Total Synthesis of a Potent Proinflammatory 5-Oxo-ETE and Its 6,7-Dihydro Biotransformation Product

Article abstract of DOI:10.1021/jo9716993

The first total synthesis of a potent inflammatory mediator 5-oxo-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid (5-oxo-ETE) 2 and its biotransformation product 6,7-dihydro-5-oxo-ETE 5 is reported. A convergent synthesis for the unstable title compounds is a

Full text of DOI:10.1021/jo9716993

J . Org. Chem. 1998, 63, 337-342
337
Tota l Syn th esis of a P oten t P r oin fla m m a tor y 5-Oxo-ETE a n d Its
6
,7-Dih yd r o Biotr a n sfor m a tion P r od u ct
†
Subhash P. Khanapure, Xiao-Xin Shi, William S. Powell, and J oshua Rokach*
Claude Pepper Institute and Department of Chemistry, Florida Institute of Technology,
50 West University Boulevard, Melbourne, Florida 32901 and Meakins-Christie Laboratories,
McGill University, 3626 St-Urbain Street, Montreal, Quebec H2X 2P2, Canada
1
Received September 11, 1997
The first total synthesis of a potent inflammatory mediator 5-oxo-6(E),8(Z),11(Z),14(Z)-eicosatet-
raenoic acid (5-oxo-ETE) 2 and its biotransformation product 6,7-dihydro-5-oxo-ETE 5 is reported.
A convergent synthesis for the unstable title compounds is accomplished via two synthons, dithiolane
aldehyde 13 and bisdienyl phosphonium bromide 19. The synthetic 5-oxo-ETE 2 and its 8,9-trans
isomer 3 were used to unequivocally confirm the structure of the biologically derived mediators.
In addition, using synthetic 6,7-dihydro-5-oxo-ETE 5 we have been able to identify in neutrophils
the formation of 6,7-dihydro-5-oxo-ETE 5.
Sch em e 1a
5
-Oxo-ETE 2, a novel arachidonate metabolite, is a
potent chemotactic agent for human neutrophils. Al-
though it is less potent than LTB in this regard, it is
4
about 100 times more potent than its precursor 5(S)-
HETE 1.1 It has recently been shown that 5-oxo-ETE is
also a potent chemotactic agent for human eosinophils
2
,3
4
which, unlike neutrophils, respond only weakly to LTB .
Of a variety of lipid mediators tested, 5-oxo-ETE was the
most active in inducing chemotaxis of these cells (5-oxo-
ETE > platelet-activating factor (PAF) ≈ 5-oxo-15-
hydroxy-ETE . LTB
low as 1 nM producing significant effects. 5-Oxo-ETE
also induces a variety of other responses in neutrophils
4
≈ LTD
4
), with concentrations as
2
1
,4
and eosinophils including calcium mobilization, de-
4
5
granulation, superoxide production, actin polymeriza-
tion,5 and the expression of cellular adhesion molecules.6
There is substantial evidence that the stimulatory effects
of 5-oxo-ETE on these cells are due to its interaction with
its own specific G protein-linked receptor.1,4,5,7
,6
Scheme 1 shows some of the proposed biochemical
transformations which we plan to study. 5-Oxo-ETE is
a product of the 5-LO pathway and is formed by a
dehydrogenase present in microsomal fractions of human
neutrophils (Scheme 1).8 This enzyme catalyzes the
oxidation of 5(S)-HETE 1, a major product of the 5-LO
pathway in these cells, to 5-oxo-ETE. This 5-hydroxy
eicosanoid dehydrogenase is highly specific for the natu-
rally occurring 5(S)-stereoisomer of 5-HETE 1, since a
(
(
1) † McGill University.
1) Powell, W. S.; Gravel, S.; MacLeod, R. J .; Mills, E.; Hashefi, M.
a
6
(
a) 5-OH-dehydrogenase, (b) ∆ reductase; (c) 5-keto reductase.
J . Biol. Chem. 1993, 268, 9280-9286.
2) Powell, W. S.; Chung, D.; Gravel, S. J . Immunol. 1995, 154,
123-4132.
3) O’Flaherty, J . T.; Kuroki, M.; Nixon, A. B.; Wijkander, J .; Yee,
(
variety of related positional and stereoisomers are not
metabolized to a significant extent.8 It also requires that
the double bond in the 6-position of 5-hydroxy eicosanoids
should be in the trans rather than the cis configuration.
4
(
E.; Lee, S. L.; Smitherman, P. K.; Wykle, R. L.; Daniel, L. W. J .
Immunol. 1996, 157, 336-342.
(4) O’Flaherty, J . T.; Cordes, J .; Redman, J .; Thomas, M. J . Biochem.
Biophys. Res. Commun. 1993, 192, 129-134.
5) Norgauer, J .; Barbisch, M.; Czech, W.; Pareigis, J .; Schwenk, U.;
Schroder, J . M. Eur. J . Biochem. 1996, 236, 1003-1009.
6) Powell, W. S.; Gravel, S.; Halwani, F.; Hii, C. S.; Huang, Z. H.;
Tan, A. M.; Ferrante, A. J . Immunol. 1997, 159, 2952-2959.
7) Powell, W. S.; MacLeod, R. J .; Gravel, S.; Gravelle, F.; Bhakar,
A. J . Immunol. 1996, 156, 336-342.
8) Powell, W. S.; Gravelle, F.; Gravel, S. J . Biol. Chem. 1992, 267,
9233-19241.
m
The high degree of specificity and the low K (200 nM)
(
of this enzyme suggest that this reaction may be of
physiological importance. On the basis of our experience
in handling 5-oxo-ETE, the isomerization of 5-oxo-ETE
to the 8,9-trans-5-oxo-ETE 3 shown in the Scheme 1
most likely occurs in vivo and ex vivo by a simple
chemical isomerization.
