First total synthesis of labeled EPA and DHA-derived A-type cyclopentenone isoprostanoids: [D2]-15-A3t-IsoP and [D 2]-17-A4t-NeuroP

Article abstract of DOI:10.1016/j.tet.2013.12.063

A-type cyclopentenone isoprostanoids are abundantly formed in vivo by radical peroxidation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are consumed daily for the prevention of cardiovascular and neurological pathologies. To facilitate in depth studies concerning the effects of these oxidized isoprostanoids on human health, labeled derivatives are necessary. In this paper, we have accomplished the first total synthesis of labeled A-type cyclopentenone isoprostanoids, namely 17,18-[D ₂]-15-A_3t-IsoP and 19,20-[D₂]-17-A _4t-NeuroP. The two enantioselective routes are highly convergent, stemming from a common intermediate, readily available by a Julia-Kocienski reaction, and feature the semihydrogenation of an alkyne moiety for the installation of the labeled lower side chain.

Full text of DOI:10.1016/j.tet.2013.12.063

Tetrahedron 70 (2014) 1484e1491
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
First total synthesis of labeled EPA and DHA-derived A-type
cyclopentenone isoprostanoids: [D2]-15-A3t-IsoP and [D2]-17-A4t-
NeuroP
*
*
Alessio Porta, Enrico Brunoldi, Giuseppe Zanoni , Giovanni Vidari
Department of Chemistry, University of Pavia, Via Taramelli 12, 27100 Pavia, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2013
Received in revised form 14 December 2013
Accepted 24 December 2013
Available online 31 December 2013
A-type cyclopentenone isoprostanoids are abundantly formed in vivo by radical peroxidation of eico-
sapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are consumed daily for the prevention
of cardiovascular and neurological pathologies. To facilitate in depth studies concerning the effects of
these oxidized isoprostanoids on human health, labeled derivatives are necessary. In this paper, we have
accomplished the first total synthesis of labeled A-type cyclopentenone isoprostanoids, namely 17,18-
[D2]-15-A3t-IsoP and 19,20-[D2]-17-A4t-NeuroP. The two enantioselective routes are highly convergent,
stemming from a common intermediate, readily available by a JuliaeKocienski reaction, and feature the
semihydrogenation of an alkyne moiety for the installation of the labeled lower side chain.
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Labeled A4-neuroprostane
Labeled A3-isoprostane
Oxidative stress
Total synthesis
EPA and DHA peroxidation
1. Introduction
peroxidation of EPA and DHA, caused by reactive oxygen species
(ROS), occurred in vitro as well in vivo in settings of oxidative
An appropriate dietary supply of eicosapentaenoic acid [EPA,
C20:5 -3] and docosahexaenoic acid [DHA, C22:6 -3], occurring
stress.2e4 A cascade of non-enzymatic free radical reactions is thus
promoted, producing a large amount of different cyclopentanoid
derivatives, namely isoprostanes (ISOPs) from EPA and neuro-
prostanes (NeuroPs) from DHA, which are structurally related to
prostaglandins. However, unlike the trans-disubstituted PGs, the
largest majority of IsoPs and NeuroPs shows cis-oriented side
chains on cyclopentane ring, as exemplified by the structures of
representative examples 1a, 2a, and 3 (Scheme 1).
u
u
mainly in fish-oils, is essential to humans, who are unable to pro-
duce adequate levels of them. In fact, DHA, which is the most
abundant polyunsaturated fatty acid esterified in neuronal plasma
membrane phospholipids,1,2 is essential for the development and
normal functioning of the human central nervous system (CNS),
and the susteinance of cognitive health.1 Moreover, considerable
evidence suggests that dietary consumption of these u-3 fatty acids
have beneficial effects in the primary and secondary prevention of
cardiovascular pathologies, including atherosclerosis, myocardial
infarction, hypertension, as well as other chronic disorders having
an inflammatory or degenerative pathogenesis, such as, for exam-
ple, rheumatoid arthritis, Alzheimer’s disease (AD), macular de-
generation, and a few types of cancer. It is noteworthy that most of
these pathologies are believed to be strictly associated to the so-
called oxidative stress and the consequent in vivo oxidative dam-
age to biomolecules, including membrane lipids.
A few years ago, Nourooz-Zadeh and collaborators, and Morrow
and collaborators, independently demonstrated that massive
* Corresponding authors. Tel.: þ39 0382987322; fax: þ39 0382 987323 (G.V.);
tel.: þ39 0382987321 (G.Z.); e-mail addresses: gzanoni@unipv.it (G. Zanoni), vi-
dari@unipv.it (G. Vidari).
Scheme 1. Structures of compounds 15-A3t-IsoP (1a). 17,18-[D2]-15-A3t-IsoP (1b),
17,18-[3H2]-15-A3t-IsoP (1c), 17-A4t-NeuroP (2a), 19,20-[D2]-17-A4t-NeuroP (2b), 19,20-
[3H2]-17-A4t-NeuroP (2c), and 4-(R,S)-F4t-NeuroP (3).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.12.063

A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
1485
These compounds have been divided in classes according to the
accepted prostaglandin (PG) nomenclature.2,5
Optimization of therapies based on -3 PUFAs-enriched food
u
supplementation would thus require the knowledge of IsoP and
NeuroP biological activities in vivo; above all, their effective health
benefits and absence of harmful effects to humans must be firmly
established.6 Moreover, since DHA is highly concentrated in the
brain, some authors have proposed NeuroPs and, in particular, F4-
NeuroPs, as potential effective markers of oxidative stress processes
in various neurodegenerative disorders, including AD.2,7
Among the different classes of IsoPs and NeuroPs, we have been
interested for years in the synthesis of A/J cyclopentenone prosta-
noids.8 Actually, in brain samples of AD patients, in which oxidized
DHA levels are significantly higher than in healthy control sub-
jects,9 the level of A4/J4-cyclopentenones was determined to be at
least fivefold higher than other NeuroPs, including the highly
abundant cerebral F4-NeuroPs.2,10 It was, therefore, suggested that
the study of A4/J4-NeuroP biology could provide valuable insights
into the pathophysiology of oxidant injury in the CNS and that
quantification of A4/J4-NeuroPs or their derivatives might be a more
sensitive indicator of DHA oxidation, and neural tissue oxidative
stress, than other classes of NeuroPs.4b
Scheme 2. Retrosynthetic analysis of 1b and 2b. TBS¼tert-butyldimethylsilyl;
PT¼phenyltetrazolyl.
protected allylic alcohol 4 could arise from JuliaeKocienski con-
densation between known enantiopure sulphone 5 and aldehyde 6
(Scheme 2).8f
The synthesis of the required aldehyde 6 started from known
(S)-glycidyl p-methoxybenzyl ether 7,15 which, upon exposure to
the complex formed between lithium butylide 8 and BF3$Et2O,
under the Yamaguchi conditions,16 afforded the secondary alcohol
9 with complete regioselectivity in 95% yield (Scheme 3). Sub-
sequent standard group manipulation in 9 readily gave primary
alcohol 10 that was smoothly oxidized by the DesseMartin peri-
odinane (DMP) reagent17 to aldehyde 6 in 86% yield. The sub-
sequent JuliaeKocienski condensation between sulphone 5 and
aldehyde 6 was performed according to the original conditions
described by Kocienski for achieving E-olefins with high stereo-
selectivity.18 As to the competitive enolization of the sulfone rela-
In addition, in seminal studies, Morrow et al. clearly
demonstrated that A3/J3-IsoPs as well as A4/J4-NeuroPs showed
potent anti-inflammatory effects in murine macrophage cells
stimulated with lipopolysaccharide (LPS), exerting this bioactivity
through inhibition of the NF-k
B signaling pathway.11 Moreover, the
vasoprotective potential of 15-A3t-IsoP was underscored by the
ability of this compound to block oxidized lipid accumulation,
a crucial step in foam cell transformation and atherosclerotic pla-
que formation.11b Finally, in another study, Gao and collaborators
demonstrated that EPA and DHA oxidation products induced Nrf2-
directed gene expression, regulating detoxification of reactive ox-
ygen species (ROS), by destabilizing the association between Keap1
and Cullin3.12
To gain further insight into the biology and in vivo biological
activity of oxidized EPA and DHA-derived A-type cyclopentenones,
and to study their distribution in human tissues and biological
fluids, the synthesis of labeled A3-IsoP and A4-NeuroP derivatives is,
therefore, mandatory.
tive to the
g-lactone group, we have previously shown that kinetic
factors govern the desired regioselective
a-deprotonation of the
former group, thus making the protection of the carbonyl moiety
unnecessary.8f Under optimized conditions, sulfone 5 immediately
delivered a yellow anion upon exposure to a slight excess of KHMDS
in DME at ꢀ78 ꢁC, and smoothly reacted with aldehyde 6, affording
the expected enyne 4 in 52% isolated yield (Scheme 4).
