communication. These decep-
tively simple molecules provide organisms with a catalogue of
opportunities for conveying information by subtle structural and
stereochemical variations. For example, insect-derived com-
pounds having [4.4], [4.5], [4.6], [5.5], and [5.6]dioxaspiroalkane
skeletons with a variety of substitution patterns, leading to over
30 structurally distinct parents, have been reported. In addition,
the configuration of the spirocenter can be inverted via a simple
ring-opening/ring-closing sequence at this acetal center. The
most stable configuration of the spirocenter reflects the free
energy balance between the anomeric effect and the configu-
ration of any substituted ring carbons.
method development for more complex systems. However, with
respect to their biosynthesis in insects (see below), little is
known. We present here for the first time an experimentally
founded biosynthetic route from primary metabolites to a suite
of related spiroacetals against which any future proposals will
have to be compared.1
Information on the biosynthesis of insect spiroacetals was
provided by our recent studies involving several Dipteran (fruit
2
fly) species.5 Incorporation studies employing H-labeled pre-
cursors have shown that oxygenated spiroacetals derive from
oxidation of the parent compounds and that tetrahydropyranols
are suitable precursors for the production of a variety of
spiroacetals via oxygenation. The proposed intervention of
monooxygenases in these transformations was confirmed by an
investigation of the patterns of 18O incorporation into spiroac-
etals when both 18O-labeled dioxygen and water were em-
ployed.6 Subtleties in the formation and processing of the
dioxygenated intermediate were revealed by the contrasting
results obtained with Bactrocera cucumis (cucumber fly) as
opposed to both Bactrocera oleae and Bactrocera cacuminata.
In the latter two species, careful consideration of 2H exchange
observed in precursors suggested that a diol rather than a
tetrahydropyranol was the natural spiroacetal precursor.7 Ad-
ditionally, the contrasting oxygen incorporation profiles for 1
For the widely distributed dioxaspiroalkane 2,8-dimethyl-1,7-
dioxaspiro[5.5]undecane (1) (Chart 1), the SRS isomer (E,E)-1
is ∼4.8 kcal/mol more stable than the SSS diastereomer (Z,Z)-1
that differs only in the configuration at the spirocenter.2,3 Despite
this, both of these diasteromers of 1 have been observed in
nature, suggesting both a kinetically controlled cyclization in
its biosynthesis and the possibility that the less-stable isomer
may convey time- and or environment-dependent information.
(4) Schwartz, B. D.; Hayes, P. Y.; Kitching, W.; De Voss, J. J. J. Org.
Chem. 2005, 70, 3054.
† The University of Queensland.
‡ Department of Primary Industries and Fisheries.
(5) Fletcher, M. T.; Kitching, W. Chem. ReV. 1995, 95, 789.
(6) (a) Fletcher, M. T.; Wood, B. J.; Brereton, I. M.; Stok, J. E.; De Voss,
J. J.; Kitching, W. J. Am. Chem. Soc. 2002, 124, 7666. (b) Fletcher,
M. T.; Mazomenos, B. E.; Georgakopoulos, J. H.; Konstantopoulou,
M. A.; Wood, B. J.; De Voss, J. J.; Kitching, W. Chem. Commun.
2002, 1302.
(1) Francke, W.; Kitching, W. Curr. Org. Chem. 2001, 5, 233.
(2) Deslongchamps, P.; Rowan, D. D.; Pothier, N.; Sauve, G.; Saunders,
J. K. Can. J. Chem. 1981, 59, 1105.
(3) Kitching, W.; Lewis, J. A.; Fletcher, M. T.; Drew, R. A. I.; Moore,
C. J.; Francke, W. J. Chem. Soc., Chem. Commun. 1986, 853.
9
10.1021/ja8036433 CCC: $40.75
2008 American Chemical Society
J. AM. CHEM. SOC. 2008, 130, 14853–14860 14853

A R T I C L E S
Schwartz et al.
Chart 1
from B. cucumis (with one oxygen atom from water and the
other from dioxygen)6a and for 1,7-dioxaspiro[5.5]undecane
from B. oleae and B. cacuminata (both oxygen atoms from
dioxygen) revealed contrasting origins for the dioxygenated
intermediates. However, the origin of the dioxygenated precursor
was unknown at the commencement of the present work.
A broader issue was whether the biosynthetic paradigm we
had developed for the latter stages of spiroacetal biosynthesis
in Bactrocera species (sp.) was generalizable across different
insect genera and orders. This is of particular interest because
many of the known spiroacetals have been isolated from
Hymenopteran (bee and wasp) as well as from Dipteran (fly)
species.8 The North American Giant Ichneumon wasp, Mega-
rhyssa nortoni nortoni (Cresson), appeared to offer the op-
portunity for simultaneous examination of these questions.9 M.
nortoni is a parasitoid wasp having a remarkable appearance
(up to 15 cm in length) and lifecycle as well as some commercial
importance. It detects the larvae of its host species, the wasp
Sirex noctilo, by the volatiles emitted by the S. noctilo symbiotic
fungus (Amylosterum areolatum). M. nortoni then employs its
ovipositor (up to 10 cm in length) to drill through the wood to
the S. noctilo larva, which is stung and paralyzed. An egg is
deposited, which hatches and consumes the host larva. As S.
noctilo infests and causes significant damage to commercial pine
species, M. nortoni has been introduced into a number of
countries as a biological control agent for it. Early work in 1985
by Davies and Madden9a suggested that M. nortoni employs a
mandibular secretion to aid in aggregation, precopulatory species
recognition, and defensive behavior. Chemical analysis9a of this
secretion revealed a number of compounds, including the
spiroacetal systems 1 and 2-ethyl-7-methyl-1,6-dioxaspiro-
[4.5]decane (2) as well as the biosynthetically suggestive
dihydropyran 3, 2-undecanone (4), and 2-undecanol (5). Here
we report further analyses of this secretion and then a pathway
for the biosynthesis of 1 and 2 in M. nortoni that is based on
the combined results of intermediate-isolation and precursor-
incorporation studies. This proposed biogenesis pathway not
only reinforces the results obtained with Bactrocera sp. but also
provides a cohesive platform for future guidance and comparisons.
