Synthesis and antifouling activity of 3-isocyanotheonellin and its analogues

Article abstract of DOI:10.1039/b206705f

A new synthesis of 3-isocyanotheonellin, a marine sesquiterpene with potent antifouling activity against the larvae of the barnacle Balanus amphirite, and its analogues is described. The highlight of the synthetic strategy is the one-step construction of

Full text of DOI:10.1039/b206705f

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Synthesis and antifouling activity of 3-isocyanotheonellin and
its analogues
Yoshikazu Kitano,*a Toshihiro Ito,a Takehiro Suzuki,a Yasuyuki Nogata,b Kyouji Shinshima,b
Erina Yoshimura,c Kazuhiro Chiba,a Masahiro Tadaa and Isamu Sakaguchib
1
a Laboratory of Bio-organic Chemistry, Tokyo University of Agriculture and Technology,
3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan. E-mail: kitayo@cc.tuat.ac.jp;
Fax: ϩ81 42 360 8830; Tel: ϩ81 42 367 5863
b Abiko Research Laboratory, Central Research Institute of Electric Power Industry,
1646 Abiko, Abiko, Chiba 270-1194, Japan
c Bio-environment Research Co. Ltd., 1-6-1 Ogawa-cho, Kanda, Chiyoda-ku, Tokyo 101-0052,
Japan
Received (in Cambridge, UK) 11th July 2002, Accepted 20th August 2002
First published as an Advance Article on the web 23rd September 2002
A new synthesis of 3-isocyanotheonellin, a marine sesquiterpene with potent antifouling activity against the larvae of
the barnacle Balanus amphirite, and its analogues is described. The highlight of the synthetic strategy is the one-step
construction of a tertiary isocyanide from an alcohol using trimethylsilyl cyanide and a silver salt. The antifouling
activities of 3-isocyanotheonellin and its analogues are also reported.
Introduction
Many benthic organisms are known to usually prevent settling
by other fouling organisms. This is considered to be because
they have developed a chemical defense system against
predators whose larvae settle on and become attached to prey.
Therefore, the metabolites of these benthic organisms are
potential non-toxic antifouling agents.1–5 A variety of natural
products with antifouling activity have been isolated from
marine organisms,6 and these may be expected to be lead com-
pounds in non-toxic antifouling agents. 3-Isocyanotheonellin 1,
isolated from a nudibranch species, is a sesquiterpene of the
bisabolene class with an isocyano functional group at the C-3
position.7,8 In spite of its simple structure, this natural product
exhibits potent antifouling activity against the larvae of the
barnacle Balanus amphirite (EC50 0.13 µg mLϪ1).9,10 However,
its toxicity in high concentrations and structure–activity
relationships with its analogues have not yet been demon-
strated. A total synthesis of 1 has previously been reported by
Ichikawa.11,12 We thought that a more efficient synthetic route
to this natural product, as well as various synthetic analogues,
and their antifouling activities would contribute to the field
of antifouling.
Recently, we reported an efficient direct method for the
preparation of isocyanides from tert-alcohols.13,14 This method
would be convenient for the preparation of isocyano com-
pounds. For this reason, we envisioned that this method could
be used to prepare an isocyano group of 1 and its analogues. We
describe herein a short total synthesis of 3-isocyanotheonellin 1
and its analogues and report on their antifouling activities.
Scheme 1 Synthetic plan.
Results and discussion
conjugated diene system of 1 and its geometrical isomer 2 could
Our synthetic plan starting with 1,4-cyclohexanedione mono-
ethylene ketal 5 is illustrated in Scheme 1. We envisioned that
analogues 2, 3, and 4 as well as 3-isocyanotheonellin 1 could be
obtained in the same manner. The key step is the direct iso-
cyanation of tert-alcohol 7 to afford isocyanosulfones 8 and 9.
Alcohol 7 could be prepared from 5 through the introduction
of an ethyl phenyl sulfonyl group followed by methylation. The
be constructed by a Julia olefination15 of 8 with 4-methylpent-
2-enal at the final stage. In addition, stereoisomer 3 and
its geometrical isomer 4 could also be prepared from 9 in the
same way.
The synthesis of tert-alcohol 7, the substrate of the key step,
is shown in Scheme 2. Ketone 5 was first reduced to alcohol
10 with NaBH4, which was then treated with TsCl and pyridine
DOI: 10.1039/b206705f
J. Chem. Soc., Perkin Trans. 1, 2002, 2251–2255
This journal is © The Royal Society of Chemistry 2002
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Table 1 Reactions of tert-alcohol 7 with TMSCN and AgX
Entry
AgX
Solvent
Yield (%)
Ratio (8 : 9)a
1
AgClO4
AgClO4
AgBF4
MeNO2
CH2Cl2
CH2Cl2
90
88
48
8 : 92
11 : 89
30 : 70
2
3b
a Determined by 1H-NMR. b 2.0 equiv. of TMSCN was used.
