Absolute Configurations of Stink Bug- And Plant-Produced Sesquipiperitols via Synthesis of All Stereoisomers

Article abstract of DOI:10.1021/acs.jnatprod.0c00517

Sesquipiperitol is a sesquiterpene alcohol, some stereoisomers of which were found in several plant species. The biological role of these compounds in plants and their absolute configurations have not been reported. Recently, we found that 1S,6S,7R stereoisomer of sesquipiperitol was a key precursor in the biosynthesis of the harlequin bug, Murgantia histrionica, pheromone, which consists of two stereoisomeric zingiberenol oxides. In addition, the Tibraca limbativentris stink bug was shown to produce two sesquipiperitol stereoisomers as minor components in their male-produced sex pheromone, the main constituents of which were zingiberenols. To determine absolute configurations of plant- and stink-bug-produced sesquipiperitols, we undertook syntheses of all stereoisomers of this sesquiterpene alcohol. The syntheses were based on 1,10-bisaboladien-3-ols (aka zingiberenols) with known configurations at C-6 and C-7, the oxidation of which provided sesquipiperitone precursors with retention of configurations of these stereogenic centers. The foremost challenge of the synthetic endeavor was the assignment of absolute configurations of secondary carbinol centers, which was resolved by NMR analyses of corresponding Mosher's esters. Thus, the availability of all eight diastereomers allowed us to assign sesquipiperitols from Fitzroya cupressoides and Argyranthemum adauctum spp. jacobaeifolium plants 1S,6S,7R (16) and 1R,6R,7S (14) configurations, respectively. A chiral-phase gas-chromatographic method was developed to determine 1S,6S,7R and 1R,6S,7R (15) configurations of T. limbativentris sesquipiperitol pheromone components.

Full text of DOI:10.1021/acs.jnatprod.0c00517

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Article
Absolute Configurations of Stink Bug- and Plant-Produced
Sesquipiperitols via Synthesis of All Stereoisomers
Ashot Khrimian,* Sravanthi D. Guggilapu, Filadelfo Guzman, Maria Carolina Blassioli-Moraes,
and Miguel Borges
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ABSTRACT: Sesquipiperitol is a sesquiterpene alcohol, some stereo-
isomers of which were found in several plant species. The biological role of
these compounds in plants and their absolute configurations have not been
reported. Recently, we found that 1S,6S,7R stereoisomer of sesquipiperitol
was a key precursor in the biosynthesis of the harlequin bug, Murgantia
histrionica, pheromone, which consists of two stereoisomeric zingiberenol
oxides. In addition, the Tibraca limbativentris stink bug was shown to
produce two sesquipiperitol stereoisomers as minor components in their
male-produced sex pheromone, the main constituents of which were
zingiberenols. To determine absolute configurations of plant- and stink-bug-
produced sesquipiperitols, we undertook syntheses of all stereoisomers of
this sesquiterpene alcohol. The syntheses were based on 1,10-bisaboladien-
3
-ols (aka zingiberenols) with known configurations at C-6 and C-7, the oxidation of which provided sesquipiperitone precursors
with retention of configurations of these stereogenic centers. The foremost challenge of the synthetic endeavor was the assignment of
absolute configurations of secondary carbinol centers, which was resolved by NMR analyses of corresponding Mosher’s esters. Thus,
the availability of all eight diastereomers allowed us to assign sesquipiperitols from Fitzroya cupressoides and Argyranthemum
adauctum spp. jacobaeifolium plants 1S,6S,7R (16) and 1R,6R,7S (14) configurations, respectively. A chiral-phase gas-
chromatographic method was developed to determine 1S,6S,7R and 1R,6S,7R (15) configurations of T. limbativentris sesquipiperitol
pheromone components.
1
esquipiperitol (2,10-bisaboladien-1-ol, Figure 1) has been
found in several plant species.
sesquipiperitols reported in the literature involved the
reduction of the corresponding ketones, or sesquipiperi-
2
−5
S
Whereas (+)-sesquipi-
peritol occurred in roots of Argyranthemum adauctum spp.
jacobaeifolium, (−)-sesquipiperitol was isolated from the
foliage of Fitzroya cupressoides. Two Zingiberaceae plant
species, Alpinia densibracteata and Zingiber officinale, have
also been reported to contain sesquipiperitol of undisclosed
absolute configuration. The biological role of sesquipiperitol in
plants remains unknown. In cooperative research, we recently
identified sesquipiperitol for the first time in animals as an
intermediate in the biosynthesis of the harlequin bug,
Murgantia histrionica, pheromone, zingiberenol epoxides
Figure 1). It was shown that an enzyme unrelated to plant
and microbial terpene synthases catalyzes conversion of (E,E)-
farnesyl diphosphate to (1S,6S,7R)-2,10-bisaboladien-1-ol
SSR-sesquipiperitol). More recently, we identified sesquipi-
peritol as a minor component of the rice stink bug, Tibraca
limbativentris, male-produced sex pheromone. Because the
main pheromone component in T. limbativentris was a
2
,6
tones, which were also isolated from several plant species.