Results
Isolation. Gas chromatography-mass spectroscopy (GC-MS)
examination of pentane extracts of the excised heads of female
wasps as well as solid-phase microextraction (SPME)-coupled
GC-MS analyses of the released volatiles revealed a more
complex range of spiroacetals than had been previously
described.9a The major spiroacetals were the (E,E) and (E,Z)
isomers of 1 and the (E,E) isomer of 2, as reported previously.9a
In addition, we also detected low levels of the (E,Z) and (Z,Z)
isomers of 2 as well as three stereoisomers [(E,E), (E,Z), and
(Z,E)] of 2-n-propyl-8-methyl-1,7-dioxaspiro[5.5]undecane (6).
Furthermore, use of an enantioselective ꢀ-cyclodextrin phase
in the GC-MS system confirmed through comparison with
authentic standards4 that (E,E)-1 was the (2S,6R,8S) enantiomer
(>98% ee) and additionally that all of the other chiral
components were highly enantiomerically enriched, particularly
(7) Schwartz, B. D.; McErlean, C. S. P.; Fletcher, M. T.; Mazomenos,
B. E.; Konstantopoulou, M. A.; Kitching, W.; De Voss, J. J. Org.
Lett. 2005, 7, 1173.
(8) A survey of the occurrence of spiroacetals in insects across the orders
Hymenoptera, Hemiptera, Diptera, and Coleoptera is presented in ref
1. In addition, see: (a) Tu, Y. Q.; Hu¨bener, A.; Zhang, H.; Moore,
C. J.; Fletcher, M. T.; Hayes, P.; Dettner, K.; Francke, W.; McErlean,
C. S.; Kitching, W. Synthesis 2000, 13, 1956. (b) Zhang, H.; Fletcher,
M. T.; Dettner, K.; Francke, W.; Kitching, W. Tetrahedron Lett. 1999,
40, 7851.
(9) (a) Davies, N. W.; Madden, J. L. J. Chem. Ecol. 1985, 11, 1115. (b)
Also see: Nuttall, M. J. In New Zealand: Insect Parasites of Sirex;
New Zealand State Forest Service Bulletin, 1980, vol. 47. (c) For a
color photo of this spectacular wasp, see: Fletcher, M. T.; Wood, B. J.;
Schwartz, B. D.; Rahm, F.; Lambert, L. K.; Brereton, I. M.; Moore,
C. J.; De Voss, J. J.; Kitching, W. ArkiVoc 2004, 10, 109 (issue
dedicated to Professor R. Rickards).
9
14854 J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008

Spiroacetal Biosynthesis in Insects
A R T I C L E S
located at C6. [A significant ion from C6H1318O at m/z 103
resulting from C5-C6 (R) cleavage was observed.] No incor-
poration of 18O from [18O]dioxygen into dihydropyran 3, the
suite of methyl ketones (4, 7, 8, and 9), or undecanol 5 occurred.
Synthesis of 2H-labeled Precursors and 10. The three key
potential precursors 4, 5, and 11 were synthesized in deuterium-
labeled form. These syntheses were based upon alkyne anion
chemistry that at once allowed construction of the desired
compounds and incorporation of the 2H labels via Pd/C-
catalyzed reduction in the presence of 2H2 (Scheme 1).
Straightforward modification of 14 to hydroxyketone 19 fol-
lowed by cyclization/dehydration by preparative gas chroma-
tography afforded the previously unreported dihydropyran 10
(Scheme 2).
Chart 2
(E,E)-2, with the most likely configuration shown in Chart 1,
which corresponds to that of (E,E)-1.
Davies and Madden9a also reported that 3, 4, and 5 were
present in the mandibular secretion of M. nortoni. We were able
to confirm these findings and substantially extend them, as 4 is
accompanied by trace amounts of a suite of other higher odd-
numbered methyl ketones: 2-tridecanone (7), 2-pentadecanone
(8), and 2-heptadecanone (9). Additionally, re-examination of
the GC-MS data following the precursor-incorporation studies
(see below) revealed that trace amounts of 6-methyl-2-pentyl-
3,4-dihydro-2H-pyran (10) (an isomer of 3) and 2,6-unde-
canediol (11) were also present.
2
Separate administration of the H-labeled monooxygenated
precursors [2H4]-4 and [2H4]-5 (as a racemate) to female wasps
demonstrated their efficient incorporation into the C11 spiroac-
etals 1 and 2, as determined on the basis of the changes in the
observed mass-spectral fragmentation patterns. Additionally,
both of the dihydropyrans 3 and 10 were found to be 2H-labeled,
and interconversion between the alcohol [2H4]-5 and the ketone
[2H4]-4 was observed when either was administered to the
wasps. The alcohol [2H4]-5 appeared to be more efficiently
incorporated than the corresponding ketone [2H4]-4, but caution
must be exercised in interpreting these results. Environmental
and physical factors, as well as location in the biosynthetic
sequence, can influence the level of incorporation. The 2H-
labeled precursor [2H4]-11 was also very efficiently incorporated
into the C11 spiroacetal systems 1 and 2 as well as into both of
the dihydropyrans 3 and 10 by a male wasp.
[18O]Dioxygen Incorporation. An apparatus described and
illustrated elsewhere9c was used to conduct studies of 18O
incorporation from [18O]dioxygen via SPME-coupled GC-MS
analysis. The sensitivity of the technique is such that a single
wasp provided sufficient volatiles for analysis in any given
experiment. Mass-spectral analysis confirmed that one oxygen
atom from dioxygen was incorporated into each of the identified
spiroacetals. Careful analysis of the mass-spectral fragmentation
pattern allowed the location of labeled oxygen in the nonsym-
metrical spiroacetals 2 and 6 to be determined. For example, in
the spiro[4.5]decane isomer 2, fragment ions containing both
oxygen atoms or selectively reporting on an oxygen atom in
only one of the two rings were identified (Chart 2 and Figure
1).