Scheme 2 Reagents and conditions: i, NaBH4, MeOH, 0 ЊC, quant.; ii,
TsCl, Pyr, rt, 98%; iii, n-BuLi, EtSO2Ph, 0 ЊC rt, 70%; iv, p-TsOH,
10% aq. acetone, 82%; v, MeLi, THF, 0 ЊC, 85% (7a : 7b, 2 : 3).
Table 2 Antifouling activities of compounds 1, 2, 3, and 4a
Compound
EC50 (µg mLϪ1
)
LD50 (µg mLϪ1
)
to give the tosylate† 11 in 98% yield over two steps. The nucleo-
philic substitution of tosylate 11 by ethyl phenyl sulfone,
lithiated with n-BuLi, yielded the desired sulfone 6 in 70% yield.
Sulfone 6 was converted to ketone 12 by deprotection of the
acetal with p-TsOH in 82% yield. Methylation of ketone 12
with MeLi led to the diastereomers of tert-alcohol 7a and 7b
(2 : 3) in 85% yield.
1
0.19
(0.13)
0.29
0.18
0.41
0.27
>100
—
>100
>100
>100
2.7
(Natural product)b
2
3
4
CuSO4
a The antifouling assay was repeated five times. b Refs. 9 and 10.
Our preliminary work had indicated that the direct isocyan-
ation of tert-alcohol 7 would produce mainly isocyanide 9,
which is the precursor of stereoisomer 3. Therefore, we
examined this step in the construction of isocyanides 8 and 9
from tert-alcohol 7 with TMSCN under various conditions to
obtain information on stereoselectivity. As indicated in Table 1,
excellent yields were obtained when the reactions of 7 were
performed with AgClO4 in nitromethane and dichloromethane.
Although 9 was the major product in all cases the stereo-
selectivity was moderately changed when AgBF4 was used in
dichloromethane, with the yield of 9 being reduced (entry 3).
Synthesis of 3-isocyanotheonellin 1 and its analogues 2, 3,
and 4 was accomplished by the Julia olefination,15 which is
shown in Scheme 3, as the final stage of the reaction. Treatment
gave the geometrical 2 : 1 mixture of 1 and (Z,E)-diene 2 in
50% yield from 8. The mixture of 1 and 2 was separated into
pure compounds by HPLC. The spectroscopic data of 1 were
identical to those reported in the literature. The analogues
3 and 4 were synthesized in 58% yield from isocyanosulfone 9
using the same method.
We next explored the structure–activity relationship of
3-isocyanotheonellin 1. The antifouling activities of 1 and its
analogues 2, 3, and 4 were evaluated against larvae of the
barnacle Balanus amphirite, and the activity of CuSO4 was also
evaluated as a positive control. Antifouling tests were carried
out using cyprid larvae cultured as follows. Adult barnacles,
Balanus amphirite, attached to bamboo poles were procured
from oyster farms in Lake Hamana, Shizuoka, and maintained
in an aquarium at 20 ЊC by feeding on Artemia salina nauplii.
Broods released I-II stage nauplii upon immersion in seawater
after drying for 1 day. Nauplii thus obtained were cultured in
80%-filtered seawater at 25 ЊC by feeding with the diatom
Chaetoceros gracilis at concentrations of 2.5 × 105 cells mLϪ1
.
During days 1–4, larvae were washed in 80%-filtered seawater
and were transferred to fresh vessels containing the C. gracilis
suspension. Larvae reached the cyprid stage in 5 days. The
cyprids were stored at 5 ЊC until used. Test samples were dis-
solved in ethanol; aliquots of the solution were added to the
wells in 24-well polystyrene tissue culture plates and were air-
dried. To each well was added 2 mL of 80%-filtered seawater
and six two-day-old cyprids. Four wells were used for each
experiment. The plates were kept in the dark for 48 h and
120 h at 25 ЊC, and the number of larvae which attached,
metamorphosed, died, or did not settle were counted under a
microscope.
The 50% settlement inhibitory effect (EC50) and 50% lethal
dose (LD50) are shown in Table 2. The activity exhibited by the
synthesized 3-isocyanotheonellin 1 was almost equivalent to
that of the natural product. Indeed, the activity exhibited by
stereoisomer 3 was almost as high as that of 1. Furthermore,
(Z,E)-dienes 2 and 4 also exhibited potent activity, although
this was slightly lower than for 1. In addition, these compounds
showed a low mortality rate (LD50 > 100 µg mLϪ1) in high
concentrations, and the antifouling activities of 1 and 11 were
Scheme 3 Reagents and conditions: i, LDA, THF, then 4-methylpent-
2-enal, Ϫ78 ЊC; ii, Ac2O, pyr, rt; iii, 5% Na–Hg, Na2HPO4, EtOAc–
MeOH, Ϫ10 ЊC, (1 : 2, 2 : 1, 50%; 3 : 4, 2 : 1, 55%).
of isocyanosulfone 8 with LDA followed by entrapment of
the generated anion with 4-methylpent-2-enal provided the
coupling product, which was converted to the corresponding
β-acetoxysulfone with acetic anhydride and pyridine. Reductive
elimination of the β-acetoxysulfone by a sodium amalgam
† The IUPAC name for tosylate is toluene-p-sulfonate.