(
(
2
(
1
S0022-3263(97)01699-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/07/1998

3
38 J . Org. Chem., Vol. 63, No. 2, 1998
Khanapure et al.
It is also possible that 5-oxo-ETE 2 could be further
stable compounds, and their syntheses require careful
planning and execution. Oxoeicosanoids1
1-14
present an
metabolized by neutrophils or other cells to the 6,7-
dihydro metabolites 5-7 (Scheme 1). We have previously
shown that neutrophils convert the 6-trans isomer of
additional degree of difficulty. For example, 5-oxo-ETE
is unstable because of the presence of a conjugated
dienone in the molecule. In addition, one of the double
bonds in this system is a cis double bond which has a
high propensity for trans isomerization. For these
reasons, we elected early in the synthesis of 5-oxo-ETE
to have the carbonyl function protected. This would
reduce the instability of the conjugated diene system to
an acceptable level. In addition, later in the synthesis
we needed to hydrolyze the ester function to acid and that
would have been impossible on a practical level without
a protected carbonyl function.
LTB
4
to similar dihydro products following initial oxida-
8
,9
tion of the 5-hydroxyl group.
In these studies the
position of the reduced double bond was not clear, but
recent mass spectrometric evidence suggests it is in the
6
,7-position,10 which we have confirmed by another
approach. To test the hypothesis that neutrophils can
also convert 5-oxo-ETE to 6,7-dihydro metabolites, 6,7-
dihydro-5-oxo-ETE 5 has also been synthesized.
Our present interest in 5-oxo-ETE stems from our long-
1
1-15
standing involvement in the area of oxoeicosanoids
as well as from recent evidence suggesting that the
inhibitory effects of 5-lipoxygenase inhibitors on antigen-
induced pulmonary eosinophil infiltration cannot be
The main focus of our synthetic plan was to prepare a
masked carbonyl aldehyde synthon, such as 13, and an
intermediate, such as bisdienyl phosphonium salt 19, and
combine these components in a convergent and stereo-
selective manner, as shown in Scheme 2, to obtain the
necessary precursor 20. The bisdienyl phosphonium salt
19 was intended to serve not only as a precursor for 5-oxo-
ETE 2, but also to prepare the 6,7-dihydro-5-oxo-ETE 5.
The key aldehyde synthon 13 was prepared in three
steps from commercially available 2-carbethoxy-1,3-dithi-
olane 8. DIBAL-H reduction of dithiolane 8 at -78 °C
to -60 °C for 2 h gave the corresponding aldehyde 9,
which was purified by Kugelrohr distillation to yield pure
2-formyl-1,3-dithiolane 9 in 92% yield. The alkylation
of dithiolane aldehyde 9 with methyl bromobutyrate 10
using NaH as a base in a mixture of DMSO/benzene (2:
3) at room-temperature overnight gave aldehyde 11 in
explained only on the basis of inhibition of leukotriene
synthesis.1
6,17
These finding raise the possibility that
5
-oxo-ETE could be important in the physiological regu-
lation of eosinophil accumulation in tissues such as the
lung, and thus may be an important mediator in diseases
such as asthma.
Because of the importance we attribute to 5-oxo-ETE,
we started a synthetic program to provide larger amounts
of this mediator in order to study its formation and
transformation in biochemical systems and to evaluate
in more detail its biological profile. Until now the source
for this conjugated oxo-eicosanoid was the biologically
derived material or the chemical oxidation of the very
expensive 5(S)-HETE.
5
9% yield after purification by column chromatography.
The Wittig coupling of 11 with triphenylphosphora-
nylidene acetaldehyde 12 afforded the desired dithio
aldehyde 13 in 56% yield (75% yield based on consumed
starting material). The bis acetylene derivative 16 was
prepared from butyn-1-ol 14.35 Alkylation of butyn-1-ol
Resu lts a n d Discu ssion
Leukotrienes which contain conjugated triene18-29 and
lipoxins3
0-34
which contain conjugated tetraene are un-
(
9) Powell, W. S.; Gravelle, F. J . Biol. Chem. 1988, 263, 2170-2177.
10) Wheelan, P.; Murphy, R. C. J . Biol. Chem. 1995, 270, 19845-
1
4 with bromooct-3-yne 15 gave bis acetylene 16 in 83%
(
yield. Hydrogenation of 16 using Lindlar catalyst af-
forded dienyl alcohol 17 in 60% yield. Bromination of
1
9852.
(
11) Wang, S. S.; Rokach, J .; Powell, W. S.; Dekle, C.; Feinmark, S.
J . Tetrahedron Lett. 1994, 35, 4051-4054.
12) Wang, S. S.; Shi, X.-X.; Powell, W. S.; Tieman, T.; Feinmark,
S. J .; Rokach, J . Tetrahedron Lett. 1994, 36, 513-516.
13) Khanapure, S. P.; Manna, S.; Rokach, J .; Murphy, R. C.;
Wheelan, P.; Powell, W. S. J . Org. Chem. 1995, 60, 1806-1813.
14) Khanapure, S. P.; Wang, S. S.; Powell, W. S.; Rokach, J . J . Org.
Chem. 1997, 62, 325-330.
15) Powell, W. S.; Hashefi, M.; Falck, J . R.; Chauhan, K.; Rokach,
J .; Wang, S. S.; Mills, E.; MacLeod, R. J . J . Leukoc. Biol. 1995, 57,
57-263.
16) Namovic, M. T.; Walsh, R. E.; Goodfellow, C.; Harris, R. R.;
Carter, G. W.; Bell, R. L. Eur. J . Pharmacol. 1996, 315, 81-88.
