Total synthesis of 8,12-iso-iPF3α-VI, an EPA-derived isoprostane: Stereoselective introduction of the fifth asymmetric center

Article abstract of DOI:10.1021/jo051916x

A new and stereoselective approach for the synthesis of all-syn isoprostanes is reported. This method, which is based on acid-catalyzed Diels-Alder reaction, allows the introduction of the side chain with a predetermined stereochemistry of the hydroxy gro

Full text of DOI:10.1021/jo051916x

Total Synthesis of 8,12-iso-iPF3r-VI, an EPA-Derived Isoprostane:
Stereoselective Introduction of the Fifth Asymmetric Center
Sheila H. Jacobo,† Chih-Tsung Chang,† Gue-Jae Lee,† John A. Lawson,‡
William S. Powell,§ Domenico Pratico,‡ Garret A. FitzGerald,‡ and Joshua Rokach*,†
Claude Pepper Institute and Department of Chemistry, Florida Institute of Technology, 150 West
UniVersity BouleVard, Melbourne, Florida 32901, The Center for Experimental Therapeutics, The
UniVersity of PennsylVania, Philadelphia, PennsylVania 19104, and Meakins-Christie Laboratories,
Department of Medicine, McGill UniVersity, 3626 St-Urbain St., Montreal, QC, Canada H2X 2P2
jrokach@fit.edu
ReceiVed September 13, 2005
A new and stereoselective approach for the synthesis of all-syn isoprostanes is reported. This method,
which is based on acid-catalyzed Diels-Alder reaction, allows the introduction of the side chain with a
predetermined stereochemistry of the hydroxy group. The first total synthesis of an eicosapentaenoic
acid (EPA)-derived iP, 8,12-iso-iPF3R-VI 10, was performed using this approach.
Introduction
acids (PUFAs). Unlike PGs (e.g., 1) whose side chains are trans
to each other, the lateral side chains of iPs (e.g., 2-4) are cis
in relation to the plane of prostane ring (Scheme 1).
Isoprostanes are relatively stable compounds, which makes
them a good and reliable index of lipid peroxidation.7-9 Over
the past few years, we have developed strategies for the synthesis
of iPs, which we have used to perform the total synthesis of
arachidonic acid (AA)-derived iPs, in particular a representative
of each of the four groups of iPs derived from AA (iPF2R-III 2,
iPF2R-IV, iPF2R-V, iPF2R-VI 3) and other iP metabolites.6,10-12
Lipid peroxidation plays an important role in the pathogenesis
of several diseases such as Alzheimer’s disease, atherosclerosis,
cancer, and other neurodegenerative diseases.1-4 Recently, a new
class of natural products, the isoprostanes (iPs), isomeric with
the enzymatically produced prostaglandins (PGs), has been
discovered.5,6 Isoprostanes are produced by a noncyclooxyge-
nase, free radical-catalyzed peroxidation of polyunsaturated fatty
* Corresponding author. Phone: (321) 674-7329. Fax: (321) 674-7743.
† Florida Institute of Technology.
‡ The University of Pennsylvania.
(7) Kadiiska, M. B.; et al. Free Radical Biol. Med. 2005, 38, 698.
(8) Kadiiska, M. B.; et al. Free Radical Biol. Med. 2005, 38, 711.
(9) Pratico`, D.; Rokach, J.; Lawson, J.; FitzGerald, G. A. Chem. Phys.
Lipids 2004, 128, 165.
(10) Hwang, S. W.; Adiyaman, M.; Khanapure, S.; Schio, L.; Rokach,
J. J. Am. Chem. Soc. 1994, 116, 10829.
(11) Pudukulathan, Z.; Manna, S.; Hwang, S. W.; Khanapure, S. P.;
Lawson, J. A.; FitzGerald, G. A.; Rokach, J. J. Am. Chem. Soc. 1998, 120,
11953.
(12) Kim, S.; Powell, W. S.; Lawson, J. A.; Jacobo, S. H.; Pratico`, D.;
FitzGerald, G. A.; Maxey, K.; Rokach, J. Bioorg. Med. Chem. Lett. 2005,
15, 1613.
§ McGill University.
(1) Steinberg, D. Circulation 1997, 95, 1062.
(2) Witztum, J. L.; Berliner, J. A. Curr. Opin. Lipidol. 1998, 9, 441.
(3) Montine, T. J.; Neely, D. M.; Quinn, J. F.; Beal, F. M.; Markesbery,
W. R.; Roberts, L. J., II; Morrow, J. D. Free Radical Biol. Med. 2002, 33,
620.
(4) Pratico, D.; Sung, S. J. Alzheimer’s Dis. 2004, 6, 171.
(5) Morrow, J. D.; Hill, K. E.; Burk, R. F.; Nammour, T. M.; Badr, K.
F.; Roberts, L. J., II. Proc. Natl. Acad. Sci. U.S.A. 1990, 87, 9383.
(6) Adiyaman, M.; Lawson, J. A.; Hwang, S. W.; Khanapure, S. P.;
FitzGerald, G. A.; Rokach, J. Tetrahedron Lett. 1996, 37, 4849.
10.1021/jo051916x CCC: $33.50 © 2006 American Chemical Society
Published on Web 01/24/2006
1370
J. Org. Chem. 2006, 71, 1370-1379

Total Synthesis of 8,12-iso-iPF3R-VI
SCHEME 1
SCHEME 2. Group VI iPs Derived from EPA
Other synthetic approaches to iPs have also been reported in
the literature.13-18
in the study, cholesterol, remains unchanged, indicating that it
is not the cholesterol that is directly responsible for the
atherosclerotic lesions, but the free-radical peroxidation of
PUFAs.
Using these synthetic standards, we have developed a GC/
MS19-21 and LC/MS/MS22,23 methodology to analyze the
distribution of individual F2-iPs in each class in human urine
and animal models. We have measured elevated urinary levels
of iPs in AD patients and found that the levels correlate with
the severity of the disease.24 Equally, the level of these iPs
increases with cardiovascular impairments.25 We have also
shown, in perhaps the most striking proof to date of free-radical
involvement in atherosclerosis, that vitamin E suppresses iP
generation in vivo and reduces atherosclerosis in apolipoprotein
E (apoE) deficient mice.26 One of the most important parameters
Of great interest are iPs derived from EPA (20:5ω-3) and
docosahexaenoic acid (DHA; 22:5ω-3), which in the case of
DHA have been named neuroprostanes.27 EPA and DHA are
the main PUFAs in fish and marine oils. Diets rich in fish and
marine animals have been associated with a lower incidence of
cardiovascular disease in Japan and Greenland.28-30 In such
population, the AA:EPA ratio has been found to be ∼1.5 as
compared to the average ratio of 11 in North America, and thus
we hypothesize that iPs derived from EPA will also be formed
in substantial amounts in such populations. Furthermore, this
could also be true for people on EPA dietary supplements that
are very popular and sold in pharmacies. Measurement of EPA-
derived iPs, in addition to AA-derived iPs, will provide a better
view of oxidant stress in these cases. Furthermore, studies on
the biological implications of the EPA-derived iPs are also of
importance and could be made possible with the availability of
synthetic standards. Evidence for the formation of F3-iPs by
chemical peroxidation of EPA has been reported.31 However,
no synthesis of EPA-derived iPs has ever been reported. As a
result, no individual iP has been identified in human biological
fluids.
