Revisiting the Chemistry of Guaiacwood Oil: Identification and Formation Pathways of 5,11- and 10,11-Epoxyguaianes

Article abstract of DOI:10.1021/acs.jnatprod.6b01068

Guaiacwood oil from Bulnesia sarmientoi Lorentz ex. Griseb is a common natural ingredient of the perfume industry used in both domestic and luxury fragrances for its highly appreciated woody-rosy odor, as well as its excellent fixative properties. Despite its long and traditional use as a perfume ingredient, guaiacwood oil has not been extensively studied. Thus, the chemical characterization of its constituents by using a full array of GC-hyphenated techniques (GC-MS, GC × GC-MS, and pc-GC) combined with conventional chemical fractionation was undertaken. In the course of this work, 15 new sesquiterpenoids mostly belonging to the 5,11- and 10,11-epoxyguaiane families were identified. Each isolated compound was fully characterized by NMR and MS. Collectively, the specific chemical relationships observed between sesquiterpene oxides and alcohols permitted the formulation of probable formation pathways regarding their presence as natural constituents of guaiacwood extracts.

Full text of DOI:10.1021/acs.jnatprod.6b01068

Article
pubs.acs.org/jnp
Revisiting the Chemistry of Guaiacwood Oil: Identification and
Formation Pathways of 5,11- and 10,11-Epoxyguaianes
Loïc Tissandie,† Marc Gaysinski,† Hugues Brevard,‡ Uwe J. Meierhenrich,† and Jean-Jacques Filippi*,†
́
́
†Institut de Chimie de Nice, Universite
́
Co
̂
te d’Azur, UMR 7272 CNRS, Parc Valrose, 06108 Nice Cedex 2, France
‡Robertet S.A., 37 Avenue Sidi Brahim, 06130 Grasse, France
S
* Supporting Information
ABSTRACT: Guaiacwood oil from Bulnesia sarmientoi Lorentz ex.
Griseb is a common natural ingredient of the perfume industry used in
both domestic and luxury fragrances for its highly appreciated woody-
rosy odor, as well as its excellent fixative properties. Despite its long
and traditional use as a perfume ingredient, guaiacwood oil has not
been extensively studied. Thus, the chemical characterization of its
constituents by using a full array of GC-hyphenated techniques (GC-
MS, GC × GC-MS, and pc-GC) combined with conventional chemical
fractionation was undertaken. In the course of this work, 15 new
sesquiterpenoids mostly belonging to the 5,11- and 10,11-epox-
yguaiane families were identified. Each isolated compound was fully
characterized by NMR and MS. Collectively, the specific chemical
relationships observed between sesquiterpene oxides and alcohols
permitted the formulation of probable formation pathways regarding their presence as natural constituents of guaiacwood
extracts.
stomachaches and rheumatism, or might even simply burn it as
mong the natural sesquiterpenes, the guaiane skeleton is
Aprobably one of the most widespread basic structures. an incense to purify the ambient atmosphere and repel pest
insects.8 Matter-of-factly, the forest exploitation of guaiacwood
Guaiol 1, a bicyclic tertiary alcohol, was one of the very first
has historically been linked with the perfume industry since
guaiacwood oil is usually prepared as a byproduct of the timber
industry by steam distillation of sawdust and crushed leftovers.
The extraction yields a yellow-to-greenish viscous essential oil
that solidifies upon a few weeks of storage at room
temperature.9 As a perfume ingredient, guaiacwood oil is
described as possessing a delicate but tenacious woody odor,
with distinct notes reminiscent of rose and violet.10 It thus
blends particularly well in rose-type compositions, where it is
mainly used as a bottom note as well as an excellent fixative.
However, because of an increasing demand in wood mainly
coming from the Asian market, and also because of the
problematic deforestation linked with intensive farming in Latin
America,11−14 B. sarmientoi is now considered an endangered
species and appears in the CITES-Appendix II in order to
regulate its worldwide trade.15,16
Natural wood oils are among the most esteemed ingredients
of the perfumer’s palette. This family includes renowned
substances such as oils of sandalwood, cedarwood, and
agarwood, which can sometimes be regarded as fragrances on
their own. Interestingly, these oils are in most cases largely
dominated by sesquiterpene constituents. Among them,
guaiacwood oil offers a very specific chemical composition,
guaianes identified in nature, since it could be readily separated
from guaiacwood oil.1 As a result, the generic guaiane name was
given to a whole family of sesquiterpenes sharing the same basic
7-isopropyl-1,4-dimethyldecahydroazulenic skeleton. Indeed,
both analytical chemistry and organic synthesis have evolved
since these early studies, so that the guaiane family now
encompasses several hundreds of members, either synthesized
or, more likely, identified in natural extracts. Thus, compounds
such as guaianolides have been described to display significant
biological activities,2,3 while others find specific applications in
flavors and fragrances.4−6 Although guaianes have attracted the
interest of many scientists worldwide, guaiacwood oilthe
original matrix for which they have been all namedhas never
really benefited from an in-depth chemical analysis based upon
current analytical chemistry methodology.
Traditionally, guaiacwood oil is obtained from the wood of
Bulnesia sarmientoi Lorentz ex. Griseb, an endemic tree from
Latin America, specifically found in the Gran Chaco region
shared by Argentina, Bolivia, Brazil, and Paraguay. The tree,
locally known as Palo Santo (i.e., holy mast/tree; this trivial
name might be a source of confusion since it also refers to
Bursera graveolens), provides a hard, compact, and quasi rot-
resistant wood that is mainly used in parquetry and cattle
fences, but also in various handicrafts. Since this wood is
particularly rich in resin,7 the local population also uses it as a
folk medicine to heal and prevent various diseases, such as
Received: November 17, 2016
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
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mostly consisting of tertiary alcohols distributed within two
biosynthetically linked families of sesquiterpenes: the guaianes
and the eudesmanes. Indeed, the two main constituents of
guaiacwood oil were early characterized as the isomeric alcohols
guaiol (1) and bulnesol (2), representing more than 70% (w/
w) of the oil.17 However, in light of recent studies, guaiacwood
oil has been reported to display a somewhat unexpectedbut
yet intriguingmolecular complexity linked with the presence
of several unknown sesquiterpene oxides and alcohols.18 In the
course of the studies on natural fragrant substances, we thus
undertook an in-depth analytical investigation of guaiacwood
oil by using an integrated analytical methodology combining
conventional fractionation methods with highly separative
chromatographic techniques. Herein, the identification of
several new guaiane oxides as natural constituents of guaiac-
wood oil is reported. In addition, the likely chemical pathways
toward these compounds via the main sesquiterpene alcohols
are discussed.
Scheme 1. Sesquiterpenes and Sesquiterpenoids 1−12
Commonly Identified in Guaiacwood Oil; Compounds 13−
15 Are Described for the First Time in Guaiacwood Oil
RESULTS AND DISCUSSION
■
Chemical Composition of Guaiacwood Oil. As
commonly observed with woody essential oils such as
sandalwood oil,19,20 vetiver oil,21,22 and patchouli oil,23−25
guaiacwood oil is almost exclusively composed of sesquiterpene
derivatives where oxygenated compounds bearing tertiary
hydroxy and oxide functionalities constitute the major part of
the oil. In concordance with previous data,17,18,26,27 the two
main constituents in our sample were guaiol (1) and bulnesol
(2), respectively accounting for 29.2% and 40.1% of the oil (w/
w). Several sesquiterpene alcohols possessing the eudesmane
skeleton were detected, including α-eudesmol (3), β-eudesmol
(4), γ-eudesmol (5), 10-epi-γ-eudesmol (6), and β-elemol (7).
Common guaiane sesquiterpenes such as α-guaiene (8), α-
bulnesene (9), and β-bulnesene (10) were also identified
(Scheme 1). Interestingly, a rather limited number of
sesquiterpene oxides such as guaioxide (11)26 and hanamyol
(12)28 could be directly identified in the sample. However,
conventional GC-MS analyses performed with both polar and
apolar stationary phases did not allow the proper determination
of all minor but visible constituents (S/N > 10) since a high
extent of coelution was observed in parts of the chromatogram
where major sesquiterpenes and alcohols eluted. Thus, we
opted for GC × GC-MS analysis, which is particularly adapted
for the analysis of complex essential oils.21 Providing both
higher resolution and sensibility than conventional gas
chromatography, GC × GC-MS dramatically improved the
detection of minor compounds. While the chemical composi-
tion of guaiacwood oil did not appear as highly complex at first
glance (Figure 1A), it revealed a much more intricate nature
when analyzed by GC × GC-MS (Figure 1B). Thus, over 250
compounds (S/N > 10) were detected in the sample.
Particularly interesting was the fact that a rather large series
of unknown constituents could tentatively be assigned as
sesquiterpene oxides (RI VF-5ms 1400−1600) and tertiary
alcohols (RI VF-5ms 1650−1700). In 2011, Rodilla and co-
workers demonstrated the occurrence of these sesquiterpene
oxides when analyzing guaiacwood oil by GC × GC-MS.18
Hanamyol (12), previously identified in Alpinia japonica,28 was
the only compound isolated and fully characterized in their
sample. Eighteen additional constituents were tentatively
reported as sesquiterpenoid oxides and alcohols solely on the
basis of their MS properties.
In this study, more than 15 constituents displaying m/z =
220 and m/z = 222 M+• ions were observed to elute among the
sesquiterpenes of guaiacwood oil (RI HP5 1400−1600). A first
step in the identification of these sesquiterpene oxides was
achieved when exploring the 2D plot by means of specific ion
extracts (Figure 2). The presence of guaioxide (11), trans-(13),
and 4-epi-trans-dihydroagarofuran (14) and that of a
sesquiterpene oxide 16, initially identified as kessane, was
assessed upon extraction of the 207 m/z ion trace from the
total ion current chromatogram (TIC; Figure 2A and B). These
two dihydroagarofurans together with α-agarofuran (15) were
established for the first time as constituents of guaiacwood oil.