17) Seeds, E. A.; Kilfeather, S.; OKiji, S.; Schoupe, T. S.; Donigi-
Gale, D.; Page, C. P. Eur. J . Pharmacol. 1995, 293, 369-376.
18) Corey, E. J .; Clark, D. A.; Goto, G.; Marfat, A.; Mioskowski, C.;
Samuelsson, B.; Hammarstrom, S. J . Am. Chem. Soc. 1980, 102, 1436-
439.
19) Rokach, J .; Girard, Y.; Guindon, Y.; Atkinson, J . G.; Larue, M.;
the alcohol 17 with CBr
vided the bromide 18 which, after purification, was
immediately treated with Ph P to generate the phospho-
4
and triphenylphosphine pro-
(
(
3
nium salt 19, purified by flash column chromatography
to give pure 19 in 92% yield. The three-step preparation
of 19 from 16, as just described, is a much improved
synthesis over the related five-step one we reported a few
years ago35 for the chloride version of 19. Wittig reaction
of the aldehyde 13 with the phosphonium salt 19, using
LHMDS as base, produced 20 in 83% yield. The methyl
(
(
2
(
(
(
2
ester 20 was treated with 1 M LiOH in THF/H O to give,
after purification by column chromatography, the dithio
1
(
Young, R. N.; Masson, P.; Holme, G. Tetrahedron Lett. 1980, 21, 1485-
(27) LeMerrer, Y.; Gravier-Pelletier, C.; Micas-Languin, D.; Mestre,
F.; Dureault, A.; Depezay, J . C. J . Org. Chem. 1989, 54, 2409.
(28) Avignon-Tropis, M.; Treilhou, M.; Leberton, J .; Pougny, J . R.;
Frechard-Ortuno, I.; Huynh, C.; Linstrumelle, G. Tetrahedron Lett.
1989, 30, 6335.
1
488.
(
20) Rosenberger, M.; Neukom, C.; Aig, E. R. J . Am. Chem. Soc.
1
983, 105, 3656-3661.
(21) Lau, C. K.; Adams, J .; Guidon, Y.; Rokach, J . In Leukotrienes
and Lipoxygenase: Chemical, Biological, and Clinical Aspects; Rokach,
J ., Ed.; Elsevier Press: Amsterdam, 1989; pp 1-141.
(29) Treilhou, M.; Fauve, A.; Pougny, J . R.; Prome, J .-C.; Vescham-
bre, H. J . Org. Chem. 1992, 57, 3203.
(30) Adams, J .; Fitzsimmons, B. J .; Rokach, J . Tetrahedron Lett.
1984, 25, 4713-4716.
(
22) Cohen, N.; Banner, B. L.; Lopresti, R. J .; Wong, F.; Rosenberger,
M.; Liu, Y.-Y.; Thom, E.; Liebman, A. A. J . Am. Chem. Soc. 1983, 105,
3
661-3672.
23) Corey, E. J .; Marfat, A.; Goto, G.; Brion, F. J . Am. Chem. Soc.
980, 102, 7984-7985.
24) Guindon, Y.; Zamboni, R.; Lau, C.-K.; Rokach, J . Tetrahedron
(31) Adams, J .; Fitzsimmons, B. J .; Girard, Y.; Leblanc, Y.; Evans,
J . F.; Rokach, J . J . Am. Chem. Soc. 1985, 107, 464-469.
(32) Leblanc, Y.; Fitzsimmons, B. J .; Adams, J .; Rokach, J . Tetra-
hedron Lett. 1985, 26, 1399-1402.
(
1
(
Lett. 1982, 23, 739-742.
(33) Corey, E. J .; Su, W. G. Tetrahedron Lett. 1985, 26, 281-284.
(34) Nicolaou, K. C.; Veale, C. A.; Webber, S. E.; Katerinopoulos,
H. J . Am. Chem. Soc. 1985, 107, 7515-7518.
(
(
25) Zamboni, R.; Rokach, J . Tetrahedron Lett. 1982, 23, 2631-2634.
26) Nicolaou, K. C.; Zipkin, R. E.; Dolle, R. E.; Harris, B. D. J . Am.
Chem. Soc. 1984, 106, 3548.
(35) Zamboni, R.; Rokach, J . Tetrahedron Lett. 1983, 24, 999-1002.

Total Synthesis of 5-Oxo-ETE
Sch em e 2a
J . Org. Chem., Vol. 63, No. 2, 1998 339
Sch em e 3a
a
(a) PhI(OCOCF3)2, room temperature, 5 min; also periodic acid,
THF/ether, room temperature 8 min (51%); (b) H2/Pd, C; (c)
LiN(SiMe3)2, HMPA, -78 °C to 0 °C; (d) 1 M LiOH, THF/H2O,
room temperature 24 h.
prepare 22 by hydrogenating 13 and continue the syn-
thesis with the dithiolane protecting group and remove
it later in the synthesis. All attempts at hydrogenation
of 13 using different catalysts such as Pd/C, Ni-boride,
tris(triphenylphosphone)chlororhodium, or Wilkinson’s
catalyst were unsuccessful, resulting in recovery of the
starting material. Presumably the sulfur atoms in the
molecule were responsible for poisoning the catalyst. We
decided, therefore, to deblock the dithio group in 13 and
then perform the hydrogenation. To our surprise, depro-
tection of dithio aldehyde 13 using [bis(trifluoroacetoxy)-
2
iodo]benzene in 9:1 MeOH:H O resulted mainly in the
formation of the dimethyl acetal derivative 23 (yield 71%)
of the desired 24. This result is interesting in its own
right since it can allow manipulation of the carbonyl
function in the presence of an aldehyde. For the purpose
of the synthesis at hand, we repeated the deprotection
a
(
a) DIBAL-H, -78 to -60 °C, 2 h; (b) NaH, room temperature;
(
c) reflux in benzene; (d) ethylmagnesium bromide/CuBr; (e) H2/
Lindlar; (f) Ph3P, CBr4 0-5 °C 30 min; (g) bromide 18 in dry
using [bis(trifluoroacetoxy)iodo]benzene in 9:1 CH
3
CN:
acetonitrile, Ph3P, reflux 36 h; (h) LiN(SiMe3)2, HMPA, -98 to 0
H
2
O and obtained 79% of the desired keto aldehyde 24.