A levorotatory sesquipiperitone was isolated from Stevia
purpurea flowers and presumed to exist in the cis conformation
2
3
4
5
10
11
about the C-6−C-7 bond. Ghisalberti et al. synthesized
sesquipiperitones from (R)-citronellal and, on the basis of the
assumption that the relative 6S,7R/6R,7S configuration in ref
10 was firmly established (which it was not), assigned the
natural sesquipiperitone from S. purpurea the 6R,7S config-
uration. The same sesquipiperitone and its epimer were
isolated from the Brazilian lantana oil from the Lasntana
6
7
(
12
camara tree and rhizomes of the medicinal plant Curcuma
13,14
longa.
(−)-Sesquipiperitone was also isolated from aerial
15,16
parts of Senecio palmensis
against the Colorado potato beetle, Leptinotarsa decemlineata.
and showed antifeedant activity
6
(
15
8
Received: May 8, 2020
8
,9
structurally related zingiberenol (Figure 1), it is conceivable
that here sesquipiperitol has a dual role: a pheromone and an
intermediate in the biosynthesis of another pheromone
component. Only two diastereomers of sesquipiperitol have
6
been stereochemically characterized thus far. Syntheses of
©
XXXX American Chemical Society and
American Society of Pharmacognosy
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A
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Figure 1. Structures of stink bug-produced sesquipiperitol and zingiberenols.
Scheme 1. Reagents and Conditions: (a) CH Li/Ether, −25 °C; (b) PCC/NaOAc/CH Cl , 0−25 °C; (c) LAH × 1.3 equiv
3
2
2
EtOH/Ether, −30 °C, HPLC Separation
A (+)- sesquipiperitone was found in the essential oil of the
RESULTS AND DISCUSSION
■
17
Ethiopian medicinal plant Cymbopogon citratus. Hagiwara et
For the preparation of sesquipiperitones needed for reduction
to sequipiperitols, we used the previously published oxidation
of zingiberenols with pyridinium chlorochromate (PCC).
al. synthesized all four stereoisomers of sesquipiperitone from
11,18
(
R)- and (S)-citronellals via a pyridinium chlorochromate
18
However, we used zingiberenols with defined configurations at
(
PCC) oxidation of intermediate zingiberenols. The stereo-
C-6 and C-7 that eliminated the need for separation by MPLC
isomers eluted slower on SiO were assigned 6S,7S and 6R,7R
18
2
(
Scheme 1). The starting cyclohexenone 1 was prepared via
configurations, and the faster-eluting stereoisomers were
presumed as having 6R,7S and 6S,7R configurations on the
a Michael addition of (R)-citronellal to methylvinylketone with
a subsequent Robinson annulation of the intermediate
19
10,11
ketoaldehyde. Ketone 1 reacted with methyl lithium to
furnish a mixture of epimeric zingiberenols, which was further
oxidized with PCC to (6R,7R)-2,10-bisaboladien-1-one
basis of the previous work,
which was largely circum-
stantial.
The goal of this work was to determine absolute
configurations of sesquipiperitols in the T. limbativentris
pheromone and essential oils from certain plants via synthesis
of all possible stereoisomers.
(
sesquipiperitone 2, Scheme 1). The diastereomeric ratio in
the starting cyclohexenone 1 was 93:7 and in the
sesquipiperitone 2 was 94:6 (as determined by NMR),
indicating that there was no change in configurations of C-6
B
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and C-7 during allylic rearrangement/oxidation. The reduction
of 2 with lithium aluminum hydride was not as chemoselective
as the analogous reduction of (6S,7R)-2,10-bisaboladien-1-
Table 1. Δδ (= δ − δ ) NMR Data for the S- and R-MTPA
S
R
(Mosher’s) esters 3a/3b, 4a/4b, 13a/13b, and 14a/14b
SR
6
Δδ (= δ − δ )
S R
one. We found that side reactions can drastically be reduced
proton
4a (S-ester)
4b (R-ester)
ppm
Hz
by diminishing the power of LAH with 1.3−2.0 equiv of
2
0
EtOH. The reduction products 3 and 4 were separated by
HPLC and characterized by DEPT, COSY, HSQS, and NMR
recordings that allowed for assignments of all hydrogens and
carbons, but NOESY failed to conclusively pinpoint the cis/
trans configuration of H-1 vs H-6 that would help to assign
H-7
1.55
0.94
1.02
1.63
5.52
1.41
0.86
0.95
1.58
5.52
+0.14
+0.08
+0.07
+0.05
0.00
+84
+48
+42
+30
0
H-14
H-8a
H-6
H-1
21,22
absolute configurations. Hence, we used Mosher’s ester
H-15
H-2
1.65
5.30
1.70
5.41
−0.05
−0.11
−30
−66
analysis (see later) to assign the epimer that eluted faster on
SiO as the 1S,6R,7R configuration 3 and the slower-eluting
3a (S-ester)
3b (R-ester)
2
epimer as the 1R,6R,7R configuration 4. The pair of
sesquipiperitols 8 and 9, enantiomers of 3 and 4, respectively,
were prepared by converting a mixture of cyclohexenones 5 to
zingiberenol 6 via a rhodium-catalyzed enantioselective
addition of trimethylaluminum in the presence of (S)-
H-15
H-2
H-1
1.74
5.81
5.41
1.26
1.04
1.69
5.78
5.40
1.28
1.10
+0.05
+0.03
+0.01
−0.02
−0.06
−0.12
−0.15
+30
+18
+6
−12
−36
−72
−90
H-6
H-8a
H-14
H-7
2
3
BINAP and then oxidizing 6 to sesquipiperitone 7 and
reducing the latter to sesquipiperitols 8 and 9 as described
above (Scheme 1). Sesquipiperitols 13 and 14 were
synthesized following the same sequence but using (R)-
BINAP instead for preparing zingiberenol 11 stereodefined at
0.77
1.22
0.89
1.37
14a (S-ester)
14b (R-ester)
H-7
1.60
1.30
0.84
1.69
5.52
1.65
5.28
1.38
1.20
0.78
1.66
5.51
+0.22
+0.10
+0.06
+0.03
+0.01
−0.05
−0.12
+132
+60
+36
+18
+6
−30
−72
H-8a
H-14
H-6
H-1
H-15
H-2
23
C-6 as the key starting material (Scheme 1). Enantiomers of
3 and 14, sesquipiperitols 15 and 16, respectively, were
1
6
synthesized in an analogous manner and described previously.