The latter products were tentatively identified on the basis of
(a) their mass spectra and (b) their retention indices;
nevertheless, their identification as trans-dihydroagarofuran
(13) and 4-epi-trans-dihydroagarofuran (14) was later con-
firmed by 13C NMR spectroscopy. Their presence was further
corroborated by considering their formation by cyclization of
10-epi-γ-eudesmol (6), also present in the sample. Compound
16 showed a mass spectrum and a retention index on apolar
stationary phase highly similar to those of kessane. However,
the retention index on polar stationary phase differed
significantly. Kessane displayed a retention index (RI) on
wax-type phase of 1779,29 while compound 16 displayed an RI
of 1733 in our sample. The difference was sufficient to confirm
that 16 was an isomer of kessane. This identification was
further confirmed by comparison of their respective 13C NMR
shifts after isolating 16 by preparative capillary gas chromatog-
raphy (pc-GC).
B
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Figure 1. (A) GC-MS analysis of guaiacwood oil depicting the major sesquiterpenes and (B) GC × GC-MS analysis of the same sample.
Sesquiterpene oxides appear as yellow blobs, whereas epoxy alcohols such as 12 and 22 are displayed in pale red. Dashed-line frames named here
TIC 1 and TIC 2 are used in Figure 2 to display expansions of the 2D chromatogram using ion extract traces.
The selective extraction of other ion traces from distinct
areas of the TIC provided useful clues for the correct location
of specific compounds on the 2D plot (Figure 2). This was
particularly the case for sesquiterpene oxides, for which the
most decisive information was obtained when extracting the
220 m/z ion trace (Figure 2C). Hence, a rather large series of
peaks could be detected, indicating the presence of several
additional sesquiterpenic oxides. In addition to hanamyol (12),
several epoxy alcohols were also detected in guaiacwood oil
when exploring the 238 M+• ion trace (Figure 2F). Since most
of these compounds could not be identified solely on the basis
of their MS data, the raw oil was fractionated to attempt their
isolation.
Fractionation and Isolation of Essential Oil Constitu-
ents. Guaiacwood oil was first chromatographed on standard
silica gel by using solvents of increasing polarity, to afford eight
fractions (F1−F8) (Figure 3). Fraction F2 contained most of
the sesquiterpene oxides in addition to guaiol (1). F2 was
further separated into several subfractions by repeated column
chromatography on AgNO3-impregnated silica gel (5% w/w).
Compounds 1, 2, 12, and 22 were isolated with sufficient purity
for NMR spectroscopic analysis. The subfractions, when
sufficiently enriched with one or a few unknown constituents,
were eventually pooled together in order to be used in pc-GC
for isolation of the target compounds. In total, 17 constituents
present at 0.1% to 0.9% in our initial oil sample were isolated
and fully characterized by NMR data analysis (Supporting
Information). The isolated compounds were distributed within
two families of guaiane oxides, either bearing the 5,11-epoxy
moiety as in guaioxide (11) (compounds 17−22 and 30) or
branched in the 10,11-position identical to hanamyol (12)
(compounds 16 and 23−27). Additional constituents were also
identified such as β-kessane (28)30 and the new 4,5;5,11-
diepoxy-seco-guaiane (29). A full description of their 13C NMR
data is given in Tables 1 and 2.
The two series of compounds were usually distinguishable by
the 13C NMR chemical shifts of the atoms involved in the oxide
moiety. The 5,11-epoxyguaianes showed chemical shifts above
90 ppm for the bridgehead C-5 and up to 110 ppm for the
diepoxide (29), while the 10,11-epoxyguaianes displayed
chemical shifts above 70 ppm for the bridgehead C-10. On
the basis of the observed 13C NMR shifts, compound 28 was
identified as β-kessane, previously isolated from Rubus rosifolius
Sm.30 However, in view of the known configuration of guaianes
identified in guaiacwood oil, particularly regarding C-4 and C-7,
28 probably corresponds to the enantiomer of the reported
compound, but no further confirmation could be obtained. As
mentioned above, compound 16 had a mass spectrum similar
to kessane, without matching the reported RI values on a polar
stationary phase. Compound 16 was isolated by pc-GC and
fully characterized using NMR data. 13C NMR shifts observed
for 16 did not correspond to the values reported for kessane29
or isokessane,30 i.e., 1-epi-kessane, the only natural epimer of
kessane. Analysis of the NOESY spectrum permitted
C
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Figure 2. TIC 1 and TIC 2 correspond to dashed-line frames depicted in Figure 1B, respectively, as (A) the elution area of low-polarity compounds
and (D) the elution area of more polar constituents. (B) Ion extract at 207 m/z from TIC 1 showing the saturated sesquiterpene oxides in
guaiacwood oil such as guaioxide 11. (C) Ion extract at 220 m/z from TIC 1 showing the series of unsaturated sesquiterpene oxides in guaiacwood
oil. (E) Ion extract at 222 m/z from TIC 2 showing the main unsaturated sesquiterpene alcohols in guaiacwood oil. (F) Ion extract at 238 m/z from
TIC 2 showing the saturated epoxyguaianols in guaiacwood oil such as hanamyol 12. A selection of EI-mass spectra for the main sesquiterpene
oxides identified in this study is presented on the bottom part of the figure.
identification of 16 as 4,5-di-epi-kessane (a comparison of the
13C NMR data for the three isomers is shown in the Supporting
resembled the literature data32 (−26.6 in EtOH) and thus
confirmed the absolute configuration of guaiol (1).
In addition to dihydroagarofurans 13 and 14, it should be
noted that compounds 16−27, 29, and 30 have not been
described in guaiacwood oil or other natural sources. However,
a few epoxyguaianes have been described as synthesized
Information).
Although examination of the NOESY data in most cases
permitted assignment of the relative configuration for
compounds 16−30, their absolute configurations could be
deduced only from that of guaiol (1) or bulnesol (2). It should
be noted that the absolute configuration of C-7 is established
early in the biogenetic pathway involving the cyclization of
farnesyl diphosphate into germacrene(s).31 Thus, 1 was isolated
from guaiacwood oil and repeatedly purified to give a white
solid with a GC purity of >99%. Attempts at X-ray
crystallographic data acquisition failed and did not lead to the
establishment of its absolute configuration. However, the
products such as 17, 18, and 22. All have been obtained in
33,34
low yields either from oxidation of 1 with Pb(OAc)4
or by
photooxygenation.35 Additionally, compound 30 was synthe-
sized by Brønsted and Lewis acid treatment of guaiol α-
epoxide.36,37 Several diastereoisomers of the epoxyguaianes
identified here were also synthesized and used as intermediates
for the preparation of liguloxide, an epimer of guaioxide, such
as 4-epi-18 and 4-epi-19.38,39
In addition to the presence of guaiane alcohols and epoxy
alcohols such as 12, 22, and 30, compounds 11, 17, 18, 23, and
isolated product gave [α]25 −22 (CH2Cl2; c 10 g/L), which
D
D
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Figure 3. Experimental chart depicting the systematic fractionation/isolation of guaiacwood oil constituents. The methodology combines the use of
column chromatographyusing either conventional or AgNO3-impregnated silica geland preparative capillary-gas chromatography (pc-GC) for
the final isolation of 5,11- and 10,11-epoxyguaianes.
Table 1. 13C NMR Chemical Shifts for Guaioxide (11) and Structurally Related Guaiane Oxides 17−22, 29, and 30 Isolated
from Guaiacwood Oil
a
b
a
a
b
a
a
b
b
C no.
11
17
18
19
20
21
22
29
30
1
55.89 (CH)
28.94 (CH2)
31.59 (CH2)
46.17 (CH)
91.72 (C)
143.03 (C)
29.49 (CH2)
31.96 (CH2)
44.28 (CH)
90.30 (C)
153.79 (C)
124.00 (C)
38.24 (CH2)
42.64 (CH)
93.60 (C)
56.16 (CH)
27.06 (CH2)
29.69 (CH2)
40.84 (CH)
90.64 (C)
57.11 (CH)
24.85 (CH2)
30.35 (CH2)
40.98 (CH)
92.08 (C)
59.61 (CH)
35.37 (CH2)
124.93 (C)
144.08 (C)
95.69 (C)
82.41 (C)
47.80 (CH)
30.27 (CH2)
33.24 (CH2)
69.17 (CH)
109.60 (C)
38.37 (CH2)
45.58 (CH)
31.35 (CH2)
33.74 (CH2)
38.34 (CH)
82.19 (C)
85.90 (C)
2
36.10 (CH2)
30.74 (CH2)
45.28 (CH)
91.96 (C)
31.17 (CH2)
29.46 (CH2)
37.95(CH)
94.88 (C)
3
4
5
6
41.21 (CH2)
45.28 (CH)
30.52 (CH2)
34.18 (CH2)
37.56 (CH)
81.67 (C)
40.38 (CH2)
45.53 (CH)
28.35 (CH2)
32.70 (CH2)
127.20 (C)
81.97 (C)
38.43 (CH2)
45.20 (CH)
31.51 (CH2)
33.88 (CH2)
33.42 (CH)
81.93 (C)
37.89 (CH2)
44.09 (CH)
32.92 (CH2)
121.66 (C)
134.34 (C)
81.84 (C)
33.77 (CH2)
44.31 (CH)
27.44 (CH2)
34.35 (CH2)
149.37 (C)
82.57 (C)
34.31 (CH2)
45.42 (CH)
30.54 (CH2)
34.48 (CH2)
36.77 (CH)
81.76 (C)
42.64 (CH2)
45.03 (CH)
28.77(CH2)
29.43 (CH2)
39.79 (CH)
83.97 (C)
31.13 (CH2)
44.27 (CH)
28.78 (CH2)
29.42 (CH2)
42.58 (CH)
82.53 (C)
7
8
9
10
11
12
13
14
15
30.57 (CH3)
23.33 (CH3)
23.47 (CH3)
16.29 (CH3)
31.51 (CH3)
24.68 (CH3)
23.23 (CH3)
13.50 (CH3)
31.24 (CH3)
23.73 (CH3)
20.61 (CH3)
13.35 (CH3)
30.58 (CH3)
24.43 (CH3)
25.72 (CH3)
13.89 (CH3)
31.78 (CH3)
26.16 (CH3)
111.33 (C)
13.98 (CH3)
31.44 (CH3)
23.30 (CH3)
22.85 (CH3)
12.34 (CH3)
30.74 (CH3)
23.09 (CH3)
18.97 (CH3)
16.51 (CH3)
29.17 (CH3)
22.80 (CH3)
22.70 (CH3)
22.70 (CH3)
31.50 (CH3)
23.43 (CH3)
18.32 (CH3)
15.04 (CH3)
a
b
Recorded in CDCl3. Recorded in benzene-d6.