The daughter ion at m/z 140 in the unlabeled compound
(Figure 2) contains only the oxygen in the five-membered ring,
while the ion at m/z 126 incorporates the tetrahydropyranyl
oxygen.10 The mass spectrum of (E,E)-2 isolated after exposure
of M. nortoni to 18O2 (Figure 1) clearly indicated a mixture of
[16O2]-2 (M ) 184) and [16O,18O]-2 (M ) 186), the former
arising from endogenous 2 present in the wasp at the start of
the experiment, and the ∼80% level of 18O2 enrichment
achievable.11 Examination of the fragment ions at m/z 126 and
128 and at m/z 140 and 142 clearly indicated that the 18O label
resided entirely in the five-membered ring.
Experimental Section
General Procedures. 1H NMR spectra were recorded at 400 or
500 MHz using the signal of residual CHCl3 in CDCl3 (δ 7.24) or
benzene in C6D6 (δ 7.15) as an internal standard. 13C NMR spectra
were recorded at 100 or 125 MHz with the central peak of either
the CDCl3 triplet (δ 77.00) or the multiplet of benzene (δ 128.0)
as an internal standard. J values are reported in Hz. The GC-MS
data were recorded at 70 eV on a gas chromatograph-mass
spectrometer fitted with a 30 m × 0.25 mm BP5 column. The
standard program was set as follows: 2 min at 100 °C, a temperature
increase to 250 °C at a heating rate of 16 °C/min, and holding for
10 min at 250 °C. Preparative gas chromatography was performed
to the following specifications: Column, 10% OV3 Chrom P; flow
rate, 100 kg/cm3; column temperature, 150 °C (isothermal); detector
temperature, 200 °C; injector temperature, 250 °C. Flash chroma-
tography was carried out using Merck Kieselgel 60 (230-400 mesh)
or Scharlau silica gel (200-400 mesh). Moisture- or air-sensitive
experiments were conducted in oven- or flame-dried glassware
under an atmosphere of nitrogen. Anhydrous tetrahydrofuran (THF)
and diethyl ether were distilled off sodium wire; dichloromethane
was distilled off CaH2 under a nitrogen atmosphere. Compounds
that contained deuterium were also synthesized in their unlabeled
form, and their subsequent spectral data has been reported.
Specimens of M. nortoni nortoni were supplied by Dr. Charlma
Phillips (Forestry SA, Mount Gambier SA) and then caged and
fed on sugar water. Fabrication of the glassware was performed
by the University of Queensland Glassblowing Services.
Similar analyses indicated that for 6, the single 18O label was
located in the n-propyl-bearing ring4,6a (such oxygen atoms are
shown as b in the structures in Figure 1). The trace levels of
dihydropyran 10 and diol 11 observed in these experiments were
also found by careful mass-spectral analysis to contain a single
18O atom derived from dioxygen. For 11, the quality of the
available mass spectrum prevented unambiguous identification
of the label position, but the data were consistent with 18O
Administration of Labeled Precursors and Analysis. Potential
precursors were administered on sugar to M. nortoni in 250 mL
conical flasks fitted with septa. The compound was dispersed onto
30-50 mg of sugar (0.25% w/w) and placed in the conical flask.
SPME samples were taken at 10 h and after 2 days or wasp death,
and then the insect heads were crushed into pentane and analyzed
by GC-MS. [18O]Dioxygen (>99 atom % 18O) was obtained from
Isotech (Miamisburg, Ohio). M. nortoni were monitored by SPME
(10) For further discussion of the underlying arguments, see ref 6a and its
Supporting Information.
(11) The sheer size of M. nortoni prevented utilization of the protocol for
18O2 incorporation studies described in ref 9c. A partial evacuation/
refill strategy was adopted that minimized harm to the wasp and
generated an atmosphere that was an ∼4:1 18O2/16O2 mixture.
(12) Marshall, J. A.; Wang, X. J. J. Org. Chem. 1991, 56, 960.
9
J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008 14855

A R T I C L E S
Schwartz et al.
Figure 1. Mass spectrum of (E,E)-2 from M. nortoni exposed to [18O]dioxygen (• ) 18O).
Figure 2. Mass spectrum of (E,E)-2 from M. nortoni in normal air.
Scheme 1
Scheme 2
during exposure to 18O2 in a purpose-built chamber.9c After 18 h,
the insect heads were crushed into pentane and analyzed by
GC-MS. SPME analyses were conducted with a Carboxen PDMS
fiber (Supelco). Nonenantioselective GC-MS analyses were con-
ducted on a J&W Scientific DB-5MS 30 m × 0.25 mm × 0.25 µm
column with the following method: 2 min at 40 °C, a temperature
increase to 260 °C at 10 °C/min, then holding at 260 °C for 6 min
(total run time of 30 min). Enantioselective GC experiments were
conducted on a J&W Scientific CDX-B (Cyclodex-B) 30 m × 0.25
mm, 0.25 µm film column with the following temperature program:
2 min at 40 °C, increased to 200 °C at 5 °C/min and then without
delay to 240 °C at 20 °C/min, where it was held for 20 min (total
9
14856 J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008

Spiroacetal Biosynthesis in Insects
A R T I C L E S
1
run time of 56 min). All of the insect GC-MS analyses were
conducted on a VG TRIO-2000 instrument (VG Biotech, Altrin-
cham, U.K.).
Data for [2H4]-15: H NMR (500 MHz, CDCl3): δ 0.02 (br s,
6H), 0.86 (s, 9H), 0.87 (t, J ) 7.0 Hz, 3H), 1.09 (d, J ) 6.1 Hz,
3H), 1.21-1.45 (m, 10H), 3.56 (br t, 1H), 3.77 (m, 1H). 13C NMR
(125 MHz, CDCl3), mixture of diastereomers: δ -4.7 and -4.69,
-4.4, 14.1, 18.2, 21.0-22.0 (m), 22.7, 23.75 and 23.79, 25.3, 25.9
(3C), 31.9, 36.6-37.2 (m), 37.4, 39.3-39.8 (m), 68.4-68.6 (m),
71.7-71.9 (m). GC-MS EI m/z (%): 305 [M+• - 1] (0.04), 247
(1), 229 (1), 215 (0.2), 203 (0.3), 172 (0.4), 159 (7), 147 (1), 133
(2), 119 (14), 98 (15), 84 (16), 75 (100), 55 (51), 43 (53), 41 (43).