Thus, these syntheses relied on zingiberenols with established
configurations at C-6 and C-7, which did not change during
PCC oxidation and further reduction of resulting sesquipiper-
itones.
1.70
5.40
1
3a (S-ester)
13b (R-ester)
H-15
H-2
H-1
1.75
5.81
5.42
1.31
0.81
1.00
1.31
1.69
5.79
5.41
1.32
0.90
1.11
1.47
+0.06
+0.02
+0.01
−0.01
−0.09
−0.11
−0.16
+36
+12
+6
The main challenge of the current undertaking was the
assignment of absolute configurations of secondary carbinol
atoms of synthesized sesquipiperitols, for which we applied the
H-6
−6
2
1,22
Mosher’s ester analyses.
nylacetic (Mosher’s) acid esters 3a/3b, 4a/4b, 13a/13b, and
4a/14b were prepared from corresponding acyl chlorides and
diastereomeric sesquipiperitols 3, 4, 13, and 14, respectively
α-Methoxy-α-trifluoromethylphe-
H-14
H-8a
H-7
−54
−66
−96
1
1
13
(
Figure S1). H and C NMR spectra of Mosher’s esters were
recorded, and COSY spectra were obtained to assist in
assignments of key protons. Table 1 shows chemical shifts of
these protons and the differences between them arranged from
positive to negative values. As data indicate, the phenyl group
exerts an anisotropic magnetic shielding effect on neighboring
and H-6 protons were shielded in R-ester 14b and H-2 and H3-
15 were upfield in S-ester 14a, both derived from 14. This is
only possible if the absolute configuration of the secondary
carbinol center in this alcohol is R (Scheme 1, Figure S1). The
reverse magnetic shielding effect was observed in R- and S-
esters 13b and 13a (Figure S1), thus indicating S configuration
of the carbon bearing the hydroxy group in alcohol 13. Hence,
alcohols 14 and 13 have 1R,6R,7S and 1S,6R,7S configurations,
respectively.
2
1,22
protons,
which could also be visualized on conformations
depicted in Figure S1. Thus, this shielding effect of the phenyl
group in R-ester 4b could most profoundly be seen on the
methine proton H-7, then the methyl group (H -14), one of
3
the protons of the methylene group of the side chain (H-8a),
and H-6, indicating a spatial proximity of these protons to the
aromatic ring. In the S-ester 4a, the olefinic H-2 and the Me
With absolute configurations of 3, 4, 13, and 14 established
via Mosher’s esters analyses, the configurations of other four
sesquipiperitols 8, 9, 15, and 16 could easily be deduced by
their enantiomeric relationship with the former four. Thus,
NMR data of sesquipiperitol 8 matched those of alcohol 3, but,
because of an opposite specific rotation, its absolute
configuration must be 1R,6S,7S. Analogously, 9 is an
enantiomer of 4 and thus should have 1S,6S,7S configuration;
15 and 16 are enantiomers of 13 and 14 and hence must have
1R,6S,7R and 1S,6S,7R configurations, respectively. In general,
regardless of the configuration at C-7, 1S,6S/1R,6R diaster-
group at the double bond (H -15) are relatively more shielded
3
than those in R-ester 4b. The opposite is true for the Mosher’s
esters 3a and 3b prepared from the epimeric alcohol 3. H-2
and H -15 protons are shielded in the NMR spectrum of R-
3
ester 3b, and the H-7, H -14, H-8a, and H-6 are relatively
3
more shielded in the spectrum of S-ester 3a. Thus, the
SR
observed Δδ (= δ − δ ) values translate directly to the R
S
R
absolute configuration of the secondary carbinol center in 4
and S configuration of this carbon atom in 3 (Scheme 1).