°
C; (i) 1 M LiOH, THF/H2O, room temperature 24 h; (j) PhI(O-
COCF3)2, -10 to -8 °C, 2 min.
We also used the periodic acid procedure for the depro-
tection and obtained the keto aldehyde 24 in 51% yield
after purification by column chromatography (Scheme 3).
The hydrogenation of 24, using Pd/C as catalyst, was
clean and gave the reduced keto aldehyde 25 in nearly
quantitative yield. We then performed the Wittig cou-
pling of 25 and the bisdienyl phosphonium bromide 19.
The more reactive aldehyde reacted preferentially with
the ylide in the presence of the less reactive ketone in a
disappointing 35% yield. Hydrolysis of 26 gave 6,7-
dihydro-5-oxo-ETE 5 in 67% yield.
It is worth mentioning that before we settled for the
convenient preparation of aldehyde 11 in a two-step
procedure from commercially available 8 as shown in
Scheme 2, we attempted to alkylate the more popular
dithiane carboxaldehyde 28 to prepare aldehyde 29 as
shown in Scheme 4. In contrast to the dithiolane
alkylation reaction, as shown in Scheme 2, the reaction
between 28 and 10 is complicated and led to mixtures of
products. The major product of this reaction was the
O-alkylation product 31, which during purification on
silica gel was converted back to dithiane carboxaldehyde
derivative of 5-oxo-ETE 21 in 98% yield. Finally, depro-
tection of the dithio acid 21 with [bis(trifluoroacetoxy)-
iodo]benzene1
3,36
gave the 5-oxo-ETE 2 in 52% yield. The
8
,9-trans isomer 3 was also isolated in 13% yield after
purification by RP HPLC and then NP HPLC (for details,
see Experimental Section). We tried our recently devel-
oped method for deblocking dithio derivatives to corre-
sponding carbonyl compounds using periodic acid in
anhydrous ether/THF.37 This method works extremely
well for most of the dithio derivatives under nonaqueous
conditions, with ease of handling and simplicity of the
workup procedure. Using this procedure to deblock 21,
we observed considerable double bond isomerization to
give a mixture of 2 and 3 in the ratio of 55:45.
The synthesis of 6,7-dihydro-5-oxo-ETE 5 is outlined
in Scheme 3. Our original intention, however, was to
(
(
36) Stork, G.; Zhao, K. Tetrahedron Lett. 1989, 30, 287-290.
37) Shi, X.-X.; Khanapure, S. P.; Rokach, J . Tetrahedron Lett. 1996,
3
7, 4331-4334.

3
40 J . Org. Chem., Vol. 63, No. 2, 1998
Khanapure et al.
Sch em e 4
solution of aldehyde 9 (1 g, 7.45 mmol) in DMSO (10 mL)
under argon atmosphere. The reaction mixture was
stirred at 0 °C for 1.5 h, and methyl bromobutyrate 10
(1.48 g, 8.2 mmol) was added dropwise at 0 °C. The
reaction mixture was stirred at 0 °C for 5 h and then at
room temperature for 20 h. The reaction mixture was
then diluted with water (50 mL) and extracted with ether
(
3 × 150 mL). The combined extracts were washed with
water (3 × 100 mL), dried over Na
2
SO , and filtered, and
4
the solvent was evaporated at reduced pressure to give
the crude product, which was purified by flash column
chromatography over silica gel using ethyl acetate/hexane
(
5
1:9) as an eluant to give the pure product 11 (1.02 g) in
1
5% yield. H NMR (CDCl
3
) δ 1.8 (m, 2 H), 1.97 (m, 2
H), 2.32 (t, J ) 7.3 Hz, 2 H), 3.5 (m, 4 H), 3.61 (s, 3 H),
1
3
9
4
-
.02 (s, 1 H). C NMR (CDCl
0.1, 71.8, 173.1, 188.0. HREIMS calcd (C
CHO) 205.0354, obsd 205.0357.
Meth yl 5,5-(Dim eth ylen ed ith io)-8-oxo-6(E)-octen -
3
) δ 21.6, 33.5, 33.6, 39.7,
8
13 2 2
H O S
, M
2
8. It is not yet clear what causes a different course of
reaction in the C-alkylation in the thiolane case versus
the O-alkylation in the dithiane one.
oa te (13). To a solution of aldehyde 11 (2.8 g, 11.95
mmol) in benzene (30 mL) was added (triphenylphos-
phoranylidene)acetaldehyde 12 (1.3 g, 4.6 mmol), and the
solution was refluxed for 2 h; 1.2 g of (triphenylphospho-
ranylidene)acetaldehyde 12 was then added and refluxed
for 2 h. Another 1.2 g of (triphenylphosphoranylidene)-
acetaldehyde 12 was added and refluxed overnight. The
reaction mixture was cooled to room temperature, filtered
through Celite, and washed with ethyl acetate and the
combined filtrate concentrated under reduced pressure
to afford the crude product, which was purified by flash
column chromatography using 20% ethyl acetate in
hexane. The less polar fractions gave 706 mg of starting
material 9, and from the more polar fractions pure
The synthetic 5-oxo-ETE 2 and its 8,9-trans isomer 3
have been used to unequivocally confirm the structure
of the biologically derived mediators. In addition, using
synthetic 6,7-dihydro-5-oxo-ETE 5, we have been able to
identify in neutrophils the formation of 6,7-dihydro-5-
oxo-ETE 5, establishing the bioreduction at 6,7-double
bond as a metabolic transformation in these cells. Pre-
liminary studies suggest that the 6,7-dihydro derivative
is approximately 100 times less potent than 5-oxo-ETE
in stimulating cytosolic calcium mobilization in human
neutrophils. It is therefore possible that reduction of this
double bond contributes to the biological inactivation of
5
-oxo-ETE.