(13) Taber, D. F.; Herr, R. J.; Gleave, D. M. J. Org. Chem. 1997, 62,
194.
(14) Taber, D. F.; Xu, M.; Hartnett, J. C. J. Am. Chem. Soc. 2002, 124,
13121.
(15) Larock, R. C.; Lee, N. H. J. Am. Chem. Soc. 1991, 113, 7815.
(16) Zanoni, G.; Fabio, A.; Meriggi, A.; Vidari, G. Tetrahedron:
Asymmetry 2001, 12, 1779.
(17) Schrader, T. O.; Snapper, M. L. J. Am. Chem. Soc. 2002, 124, 10998.
(18) Quan, L. G.; Cha, J. K. J. Am. Chem. Soc. 2002, 124, 12424.
(19) Pratico`, D.; Barry, O. P.; Lawson, J. A.; Adiyaman, M.; Hwang, S.
W.; Khanapure, S. P.; Iuliano, L.; Rokach, J.; FitzGerald, G. A. Proc. Natl.
Acad. Sci. U.S.A. 1998, 95, 3449.
(20) Lawson, J. A.; Li, H.; Rokach, J.; Adiyaman, M.; Hwang, S. W.;
Khanapure, S. P.; FitzGerald, G. A. J. Biol. Chem. 1998, 273, 29295.
(21) Adiyaman, M.; Lawson, J. A.; Khanapure, S. P.; FitzGerald, G.
A.; Rokach, J. Anal. Biochem. 1998, 262, 45.
(22) Lawson, J. A.; Rokach, J.; FitzGerald, G. A. J. Biol. Chem. 1999,
274, 24441.
(27) Roberts, L. J., II; Montine, T. J.; Markesbery, W. R.; Tapper, A.
R.; Hardy, P.; Chemtob, S.; Dettbarn, W. D.; Morrow, J. D. J. Biol. Chem.
1998, 273, 13605.
(23) Li, H.; Lawson, J. A.; Reilly, M.; Adiyaman, M.; Hwang, S. W.;
Rokach, J.; FitzGerald, G. A. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 13381.
(24) Pratico`, D.; Clark, C. M.; Liun, F.; Rokach, J.; Lee, V. Y. M.;
Trojanowski, J. Q. Arch. Neurol. 2002, 59, 972.
(25) Polidori, M. C.; Pratico`, D.; Savino, K.; Rokach, J.; Stahl, W.;
Mecocci, P. J. Card. Failure 2004, 10, 334.
(28) Yamori, Y.; Nara, Y.; Iritani, N.; Workman, R. J.; Inagami, T. J.
Nutr. Sci. Vitaminol. 1985, 31, 417.
(29) Dyeberg, J.; Bang, H. O.; Stoffersen, E.; Moncada, S.; Vane, J. R.
Lancet 1978, 2, 117.
(30) Dewailly, E.; Blanchet, C.; Lemieux, S.; Sauve, L.; Gingras, S.;
Ayotte, P.; Holub, B. J. Am. J. Clin. Nutr. 2001, 74, 464.
(31) Nourooz-Zadeh, J.; Halliwell, B.; Anggard, E. E. Biochem. Biophys.
Res. Commun. 1997, 236, 467.
(26) Pratico`, D.; Tangirala, R. K.; Rader, D. J.; Rokach, J.; FitzGerald,
G. A. Nat. Med. 1998, 4, 1189.
J. Org. Chem, Vol. 71, No. 4, 2006 1371

Jacobo et al.
FIGURE 1. HPLC/MS/MS of a mixture of four synthetic iPs. Representatives of each of the four F2-iP classes were mixed and analyzed during
a single multiple reaction-monitoring LC/MS/MS run.
We herein report a novel and stereoselective approach to all-
syn iPs (the two OH groups and the two side chains are on the
same face of the prostane ring), for example, 4. To demonstrate
our approach, which is based on acid-catalyzed Diels-Alder
reaction, the first total synthesis of 8,12-iso-iPF3R-VI 10, an all-
syn EPA-derived iP of group VI, was performed. As shown in
Scheme 2, there are a total of 16 group VI iPs that can be
generated from EPA by an endoperoxide mechanism.32
catalyzed Diels-Alder reaction is known to favor products from
a syn approach,11,34 we decided to design a synthetic route based
on it. As shown in Scheme 3, using 1,3-butadiene 21 as the
diene component, an all-syn tetrasubstituted intermediate such
as 18 can be generated wherein the two functional groups in
the prostane ring are the same but can be differentiated to allow
the introduction of different top and bottom side chains.
Another important objective of this synthesis is an attempt
to introduce the side chain with a predetermined stereochemistry
of the hydroxy group. In our previous syntheses of iPs, we have
constructed the stereochemistry of the hydroxy group in the side
chain via the BINAL-H reduction of its keto-derivative.10,11 We
have found this process to be very useful and result in good
ee’s. However, the process is not universal and has excep-
tions,35,36 and, in such cases, the identity of the product is in
doubt. Thus, development of an approach to introduce the side
chain with predetermined stereochemistry of the hydroxy group
is of importance. In the present case, we have envisioned that
this could be accomplished by a crossed olefin metathesis
between prostane ring synthons such as 16 or 17 and the side
chain intermediate. By design, synthons 16 and 17 already
contain substitutions with the required stereochemistry, in this
case, all-syn, necessary for the construction of the top and
bottom side chains. The use of such intermediates for the
Results and Discussion
The selection of 10 as a synthetic target is based on our
previous discovery that the two all-syn AA-derived iPs, 8,12-
iso-iPF2R-VI 4 and its epimer, 5-epi-8,12-iso-iPF2R-VI, are the
most abundant iPs discovered in human urine (Figure 2).20 Also,
a previous report on the radical peroxidation of linolenic acid
shows a preponderance of all-syn products as compared to the
syn-anti-syn isomers (the two hydroxy groups are cis to each
other and anti to the two side chains).33 Because the structural
differences between AA and EPA are minimal, it is not
unreasonable to expect that all-syn iP 10 and 11 will also be
the major iPs derived from EPA.
Synthetic Approach. We have previously reported a thermal
Diels-Alder procedure for the preparation of syn-anti-syn
iPs, for example, 2 and 3.11 In the present case, we are interested
in developing a flexible route to all-syn iPs. Because acid-
(34) Jeroncic, L. O.; Cabal, M. P.; Danishefsky, S. J. J. Org. Chem.
1991, 56, 387.
(32) Rokach, J.; Khanapure, S. P.; Hwang, S. W.; Adiyaman, M.;
Lawson, J. A.; FitzGerald, G. A. Prostaglandins 1997, 54, 823.
(33) O’Connor, D. E.; Mihelich, E. D.; Coleman, M. C. J. Am. Chem.
Soc. 1984, 106, 3577.
(35) Noyori, R.; Tomino, I.; Yamada, M.; Nishizawa, M. J. Am. Chem.
Soc. 1984, 106, 6717.
(36) Kim, S.; Bellone, S.; Maxey, K.; Powell, W. S.; Lee, G. J.; Rokach,
J. Bioorg. Med. Chem. Lett. 2005, 15, 1873.
1372 J. Org. Chem., Vol. 71, No. 4, 2006

Total Synthesis of 8,12-iso-iPF3R-VI
FIGURE 2. HPLC/MS/MS of urinary iPs. Selected peaks were identified by comparison with synthetic standards.