Herein, in connection with our ongoing synthetic program on
IsoP and NeuroP derivatives, we report the first synthesis of a la-
beled A3-IsoP, as well as of a labeled A4-NeuroP, namely 17,18-[D2]-
15-A3t-IsoP (1b) and 19,20-[D2]-17-A4t-IsoP (2b), respectively.13,14
2. Results and discussion
2.1. Synthesis of 17,18-[D2]-15-A3t-IsoP
The reason of choosing labeled compounds 1b and 2b as syn-
thetic targets stemmed from our plan to generate both of them by
a flexible convergent strategy and to introduce labeled atoms into
the lower side chains of IsoPs and NeuroPs, as this would avoid the
Scheme 3. Synthesis of aldehyde 6. PMB¼4-methoxybenzyl; Im¼imidazole;
DMAP¼4-N,N-dimethylaminopyridine; DCM¼dichloromethane; DDQ¼2,3-dichloro-
5,6-dicyano-p-benzoquinone; DMP¼DesseMartin periodinane.
loss of the label as a result of acid
advantage in labeling the -3 double bond in 1b and 2b, was the
b
-oxidation.14 An additional
u
possibility of using an alkyne derivative as the immediate precursor
of the (Z)-double bond, thus delaying the labeling step onto an
advanced synthetic intermediate. This strategy also permitted us to
envisage the practical synthesis of the ditritiated analogues 1c and
2c by tritium hydrogenation of the triple bond.
After chromatographic purification, the 13C NMR spectrum in-
dicated compound 4 to be diastereomerically pure, while the vici-
nal coupling constant of 15.5 Hz between 13-H and 14-H in the
corresponding 1H NMR spectrum established the (E)-stereochem-
istry for the D
13-olefin, proving the excellent stereoselectivity of the
From a retrosynthetic point of view, we planned to introduce the
labeling of both 1b and 2b by the regio- and stereoselective cis-
deuteration reaction of alkyne 4 (Scheme 2), from which the upper
chains of target compounds could subsequently be installed
through two different prostaglandin-like Wittig olefination re-
actions.8 In accordance with our previous work in the field,
JuliaeKocienski reaction.
Having secured a reliable and scalable access to the key in-
termediate 4, the synthesis proceeded with the regio- and stereo-
selective cis-reduction of the alkyne functionality in 4 to give the
desired diene 11a with E,Z-configured double bonds in the side
chain. After some experiments we found that hydrogenation of 4 in

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A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
DIBAL-H reduction of 11b provided lactol 12b, as a mixture of
anomers, in quantitative yield. Subsequent Wittig condensation
with commercially available phosphonium salt 13 delivered the
desired olefin 14 as a single Z-stereomer (13C NMR) in 90% isolated
yield. Finally, cyclopentenol DesseMartin periodinane (DMP) oxi-
dation,17 followed by 48% aqueous HF cleavage of the O-TBS ether
group, smoothly gave 15-A3t-IsoP (1b) in 53% overall isolated yield,
with complete conservation of the cis-stereochemistry at the labile
stereocenters C-8 and C-12 (NOE experiments).
2.2. Synthesis of 19,20-[D2]-17-A4t-NeuroP
Contrary to our expectations, the preparation of 19,20-[D2]-17-
A4t-NeuroP (2b) required a modification of the synthetic strategy
developed for achieving 1b, namely, through Wittig olefination of
lactol 12b. Actually, in an exploratory experiment, Wittig conden-
sation of lactol 12a with the ylide generated by deprotonation of
phosphonium salt 20,21 readily prepared from known aldehyde
1622 (Scheme 5), afforded diene 21 with low (7Z)-stereoselectivity
(7Z/7E, 4:1) (Scheme 6).
Scheme 5. Synthesis of phosphonium salt 20. TBDPS¼tert-butyldiphenylsilyl;
TBAF¼tetrabutylammonium fluoride; DMF¼N,N-dimethylformamide.
Scheme 4. Synthesis of 17,18-[D2]-15-A3t-IsoP (1b). KHMDS¼potassium hexame-
thyldisilyl amide; DME¼dimethoxyethane; DIBAL-H¼diisobutylaluminium hydride.
EtOAc/hexane, using Lindlar catalyst19 (5% Pd/CaCO3 poisoned with
lead), in the presence of excess hex-1-ene, added as a hydrogena-
tion competitive olefin, provided 11a in quantitative yield. NMR
spectroscopy analysis, as well as GC/MS (EI) analysis revealed that
a chromatographically isolated sample was >98% pure, containing
insignificant amounts of over-reduced products.
With this protocol in hand, switching H2 gas for D2 gas (ꢂ99.9%
pure), we then submitted alkyne 4 to the dideuteration reaction;
however, the formed reduction product 11b contained significant
amounts of the dihydro derivative 11a, possibly resulting from
hydrogen-transfer from the added olefin. In fact, by substituting
hex-1-ene with a large excess of hept-1-yne as a deuteration
competitive substrate, uncontaminated dideuterated (E,Z)-diene
11b was obtained in 95% yield after flash column chromatography
purification. Comparison of the 1H broad-band decoupled 13C NMR
spectra of 11a and 11b clearly showed the absence of protonated
carbons C-17 and C-18 in the spectrum of 11b, while the corre-
sponding deuterium bonded olefinic carbons were shifted upfield
of about 0.5 ppm (see the Experimental section), as expected.20 On
the basis of these results, deuterium-labeling of 11b was estimated
to be at least 95%.
Subsequent conversion of lactone 11b to neuroprostane 1b, was
accomplished uneventfully by using standard prostaglandin
chemistry,8 submitting [D2]-derivatives to reactions, which were
previously optimized on unlabeled compounds. The absence of the
signals for protonated carbons C-17 and C-18 in the 13C NMR
spectra of different deuterated intermediates indicated that the
high percentage of D-labeling in 11b remained unaffected until the
end of the synthesis.
Scheme 6. Synthesis of 19,20-[D2]-15-A3t-IsoP (2b). EE¼1-ethoxyethyl; EVE¼ethyl
vinyl ether; PPTS¼pyridinium p-toluenesulfonate; DMPU¼1,3-dimethyl-3,4,5,6-
tetrahydro-2(1H)-pyrimidinone; MTBE¼methyl tert-butyl ether.

A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
1487
To surmise this difficulty, we decided to construct the upper side
chain of 2b via Wittig olefination of O-EE-protected cyclopentenol-
aldehyde 23, which was smoothly achieved from lactone 4 via
Weinreb amide 22 (Scheme 6). To maximize (Z)-stereoselectivity in
the subsequent Wittig reaction, aldehyde 23 was then exposed to
the ylide generated from salt 20, in THFeDMPU at ꢀ78 ꢁC.23 Under
this condition, tetraenyne 24 was produced in 56% overall yield
from 4, as a mixture 9:1 of 7Z/7E olefins.
Having assembled the entire carbon backbone of the target
product, conversion of protected cyclopentenol 24 to neuro-
prostane 2b required at first selective O-EE acetal deprotection,
which was executed on treatment 24 with PPTS in CH2Cl2/EtOH to
deliver allylic alcohol 25. Subsequently, cyclopentenol DMP oxi-
dation,17 followed by O-TBS ether cleavage, readily afforded key
enone 26 in 41% overall yield from 24, with complete conservation
of the cis-stereochemistry at the labile stereocenters C-10 and C-14
(NOE experiments).
Regioselective deuterium cis-addition to the alkyne moiety of
tetraenyne 26 to afford 19,20-dideuterated ester 27 then proceeded
uneventfully by using the same procedure previously optimized in
the deuteration of lactone 4. The ꢂ95% D-labeling of 27 was
established by the procedure described for olefin 11b. Finally,
smooth ethyl ester cleavage catalyzed by polymer supported lipase
from Candida antartica,24 afforded [D2]-17-A4t-NeuroP (2b) in 54%
yield. The spectra of 2b were consistent with the structure.
obtained from supplier. Organic layers were dried using MgSO4.
Reactions were monitored by TLC, using pre-coated silica gel 60
(0.25 mm), aluminum-supported TLC plates. Visualization of re-
action components was achieved by UV irradiation at a wavelength
of 254 nm, or stained by exposure to a 0.5% solution of vanillin in
H2SO4/EtOH, followed by gentle heating. Column chromatography
was carried using silica gel 40e63 mm. Infrared spectra were re-
ported as wavenumber (cmꢀ1) of significant peaks. Electrospray
mass spectra (MS) were obtained by ionization methods. Melting
points are uncorrected. 1H NMR spectra were obtained at 300 MHz.