product 13 (1.75 g, 56%) was obtained (yield based on
Exp er im en ta l Section
Rea gen ts a n d Meth od s. Unless stated otherwise, all
1
consumed starting material 75%). H NMR (CDCl
3
) δ
1.80 (m, 2 H), 2.14 (m, 2 H), 2.32 (t, J ) 7.2 Hz, 2 H),
3.21 (m, 2 H), 3.32 (m, 2 H), 3.61 (s, 3 H), 6.25 (dd, J )
reagents and chemicals were obtained from commercial
sources and used without further purification.
15.2 and 7.7 Hz, 1 H), 6.78 (d, J ) 15.2, 1 H), 9.58 (d, J
1
13
H NMR spectra were recorded on a 360 MHz spec-
) 7.8, 1 H). C NMR (CDCl ) δ 22.3, 33.2, 39.0 (2 x C),
3
trometer with tetramethylsilane as an internal standard
and J values are given in hertz.
39.5, 51.2, 68.5, 128.5, 158.9, 172.8, 193.1. HREIMS
+
calcd (C11
16 3 2
H O S , M ) 260.0541, obsd 260.0545.
All reactions were carried out under an inert (nitrogen
or argon) atmosphere with dry, freshly distilled solvents
under anhydrous conditions unless otherwise noted.
3,6-Dod eca d iyn -1-ol (16). At room temperature 40
mL of ethylmagnesium bromide (3.0 M in ether, 120
mmol) was slowly added dropwise to a solution of butyn-
1-ol 14 (3.85 g, 55 mmol) in dry THF (200 mL) under
argon. The reaction mixture was refluxed for 1.5 h and
then cooled to room temperature, CuBr (0.715 g) was
added, and the mixture was stirred at room temperature
for 15 min. To the milky white suspension obtained was
added a solution of bromooct-3-yne 15 (9.45 g, 50 mmol)
in THF (20 mL) dropwise and the reaction mixture was
refluxed for 2 h. The reaction mixture was diluted with
ether (50 mL), quenched with aqueous ammonium chlo-
ride solution (30 mL), and extracted with ether (2 × 100
mL) and the combined extract washed with water (4 ×
Yields refer to chromatographically and spectroscopically
1
(
H NMR) homogeneous materials.
-F or m yl-1,3-d ith iola n e (9). To a cooled (-78 °C)
2
stirred solution of dithiolane ester 8 (11.9 g, 66.7 mmol)
in anhydrous dichloromethane (100 mL) was added
DIBAL-H (1.0 M in toluene, 67 mL) (67 mmol) dropwise
under argon. The reaction mixture was stirred at -78
°
C to -60 °C for 1 h and then quenched with methanol
(10 mL). 2 N HCl was added to adjust the pH to
approximately 4, and the resulting mixture was extracted
with dichloromethane (2 × 100 mL). The combined
organic layers were washed with water (2 × 25 mL) and
2 4
50 mL), dried over anhydrous Na SO , filtered, and
brine (1 × 25 mL), dried over anhydrous Na
2
SO
4
, filtered,
concentrated under reduced pressure to afford the crude
product. This was purified by flash column chromatog-
raphy with 8:2 hexane/ethyl acetate to afford the pure
and concentrated in vacuo to give the crude product 9. It
was purified by Kugelrohr distillation to give 8.2 g (92%)
bisacetylenic alcohol 16 (7.3 g, 83%). 1H NMR (CDCl
) δ
of the pure dithiolane aldehyde 9 as a colorless thick oil.
3
1
H NMR (CDCl
.91 (d, J ) 5.9 Hz, 1 H): (CDCl
Meth yl 5,5-(Dim eth ylen ed ith io)-6-oxoh exa n oa te
11). To a 0 °C cooled and stirred suspension of sodium
3
) δ 3.26 (s, 4 H), 4.57 (d, J ) 5.9 Hz, 1 H)
0.83 (t, J ) 6.9 Hz, 3 H), 1.30 (m, 4 H), 1.45 (m, 2 H),
2.01 (m, 2 H), 2.40 (m, 2 H), 3.08 (m, 2 H), 3.64 (t, J )
8
3
) δ 38.9, 55.5, 188.1.
1
3
6.4 Hz, 2 H). C NMR (CDCl ) δ 9.85, 14.01, 22.3, 23.2,
3
(
28.5, 31.2, 61.2, 74.1, 76.95, 76.97, 80.97.
hydride (350 mg, 60%) in anhydrous DMSO (50 mL) and
anhydrous benzene (100 mL) was added dropwise a
3(Z),6(Z)-Dod eca d ien -1-ol (17). To a solution of 16
(7.1 g) in ethanol (100 mL) were added triethylamine (1

Total Synthesis of 5-Oxo-ETE
J . Org. Chem., Vol. 63, No. 2, 1998 341
mL) and Lindlar catalyst (1 g) under argon at room
temperature. Hydrogenation was performed at atmo-
spheric pressure using a glass buret apparatus at 0 to 5
127.4, 127.5, 128. 8, 130.4, 130.6, 137.6, 173.4. HREIMS
+
calcd (C23
H
36
O
2
S
2
, M ) 408.2157, obsd 408.2148.
