Novel synthetic approach to (S)-coriolic acid

Article abstract of DOI:10.1016/S0040-4020(99)01003-0

A new synthetic approach to (S)-coriolic acid 1 has been developed, starting from the readily available (E)-1-bromo-2-trimethylsilylethene 4 and trimethylsilylacetylene 5. A simple acylation reaction of 4, followed by a coupling reaction of the halogenoderivative intermediate with 5 in the presence of a Pd(0) catalyst affords the monosilylated ketoenyne 7. After desilylation of 7, enantioselective reduction of the carbonyl group with (S)- BINAL-H leads to the alcohol 2 (e.e.=94%). A subsequent coupling reaction and stereoselective reduction of the triple bond affords the target molecule 1.

Full text of DOI:10.1016/S0040-4020(99)01003-0

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 327–331
Novel Synthetic Approach to (S)-Coriolic Acid
*
Francesco Babudri, Vito Fiandanese, Giuseppe Marchese and Angela Punzi
`
Centro CNR di Studio sulle Metodologie Innovative di Sintesi Organiche, Dipartimento di Chimica, Universita di Bari, via Amendola 173,
70126 Bari, Italy
Received 21 September 1999; revised 19 October 1999; accepted 4 November 1999
Abstract—A new synthetic approach to (S)-coriolic acid 1 has been developed, starting from the readily available (E)-1-bromo-2-trimethyl-
silylethene 4 and trimethylsilylacetylene 5. A simple acylation reaction of 4, followed by a coupling reaction of the halogenoderivative
intermediate with 5 in the presence of a Pd(0) catalyst affords the monosilylated ketoenyne 7. After desilylation of 7, enantioselective
reduction of the carbonyl group with (S)-BINAL-H leads to the alcohol 2 ꢀe:e:ˆ94%†: A subsequent coupling reaction and stereoselective
reduction of the triple bond affords the target molecule 1. ᭧ 1999 Elsevier Science Ltd. All rights reserved.
Introduction
synthesis of a series of natural compounds18–23 with a conju-
gated polyenyl structure, starting from unsaturated silyl
derivatives. Thus, we considered compound 1 as an attrac-
tive target for synthesis and now we wish to report a novel
synthetic approach to (S)-coriolic acid.
Coriolic acid 1 is an oxygenated unsaturated fatty acid
deriving from the metabolism of linoleic acid in plants
and animals and possessing interesting biological proper-
ties. Compound 1 has been isolated from rice (Oryza sativa
L.) and shown to act as a self defense substance against rice
blast disease.1 Furthermore, coriolic acid 1 is present in
bovine heart mitochondria2 and in the sera of patients with
familiar Mediterranean fever.3 These properties have
prompted numerous synthetic4–9 and chemo-enzymatic10–16
approaches to this valuable compound. Frequently the
Wittig reaction4 is employed between a chiral unsaturated
hydroxy aldehyde and the appropriate phosphonium salt in
order to generate the (E,Z)-dienyl moiety5,6,10 or compound
1 can be conveniently obtained by the action of soybean
lipoxygenase on linoleic acid followed by sodium boro-
hydride reduction.11–14 Alternative methodologies involve
coupling reactions of chiral hydroxy vinyl halides with
fatty acids containing a terminal triple bond,7,15 or of a chiral
alkynol with the appropriate (Z)-vinyl halide,9 or coupling
reactions of chiral (E)-hydroxy vinylstannanes with
(Z)-vinyl halides.8,16
Results and Discussion
Our overall synthesis design is summarized in a retro-
analytical fashion in Scheme 1.
Thus, the disconnection of the C8–C9 bond leads to the
chiral fragment 2, whose stereogenic center can be obtained
by enantioselective reduction of the unsaturated carbonyl
compound 3. The unsaturated moiety of the ketone 3 can
be realized by employing simple silyl derivatives 4 and 5.
The key steps leading to compound 1 require a coupling
reaction of the chiral fragment 2 with the appropriate halo-
geno acid and stereoselective reduction of the triple bond.
Accordingly, the synthesis of the alcohol 2 was performed
as depicted in Scheme 2. The intermediate 6 was obtained in
99% yield, by a simple acylation reaction24 of (E)-1-bromo-
2-trimethylsilylethene 4 with the hexanoyl chloride/AlCl3
complex, as a 70:30 mixture of compound 6a (the bromo-
vinylketone) and compound 6b (the chlorovinylketone).