Data for unlabeled 15 (mixture of diastereomers): 1H NMR (400
MHz, CDCl3) δ 0.026 (s, 6H), 0.86 (9H), 0.87 (t, J ) 6.9 Hz, 3H),
1.10 (d, J ) 6.1 Hz, 3H), 1.24-1.50 (m, 14H), 3.54-3.60 (m,
1H), 3.73-3.80 (m, 1H). 13C NMR (100 MHz, CDCl3): δ -4.7,
-4.4, 14.0, 18.2, 21.7 and 21.9, 22.6, 23.75 and 23.80, 25.29 and
25.31, 25.9 (3C), 31.90 and 31.91, 37.4, 37.45 and 37.55, 39.6 and
39.7, 68.5 and 68.6, 71.9 and 72.0. Anal. Calcd for C17H38O2Si: C,
67.48; H, 12.66. Found: C, 67.50; H, 12.52.
[3,3,4,4-2H4]-2-Undecanone ([2H4]-4) and [3,3,4,4-2H4]-2-Un-
decanol ([2H4]-5). Palladium catalyst (10% on carbon) was added
to a solution of undec-3-yn-2-ol12 (12) (200 mg, 1.20 mmol) in
EtOAc (10 mL) and left to stir under a deuterium atmosphere. After
3 h, the reaction was diluted with ether and filtered through Celite.
The solution was concentrated in vacuo and purified by flash
chromatography on silica gel (1:5 EtOAc/hexane), furnishing [2H4]-
4 (86 mg, 41%) and [2H4]-5 (78 mg, 37%) as colorless oils. The
13C NMR spectra clearly showed that there were no residual
unlabeled methylenes at either C3 or C4 (see the Supporting
Information), although a significant amount of monodeuteration
occurred at C3 and C4.
1
Data for [2H4]-4: H NMR (500 MHz, CDCl3): δ 0.86 (t, J )
6.7 Hz, 3H), 1.24 (m, 12H), 1.51-1.56 (m, 1H, from scattered
reduction), 2.11 (s, 3H), 2.40-2.41 (m, 1H, from scattered
reduction). 13C NMR (125 MHz, CDCl3): δ 14.1, 22.6, 22.9-23.8
(m), 28.9-29.0 (m), 29.2, 29.3-29.4 (m), 29.4, 29.8, 31.8,
43.1-43.4 (m), 209.5 (m). GC-MS EI m/z (%): 174 [M+•] (6),
159 (2), 143 (1), 131 (1), 114 (4), 99 (3), 86 (9), 74 (27), 60 (91),
43 (100).
[4,4,5,5-2H4]-2,6-Undecanediol ([2H4]-11). Alcohol [2H4]-15
(550 mg, 1.80 mmol) was dissolved in 6:2:2 (v/v) AcOH/THF/
H2O (10 mL) and heated at 50 °C for 12 h. The solution was
concentrated in vacuo, and the residue was purified by flash
chromatography (1:1 EtOAc/hexane) to give [2H4]-11 (302 mg,
87%) as a colorless paste.
1
Data for [2H4]-5: H NMR (500 MHz, CDCl3): δ 0.86 (t, J )
1
Data for [2H4]-11: H NMR (400 MHz, CDCl3): δ 0.83 (t, J )
7.1 Hz, 3H), 1.15 (d, J ) 6.2 Hz, 3H), 1.18-1.29 (m, 12 H),
1.34-1.43 (m, 1.96H, OH and 1H from scattered reduction), 3.76
(quintet, J ) 6.1 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 14.0,
22.7, 23.3-23.4 (m), 24.4-25.7 (m, COCD2CD2), 28.2-29.6 (m,
4C), 31.9, 38.0-39.3 (m, COHCD2), [67.96 (s, COHCD2), 68.0
6.9 Hz, 3H), 1.12 (d, J ) 6.2 Hz, 3H), 1.18-1.45 (m, 10H), 2.68
(br s, 2H), 3.51-3.52 (br m, 1H), 3.70-3.77 (m, 1H). 13C NMR
(100 MHz, CDCl3), mixture of diastereomers: δ 13.9, 20.5-21.6
(m), 22.5, 23.3 and 23.4, 25.3, 31.8, 36.0-37.1 (m), 37.3 and 37.4
(br), 38.6-40.0 (m), 67.4 and 67.7 (br), 71.3-71.6 (m). GC/MS
EI m/z (%): 192 [M+•] (0.03), 175 (0.1), 174 (0.1), 158 (0.2), 145
(1), 129 (1), 119 (1), 101 (19), 83 (45), 72 (13), 55 (53), 45 (74),
43 (100), 41 (47).
(s, COHCDH), 68.1 (s, COHCH2)]. GC-MS EI m/z (%): 176 [M+•
]
(2), 158 (1), 145 (0.4), 133 (1), 114 (3), 101 (2), 88 (6), 75 (14),
62 (79), 43 (100).
1
2-(tert-Butyldimethylsilyloxy)undec-4-yn-6-ol (14). tert-Bu-
tyldimethyl(pent-4-yn-2-yloxy)silane13 (13) (5.80 g, 29.2 mmol)
was cooled to -20 °C (EtOH/H2O/CO2) in THF (25 mL) under
N2, and then methyllithium (20.9 mL, 29.2 mmol, 1.4 M in Et2O)
was added dropwise. The solution was allowed to stir at -20 °C
for 30 min, and then hexanal (2.92 g, 29.2 mmol) in THF (25 mL)
was added over 5 min. After 2 h, the mixture was poured onto
ice-cold aqueous NH4Cl, and the resulting mixture was extracted
into ether (3 × 50 mL). The organic layers were combined, washed
with brine (30 mL), and dried (MgSO4). The ethereal solution was
concentrated in vacuo, and the residue was purified by flash
chromatography (eluting with 1:10 EtOAc/hexane) to yield alkynol
Data for unlabeled 11: H NMR (400 MHz, CDCl3): δ 0.85 (t,
J ) 7.2 Hz, 3H), 1.14 (d, J ) 6.4 Hz, 3H), 1.20-1.32 (m, 5H),
1.33-1.48 (m, 9H), 2.24 (br s, 2H), 3.50-3.58 (m, 1H), 3.71-3.80
(m, 1H). 13C NMR (100 MHz, CDCl3), mixture of diastereomers:
δ 14.0, 21.6 and 21.8, 22.6, 23.4 and 23.5, 25.4, 31.9, 37.0 and
37.2, 37.4 and 37.6, 39.0 and 39.1, 67.7 and 67.9, 71.6 and 71.7.