Hence, the absolute configuration of alcohol 4 is 1R,6R,7R and
that of alcohol 3 is 1S,6R,7R.
eomers eluted slower on SiO as compared with 1S,6R/1R,6S
2
diastereomers.
It is noteworthy that the Mosher’s ester analysis confirmed
the identification of the intermediate in the biosynthesis of the
harlequin bug pheromones as 1S,6S,7R sesquipiperitol 16. We
The Mosher’s ester analyses of the other pair of epimeric
alcohols, 14 and 13, provided similar results. H-7, H -14, H-8a,
3
C
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Figure 2. Gas-chromatography flame ionization detector (GC-FID) analyses of (A) a mixture of sesquipiperitols, (B) T. limbativentris pheromone,
and (C) a mixture of sesquipiperitols and T. limbativentris pheromone. Conditions: column 50 m × 0.25 μm Lipodex G. Cool-on-column injection
at 50 °C; Det 170 °C; carrier gas H at 2.0 mL/min; oven 50 °C (5 min) to 130 °C at 10 °C/min.
2
earlier determined it by finding a trans orientation H-1 and H-
and chemical correlations that determined 6S,7R config-
In conclusion, we synthesized all stereoisomers of
sesquipiperitol from zingiberenols with known configurations
of carbons 6 and 7. A chiral-phase gas-chromatographic
method was developed to determine 1S,6S,7R and 1R,6S,7R
configurations of T. limbativentris sesquipiperitol pheromone
components. Sesquipiperitols from Fitzroya cupressoides and
Argyranthemum adauctum spp. jacobaeifolium plants were found
to have 1S,6S,7R and 1R,6R,7S configurations, respectively.
6
6
uration. As to other naturally occurring compounds,
+)-sesquipiperitol that occurred in roots of Argyranthemum
(
10
adauctum spp. jacobaeifolium matched stereoisomer 14 by
NMR and the specific rotation and thus has 1R,6R,7S
configurations. (−)-Sesquipiperitol from Fitzroya cupressoides
that was identical to 16 has 1S,6S,7R configuration. NMR data
3
1
2
of the sesquipiperitol isolated from Alpinia densibracteata
EXPERIMENTAL SECTION
General Experimental Procedures. Optical rotations were
obtained using a PerkinElmer 241 polarimeter with a 1.0 mL cell.
H NMR spectra were obtained at 600 MHz and C spectra at 151
were identical to those of 16 and 14, but, in the absence of a
reported specific rotation, its absolute configuration remains
unknown.
■
1
13
Having all stereoisomers of sesquipiperitol in hand, we
developed a chiral-phase gas-chromatography method to
expedite assignment of absolute configurations of sesquipiper-
itols in rice stalk stink bugs, T. limbativentris, pheromone
MHz on a Bruker AVIII-600 MHz spectrometer. Chemical shifts are
1
referenced to the residual CDCl (7.26 ppm for H and 77.2 ppm for
3
1
3
1
13
C) or CD Cl (5.32 ppm for H and 53.8 ppm for C) solvents
2
2
1
3
signal. COSY, C-DEPT, HSQC, and NOESY spectra were also
recorded to assign protons and carbons of compounds 3 and 4. GC−
MS analyses were performed in electron impact (EI) ionization mode
at 70 eV with an Agilent Technologies 5973 mass selective detector
interfaced with 6890 N GC system and equipped with either 30 m ×
.25 mm i.d. × 0.25 μm film HP-5MS Agilent J&W column or 30 m ×
.25 mm × 0.25 μm Rtx 1701 Restek columns. The column
8
collection and possibly other natural sources. Figure 2A shows
a gas-chromatogram of a mixture of all sesquipiperitol
stereoisomers on a Lipodex G column where only a pair of
enantiomers 4 and 9 were not separated. Despite this minor
shortcoming, the method appeared handy in the identification
of minor T. limbativentris pheromone components. Figure 2B
shows a GC trace of the pheromone collection, in which
natural sesquipiperitols lined up with 1R,6S,7R isomer 15 and
0
0
temperature was maintained at 40 °C for 5 min and then was raised to
40 °C at 7 °C/min and to 270 at 15 °C/min. Helium was used as a
carrier gas at 1 mL/min. Injections were done either splitless at 260
C or using a cool-on-column at 70 °C. GC−HRMS analyses were
2
°
1
S,6S,7R isomer 16. Co-elutions of these compounds with
performed in TOF EI+ mode on a Waters GCT Premier instrument
equipped with a 30 m × 0.25 mm × 0.25 μm DB-1701 column. The
oven temperature was set at 40 °C for 3 min, then increased at 6 °C/
min to 230 °C, and held for 5 min with a He flow of 1 mL/min. GC
analysis of a mixture of sesquipiperitols was performed on an Agilent
Technologies 6890N instrument equipped with a flame ionization
detector and a 50 m × 0.25 μm ID Lipodex G capillary column
synthetic standards 15 and 16 were confirmed by the GC
analysis of the mixture (Figure 2C). Two main pheromone
components of T. limbativentris, RSR- and SSR-zingiberenols,
8
were identified earlier.