2252
J. Chem. Soc., Perkin Trans. 1, 2002, 2251–2255

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stronger than those observed for CuSO4. From these results, we
determined that the isocyano function was an important factor
in the exhibition of potent antifouling activity.
29.13, 21.65; IR (KBr) 3043, 2958, 2881, 1598, 1448, 1351,
1189, 1095 cmϪ1; LR-EIMS: m/z (%) 312 (Mϩ, 15), 140 (39), 99
(100), 86 (11); HR-EIMS: calcd for C15H20O5S 312.1031, found
312.1020.
Conclusion
4-[(1-Phenylsulfonyl)ethyl]cyclohexan-1-one ethylene ketal 6
In conclusion, we have achieved a short total synthesis of
3-isocyanotheonellin 1 using a one-step construction of iso-
cyanide from a tert-alcohol as a key step. Moreover, three
analogues were synthesized in the same manner, and their
antifouling activities were evaluated against the larvae of the
barnacle Balanus amphirite. The synthesized 1 and its ana-
logues exhibited high antifouling activity without significant
toxicity. These results will allow us to investigate the structure–
activity relationships in more detail by using various derivatives
of 3-isocyanotheonellin 1 in the future.
To a solution of ethyl phenyl sulfone (5.31 g, 31.2 mmol) in
THF (100 mL) cooled at 0 ЊC was added n-BuLi (1.6 M in
hexane, 19.5 mL, 31.2 mmol) under an argon atmosphere. The
resulting yellow solution was stirred for 30 min, and then a
solution of tosylate 11 (6.5 g, 20.8 mmol) in THF (40 mL) was
added over 10 min at 0 ЊC under an argon atmosphere. The
reaction mixture was warmed to room temperature and stirred
at ambient temperature for an additional 40 h. After the reac-
tion was quenched by addition of aqueous NH4Cl (20 mL), the
mixture was extracted with EtOAc (300 mL). The combined
extracts were washed with water and brine, dried (MgSO4), and
concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel (EtOAc–hexane =
1 : 3–1 : 1) to give a white solid of 6 (4.5 g, 70%). Recrystalliza-
tion from EtOAc–hexane provided an analytically pure crystal-
line sample of sulfone 11; white crystals, mp 104–105 ЊC (from
EtOAc–hexane); 1H NMR δ 7.90–7.87 (2H, m), 7.67–7.63 (1H,
m), 7.59–7.54 (2H, m), 3.96–3.90 (4H, m), 3.01–2.92 (1H, dq,
J = 7 and 2.5 Hz), 2.30–2.23 (1H, m), 2.04–1.98 (1H, m),
1.81–1.75 (2H, m), 1.67–1.51 (4H, m), 1.50–1.41 (1H, m), 1.22
(3H, d, J = 7.0 Hz); 13C NMR δ 138.51, 133.53, 129.15, 128.65,
108.07, 64.31, 64.27, 63.97, 34.95, 34.82, 34.22, 29.46, 24.17,
9.31; IR (KBr) 3064, 2985, 2931, 2875, 1448, 1303, 1159, 1139,
1103 cmϪ1; LR-EIMS: m/z (%) 310 (Mϩ, 3), 169 (20), 141 (33),
99 (100), 77 (9); HR-EIMS: calcd for C16H22O4S 310.1239,
found 310.1239.
Experimental
Mps were determined on a MEL-TEMP (Laboratory Device)
and are uncorrected. NMR spectra were obtained in CDCl3 on
a JEOL Alpha-600 spectrometer. All 1H NMR spectra are
reported in ppm relative to TMS. All 13C NMR spectra are
reported in ppm relative to the central line of the triplet for
CDCl3 at 77.03 ppm. IR spectra were recorded on a JEOL
WINSPEC-50 spectrometer. Low- and high-resolution mass
spectra were recorded on a JEOL SX-102A spectrometer under
ionization conditions (70 eV). Chromatographic separations
were carried out on a silica gel column (Fuji Silysia Chemical
BW-127ZH; 100–270 mesh). HPLC was performed on a
HITACHI L-6000 Pump instrument equipped with an L-4000
UV Detector (254 nm). The stereochemistry of compounds
7a and 7b were established from NOE experiments.