The 1H NMR spectra are reported as follows: chemical shift in parts
per million (ppm) (multiplicity, coupling constant(s) J (Hz), relative
integral) where multiplicity is defined as: br¼broad, m¼multiplet,
s¼singlet, d¼doublet, t¼triplet, q¼quartet, qu¼quintuplet, or
combination thereof. Selected 13C NMR spectra were determined at
75 MHz using a J modulated sequence and, where appropriate, the
central peak of the CDCl3 triplet (77.00 ppm), or the CD2Cl2 quin-
tuplet (54.22 ppm), or the MeOH-d4 septuplet (49.86 ppm), or the
MeCN-d3 singlet (117.3 ppm), was used as an internal reference. The
assignments of NMR spectra were determined by DEPT experi-
ments and are reported as follows: CH3¼q, CH2¼t, CH¼d, CD¼t, and
C¼s.
4.2. Synthetic procedures
4.2.1. (S)-1-(4-Methoxybenzyloxy)hept-4-yn-2-ol (9). 1-Butyne gas
was condensed in a flask cooled at ꢀ30 ꢁC under an Ar atmo-
sphere and dry THF was added to give a 0.25 M solution, 4.0 mL of
which (1.0 mmol) were then transferred to another flask cooled to
ꢀ78 ꢁC. 1.6 M BuLi in hexane (1.25 mL, 2.0 mmol, 2 equiv) was
added and the solution was stirred at ꢀ30 ꢁC for 30 min. Sub-
sequently, BF3$Et2O (2.0 mmol, 2 equiv) was added and, after
10 min, the solution was cooled to ꢀ78 ꢁC and epoxide 7 (100 mg,
0.515 mmol) in dry THF (0.75 mL) was added. After 2 h of stirring,
Et2O (20 mL) and saturated aqueous NH4Cl (20 mL) were added,
the two layers were separated, and the aqueous phase was
extracted with Et2O (3ꢃ25 mL). The combined organic phases
were dried (MgSO4) and evaporated in vacuo. The resulting resi-
due was purified by flash column chromatography on silica gel.
Elution with hexane/EtOAc, 4:1, gave alcohol 9 (122 mg, 95%) as
3. Conclusion
In conclusion, we have accomplished the synthesis of 17,18-[D2]-
15-A3t-IsoP (1b) and 19,20-[D2]-17-A4t-NeuroP (2b), thus achieving
the first total synthesis of labeled A-type cyclopentenone de-
rivatives formed by in vitro as well as in vivo radical-catalyzed
peroxidation of the physiologically important
DHA.
u
-3 PUFAs EPA and
Our
synthetic
strategy
features
a
stereoselective
JuliaeKocienski olefination between enantiopure sulphone 5 and
aldehyde 6 for the preparation of the key intermediate enyne 4,
and two highly regio- and stereoselective cis-deuteration reactions
of alkynes 4 and 26, by using Lindlar Pd-catalyst, to deliver the
desired labeled compounds. We envision that the synthesis of the
ditritiated analogues 1c and 2c could also be achieved by this
standardized protocol.
The availability of labeled compounds will facilitate further in
depth studies on the biology and in vivo biological activity of EPA
and DHA-derived A-type cyclopentenones, as well as their distri-
bution in human tissues and biological fluids. In particular, the role
played by these molecules in the multi-faceted relationship be-
tween ROS oxidation of membrane lipids and oxidative stress-
related diseases, is far for having been fully clarified. Indeed, fur-
ther shedding light on the etiology of severe diseases, a more
thorough comprehension of the mechanisms of action of DHA and
EPA, as well as the oxidized lipids formed in vivo may lead to the
development of targeted strategies that afford greater therapeutic
a colorless oil, TLC Rf (EtOAc/hexane 15:85) 0.35; [
a
]
20 þ9.3 (c 1.3,
D
CH2Cl2); nmax (liquid film) 3430 (br), 2975, 1613, 1514, 1248, 1103,
1035 cmꢀ1
; dH (300 MHz, CDCl3) 7.24 (2H, d, J 7.9 Hz), 6.80 (2H, d, J
7.9 Hz), 4.53 (2H, s), 3.96e3.82 (1H, m), 3.79 (3H, s), 3.55 (1H, dd, J
9.5, 3.5 Hz), 3.47 (1H, dd, J 9.5, 6.7 Hz), 2.72 (1H, br, OH),
2.44e2.32 (2H, m), 2.20e2.10 (2H, m), 1.09 (3H, t, J 7.1 Hz); dC
(75 MHz, CDCl3) 159.2 (s), 130.0 (s), 129.3 (2ꢃd), 113.7 (2ꢃd), 84.0
(s), 74.8 (s), 72.9 (t), 72.6 (t), 69.0 (d), 55.1 (q), 23.7 (t), 14.0 (q),
12.3 (t); HRMS (ESIþ): MHþ, found 249.1492. C15H20O3 requires
249.1491.
4.2.2. (S)-2-(tert-Butyldimethylsilyloxy)hept-4-ynal
(6). DMP
(187 mg, 1.2 equiv) was added to alcohol 10 (90.2 mg, 0.369 mmol)
in CH2Cl2 (4 mL), obtained from 9 by a standard protocol. After
stirring the solution at room temperature for 1 h, a saturated
aqueous solution of Na2S2O3 (5 mL) was added, the two layers were
separated, and the aqueous phase was extracted with CH2Cl2
(3ꢃ5 mL). The combined organic phases were dried (MgSO4) and
evaporated in vacuo. The resulting residue was purified by flash
column chromatography on silica gel. Elution with hexane/EtOAc,
potential for diets based on
u-3 fatty acids.
4. Experimental section
4.1. Instrumentation and chemicals
All reactions requiring anhydrous conditions were conducted in
flame-dried glassware with magnetic stirring under a positive
static atmosphere of argon. Syringes and needles for the transfer of
reagents were dried at 140 ꢁC and allowed to cool in a dessicator
over CaCl2 before use. THF, Et2O were redistilled from sodium
diphenyl ketyl; CH2Cl2 from CaH2, toluene from Na/K. Other sol-
vents and reagents were of commercial quality and used as
9:1, gave aldehyde 6 (77.8 mg, 86%) as a colorless oil, TLC Rf (EtOAc/
20
hexane 10:90) 0.31; [
a
]
D
ꢀ14.2 (c 0.8, CH2Cl2); nmax (liquid film)
2955, 2930, 1741, 1254, 839, 780 cmꢀ1
; dH (300 MHz, CDCl3) 9.61
(1H, d, J 1.4 Hz), 4.08 (1H, td, J 6.0, 1.4 Hz), 2.65e2.37 (2H, m),
2.25e2.08 (2H, m), 1.10 (3H, t, J 7.2 Hz), 0.98 (3ꢃ3H, s), 0.09 (2ꢃ3H,
s); dC (75 MHz, CDCl3) 202.2 (d), 84.2 (s), 76.3 (d), 74.0 (s), 25.4

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A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
(3ꢃq), 23.3 (t), 18.1 (s), 13.8 (q), 12.3 (t), ꢀ4.9 (q), ꢀ5.0 (q); HRMS
(s), 14.1 (q), ꢀ4.5 (q), ꢀ4.7 (q); HRMS (ESIþ): MHþ, found 365.2482.
(ESIþ): MHþ, found 241.1620. C13H25O2Si requires 241.1624.
C21H33D2O3Si requires 365.2481.