[The acylation reaction, which should be an addition reac-
tion of the acyl chloride, followed by an elimination reac-
tion of trimethylsilyl chloride,25 probably also involves the
elimination of trimethylsilyl bromide.] The subsequent
reaction of compound 6 with trimethylsilylacetylene 5 in
the presence of a Pd(0) catalyst26 led to the monosilylated
ketoenyne 7 in 61% yield. Desilylation of compound 7 with
KF/MeOH led to the ketone 3 (72% yield), which was
subjected to enantioselective reduction of the carbonyl
group with (S)-BINAL-H.27 The (S)-alcohol 2 was obtained
In our recent studies on the synthesis of stereodefined
compounds17 we have devised new methodologies for the
Keywords: silicon and compounds; stereoselective synthesis; natural
products.
* Corresponding author.
0040–4020/00/$ - see front matter ᭧ 1999 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(99)01003-0

328
F. Babudri et al. / Tetrahedron 56 (2000) 327–331
Scheme 1.
Scheme 2.
Scheme 3.
in 88% yield. The enantiomeric excess was evaluated to be
94%, by 1H NMR analysis of the esters obtained by reaction
of the alcohol 2 with the (R)-b,b,b-trifluoro-a-methoxy-a-
phenylpropionyl chloride, according to Mosher’s proce-
dure.28
The product 8 was obtained in 54% yield. Stereoselective
reduction of the triple bond of the alcohol 8 with activated
Zn30 led to the target molecule 1 in 74% yield.
In conclusion, our synthetic approach to (S)-coriolic acid
compares favorably with other procedures. A special advan-
tage of our strategy is represented by the possibility of
creating different stereoisomers, both in the reduction step
of the triple bond and in the reduction of the acetylenic
The completion of the synthetic strategy described in
Scheme 1 required a coupling reaction of the (S)-alkynol
2 with the appropriate bromoacid29 (Scheme 3).

F. Babudri et al. / Tetrahedron 56 (2000) 327–331
329
ketone by the same chiral reagent, but in the opposite
configuration. Moreover, the ready availability of the silyl
derivatives employed and the simplicity of the operations
involved are additional features making the procedure very
useful.
Pd(PPh3)4 (0.65 g, 0.56 mmol) in benzene (70 mL). After
reaction completion (7 h), the mixture was quenched with
a saturated aqueous solution of NH4Cl (100 mL), and
extracted with ethyl acetate ꢀ3×50 mL†: The organic
extracts were dried over Na2SO4 and concentrated under
vacuum. The residue, containing a small amount of
unreacted compound 6b (ϳ7%), was purified by flash
chromatography (silica gel, petroleum ether/ethyl acetate
9.7:0.3) affording 3.03 g (61% yield) of pure 7 as a yellow
oil.
Experimental
Macherey–Nagel silica gel (60, particle size 0.040–
0.063 mm) for flash column chromatography and
Macherey–Nagel aluminum sheets with silica gel 60 F254
for TLC were used. GC analysis was performed on a
Hewlett–Packard 5890 series II gas chromatograph equipped
with a SE-30 (methylsilicone, 30 m×0:25 mm id† capillary
column. GC–mass-spectrometry analysis was performed on
a Shimadzu GCMS-QP5000 gas chromatograph–mass spec-
trometer equipped with a MDN-1 capillary column (methyl-
silicone, 30 m×0:25 mm id). 1H NMR spectra were recorded
in deuterochloroform on a Bruker AM 500 spectrometer at
500 MHz and on a Varian XL 200 spectrometer at 200 MHz.
13C NMR spectra were recorded in deuterochloroform on a
Bruker AM 500 spectrometer at 125.7 MHz. IR spectra were
recorded on a Perkin Elmer 1710 FT spectrometer.
1H NMR data (500 MHz, CDCl3): d 0.14 (s, 9H), 0.82 (t,
Jˆ7.0 Hz, 3H), 1.15–1.30 (m, 4H), 1.54 (quintet, Jˆ7.4 Hz,
2H), 2.44 (t, Jˆ7.4 Hz, 2H), 6.46 (d, Jˆ16.0 Hz, 1H), 6.55
(d, Jˆ16.0 Hz, 1H) ppm. 13C NMR data (125.7 MHz,
CDCl3): d Ϫ0.52, 13.78, 22.33, 23.60, 31.26, 41.01,
101.88, 105.38, 122.35, 137.82, 199.02 ppm. IR (neat) n
1694, 1677, 1594, 1252, 847 cmϪ1. MS m/z 207 (MϩϪ15,
22), 166 (59), 151 (100), 97 (60), 75 (32), 43 (32). Anal.
Calcd for C13H22OSi: C, 70.21; H, 9.97. Found: C, 69.90; H,
9.80.