GC/MS EI m/z (%): 171 [M+• - 17] (0.1), 170 (0.2), 155 (0.4),
145 (1), 127 (1), 117 (2), 99 (21), 83 (17), 81 (46), 70 (18), 57
(37), 55 (82), 45 (46), 43 (100), 41 (62).
2-(tert-Butyldimethylsilyloxy)-6-(tert-butyldiphenylsilylox-
y)undec-4-yne (16). To a solution of 14 (1.53 g, 5.13 mmol) in
CH3CN (30 mL) was added TBDPSCl (1.64 g, 5.98 mmol) followed
by portionwise addition of imidazole (610 mg, 9.0 mmol). The
reaction mixture was allowed to stir under a nitrogen atmosphere
overnight and then concentrated in vacuo. The residue was then
suspended in hexane (50 mL) and stirred vigorously for 5 min.
The mixture was filtered and concentrated in vacuo, and the
resulting oil was purified by flash chromatography (1:30 EtOAc/
1
14 (7.40 g, 85%) as a colorless oil. H NMR (400 MHz, CDCl3):
δ 0.038 (s, 3H), 0.046 (s, 3H), 0.86 (br s, 12H), 1.20 (d, J ) 5.9
Hz, 3H), 1.23-1.33 (m, 4H), 1.37-1.45 (m, 2H), 1.57-1.69 (m,
2H), 1.85 (br s, OH), 2.27 (dddd, J ) 16.4, 7.1, 2.0, and 1.0 Hz,
1H), 2.35 (ddd, J ) 16.4, 5.5, and 1.9 Hz, 1H), 3.89 (m, 1H), 4.31
(ddt, J ) 12.0, 6.5, and 1.9 Hz, 1H). 13C NMR (100 MHz, CDCl3),
mixture of diastereomers: δ -4.8, -4.7, 14.0, 18.1, 22.6, 23.3, 24.9,
25.8 (3C), 29.6, 31.5, 38.1, 62.7, 67.64 and 67.65, 82.64 and 82.65,
82.82 and 82.84. GC/MS EI m/z (%): 298 [M+•] (0.03), 283 (0.1),
241 (4), 159 (49), 119 (100), 103 (11), 75 (82), 73 (64), 43 (21).
Anal. Calcd for C17H34O2Si: C, 68.39; H, 11.48. Found: C, 68.27;
H, 11.77.
1
hexane) to give 16 (2.05 g, 73%). H NMR (400 MHz, CDCl3) δ
0.030-0.042 (m, 6H), 0.85 (t, J ) 7.2 Hz, 3H), 0.86-0.88 (br s,
9H), 1.07 (br s, 9H), 1.11 (dd, J ) 7.0 and 6.1 Hz, 3H), 1.17-1.28
(m, 4H), 1.35-1.42 (m, 2H), 1.58-1.64 (m, 2H), 2.09 (dddd, J )
16.4, 8.2, 2.0, and 0.6 Hz, 1H), 2.21-2.28 (m, 1H), 3.72-3.80
(m, 1H), 4.33-4.37 (m, 1H), 7.31-7.44 (m, 6H), 7.66-7.71 (m,
2H), 7.73-7.78 (m, 2H). 13C NMR (100 MHz, CDCl3), mixture
of diastereomers: δ -4.77 and -4.74, -4.69 and -4.68, 14.0, 18.1,
19.3, 22.5, 23.15 and 23.2, 24.62 and 24.63, 25.8 (3C), 27.0 (3C),
29.6, 31.4, 38.6, 64.1, 67.70 and 67.74, 82.29 and 82.3, 83.10 and
83.12, 127.25 and 127.26, 127.5, 127.6, 129.4, 129.5, 129.6, 134.0,
134.1, 134.2 and 134.10, 135.5, 135.8, 136.0. Anal. Calcd for
C33H52O2Si2: C, 73.82; H, 9.76. Found: C, 73.82; H, 9.78.
[4,4,5,5-2H4]-2-(tert-Butyldimethylsilyloxy)undecan-6-ol ([2H4]-
15). Palladium (10 mg, 5% on BaSO4) was added to a solution of
alkyne 14 (1.50 g, 5.03 mmol) in 2-propanol (20 mL) and
triethylamine (1 mL) and left to stir under a deuterium atmosphere.
After 15 min, the mixture changed color from brown to black and
was then left to stir for 1 h, after which GC-MS analysis revealed
that reduction was complete. The suspension was filtered through
Celite, concentrated in vacuo, and purified by flash chromatography
on silica gel (1:5 EtOAc/hexane), furnishing [2H4]-15 as a colorless
oil (1.31 g, 85%).
2-(tert-Butyldimethylsilyloxy)-6-(tert-butyldiphenylsilyloxy)-
undecane (17). Palladium catalyst (10% on carbon) was added to
a solution of alkyne 16 (1.19 g, 2.22 mmol) in EtOAc (10 mL)
and TEA (1 mL) and left to stir under a hydrogen atmosphere.
After 1 h, GC-MS analysis revealed that reduction was complete,
and the suspension was filtered through a plug of Celite and
(13) Dimitriadis, C.; Gill, M.; Harte, M. F. Tetrahedron: Asymmetry 1997,
8, 2153.
(14) DattaGupta, A.; Sing, R.; Singh, V. K. Synlett 1996, 69.