4.2.3. (3aS,4R,6aR)-4-[(S,E)-3-(tert-Butyldimethylsilyloxy)oct-1-en-
5-ynyl]-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one
(4). KHMDS (0.66 M in toluene, 1.58 mL, 1.04 mmol, 1.14 equiv) was
added to a stirred solution of sulfone 58f (315 mg, 0.91 mmol,1 equiv)
in dry DME (10 mL) under Ar at ꢀ78 ꢁC. After 50 min a solution of
aldehyde 6 (262 mg, 1.09 mmol, 1.2 equiv) in dry DME (5 mL) was
added and the reaction mixture was allowed to warm to room
temperature for 2 h, then a saturated solution of NH4Cl (30 mL) and
Et2O (10 mL) was added. The layers were separated and the aqueous
phase was extracted with Et2O (3ꢃ50 mL). The combined organic
phases were washed with brine, dried over MgSO4, filtered, and
concentrated in vacuo. The resulting residue was purified by flash
chromatography on silica gel. Elution with hexane/EtOAc (92:8) gave
compound 4 (171 mg, 52%) as a colorless oil, TLC Rf (EtOAc/hexane
4.2.5. (3aS,4R,6aR)-4-{5,6-[D2]-(S,1E,5Z)-3-(tert-Butyldimethylsily-
loxy)octa-1,5-dienyl}-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-
ol (12b). A stirred solution of lactone 11b (453 mg, 1.24 mmol) in
DCM (3 mL) was cooled to ꢀ78 ꢁC, and DIBAL-H (1.87 mL, 1 M in
hexane, 1.51 equiv) was added dropwise. Stirring was continued for
an additional 1 h, and then a saturated solution of NH4Cl (5 mL) was
added at ꢀ78 ꢁC. The mixture was gradually warmed to rt, diluted
with DCM (30 mL), and a saturated aqueous Rochelle salt solution
(30 mL) was added. The aqueous layer was extracted with DCM
(3ꢃ25 mL), and the combined organic phases were washed with
H2O and brine and dried on MgSO4. Evaporation in vacuo of the
volatiles gave lactol 12b (493 mg, 98%), mixture about 9:1 of
hemiacetals, as a colorless oil; TLC Rf (EtOAc/hexane 15:ꢀ85) 0.19;
nmax (liquid film) 3406, 3010, 2963, 2857, 1471, 1463, 1253, 1107,
1071, 1032, 834, 776; dH (300 MHz, CDCl3) 5.82 (1H, br d, J 5.7 Hz),
5.68 (1H, br d, J 5.7 Hz), 5.55e5.40 (2H, m), 5.25 (1H, d, J 7.4 Hz),
4.19e4.03 (1H, m), 3.49e3.41 (1H, m), 3.24 (1H, qu, J 7.5 Hz), 2.85
(1H, br, OH), 2.30e2.11 (2H, m), 2.05 (2H, distorted q, J 7.5 Hz),
1.85e1.65 (2H, m), 0.96 (3H, t, J 7.6 Hz), 0.91 (3ꢃ3H, s), 0.07 (3H, s),
0.04 (3H, s); main hemiacetal dC (75 MHz, CDCl3) 135.2 (d), 134.8
(d), 132.8 (t, Jc1ed 23.2 Hz), 131.2 (d), 128.3 (d), 124.0 (t, Jc1ed 23.2 Hz),
99.1 (d), 88.4 (d), 73.0 (d), 47.6 (d), 42.4 (d), 36.2 (t), 35.5 (t), 25.8
(3ꢃq), 20.6 (t), 18.2 (s), 14.1 (q), ꢀ4.6 (q), ꢀ4.8 (q). HRMS (ESIþ):
MHþ, found 367.2641. C21H35D2O3Si requires 367.2638.
15:85) 0.38; [
a
]
20 þ21.2 (c 2, CH2Cl2); nmax (liquid film) 3057, 2956,
D
2930, 2857, 1775, 1266, 1170, 739 cmꢀ1
;
dH (300 MHz, CDCl3) 6.02
(1H, d, J 5.8 Hz), 5.97 (1H, d, J 5.8 Hz), 5.67 (1H, dd, J 15.5, 5.6 Hz), 5.51
(1H, dd, J 15.5, 7.8 Hz), 5.48 (1H, d, J 7.5 Hz), 4.24 (1H, q, J 6.5 Hz), 3.58
(1H, t, J 7.2 Hz), 3.26 (1H, qu, J 7.5 Hz), 2.50e2.12 (6H, m), 1.10 (3H, t, J
7.5 Hz), 0.88 (3ꢃ3H, s), 0.08 (3H, s), 0.06 (3H, s); dC (75 MHz, CDCl3)
176.8 (s),139.3 (d),136.1 (d),129.2 (d),128.2 (d), 88.6 (d), 83.7 (s), 75.9
(s), 72.0 (d), 49.1 (d), 40.1 (d), 30.5 (t), 28.8 (t), 25.8 (3ꢃq),18.2 (s),14.1
(q), 12.4 (t), ꢀ4.6 (q), ꢀ4.8 (q); HRMS (ESIþ): MHþ, found 361.2198.
C21H33O3Si requires 361.2199.
4.2.4. Hydrogenation and deuteration protocol: (3aS,4R,6aR)-4-
[(S,1E,5Z)-3-(tert-butyldimethylsilyloxy)octa-1,5-dienyl]-3,3a,4,6a-
tetrahydro-2H-cyclopenta[b]furan-2-one (11a) and (3aS,4R,6aR)-4-
{5,6-[D2]-(S,1E,5Z)-3-(tert-butyldimethylsilyloxy)octa-1,5-dienyl}-
3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one (11b). Palladium
on calcium carbonate poisoned with lead (Lindlar catalyst, 4.2 mg)
4.2.6. (Z)-7-[(1S,2R,5R)-2-{5,6-[D2]-(S,1E,5Z)-3-(tert-Butyldime-
thylsilyloxy)octa-1,5-dienyl}-5-hydroxycyclopent-3-enyl]hept-5-
enoic acid (14). Solid phosphonium salt 13 (2.24 g, 4.94 mmol,
4 equiv) was suspended in dry THF (15 mL) in a two-neck round-
bottom flask under an argon atmosphere. To the suspension was
added freshly sublimed potassium tert-butoxide (1.13 g, 9.88 mmol,
8 equiv) portionwise at rt. After being stirred for 20 min, the so-
lution became deeply orange and a THF solution (8.1 mL) of lactol
12b (461 mg, 1.23 mmol) was added via cannula dropwise at rt.
Stirring was continued for an additional 2 h, and the reaction was
quenched by adding a saturated aqueous solution of NH4Cl (15 mL)
and acetic acid (0.593 mL,1.05 equiv vs tert-butoxide); Et2O (60 mL)
was added to the mixture and the organic layer was separated,
whereas the aqueous phase was extracted with an additional Et2O
(3ꢃ50 mL). The organic phases were combined, dried over MgSO4,
filtered, and concentrated at reduced pressure. The residue was
purified on silica gel, using hexane/EtOAc (8:2) as eluent, to give
acid 14 (515 mg, 91%) as a pale yellow oil, TLC Rf (EtOAc/hexane
25:75) 0.32; nmax (liquid film) 3310e2590 (OH and COOH), 2931,
2854, 1714, 1463, 1250, 1066, 838, 776; dH (300 MHz, CDCl3)
6.11e6.06 (1H, m), 6.01 (1H, dd, J 5.7, 2.6 Hz), 5.65e5.30 (4H, m),
4.51 (1H, dd, J 5.4, 2.5 Hz), 4.08 (1H, q, J 6.3 Hz), 3.22e3.12 (1H, m),
2.45e1.98 (11H, m), 1.74 (2H, qu, J 7.4 Hz), 0.97 (3H, t, J 7.4 Hz), 0.91
(3ꢃ3H, s), 0.06 (3H, s), 0.05 (3H, s); dC (75 MHz, CDCl3) 178.1 (s),
139.1 (d), 134.7 (d), 133.1 (d), 132.8 (t, Jc1ed 23.3 Hz), 131.8 (d), 129.5
(d), 129.2 (d), 124.1 (t, Jc1ed 23.3 Hz), 76.3 (d), 73.3 (d), 49.2 (d), 46.8
(d), 36.2 (t), 33.3 (t), 26.5 (t), 25.8 (3ꢃq), 24.4 (t), 23.9 (t), 20.6 (t),
18.1 (s), 14.1 (q), ꢀ4.5 (q), ꢀ4.8 (q). HRMS (ESIþ): MHþ, found
451.3216. C26H43D2O4Si requires 451.3213.
was added to a stirred solution of hept-1-yne (212.5 mL,1.625 mmol,
25 equiv) in 1:1 EtOAc/hexane (1.4 mL). A static atmosphere of H2
was created, and the mixture was stirred for 40 min. A solution of
alkyne 4 (25 mg, 0.065 mmol) in EtOAc (0.5 mL) was then added
and the resulting mixture was stirred under H2 atmosphere for 1 h.
The mixture was then filtered through a small pad of CeliteÒ and
concentrated in vacuo at room temperature. The resulting residue
was purified by flash column chromatography on silica gel. Elution
with hexane/EtOAc, 7:3, gave diene 11a (24 mg, 96%) as a colorless
20
oil, TLC Rf (EtOAc/hexane 10:90) 0.35; [
a
]
D
þ29.9 (c 1.1, CH2Cl2);
nmax (liquid film) 2958, 2930, 2857, 1780, 1166, 835, 778 cmꢀ1
; dH
(300 MHz, CDCl3) 6.02 (1H, d, J 6.0 Hz), 5.97 (1H, d, J 6.0 Hz), 5.66
(1H, dd, J 15.5, 5.5 Hz), 5.50e5.25 (4H, m), 5.48 (1H, d, J 8.5 Hz), 4.15
(1H, q, J 6.1 Hz), 3.55 (1H, t, J 7.2 Hz), 3.25 (1H, qu, J 7.5 Hz), 2.50 (2H,
d, J 8.5 Hz), 2.40e2.13 (2H, m), 2.12e1.99 (2H, distorted qu, J 7.4 Hz),
0.96 (3H, t, J 7.5 Hz), 0.90 (3ꢃ3H, s), 0.06 (3H, s), 0.04 (3H, s); dC
(75 MHz, CDCl3) 176.8 (s), 139.2 (d), 136.9 (d), 133.7 (d), 129.2 (d),
127.4 (d), 124.3 (d), 88.7 (d), 72.7 (d), 48.9 (d), 40.1 (d), 36.2 (t), 30.5
(t), 25.8 (3ꢃq), 20.7 (t), 18.2 (s), 14.2 (q), ꢀ4.5 (q), ꢀ4.7 (q); HRMS
(ESIþ): MHþ, found 363.2358. C21H35O3Si requires 363.2355.