Thus, sesquipiperitols in T. limbativentris pheromone share
the same 6S,7R configurations with the main pheromone
components zingiberenols. This finding suggests that, as in the
M. histrionica stink bug, sesquipiperitols here could also
function as biochemical precursors to zingiberenols.
(
Macherey-Nagel GmbH & Co. KG). See Figure 2 for conditions of
analysis. TLC analyses were conducted on Whatman AL SIL G/UV
plates using 20% EtOH solution of phosphomolybdic acid and/or UV
for visualization of spots. Flash chromatography was carried out with
D
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2
30−400 mesh silica gel from Fisher Scientific. All reagents and
4H, H-4, H-9), 4.14 (m, H-1), 5.12 (tqq, J = 7.1, 1.5, 1.5 Hz, H-10).
1
3
solvents were purchased from Aldrich Chemical Co. The collection of
volatile pheromone from T. limbativentris was described previously.
5.64 (dm, J = 5.4 Hz, H-2). C NMR (CDCl ): 17.2 (C-14), 17.8
3
8
(C-13), 20.8 (C-5), 23.5 (C-15), 25.3 (C-9), 25.9 (C-12), 31.7 (C-4),
33.3 (C-7), 34.5 (C-8), 44.3 (C-6), 65.3 (C-1), 123.9 (C-2), 125.2
(C-10), 131.3 (C-11), 139.9 (C-3). GC−MS (m/z, %): 204 (21), 189
(8), 161 (18), 137 (15), 121 (38), 119 (100), 109 (27), 105 (27), 93
(77), 91 (46), 77 (36), 69 (57), 55 (29), 41 (49). HRMS (EI-TOF)
Cyclohexenone 1. Cyclohexenone 1 was prepared from (R)-
19
citronellal following the published procedure. Cyclization of the
intermediate (2R,3R)-3,7-dimethyl-2-(3-oxobutyl)oct-6-enal to ke-
tone 1 was achieved with 6% lithium hydroxide monohydrate (10% in
+·
ref 19). The yield of 1 was 77%, and the diastereomeric ratio (dr) of
m/z 222.1977 M (calcd for C H O 222.1984).
15 26
1
20
9
3:7 as determined by NMR; Literature from ref 19 dr 89:11. H
The slower moving compound was identified as alcohol 4. [α]
D
1
NMR (δ, CD Cl ): 0.93 (d, J = 6.7 Hz, 3H), 1.26 (m, 1H), 1.40 (m,
+22 (c 1.37, CHCl ). H NMR (CDCl ): 0.97 (d, J = 6.8 Hz, H -14),
2
2
3
3
3
1
(
H), 1.61 (br s, 3H), 1.66 (m, 1H), 1.69 (br d, J = 0.6 Hz, 3H), 1.80
m, 1H), 1.97 (m, 2H), 2.06 (m, 1H), 2.33 (m, 1H), 2.44 (m, 2H),
.11 (tqq, J = 6.9, 2.3, 2.3 Hz, 1H), 5.96 (ddd, J = 10.2, 2.7, 0.9 Hz,
1.05 (m, H-8a), 1.24−1.37 (m, 2H, H-5a, H-6), 1.43 (m, H-8b), 1.61
(br s, H-13), 1.66 (m, H-5b), 1.67 (br s, H-12), 1.68 (br s, H -15),
3
5
1
1
1
1.79 (m, H-7), 1.86−2.01 (m, 3H, H-4, H-9a), 2.07 (m, H-9b), 4.07
1
3
13
H), 6.87 (ddd, J = 10.2, 2.0, 2.0 Hz, 1H). C NMR (δ, CD Cl ):
6.7, 17.8, 25.8, 26.3, 26.3, 34.3, 36.5, 38.1, 42.2, 124.7, 130.1, 132.0,
54.5, 199.9. NMR data matched those recorded in CDCl3.
(m, H-1), 5.11 (tqq, J = 6.9, 1.3, 1.3 Hz, H-10). 5.38 (m, H-2).
C
2
2
NMR (CDCl ): 17.8 (C-14), 18.0 (C-13), 22.1 (C-5), 23.3 (C-15),
3
19
25.9 (C-9), 26.5 (C-12), 30.5 (C-4), 32.1 (C-7), 32.4 (C-8), 48.1 (C-
6), 69.0 (C-1), 122.1 (C-2), 125.5 (C-10), 131.5 (C-11), 137.7 (C-
Cyclohexenones 5 and 10 and zingiberenols 6 and 11 were prepared
23
+
as described.
6R,7R)-2,10-Bisaboladien-1-one (2). To a cyclohexenone 1 (300
mg, 1.45 mmol) in dry ether (15 mL) in a N atmosphere was added
3). GC−MS (m/z, %): 222 (M , 5), 204 (21), 189 (9), 161 (16), 137
(
(62), 121 (44), 119 (100), 105 (30), 93 (76), 91 (46), 84 (31),
+·
77(33), 69 (58), 41 (48). HRMS (EI-TOF) m/z 222.1991 M (calcd
2
a methyllithium solution in ether (1.18 mL of 1.6 M, 1.89 mmol) at
for C H O 222.1984).