9
J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008 14857

A R T I C L E S
Schwartz et al.
concentrated in vacuo. The residue was purified by flash chroma-
- 18] (13), 153 (0.4), 139 (4), 125 (1), 115 (5), 110 (11), 97 (24),
71 (97), 58 (45), 55 (44), 43 (100), 41 (44). HRMS m/z Calcd for
C11H22O2: 186.1620. Found: 186.1619.
tography (1:30 EtOAc/hexane), affording 17 (1.15 g, 95%) as a
1
colorless oil. H NMR (400 MHz, CDCl3), mixture of diastereo-
mers: δ -0.012 and -0.008 (s, 3H), -0.001 (s, 3H), 0.79 and 0.80
(t, J ) 7.1 Hz, 3H), 0.84 and 0.85 (s, 9H), 1.03 (br m, 12H),
1.05-1.42 (m, 14H), 3.60-3.72 (m, 2H), 7.31-7.41 (m, 6H),
7.62-7.68 (m, 4H). 13C NMR (100 MHz, CDCl3): δ -4.7, -4.4,
14.0, 18.2, 19.4, 21.1 and 21.2, 22.6, 23.71 and 23.74, 24.5 and
24.6, 25.9 (3C), 27.1 (3C), 31.9, 36.18 and 36.2, 36.3 and 36.5,
39.8 and 39.9, 68.6 and 68.7, 73.2 and 73.3, 127.34 (4C), 129.3
(2C), 134.8 (2C), 135.9 (4C). Anal. Calcd for C33H56O2Si2: C, 73.27;
H, 10.43. Found: C, 73.52; H, 10.57.
6-Methyl-2-pentyl-3,4-dihydro-2H-pyran (10). Preparative gas
chromatography of a portion of hydroxyketone 19 provided
dihydropyran 10 by thermal cyclization/dehydration. 1H NMR (500
MHz, C6D6): δ 0.97 (t, J ) 7.2 Hz, 3H), 1.25-1.64 (m, 9H),
1.69-1.78 (m, 1H), 1.87-1.88 (m, 3H), 1.91-1.99 (m, 1H),
2.02-2.11 (m, 1H), 3.79 (dddd, J ) 9.9, 7.2, 4.8, and 2.3 Hz, 1H),
4.56 (ttd, J ) 4.4, 2.1, and 1.1 Hz, 1H). 13C NMR (125 MHz,
C6D6): δ 14.2, 20.4, 21.0, 22.9, 25.4, 27.7, 32.2, 35.7, 75.4, 95.0,
151.2. GC/MS EI m/z (%): 168 [M+•] (15), 153 (1), 139 (4), 125
(3), 110 (11), 97 (13), 95 (7), 71 (100), 55 (30), 43 (71), 41 (35).
HRMS m/z Calcd for C11H20O: 168.1514. Found: 168.1516.
6-(tert-Butyldiphenylsilyloxy)undecan-2-ol (18). The procedure
was analogous to that of Singh et al.14 To an ice-cold solution of
protected diol 17 (1.00 g, 1.85 mmol) in MeOH (20 mL) was added
ammonium cerium(IV) nitrate (1.01 g, 1.85 mmol) in one portion.
After the solution was stirred for six hours at 0 °C, brine (35 mL)
was added to the reaction mixture, which was then extracted with
hexane (3 × 30 mL). The organic layers were combined, dried
(MgSO4), and concentrated in vacuo to give a crude oil, which
was purified on silica (1:20 to 1:10 EtOAc/hexane) to afford 18
Discussion
Spiroacetals constitute a structural class that is widely
observed in insects and are postulated to function as semio-
chemicals in the organisms in which they occur.1 However, little
is known to date about their biogenesis. Early work demon-
strated the incorporation of some simple precursors such as
acetate, citrate, and malonate into spiroacetals, presumably via
the TCA cycle.15 Subsequently, a variety of origins were
considered, including polyketide pathways,16 propionate po-
lymerization, and the involvement of oxodicarboxylic acids.15
Definition of the pathway has been provided only for the
penultimate steps in selected Dipteran (Bactrocera sp.) fruit flies:
as we have previously demonstrated,6 these insects utilize a
monooxgenase-catalyzed functionalization of an unactivated
C-H bond to produce a ketodiol equivalent that spontaneously
cyclizes to the spiroacetal. The results now presented permit
the description of a pathway from primary metabolites to
spiroacetals in the Hymenopteran wasp M. nortoni (Schemes
3 and 4).
1
(565 mg, 72%) as a colorless oil. H NMR (400 MHz, CDCl3): δ
0.81 (t, J ) 7.3 Hz, 3H), 1.04 (s, 9H), 1.08 (d, J ) 6.2 Hz, 3H),
1.11-1.27 (m, 10H), 1.37-1.44 (m, 4H), 3.59-3.67 (m, 1H), 3.70
(m, 1H), 7.31-7.42 (m, 6H), 7.64-7.68 (m, 4H). 13C NMR (100
MHz, CDCl3), mixture of diastereomers: δ 14.0, 19.4, 21.0 and
21.1, 22.6, 23.27 and 23.34, 24.6, 27.1 (3C), 31.9, 36.2 and 36.3,
36.3 and 36.4, 39.32 and 39.34, 67.95 and 68.0, 73.1 and 73.2,
127.4 (4C), 129.4 (2C), 134.68 and 134.70, 134.8, 135.9 (4C). Anal.
Calcd for C27H42O2Si: C, 76.00; H, 9.92. Found C, 76.06; H, 10.01.
6-(tert-Butyldiphenylsilyloxy)undecan-2-one. To an ice-cold
solution of 18 (550 mg, 1.3 mmol) in acetone (20 mL) was added
Jones’ reagent dropwise until the solution remained yellow.