24 were also identified in the wood oil of Neocallitropsis
pancheri, proving that these compounds are not artifacts. This
observation prompted an investigation into their possible
formation pathways.
Formation of Sesquiterpene Oxides in Guaiacwood
Oil. Guaioxide (11) was previously shown to form upon the
acid-mediated cyclization of guaiol (1).26 Thus, several
sesquiterpene oxides identified herein may be related to the
transformation of precursors present in guaiacwood oil. In
order to propose formation pathways based on their occurrence
in the oil, the chemistry of these oxides was investigated by
means of simple transformations from readily available guaiane
sesquiterpenols. Guaiol (1) was transformed by cyclization into
guaioxide (11) under mild acidic conditions using either
montmorillonite K10 or p-TsOH as catalyst (Scheme 2),
confirming the relationship of 11 and 1.26,34,40 Several
E
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Table 2. 13C NMR Chemical Shifts for Hanamyol (12) and Structurally Related Guaiane Oxides 16 and 23−28 Isolated from
Guaiacwood Oil
a
a
a
b
b
b
b
a
C no.
12
16
23
24
25
26
27
28
1
90.85 (C)
56.40 (CH)
23.31 (CH2)
30.24 (CH2)
38.42 (CH)
40.33 (CH)
25.78 (CH2)
37.14 (CH)
19.43 (CH2)
31.76 (CH2)
73.16 (C)
151.75 (C)
121.91 (C)
40.48 (CH2)
34.50 (CH)
44.90 (CH)
27.67 (CH2)
37.46 (CH)
20.01 (CH2)
31.93 (CH2)
70.62 (C)
142.92 (C)
33.12 (CH2)
31.86 (CH2)
44.20 (CH)
139.00 (C)
34.70 (CH2)
36.94 (CH)
23.22 (CH2)
35.67 (CH2)
71.17 (C)
57.66 (CH)
25.16 (CH2)
31.09 (CH2)
36.18(CH)
148.89 (C)
122.66 (C)
38.02 (CH)
25.39 (CH2)
34.11 (CH2)
72.85 (C)
59.75 (CH)
28.40 (CH2)
36.61 (CH2)
133.22 (C)
134.75 (C)
34.56 (CH2)
36.23 (CH)
24.36 (CH2)
34.51 (CH2)
73.82 (C)
153.30 (C)
126.28 (C)
40.06 (CH2)
36.12 (CH)
153.47 (C)
122.60 (C)
39.71 (CH)
25.05 (CH2)
32.93 (CH2)
72.16 (C)
50.73 (CH)
27.10 (CH2)
33.44 (CH2)
37.47 (CH)
38.68 (CH)
28.31 (CH2)
84.03 (C)
2
32.50 (CH2)
29.70 (CH2)
35.57 (CH)
48.04 (CH)
24.61 (CH2)
36.57 (CH)
19.38 (CH2)
26.33 (CH2)
75.81 (C)
3
4
5
6
7
8
37.45 (CH2)
30.79 (CH2)
80.99 (C)
9
10
11
12
13
14
15
73.78 (C)
73.73 (C)
74.49 (C)
74.31 (C)
76.60 (C)
74.07 (C)
77.03 (C)
36.53 (CH)
17.53 (CH3)
17.48 (CH3)
29.38 (CH3)
14.86 (CH3)
29.29 (CH3)
29.47 (CH3)
26.85 (CH3)
15.24 (CH3)
29.48 (CH3)
30.27 (CH3)
31.11 (CH3)
15.57 (CH3)
29.57 (CH3)
30.91 (CH3)
28.60 (CH3)
16.41 (CH3)
29.92 (CH3)
30.98 (CH3)
28.77 (CH3)
19.55 (CH3)
30.35 (CH3)
29.71 (CH3)
29.92 (CH3)
18.94 (CH3)
29.18 (CH3)
31.05 (CH3)
28.84 (CH3)
14.27 (CH3)
30.17 (CH3)
30.14 (CH3)
28.78 (CH3)
22.23(CH3)
a
b
Recorded in CDCl3. Recorded in benzene-d6.
Scheme 2. Preparation of Epoxyguaianols 12 and 30 (MW 238 g/mol) from Epoxides of Guaiol (1) and Bulnesol (2) and Their
a
Subsequent Dehydration into 5,11- and 10,11-Epoxyguaienes
a
Reagents and conditions: (a) m-CPBA, CH2Cl2, RT, 5 min; (b) AlCl3, THF, RT, 2 h; (c) sealed tube, 200 °C, 1.5 h; (d) activated montmorillonite
K10, CH2Cl2, RT, 30 min; and (e) p-TSOH, CH2Cl2, RT, 3 h.
approaches and conditions, e.g., Pb(OAc)4, (photo)oxidation,
and Clayfen/μ-waves, toward the direct formation of C15H24O
oxides (MW 220 g/mol) from 1 were tested. None afforded the
target compounds in significant amounts. Hence, the
occurrence of most of the M+ 220 m/z epoxyguaianes identified
in guaiacwood oil could not be explained by simple cyclization
F
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from an alcohol precursor or by dehydrogenation of a C15H26O
oxide precursor (MW 222 g/mol). Thus, the direct formation
of these compounds from 1 or 2 is not likely to occur.
However, a dehydration of a hydroxylated oxide precursor
C15H26O2 (238 g/mol) such as 12 is indeed highly probable
during hydrodistillation. Thus, 5,11-epoxyguaienes 17 and 18
are likely to form by dehydration of 22 and 30. Hanamyol (12)
would similarly serve as the precursor to the corresponding
10,11-epoxyguaienes 23 and 24.
Compounds 12 and 30 were thus synthesized in two steps
from bulnesol (2) and guaiol (1), respectively (Scheme 2).
When reacted with m-chloroperoxybenzoic acid (m-CPBA),
each alcohol provided a mixture of two epoxides, 31a and 31b,
for guaiol37 and 32a and 32b for bulnesol, which were
separated on silica gel. Subsequently, each epoxide was
subjected to an AlCl3-mediated cyclization involving the
opening of the oxirane moiety by the tertiary hydroxy group
to form the corresponding epoxyguaian-1-ol. Only the α-
positioned epoxides 31a and 32a, respectively, led to the target
products 30 and 12, while 31b and 32b failed to give the
expected epoxyguaianols.
In conclusion, using a combination of conventional
fractionation methods with preparative gas chromatography,
several new constituents from guaiacwood oil, mostly belonging
to the 5,11- and 10,11-epoxyguaiane families, were isolated and
identified. Despite their low abundances, these compounds
were unambiguously detected by comprehensive two-dimen-
sional gas chromatography, ensuring these compounds were
not artifacts. Their presence in guaiacwood oil led to the
formulation of hypotheses related to their probable formation
pathways. Some of the epoxyguaianes were synthesized and
subjected to different chemical transformations in order to
validate the hypotheses. Thus, a clear structural relationship
between several epoxyguaianols and their oxide counterparts
was established. Moreover, it was shown that the 5,11- and
10,11-epoxyguaianes were also present in other natural extracts
such as N. pancheri oil (candlewood oil), indicating that they
might probably be common to several essential oils and extracts
where guaiane tertiary alcohols are present. In addition, the
chemistry described for the guaiane family might apply to other
common sesquiterpene families. These results may help to
rejuvenate research on guaiacwood, a fascinating but somewhat
forgotten natural substance.
To assess the validity of the aforementioned hypotheses,
hanamyol (12) was subjected to different conditions aimed at
the formation of sesquiterpene oxides. Surprisingly, treatment
of 12 with either montmorillonite K10 or BF3·Et2O did not
lead to the formation of the expected compounds. However,
when 12 was kept at 200 °C for 1.5 h in a sealed glass vial,
sesquiterpene oxides 23 and 24 were detected as main
products, accompanied by small amounts of 25 and 26
(Supporting Information). Compound 30 was subjected to
thermal degradation and afforded the expected 5,11-epox-
yguaianes 17 and 18, along with 24 probably arising from 17.
Surprisingly, 1β-hydroguaioxide 22 isolated from the oil did not
yield any 5,11-epoxyguaianes when heated at 200 °C. Instead,
22 showed a rather high thermal stability, giving almost no
trace of decomposition. This higher stability is probably due to
the hydrogen bond present between the epoxide bridge and the
tertiary hydroxy group, as seen in the 1H NMR spectrum of 22
recorded in CDCl3 (Supporting Information). Other sesqui-
terpene oxides present in guaiacwood oil such as 20 or 25
might form by isomerization of the olefinic bond of the major
epoxyguaienes 17, 18, 23, and 24.