SCHEME 3. Retrosynthetic Analysis
introduction of side chains containing preformed hydroxy groups
has never been attempted before.37 An advantage of this
approach is that it is not specifically designed for a certain iP
group and thus offers a large degree of flexibility in the synthesis
of iPs. As can be seen, the chirality of the hydroxy group in 20
determines the stereochemistry of the four substituents on the
five-membered ring.
Preparation of ene-Lactone 33. 4(S)-Hydroxycyclopent-2-
enone 20 was prepared as described by us previously.38,39
Protection of 20 with TBDMSCl was done in preference to
TBDPSCl.11,34 Diels-Alder reaction of dienophile 22 and 1,3-
butadiene 21 in toluene catalyzed by AlCl3 afforded the desired
all-syn product 23 and the syn-anti-syn product (not shown)
in 70% combined yield.11,34 About 8% of the deprotected
derivatives of 23 and the syn-anti-syn product was also
isolated. With the recovered 8%, the total yield is ∼78%.
Oxidation of 23 with a catalytic amount of OsO4, in the
presence of trimethylamine-N-oxide, afforded 24 in 90% yield
(Scheme 4). A small quantity of its isomer (∼9%) 25, a product
generated from the approach from the more hindered concave
face, was also isolated. Cleavage of the diol 24 by NaIO4 in
the presence of ruthenium chloride hydrate afforded bis-acid
26 in 95% yield. Probably because of steric hindrance, a much
slower oxidation was observed for 25, wherein intermediate
aldehyde-acids were isolated. Bis-acid 26 was esterified with
diazomethane to give 27 in 91% yield.
The success of this approach depends on whether we can
differentiate the two generated ester groups in 27 in Scheme 4.
This was accomplished through the stereocontrolled reduction
of the keto-group. We have chosen the bulky L-Selectride as
reducing agent to ensure a hydride attack from the â face, which
we anticipated to be the less crowded face, to yield the desired
R-hydroxy intermediate. The L-Selectride reduction of the keto-
(37) AAANMR1.
(38) Khanapure, S. P.; Najafi, N.; Manna, S.; Yang, J.-J.; Rokach, J. J.
Org. Chem. 1995, 60, 7548.
(39) Chang, C. T.; Jacobo, S. H.; Powell, W. S.; Lawson, J. A.;
FitzGerald, G. A.; Pratico, D.; Rokach, J. Tetrahedron Lett. 2005, 46, 6325.
J. Org. Chem, Vol. 71, No. 4, 2006 1373

Jacobo et al.
SCHEME 4. Preparation of ene-Lactone 33a
a Reagents and conditions: (a) TBDMSCl, Et3N, DMAP, CH2Cl2, rt, 8 h; (b) AlCl3, toluene, rt, 1.5 h; (c) (CH3)3N(O)‚2H2O, t-BuOH/CH3CN/H2O
(21:11:5), rt, 1 h; (d) RuCl3‚xH2O, CH3CN/CCl4/H2O (2:2:3), rt, 2.5 h; (e) Et2O, rt, 1 h; (f) THF, -78 °C (30 min) to -40 °C (45 min); (g) i-PrOH, rt, 2.5
h; (h) THF, 0 °C (30 min) to rt (1 h); (i) n-Bu3P, THF, rt, 8 h; (j) THF, rt, 3 h.
SCHEME 5. Preparation of Top Side Chain Synthon 39a
a Reagents and conditions: (a) NaHMDS, THF, -60 °C to rt, 1.25 h; (b) THF, rt, 12 h; (c) Et2O, rt, 1 h.
group afforded 28 in 73.5% yield. The five-membered ring
lactone in 28 is formed in the same step. The formation of a
bottom lactone also confirms that we have an intermediate
whose substitutions are all on the same face (all-syn) in reference
to the plane of the ring.
Scheme 5, in such a way that it is amenable to large scale
preparation and, at the same time, the hydroxy group will have
an optically pure “S” stereochemistry. These prerequisites were
satisfied by using cheap and commercially available D-arabinose
34. Synthesis of 36 from D-arabinose was done in nine steps,
as described by us previously.41 36 was coupled with the
phosphorane derived from the commercially available one-
carbon phosphonium salt 37 to give 38 in 77% yield. Desilyl-
ation of 38 with TBAF afforded a mixture of hydroxy-ester 39
(∼22%), hydroxy-acid 40 (73%), and lactone 41 (5%), with a
combined yield of 92%. 39, 40, and 41 can be easily purified
and separated by column chromatography. 40 was esterified
back to 39 using diazomethane in quantitative yield.
Synthesis of 8,12-iso-iPF3r-VI. The completion of the
synthesis of 8,12-iso-iPF3R-VI 10 is shown in Scheme 6. As
mentioned earlier, we have planned to introduce the top side
chain of 10 by crossed olefin metathesis. The metathesis reaction
between ene-lactone 33 and the top side chain synthon 39 was
performed in CH2Cl2 at room temperature and was catalyzed
by Grubbs’ catalyst (2nd generation). The reaction was allowed
to run for 3-4 days, and addition of 1 equiv of 39 and 20-
Hydrolysis of the methyl ester using LiOH in 2-propanol
afforded 29 in 97% yield. It is possible that the LiOH also
hydrolyzed the lactone. Under workup conditions, the lactone
is automatically re-formed. To selectively reduce the carboxy
acid in the presence of the lactone, we used BH3‚THF as
reducing agent. The reaction went well to afford 30 in 93.5%
yield. The alcohol was converted to ene-lactone 33 in two steps.
The first step involved the derivatization of the alcohol using
o-nitrophenylselenocyanate 31 to form intermediate 32 in 87%
yield.40 Oxidation of 32 with H2O2 in THF afforded 33 in 80%
yield. In addition to the chemical transformations, the confirma-
tion of the structural assignment of 33 is provided by 1H NMR,
13C NMR, IR, MS data, decoupling studies, and NOESY (see
Supporting Information).
Preparation of the Top Side Chain Synthon 39. We have
designed the synthesis of top side chain synthon 39, shown in
(40) Grieco, P. A.; Gilman, S.; Nishizawa, M. J. Org. Chem. 1976, 41,
1485.
(41) Adams, J.; Fitzsimmons, B. J.; Rokach, J. Tetrahedron Lett. 1984,
25, 4713.
1374 J. Org. Chem., Vol. 71, No. 4, 2006

Total Synthesis of 8,12-iso-iPF3R-VI
SCHEME 6. Synthesis of 8,12-iso-iPF3r-VI 10a
a Reagents and conditions: (a) CH2Cl2, rt, 3-4 days; (b) Et3N, DMAP, CH2Cl2, reflux, 3.5 h; (c) ether/MeOH, rt, 35 min; (d) Et3N, DMAP, CH2Cl2,
i
reflux, 2.5 h; (e) CH2Cl2, -70 °C to -50 °C, total time ) 2 h; (f) NaHMDS, THF, -60 °C (30 min) to rt (30 min); (g) THF, rt, 8 h; (h) PrOH/H2O, rt,
3 h.