4-[(1-Phenylsulfonyl)ethyl]cyclohexan-1-one 12
4,4-Ethylenedioxycyclohexan-1-ol 10
To a solution of acetal 11 (4.4 g, 14.17 mmol) in acetone–water
(100 mL, 9 : 1) was added TsOHؒH2O (266 mg, 1.4 mmol), and
the resulting solution was refluxed for 12 h. After removal of
the solvent under reduced pressure, the residue was diluted with
EtOAc (200 mL). The organic layers were then washed with
aqueous NaHCO3 and brine, dried (MgSO4), and concentrated
under reduced pressure. The residue was purified by recrystal-
lization from EtOAc–hexane to give white crystals of ketone
12 (3.1 g, 82%); white crystals, mp 124–126 ЊC (from EtOAc–
To a solution of ketone 5 in methanol (50 mL) was added
sodium borohydride (1.46 g, 38.4 mmol) at 0 ЊC, and the reac-
tion mixture was stirred at 0 ЊC for 2 h. After removal of the
solvent under reduced pressure, brine (30 mL) was added to the
residue, and the resultant mixture was then extracted with
EtOAc (300 mL). The combined extracts were washed with
water and brine, dried (MgSO4), and concentrated under
reduced pressure. The obtained crude alcohol 10 (5.06 g,
quant.) was used in the next experiment without purification.
1H NMR δ 3.98–3.92 (4H, m), 3.83–3.78 (1H, m), 1.91–1.86
(2H, m), 1.84–1.79 (2H, m), 1.70–1.55 (4H, m), 1.37 (1H, br s);
13C NMR δ 108.26, 68.20, 64.33, 64.30, 32.06, 31.58; IR (neat)
3500 (br), 2940, 2886, 1234, 1143, 1105 cmϪ1; LR-EIMS:
m/z (%) 158 (Mϩ, 31), 140 (7), 111 (19), 99 (100), 86 (94);
HR-EIMS: calcd for C8H14O3 158.0943, found 158.0945.
1
hexane); H NMR δ 7.93–7.89 (2H, m), 7.70–7.66 (1H, m),
7.62–7.57 (2H, m), 3.08 (1H, dq, J = 7 and 3 Hz), 2.79–2.72 (1H,
m), 2.47–2.35 (5H, m), 1.98–1.92 (1H, m), 1.78–1.67 (1H, m),
1.66–1.56 (1H, m), 1.21 (3H, d, J = 7 Hz); 13C NMR δ 210.13,
138.19, 133.81, 129.31, 128.68, 63.26, 41.06, 40.48, 34.58, 31.80,
26.91, 9.52; IR (KBr) 3083, 2970, 2929, 2867, 1714, 1583, 1479,
1313, 1265, 1174 cmϪ1; LR-EIMS: m/z (%) 266 (Mϩ, 3), 124
(100), 97 (12), 77 (19); HR-EIMS: calcd for C14H18O3S
266.0977, found 266.0976.
4,4-Ethylenedioxycyclohexyl toluene-p-sulfonate 11
To a solution of alcohol 10 (5.0 g, 31.6 mmol) in dry pyridine
(30 mL) was added toluene-p-sulfonyl chloride (7.24 g,
38 mmol). After the reaction mixture was stirred at ambient
temperature for 18 h, the reaction was quenched with brine
(30 mL), and the resultant mixture was then extracted with
EtOAc (300 mL). The combined extracts were washed with 3 M
HCl, aqueous NaHCO3, and brine, dried (MgSO4), and con-
centrated under reduced pressure. The residue was purified by
column chromatography on silica gel (EtOAc : hexane = 1 : 2) to
give a white solid of tosylate 11 (9.67 g, 98%). Recrystallization
from EtOAc–hexane provided an analytically pure crystalline
sample of tosylate 11; white crystals, mp 67–68 ЊC (from
EtOAc–hexane); 1H NMR δ 7.80 (2H, d, J = 8 Hz), 7.33 (2H, d,
J = 8 Hz), 4.67–4.62 (1H, m), 3.95–3.88 (4H, m), 2.45 (3H, s),
1.90–1.75 (6H, m), 1.59–1.51 (2H, m); 13C NMR δ 144.50,
134.55, 129.80, 127.59, 107.40, 78.90, 64.38, 64.35, 30.67,
trans-1-Methyl-4-[(1-phenylsulfonyl)ethyl]cyclohexan-1-ol 7a
and cis-1-methyl-4-[(1-phenylsulfonyl)ethyl]cyclohexan-1-ol 7b
To a solution of MeLi (1.14 M in Et2O, 25.0 mL, 28.5 mmol) in
THF (30 mL) cooled at 0 ЊC was added a solution of ketone
12 (2.48 g, 9.31 mmol) in THF (20 mL) under an argon atmos-
phere. After the reaction mixture was stirred at 0 ЊC for 1 h, the
reaction was quenched and neutralized with 3M HCl (9.5 mL),
and the resultant mixture was then extracted with EtOAc (200
mL). The combined extracts were washed with water and brine,
dried (MgSO4), and concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel
(EtOAc–hexane = 1 : 2–1 : 1) to give white crystals of 7a and 7b
(922 mg and 1.31 g, 85%). Recrystallization from EtOAc–
hexane provided analytically pure crystalline samples of alco-
hol 7a and 7b.