3(E)-decen-1-yn-5-one (3). 4.71 g of KF (81.04 mmol)
were added at room temperature to a solution of 7
(2.575 g, 11.58 mmol) in CH3OH (100 mL). The reaction
mixture was stirred for 2 h, quenched with a saturated
aqueous solution of NH4Cl (200 mL), and extracted with
ethyl acetate ꢀ3×150 mL†: The organic extracts were
washed with water ꢀ3×100 mL†; dried over Na2SO4 and
concentrated under vacuum. Purification by flash chroma-
tography (silica gel, petroleum ether/ethyl acetate 9.5:0.5)
led to compound 3 (1.25 g, 72% yield) as a dark yellow oil.
1-Bromo-1(E)-octen-3-one (6a) and 1-chloro-1(E)-octen-
3-one (6b). A CH2Cl2 solution (40 mL) of freshly distilled
hexanoyl chloride (3.61 g, 26.82 mmol) was added, under
nitrogen, to a cold (0ЊC) suspension of anhydrous AlCl3
(3.58 g, 26.82 mmol) in 40 mL of CH2Cl2. The resulting
mixture was stirred for 10 min at 0ЊC, then a solution of
(E)-1-bromo-2-trimethylsilylethene 4 (4.00 g, 22.33 mmol)
in 40 mL of CH2Cl2 was added dropwise. After complete
addition, the reaction mixture was stirred at 0ЊC for 1 h,
quenched with a saturated aqueous solution of NH4Cl
(100 mL), and extracted with ethyl acetate ꢀ3×50 mL†:
The organic extracts were dried over Na2SO4 and concen-
trated under vacuum. The residue was purified by flash
chromatography (silica gel, petroleum ether/ethyl acetate
9.5:0.5) leading to a 70:30 mixture of (E)-1-bromo-1-
octen-3-one 6a15 and (E)-1-chloro-1-octen-3-one 6b31
(4.20 g, 99% yield). The mixture of 6a and 6b was
employed for the preparation of compound 7.
1H NMR data (500 MHz, CDCl3): d 0.82 (t, Jˆ7.0 Hz, 3H),
1.17–1.31 (m, 4H), 1.55 (quintet, Jˆ7.4 Hz, 2H), 2.47 (t,
Jˆ7.4 Hz, 2H), 3.33 (s, 1H), 6.52 (s, 2H) ppm. 13C NMR
data (125.7 MHz, CDCl3): d 13.75, 22.30, 23.44, 31.20,
41.02, 80.66, 86.28, 121.41, 138.93, 198.85 ppm. IR
(neat) n 3304, 3256, 2102, 1694, 1599, 963 cmϪ1. MS m/z
135 (MϩϪ15, Ͻ1), 121 (3), 107 (5), 94 (84), 79 (100), 66
(17), 51 (54), 43 (19), 41 (17). Anal. Calcd for C10H14O: C,
79.96; H, 9.39. Found: C, 79.61; H, 9.46.
(S)-3(E)-decen-1-yn-5-ol (2). 6.4 mL of a 1 M solution of
EtOH in THF (6.40 mmol) were added dropwise at room
temperature, under nitrogen, to a stirred solution of LiAlH4
in THF (1 M, 6.4 mL, 6.40 mmol). Then 25 mL of a THF
solution of (S)-binaphthol (1.83 g, 6.40 mmol) were added
dropwise at the same temperature. The resulting mixture of
BINAL-H reagent27 was stirred for 30 min at room tempera-
ture, then cooled to Ϫ100ЊC. A solution of 3 (0.32 g,
2.13 mmol) in THF (15 mL) was added dropwise over a
period of 20 min at Ϫ100ЊC. The reaction mixture was stir-
red for 1 h at this temperature and at Ϫ80ЊC for an addi-
tional 1 h. After addition of 1 mL of CH3OH at Ϫ80ЊC, the
mixture was warmed to room temperature. Then, dilute HCl
was added (50 mL) and the reaction mixture extracted with
ethyl acetate ꢀ3×80 mL†: The organic extracts were washed
with water (100 mL), dried over Na2SO4 and concentrated
under vacuum. n-Pentane (50 mL) was added to the residue
and pure (S)-binaphthol was recovered by filtration. Finally,
the organic solution was concentrated and the residue was
purified by flash chromatography (silica gel, petroleum
(6a)ϩ(6b) 1H NMR data (200 MHz, CDCl3): d 0.86
(t, Jˆ6.7 Hz, 3H), 1.15–1.40 (m, 4H), 1.45–1.70 (m, 2H),
2.49 (t, Jˆ7.4 Hz, 2H), 6.50 (d, Jˆ13.6 Hz, vinylic H of
6b), 6.77 (d, Jˆ14.0 Hz, vinylic
H of 6a), 7.26
(d, Jˆ13.6 Hz, vinylic H of 6b), 7.50 (d, Jˆ14.0 Hz, vinylic
H of 6a) ppm. IR (neat) n 1700, 1682, 1585, 943 cmϪ1
.