5,5-(Dim eth ylen ed ith io)-6(E),8(Z),11(Z),14(Z)-eico-
sa tetr a en oic Acid (21). A solution of the dithio com-
pound 20 (220 mg) in THF (50 mL) and 1 M LiOH (10
mL) was stirred at room temperature for 20 h. The
reaction mixture was adjusted to pH 5 by the addition
°
C for 5 h and then at room temperature for 24 h. The
solution was filtered to remove the catalyst, and the
filtrate was then evaporated at reduced pressure to give
bisdienyl alcohol 17 (7.1 g), which was purified by column
chromatography to give 4.35 g of pure 17 in 60% yield.
of 5% KHSO
(2 × 50 mL). The combined ethyl acetate extract was
4
washed with cold water, dried over anhydrous Na SO ,
and filtered and the solvent evaporated under reduced
pressure to afford the dithio acid 21, which was purified
by flash column chromatography over silica gel using 1:19
4
(120 mL) and extracted with ethyl acetate
1
H NMR (CDCl ) δ 0.88 (t, J ) 6.9 Hz, 3 H), 1.35 (m, 6
3
H), 2.05 (t, J ) 6.9 Hz, 2 H), 2.35 (m, 2 H), 2.81 (t, J )
.0 Hz, 2 H), 3.65 (m, 2 H), 5.25-5.56 (m, 4 H).
(Z),6(Z)-D o d e c a d ie n -1-y lt r ip h e n y lp h o s p h o -
2
7
3
n iu m Br om id e (19). To a cooled (0-5 °C), stirred
solution of alcohol 17 (3.64 g, 20 mmol) and triph-
MeOH/CH
9
1
2
Cl
2%). 1H NMR (CDCl
.40 (m, 6 H), 1.78-1.88 (m, 2 H), 2.06 (q, J ) 6.9 Hz, 2
2
to give the pure dithio acid 21 (195 mg,
3
) δ 0.84 (t, J ) 7.0 Hz, 3 H), 1.25-
enylphosphine (7.89 g, 30 mmol) in dry CH
was slowly added dropwise a solution of carbon tetra-
bromide (9.55 g, 30 mmol) in dry CH Cl (10 mL) under
argon. The reaction mixture was stirred for 30 min at
-5 °C and then diluted with hexane/ethyl acetate (9:1)
400 mL), and the resulting solution of the bromide 18
2 2
Cl (50 mL)
H), 2.12-2.18 (m, 2 H), 2.41 (t, J ) 7.3 Hz, 2 H), 2.83
m, 2 H), 2.90 (m, 2 H), 3.31-3.37 (m, 4 H), 5.4 (m, 5 H),
2
2
(
5
6
.80 (d, J ) 14.7 Hz, 1 H), 6.04 (t, J ) 10.9 Hz, 1 H),
.71 (dd, J ) 14.6, 11.2 Hz, 1 H). 13C NMR (CD
COCD )
3
0
(
3
δ 14.8, 23.6, 24.1, 26.6, 27.2, 28.0, 30.4, 33.5, 34.3, 40.0
2 × C), 42.59, 71.6, 125.0, 128.5, 128.7, 128.9, 129. 8,
31.1, 131.3, 139.3, 175.0.
-Oxo-6(E),8(Z),11(Z),14(Z)-eicosa tetr a en oic Acid
5-oxo-ETE) (2). To a -10 °C cooled solution of dithio
acid 21 (52 mg, 0.1318 mmol) in methanol/H O (9:1, 25
was filtered through Celite. The filtrate was evaporated
at reduced pressure and the residue purified by flash
column chromatography with 9:1 hexane/ethyl acetate to
afford the pure bromide 18 (4.1 g, 84%). The bromide
(
1
5
(
1
1
8 was immediately converted to the phosphonium salt
9.
2
mL) was added 4-hydroxy-TEMPO (50 µg) in EtOAc (50
µL) followed by a solution of [bis(trifluoroacetoxy)iodo]-
benzene (120 mg, 0.279 mmol) in methanol (1 mL) and
stirred at -10 °C to -8 °C for 2 min. The reaction mix-
The bromide 18 (4.9 g, 20 mmol) was dissolved in dry
acetonitrile (100 mL), and triphenylphosphine (10.59 g,
0 mmol) was added. The reaction mixture was refluxed
4
for 36 h under argon atmosphere and then concentrated
in vacuo. The phosphonium salt 19 was purified by flash
column chromatography with 19:1 methylene chloride/
methanol to afford the pure phosphonium salt 19 (9.35
ture was quenched with a pH 7.5 buffer solution (NaH
PO /Na HPO ) (20 mL) and extracted with ethyl acetate
150 mL). The ethyl acetate extract was washed with
cold water (3 × 30 mL) and brine (1 × 30 mL), dried over
anhydrous Na SO , and filtered. The solvent was evapo-
2
-
4
2
4
(
g, 92%) as a colorless fluffy solid. 1H NMR (CDCl
(
) δ 0.7
t, J ) 7.2 Hz, 3 H), 1.07 (m, 6 H), 1.71 (q, J ) 7.0 Hz, 2
3
2
4
rated under reduced pressure to approximately 2 mL
solution, and the product was purified by reverse phase
HPLC [Sperisorb SW 10, novapack C-18, 10 × 250 mm
H), 2.25-2.43 (m, 4 H), 3.66 (m, 2 H), 4.97-5.04 (m, 1
H), 5.1-5.3 (m, 2 H), 5.4-5.5 (m, 1 H), 7.55 (m, 6 H),
7
2
.75 (m, 9 H); 13C NMR (CDCl
3
) δ 14.1, 20.5, 22.6 (split),
3.4, 25.6, 25.61, 27.2, 29.1, 31.5, 117.7, 118.7, 126.6
3 2
column; solvent system: CH CN:H O:AcOH (80:20:
0
.02%); flow rate 2 mL/min to give a mixture of cis and
trans isomers. The eluant containing the mixture of
-oxo-ETE 2 and 8,9-trans-5-oxo-ETE 3 was neutralized
with Et N before evaporation of the solvents. The
(split), 130.7, 130.9, 133.7, 135.3.
