Stereoselective synthesis of MaR2n-3 DPA

Article abstract of DOI:10.1016/j.tetlet.2019.151510

The first total synthesis of the n-3 docosapentaenoic derived oxygenated product MaR2_{n-3 DPA} has been achieved. The 13R and 14S stereogenic centers were introduced using 2-deoxy-D-ribose in a chiral pool strategy. The geometry of the Z,E,E-triene moiety was prepared using highly E-selective Wittig- and Takai-olefination reactions as well as the Z-stereoselective Lindlar reduction. LC/MS-MS data of synthetic MaR2_{n-3 DPA} matched data for the biosynthetic formed product that enabled the configurational assignment of this oxygenated natural product to be (7Z,9E,11E,13R,14S,16Z,19Z)-13,14-dihydroxydocosa-7,9,11,16,19-pentaenoic acid.

Full text of DOI:10.1016/j.tetlet.2019.151510

Tetrahedron Letters xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Stereoselective synthesis of MaR2n-3 DPA
Jeanne Sønderskov a, Jørn E. Tungen b, Francesco Palmas c, Jesmond Dalli c,d, Charles N. Serhan e,
Yngve Stenstrøm a, Trond Vidar Hansen a,b,
⇑
a Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, 1432 Ås, Norway
b Department of Pharmacy, Section for Pharmaceutical Chemistry, University of Oslo, PO Box 1068 Blindern, N-0316 Oslo, Norway
c Lipid Mediator Unit, Center for Biochemical Pharmacology, William Harvey Research Institute, Barts and The London School of Medicine, Queen Mary University of
London, Charterhouse Square, London EC1M 6BQ, UK
d Centre for Inflammation and Therapeutic Innovation, Queen Mary University of London, London, UK
e Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Hale Building for Transformative Medicine,
Brigham and Women’s Hospital and Harvard Medical School, Boston, MA 02115, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The first total synthesis of the n-3 docosapentaenoic derived oxygenated product MaR2n-3 DPA has been
Received 16 October 2019
Revised 25 November 2019
Accepted 6 December 2019
Available online xxxx
achieved. The 13R and 14S stereogenic centers were introduced using 2-deoxy-D-ribose in a chiral pool
strategy. The geometry of the Z,E,E-triene moiety was prepared using highly E-selective Wittig- and
Takai-olefination reactions as well as the Z-stereoselective Lindlar reduction. LC/MS-MS data of synthetic
MaR2n-3 DPA matched data for the biosynthetic formed product that enabled the configurational assign-
ment of this oxygenated natural product to be (7Z,9E,11E,13R,14S,16Z,19Z)-13,14-dihydroxydocosa-
7,9,11,16,19-pentaenoic acid.
Keywords:
Maresins
Ó 2019 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
MaR2n-3
DPA
n-3 docosapentaenoic acid
Specialized pro-resolving mediator
Recent studies have demonstrated that polyunsaturated fatty
acids (PUFAs) derived specialized pro-resolving mediators (SPMs)
actively govern and promote the resolution of inflammation [1].
PUFAs are enzymatically converted into different families of SPMs,
e.g. the lipoxins, resolvins, protectins and maresins [2]. Maresin 1
(MaR1) is biosynthesized [3] from docosahexaenoic acid (DHA) in
the presence of 12-lipoxygenase and was the first member of the
maresin family of SPMs to be reported [4] and prepared by total
synthesis [5].
In 2013 Dalli and co-workers reported several new SPMs
biosynthesized from n-3 docosapentaenoic acid (n-3 DPA) [6]. n-
3 DPA, consisting of 22 carbons and five all-Z double bonds, is an
elongated product of eicosapentaenoic acid and an intermediate
in the biosynthesis of DHA [7]. Using a self-limited model of
inflammation and targeted metabololipidomics during the onset
and resolution of acute inflammation, Dalli and co-workers [6]
uncovered several novel n-3 DPA SPMs that are potent bioactive
molecules. The structures of MaR1n-3 DPA (1), MaR2n-3 DPA (2) and
MaR3n-3 DPA (3) are shown in Fig. 1.
Based on their novel pro-resolving and anti-inflammatory
bioactions, SPMs have attracted significant interest from the
biomedical, pharmacological and synthetic organic communities
[8]. SPMs act as agonists on individual GPCRs [9] exhibiting
nanomolar pro-resolution and anti-inflammatory bioactions [10].
Some SPMs have entered initial clinical trial development pro-
grams [11]. These endogenously formed products are available in
minute amounts from their natural sources and contain several
stereogenic centers and conjugated E- and Z-double bonds. Hence,
stereoselective synthesis for configurational assignment and
extensive biological testing becomes necessary.
A few of the n-3 DPA-derived SPMs have recently been prepared
[12] and subjected to biological evaluations [13], but MaR2n-3 DPA
(2) has not been synthesized to date and its absolute configuration
at C-13 remained to be determined. These facts, as well as the high
demand for sufficient material for biological and pharmacological
testing, inspired us to report the first total synthesis of
MaR2n-3 DPA (2).
The three key intermediates 4, 5 and 6 in our retrosynthetic
analysis are depicted in Scheme 1. The stereogenic centers at C13
and C14 were assumed to be R and S, respectively, based on biosyn-
thetic considerations [6]. Hence, 2-deoxy-
a suitable commercially available starting material for preparing
D
-ribose (7) was deemed
⇑
Corresponding author.
E-mail address: t.v.hansen@farmasi.uio.no (T. Vidar Hansen).
https://doi.org/10.1016/j.tetlet.2019.151510
0040-4039/Ó 2019 The Author(s). Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: J. Sønderskov, J. E. Tungen, F. Palmas et al., Stereoselective synthesis of MaR2n-3 DPA, Tetrahedron Letters, https://doi.org/10.1016/
j.tetlet.2019.151510