An identical procedure was followed for the deuteration of al-
kyne 4, by substituting a static atmosphere of H2 with ꢂ99.9% pure
D2. After chromatographic purification on silica gel, diene 11b was
obtained in 95% yield as a colorless oil, TLC Rf (EtOAc/hexane 10:90)
0.35; [
a]
20 þ30.2 (c 1.2, CH2Cl2); dH (300 MHz, CDCl3) 6.00 (1H, d, J
4.2.7. (Z)-7-[(1S,2S)-2-{5,6-[D2]-(S,1E,5Z)-3-(tert-Butyldimethylsily-
D
5.7 Hz), 5.95 (1H, d, J 5.7 Hz), 5.48 (1H, d, J 8.0 Hz), 5.44 (1H, dd, J
15.5, 7.5 Hz), 4.15 (1H, q, J 6.0 Hz), 3.55 (1H, t, J 7.4 Hz), 3.25 (1H, qu, J
8.0 Hz), 2.47 (2H, d, J 8.5 Hz), 2.35e2.12 (2H, m), 2.05 (2H, distorted
q, J 7.5 Hz), 0.97 (3H, t, J 7.5 Hz), 0.90 (3ꢃ3H, s), 0.07 (3H, s), 0.05
(3H, s); dC (75 MHz, CDCl3) 176.8 (s), 139.2 (d), 136.9 (d), 133.2 (t,
Jc1ed 23.2 Hz), 129.2 (d), 127.4 (d), 123.8 (t, Jc1ed 23.2 Hz), 88.7 (d),
72.7 (d), 48.9 (d), 40.1 (d), 36.1 (t), 30.5 (t), 25.8 (3ꢃq), 20.6 (t), 18.2
loxy)octa-1,5-dienyl}-5-oxocyclopent-3-enyl]hept-5-enoic
acid
(15). To a solution of allylic alcohol 14 (70 mg, 0.156 mmol) in DCM
(3.4 mL) at rt was added solid DesseMartin periodinane (79.1 mg,
0.187 mmol, 1.2 equiv) in one portion. After the homogeneous so-
lution was stirred for 3 h, the reaction was quenched by adding dry
Et2O (15 mL) and the suspension was quickly filtered on a short pad
of CeliteÒ. The CeliteÒ layer was washed with Et2O (3ꢃ30 mL), and

A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
1489
the organic phases were combined and concentrated at reduced
pressure WITHOUT HEATING. The residue was purified by flash
chromatography on silica gel (SiO2, 4.5 g); elution with hexane/
EtOAc (7:3) gave enone 15 (49 mg, 70%) as a pale yellow oil, TLC Rf
(EtOAc/hexane 30:70) 0.33; nmax (liquid film) 3210e2600 (COOH),
2932, 2855, 1712, 1586, 1460, 1251, 1082, 973, 836, 776; dH
(300 MHz, CD2Cl2) 7.55 (1H, dd J 5.7, 2.8 Hz), 6.19 (1H, dd, J 5.7,
1.7 Hz), 5.65e5.34 (4H, m), 4.18 (1H, q, J 6.1 Hz), 3.79e3.69 (1H, m),
2.58e2.00 (11H, m), 1.72 (2H, qu, J 7.4 Hz), 0.98 (3H, t, J 7.4 Hz), 0.91
(3ꢃ3H, s), 0.08 (3H, s), 0.06 (3H, s); dC (75 MHz, CD2Cl2) 211.0 (s),
179.1 (s), 165.8 (d), 138.1 (d), 134.3 (d), 132.8 (t, Jc1ed 23.2 Hz), 130.4
(d), 129.2 (d), 127.6 (d), 124.7 (t, Jc1ed 23.2 Hz), 73.7 (d), 50.5 (d), 48.3
(d), 36.8 (t), 33.9 (t), 27.4 (t), 26.4 (3ꢃq), 25.4 (t), 25.2 (t), 21.5 (t),
18.8 (s), 14.8 (t), ꢀ3.9 (q), ꢀ4.2 (q). HRMS (ESIþ): MHþ, found
449.3061. C26H41D2O4Si requires 449.3056.
atmosphere; TBAF (1 M solution in THF, 0.54 mL, 0.54 mmol,
1.17 equiv) was added at 22 ꢁC and the reaction mixture was stirred
for 1 h. Volatiles were removed under reduced pressure and the
residue was purified by flash chromatography on silica gel. Elution
with hexane/EtOAc (80:20) gave the expected alcohol (Z)-ethyl 7-
hydroxyhept-4-enoate (73 mg, 92%) as a colorless oil.21 Sub-
sequently, this ester (207 mg, 1.20 mmol) was dissolved in dry DMF
(12 mL) under an argon atmosphere. The resulting solution was
cooled to 0 ꢁC and CBr4 (474 mg, 1.43 mmol, 1.19 equiv) was added
under vigorous stirring, followed by PPh3 (435 mg, 1.66 mmol,
1.38 equiv). The ice bath was removed and the reaction mixture was
stirred for 1 h at 22 ꢁC, then quenched with water (25 mL) and
diluted with Et2O (40 mL); the aqueous phase was extracted with
Et2O (3ꢃ25 mL). The combined organic phases were dried over
MgSO4, filtered, and concentrated under reduced pressure. The
crude bromide was purified by flash chromatography on silica gel.
Elution with hexane/EtOAc (95:5) gave known bromide 1921
(203 mg, 72%) as a pale yellow oil, TLC Rf (EtOAc/hexane 2:98)
0.22; dH (300 MHz, CDCl3) 5.65e5.32 (m, 2H), 4.13 (q, J 7.1, 2H), 3.42
(t, J 7.1, 2H), 2.70 (q, J 7.0, 2H), 2.50e2.40 (m, 4H),1.21 (t, J 7.1, 3H); dC
(75 MHz, CDCl3) 172.8 (s), 130.5 (d), 127.3 (d), 60.3 (t), 33.9 (t), 32.3
(t), 30.6 (t), 22.8 (t), 14.1 (q).
4.2.8. 17,18-[D2]-15-A3t-IsoP (1b). Excess 48% aqueous HF
(0.098 mL) was added to silyl ether 15 (30 mg, 0.067 mmol) dis-
solved in MeCN (3.25 mL) in a polyethylene test tube. After 4 h at
room temperature, a pH 6.8 phosphate buffer (5 mL) and EtOAc
(10 mL) were added, and the two layers were separated. The
aqueous phase was extracted with EtOAc (4ꢃ5 mL), and the com-
bined organic layers were dried over MgSO4, filtered, and concen-
trated in vacuo. The residue was purified by a short flash column
chromatography on silica gel. Elution with hexane/EtOAc (1:1) gave
4.2.11. (Z)-[6-(Ethoxycarbonyl)hex-3-enyl]triphenylphosphonium
bromide (20). Bromide 19 (212 mg, 0.90 mmol) was dissolved in
dry MeCN (2 mL) under an argon atmosphere and PPh3 (284 mg,
1.08 mmol, 1.2 equiv) was added. The reaction mixture was heated
to reflux for 45 h, then MeCN was removed in vacuo. The residue
was purified by flash chromatography on silica gel. Elution with
DCM/MeOH (95:5) gave known phosphonium salt 2021 (403 mg,
90%) as a pale yellow oil, TLC Rf (DCM/MeOH 90:10) 0.25; dH
(300 MHz, CDCl3) 7.9e7.5 (m, 15H), 5.60e5.25 (m, 2H), 3.91 (q, J 7.1,
2H), 3.88e3.72 (m, 2H), 2.33e2.28 (m, 2H), 2.23e2.18 (m, 2H),
2.14e2.09 (m, 2H), 1.1 (t, J 7.1, 3H). dC (75 MHz, CDCl3) 172.7 (s),
135.0 (d), 133.4 (d), 130.3 (d), 127.5 (d), 127.3 (d), 118.5 (s), 117.4 (s),
60.2 (t), 33.4 (t), 23.0 (t), 22.4 (t), 20.3 (t), 14.1 (q).