2-Propanol (∼1 mL) was then added, and the reaction mixture was
left to stir for 30 min. The mixture was then decanted and
concentrated in vacuo to afford a residue that was purified by flash
chromatography on silica gel (1:20 EtOAc/hexane), furnishing
6-(tert-butyldiphenylsilyloxy)undecan-2-one (450 mg, 82%) as a
The first committed metabolite in the biosynthesis of the C11
spiroacetals 1 and 2 appears to be 4, which occurs naturally in
M. nortoni and is incorporated into 1 and 2 when exogenously
1
colorless oil. H NMR (400 MHz, CDCl3): δ 0.81 (t, J ) 7.3 Hz,
3H), 1.04 (s, 9H), 1.06-1.12 (m, 2H), 1.14-1.24 (m, 4H),
1.34-1.45 (m, 4H), 1.51 (quintet, J ) 7.7 Hz, 2H), 2.03 (s, 3H),
2.21 (t, J ) 7.5 Hz, 2H), 3.70 (quintet, J ) 5.6 Hz, 1H), 7.33-7.42
(m, 6H), 7.65-7.67 (m, 4H). 13C NMR (100 MHz, CDCl3): δ 14.0,
19.2, 19.4, 22.5, 24.5, 27.1 (3C), 29.7, 31.8, 35.6, 36.2, 43.7, 72.9,
127.38 (2C), 127.41 (2C), 129.4 (2C), 134.60, 134.61, 135.9 (4C),
209.0. Anal. Calcd for C27H40O2Si: C, 76.36; H, 9.49. Found: C,
76.40; H, 9.53.
2
administered in H-labeled form (Table 1). Methyl ketone 4
presumably arises from decarboxylation of a biological equiva-
lent of the C12 ꢀ-ketoacid 20 (Scheme 3), the thioester of which
would participate in primary metabolic processing of fatty acids
by ꢀ-oxidation. Such a biosynthetic origin is supported by the
co-occurrence in M. nortoni of a suite of methyl ketones
containing an odd number of carbons, with the ones observed
putatively arising from decarboxylation of C12, C14, C16, and
6-Hydroxyundecan-2-one (19). To a solution of 6-(tert-butyl-
diphenylsilyloxy)undecan-2-one (310 mg, 0.73 mmol) in THF (1
mL) was added TBAF (1.45 mL, 1.45 mmol, 1 M in THF), and
the solution was left to stir for 48 h. The reaction mixture was
diluted with CuSO4 (10 mL, 5%), transferred to a separatory funnel,
and extracted into ether (3 × 15 mL). The combined ethereal layers
were washed again with CuSO4 (15 mL, 5%) and then with brine
(15 mL), dried (Na2SO4), and concentrated in vacuo. The product
was purified on silica (1:5 EtOAc/hexane) to give a mixture of 19
and the corresponding tetrahydropyranol 2-methyl-6-pentyltetrahy-
dro-2H-pyran-2-ol (88 mg, 65%) as a colorless oil. The intercon-
verting forms (cyclic tetrahydropyranol and open-chain hydrox-
C18 fatty acid precursors. Additionally, ꢀ-oxidation incorporates
oxygen from water rather than molecular oxygen, in accord with
the observed absence of oxygen incorporation from 18O2 into
the methyl ketones and the single dioxygen-derived oxygen
in the spiroacetals of M. nortoni.
In progressing from 4 to an advanced precursor such as
21, reduction of the C2 carbonyl as well as hydroxylation
and subsequent oxidation at C6 must occur (Scheme 4). Thus,
a reasonable pathway proceeds through the (S) isomer of 5
to 11 and then to the ketoalcohol 21. Such a progression is
supported by the observation that both 5 and 11 occur
naturally in M. nortoni and that dihydropyran 3, which results
from dehydration of 14, occurs in the extracts and emitted
volatiles. Additionally, when 2H-labeled 5 and 11 were
administered via diet to M. nortoni, both were incorporated
1
yketone) resulted in complex NMR spectra. H NMR (500 MHz,
C6D6): δ 1.02 (t, open-chain, J ) 7.2 Hz, 3H), 1.02 (t, cyclic, J )
7.0 Hz, 3H) 1.15-1.82 (m), 1.41 (s, cyclic, 3H), 1.76 (s, open-
chain, 3H), 2.10 (t, J ) 7.1 Hz, 2H), 3.46 (quintet, open-chain, J
) 6.6 Hz, 1H), 3.99 (dddd, cyclic, J ) 12.0, 7.3, 5.0, and 2.2 Hz,
1H). 13C NMR (125 MHz, C6D6): δ 14.0 (2C), 19.4, 19.7, 20.7,
22.76, 22.79, 25.5, 29.0, 30.7, 31.0, 32.0, 32.1, 34.7, 36.6, 36.9,
37.7, 42.9, 69.7, 70.9, 94.9, 206.7. GC/MS EI m/z (%): 168 [M+•
(16) Vanderwel, D.; Oehlschlager, A. C. Pheromone Biochemistry; Aca-
demic Press: New York, 1987.
(15) Pomonis, J. G.; Mazomenos, B. E. Int. J. InVertebr. Reprod. DeV.
1986, 10, 169.
(17) Stok, J. E.; Lang, C.-S.; Schwartz, B. D.; Fletcher, M. T.; Kitching,
W.; De Voss, J. J. Org. Lett. 2001, 3, 397.
9
14858 J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008

Spiroacetal Biosynthesis in Insects
A R T I C L E S
Scheme 3
Scheme 4
into the spiroacetals 1 and 2 as well as into the dihydropyran
3. Also, as expected for more advanced precursors, admin-
istration of [2H4]-5 and [2H4]-11 resulted in higher levels of
2H-labeled spiroacetals than administration of [2H4]-4 (Table
1). Finally, in accord with this biosynthetic progression, the
diol 11 found in wasps after exposure to an atmosphere of
18O2 contained a single labeled oxygen atom, and the mass-
spectral characteristics of this isotopomer were consistent
with the label being located at C6.
Although 5 could be synthesized in highly enantiomerically
enriched form and the enantiomers separated by enantioselective
GC, the very low natural levels did not permit a confident direct
assignment of its absolute configuration. However, given the
apparent ubiquity of the (S) configuration at the methyl-
substituted centers of spiroacetals in both M. nortoni (see above)
and elsewhere,1,5 it is very likely that 14 occurs as the (2S)
isomer.
9
J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008 14859

A R T I C L E S
Schwartz et al.