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J. Sønderskov et al. / Tetrahedron Letters xxx (xxxx) xxx
Fig. 1. Structures of MaR1n-3
(1), MaR2n-3
(2) and MaR3n-3
(3). The absolute configuration is presented where established.
DPA
DPA
DPA
MaR2n-3 DPA (2). This carbohydrate has been used in the stereose-
lective total synthesis of other SPMs [14].
The phosphonium salt 8 was synthesized from Z-hex-3-en-1-ol
(9) as previously described [12c]. Intermediate 11 was obtained
from known TBS-protected aldehyde 10 [12d] using a highly Z-
selective Wittig reaction with the in situ generated ylide of 8
(Scheme 2). This produced 11 as one diastereomer in 84% yield
(ESI). Next, selective deprotection of the primary TBS-group in 11
was achieved with para-toluene sulfonic acid (PTSA) in MeOH at
À20 °C giving alcohol 12 that was oxidized (Dess-Martin periodi-
nane (DMP), NaHCO3, CH2Cl2) to its aldehyde 13 in 40% yield over
the two steps. Aldehyde 13 was dissolved in toluene and 1.3 equiv.
of the stabilized ylide (triphenyl-phosphoranylidene)acetaldehyde
was added. The reaction mixture was heated at reflux for 19 h to
afford the E-configured
a,b-unsaturated aldehyde 14 in 60% yield
after purification by column chromatography (ESI). To complete
the formation of fragment 4, a Takai reaction was performed on
aldehyde 14. After acidic work-up and purification by column
chromatography the sensitive E,E-vinylic iodide 4 was isolated in
73% yield (Scheme 2).
Terminal alkyne 5 was conveniently prepared in a four-step
sequence, starting from cycloheptanone (15), see Scheme 3.
Bayer-Villiger oxidation on 15 followed by Fischer-esterification
gave hydroxyl-ester 16 that was oxidized to aldehyde 17 and
reacted in the Ohira-Bestmann reaction affording alkyne 5 in 12%
yield from 15.
The Sonogashira coupling reaction with key fragments 4 and 5
produced alkyne 18 in 50% isolated yield after careful chromato-
graphic purification (Scheme 4). Next, removal of the two-TBS
groups in 18 with excess TBAF in THF produced diol 19. Reduction
of the internal alkyne in 19 using the Lindlar-reduction (Pd-CaCO3,
EtOAc/pyridine/1-octene, H2 1 atm) gave the methyl ester of
MaR2n-3 DPA (20) in 55% isolated yield over the two steps and with
>95% chemical purity (HPLC, ESI). Finally, careful saponification
(LiOH, H2O, MeOH, 0 °C) of 20 gave MaR2n-3 DPA (2) in 97% yield
(Scheme 4). Data from NMR, LC/MS-MS and UV experiments (ESI)
confirmed the structure of 2.
We next tested whether synthetic 2 matched the endogenous
MaR2n-3
(2) prepared from human samples. We first isolated
Scheme 1. Retrosynthetic analysis of MaR2n-3
(2).
DPA
DPA
Please cite this article as: J. Sønderskov, J. E. Tungen, F. Palmas et al., Stereoselective synthesis of MaR2n-3 DPA, Tetrahedron Letters, https://doi.org/10.1016/
j.tetlet.2019.151510