30% mol of Grubbs’ catalyst was done each day to afford 42
in 67% yield. As expected, the dimerization product of 39 was
also formed. Protection of 42 with TBDMSCl afforded 43 in
85% yield.
m/z 115 is the characteristic fragment ion of group VI, m/z 151
for group V, m/z 127 for group IV, and m/z 193 for group III
(Figure 1).23 Using this information, we were able to establish
an assay that allows simultaneous analysis of selected isomers
of each of the four groups using high performance liquid
chromatography/electrospray/tandem mass spectrometry (HPLC/
ESI/MS/MS) through selective ion monitoring. The high
specificity of each fragment ion is illustrated in the good mass
spectrometric resolution shown in Figure 1. Chromatograms of
groups IV, V, and VI are not contaminated with any peaks from
other groups. The chromatogram of group III contains a slight
contamination from group VI. This does not create any
ambiguities in the analysis because the peaks of groups III and
VI are well resolved. With selective ion monitoring, we were
able to measure with one injection the urinary profile of the
four groups of AA-derived iPs as shown in Figure 2.
Figure 3 shows the mass spectrum of 8,12-iso-iPF3R-VI 10.
As anticipated, an ion at m/z 115 dominated the fragment ion
spectrum as was the case for iPF2R-VI 3.23 The selective ion
monitoring at m/z 351 (molecular ion peak) and at ion fragment
m/z 115 in the case of group VI guarantees the noninterference
by m/z 115 of F2-iPs. These preliminary results are promising,
and we are hopeful that, as in the case of F2-iPs, we will be
able to develop a sensitive LC/MS/MS methodology to analyze
and measure the distribution EPA-derived iPs in biological
fluids.
Reduction of 43 with DIBAL-H at -78 °C afforded the lactol
derivative (not shown) in 60% yield. Wittig reaction of the lactol
and the phosphorane derived from phosphonium salt 4842 failed
to produce the desired product, and lactol was recovered
unchanged. With all of the substituents of the prostane ring on
the same face and the presence of silyl protecting groups, Wittig
reaction of such sterically hindered lactol may not be possible.
Thus, we decided to reduce the lactone completely using NaBH4
to form diol 44. Bis-silylation with TESCl afforded 46 in 85%
yield. One step conversion of 46 to aldehyde 47 was ac-
complished in 81% yield using Swern oxidation, which greatly
favored the oxidation of the primary silyl group.43 Coupling of
47 with the phosphorane generated from 48 afforded 49 in 82%
yield. The removal of the tris-silyl groups in 49 was performed
in THF using 0.5 N HCl. Finally, hydrolysis with LiOH in
2-propanol afforded the desired compound, 8,12-iso-iPF3R-VI
10, in 92% yield.
As can be seen from Schemes 1 and 2, there is only a slight
structural difference between F2-iPs and F3-iPs. We are hypoth-
esizing that the mass spectral fragmentation of F3-iPs will be
very similar to those of F2-iPs. In the past, we have shown that
each group of F2-iP has an abundant fragment ion, which is
specific to that group and not present in the others. For example,
Conclusion
(42) Kim, S.; Lawson, J. A.; Pratico`, D.; FitzGerald, G. A.; Rokach, J.
Tetrahedron Lett. 2002, 43, 2801.
(43) Rodriguez, A.; Nomen, M.; Spur, B. W.; Godfroid, J. J. Tetrahedron
Lett. 1999, 40, 5161.
In summary, we have described an interesting variation of
our Diels-Alder approach to isoprostanes. A key feature of this
approach is the introduction of the side chain containing a
J. Org. Chem, Vol. 71, No. 4, 2006 1375

Jacobo et al.
FIGURE 3. Fragment ion spectra of 8,12-iso-iPF3R-VI.
[3-(tert-Butyl-dimethylsilyl)oxy-2-carboxymethyl-5-oxo-cyclo-
pentyl]acetic Acid (26). To a stirred solution of 24 (0.420 g, 1.4
mmol) in the CH3CN/CCl4/H2O solvent system (total volume )
21 mL; 2:2:3) were added NaIO4 (2.38 g, 11.12 mmol) and RuCl3‚
xH2O (6.39 mg, 0.0308 mmol). After being stirred at room
temperature for 2.5 h, the reaction mixture was diluted with CH2-
Cl2 (10 mL). Layers were separated. The aqueous layer was
extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts
were dried (Na2SO4) and concentrated under vacuum. Purification
by silica gel chromatography with 10-15% MeOH/CH2Cl2 as
hydroxy group with predetermined stereochemistry. The first
total synthesis of an EPA-derived iP, 8,12-iso-iPF3R-VI 10, was
performed using this approach. The identification of a major
fragment ion m/z 115 bodes well for the development of a
quantitative method for the measurement of EPA-derived iPs.
This is the first step in the evaluation of EPA-derived iPs and
lipid peroxidation in humans. Work is in progress for the
identification of this iP in human urine.
1
eluent afforded 26 (0.4363 g, 95%). H NMR (CDCl3) δ 4.40-
Experimental Section
4.51 (1H, br), 2.15-3.10 (8H, m), 0.88 (9H, s), 0.07 (3H, s), 0.12
(3H, s); ΙR (cm-1) 1751.92, 1721.19; MS (EI) for C15H26O6Si [M]+,
330.16.
Dihydroxylation of (1S,6R,7S)-7-[(tert-Butyldimethylsilyl)oxy]-
bicyclo[4.3.0]non-3-en-9-one (24). To 23 (0.085 g, 0.319 mmol)
in the t-BuOH/CH3CN/H2O solvent system (2.5 mL; 21:11:5) was
added (CH3)3N(O)‚2H2O (0.107 g, 0.959 mmol). The resulting
solution was treated with OsO4 (2.5% in t-BuOH, 0.0892 mL). After
the mixture was stirred for 1 h at room temperature, the solvent
was evaporated and the remaining aqueous layer was extracted with
ethyl ether (3 × 7 mL). The combined organic extracts were dried
(Na2SO4) and concentrated under reduced pressure. Purification of
the residue by silica gel chromatography with 5% MeOH in CH2-
Cl2 as eluent afforded 24 (86.5 mg, 90%) and 25 (9.1 mg, 9%),
both white solids.
[3-(tert-Butyldimethylsilyl)oxy-2-methoxycabonylmethyl-5-
oxo-cyclopentyl]acetic Acid Methyl Ester (27). CH2N2 in ether
was added to 26 (0.214 g, 0.60 mmol) at 0 °C. The light yellow
solution was stirred at room temperature for 45 min. The ether was
evaporated, and the residue was purified by silica gel chromatog-
raphy with 5% ethyl acetate in hexane as eluent to afford 27 (211.9
1
mg, 91%). H NMR (CDCl3) δ 4.50-4.58 (1H, br), 3.71 (3H, s),
3.69 (3H, s), 2.88-3.0 (1H, m, br), 2.18-2.73 (7H, m), 0.88 (9H,
s), 0.055 (3H, s), 0.045 (3H, s); 13C NMR (CDCl3) δ 216.3, 173.0,
173.0, 70.9, 52.2, 51.9, 47.1, 46.6, 41.2, 32.3, 29.9, 25.9, 18.1, -4.6,
-5.1; IR (cm-1) 1735.92 (br); MS (EI) for C17H32O6Si [M]+,
358.86.