J. Chem. Soc., Perkin Trans. 1, 2002, 2251–2255
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1
7a; White crystals, mp 94–96 ЊC (from EtOAc–hexane); H
0.8 mmol)] in THF (5 mL) cooled at Ϫ78 ЊC was added a
solution of isocyanide 8 (115 mg, 0.395 mmol) in THF (5 mL)
under an argon atmosphere. After the mixture was stirred at
Ϫ78 ЊC for 20 min, 4-methylpent-2-enal (10 µL, 0.86 mmol) was
added and stirring was continued for a further 30 min under an
argon atmosphere. After the reaction was quenched by addition
of aqueous NH4Cl (20 mL), the mixture was extracted with
EtOAc (150 mL). The combined extracts were washed with
water and brine, dried (MgSO4), and concentrated under
reduced pressure. The residue was roughly purified by column
chromatography on silica gel (EtOAc–hexane = 1 : 3–1 : 2) to
give a crude β-hydroxysulfone (135 mg). This was dissolved in a
mixture of acetic anhydride (2 mL) and pyridine (2 mL). After
the mixture was stirred at ambient temperature for 10 h, the
reaction was quenched with brine (10 mL), and the resultant
mixture was then extracted with EtOAc (150 mL). The com-
bined extracts were washed with 1 M HCl, aqueous NaHCO3,
and brine, dried (MgSO4), and concentrated under reduced
pressure. The residue was roughly purified by column chrom-
atography on silica gel (EtOAc–hexane = 1 : 2) to give a crude
β-acetoxysulfone (140 mg). This, dissolved in MeOH–EtOAc
(15 mL, 2 : 1), was treated with Na2HPO4 (150 mg, 1.05 mmol)
followed by 5% sodium amalgam (1.3 g) at Ϫ10 ЊC under an
argon atmosphere. After the reaction mixture was stirred at
ambient temperature for 12 h, the reaction was quenched with
water and the resultant mixture was then extracted with Et2O
(150 mL). The combined extracts were washed with water
and brine, dried (MgSO4), and concentrated under reduced
pressure. The residue was purified by column chromatography
on silica gel (EtOAc–hexane = 1 : 20) to give a mixture of
3-isocyanoteonellin 1 and 2 (2 : 1, 45 mg, 50%). A part of
the mixture was further purified by reversed-phase HPLC
(Mightysil RP-18, 250–50 mm; 80% MeOH) to give pure 1
(24 mg) and 2 (12 mg).
NMR δ 7.91–7.86 (2H, m), 7.68–7.63 (1H, m), 7.60–7.54 (2H,
m), 2.99 (1H, dq, J = 7 and 3 Hz), 2.23–2.13 (1H, m), 2.01–1.92
(1H, m), 1.78–1.70 (2H, m), 1.60–1.45 (3H, m), 1.44–1.34 (2H,
m), 1.33–1.24 (1H, m), 1.22 (3H, s), 1.21 (3H, d, J = 7 Hz);
13C NMR δ 138.49, 133.55, 129.16, 128.62, 70.25, 63.79,
40.16, 39.71, 35.87, 29.33, 25.41, 24.60, 9.62; IR (KBr) 3502,
3372, 3062, 2977, 2942, 2854, 1448, 1303, 1145, 1085 cmϪ1; LR-
EIMS: m/z (%) 282 (Mϩ, 2), 267 (8), 212 (14), 170 (4), 143 (23),
123 (100), 81 (74); HR-EIMS: calcd for C15H22O3S 282.1290,
found 282.1290.