These experiments permitted the comprehension of the
formation pathways leading to these sesquiterpene oxides in
guaiacwood oil. It also permitted assessment of the presence of
most of these compounds in the wood oil of Neocallitropis
pancheri. Sesquiterpene oxides corresponding to C15H26O
(MW 222 g/mol) such as guaioxide (11) are assumed to
originate from the acid-mediated cyclization of their parent
tertiary alcohols. This process is likely to occur in the plant
itself, but part of it could also take place during hydro-
distillation. The 5,11- and 10,11-epoxyguaianes (MW 220 g/
mol; C15H24O) originate from the dehydration of a parent
epoxyguaianol (MW 238 g/mol; C15H26O2), and this trans-
formation might probably occur during the extraction of the
essential oil. Surprisingly, no 1,11-epoxyguaiane could so far be
detected in guaiacwood oil. It is likely that epoxyguaianols such
as 12, 22, and 30 would concentrate in the resinous wood via a
probable enzymatic epoxidation of the most abundant
precursors, namely, guaiol (1) and bulnesol (2). Future
investigations performed on guaiacwood itself might give a
clue in this sense and indicate whether our assumptions are
valid.
EXPERIMENTAL SECTION
■
Extracts and Chemicals. Guaiacwood essential oil from Paraguay
was obtained from Robertet S.A. (Grasse, France). AgNO3 (analytical
grade), Pb(OAc)4, BF3·Et2O, AlCl3, m-CPBA, CH2Cl2, tert-butyl
methyl ether (MTBE), Et2O, petroleum ether, benzene-d6 (99.6% D),
and CDCl3 (99.8% D) were purchased from Sigma−Aldrich (Saint-
Quentin-Fallavier, France). Montmorillonite K10 was obtained from
Fluka. p-TsOH was obtained from Acros (Illkirch, France). Organic
solvents were distilled at atmospheric pressure prior to use in column
chromatography. THF was dried and distilled over Na-benzophenone
prior to use in organic synthesis.
Fractionation of Guaiacwood Oil. The oil (25.36 g, solid at RT,
greenish-yellow color) was fractionated by open column chromatog-
raphy using 600 g of silica gel (40/60 μm) and solvents of increasing
polarities. The hydrocarbon fraction (F1; 0.78 g) was eluted with
100% petroleum ether. F2 (95:5; v/v; petroleum ether/Et2O; 1.51 g)
contained mostly sesquiterpene oxides and guaiol (1). The following
fractions contained mostly sesquiterpene alcohols (F3 to F8; 90:10 to
50:50; petroleum ether/Et2O; 22.96 g). All fractions were analyzed by
GC-MS and GC × GC-MS. F2 (1.51 g) was further separated on
AgNO3-impregnated silica gel (5% w/w) into three subfractions (F2.1
to F2.3) using the solvent gradient system described above (petroleum
ether/Et2O, 98:2 to 90:10). F2.1 (579 mg) and F2.2 (57.4 mg) had
the highest content of unknown sesquiterpene oxides and were
rechromatographed over AgNO3-impregnated silica gel (5% w/w) to
give compounds 18 and 22. Other significant subfractions were pooled
for use in pc-GC. A fractionation scheme is given in Figure 3.
Preparative Capillary Gas Chromatography (pc-GC). pc-GC
was performed using an Agilent 6890 Plus gas chromatograph coupled
to a Gerstel preparative fraction collector (PFC) operated under
Chemstation Rev A.10.02/Gerstel Maestro 1.3.8.14. The GC was
equipped with a Supelcowax megabore capillary column (Supelco,
Saint Quentin-Fallavier, France; 30 m × 0.53 mm; 0.5 μm film thick).
A Graphpack effluent splitter was connected to the column outlet and
additionally mounted with 0.1 mm and 0.32 mm deactivated fused-
silica capillary restrictors (1 m each) to provide an FID/PFC ratio of
∼1:9. The transfer line and the PFC were maintained at 230 °C. The
oven temperature was ramped from 100 to 230 °C at 8 °C/min, unless
the temperature program was adapted to the analytes’ volatility and/or
the requirements of their separation. The system was operated in
constant pressure mode at 35 kPa. Compounds were trapped at room
temperature (22 °C) in Gerstel U-type glass tubes by programming
cutting times into the operating software allowing accurate automated
operation. Typically, the isolation of any unknown compound in
G
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Journal of Natural Products
Article
amounts sufficient for NMR analysis required 150−400 GC runs,
provided that this analyte was sufficiently concentrated in the
analytical sample (at least 20% w/w; 40−60 mg of sample/mg of
MTBE), and to avoid all contaminations, the product collection is
done directly in a NMR tube.
shifts (δ) are expressed in parts per million (ppm), and coupling
constants (J) in hertz. All NMR experiments were performed using
pulse sequences supplied by the spectrometer manufacturer (Bruker
TopSpin 2.1) and processed via Mestrelab MestreNOVA software
(version 6.0.2-5475).
Gas Chromatography and Gas Chromatography−Mass
Spectrometry (GC-FID and GC-MS). Routine GC analyses were
performed using an Agilent 6890A gas chromatograph equipped with a
flame ionization detector and mounted with either a Restek Rtx-5 (10
m × 0.18 mm; 0.2 mm film thick) or a J&W Innowax (25 m × 0.20
mm; 0.4 μm 0.1 mm film thick). The chromatograph was operated
under a constant hydrogen flow of 0.8 mL/min. The GC oven
temperature was programmed from 120 to 250 °C and increased at 10
°C/min. Injection volume 0.2 μL; split ratio 1:20 to 1:50; inlet
temperature 250 °C; detector temperature 250 °C. GC-MS analyses
were performed using two different Agilent 6890N/5973N systems
mounted with either a ChromPack VF-5ms (30 m × 0.25 mm; 0.5 μm
film thick) or a ChromaPack CP-52 Carbowax-type capillary column
HP-1 (50 m × 0.20 mm; 0.33 μm film thick). Sample concentration,
injection volume, and column flow were the same as indicated for GC
× GC-MS analysis. Split ratio was 1:100. The oven temperature was
generally programed from 80 to 250 °C at 2 °C/min (4.5 min final
isotherm). Other temperature programs are given in the Supporting
Information.
Guaiol [(4αH,7αH,10αH)-guai-1(5)-en-11-ol] (1): RI (VF-5ms/
1
wax) 1609/2083; [α]25 −22 (c 1, CH2Cl2); H NMR (500 MHz,
D
CDCl3) δ 2.54 (1H, qd, J = 6.5, 1.6 Hz, H-4), 2.47−2.39 (1H, m, H-
2a), 2.33−2.26 (1H, m, H-10), 2.14 (1H, d, J = 15.7 Hz, H-6a), 2.12−
2.08 (1H, m, H-2b), 2.01−1.87 (2H, m, H-3a,H6b), 1.85−1.78 (1H,
m, H-8a), 1.75−1.67 (1H, m, H-9a), 1.61−1.51 (2H, m, H-9b,H-7),
1.49−1.41 (1H, m, H-8b), 1.33−1.25 (1H, m, H-3b), 1.19 (3H, s, H-
12), 1.16 (3H, s, H-13), 0.99 (3H, d, J = 7.2 Hz, H-14), 0.95 (3H, d, J
= 6.9 Hz, H-15); 13C NMR (126 MHz, CDCl3) δ 140.21, 139.04,
73.70, 49.78, 46.45, 35.53, 33.92, 33.84, 31.09, 28.02, 27.55, 27.47,
26.13, 20.08, 19.91; EIMS in agreement with literature data.42
Bulnesol [(4αH,5αH,7αH)-guai-1(10)-en-11-ol] (2): RI (VF-5ms/
wax) 1675/2198; [α]25 +2 (c 1, CH2Cl2); 1H NMR (500 MHz,
D
CDCl3) δ 2.39 (1H, t, J = 9,2 Hz, H-5), 2.35−2.27 (1H, m, H-2a),
2.22−2.03 (4H, m, H-2b, H-4, H-9a, H-9b), 1.93−1.87 (1H, m, H-8a),
1.86−1.82 (1H, m, H-6a), 1.71−1.60 (4H, m, H-14, H-3a), 1.46−1.33
(2H, m, H-7, H-3b), 1.17 (6H, s, H-12, H-13), 1.10−1.00 (1H, m, H-
8b), 0.90 (3H, d, J = 7.1 Hz, H-15), 0.79 (1H, q, J = 11.8 Hz, H-6b);
13C NMR (126 MHz, CDCl3) δ 141.81, 128.99, 73.93, 54.23, 46.39,
Comprehensive Two-Dimensional Gas Chromatography−
Mass Spectrometry. GC × GC-MS was performed using an Agilent
6890N/5973N GC−MS system equipped with a GC × GC ZOEX kit
(cryogenic dual-stage jet-loop modulator and a secondary oven
installed in the main GC oven). The two-dimensional GC column set
was composed of a ChromPack VF-5ms (30 m × 0.25 mm; 0.2 μm
film thick; referred to as column 1) and a J&W DB-Wax (1.25 m ×
0.10 mm; 0.1 μm film thick; referred to as column 2) both connected
to a deactivated fused silica capillary tube (1.25 m × 0.10 mm)
installed as a loop passing twice through the jets in the cryogenic
modulator. Column flow (He) 0.7 mL/min; split ratio 1:50.
Temperature program for oven #1: 60 to 140 °C at 10 °C/min,
140 to 188 °C at 1 °C/min, 188 to 200 °C at 2 °C/min, then 200 to
250 °C at 20 °C/min (4.5 min final isotherm). Temperature program
for oven #2: 50 to 140 °C at 10 °C/min, 140 to 150 °C at 1.25 °C/
min, 150 to 250 °C at 3 °C/min. Modulation period PM 5.5 s; hot jet
temperature 295 °C; hot pulse duration 350 ms. The mass
spectrometer was operated at 70 eV in fast scan mode (10 000
amu/s) over a 50−250 m/z range, giving a 24.67 Hz acquisition rate.
Comprehensive two-dimensional chromatograms were processed with
GC-Image 1.9b6 (ZOEX Corp. Ltd.), allowing the integration of
chromatographic peaks upon their volume (3D-shape). Guaiacwood
oil constituents were identified upon cross-correlation of their
retention indices calculated from a series of n-alkanes, and their
mass spectra matched against commercial libraries (Wiley275,
NIST08) or in-house MS databases built from literature informa-
tion41,42 and isolated or synthesized substances whenever possible.