[D2]-15-A3t-IsoP (1b) (16 mg, 76%) as a colorless oil, TLC Rf (EtOAc/
20
hexane 50:50) 0.25; [
a
]
þ136.2 (c 1.0, EtOAc); nmax (liquid film)
D
3320 (br), 2930, 1710, 1580, 1240, 970 cmꢀ1
; dH (300 MHz, CD2Cl2)
7.60 (1H, dd, J 5.8, 2.8 Hz), 6.25 (1H, dd, J 5.8, 1.8 Hz), 5.65e5.34 (4H,
m), 4.20 (1H, q, J 6.3 Hz), 3.77e3.74 (1H, m), 2.60e2.48 (1H, m),
2.45e2.25 (5H, m), 2.20e2.05 (5H, m), 1.70 (2H, qu, J 7.4 Hz), 0.99
(3H, t, J 7.4 Hz); dC (75 MHz, CD2Cl2) 211.0 (s), 178.3 (s), 165.6 (d),
136.8 (d), 135.8 (d), 133.1 (t, Jc1ed 23.3 Hz), 130.3 (d), 129.5 (d), 128.8
(d), 123.9 (t, Jc1ed 23.3 Hz), 72.6 (d), 50.3 (d), 48.0 (d), 35.8 (t), 33.7
(t), 27.3 (t), 25.7 (t), 25.1 (t), 21.5 (t), 14.7 (q); HRMS (ESIþ): MHþ,
found 335.2192. C20H27D2O4 requires 335.2191.
4.2.9. (Z)-Ethyl 7-(tert-butyldimethylsilyloxy)hept-4-enoate
(18). Commercially available phosphonium salt 17 (6.41 g,
14 mmol, 4.3 equiv) was dried under high vacuum at rt for 1 h and
then suspended in dry PhMe (93 mL). KHMDS (0.5 M solution in
PhMe, 26.8 mL, 13.4 mmol, 4 equiv) was added slowly, under vig-
orous stirring, at room temperature. The orange suspension was
stirred at the same temperature for 1 h, then stirring was stopped
for 1 h. The resulting clear ylide solution (82 mL, ca. 3 equiv) was
transferred into a two-neck round-bottom flask and was cooled to
ꢀ100 ꢁC; a solution of known aldehyde 1622 (1.00 g, 3.20 mmol,
1 equiv) in dry PhMe (30 mL) was added dropwise via cannula. The
resulting reaction mixture was vigorously stirred for 30 min, then
quenched with a saturated solution of NH4Cl (20 mL), and diluted
with Et2O (50 mL). The layers were separated and the aqueous
phase was extracted with Et2O (3ꢃ30 mL). The combined organic
phases were then dried over Na2SO4, filtered, and concentrated in
vacuo. The residue was purified by flash column chromatography
on silica gel. Elution with hexane/EtOAc (99:1) gave known ester
1821 (1.26 g, 96%) as a colorless oil, TLC Rf (EtOAc/hexane 2:98) 0.28;
dH (300 MHz, CDCl3) 7.75e7.60 (4H, m), 7.45e7.35 (6H, m),
5.52e5.35 (2H, m), 4.12 (2H, q, J 7.1 Hz), 3.70 (2H, t, J 6.8 Hz),
2.50e2.25 (6H, m), 1.28 (3H, t, J 7.1 Hz), 1.12 (3ꢃ3H, s); dC (75 MHz,
CDCl3) 173.0 (s), 135.5 (d), 133.8 (s), 129.5 (d), 129.2 (d), 127.5 (d),
127.2 (d), 63.4 (t), 60.2 (t), 34.2 (t), 30.7 (t), 26.7 (3ꢃq), 22.8 (t), 19.1
(s), 14.2 (q). HRMS (ESIþ): MHþ, found 411.2354. C25H35O3Si re-
quires 411.2355.
4.2.12. 2-{(1S,2R,5R)-2-[(S,E)-3-(tert-Butyldimethylsilyloxy)oct-1-
en-5-ynyl]-5-(1-ethoxyethoxy)cyclopent-3-enyl}-N-methoxy-N-
methylethanamide (22). BuLi (2.5 M in hexane, 2.39 mL, 12 equiv)
was added to ClHNMeOMe (0.292 g, 3.0 mmol, 6 equiv) in dry THF
(4.75 mL) under Ar at ꢀ78 ꢁC. After 5 min the solution was stirred at
room temperature for 15 min and then cooled again to ꢀ78 ꢁC.
Lactone 4 (0.180 mg, 0.5 mmol) in dry THF (5.2 mL) was then added
and the mixture was stirred at ꢀ78 ꢁC for 1 h. Saturated aqueous
NH4Cl (10 mL), followed by brine (5 mL) and Et2O (10 mL) was
added; the two layers were separated, and the aqueous phase was
extracted with Et2O (3ꢃ10 mL). The combined organic layers were
then dried over MgSO4, filtered, and concentrated in vacuo. The
crude residue was dissolved in 3 mL of CH2Cl2/EVE, 2:1, and a cat-
alytic amount of PPTS was added. After 2 h of stirring at room
temperature, the mixture was added to saturated aqueous NaHCO3
(10 mL). The two layers were separated and the aqueous phase was
extracted with CH2Cl2 (3ꢃ10 mL). The combined organic layers
were dried over Na2SO4, filtered, and concentrated in vacuo. The
residue was purified by flash column chromatography on silica gel.
Elution with CH2Cl2/EtOAc (98:2) gave Weinreb amide 22 (0.172 g,
70%), mixture of anomers, as a colorless oil; TLC Rf (DCM/EtOAc
80:20) 0.31; nmax 2930, 1668, 1463, 1386, 1254, 1123, 1005, 964,
837 cmꢀ1
; dH (300 MHz, CDCl3) 6.03e5.97 (1H, m), 5.97e5.90 (1H,
m), 5.55 (1H, dd, J 15.5, 5.2 Hz), 5.37 (1H, dd, J 15.5, 5.2 Hz), 4.74
(0.5H, q, J 5.2 Hz), 4.67 (0.5H, q, J 5.2 Hz), 4.52 (0.5H, br d, J 3.9 Hz),
4.47 (0.5H, br d, J 3.9 Hz), 4.15 (1H, distorted q, J 6.0 Hz), 3.72 (1.5H,
s), 3.71 (1.5H, s), 3.73e3.52 (1H, m), 3.51e3.31 (1H, m), 3.25e3.13
(1H, m), 3.15 (3H, s), 2.80e2.55 (2H, m), 2.40e2.12 (5H, m),
1.30e1.05 (9H, 2tþ1d, 3H each), 0.90 (3ꢃ3H, s), 0.06 (3H, s), 0.04
4.2.10. (Z)-Ethyl 7-bromohept-4-enoate (19). Silyl ether 18 (192 mg,
0.46 mmol) was dissolved in dry THF (5.0 mL) under an argon

1490
A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
(3H, s); dC (75 MHz, CDCl3) 174.1 (s), 139.3 (d), 138.1 (d), 133.7 (d),
132.2 (d), 131.3 (d), 130.9 (d), 100.7 (d), 98.0 (d), 83.0 (s), 82.1 (d),
77.9 (d), 76.4 (s), 71.9 (d), 60.9 (q), 60.5 (t), 59.4 (t), 50.4 (d), 50.3 (d),
40.9 (d), 40.7 (d), 32.1 (q), 28.9 (t), 28.4 (t), 28.2 (t), 25.7 (3ꢃq), 20.8
(q), 20.1 (q), 18.1 (s), 15.2 (q), 14.0 (q), 12.3 (t), ꢀ4.5 (q), ꢀ5.0 (q);
HRMS (ESIþ): MHþ, found 494.3304. C27H48NO5Si requires
494.3302.
ꢀ4.8 (q); HRMS (ESIþ): MHþ, found 501.3404. C30H49O4Si requires
501.3400.