Spectral Data of (1S,3S,4R,6R,7S)-3,4-Dihydroxy-7-[(tert-
butyldimethylsilyl)oxy]bicyclo[4.3.0]non-3-en-9-one (24). 1H NMR
(CDCl3) δ 4.52 (1H, qt, J ) 7.4, 6.4), 4.024 (1H, br), 3.578 (1H,
m), 2.62-2.78 (1H, m), 2.54 (1H, dd, J ) 11.49, 7.75), 1.91-
2.25 (3H, m), 1.74-1.91 (1H, m), 1.21-1.37 (1H, m), 0.891 (9H,
s), 0.098 (3H, s), 0.069 (3H, s); 13C NMR (CDCl3) δ 216.6, 70.0,
The diazomethane was prepared from commercially available
1-methyl-3-nitro-1-nitrosoguanidine (MNNG) as follows: At 0 °C,
400 mg of MNNG was slowly added to the mixture of 4 mL of
40% KOH and 10.0 mL of ethyl ether. The reaction was allowed
to stir for ∼5 min. The yellow ether layer was transferred to a
flask containing 1-2 pellets of KOH and allowed to stand for a
minute. The resulting yellow solution was subsequently used for
esterification.
(3aS,4R,5S,6aR)-Methyl-[5-(tert-butyldimethylsilyl)oxy-2-oxo-
hexahydro-cyclopenta[b]furan-4-yl]acetate (28). To a solution of
27 (0.155 g, 0.4329 mmol) in THF (3.5 mL) was added L-Selectride
(0.5628 mL, 1 M in THF) at -78 °C. The reaction mixture was
stirred at -78 °C for 30 min and then warmed gradually to -40
68.9, 48.6, 44.5, 36.6, 27.3, 26.0, 25.4, 18.2, -4.731. IR (cm-1
)
)
3329.16, 1741.68; HRMS calcd for C15H29O4Si [M + H]+
301.1835, obsd 301.1827.
Spectral Data of (1S,3R,4S,6R,7S)-3,4-Dihydroxy-7-[(tert-
butyldimethylsilyl)oxy]bicyclo[4.3.0]non-3-en-9-one (25). 1H NMR
δ 4.50 (1H, t), 4.02-4.16 (2H, m), 2.64 (1H, dd, J ) 6.08, 13.58),
2.33-2.49 (2H, m), 1.84-2.10 (5H, m), 0.894 (9H, s), 0.083 (2 ×
3H, 2s); 13C NMR (CDCl3) δ 215.8, 69.9, 69.3, 68.2, 45.6, 35.2,
26.0, 26.0, 18.1, -4.6.
1376 J. Org. Chem., Vol. 71, No. 4, 2006

Total Synthesis of 8,12-iso-iPF3R-VI
°C. After being stirred for 45 min at -40 °C, the reaction was
quenched with water (5 mL). The aqueous layer was extracted with
ethyl acetate (3 × 7 mL). The combined organic extracts were dried
(Na2SO4) and concentrated under reduced pressure. Purification of
the residue with 10% ethyl acetate as eluent afforded 28 (0.142 g,
at room temperature for 3 h. The reaction mixture was diluted with
ethyl ether (1.5 mL) and 0.5 mL of H2O. Layers were separated.
The aqueous layer was extracted with ether (3 × 1.0 mL). The
combined organic extracts were dried (Na2SO4) and concentrated
under vacuum. The residue was purified by silica gel chromatog-
raphy with 10% ethyl acetate in hexane as eluent to afford 33
1
73.5%) as a white solid. H NMR (CDCl3) δ 5.098 (1H, t, J )
1
7.15), 4.251 (1H, m), 3.701 (3H, s), 3.065-3.191 (1H, m), 2.579-
2.707 (2H, m), 2.410-2.559 (2H, m), 2.270-2.384 (1H, m), 2.223
(1H, d, J ) 15.19), 1.842-1.980 (1H, m), 0.879 (9H, s), 0.068
(3H, s), 0.027 (3H, s); 13C NMR (CDCl3) 177.4, 173.8, 83.0, 75.0,
(0.0446 g, 80%) as a white solid. H NMR (CDCl3) δ 6.02 (1H,
ddd, J ) 17.5, 10.5, 8.3), 5.23 (1H, ddd, J ) 10.4, 1.9, 0.7), 5.18
(1H, ddd, J ) 17.3, 1.9, 1.1), 5.11 (1H, t, J ) 7.3), 4.230 (1H, t.
J ) 3.6), 3.10 (1H, dtd, J ) 12.2, 8.3, 4.9), 2.87 (1H, dd, J )
18.6, 4.9), 2.54 (1H, td, J ) 8.4, 3.5), 2.52 (1H, dd, J ) 18.6,
11.9), 2.19 (1H, d, J ) 15.1), 1.93 (1H, dddd, J ) 15.0, 6.8, 3.7,
0.4), 0.877 (9H, s), 0.062 (3H, s), 0.044 (3H, s); 13C NMR (CDCl3)
δ 177.8, 135.1, 118.3, 85.0, 77.0, 52.2, 42.5, 41.8, 31.3, 25.9, 18.2,
-4.5, -5.0; HRMS calcd for C15H26O3Si [M + H]+, 283.1729;
obsd 283.1724.
51.8, 42.8, 42.0, 40.2, 31.3, 30.8, 25.9, 18.2, -5.8, -6.0; IR (cm-1
)
1770.87, 1735.92; HRMS calcd for C16H29O5Si [M + H]+,
329.1784; obsd, 329.1790.
(3aS,4R,5S,6aR)-[5-(tert-Butyldimethylsilyl)oxy-2-oxo-hexahy-
dro-cyclopenta[b]furan-4-yl]acetic Acid (29). To a stirred solution
of ester 28 (0.110 g, 0.335 mmol) in i-PrOH (2.3 mL)/H2O (2.2
mL) was added LiOH (40.2 mg, 1.68 mmol). The solution was
stirred at room temperature for 2.5 h. The reaction was quenched
with 0.250 mL of 20% HCl. The aqueous layer was extracted with
EtOAc (3 × 1.0 mL). The combined organic extracts were dried
(Na2SO4) and concentrated under vacuum. Purification of the
residue with 2% MeOH/CH2Cl2 afforded 29 (0.101 g, 97%) as a
white solid. 1H NMR (CDCl3) δ 5.108 (1H, t, J ) 7.3), 4.272 (1H,
t), 3.093-3.266 (1H, m), 2.446-2.776 (4H, m), 2.269-2.400 (1H,
m), 2.186 (1H, d, J ) 15.4), 1.873-2.023 (1H, m), 0.883 (9H, s),
0.079 (3H, s), 0.046 (3H, s); 13C NMR δ 178.0, 177.7, 84.7, 84.8,
Methyl-5(S)-(tert-butyldiphenylsilyl)oxy-hept-6-enoate (38).
To a stirred solution of 37 in dry THF (15.5 mL) was added sodium
hexamethyldisilazide (3.0 mL, 1.0 M in THF) at -60 °C. The
reaction was stirred at this temperature for 15 min, and aldehyde
36 (0.446 g, 2.7 mmol) in dry THF (10.0 mL) was added at -60
°C. The reaction mixture was warmed to room temperature and
stirred at this temperature for 1.25 h. The reaction was quenched
with a saturated solution of NH4Cl (10 mL) and extracted with
ethyl acetate (3 × 15 mL). The combined organic extracts were
dried (Na2SO4) and concentrated under vacuum. The residue was
purified by silica gel chromatography with 5% ethyl acetate in
hexane as eluent to afford 38 (0.342 mg, 77%). 1H NMR (CDCl3)
δ 7.608-7.730 (4H, m), 7.308-7.469 (6H, m), 5.716-5.848 (1H,
s), 4.939-5.051 (2H, m), 4.161 (1H, qt, J ) 5.3), 3.634 (3H, s),
2.172 (2H, t, J ) 7.17), 1.392-1.671 (4H, m), 1.069 (9H, s); 13C
NMR (CDCl3) δ 174.3, 140.9, 136.2 (2 C), 134.5 (2 C), 129.7 (2
C), 127.5 (2 C), 114.8, 74.5, 51.7, 37.0, 34.2, 27.2, 20.0, 19.5.