Gas Chromatography−High-Resolution Mass Spectrometry
(GC-HRMS). High-resolution EI-mass spectra were recorded using an
Agilent 7200 GC-QTOF system equipped with a J&W DB1 capillary
column (30 m × 0.25 mm; 0.25 μm film thick). The mass
spectrometer was operated at 70 eV with an acquisition rate of 2
GHz over a 35−450 m/z range, affording a resolution of ∼8000
around 218−220 m/z. Injection volume 1 μL; split ratio 1:20; inlet
temperature 250 °C, detector temperature 230 °C; column flow (He)
1.2 mL/min; temperature program for oven 60 °C (5 min isotherm)
to 230 °C at 5 °C/min (5 min final isotherm).
39.13, 34.97, 33.15, 30.46, 28.83, 27.84, 27.34, 27.26, 22.46, 15.47;
EIMS in agreement with literature data.42
Guaioxide [(1βH,4αH,5β,7αH,10αH)-5,11-epoxyguaiane] (11). To
a stirred solution of guaiol 1 (111.5 mg, 0.50 mmol) in CH2Cl2 (2
mL) was added montmorillonite K10 (223 mg, 2 equiv w/w). After 1
h, the mixture was filtrated through cotton wool and concentrated in
vacuo. The residue was subsequently chromatographed on silica gel
(petroleum ether/Et2O, 98:2) to give 11 (80.3 mg, 72%); RI (VF-
5ms/wax) 1496/1679; 1H NMR (500 MHz, CDCl3) δ 2.00−1.93
(2H, m, H-6a, H-6b), 1.93−1.81 (3H, m, H-7, H-2a, H-8a), 1.78−1.65
(3H, m, H-9a, H-4, H-3a), 1.44 (2H, m, H-1, H-10), 1.41 (1H, dd, J =
8.5, 2.5 Hz, H-9b), 1.35 (1H, dt, J = 13.9, 3.9 Hz, H-8b), 1.31 (3H, s,
H-13), 1.28−1.20 (1H, m, H-3b), 1.16 (3H, s, H-12), 0.98 (3H, d, J =
6.9 Hz, H-15), 0.96−0.92 (1H, m, H-2b), 0.90 (3H, d, J = 6.2 Hz, H-
14); 13C NMR (126 MHz, CDCl3) δ 91.72, 81.67, 55.89, 46.17, 45.28,
41.21, 37.56, 34.18, 31.59, 30.57, 30.52, 28.94, 23.47, 23.33, 16.29;
EIMS m/z 222 [M]+ (5), 207 (100), 189 (41), 164 (11), 149 (28),
137 (28), 125 (11), 123 (11), 109 (26), 107 (17), 95 (22), 81 (25), 79
(10), 69 (17), 67 (12), 55 (23), 43 (16), 41 (20); HREIMS m/z
222.1977 (calcd for C15H26O, 222.1978).
Hanamyol [(1α,4αH,5αH,7αH,10β)-10,11-epoxyguaian-1α-ol]
(12). To a stirred solution of AlCl3 (25.3 mg, 0.19 mmol) in dry
THF (1 mL) under N2 was added dropwise a solution of 32a (37.5
mg, 0.16 mmol) in dry THF (1.5 mL). After stirring at RT for 2.5 h,
the reaction was quenched by slowly adding a saturated NaHCO3
solution (0.5 mL). After 15 min of stirring, the mixture was extracted
with Et2O (3 × 10 mL). The combined organic layers were washed
with brine (5 mL), dried over anhydrous MgSO4, and filtered. The
filtrate was concentrated in vacuo, and the residue purified by silica gel
column chromatography (petroleum ether/Et2O, 85:15) to give 12
(26.5 mg, 71%); RI (VF-5ms/wax) 1679/2215; [α]25 −17 (c 1,
D
1
CH2Cl2); H NMR (500 MHz, CDCl3) δ 2.64−2.54 (1H, m, H-4),
2.51−2.43 (1H, m, H-2a), 2.11−2.03 (1H, m, H-9a), 1.97−1.90 (1H,
m, H-8a), 1.90−1.79 (2H, m, H-3a, H-5), 1.71−1.65 (2H, m, H-7, H-
8b), 1.65−1.59 (1H, m, H-9b), 1.53 (1H, t, J = 13.6 Hz, H-6a), 1.44
(1H, t, J = 7.5 Hz, H-6b), 1.41−1.30 (2H, m, H-3b, H-2b), 1.29 (3H,
s, H-13), 1.19 (3H, s, H-12), 1.10 (3H, s, H-14), 0.95 (3H, d, J = 7.0
Hz, H-15); 13C NMR (126 MHz, CDCl3) δ 90.85, 75.81, 73.78, 48.04,
36.57, 35.57, 32.50, 29.70, 29.47, 29.29, 26.85, 26.33, 24.6, 19.38,
15.24; EIMS m/z 238 [M]+ (12), 220 (7), 205 (15), 177 (24), 153
(15), 126 (24), 111 (100), 109 (16), 97 (21), 69 (25), 55 (28), 43
(60), 41 (31); HREIMS m/z 238.1909 (calcd for C15H26O2,
238.1927).
1D and 2D NMR. NMR spectra were recorded in CDCl3 or in
benzene-d6 at 298 K (BCU05-BVT 3000) on a Bruker AVANCE I
1
DRX 500 spectrometer operating at 500.13 MHz for H and 125.75
MHz for 13C. In order to increase sensitivity, broadband 13C NMR
spectra were acquired with a direct probe head (5 mm PADUL
13C−1H Z-GRD). 1D and 2D NMR spectra such as 1H, COSY,
TOCSY, NOESY, HSQC, and HMBC were run with an inverse probe
trans- (13) and 4-Epi-trans-dihydroagarofuran (14) (isolated as
a mixture). 13: RI (VF-5ms/wax) 1517/1702; 13C NMR (126 MHz,
CDCl3) δ 87.98, 81.12, 44.69, 40.50, 38.66, 38.48, 38.15, 37.56, 30.68,
1
head (5 mm PHTXI H−13C/15N Z-GRD). Spectrum calibration was
performed by using the solvent signal as internal reference.43 Chemical
H
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Journal of Natural Products
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29.53, 25.10, 23.70, 23.00, 17.90, 17.03, in good agreement with NMR
data described in ref 44; EIMS m/z 222 [M]+ (8), 208 (15), 207
(100), 189 (31), 179 (6), 164 (13), 149 (27), 137 (55), 123 (15), 109
(33), 95 (18), 81 (16), 69 (18), 55 (19), 43 (16), 41 (19).
1), 1.85−1.71 (4H, m, H-3a, H-4, H-8a, H-7), 1.61−1.53 (1H, m, H-
2b), 1.50 (1H, d, J = 12.7 Hz, H-6b), 1.49−1.41 (2H, m, H-3b, H-8b),
1.22 (3H, s, H-13), 1.11 (3H, s, H-12), 1.03 (3H, d, J = 6.5 Hz, H-15);
13C NMR (126 MHz, C6D6) δ 149.37, 111.33, 92.08, 82.57, 57.11,
44.31, 40.98, 34.35, 33.77, 31.78, 30.35, 27.44, 26.16, 24.85, 13.98;
EIMS m/z 220 [M]+ (100), 205 (48), 192 (26), 191 (24), 187 (17),
177 (74), 159 (24), 149 (42), 147 (32), 135 (26), 123 (37), 109 (30),
107 (46), 105 (29), 93 (35), 91 (37), 81 (36), 79 (40), 77 (22), 69
(24), 67 (25), 55 (29), 43 (31), 41 (42); HREIMS m/z 220.1813
(calcd for C15H24O, 220.1822).
14: RI (VF-5ms/wax) 1522/1707; 13C NMR (126 MHz, CDCl3) δ
87.49, 81.20, 43.90, 38.77, 38.20, 38.20, 36.21, 32.27, 32.27, 30.38,
25.17, 23.63, 23.11, 21.49, 15.84, in good agreement with NMR data
described in ref 44; EIMS m/z 222 [M]+ (8), 208 (15), 207 (100),
189 (31), 179 (6), 164 (13), 149 (27), 137 (55), 123 (15), 109 (33),
95 (18), 81 (16), 69 (18), 55 (19), 43 (16), 41 (19).
4,5-Di-epi-kessane [(1αH,4αH,5αH,7αH,10β)-10,11-epoxy-
(1βH,5β,7αH,10αH)-5,11-Epoxyguai-3-ene (21): RI (VF-5ms/wax)
1
1
guaiane] (16): RI (VF-5ms/wax) 1533/1733 ; H NMR (500 MHz,
1552/1798; H NMR (500 MHz, CDCl3) δ 5.38 (1H, dt, J = 2.9, 1.3
CDCl3) δ 2.08−2.01 (1H, m, H-5), 2.00−1.91 (3H, m, H-4, H-1, H-
8a), 1.88−1.80 (2H, m, H-2a, H-9a), 1.74−1.71 (2H, m, H-9b, H-8b),
1.71−1.67 (1H, m, H-3a), 1.67−1.62 (1H, m, H-7), 1.62−1.57 (2H,
m, H-6a, H-2b), 1.45−1.38 (1H, m, H-6b), 1.32−1.29 (1H, m, H-3b),
1.27 (3H, s, H-13), 1.22 (3H, s, H-12), 1.04 (3H, s, H-14), 0.91 (3H,
d, J = 6.7 Hz, H-15); 13C NMR (126 MHz, CDCl3) δ 73.73, 73.16,
56.40, 40.33, 38.42, 37.14, 31.76, 31.11, 30.27, 30.24, 29.48, 25.78,
23.31, 19.43, 15.57; EIMS m/z 222 [M]+ (7), 207 (10), 189 (9), 161
(12), 149 (24), 126 (100), 121 (20), 109 (34), 108 (72), 107 (23), 97
(12), 95 (23), 93 (24), 83 (19), 82 (32), 81 (43), 71 (16), 69 (19), 67
(21), 55 (21), 43 (42), 41 (21); HREIMS m/z 222.1977 (calcd for
C15H26O, 222.1978).