(6a) MS m/z: 163 (2), 161 (2), 150 (67), 148 (71), 135 (99),
133 (100), 125 (27), 107 (15), 105 (14), 82 (11), 69 (15), 55
(48), 43 (82), 41 (54).
(6b) MS m/z: 125 (17), 106 (15), 104 (48), 91 (31), 89 (100),
69 (9), 63 (4), 61 (13), 55 (17), 43 (36), 41 (27).
1-Trimethylsilyl-3(E)-decen-1-yn-5-one (7). A solution of
ethynyltrimethylsilane 5 (2.75 g, 28.00 mmol) in benzene
(50 mL) was added at room temperature, under nitrogen,
to a stirred mixture of 6 (4.20 g, 22.21 mmol), Et3N
(4.25 g, 42.00 mmol), CuI (0.27 g, 1.40 mmol) and

330
F. Babudri et al. / Tetrahedron 56 (2000) 327–331
ether/ethyl acetate 8:2) leading to compound 232 (0.285 g,
88% yield) as a yellow oil. [a]2D0ˆϩ16.2 (c 2.6, chloro-
form).
151 (25), 121 (7), 107 (13), 95 (20), 91 (13), 81 (32), 71
(21), 67 (20), 55 (37), 43 (100), 41 (62). Anal. Calcd for
C18H30O3: C, 73.43; H, 10.27. Found: C, 73.61; H, 10.24.
1H NMR data (500 MHz, CDCl3): d 0.84 (t, Jˆ6.9 Hz, 3H),
1.12–1.40 (m, 6H), 1.41–1.56 (m, 2H), 2.18 (br s, 1H), 2.85
(d, Jˆ2.2 Hz, 1H), 4.09 (broad q, Jˆ6.3 Hz, 1H), 5.63 (ddd,
Jˆ16.0, 2.2, 1.5 Hz, 1H), 6.19 (dd, Jˆ16.0, 5.9 Hz, 1H)
ppm. 13C NMR data (125.7 MHz, CDCl3): d 13.94, 22.48,
24.83, 31.59, 36.72, 71.95, 77.74, 81.66, 108.45,
147.67 ppm. IR (neat) n 3400–3100, 2105, 958 cmϪ1. MS
m/z 109 (3), 99 (9), 96 (12), 95 (25), 81 (100), 71 (13), 55
(19), 53 (79), 51 (18), 43 (77), 41 (33).
13(S)-Hydroxy-9(Z),11(E)-octadecadienoic acid (1)-(S)-
coriolic acid. Nitrogen was passed through a stirred suspen-
sion of 2 g of Zn dust (Ͻ325 mesh)30 in 12 mL of H2O for
15 min, and 0.2 g of Cu(OAc)2·H2O were added. Stirring
was continued for 15 min, then 0.2 g of AgNO3 were
added and the suspension was stirred for a further 30 min.
The metal was collected by vacuum filtration and washed
with H2O ꢀ2×15 mL†; MeOH ꢀ2×15 mL†; acetone
ꢀ2×15 mL†; and finally Et2O ꢀ2×15 mL†: The Et2O–moist
Zn was transferred into 8 mL of H2O/MeOH 1:1 (v/v) and
was ready for use. A solution of 8 (0.183 g 0.62 mmol) in
MeOH (4 mL) was added to the suspension of activated Zn
and the mixture was stirred at 50ЊC for 24 h, then cooled at
room temperature. A saturated aqueous solution of NH4Cl
(50 mL) and ethyl acetate (50 mL) were added, and after
vigorous stirring, the metal was removed by filtration and
washed with ethyl acetate (30 mL). The mixture was acidi-
fied to pH 2 by adding dilute HCl (20 mL), the organic layer
was separated, and the aqueous layer was extracted twice
with ethyl acetate (50 mL). The combined organic extracts
were washed with water (100 mL), dried over Na2SO4 and
concentrated under vacuum. The residue was purified by
flash chromatography (silica gel, petroleum ether/ethyl
acetate 7:3) leading to compound 1 (0.136 g, 74% yield)
as a pale yellow oil. [a]Dˆϩ8.7 (c 1.22, chloroform), lit.9
[a]Dˆϩ9.3 (c 1.29, chloroform).