Meth yl 5,5-(Dim eth ylen ed ith io)-6(E),8(Z),11(Z),-
5
1
4(Z)-eicosa tetr a en oa te (20). To a cooled (-78 °C),
3
stirred solution of the phosphonium salt 19 (2.03 g, 4
mmol) in THF (20 mL) was added lithium hexamethyl-
disilazide (1 M, 4 mL, 4 mmol) dropwise under argon.
After stirring for 2 h at -78 °C, HMPA (2 mL) was added,
the reaction mixture was stirred for 10 min, and then
aldehyde 13 (521 mg, 2 mmol) in THF (4 mL) was added
to the resulting red solution. The reaction mixture was
stirred for 1 h at -78 °C and then allowed to warm slowly
to 0 °C over a period of 1 h. It was then quenched by
the addition of 2 N HCl solution (1 mL) and extracted
with diethyl ether (3 × 50 mL). The combined extracts
were washed with cold water (3 × 25 mL), dried over
separation of the individual isomers 2 and 3 was carried
out by NP HPLC (µ-porasil, Sperisorb 10 × 250 mm
column, solvent system: 4.5% 2-propanol in hexane
containing 0.05% AcOH; flow rate 4.5 mL/min). Analyti-
cal separation showed that 8,9-cis and 8,9-trans isomers
2 and 3 were obtained in the ratio of 5:1, t 8,9-cis 16.49
r
min, tr 8,9-trans 19.73 min. To each of the eluants
containing the pure 5-oxo-ETE 2 and 8,9-trans-5-oxo-ETE
3 was added equal amounts of ethyl acetate, and they
were washed with water to remove the 2-propanol and
acetic acid to give pure 5-oxo-ETE 2 22 mg, in 52% yield.
1
H NMR (CD COCD ) δ 0.87 (t, J ) 7.0 Hz, 3 H), 1.27-
3
3
anhydrous Na
2
SO
4
, filtered, and concentrated under
1.39 (m, 10 H), 1.86 (m, 2 H), 2.34 (t, J ) 7.3 Hz, 2 H),
2.72 (t, J ) 7.2 Hz, 2 H), 3.16 (t, J ) 6.6 Hz, 2 H), 5.35-
5.5 (m, 4 H), 5.90 (m, 1 H), 6.24 (m, 2 H), 7.63 (dd, J )
15.3, 11.6 Hz, 1 H). 8,9-trans-5-Oxo-ETE 3 was obtained
reduced pressure to afford the crude product which was
purified by flash column chromatography using 5% ethyl
1
acetate in hexane to give pure 20 (676 mg, 83%).
NMR (CDCl
H
1
3
) δ 0.88 (t, J ) 6.9 Hz, 3 H), 1.23-1.38 (m,
5.5 mg in 13% yield. H NMR (CD COCD ) δ 0.86 (t, J
3
3
6
7
4
H), 1.77-1.86 (m, 2 H), 2.03-2.16 (m,4 H), 2.35 (t, J )
.3 Hz, 2 H), 2.84 (m, 2 H), 2.98 (m, 2 H), 3.2-3.34 (m,
H), 3.66 (s, 3 H), 5.4 (m, 5 H), 5.79 (d, J ) 14.6 Hz, 1
) 7.0 Hz, 3 H), 1.18 (m, 10 H), 1.84 (m, 2 H), 2.33 (t, J )
7.3 Hz, 2 H), 2.66 (t, J ) 7.3 Hz, 2 H), 3.0 (t, J ) 5.8 Hz,
2 H), 5.3-5.51 (m, 4 H), 6.13 (d, J ) 15.6 Hz, 1 H), 6.28
(m, 2 H), 7.23 (dd, J ) 15.7, 9.7 Hz, 1 H).
Meth yl-5,8-Dioxo-6(E)-octen oa te (24). P r oced u r e
a : To a solution of dithio aldehyde 13 (170 mg, 0.653
H), 6.03 (t, J ) 15.0 Hz, 1 H), 6.70 (dd, J ) 14.7, 11.9
Hz, 1 H). 13C NMR (CDCl
) δ 13.7, 22.5, 22.9, 25.5, 26.2,
7.1, 29.2, 31.4, 33.8, 38.9, 41.6, 51.4, 70.6, 124.2, 127.3,
3
2

3
42 J . Org. Chem., Vol. 63, No. 2, 1998
Khanapure et al.
mmol) in acetonitrile/H
2
O (9:1, 7 mL) was added [bis-
(0.4 mL) was added, and the reaction mixture was stirred
for 2 min. Then aldehyde 25 (21 mg, 0.112 mmol) in THF
(0.5 mL) was added to the resulting red solution. The
reaction mixture was stirred for 20 min at -78 °C and
allowed to warm slowly to 0 °C over a period of 1.5 h. It
was then quenched by the addition of 1:1 THF water and
extracted with ethyl acetate (3 × 25 mL). The combined
extracts were washed with cold water (3 × 20 mL), dried
(trifluoroacetoxy)iodo]benzene (1.13 g, 2.61 mmol) and the
reaction mixture stirred at room temperature for 5 min.
The reaction mixture was quenched with water (50 mL)
and extracted with ethyl acetate (2 × 75 mL). The
combined ethyl acetate extract was washed with cold
water (3 × 30 mL) and brine (1 × 30 mL), dried over
2 4
anhydrous Na SO , and filtered. The solvent was evapo-
rated under reduced pressure, and the product was
purified by flash column chromatography over silica
using 20% ethyl acetate in hexane to give the pure
2 4
over anhydrous Na SO , filtered, and concentrated under
reduced pressure to afford the crude product which was
purified by flash column chromatography using 10% ethyl
1
product 24 95 mgs, in 79% yield as a thick oil (solidified
acetate in hexane to give pure 26 (13.1 mg, 35%).