Hz, H-3), 2.39−2.32 (1H, m, H-2a), 2.08 (1H, ddd, J = 12.8, 6.9, 1.8
Hz, H-6a), 2.01−1.98 (1H, m, H-7), 1.92−1.85 (1H, m, H-8a), 1.80
(1H, d, J = 12.8 Hz, H-6b), 1.77−1.70 (2H, m, H-9a, H-1), 1.67 (3H,
q, J = 2.1 Hz, H-15), 1.67−1.63 (1H, m, H-2b), 1.62−1.57 (1H, m, H-
10), 1.50−1.42 (2H, m, H-9b, H-8b), 1.33 (3H, s, H-13), 1.22 (3H, s,
H-12), 0.90 (3H, d, J = 6.5 Hz, H-14); 13C NMR (126 MHz, CDCl3)
δ 144.08, 124.93, 95.69, 81.76, 59.61, 45.42, 36.77, 35.37, 34.48, 34.31,
31.44, 30.54, 23.30, 22.85, 12.34; EIMS m/z 220 [M]+ (3), 206 (18),
205 (100), 187 (9), 162 (10), 147 (19), 133 (12), 123 (17), 119 (10),
109 (11), 105 (16), 96 (10), 95 (9), 94 (17), 93 (8), 91 (14), 79 (7),
55 (6), 43 (8), 41 (7); HREIMS m/z 220.1814 (calcd for C15H24O,
220.1822).
(4αH,5β,7αH)-5,11-Epoxyguai-1(10)-ene (17): RI (VF-5ms/wax)
(1β,4αH,5β,7αH,10αH)-5,11-Epoxyguaian-1β-ol (22): RI (VF-
1
1
1541/1790; H NMR (500 MHz, C6D6) δ 2.54−2.45 (1H, m, H-9a),
5ms/wax) 1656/1985; H NMR (500 MHz, CDCl3) δ 3.41 (1H, s,
2.39 (1H, dd, J = 16.1, 7.9 Hz, H-2a), 2.13 (1H, ddd, J = 12.1, 6.5, 1.5
Hz, H-6a), 2.10−2.00 (2H, m, H-2b, H-9b), 1.88−1.79 (2H, m, H-7,
H-8a), 1.70 (1H, d, J = 12.3 Hz, H-6b), 1.71−1.63 (2H, m, H-4, H-
3a), 1.61 (1H, dt, J = 8.0, 1.4 Hz, H-3b), 1.58 (3H, d, J = 0.8 Hz, H-
14), 1.57−1.50 (1H, m, H-8b), 1.33 (3H, s, H-13), 1.16 (3H, s, H-12),
1.14 (3H, d, J = 6.5 Hz, H-15); 13C NMR (126 MHz, C6D6) δ 143.03,
127.20, 90.30, 81.97, 45.53, 44.28, 40.38, 32.70, 31.96, 31.51, 29.49,
28.35, 24.68, 23.23, 13.50; EIMS m/z 220 [M]+ (16), 205 (25), 187
(33), 162 (92), 159 (100), 149 (23), 147 (50), 145 (29), 119 (34),
107 (19), 105 (62), 93 (17), 91 (33), 79 (17), 55 (15), 43 (22), 41
(22); HREIMS m/z 220.1826 (calcd for C15H24O, 220.1822).
O−H), 2.13−2.04 (2H, m, H-6a, H-6b), 1.95−1.90 (1H, m, H-7),
1.89 (1H, ddd, J = 13.0, 6.5, 1.9 Hz, H-2a), 1.86−1.81 (1H, m, H-4),
1.79−1.73 (1H, m, H-9a), 1.72−1.62 (2H, m, H-10, H-3a), 1.53−1.46
(1H, m, H-3b), 1.44−1.36 (1H, m, H-8a), 1.34 (3H, s, H-13), 1.27−
1.15 (3H, m, H-8b, H-2b, H-9b), 1.21 (3H, s, H-12), 0.97 (3H, d, J =
7.1 Hz, H-15), 0.92 (3H, d, J = 6,7 Hz, H-14); 13C NMR (126 MHz,
CDCl3) δ 91.96, 83.97, 82.41, 45.28, 45.03, 42.64, 39.79, 36.10, 31.29,
30.74, 29.77, 29.43, 23.09, 18.97, 16.51; EIMS m/z 238 [M]+ (46),
223 (77), 220 (50), 205 (100), 196 (17), 187 (30), 182 (40), 162
(39), 159 (45), 153 (45), 139 (76), 125 (40), 123 (41), 114 (50), 109
(60), 95 (46), 85 (61), 72 (50), 69 (61), 55 (72), 43 (63), 41 (65);
HREIMS m/z 238.1902 (calcd for C15H26O2, 238.1927).
(4αH,5β,7αH,10αH)-5,11-Epoxyguai-1-ene (18): RI (VF-5ms/
1
wax) 1560/1851; H NMR (500 MHz, CDCl3) δ 5.47 (1H, q, J =
(4αH,5αH,7αH,10β)-10,11-Epoxyguai-1-ene (23): RI (VF-5ms/
1
2.2 Hz, H-2), 2.30 (1H, ddd, J = 12.8, 6.3, 2.2 Hz, H-6a), 2.29−2.25
(1H, m, H-10), 2.23−2.15 (1H, m, H-3a), 2.13 (1H, ddd, J = 8.5, 3.7,
1.8 Hz, H-3b), 2.04−1.94 (3H, m, H-4, H-8a, H-7), 1.83 (1H, dt, J =
14.5, 2.8 Hz, H-9b), 1.78 (1H, d, J = 12.8 Hz, H-6b), 1.54−1.48 (2H,
m, H-9b, H-8b), 1.32 (3H, s, H-13), 1.17 (3H, s, H-12), 1.12 (3H, d, J
= 6.6 Hz, H-14), 1.07 (3H, d, J = 6.9 Hz, H-15); 13C NMR (126 MHz,
CDCl3) δ 153.79, 124.00, 93.60, 81.93, 45.20, 42.64, 38.43, 38.24,
33.88, 33.42, 31.51, 31.24, 23.73, 20.61, 13.35; EIMS m/z 220 [M]+
(83), 205 (100), 187 (17), 177 (15), 163 (28), 159 (14), 147 (43),
133 (12), 124 (18), 119 (22), 109 (17), 105 (43), 95 (13), 93 (19), 91
(32), 81 (13), 79 (16), 77 (17), 69 (13), 55 (21), 43 (29); HREIMS
m/z 220.1800 (calcd for C15H24O, 220.1822).
wax) 1536/1787; H NMR (500 MHz, CDCl3) δ 5.47 (1H, q, J =
2.2 Hz, H-2), 2.91−2.80 (1H, m, H-5), 2.53−2.46 (1H, m, H-3b),
2.48−2.40 (2H, m, H-4), 2.13−2.01 (1H, m, H-8b), 1.96−1.83 (2H,
m, H3a, H-6b), 1.71 (4H, m, H-7, H-9a, H-9b, H-8a), 1.49−1.40 (1H,
dt, J = 13.9, 7.1 Hz, H-6a), 1.30 (3H, s, H-14), 1.27 (3H, s, H-13), 1.14
(3H, s, H-12), 0.97 (3H, d, J = 7.0 Hz, H-15); 13C NMR (126 MHz,
CDCl3) δ 151.75, 121.91, 74.49, 70.62, 44.90, 40.48, 37.46, 34.50,
31.93, 30.91, 29.57, 28.60, 27.67, 20.01, 16.41; EIMS m/z 220 [M]+
(22), 205 (64), 192 (39), 187 (21), 177 (15), 162 (52), 159 (20), 149
(28), 147 (43), 136 (48), 134 (36), 124 (47), 123 (58), 121 (100),
119 (36), 105 (51), 93 (49), 91 (45), 81 (31), 79 (27), 77 (26), 69
(23), 55 (15), 43 (45); HREIMS m/z 220.1809 (calcd for C15H24O,
220.1822).
(4αH,7αH,10β)-10,11-Epoxyguai-1(5)-ene (24): RI (VF-5ms/wax)
1494/1710; 1H NMR (500 MHz, C6D6) δ 2.70−2.62 (1H, dt, J = 18.1,
2.5 Hz, H-6a), 2.49−2.40 (2H, m, H-4, H-2a), 2.10−2.00 (2H, m, H-
2b, H-8a), 1.99−1.92 (1H, m, H-3a), 1.84−1.74 (3H, m, H-6b, H-9a,
H-9b), 1.59−1.49 (2H, m, H-8b, H-7), 1.37−1.33 (1H, m, H-3b), 1.32
(6H, s, H-12, H-13), 1.27 (3H, s, H-14), 1.02 (3H, d, J = 6.8 Hz, H-
15); 13C NMR (126 MHz, C6D6) δ 142.92, 139.00, 74.31, 71.17,
44.20, 36.94, 35.67, 34.70, 33.12, 31.86, 30.98, 29.92, 28.77, 23.22,
19.55; EIMS m/z 220 [M]+ (72), 205 (99), 191 (9), 177 (82), 163
(15), 159 (10), 149 (100), 138 (45), 135 (20), 123 (18), 121 (19),
119 (17), 109 (18), 107 (17), 105 (27), 95 (16), 91 (27), 79 (13), 77
(14), 69 (9), 55 (9), 43 (25); HREIMS m/z 220.1833 (calcd for
C15H24O, 220.1822).