4.2.15. (4Z,7Z)-Ethyl 9-{(1S,2S)-2-[(S,E)-3-hydroxyoct-1-en-5-ynyl]-
5-oxocyclopent-3-enyl}nona-4,7-dienoate (26). DMP (41.9 mg,
0.098 mmol, 1.2 equiv) was added to alcohol 25 (40.2 mg,
0.082 mmol) in dry DCM (1.5 mL). After 1 h of stirring at room
temperature, Et2O (10 mL) was added and the suspension was fil-
tered through a short pad of silica gel, which was abundantly
washed with Et2O. The filtrate was evaporated in vacuo to give
a residue, which was purified by flash column chromatography on
silica gel. Elution with hexane/EtOAc (90:10) gave the O-TBS ether
4.2.13. (4Z,7Z)-Ethyl 9-{(1S,2R,5R)-2-[(S,E)-3-(tert-butyldimethylsi-
lyloxy)oct-1-en-5-ynyl]-5-(1-ethoxyethoxy)cyclopent-3-enyl}nona-
4,7-dienoate (24). DIBAL-H (1 M in hexane, 0.210 mL,1.2 equiv) was
added to well-dried amide 22 (85.2 mg, 0.175 mmol) in dry THF
(1.75 mL) under Ar at ꢀ78 ꢁC. After 1 h, the reaction was quenched
by adding a saturated aqueous Rochelle salt solution (10 mL) and
Et2O (10 mL). After 3 h of stirring, the two layers were separated
and the aqueous phase was extracted with Et2O (3ꢃ10 mL). The
combined organic layers were dried over Na2SO4, filtered, and
concentrated in vacuo to give crude aldehyde 23, which was im-
mediately submitted to the olefination reaction.
of hydroxy-enone 26 (33.1 mg, 79%), as a colorless oil, TLC Rf (EtOAc/
20
hexane 10:90) 0.33; [
a]
þ118.5 (c 1.8, CH2Cl2); dH (300 MHz,
D
MeCN-d3) 7.61 (1H, dd, J 5.8, 2.8 Hz), 6.19 (1H, dd, J 5.8, 1.7 Hz), 5.62
(1H, dd, J 15.5, 5.5 Hz), 5.55e5.31 (5H, m), 4.27 (1H, q, J 6.0 Hz), 4.08
(2H, q, J 7.1 Hz), 3.80e3.72 (1H, m), 2.89e2.70 (2H, m), 2.55e2.02
(11H, m), 1.24 (3H, t, J 7.1 Hz), 1.10 (3H, t, J 7.5 Hz), 0.90 (3ꢃ3H, s),
0.10 (3H, s), 0.07 (3H, s).
KHMDS (0.66 M in toluene, 0.70 mL, 0.46 mmol, about
2.6 equiv) was added to a suspension of phosphonium salt 21
(0.231 g, 0.46 mmol, about 2.6 equiv) in dry THF (2 mL) under Ar at
ꢀ40 ꢁC. After 30 min, DMPU (0.11 mL) was added, the mixture was
cooled to ꢀ78 ꢁC, and crude aldehyde 23 in THF (1 mL) was added
via cannula. After 2 h, the reaction was quenched by adding
a saturated aqueous NH4Cl solution (10 mL) and Et2O (10 mL). The
two layers were separated and the aqueous phase was extracted
with Et2O (3ꢃ10 mL). The combined organic layers were dried over
Na2SO4, filtered, and concentrated in vacuo. The residue was pu-
rified by flash column chromatography on silica gel. Elution with
hexane/EtOAc (95:5) gave anomers 24 (65.2 mg, 75%), each con-
stituted by a mixture 90:10 of 7Z/7E stereoisomers, as a colorless
Excess 48% aqueous HF (0.098 mL) was added to the O-TBS ether
of hydroxy-enone 26 (30 mg, 0.060 mmol) dissolved in MeCN
(3.25 mL). After 4 h of stirring at room temperature, a pH 6.8
phosphate buffer (5 mL) and EtOAc (10 mL) were added, and the
two layers were separated. The aqueous phase was extracted with
EtOAc (4ꢃ5 mL), and the combined organic layers were dried over
MgSO4, filtered, and concentrated in vacuo. The residue was puri-
fied by flash column chromatography on silica gel. Elution with
hexane/EtOAc (1:1) gave free alcohol 26 (17.2 mg, 74%) as a color-
less oil, TLC Rf (EtOAc/hexane 15:85) 0.35; [
a
]
20 þ96.3 (c 1.3, EtOAc);
D
nmax (liquid film) 3320 (br), 2930, 1710, 1580, 1240, 970 cmꢀ1
;
dH
(300 MHz, MeCN-d3) 7.61 (1H, dd, J 5.7, 2.7 Hz), 6.18 (1H, dd, J 5.7,
1.8 Hz), 5.60 (1H, dd, J 15.5, 5.5 Hz), 5.60e5.31 (5H, m), 4.18e4.01
(1þ2H, mþq, J 7.0 Hz), 3.80e3.65 (1H, m), 3.10e3.0 (1H, br s),
2.89e2.70 (2H, m), 2.55e2.02 (11H, m), 1.25 (3H, t, J 7.1 Hz), 1.10
(3H, t, J 7.5 Hz); dC main (7Z)-stereoisomer (75 MHz, MeCN-d3)
209.8 (s), 172.8 (s), 165.3 (d), 135.7 (d), 132.2 (d), 128.9 (d), 128.6 (d),
128.3 (d), 128.1 (d), 128.0 (d), 83.5 (s), 75.7 (s), 70.3 (d), 59.9 (t), 49.6
(d), 47.1 (d), 33.8 (t), 27.5 (t), 25.4 (t), 24.3 (t), 22.5 (t), 13.6 (2ꢃq),
11.9 (t); HRMS (ESIþ): MHþ, found 385.2386. C24H33O4 requires
385.2379.
oil; nmax 2929, 1730, 1465, 1372, 1251, 1163, 1124, 837, 776 cmꢀ1
; dH
(300 MHz, MeCN-d3) 6.05e5.98 (1H, m), 6.0e5.90 (1H, m),
5.55e5.26 (6H, m), 4.80e4.71 (1H, m), 4.50e4.30 (1H, m),
4.30e4.20 (1H, m), 4.15 (2H, distorted q, J 6.0 Hz), 3.67e3.35 (2H,
m), 3.20e3.12 (1H, m), 2.85e2.75 (2H, m), 2.40e2.0 (10H, m),
1.26e1.20 (6H, tþd, 3H each), 1.20 (3H, t, J 7.1 Hz), 1.09 (3H, t, J
7.0 Hz), 0.93 (3ꢃ3H, s), 0.05 (3H, s), 0.04 (3H, s); dC (75 MHz,
MeCN-d3) 172.6 (s), 139.4 (d), 138.5 (d), 133.1 (d), 132.5 (d), 131.7
(d), 131.6 (d), 129.3 (d), 129.2 (d), 127.8 (d), 127.7 (d), 100.3 (d), 97.8
(d), 83.0 (s), 81.3 (d), 77.5 (d), 76.3 (s), 72.2 (d), 60.3 (t), 59.9 (t),
59.3 (t), 50.6 (d), 50.5 (d), 46.7 (d), 33.8 (t), 28.5 (t), 25.5 (t), 25.3
(3ꢃq), 23.9 (t), 22.5 (t), 20.3 (q), 19.8 (q), 17.8 (s), 14.7 (q), 13.1 (q),
11.9 (t), ꢀ5.2 (q), ꢀ5.6 (q); HRMS (ESIþ): MHþ, found 484.3368.
4.2.16. (4Z,7Z)-Ethyl 9-[(1S,2S)-2-{[5,6-D2]-(S,1E,5Z)-3-hydroxyocta-
1, 5-dienyl}-5-oxocyclopent-3-enyl]nona-4, 7-dienoate
(27). Tetraenyne 26 (15 mg) was submitted to the standardized
deuteration protocol described in paragraph 4.2.4. After flash col-
umn chromatographic separation on silica gel, dideuterated enone
27 (14 mg, 95%) was obtained as colorless oil, TLC Rf (EtOAc/hexane
C
30H48O3Si requires 484.3373.
4.2.14. (4Z,7Z)-Ethyl 9-{(1S,2R,5R)-2-[(S,E)-3-(tert-butyldimethylsi-
lyloxy)oct-1-en-5-ynyl]-5-hydroxycyclopent-3-enyl}nona-4,7-
dienoate (25). A catalytic amount of PPTS was added to acetals 24
(60 mg, 0.12 mmol) in 15% CH2Cl2/EtOH/(7 mL) at room tempera-
ture. After 9 h, the reaction was quenched by adding excess solid
NaHCO3; subsequently, the mixture was filtered and evaporated in
vacuo. The residue was purified by flash column chromatography
on silica gel. Elution with hexane/EtOAc (90:10) gave allylic alcohol
15:85) 0.38; [
a
]
20 þ78.3 (c 1.2, EtOAc); nmax (liquid film) 3330 (br),
D
2935, 1720, 1575, 1230 cmꢀ1
;
dH (300 MHz, MeCN-d3) 7.62 (1H, dd, J
5.7, 2.6 Hz), 6.18 (1H, dd, J 5.7, 1.8 Hz), 5.65e5.30 (6H, m), 4.17e4.01
(1þ2H, mþq, J 7.0 Hz), 3.80e3.72 (1H, m), 2.88e2.72 (3H, m),
2.55e1.99 (11H, m), 1.23 (3H, t, J 7.1 Hz), 0.96 (3H, t, J 7.5 Hz); dC
main (7Z)-stereoisomer (75 MHz, MeCN-d3) 209.9 (s), 172.8 (s),
165.5 (d), 136.8 (d), 132.9 (t, Jc1ed 23.2 Hz), 132.1 (d), 128.9 (d), 128.6
(d),128.1 (d),128.0 (d), 127.5 (d),124.2 (t, Jc1ed 23.2 Hz), 71.3 (d), 59.9
(t), 49.5 (d), 47.0 (d), 34.9 (t), 33.7 (t), 25.4 (t), 24.3 (t), 22.5 (t), 20.4
(t), 13.6 (q), 13.5 (q); HRMS (ESIþ): MHþ, found 389.2668.