7b; White crystals, mp 119–121 ЊC; 1H NMR δ 7.91–7.86 (2H,
m), 7.67–7.63 (1H, m), 7.59–7.54 (2H, m), 2.96 (1H, dq, J = 7
and 2.5 Hz), 2.24–2.16 (1H, m), 1.85–1.79 (1H, m), 1.75–1.33
(7H, m), 1.23 (3H, d, J = 7 Hz), 1.21 (3H, s), 0.99 (1H, br s); 13
C
NMR δ 138.66, 133.47, 129.12, 128.64, 68.65, 64.44, 38.67,
38.25, 35.34, 31.56, 27.32, 22.23, 9.45; IR (KBr) 3504, 3426,
3068, 2958, 2927, 2877, 2854, 1446, 1295, 1137, 1087 cmϪ1
;
LR-EIMS: m/z (%) 282 (Mϩ, 0.7), 267 (5), 212 (4), 170 (4), 143
(18), 123 (100), 81 (62); HR-EIMS: calcd for C15H22O3S
282.1290, found 282.1291.
trans-1-Methyl-4-[(1-phenylsulfonyl)ethyl]cyclohexyl isocyanide
8 and cis-1-methyl-4-[(1-phenylsulfonyl)ethyl]cyclohexyl
isocyanide 9
To a solution of alcohol 7 (2 : 3 mixture of 7a and 7b, 141 mg,
0.5 mmol) in dichloromethane (1 mL) were added TMSCN
(135 µL, 1.0 mmol) and then AgBF4 (194 mg, 0.5 mmol) under
an argon atmosphere. The reaction mixture was stirred at
ambient temperature for 2 h, and the reaction was then
quenched with aqueous NaHCO3 (1 mL). After being stirred
for an additional 10 min, the mixture was filtered with celite and
washed with EtOAc (100 mL). The combined extracts were
washed with water and brine, dried (MgSO4), and concentrated
under reduced pressure. The residue was passed through a short
silica gel column (EtOAc–hexane = 1 : 1) to give a 3 : 7 mixture
of isocyanides 8 and 9 (70 mg, 48%). Pure isocyanides 8 and
9 were obtained by collecting the products of a repeated
reaction and then using silica gel column chromatography
(EtOAc–hexane = 1 : 3) and preparative TLC. Recrystallization
from ethyl acetate–hexane provided analytically pure crystalline
samples of isocyanide 8 and 9.
1
1; Colorless oil; H NMR δ 6.21 (1H, ddd, J = 15, 10.5 and
1 Hz), 5.80 (1H, dd, J = 10.5 and 1 Hz), 5.59 (1H, dd, J = 15 and
7 Hz), 2.39–2.31 (1H, m), 2.00–1.88 (3H, m), 1.86–1.78 (2H, m),
1.75–1.67 (5H, m) including 1.72 (3H, br s), 1.47–1.37 (5H, m)
including 1.44 (3H, t, J = 2 Hz), 1.01 (6H, d, J = 6.5 Hz) [lit.12
(300 MHz, CDCl3) δ 6.20 (1H, ddd, J = 15, 10.8, 1 Hz), 5.79
(1H, d, J = 10.8 Hz), 5.58 (1H, dd, J = 15, 6.8 Hz), 2.33 (1H, m),
1.70 (3H, br s), 1.42 (3H, t, J = 2 Hz), 0.99 (6H, d, J = 6.8 Hz);
lit.7 (200 MHz, CDCl3) δ 6.21 (1H, dd, J = 15, 10 Hz), 5.80 (1H,
d, J = 10 Hz), 5.60 (1H, dd, J = 15, 7 Hz), 2.35 (1H, m), 1.72
(3H, s), 1.43 (3H, br s), 1.01 (6H, d, J = 7 Hz)]; 13C NMR
δ 152.14 (t, J = 5 Hz), 140.75, 140.75, 138.70, 123.87, 123.42,
56.77 (t, J = 5 Hz), 44.81, 38.27, 31.42, 26.48, 25.12, 22.54, 15.24
[lit.12 (75 MHz, CDCl3) δ 152.2, 140.5, 138.4, 123.7, 123.3, 56.6,
44.6, 38.1, 31.5, 26.3, 22.4, 15.1; lit.7 (67.80 MHz, CDCl3)
δ 152.2 (br t, J = 4 Hz), 140.6, 138.6, 123.8, 123.4, 56.7, 44.8,
38.2 (t, J = 5 Hz), 31.4, 26.4, 25.1, 22.5, 15.2]; IR (neat) 3033,
2954, 2923, 2852, 2129, 1463, 1380, 1259, 1126, 964 cmϪ1 [lit.12
(neat) 3040, 2970, 2880, 2130, 1470, 1385, 1128, 965 cmϪ1; lit.7
(CHCl3) 2120 (NC), 1460, 1370, 1120 cmϪ1]; LR-EIMS: m/z (%)
231 (Mϩ, 46), 216 (8), 204 (21), 189 (25), 188 (14), 161 (54),
121 (49), 105 (88), 95 (73), 93 (100); HR-EIMS: calcd. for
C16H25N 231.1987, found 231.2004 [lit.12 found 231.1975; lit.7
231.1970].