Methyl-5(S)-hydroxy-hept-6-enoate (39). To a stirred solution
of 38 (726.4 mg, 1.83 mmol) in THF (5.5 mL) was added TBAF
(2.75 mL, 1.0 mL in THF). The reaction mixture was stirred at
room temperature overnight. The reaction was quenched with a
saturated solution of NH4Cl solution (10 mL) and extracted with
ethyl acetate (3 × 15 mL). The combined organic extracts were
dried (Na2SO4) and concentrated under vacuum to give 39 (60.73
mg), 40 (176.5 mg), and 41 (11.62 mg) in 92% combined yield.
40 was esterified back to 39 using diazomethane prepared as
described above. 1H NMR (CDCl3) δ 5.78-5.93 (1H, s), 5.19 (2H,
dd, J ) 17.1, 10.4), 4.161 (1H, qt, J ) 6.1), 3.671 (3H, s), 2.35
(2H, t, J ) 7.2), 1.453-1.821 (4H, m); 13C NMR (CDCl3) δ 171.2,
136.3, 117.1, 80.4, 51.1, 29.8, 28.2, 18.3.
75.1, 43.6, 42.1, 40.1, 31.2, 30.9, 25.9, 18.1, -4.5, -5.2; IR (cm-1
)
1762.16, 1700.71; HRMS calcd for C15H26O5SiNa [M + Na]+,
337.1147; obsd, 337.1433.
(3aS,4R,5S,6aR)-Hexahydro-5-(tert-butyldimethylsilyl)oxy-4-
(2-hydroxy-ethyl)-cyclopenta[b]furan-2-one (30). To a solution
of 29 (0.0238 g, 0.076 mmol) in THF (1.0 mL) at 0 °C was added
BH3‚THF (1.0 M, 0.121 mL). The colorless solution was stirred at
0 °C for 30 min and allowed to warm to room temperature and
was stirred at this temperature for another hour. The reaction was
quenched with 0.5 mL of H2O. The aqueous layer was extracted
with EtOAc (5 × 1.0 mL). The combined organic extracts were
dried (Na2SO4) and concentrated under vacuum. Purification of the
residue by silica gel chromatography with 2% MeOH/CH2Cl2 as
1
eluent afforded 30 (0.0212 g, 93.5%) as a colorless oil. H NMR
(CDCl3) δ 5.089 (1H, t, J ) 7.4), 4.819 (1H, t, J ) 3.3), 3.622-
3.809 (2H, m), 2.987-3.135 (1H, m), 2.7545 (1H, dd, J ) 13.2,
5.2), 2.4865 (1H, dd, J ) 11.8, 6.6), 2.105-2.231 (1H, d, J )
15.2), 2.020-2.100 (1H, m), 1.821-1.950 (2H, m), 1.667-1.790
(1H, m), 0.880 (9H, s), 0.079 (3H, s), 0.060 (3H, s); 13C NMR
(CDCl3) δ 178.0, 84.9, 75.4, 61.5, 44.5, 42.3, 40.1, 30.8, 29.4, 25.9,
18.2, -4.4, -5.1; IR (cm-1) 3457.18, 1764.80; HRMS calcd for
C15H28O4SiNa [M + Na]+, 323.1649; obsd, 323.1641.
(3aS,4R,5S,6aR)-7-[5-(tert-Butyl-dimethylsilyl)oxy-2-oxo-hexahy-
do-cyclopenta[b]furan-4-yl]-5-hydroxy-hept-6-enoic Acid Meth-
yl Ester (42). To a stirred solution of 33 (0.025 g, 0.0882 mmol)
and Grubbs’ catalyst (2nd generation, 0.019 g, 0.0222 mmol) in
CH2Cl2 (1.0 mL) at room temperature was added 39 (0.028 g,
0.1774 mmol). The reaction was stirred at room temperature for 4
days. One equivalent of 39 and 20-30% of the catalyst were added
each day. On the fourth day, the solvent was evaporated and the
residue was purified by silica gel chromatography using 2% MeOH
in CH2Cl2 as eluent to afford 42 (20 mg, 67%). The yield was based
(3aS,4R,5S,6aR)-Hexahydro-5-(tert-butyldimethylsilyl)oxy-4-
(2-(2-nitrophenylselanyl)-ethyl)-cyclopenta[b]furan-2-one (32).
To a solution of 30 (0.090 g, 0.302 mmol) in THF (3.0 mL) were
added o-nitrophenylselenocyanate 31 (0.343 g, 1.5 mmol) and
n-Bu3P (0.376 mL, 1.50 mmol) at room temperature. The reaction
mixture was stirred at room temperature for 8 h. The solvent was
evaporated under reduced pressure, and the residue was purified
by silica gel chromatography with 20% ethyl acetate in hexane as
1
1
eluent to afford 32 (0.1262 g, 87%) as a yellow solid. H NMR
on the recovered starting material (5.4 mg). H NMR (CDCl3) δ
(CDCl3) δ 8.310 (1H, d, J ) 8.2), 7.470-7.590 (2H, m), 7.351
(1H, t, J ) 7.4), 5.110 (1H, t, J ) 7.2), 4.231 (1H, br), 3.021-
3.165 (1H, m), 2.851-3.018 (2H, m), 2.721 (1H, dd, J ) 18.2,
4.6), 2.430-2.580 (1H, dd, J ) 18.2, 11.8), 1.820-2.210 (5H, m),
0.88 (9H, s), 0.079 (3H, s), 0.046 (3H, s); 13C NMR (CDCl3) δ
177.5, 147.2, 133.9, 129.2, 126.8, 125.9, 84.7, 74.9, 47.9, 42.2,
30.6, 25.9, 25.8, 24.6, 18.2, -4.5, -5.2; IR 1762.16; HRMS calcd
for C21H31O5NSeSiNa [M + Na]+, 508.1029; obsd, 508.1071.
(3aS,4R,5S,6aR)-Hexahydro-5-(tert-butyldimethylsilyl)oxy-4-
vinyl-cyclopenta[b]furan-2-one (33). To a solution of 32 (0.096
g, 0.199 mmol) in THF (0.720 mL) was added H2O2 (0.220 mL,
30% (w/w) solution, commercial). The resulting solution was stirred
6.765-5.881 (1H, dd, J ) 15.5, 8.6), 5.513-5.604 (1H, dd, J )
15.5, 5.7), 5.090 (1H, t), 4.104-4.211 (2H, m), 3.676 (3H, s),
2.971-3.122 (1H, m), 2.829 (1H, dd, J ) 18.3, 4.9), 2.388-2.569
(2H, m), 2.321 (2H, t, J ) 7.3), 2.169 (1H, d, J ) 15.1), 1.831-
1.961 (1H, m), 1.387-1.743 (5H, m), 0.898 (9H, s), 0.885 (9H, s),
-0.006-(0.096) (12H, m); 13C NMR (CDCl3) δ 177.6, 174.1,
136.5, 128.1, 84.9, 77.7, 72.6, 51.7, 50.8, 42.5, 41.9, 36.7, 34.0,
31.3, 25.6, 21.0, 18.2, -4.5, -5.0.