1
5
26
−25 °C. After stirring for 2 h, the mixture was warmed to room
(6S,7S)-2,10-Bisaboladien-1-one (7). Zingiberenol 6 (350 mg,
23
temperature and quenched with a saturated ammonium chloride
solution. The ether layer was separated, and the aqueous one
extracted with ether (3 × 10 mL). The combined organic extract was
washed with brine, dried (Na SO ), and concentrated. Flash
1.57 mmol, 96:4 dr ) was stirred with PCC (1.696 g, 7.87 mmol)
and NaOAc (129 mg, 1.59 mmol) in dry CH Cl (7 mL) at 0 to 25
2
2
°C and then worked-up as described in the preparation of 2. Flash
chromatography with hexanes/EtOAc, 10:1, provided 7 (238 mg,
2
4
2
0
1
chromatography with hexanes/EtOAc, 9:1 to 4:1, afforded a ∼1:1
mixture of zingiberenols (203 mg, 0. 91 mmol), which was stirred
with PCC (983 mg, 4.56 mmol) and anhydrous sodium acetate (74
mg, 0.90 mmol) in dry CH Cl (5 mL) in a N atmosphere starting at
69%). [α] +22 (c 1.05, CHCl ); dr 95:5 (GC on Rtx 1701). H
D 3
1
3
and C NMR spectra matched those of the enantiomeric
sesquipiperitone 2 (see the Supporting Information).
(1R,6S,7S)-2,10-Bisaboladien-1-ol (8) and (1S,6S,7S)-2,10-Bisa-
boladien-1-ol (9). Analogously to the reduction of 2, a solution of
LAH in diethyl ether (1 mL of 1.0 M in ether, 1 mmol) was diluted
with dry ether (1 mL) and treated with a solution of absolute EtOH
(76 μL, 1.29 mmol) in ether (500 μL) at −30 °C, followed by the
addition of a solution of ketone 1 (142 mg, 0.64 mmol) in ether (1
mL). After completion of the reaction and the work up described
2
2
2
0
°C and gradually warming to 25 °C for 2 h. The mixture was diluted
with ether (10 mL) and filtered. The filtrate was washed with 5%
NaOH, 2% HCl, dilute NaHCO , and brine and then dried with
3
Na SO . The solution was evaporated and flash-chromatographed
2
4
with hexanes/EtOAc, 10:1, to provide sesquipiperitone 2 (119 mg,
3
0
7% from 1) in 94:6 dr determined by integration of NMR signals at
2
0
.93 (H -14) and 0.79 ppm. [α] −21 (c 1.20, CHCl ). Literature
above, a mixture of alcohols 8 and 9 (110 mg, 77%) was isolated.
HPLC separation of this mixture provided 18 mg of 8, [α]
3
D
3
20
1
20
from ref 18 [α]D −16. H NMR (CDCl ): 0.93 (d, J = 6.9 Hz, 3H),
1
1
D
+141 (c
). H and
3
2
D
0
1
.10 (m, 1H), 1.33 (m, 1H), 1.59 (br s, 3H), 1.67 (br s, 3H), 1.81 (m,
H), 1.90 (m, 1H), 1.92 (br s, 3H), 1.97 (m, 1H), 2.02 (m, 1H), 2.07
1.28, CHCl
3
) and 23 mg of 9 [α]
−22 (c 0.42, CHCl
3
1
3
C NMR spectra of 8 and 9 matched those of their enantiomers 3
(
1
m, 1H), 2.18 (m, 1H), 2.29 (m, 2H), 5.10 (tqq, J = 6.9, 1.3, 1.3 Hz,
and 4, respectively (Supporting Information).
13
H), 5.83 (m, 1H). C NMR (CDCl ): 17.5, 17.8, 23.6, 24.2, 25.8,
(6R,7S)-2,10-Bisaboladien-1-one (12). Zingiberenol 11 (686 mg,
3
23
2
6.3, 30.8, 31.0, 33.5, 51.4, 124.9, 127.2, 131.4, 161.1, 201.2. NMR
3.10 mmol, 94:6 dr ) was stirred with PCC (3.32 g, 15.4 mmol) and
18
data are in agreement with reported.