1
8; White crystals, mp 115–116 ЊC (from EtOAc–hexane); H
NMR δ 7.90–7.85 (2H, m), 7.69–7.64 (1H, m), 7.60–7.55 (2H,
m), 2.97 (1H, dq, J = 7 and 3.5 Hz), 2.23–2.16 (1H, m), 2.00–
1.80 (5H, m), 1.64–1.57 (1H, m), 1.52–1.44 (4H, m), 1.43 (3H, t,
J = 2 Hz), 1.39–1.31 (1H, m), 1.20 (3H, d, J = 7.5 Hz); 13C NMR
δ 152.74 (t, J = 5 Hz), 138.27, 133.73, 129.25, 128.63, 63.19,
56.15 (t, J = 5 Hz), 38.26, 37.86, 35.19, 26.82, 24.72, 23.01,
10.15; IR (KBr) 3068, 2985, 2946, 2865, 2134, 1448, 1303, 1141,
1087 cmϪ1; LR-EIMS: m/z (%) 291 (Mϩ, 1), 265 (1), 167 (4),
150 (7), 123 (60), 122 (100), 107 (30), 93 (49); HR-EIMS: calcd
for C16H21O2NS 291.1293, found 291.1294.
1
9; White crystals, mp 105–106 ЊC (from EtOAc–hexane); H
NMR δ 7.91–7.86 (2H, m), 7.69–7.64 (1H, m), 7.61–7.55 (2H,
m), 3.00–2.94 (1H, dq, J = 7 and 2.5 Hz), 2.33–2.25 (1H, m),
2.03–1.91 (3H, m), 1.73–1.51 (3H, m), 1.50–1.37 (5H, m)
including 1.43 (3H, br s), 1.24 (3H, d, J = 7.5 Hz); 13C NMR
δ 154.33 (t, J = 5 Hz), 138.37, 133.63, 129.20, 128.60, 63.94,
57.61 (t, J = 5 Hz), 38.10, 37.52, 34.42, 29.77, 27.25, 22.39, 9.50;
IR (KBr) 3062, 2985, 2929, 2859, 2132, 1446, 1301, 1143, 1089
cmϪ1; LR-EIMS: m/z (%) 291 (Mϩ, 1), 264 (2), 167 (2), 150 (12),
123 (81), 122 (100), 107 (30), 93 (49); HR-EIMS: calcd for
C16H21O2NS 291.1293, found 291.1291.
2; Colorless oil; 1H NMR δ 6.19 (1H, dd, J = 15 and 11 Hz),
5.76 (1H, d, J = 11 Hz), 5.56 (1H, dd, J = 15 and 7.5 Hz), 2.61
(1H, tt, J = 12 and 4 Hz), 2.39–2.30 (1H, m), 2.03–1.97 (2H, m),
1.95–1.88 (2H, m), 1.67 (3H, br s), 1.54–1.40 (6H, s) including
1.47 (3H, t, J = 2 Hz), 1.33–1.25 (1H, m), 1.01 (6H, d, J = 7 Hz);
13C-NMR δ 152.00 (t, J = 5 Hz), 140.79, 138.60, 126.10, 122.23,
56.33 (t, J = 5 Hz), 38.80, 31.47, 26.21, 24.36, 22.62, 19.73,
14.14; IR (neat) 3033, 2958, 2923, 2854, 2129, 1456, 1380, 1255,
1120, 964 cmϪ1; LR-EIMS: m/z (%) 231 (Mϩ, 60), 216 (11),
204 (26), 189 (35), 188 (19), 161 (48), 121 (65), 105 (89), 95
(84), 93 (100); HR-EIMS: calcd for C16H25N 231.1987, found
231.1981.
3-Isocyanotheonellin 1 and trans-4-[(Z,E )-1,5-dimethylhexan-
1,3-dienyl]-1-methylcyclohexyl isocyanide 2
To a solution of LDA [prepared from diisopropylamine
(0.12 mL, 0.84 mmol) and n-BuLi (1.6 M in hexane, 0.5 mL,
2254
J. Chem. Soc., Perkin Trans. 1, 2002, 2251–2255

View Article Online
cis-4-[(E,E )-1,5-Dimethylhexan-1,3-dienyl]-1-methylcyclohexyl
isocyanide 3 and cis-4-[(Z,E )-1,5-dimethylhexan-1,3-dienyl]-1-
methylcyclohexyl isocyanide 4
Acknowledgements
We express our sincere thanks to Professor N. Fusetani of
The University of Tokyo for his helpful suggestions. We also
gratefully acknowledge Associate Professor K. Okamoto of
The University of Tokyo for providing the collection of
barnacles. This work was partly supported by the Sasakawa
Scientific Research Grant from The Japan Science Society.
These compounds were obtained from isocyanide 9 (314 mg,
1.07 mmol) by the same procedure described for its isomer to
give a mixture of 3 and 4 (2 : 1, 146 mg, 59%). A part of the
mixture was also further purified by the same procedure to give
pure 3 (40 mg) and 4 (20 mg).