(3aS,4R,5S,6aR)-5-(tert-Butyl-dimethylsilyl)oxy-7-[5-(tert-bu-
tyldimethylsilyl)oxy-2-oxo-hexahydo-cyclopenta[b]furan-4-yl]-
5-hydroxy-hept-6-enoic Acid Methyl Ester (43). To a stirred
solution of 42 (0.033 g, 0.0776 mmol) in CH2Cl2 (1.0 mL) was
J. Org. Chem, Vol. 71, No. 4, 2006 1377

Jacobo et al.
added Et3N (0.109 mL, 0.776 mmol). After the mixture was stirred
at room temperature for 5 min, TBDMSCl (58.48 mg, 0.388 mmol)
and a catalytic amount of DMAP were added. The reaction mixture
was stirred at reflux for 3.5 h. The reaction was allowed to cool to
room temperature, after which a saturated solution of NH4Cl (0.7
mL) was added. The two layers were separated. The aqueous layer
was extracted with CH2Cl2 (3 × 0.5 mL). The combined organic
extracts were dried (Na2SO4) and concentrated under vacuum. The
residue was purified by silica gel chromatography with CH2Cl2 as
was cooled to -70 °C, Et3N (0.0263 mL, 0.188 mmol) was added.
The solution was allowed to warm to room temperature and stirred
for another hour. The mixture was diluted with H2O (0.5 mL). The
aqueous layer was extracted with CH2Cl2 (3 × 1.0 mL). The
combined organic layer was dried (Na2SO4) and concentrated under
vacuum. The residue was purified by flash chromatography to afford
47 (0.0056 mg, 81%). 1H NMR (acetone-d6) δ 9.759 (1H, s), 5.833
(1H, dd, J ) 15.0, 8.9), 5.445 (1H, dd, J ) 15.5, 5.5), 4.261-
4.405 (1H, m), 4.113-4.250 (2H, m), 3.606 (3H, s), 2.386-2.931
(3H, m), 2.305 (2H, t, J ) 7.3), 1.426-1.706 (7H, m), 0.781-
1.036 (27H, m), 0.451-0.663 (6H, m), -0.030-(0.152) (12H, m).
13C NMR (acetone-d6) 202.7, 173.9, 136.6, 128.4, 74.7, 73.8, 73.3,
51.4, 50.7, 45.4, 43.5, 41.5, 38.6, 34.3, 26.4, 26.3, 21.5, 18.7, 10.6,
8.8.
Methyl-7-{3r-triethylsilyl)oxy-5r-tert-butyldimethylsilyl)oxy)-
2r-[2,5-(Z,Z)-octadien]-1r-cyclopentane}-5(S)-tert-butyldimeth-
ylsilyl)oxy-hept-6-(E)-enoate (49). To a stirred solution of 48 (0.05
g, 0.106 mmol) in THF was added sodium hexamethyldisilazide
(1.0 M, 95.4 µL) at -78 °C. The resulting deep orange reaction
mixture was stirred at -78 °C for 10 min, after which 47 (0.008 g,
0.0125 mmol) and HMPA (8 µL) were added. The reaction was
stirred at -78 °C for 20 min, allowed to warm to -40 °C, and
was stirred at this temperature for another 30 min. The reaction
was quenched with brine (1.0 mL). The aqueous layer was extracted
with EtOAc (3× ∼1.5 mL). The combined organic extracts were
dried (Na2SO4) and concentrated under vacuum. Purification of the
residue by silica gel chromatography afforded 49 (0.0073 g, 82%).
1H NMR (acetone-d6) δ 5.853 (1H, s), 5.221-5.500 (4H, m),
2.435-2.619 (2H, m), 2.010-2.350 (H, m), 1.810-1.889 (1H, m),
1.615-1.720 (4H, m), 1.485-1.585 (2H, m), 0.875-1.150 (27H,
m), 0.630 (6H, m), 0.02-0.135 (12H, m); 1H NMR (CDCl3) 5.750
(1H, dd, J ) 15.3, 10.1), 5.200-5.450 (5H, m), 4.010-4.120 (3H,
m), 3.650 (3H, s), 2.720-2.810 (2H, m), 2.057-2.410 (8H, m),
1.450-1.750 (7H, m), 0.851-0.995 (27H, m), 0.545-0.625 (6H,
m), 0.001-0.079 (12H, m); 13C NMR (acetone-d6) 173.9, 136.1,
132.2, 130.6, 129.3, 128.5, 128.3, 74.9, 74.1, 73.2, 51.6, 51.4, 48.8,
45.6, 38.8, 34.4, 26.5, 26.4, 26.4, 24.7, 21.6, 21.1, 20.4, 18.8, 18.8,
14.6, 10.4, 8.6.
1
eluent to afford 43 (0.0347 g, 85%). H NMR (CDCl3) δ 5.765-
5.881 (1H, dd, J ) 15.5, 8.6), 5.513-5.604 (1H, dd, J ) 15.5,
5.7), 5.090 (1H, t), 4.104-4.211 (2H, m), 3.676 (3H, s), 2.971-
3.122 (1H, m), 2.829 (1H, dd, J ) 18.3, 4.9), 2.388-2.569 (2H,
m), 2.321 (2H, t, J ) 7.3), 2.169 (1H, d, J ) 15.1), 1.831-1.961
(1H, m), 1.387-1.743 (5H, m), 0.898 (9H, s), 0.885 (9H, s),
-0.006-(0.096) (12H, m); 13C NMR (CDCl3) 177.8, 174.1, 137.1,
125.8, 84.9, 76.9, 72.7, 51.7, 51.0, 42.6, 42.4, 37.8, 34.2, 31.3, 26.1,
25.9, 20.7, 18.4, 18.2, -4.0, -4.5, -4.7, -4.9; HRMS calcd for
C23H41O6Si2 [M - C4H9]+, 469.2442; obsd, 469.2426; HRMS calcd
for C26H47O6Si2 [M - CH3]+, 511.2914; obsd, 511.2911.
Methyl-7-{3r-hydroxy-5r-tert-butyldimethylsilyl)oxy)-2-(2-
hydroxyethyl)-r-cyclopentane}-5(S)-tert-butyldimethylsilyl)oxy-
hept-6-(E)-enoate (44). To a solution of 43 (0.034 g, 0.065 mmol)
in MeOH/ether (0.375 mL/0.750 mL) was added NaBH4 (37.83
mg, 0.517 mmol). Bubbling was observed. The reaction was stirred
at room temperature for 35 min and then quenched with H2O (0.5
mL). The aqueous layer was extracted with ethyl acetate (5 × 1.0
mL). The combined organic extracts were dried (Na2SO4) and
concentrated under vacuum. Purification of the residue by silica
gel chromatography with 30% ethyl acetate in hexane as eluent
afforded 44 (0.0193 g, 72.2%) and 45 (0.0062 g, 24.6%). Yields
were calculated based on recovered starting material 55 (0.0075
g). 1H NMR (CDCl3) δ 5.734 (1H, dd, J ) 15.3, 10.1), 5.429 (1H,
J ) 15.4, 5.6), 4.0701-4.308 (3H, m), 3.554-3.816 (5H, m),
2.545-2.673 (1H, m), 2.321 (2H, t, J ) 7.3), 2.088-2.239 (1H,
m), 1.421-1.74 (8H, m), 0.897 (18H, s), -0.029-(0.133) (12H,
m); 13C NMR (CDCl3) 174.4, 136.2, 127.7, 77.6, 74.6, 72.8, 63.0,
51.7, 51.4, 45.9, 43.1, 38.2, 34.3, 31.3, 26.1, 20.9, 18.4, 18.3, -4.1,
-4.5.