Table 1. Comparison of Percentage Deuterium Incorporation into
(E,E)-1 and (E,E)-2 after Administration of Substrates to M.
nortonia
and (Z,Z)-2] of the molecular signature of M. nortoni are
generated from a single precursor 21, most likely in a hydroxy-
lation reaction catalyzed by a single monooxygenase. The regio-
and stereoselectivity, or lack of it, in this hydroxylation step
allows access to a range of spiroacetals, whereas the specific
ratio of the oxidation products determines the exact composition
of the emitted volatiles. For example, in M. nortoni, the ω - 1
hydroxylation that leads to 1 is not stereoselective and thus leads
to an ∼1:1 mixture of the diastereomers (E,E)-1 and (E,Z)-1,
while the ω - 2 oxidation is quite specific and leads mainly to
(E,E)-2. However, in B. cucumis, even though the same
precursor 21 is employed and processed similarly to the
spiroacetal systems 1 and 2, the emitted volatiles are quite
distinct from those of M. nortoni, having one predominant regio-
and stereochemistry of oxidation that leads mainly to (E,E)-1
and (Z,Z)-1, which account for 89% of the spiroacetal volatiles
observed.19 It is tempting to speculate further that members of
the C13 spiroacetal system 6 observed in M. nortoni are products
of the same set of biosynthetic enzymes that result from a lack
of substrate specificity of the biosynthetic machinery but further
modify the molecular signature of the insect. Proof of these
hypotheses awaits isolation and characterization of the enzymes
involved in these pathways.
Only recently, the role of a decarboxylase was proposed in
the biosynthesis of (S)-4-methyl-3-heptanone from three prop-
rionate units20 and in honeybee biosynthesis of various C10 acids
from stearic acids, with the sequence involving hydroxylation
followed by chain shortening and finally alcohol oxidation.21
Equally of interest is the variety of processing steps (probably
from fatty acids) toward this putative intermediate. The present
work describes the first cohesive and internally consistent
hypothesis for the generation of spiroacetals in insects, against
which subsequent information and interpretations will have to
be compared.
% deuteration
substrate
(E,E)-1
(E,E)-2
[2H4]-4
[2H4]-5
[2H4]-11
4
16
91
5
16
72
a Incorporation calculated by comparing the integration of the
GC-MS single-ion trace for the unlabeled spiroacetal with the sum of
the single-ion traces for the labeled spiroacetals (1-3 deuterons).
Despite the intrinsically appealing simplicity of the above
path from 4 to 1 and 2, it should be noted that dihydropyran 10
2
was also observed in M. nortoni and that it incorporated H
from labeled 4, 5, and 11 as well as an oxygen atom from
[18O]dioxygen. 10 could arise from dehydrative cyclization of
ketoalcohol 19 (Scheme 4). These results suggest the operation
of a metabolic grid in which the various compounds are
interconnected via oxidation-reduction reactions. The existence
of such transformations is supported by the present observation
of interconversion between labeled 4 and 5 fed to the wasp and
the transformation of 11 into both of the dihydropyrans 3 and
10. Determination of the metabolic flux through each of the
individual arms of the grid must await isolation of the relevant
enzymes and characterization of their substrate specificities.
Completion of spiroacetal biosynthesis requires monooxy-
genase-catalyzed hydroxylation of hydroxyketone 21 (Scheme
4) followed by spontaneous cyclization of the resultant ketodiol.
Such steps are in accord with the incorporation of a single 18
O
label from 18O2 into spiroacetal systems 1, 2, and 6 as well as
the extensive data that we have accumulated on the analogous
steps in Bactrocera sp. fruit flies.17,18 The biosynthetic origins
of the C13 spiroacetal system 6 can be similarly explained by
an analogous sequence of steps commencing with the observed
2-tridecanone. This proposed biogenesis, initiated by the de-
carboxylation of a fatty acid, nicely explains the predominance
in insects of spiroacetals with an odd number of carbon atoms.1,5
The final step proposed for spiroacetal biosynthesis, mo-
nooxygenase-mediated hydroxylation of a tetrahydropyranol, is
notable in several respects. First, it links results from two
different insect orders, Hymenoptera (bees, wasps) and Diptera
(true flies), supporting the thesis of a commonality of biosyn-
thetic origin for insect-derived spiroacetals. Second, it appears
to be a remarkable example of natural efficiency in which
considerable molecular diversity is generated in a single step.
Five different components [(E,E)-1, (E,Z)-1, (E,E)-2, (E,Z)-2,
Acknowledgment. The authors are grateful to the Australian
Research Council (ARC) for support of this work, to Stiftelsen
Bengt Lundqvist Minne for financial support to F.R., and to Dr.
Charlma Phillips (Forestry SA, Mount Gambier SA) for specimens
of M. nortoni nortoni.
Supporting Information Available: Annotated GC-MS analy-
ses of M. nortoni extracts after exposure to [18O]dioxygen,
including mass spectra of key labeled and unlabeled metabolites,
and spectral characterization of [2H4]-4, -5, -11, and 15 and
unlabeled 10, 11, 14, 15, and 19. This material is available free
of charge via the Internet at http://pubs.acs.org.
JA8036433
(18) A pathway in which hydroxylation of 2,6-undecanediol to the triol
precedes C6 oxidation is also possible and is analogous to one recently
proposed for B. oleae and B. cacuminata. However, the significant
amount of dihydropyran 3 found in M. nortoni (formed via dehydrative
cyclization of 21) suggests that 21 is a bona fide intermediate.
(19) Kitching, W.; Lewis, J. A.; Perkins, M. V.; Drew, R.; Moore, C. J.;
Schurig, V.; Konig, W. A.; Francke, W. J. Org. Chem. 1989, 54, 3893.
(20) (a) Jarvis, A. P.; Liebig, J.; Ho¨lldobler, B.; Olaham, N. J. Chem.
Commun. 2004, 1196. Also see: (b) Islam, W.; Bacala, R.; Moore,
A.; Vanderwel, D. Insect Biochem. Mol. Biol. 1999, 29, 201.
(21) Plettner, E.; Slessor, K. N.; Winston, M. L.; Oliver, J. E. Science 1996,
271, 1851.
9
14860 J. AM. CHEM. SOC. VOL. 130, NO. 44, 2008