NMR (CDCl
H
1
on cooling). H NMR (CDCl
3
) δ 1.98 (m, 2 H), 2.39 (t, J
3
) δ 0.89 (t, J ) 7.0 Hz, 3 H), 1.23-1.40 (m,
6 H), 1.91 (m, 2 H), 2.05 (m, 2 H), 2.36 (m, 4 H), 2.36 (m,
)
7.1 Hz, 2 H), 2.79 (t, J ) 7.1 Hz, 2 H), 3.81 (s, 3 H),
6
.67 (dd, J ) 16.2 and 7.2 Hz, 1 H), 6.79 (d, J ) 16.2, 1
4 H), 2.50 (m, 4 H), 2.82 (m, 2 H), 3.67 (s, 3 H), 5.30-
1
3
13
H), 9.77 (d, J ) 7.2, 1 H). C NMR (CDCl
3
) δ 18.5, 32.5,
3
5.44 (m, 6 H). C NMR (CDCl ) δ 14.0, 18.9, 21.6, 22.6,
3
9.8, 51.4, 137.2, 144.4, 173.1, 193.1, 198.9.
25.5, 25.6, 27.2, 29.3, 31.5, 33.1, 41.6, 42.5, 51.5, 127.5,
127.8, 128.2, 128.6, 129.1, 130.5, 173.6, 209.5.
P r oced u r e b: To a 0 °C cooled solution of aldehyde
3 (190 mg, 0.73 mmol) in anhydrous ethyl ether (1 mL)
1
5-Oxo-8(Z),11(Z),14(Z)-eicosa t r ien oic Acid (6,7-
d ih yd r o-5-oxo-ETE) (5). A solution of ester 26 (7 mg)
in THF (2 mL) and 1 M LiOH (0.52 mL) was stirred at
room temperature overnight. The reaction mixture was
diluted with water (2 mL) and extracted with hexane (10
mL). The aqueous layer was separated, and the organic
layer was extracted with water (3 × 10 mL). The
combined aqueous extracts were acidified to pH 5 with
was slowly added dropwise a solution of periodic acid (333
mg, 1.46 mmol) in dry THF (1 mL) under argon. The ice
bath was removed, and the reaction mixture was stirred
for 8 min at room temperature. A white solid was
precipitated. The reaction mixture was diluted with
ether (5 mL), filtered through Celite/florisil, and washed
with ether (30 mL), and the combined filtrate was washed
with aqueous Na
dried over anhydrous Na
2
SO
3
(10 mL) and water (2 × 10 mL),
5% aqueous KHSO and extracted with ethyl acetate (2
4
2
SO , filtered, and concentrated
4
× 25 mL). The combined ethyl acetate extract was
under reduced pressure to afford the crude product which
was purified by flash column chromatography with 8:2
hexane/ethyl acetate to afford the pure aldehyde 24 (68
mg, 51%). The spectral data was identical as described
above.
washed with cold water (2 × 10 mL), dried over anhy-
drous Na SO , and filtered and the solvent evaporated
2
4
under reduced pressure to afford the 6,7-dihydro-5-oxo-
ETE 5, which was purified by flash column chromatog-
raphy over silica gel using 1:19 MeOH/CH Cl to give the
2
2
1
Meth yl-5,8-Dioxoocta n oa te (25). To a solution of 24
pure 6,7-dihydro-5-oxo-ETE 5 (4.5 mg, 67%). H NMR
(27 mg) in ethyl acetate:hexane (1:1) (15 mL) was added
(CDCl ) δ 0.89 (t, J ) 7.0 Hz, 3 H), 1.23-1.40 (m, 8 H),
3
1
0% Pd on carbon (25 mg) under argon at room temper-
2.12 (m, 2 H), 2.17 (m, 2 H), 2.31-2.47 (m, 4 H), 2.48-
ature. Hydrogenation was performed at atmospheric
pressure using a glass buret apparatus at room temper-
ature for 10 h. The solution was filtered to remove the
catalyst, and the filtrate was then evaporated at reduced
pressure to give aldehyde 25 (27 mgs, 99% yield) which
was used as such in the next step. H NMR (CDCl
2.56 (m, 4 H), 2.83 (m, 4 H), 5.37 (m, 6 H).
Ack n ow led gm en t. We acknowledge the National
Institutes of Health for support under Grant DK-44730
(
3
J .R.), the National Science Foundation for an AMX-
60 NMR instrument (Grant CHE-9013145), and the
1
3
) δ
1
.90 (m, 4 H), 2.34 (t, J ) 7.2 Hz, 2 H), 2.44-2.58 (m, 2
Medical Research Council of Canada for support under
grant MT-6254 (W.S.P.).
13
H), 2.66-2.78 (m, 2 H), 3.65 (s, 3 H), 9.79 (s, 1 H).
C
NMR (CDCl
00.3, 207.7.
Meth yl 5-Oxo-8(Z),11(Z),14(Z)-eicosatr ien oate (26).
3
) δ 18.8, 32.8, 34.5, 37.3, 41.3, 51.4, 173.4,
2
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
and 13C NMR spectral data for new compounds described
herein (23 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
To a cooled (-78 °C), stirred solution of the phosphonium
salt 19 (165 mg, 0.329 mmol) in THF (3 mL) was added
lithium hexamethyldisilazide (1 M, 0.25 mL, 0.25 mmol)
dropwise under argon. After stirring for 1 h at -78 °C
to -60 °C, it was cooled to -98 °C (MeOH/liq N
2
), HMPA
J O9716993