(1αH,4αH,5β,7αH)-5,11-Epoxyguai-9-ene (19): RI (VF-5ms/wax)
1
1543/1785; H NMR (500 MHz, CDCl3) δ 5.32 (1H, m, H-9), 2.47
(1H, ddd, J = 12.3, 7.2, 1.7 Hz, H-6a), 2.39−2.30 (1H, m, H-8a),
2.23−2.17 (1H, m, H-1), 2.17−2.10 (1H, m, H-8b), 1.97 (1H, dt, J =
7.3, 3.8 Hz, H-7), 1.95−1.88 (1H, m, H-4), 1.87−1.77 (2H, m, H-3a,
H-2a), 1.67 (3H, td, J = 2.5, 1.2 Hz, H-14), 1.64−1.60 (1H, m, H-2b),
1.60−1.57 (1H, m, H-6b), 1.40−1.34 (1H, m, H-3b), 1.24 (3H, s, H-
13), 1.17 (3H, s, H-12), 0.96 (3H, d, J = 6.6 Hz, H-15); 13C NMR
(126 MHz, CDCl3) δ 134.34, 121.66, 90.64, 81.84, 56.16, 44.09, 40.84,
37.89, 32.92, 30.58, 29.69, 27.06, 25.72, 24.43, 13.89; EIMS m/z 220
[M]+ (61), 205 (15), 202 (20), 187 (15), 177 (5), 163 (11), 159 (16),
150 (65), 137 (100), 124 (19), 123 (18), 109 (27), 107 (19), 105
(23), 95 (16), 93 (17), 91 (23), 81 (40), 79 (22), 69 (13), 55 (14), 41
(25); HREIMS m/z 220.1796 (calcd for C15H24O, 220.1822).
(1αH,4αH,5β,7αH)-5,11-Epoxyguai-10(14)-ene (20): RI (VF-5ms/
wax) 1550/1805; 1H NMR (500 MHz, C6D6) δ 4.92−4.90 (1H, m, H-
14a), 4.89 (1H, t, J = 2.1 Hz, H-14b), 2.28 (1H, ddd, J = 13.2, 6.4, 1.8
Hz, H-9a), 2.07 (1H, dd, J = 12.8, 7.5 Hz, H-6a), 2.03 (1H, dd, J =
11.7, 6.6 Hz, H-2a), 1.98−1.90 (1H, m, H-9b), 1.90−1.85 (1H, m, H-
(1αH,4αH,7αH,10β)-10,11-Epoxyguai-5-ene (25): RI (VF-5ms/
wax) 1499/1712; H NMR (500 MHz, C6D6) δ 5.58 (1H, dt, J =
8.5, 2.3 Hz, H-6), 2.43−2.33 (1H, m, H-4), 2.31−2.25 (1H, m, H-1),
2.02−1.94 (1H, m, H-8a), 1.93−1.86 (2H, m, H-8b, H-9a) 1.82−1.74
(3H, m, H-2a, H-7, H-3a), 1.64−1.56 (1H, m, H-9b), 1.52 (1H, ddd, J
1
I
DOI: 10.1021/acs.jnatprod.6b01068
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
= 9.4, 6.1, 2.6 Hz, H-2b), 1.27 (3H, s, H-13), 1.26 (3H, s, H-12),
1.22−1.16 (1H, m, H-3b), 1.13 (3H, s, H-14), 1.07 (3H, d, J = 6.7 Hz,
H-15); 13C NMR (126 MHz, C6D6) δ 148.89, 122.66, 76.60, 72.85,
57.66, 38.02, 36.18, 34.11, 31.09, 30.35, 29.92, 29.71, 25.39, 25.16,
18.94; EIMS m/z 220 [M]+ (16), 202 (14), 187 (10), 177 (16), 162
(79), 159 (8), 149 (26), 147 (100), 133 (23), 121 (26), 120 (35), 119
(36), 107 (27), 105 (65), 95 (15), 93 (23), 91 (48), 81 (15), 79 (20),
77 (17), 67 (8), 55 (12), 43 (30); HREIMS m/z 220.1821 (calcd for
C15H24O, 220.1822).
by slowly adding a saturated NaHCO3 solution (0.5 mL). After 15 min
of stirring, the mixture was extracted with Et2O (3 × 10 mL). The
combined organic layers were washed with brine (5 mL), dried over
anhydrous MgSO4, and filtered. The filtrate was concentrated in vacuo,
and the residue purified by silica gel column chromatography
(petroleum ether/Et2O, 90:10) to give 30 (17.7 mg, 76%): RI (VF-
5ms/wax) 1715/2205; 1H NMR (500 MHz, C6D6) δ 2.50−2.39 (1H,
m, H-4), 2.05 (1H, ddd, J = 12.6, 11.5, 6.9 Hz, H-2a), 1.98 (1H, dd, J =
13.2, 6.1 Hz, H-6a), 1.90 (1H, d, J = 13.1 Hz, H-6b), 1.88−1.83 (1H,
m, H-3a), 1.82−1.73 (2H, m, H-8a, H-9a), 1.64 (1H, td, J = 5.7, 3.0
Hz, H-7), 1.61−1.51 (2H, m, H-10, H9b), 1.47−1.37 (1H, m, H-3b),
1.31−1.26 (1H, m, H-8b), 1.26 (3H, s, H-13), 1.15 (1H, ddd, J = 12.7,
9.0, 2.6 Hz, H-2b), 1.07 (3H, s, H-12), 1.04 (3H, d, J = 6.4 Hz, H-15),
1.03 (3H, d, J = 6.6 Hz, H-14); 13C NMR (126 MHz, C6D6) δ 94.88,
85.90, 82.53, 44.27, 42.58, 37.95, 31.50, 31.17, 31.13, 29.46, 29.42,
28.78, 23.43, 18.32, 15.04; EIMS m/z 238 [M]+ (15), 223 (25), 220
(68), 205 (100), 187 (33), 182 (17), 177 (20), 163 (32), 162 (51),
159 (66), 147 (46), 139 (42), 109 (49), 105 (55), 95 (37), 91 (40), 85
(37), 81 (33), 69 (46), 55 (56), 43 (55), 41 (51); HREIMS m/z
238.1947 (calcd for C15H26O2, 238.1927).
(1α,4αH,5α,7αH,10αH)-1,5-Epoxyguaian-11-ol (31a) and
(1β,4αH,5β,7αH,10αH)-1,5-epoxyguaian-11-ol (31b). To a stirred
solution of 1 (54 mg, 0.24 mmol) in CH2Cl2 (1 mL) at RT was added
dropwise a solution of m-CPBA (77%, 65 mg, 0.29 mmol) in CH2Cl2
(1 mL). After 10 min of stirring, the reaction was washed with
saturated NaHCO3 solution. The mixture was extracted with Et2O (3
× 10 mL). The combined organic layers were washed with brine (10
mL), dried over anhydrous MgSO4, and filtered. The filtrate was
concentrated in vacuo, and the residue purified by silica gel CC
(petroleum ether/Et2O, 80:20) to give 31a (25 mg, 43%) and 31b
(30.1 mg, 52%).
(1αH,7αH,10β)-10,11-Epoxyguai-4-ene (26): RI (VF-5ms/wax)
1
1535/1777; H NMR (500 MHz, C6D6) δ 2.81 (1H, dd, J = 16.5,
4.5 Hz, H-6a), 2.59−2.50 (1H, m, H-1), 2.18−2.10 (1H, m, H-3a),
2.10−2.00 (2H, m, H-3b, H-8a), 1.89−1.79 (3H, m, H-6b, H-2a, H-
9a), 1.74 (1H, dtd, J = 11.5, 6.7, 1.1 Hz, H-2b), 1.62−1.60 (3H, m, H-
15), 1.57 (1H, ddd, J = 13.4, 11.0, 1.3 Hz, H-9b), 1.52−1.45 (2H, m,
H-7, H-8b), 1.26−1.23 (3H, s, H-13), 1.22−1.19 (3H, s, H-12), 1.13
(3H, s, H-14); 13C NMR (126 MHz, C6D6) δ 134.75, 133.22, 74.07,
73.82, 59.75, 36.61, 36.23, 34.56, 34.51, 31.05, 29.18, 28.84, 28.40,
24.36, 14.27; EIMS m/z 220 [M]+ (16), 203 (17), 202 (100), 187
(32), 177 (11), 162 (42), 159 (12), 149 (27), 147 (55), 145 (20), 135
(17), 125 (54), 121 (20), 119 (34), 107 (31), 105 (28), 95 (89), 94
(58), 91 (41), 79 (79), 77 (30), 67 (11), 55 (15), 43 (59); HREIMS
m/z 220.1823 (calcd for C15H24O, 220.1822).
(4αH,7αH,10β)-10,11-Epoxyguaia-1,5-diene (27): RI (VF-5ms/
1
wax) 1497/1763; H NMR (500 MHz, C6D6) δ 5.57 (1H, d, J = 8.5
Hz, H-6), 5.41 (1H, td, J = 2.5, 1.8 Hz, H-2), 2.71−2.63 (1H, m, H-4),
2.52 (1H, ddd, J = 17.3, 7.9, 2.5 Hz, H-3a), 2.06−1.98 (1H, m, H-8a),
1.94−1.85 (3H, m, H-9a, H-3b, H-7), 1.83−1.79 (1H, m, H-8b), 1.70
(1H, ddd, J = 10.6, 8.3, 2.7 Hz, H-9b), 1.44 (3H, s, H-14), 1.32 (3H, s,
H-12), 1.30 (3H, s, H-13), 1.10 (3H, d, J = 7.0 Hz, H-15); 13C NMR
(126 MHz, C6D6) δ 153.47, 153.30, 126.28, 122.60, 77.03, 72.16,
40.06, 39.71, 36.12, 32.93, 30.17, 30.14, 28.78, 25.04, 22.23; EIMS m/z
218 [M]+ (9), 160 (72), 146 (13), 145 (100), 132 (34), 131 (71), 129
(13), 128 (12), 119 (16), 118 (34), 117 (21), 115 (13), 105 (24), 91
(18), 77 (9), 65 (4), 53 (3), 43 (13); HREIMS m/z 218.1662 (calcd
for C15H22O, 218.1665).