7-{3r,5r-Dihydroxy-2r-[2,5-(Z,Z)-octadien]-1r-cyclopentane}-
5(S)-hydroxy-hept-6-(E)-enoic Acid: 8,12-iso-iPF3r-VI (10). To
a stirred solution of 49 (0.0103 g, 0.0145 mmol) in THF (1.0 mL)
was added 0.5 N HCl (0.580 mL). After being stirred at room
temperature for 8 h, the reaction was quenched with a saturated
solution of NaHCO3 solution (pH was adjusted to ∼7). The aqueous
layer was extracted with EtOAc (5× ∼1.0 mL). The combined
organic extracts were washed with H2O (2 × 1.5 mL), dried
(Na2SO4), filtered, and concentrated under vacuum. At 0 °C, CH2N2
in ether was added dropwise to the crude product. The light yellow
solution was allowed to stir at room temperature for 30 min, after
which the solvent was evaporated under reduced pressure. The
residue was purified by flash chromatography to afford the ester
Methyl-7-{3r-triethylsilyl)oxy-5r-tert-butyldimethylsilyl)oxy)-
2-(2-triethylsilyl)oxyethyl)-r-cyclopentane}-5(S)-tert-butyldim-
ethylsilyl)oxy-hept-6-(E)-enoate (46). To a stirred solution of 44
(0.0193 mg, 0.0364 mmol) in CH2Cl2 (1.0 mL) was added Et3N
(0.0613 mL, 0.437 mmol). After the mixture was stirred at room
temperature for 5 min, TESCl (49.0 µL, 0.219 mmol) and a catalytic
amount of DMAP were added. The reaction mixture was stirred at
reflux (56 °C) for 2.5 h and allowed to cool to room temperature,
after which a saturated solution of NH4Cl (1.0 mL) was added.
Layers were separated. The aqueous layer was extracted with EtOAc
(3 × 1.0 mL). The combined organic extracts were washed with
H2O, dried (Na2SO4), and concentrated under vacuum. The residue
was purified by silica gel chromatography with 5% ethyl acetate
in hexane as eluent to afford 46 (0.0233 g, 85%). 1H NMR δ 5.860
(1H, dd, J ) 15.3, 10.1), 5.415 (1H, dd, J ) 15.6, 5.6), 4.132-
4.247 (3H, m), 3.562-3.706 (5H, m), 2.419-2.627 (2H, m), 2.300
(2H, t, J ) 7.3), 1.926-2.014 (1H, m), 1.460-1.777 (7H, m),
0.837-1.061 (36H, m), 0.483-0.681 (12H, m), 0.009-0.149 (12H,
m); 13C NMR (acetone-d6) 173.9, 136.1, 129.4, 75.1, 74.0, 73.4,
62.4, 51.4, 45.1, 43.9, 38.8, 34.4, 26.5, 26.4, 21.6, 18.9, 18.7, 10.8,
10.4, 8.8, 8.6; HRMS calcd for C39H81O6Si4 [M]+, 757.5110; obsd,
757.5111.
1
derivative of 10 (0.004 g, 75%). H NMR (acetone-d6) δ 5.963
(1H, dd, J ) 15.6, 10.4), 5.541-5.225 (5H, m), 4.222-3.995 (3H,
m), 2.690-2.581 (1H, m), 1.979-2.390 (7H, m), 1.424-1.910 (7H,
m), 0.947 (3H, t, J ) 7.5); 13C NMR (acetone-d6) δ 174.1, 138.0,
132.1, 130.4, 129.7, 128.7, 128.4, 75.1, 72.8, 71.2, 51.6, 51.4, 48.3,
44.1, 37.8, 34.3, 26.2, 25.1, 21.9, 21.1, 14.6.
i
To the solution of the ester (0.004 g, 0.011 mmol) in PrOH/
H2O (1.2:1, 0.500 mL) was added 395 µL of LiOH (0.1 M in iPrOH/
H2O), and the reaction was stirred at room temperature for 3 h.
The reaction mixture was acidified with 0.5 N HCl and extracted
with ethyl acetate (5 × 0.5 mL). The combined organic layer was
washed with brine, dried (Na2SO4), and concentrated in a vacuum
to give 10 (3.5 mg, 92% yield). 1H NMR (acetone-d6) δ 5.821 (1H,
dd, J ) 15.3, 10.5), 5.220-5.525 (5H, m), 4.150-4.195 (3H, m),
2.65 (1H, m), 2.010-2.30 (8H, m), 1.532-1.950 (7H, m), 0.985
(3H, t, J ) 7.5); MS [M]+ ) 351; HRMS calcd for C20H32O5Na
[M + Na]+, 375.21436; obsd, 375.21420; HRMS calcd for
Methyl-7-{3r-triethylsilyl)oxy-5r-tert-butyldimethylsilyl)oxy)-
2-ethanal-1r-cyclopentane}-5(S)-tert-butyldimethylsilyl)oxy-
hept-6-(E)-enoate (47). At -70 °C, (COCl)2 (0.027 mL, 2.0 M in
CH2Cl2) was added to a solution of DMSO (8.34 µL, 0.1078 mmol)
in CH2Cl2. After the mixture was stirred at -70 °C for 15 min, 46
(0.0082 mg, 0.011 mmol) in CH2Cl2 was added dropwise. The
resulting solution was stirred at -70 °C for 20 min and allowed to
warm to -50 °C and stirred for another 20 min. After the mixture
1378 J. Org. Chem., Vol. 71, No. 4, 2006

Total Synthesis of 8,12-iso-iPF3R-VI
C20H32O5K [M + K]+, 391.18842; obsd, 391.18813; HRMS calcd
for C20H31O5 [M - H]-, 351.21674, obsd, 351.21770.
and NOESY, respectively. We thank Dr. O. Phansteil of the
University of Central Florida for allowing us to use their NMR
facilities. We are also grateful to Dr. O. A. Mamer and Sylvie
Gravel of McGill University for the assistance with the HRMS
and HPLC analysis of the final compound.
Acknowledgment. This work was supported by grants from
the National Institutes of Health (DK-44730 (J.R.), HL-69835
(J.R.), HL-81873 (J.R.), HL-70128 (G.A.F.), AG-11542 (D.P.));
the NSF for an AMX-360 NMR instrument (CHE-90-13145);
the Canadian Institutes of Health Research (MOP-6254) (W.S.P.);
and the Heart and Stroke Foundation of Que´bec (W.S.P.). We
are grateful to Dr. D. H. Powell and Dr. I. Ghiviriga of the
University of Florida for assistance with the mass spectrometry
Supporting Information Available: 1H and 13C NMR spectra
of all compounds, NOESY of compound 33, and HPLC tracing of
compound 10. Complete refs 7 and 8. This material is available
free of charge via the Internet at http://pubs.acs.org.
JO051916X
J. Org. Chem, Vol. 71, No. 4, 2006 1379