To evaluate the enantiomeric excess of (S)-2, the Mosher’s
esters of (S)-2 and racemic 2 were prepared according to the
following procedure. To a sample of enynol 2 (0.025 g,
0.164 mmol) were added 0.083 g (0.329 mmol) of
(R)-b,b,b-trifluoro-a-methoxy-a-phenylpropionyl chloride,
pyridine (five drops) and CCl4 (five drops). The mixture
was stirred at room temperature for 2 h, then quenched
with dilute HCl (10 mL) and extracted with ethyl acetate
ꢀ3×10 mL†: The organic extracts were washed with water
ꢀ2×10 mL†; dried over Na2SO4 and concentrated under
vacuum. The crude product was subjected to 1H NMR
analysis and then purified by flash chromatography (yields
in the range 75–81%). The derivative of racemic 2
displayed two sets of signals due to vinylic protons (ddd,
d 5.62 and 5.73, dd d 6.05 and 6.14), the chiral-2 derivative
showed the vinylic signals of the (S)-ester at d 5.73 and 6.14
(97%) and that of the (R)-ester at d 5.62 and 6.05 (3%),
indicating an enantiomeric excess of 94%.
1H NMR data (500 MHz, CDCl3ϩD2O): d 0.84 (t, Jˆ6.9 Hz,
3H), 1.15–1.63 (m, 18H), 2.12 (broad q, Jˆ7.7 Hz, 2H),
2.27 (t, Jˆ7.4 Hz, 2H), 4.11 (q, Jˆ6.9 Hz, 1H), 5.38 (dt,
Jˆ10.7, 7.7 Hz, 1H), 5.59 (dd, Jˆ15.2, 6.9 Hz, 1H), 5.92
(apparent t, Jˆ11 Hz, 1H), 6.42 (dd, Jˆ15.2, 11.0 Hz, 1H)
ppm. 13C NMR data (125.7 MHz, CDCl3): d 13.93, 22.49,
24.54, 24.97, 27.51, 28.77, 28.82, 28.85, 29.31, 31.66,
33.91, 37.05, 72.81, 125.73, 127.81, 132.56, 135.53,
13(S)-Hydroxy-11(E)-octadecen-9-ynoic acid (8). A solu-
tion of n-BuLi 1.4N in hexane (4.7 mL, 6.58 mmol) was
added, under nitrogen, at Ϫ80ЊC, to a solution of 2
(0.50 g, 3.29 mmol) in THF (12 mL) and HMPA
(1.72 mL, 9.87 mmol). The temperature was slowly raised
to Ϫ30ЊC and maintained for 45 min at this temperature.29
Then a solution of the dilithium salt of 2 was added, under
nitrogen, at Ϫ90ЊC, to a suspension of Br(CH2)7COOLi,
generated by addition of n-BuLi (2.4 mL, 3.29 mmol) to a
cold (Ϫ90ЊC) solution of 8-bromooctanoic acid (0.734 g,
3.29 mmol) in THF (12 mL). After complete addition, the
temperature was slowly raised to room temperature. The
reaction mixture was stirred for 15 h, quenched with dilute
HCl (30 mL), and extracted with ethyl acetate ꢀ3×50 mL†:
The organic extracts were washed with water (100 mL),
dried over Na2SO4 and concentrated under vacuum. The
residue was purified by flash chromatography (silica gel,
petroleum ether/ethyl acetate 7:3) leading to compound 8
(0.523 g, 54% yield) as a pale yellow oil. [a]2D0ˆϩ7.8 (c
2.7, chloroform).
179.01 ppm. IR (neat) n 3600–2400, 1713 cmϪ1
.
Acknowledgements
This work was financially supported in part by the Ministero
`
dell’Universita e della Ricerca Scientifica e Tecnologica,
Rome, and the University of Bari (National Project ‘Stereo-
selezione in Sintesi Organica. Metodologie ed Appli-
cazioni’). We thank Miss Lucia Partipilo for preliminary
experiments.
References
1H NMR data (500 MHz, CDCl3): d 0.84 (t, Jˆ7.0 Hz, 3H),
1.12–1.63 (m, 18H), 2.24 (td, Jˆ7.0, 2.1 Hz, 2H), 2.29 (t,
Jˆ7.5 Hz, 2H), 4.06 (broad q, Jˆ6.5 Hz, 1H), 5.61 (dtd,
Jˆ15.9, 2.1, 1.1 Hz, 1H), 5.98 (dd, Jˆ15.9, 6.5 Hz, 1H),
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