31a: RI (VF-5ms/wax) 1729/2355; 13C NMR (50 MHz, C6D6) δ
73.48, 73.02, 72.57, 47.35, 40.72, 32.71, 31.65, 29.69, 29.61, 27.58,
27.56, 26.31, 25.31, 17.00, 16.13; EIMS m/z 238 [M]+ (1), 220 (7),
205 (28), 187 (12), 177 (13), 165 (73), 156 (45), 5147 (37), 138
(45), 125 (56), 123 (71), 109 (43), 95 (47), 81 (38), 67 (33), 59
(100), 55 (33), 43 (42), 41 (35); in agreement with reported data;37
HREIMS m/z 238.1922 (calcd for C15H26O2, 238.1927).
(1αH,4αH,5αH,7α,10α)-7,10-Epoxyguaiane (28): RI (VF-5ms/
1
wax) 1488/1656; H NMR (500 MHz, CDCl3) δ 2.42 (1H, td, J =
31b: RI (VF-5ms/wax) 1686/2300; 13C NMR (50 MHz, C6D6) δ
73.92, 72.55, 72.52, 46.47, 37.80, 34.87, 31.20, 28.69, 28.26, 28.03,
28.02, 26.58, 25.22, 19.06, 13.93; EIMS m/z 238 [M]+ (1), 220 (8),
205 (26), 187 (13), 177 (15), 165 (74), 156 (52), 147 (36), 138 (49),
125 (62), 123 (79), 109 (45), 95 (48), 81 (38), 67 (34), 59 (100), 55
(35), 43 (44), 41 (37); in agreement with reported data;45 HREIMS
m/z 238.1925 (calcd for C15H26O2, 238.1927).
10.0, 9.4, 3.9 Hz, H-1), 2.06 (1H, dq, J = 12.0, 8.4 Hz, H-5), 2.00−1.93
(1H, m, H-4), 1.89−1.85 (1H, m, H-9a), 1.84 (1H, hept, J = 7.0 Hz,
H-11), 1.69−1.60 (3H, m, H-6a, H-3a, H-2a), 1.52−1.47 (2H, m, H-
8a, H-8b), 1.41−1.36 (1H, m, H-9b), 1.35−1.28 (1H, m, H-2b), 1.27
(3H, s, H-14), 1.28−1.24 (1H, m, H-3b), 0.94 (3H, d, J = 6.7 Hz, H-
13), 0.91 (3H, d, J = 7.0 Hz, H-15), 0.90 (3H, d, J = 6.9 Hz, H-12);
13C NMR (126 MHz, CDCl3) δ 84.03, 80.99, 50.73, 38.68, 37.47,
37.45, 36.53, 33.44, 30.79, 29.38, 28.31, 27.10, 17.53, 17.48, 14.86;
EIMS m/z 222 [M]+ (6), 204 (5), 179 (18), 164 (12), 161 (16), 136
(60), 127 (100), 125 (27), 123 (49), 122 (54), 121 (37), 107 (54), 97
(36), 95 (48), 83 (25), 82 (30), 81 (38), 71 (43), 67 (30), 55 (32), 43
(73); HREIMS m/z 222.1968 (calcd for C15H26O, 222.1978).
(1α,4αH,5αH,7αH,10α)-1,10-Epoxyguaian-11-ol (32a) and
(1β,4αH,5αH,7αH,10 β)-1,10-epoxyguaian-11-ol (32b). To a stirred
solution of 2 (49.6 mg, 0.22 mmol) in CH2Cl2 (1 mL) at RT was
added dropwise a solution of m-CPBA (77%, 57.8 mg, 0.26 mmol) in
CH2Cl2 (1 mL). After 10 min of stirring, the reaction was washed with
saturated NaHCO3 solution. The mixture was extracted with Et2O (3
× 10 mL). The combined organic layers were washed with brine (10
mL), dried over anhydrous MgSO4, and filtered. The filtrate was
concentrated in vacuo, and the residue purified by silica gel CC
(petroleum ether/Et2O, 80:20) to give 32a (36.7 mg, 69%) and 32b
(11.5 mg, 22%).
(1βH,4αH,5β,7αH,10αH)-4,5;5,11-Diepoxy-4,5-seco-guaiane (29):
1
RI (VF-5ms/wax) 1611/1929; H NMR (500 MHz, C6D6) δ 3.26
(1H, dqd, J = 12.2, 6.1, 2.2 Hz, H-4), 2.12 (1H, tdd, J = 13.5, 10.4, 3.0
Hz, H-9a), 2.05 (1H, dddd, J = 12.4, 6.4, 1.9, 0.9 Hz, H-6a), 1.88 (1H,
ddd, J = 13.5, 7.4, 4.0 Hz, H-2a), 1.77−1.71 (2H, m, H-7, H-8a), 1.70
(1H, d, J = 12.3 Hz, H-6b), 1.38 (3H, s, H-12), 1.26 (3H, s, H-13),
1.31−1.21 (3H, m, H-9b, H-3a, H-1), 1.18 (3H, d, J = 6.2 Hz, H-15),
1.15−1.09 (1H, m, H-3b), 1.07−1.00 (1H, m, H-8b), 0.96−0.90 (1H,
m, H-10), 0.89 (3H, d, J = 5.3 Hz, H-14), 0.85−0.78 (1H, m, H-2b);
13C NMR (126 MHz, C6D6) δ 109.60, 82.19, 69.75, 47.80, 45.58,
38.37, 38.34, 33.74, 33.24, 31.35, 30.27, 29.17, 22.80, 22.70, 22.70;
EIMS m/z 238 [M]+ (66), 223 (78), 195 (15), 180 (51), 179 (22),
178 (22), 165 (22), 141 (29), 124 (42), 123 (68), 114 (44), 113 (73),
110 (44), 109 (52), 107 (21), 97 (28), 96 (32), 95 (100), 83 (32), 82
(36), 81 (81), 69 (72), 68 (55), 67 (39), 55 (85), 43 (51), 41 (56);
HREIMS m/z 238.1943 (calcd for C15H26O2, 238.1927).
1
32a: RI (VF-5ms/wax) 1756/2391; H NMR (500 MHz, C6D6) δ
2.43−2.33 (1H, m, H-4), 2.05−1.93 (2H, m, H-9a, H-2a), 1.88 (1H,
ddd, J = 13.6, 3.1, 1.8 Hz, H-6a), 1.81−1.61 (4H, m, H-8a, H-5, H-3a,
H-2b), 1.51 (1H, t, J = 12.8 Hz, H-9b), 1.18 (3H, d, J = 0.7 Hz, H-14),
1.15−1.10 (2H, m, H-3b, H-7), 1.00 (3H, s, H-12), 0.99 (3H, s, H-
13), 0.94 (3H, d, J = 6.9 Hz, H-15), 0.92−0.89 (1H, m, H-8b), 0.71
(1H, dt, J = 13.2, 11.7 Hz, H-6b); 13C NMR (126 MHz, C6D6) δ
75.51, 72.76, 63.03, 54.50, 49.24, 38.19, 37.55, 31.08, 29.53, 27.63,
27.06, 26.23, 25.20, 20.54, 15.37; EIMS m/z 238 [M]+ (3), 220 (32),
205 (20), 202 (37), 187 (42), 179 (30), 177 (36), 162 (39), 161 (31),
159 (100), 147 (47), 133 (35), 121 (51), 111 (67), 110 (57), 107
(50), 105 (61), 95 (62), 93 (45), 91 (47), 83 (45), 81 (68), 59 (99),
55 (35), 43 (71); HREIMS m/z 238.1908 (calcd for C15H26O2,
238.1927).
(1α,4αH,5β,7αH,10αH)-5,11-Epoxyguaian-1α-ol (30). To a stirred
solution of AlCl3 (15.7 mg, 0.12 mmol) in dry THF (2 mL) under N2
was added dropwise a solution of 31a (23.3 mg, 0.1 mmol) in dry
THF (1.5 mL). After stirring at RT for 2 h, the reaction was quenched
J
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1
32b: RI (VF-5ms/wax) 1759/2356; H NMR (500 MHz, C6D6) δ
2.03−1.96 (1H, m, H-4), 1.91 (1H, ddd, J = 6.2, 5.5, 2.3 Hz, H-9a),
1.87 (1H, ddd, J = 11.9, 8.6, 1.7 Hz, H-2a), 1.80 (1H, dd, J = 10.5, 8.9
Hz, H-2b), 1.74 (1H, ddd, J = 11.5, 5.7, 2.1 Hz, H-5), 1.67 (1H, ddd, J
= 12.7, 4.2, 2.2 Hz, H-6a), 1.64−1.54 (2H, m, H-8a, H-9b), 1.52−1.44
(1H, m, H-3a), 1.44−1.33 (2H, m, H-3b, H-8b), 1.31 (1H, dd, J =
11.6, 1.3 Hz, H-6b), 1.16 (3H, s, H-14), 1.01 (3H, s, H-12), 1.01 (3H,
s, H-13), 1.01 (3H, d, J = 7.2 Hz, H-15), 0.86−0.83 (1H, m, H-7); 13C
NMR (126 MHz, C6D6) δ 72.81, 72.11, 60.52, 53.98, 47.18, 39.76,
35.02, 31.36, 30.50, 28.16, 27.34, 27.05, 26.01, 23.63, 15.29; EIMS m/z
238 [M]+ (1), 220 (19), 205 (20), 202 (21), 187 (24), 179 (33), 162
(41), 159 (43), 147 (59), 133 (28), 125 (74), 121 (58), 111 (71), 107
(68), 95 (76), 83 (58), 81 (86), 59 (87), 55 (46), 43 (100); HREIMS
m/z 238.1917 (calcd for C15H26O2, 238.1927).
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ASSOCIATED CONTENT
* Supporting Information
■
(18) Rodilla, J. M.; Silva, L. A.; Martinez, N.; Lorenzo, D.; Davyt, D.;
S
Castillo, L.; Gimen
́ ́
ez, C.; Cabrera, R.; Gonzalez-Coloma, A.;
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.6b01068.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: jfilippi@unice.fr.
ORCID
Jean-Jacques Filippi: 0000-0001-5701-8912
Notes
The authors declare no competing financial interest.
■
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