25 (42.5 mg, 71%), as a colorless oil, TLC Rf (EtOAc/hexane 15:85)
20
0.31; [
a]
þ81.3 (c 2.1, CH2Cl2); nmax 3501 (br), 2930, 1720, 1470,
D
1360, 1255, 1076, 987, 776 cmꢀ1
;
dH (300 MHz, CDCl3) 6.05 (1H, br
C24H33D2O4 requires 389.2661.
s), 6.02 (1H, br s), 5.65e5.30 (6H, m), 4.50 (1H, distorted q, J 6.0 Hz),
4.25e4.05 (1Hþ2H, mþq), 3.20e3.12 (1H, m), 2.95e2.75 (2H, m),
2.48e2.05 (11H, m), 1.26 (3H, t, J 7.1 Hz), 1.12 (3H, t, J 7.5 Hz), 0.91
(3ꢃ3H, s), 0.06 (3H, s), 0.04 (3H, s); dC main (7Z)-stereoisomer
(75 MHz, CDCl3) 173.2 (s), 139.1 (d), 133.9 (d), 133.3 (d), 132.4 (d),
129.4 (d), 128.9 (d), 128.4 (d), 127.9 (d), 83.4 (s), 76.3 (d), 76.2 (s),
72.2 (d), 60.3 (t), 49.5 (d), 47.0 (d), 34.3 (t), 29.0 (t), 25.8 (t), 25.8
(3ꢃq), 24.0 (t), 22.8 (t), 18.2 (s), 14.2 (q), 14.1 (q), 12.4 (t), ꢀ4.5 (q),
4.2.17. 19,20-[D2]-17-A4t-NeuroP (2b). Ethyl ester 27 (12 mg,
0.03 mmol, 1 equiv) was dissolved in HPLC grade MTBE (0.5 mL),
and HPLC grade H2O (50 mL) was added. To the resulting stirred
solution was added lipase immobilized from C. antartica (CAL-B,
50 mg), and the suspension was gently stirred at 35 ꢁC for 18 h. The
enzyme was filtered off over a sintered glass funnel, and the solid
was carefully washed with MeCN/MTBE (1:1, 25 mL). Filtrates were

A. Porta et al. / Tetrahedron 70 (2014) 1484e1491
1491
ꢀ
7. Oger, C.; Bultel-Ponce, V.; Guy, A.; Balas, L.; Rossi, J.-C.; Durand, T.; Galano, J.-M.
Chem.dEur. J. 2010, 16, 13976e13980.
collected and evaporated in vacuo. The residue was purified by flash
column chromatography on silica gel. Elution with hexane/EtOAc
(50:50) afforded 19,20-[D2]-17-A4t-NeuroP (2b) (6 mg, 54%) as
8. Representative references: (a) Zanoni, G.; Porta, A.; Vidari, G. J. Org. Chem. 2002,
67, 4346e4351; (b) Zanoni, G.; Porta, A.; Castronovo, F.; Vidari, G. J. Org. Chem.
2003, 68, 6005e6010; (c) Zanoni, G.; Porta, A.; De Toma, Q.; Castronovo, F.;
Vidari, G. J. Org. Chem. 2003, 68, 6437e6439; (d) Zanoni, G.; Castronovo, F.;
Perani, E.; Vidari, G. J. Org. Chem. 2003, 68, 6803e6805; (e) Zanoni, G.; Porta, A.;
Brunoldi, E.; Vidari, G. J. Org. Chem. 2006, 71, 8459e8466; (f) Zanoni, G.; Bru-
noldi, E. M.; Porta, A.; Vidari, G. J. Org. Chem. 2007, 72, 9698e9703; (g) Zanoni,
G.; D’Alfonso, A.; Porta, A.; Feliciani, L.; Nolan, S. P.; Vidari, G. Tetrahedron 2010,
66, 7472e7478.
9. Montine, T. J.; Morrow, J. D. Am. J. Pathol. 2005, 166, 1283e1289.
10. (a) Musiek, E. S.; Milne, G. L.; McLaughlin, B.; Morrow, J. D. Brain Pathol. 2005,
15, 149e158; (b) Milne, G. L.; Yin, H.; Morrow, J. D. J. Biol. Chem. 2008, 283,
15533e15537.
11. (a) Musiek, E. S.; Brooks, J. D.; Joo, M.; Brunoldi, E.; Porta, A.; Zanoni, G.; Vidari,
G.; Blackwell, T. S.; Montine, T. J.; Milne, G. L.; McLaughlin, B.; Morrow, J. D. J.
Biol. Chem. 2008, 283, 19927e19935; (b) Brooks, J. D.; Musiek, E. S.; Koestner, T.
R.; Stankowski, J. N.; Howard, J. R.; Brunoldi, E. M.; Porta, A.; Zanoni, G.; Vidari,
G.; Morrow, J. D.; Milne, G. L.; McLaughlin, B. J. Neurochem. 2011, 119, 604e616.
12. Gao, L.; Wang, J.; Sekhar, K. R.; Yin, H.; Yared, N. F.; Schneider, S. N.; Sasi, S.;
Dalton, T. P.; Anderson, M. E.; Chan, J. Y.; Morrow, J. D.; Freeman, M. L. J. Biol.
Chem. 2007, 282, 2529e2537.
a colorless oil, TLC Rf (EtOAc/hexane 50:50) 0.23; [
a
]
D
20 þ96.7 (c 0.2,
EtOAc); nmax (liquid film) 3412 (br), 2929, 1703, 1581, 1239,
969 cmꢀ1
; dH (300 MHz, MeCN-d3) 7.61 (1H, dd, J 5.7, 2.6 Hz), 6.18
(1H, dd, J 5.7, 1.8 Hz), 5.70e5.30 (6H, m), 4.05 (1H, distorted q, J
6.0 Hz), 3.80e3.72 (1H, m), 2.88e2.65 (2H, m), 2.55e2.00 (m, 11H),
0.98 (t, J 7.5, 3H). dC main (7Z)-stereoisomer (75 MHz, MeCN-d3)
210.0 (s), 173.6 (s), 165.6 (d), 136.7 (d), 132.9 (t, Jc1ed 23.3 Hz), 132.1
(d), 128.9 (d), 128.6 (d), 128.1 (d), 128.0 (d), 127.5 (d), 124.1 (t, Jc1ed
23.3 Hz), 71.4 (d), 49.5 (d), 47.0 (d), 35.0 (t), 33.2 (t), 25.4 (t), 24.4 (t),
22.5 (t), 20.4 (t), 13.5 (q). HRMS (ESIꢀ): MꢀHꢀ, found 359.2206.
C
22H27D2O4 requires 359.2191.
Acknowledgements
We thank Prof. Mariella Mella and Prof. Giorgio Mellerio for
NMR and mass spectral measurements, respectively. Financial
support from the Italian MIUR (Funds PRIN) and Regione Lombardia
(Iniziativa Lombardia Eccellente) is acknowledged.
13. Previous syntheses of deuterated NeuroPs. [D4]-7-F4t-NeuroP: Kim, S.; Lawson,
J. A.; Pratico, D.; FitzGerald, G. A.; Rokach, J. Tetrahedron Lett. 2007, 43,
2801e2804 [D4]-4-F4t-NeuroP: Ref. 7.
14. Previous syntheses of deuterated IsoPs from EPA. [D4]-5-F3c-IsoP and [D4]-5-
epi-5-F3c-IsoP: Chang, C.-T.; Patel, P.; Gore, V.; Song, W.-L.; Lawson, J. A.; Powell,
W. S.; FitzGerald, G. A.; Rokach, J. Bioorg. Med. Chem. Lett. 2009, 19, 6755e6758.
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16. Yamaguchi, M.; Hirao, I. Tetrahedron Lett. 1983, 24, 391e394.
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18. For a review see: Blakemore, P. R. J. Chem. Soc., Perkin Trans. 1 2002, 2563e2585.
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