1
3; Colorless oil; H NMR δ 6.22 (1H, ddd, J = 15, 10.5 and
1 Hz), 5.84 (1H, d, J = 10.5 Hz), 5.60 (1H, dd, J = 15 and 7 Hz),
2.40–2.31 (1H, m), 1.98–1.93 (2H, m), 1.88–1.81 (1H, m), 1.75
(3H, br s), 1.74–1.61 (4H, m), 1.43 (3H, t, J = 2 Hz), 1.41–1.33
(2H, m), 1.02 (6H, d, J = 6.5 Hz); 13C NMR δ 153.93 (t, J = 4
Hz), 140.49, 139.60, 123.84, 123.44, 57.75 (t, J = 5 Hz), 46.02,
38.31, 31.40, 30.06, 26.71, 22.54, 14.77 [lit.;11 (CDCl3) δ 153.9,
140.2, 139.2, 123.7, 123.3, 57.6, 46.0, 38.3, 31.3, 30.0, 26.7,
22.5, 14.7]; IR (neat) 3033, 2958, 2931, 2854, 2129, 1456,
1380, 1249, 1124, 964 cmϪ1; LR-EIMS: m/z (%) 231 (Mϩ, 73),
216 (33), 204 (35), 189 (100), 188 (78), 136 (63), 121 (61), 95
(89), 93 (83); HR-EIMS: calcd for C16H25N 231.1987, found
231.1975.
References
1 A. R. Davis, N. M. Target, O. J. McConnell, C. M. Young, in
Bioorganic Marine Chemistry, ed. P. J. Scheuer, Springer-Verlag,
Berlin, 1989, vol. 3, pp. 83–114.
2 M. Wahl, Mar. Ecol.: Prog. Ser., 1989, 58, 301–312.
3 A. S. Clare, D. Rittschof, D. J. Gerhart and J. S. Maki, Invert.
Reprod. Dev., 1992, 22, 67–76.
4 J. R. Pawlik, Oceanogr. Mar. Biol. Annual Review, 1992, 30, 273–335.
5 S. Abarzua and S. Jakubowski, Mar. Ecol.: Prog. Ser., 1995, 123,
301–312.
6 For examples, see: refs. 3 and 4.
7 N. K. Gulavita, E. D. Silva, M. R. Hagadone, P. Karuso, P. J.
Scheuer, G. D. Van Duuyne and J. Clardy, J. Org. Chem., 1986, 51,
5136–5139.
8 K. E. Kassühlke, B. C. M. Potts and D. J. Faulkner, J. Org. Chem.,
1991, 56, 3747–3750.
9 T. Okino, E. Yoshimura, H. Hirota and N. Fusetani, Tetrahedron,
1996, 52, 9447–9454.
10 N. Fusetani, H. Hirota, T. Okino, Y. Tomono and E. Yoshimura,
J. Nat. Toxins, 1996, 5, 249–259.
11 Y. Ichikawa, Synlett, 1991, 715–716.
12 Y. Ichikawa, J. Chem. Soc., Perkin Trans. 1, 1992, 2135–2139.
13 Y. Kitano, K. Chiba and M. Tada, Tetrahedron Lett., 1998, 38,
1911–1912.
14 Y. Kitano, K. Chiba and M. Tada, Synthesis, 2001, 437–443.
15 M. Julia and J. M. Paris, Tetrahedron Lett., 1973, 4833–4836.
4; Colorless oil; 1H NMR δ 6.19 (1H, dd, J = 15 and 11 Hz),
5.77 (1H, d, J = 11 Hz), 5.55 (1H, dd, J = 15 and 7 Hz), 2.53
(1H, tt, J = 12 and 3 Hz), 2.38–2.28 (1H, m), 1.99–1.92 (2H, m),
1.84–1.75 (2H, m), 1.74 (3H, br s), 1.54–1.39 (7H, m) including
1.45 (3H, t, J = 2 Hz), 1.00 (6H, d, J = 7 Hz); 13C NMR δ 154.00
(t, J = 5 Hz), 140.36, 139.61, 125.61, 122.35, 57.67 (t, J = 5 Hz),
38.53, 38.18, 31.47, 26.01, 22.64, 19.81; IR (neat) 3033, 2962,
2935, 2865, 2127, 1446, 1380, 1245, 1128, 966 cmϪ1; LR-EIMS:
m/z (%) 231 (Mϩ, 78), 216 (43), 204 (19), 189 (88), 188 (100), 136
(75), 121 (66), 95 (93), 93 (83); HR-EIMS: calcd for C16H25N
231.1987, found 231.1968.
J. Chem. Soc., Perkin Trans. 1, 2002, 2251–2255
2255