NaOAc (246 mg, 3.0 mmol) in dry CH Cl (16 mL) at 0 to 25 °C
2
2
(1S,6R,7R)-2,10-Bisaboladien-1-ol (3) and (1R,6R,7R)-2,10-Bisa-
and then worked-up as described in the preparation of 2. Flash
boladien-1-ol (4). In a 5 mL oven-dried round-bottom flask in a N
chromatography with hexanes/EtOAc, 10:1, provided sesquipiper-
2
2
D
0
atmosphere was placed dry ether (1 mL). The flask was cooled to −30
C, and a solution of lithium aluminum hydride in diethyl ether (400
itone 12 (462 mg, 70%). [α] −41 (c 1.1, CHCl ); literature from
3
2
0
1
°
ref 18 [α]D −46 (c 3.1, CHCl ); dr 93:7 (GC on Rtx 1701). H
3
μL of 1.0 M, 0.40 μmol) was added. A solution of absolute EtOH (30
μL, 0.51 mmol) in ether (500 μL) was added slowly at −30 °C,
followed by a solution of ketone 1 (61 mg, 0.28 mmol) in ether (1
mL). The reaction was stirred at −30 to −25 °C for 1 h, at which
point TLC with hexanes/EtOAc, 10:1, shows a completion of the
NMR (CDCl ): 0.79 (d, J = 6.9 Hz, 3H), 1.29 (m, 2H), 1.59 (s, 3H),
3
1.68 (s, 3H), 1.77 (m, 1H), 1.93 (m, 3H), 1.89−1.97 (m, 2H), 2.01
(m, 1H), 2.15 (dt, J = 14.1, 4.6 Hz, 1H), 2,30 (m, 2H), 2.33 (m, 1H),
1
3
5.11 (tm, J = 7.2 Hz, 1H), 5.86 (m, 1H). C NMR (CDCl ): 15.8,
3
17.8, 22.2, 24.3, 25.9, 26.2, 30.4, 31.1, 34.9, 50.0, 124.7, 127.3, 131.6,
1
13
reaction. The mixture was quenched with 400 μL of H O, followed by
addition of 400 μL of 15% NaOH and 1.2 mL of H O. A white
161.3, 201.2. H and C NMR data matched those previously
18
2
2
described.
precipitate was filtered, and the ether solution was concentrated and
flash-chromatographed with hexanes/EtOAc, 11:1, to yield a mixture
of epimeric alcohols 3 and 4 (55 mg, 88%) in a 65:35 ratio by GC−
MS. This was further purified on a YMC 250 × 4.6 mm i.d. silica 5
μm, 12 nm HPLC column using two Waters Associates, Inc. pumps
(
model: m-6000) to achieve a gradient: hexanes (1 min) to hexanes/
EtOAc/MeOH, 10:0.5:0.2; flow rate 2 mL/min. The fractions (2 mL)
were monitored by TCL and GC−MS. Thus, we collected 12 mg of
the faster moving compound, 14 mg of the slower moving compound,
and 16 mg of a mixture.
2
0
2
0
The faster moving compound was identified as alcohol 3. [α]
D
1
−
135 (c 0.82, CHCl ). H NMR (CDCl ): 1.00 (d, J = 6.8 Hz, H -
3
3
3
1
4), 1.10 (m, H-6), 1.15 (m, H-8a), 1.35 (ddd, J = 24.8, 12.2, 5.8 Hz,
H-5a), 1.52 (m, H-7), 1.58 (m, H-8b), 1.61 (br s, H-13), 1.68 (br d, J
0.9 Hz, H-12), 1.69 (br s, H -15), 1.73 (m, H-5b), 1.87−2.09 (m,
=
3
E
https://dx.doi.org/10.1021/acs.jnatprod.0c00517
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
1
4
H). 13C NMR: 17.3, 17.8, 20.5, 23.6, 25.4, 25.9, 31.7, 33.1, 34.4,
(4) Sy, L.-K.; Brown, G. D. Phytochemistry 1997, 45, 537−544.
(5) Hong, S. S.; Oh, J. S. Arch. Pharmacal Res. 2012, 35, 315−320.
(6) Lancaster, J.; Khrimian, A.; Young, S.; Lehner, B.; Luck, K.;
Wallingford, A.; Ghosh, S. K. B.; Zerbe, P.; Muchlinski, A.; Marek, P.
4.3, 65.5, 123.9, 125.2, 131.4, 139.8. GC−MS (m/z, %): 222 (0.7%,
+
M ), 204 (30), 189 (8), 161 (32), 137 (24), 121 (35), 119 (100), 109
(
26), 105 (34), 93 (84), 91 (56), 77 (37), 69 (57), 55 (24), 41 (43).
20
D
Alcohol 14: [α]
+12 (c 0.67, CHCl ). Literature from ref 6
E.; Sparks, M. E.; Tokuhisa, J. G.; Tittiger, C.; Kollner, T. G.; Weber,
̈
3
α]D20 −15 (c 0.91, CHCl ) for enantiomeric alcohol 16. H NMR
1
[
(
3
4
D. C.; Gundersen-Rindal, D. E.; Kuhar, T. P.; Tholl, D. Proc. Natl.
Acad. Sci. U. S. A. 2018, 115, E8634−E8641.
3
CDCl ): 0.82 (d, J = 6.6 Hz, 3H), 1.20−1.37 (m, 5H), 1.60 (br. s,
3
H), 1.62 (m, 1H), 1.68 (br. s, 3H), 1.68 (br. s, 3H), 1.86−2.07 (m,
H), 4.03 (m, 1H), 5.12 (tm, J = 6.0 Hz, 1H), 5.39 (m, 1H).
(7) Khrimian, A.; Shirali, S.; Vermillion, K. E.; Siegler, M. A.;
Guzman, F.; Chauhan, K.; Aldrich, J. R.; Weber, D. C. J. Chem. Ecol.
2014, 40, 1260−1268.
1
3
C
NMR: 14.6, 17.9, 21.1, 23.3, 25.9, 26.4, 30.7, 31.2, 35.7, 46.67 69.4,
+
1
25.0, 125.9, 131.4, 137.6. GC-MS (m/z, %): 222 (1%, M ), 204
(8) Blassioli-Moraes, M. C.; Khrimian, A.; Michereff, M. F. F.;
Magalhaes, D. M.; Hickel, E.; de Freitas, T. F. S.; Barrigossi, J. A. F.;
Laumann, R. A.; Silva, A. T.; Guggilapu, S. D.; Silva, C. C.; Sant’Ana,
J.; Borges, M. J. Chem. Ecol. 2020, 46, 1−9.
(
26), 189 (7), 161 (21), 137 (34), 121 (40), 119 (100), 109 (21),
1
1
05 (34), 93 (68), 91 (46), 77 (29), 69 (53), 55 (24), 41 (40). H
13
and C NMR data for alcohols 13 and 14 matched those of the
enantiomeric alcohols 15 and 16, respectively.
6
(9) Borges, M.; Birkett, M.; Aldrich, J. R.; Oliver, J. E.; Chiba, M.;
Murata, Y.; Laumann, R. A.; Barrigossi, J. A.; Pickett, J. A.; Moraes, M.
C. B. J. Chem. Ecol. 2006, 32, 2749−2761.
ASSOCIATED CONTENT
■
(
3
(
10) Bohlmann, F.; Zdero, C.; Scho
366−3370.
11) Ghisalberti, E. L.; Jefferies, P. R.; Stuart, A. D. Aust. J. Chem.
̈
neweiss, S. Chem. Ber. 1976, 109,
*
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jnatprod.0c00517.
1
979, 32, 1627−1630.
Discussions of preparation Mosher’s esters and figures of
(12) Weyerstahl, P.; Marschall, H.; Eckhardt, A.; Christiansen, C.
1
13
ester structures, H, C, and 2D NMR spectra, and
COSY spectra (PDF)
Flavour Fragrance J. 1999, 14, 15−28.
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(
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6, 424−426.
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Suzuki, T.; Ando, M. J. Chem. Soc., Perkin Trans. 2002, 1, 895−900.
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J. 2010, 16, 7678−7682.
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085.
AUTHOR INFORMATION
■
Corresponding Author
́
Ashot Khrimian − Invasive Insect Biocontrol and Behavior
Laboratory, USDA-ARS, Beltsville Agricultural Research Center,
Beltsville, Maryland 20705, United States; orcid.org/0000-
(
́
ez-
(
4
(
0
003-3609-0370; Phone: (301) 504-6138;
Email: ashot.khrimian@usda.gov; Fax: (301) 504-5104
Authors
(
Sravanthi D. Guggilapu − Invasive Insect Biocontrol and
Behavior Laboratory, USDA-ARS, Beltsville Agricultural
Research Center, Beltsville, Maryland 20705, United States;
National Institute of Diabetes and Digestive and Kidney
Diseases, Laboratory of Bioorganic Chemistry, National
Institutes of Health, Bethesda, Maryland 20892, United States
Filadelfo Guzman − Invasive Insect Biocontrol and Behavior
Laboratory, USDA-ARS, Beltsville Agricultural Research Center,
Beltsville, Maryland 20705, United States
(
1
(21) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1973, 95, 512−519.
(22) Hoye, T. R.; Jeffrey, C. S.; Shao, F. Nat. Protoc. 2007, 2, 2451−
2558.
(23) Khrimian, A.; Zhang, A.; Weber, D. C.; Ho, H.-Y.; Aldrich, J.
R.; Vermillion, K. E.; Siegler, M. A.; Shirali, S.; Guzman, F.; Leskey, T.
C. J. Nat. Prod. 2014, 77, 1708−1717.
Maria Carolina Blassioli-Moraes − Semiochemicals, Embrapa
Genetic Resources and Biotechnology, 70770-917 Brasilia-DF,
Brazil
Miguel Borges − Semiochemicals, Embrapa Genetic Resources
and Biotechnology, 70770-917 Brasilia-DF, Brazil
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jnatprod.0c00517
Notes
Mention of trade names or commercial products in this
publication is solely for the purpose of providing specific
information and does not imply recommendation or endorse-
ment by the U.S. Department of Agriculture
The authors declare no competing financial interest.
REFERENCES
■
(
1) For terpene nomenclature see: Connolly, J. D.; Hill, R. A.
Dictionary of Terpenoids; Chapman and Hall: London, 1991; Vol. 1, p
1
(
2
(
80.
2) Bohlmann, F.; Tsankova, E.; Jakupovic, J. Phytochemistry 1984,
3, 1103−1104.
3) Cool, L. G. Phytochemistry 1996, 42, 1015−1019.
F
https://dx.doi.org/10.1021/acs.jnatprod.0c00517
J. Nat. Prod. XXXX, XXX, XXX−XXX