J. Sønderskov et al. / Tetrahedron Letters xxx (xxxx) xxx
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Scheme 2. Synthesis of vinylic iodide 4. Reagents and conditions: i) NaHMDS, CH2Cl2, À 78 °C; ii) para-toluene sulfonic acid (PTSA), MeOH, À20 °C; iii) DMP, NaHCO3, CH2Cl2;
iv) toluene, (triphenyl-phosphoranylidene)acetaldehyde, ; v) CrCl2, dioxane, THF, CHI3, 0 °C.
D
Scheme 3. Synthesis of alkyne 5. Reagents and conditions: i) a) m-CPBA, CH2Cl2; b) MeOH, H2SO4; ii) DMP, NaHCO3, CH2Cl2; iii) dimethyl(1-diazo-2-oxopropyl) phosphonate;
K2CO3, MeOH.
Scheme 4. Total synthesis of MaR2n-3 DPA (2). Reagents and conditions: i) CuI, Et2NH, Pd(PPh3)4 (5%); ii) TBAF, THF; iii) Pd/CaCO3, EtOAc/pyridine/1-octene, H2; iv) LiOH, H2O,
MeOH, 0 °C.
Please cite this article as: J. Sønderskov, J. E. Tungen, F. Palmas et al., Stereoselective synthesis of MaR2n-3 DPA, Tetrahedron Letters, https://doi.org/10.1016/
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material from human serum and the retention time of the endoge-
nous mediator using RP-HPLC-MS-MS lipid mediator profiling
experiments [15]. Using multiple reaction monitoring (MRM) of
the parent ion with m/z 361 and the daughter ions m/z 223 or
m/z 193, we obtained a sharp peak with retention time (RT) of
14.4 min (Fig. 2A). Of note, a similar retention time of 14.4 min
was obtained with synthetic 2 (see Fig. 2A). Moreover, co-injection
in accordance with published findings [6], MaR2n-3 DPA from both
human serum and platelet rich plasma gave the following ions
m/z 361 = MÀH, m/z 344 = MÀHÀH2O, m/z 325 = MÀHÀ2H2O,
m/z 317
=
MÀHÀCO2, m/z 299
=
MÀHÀH2OÀCO2, m/z
281 = MÀHÀ2H2OÀCO2, m/z 179 = 223-CO2, m/z 161 = 223-H2-
OÀCO2, m/z 149 = 193-CO2, ions that were also found in the MS/
MS spectrum of synthetic 2 (Fig. 3).
(2
l
L) of a homogenous sample of biological MaR2n-3 DPA (2) with
The SPMs are among the most exciting small and naturally
occurring molecules currently undergoing investigations towards
drug development of new anti-inflammatory drugs [1,16]. The
stereoselective synthesis of 2 using the Lindlar reaction, the
Sonogashira coupling reaction and the Takai olefination
produced multi milligram quantities of 2 that is now available
for further biological and pharmacological evaluations to be
conducted.
synthetic 2 in a 1:10 M ratio, respectively, gave a single sharp peak
in MRM experiments, with RT 14.4 min (Fig. 2A). Similar findings
were made with platelet rich plasma, where endogenous
MaR2n-3 DPA (5) gave a RT of 14.4 min that co-eluted with synthetic
2 (Fig. 2B). To obtain further evidence that the chemical structure
for synthetic 2 matches that of endogenous MaR2n-3 DPA we next
assessed the MS/MS fragmentation spectra. Here we found that,
Fig. 2. Synthetic 2 matches endogenous MaR2n-3 DPA in human serum and cells. (A) human serum (B) platelet rich plasma were collected, placed in ice-cold methanol, lipid
mediators were extracted and MaR2n-3 DPA was identified using lipid mediator profiling. Panels depict representative MRM chromatograms for m/z 361 > 223 (human serum)
or m/z 361 > 193 (platelet rich plasma). Top panels depict the chromatograms obtained with biological material, center panels depict chromatograms obtained with synthetic
2 and bottom panels depict chromatograms obtained with the biological material co-injected with synthetic 2. Results are representative of three determinations for A and
n = 3 distinct human donors for B.
Please cite this article as: J. Sønderskov, J. E. Tungen, F. Palmas et al., Stereoselective synthesis of MaR2n-3 DPA, Tetrahedron Letters, https://doi.org/10.1016/
j.tetlet.2019.151510

J. Sønderskov et al. / Tetrahedron Letters xxx (xxxx) xxx
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Acknowledgments
T. V. H. is grateful for funding from the Norwegian Research
Council (FRIPRO-FRINATEK 230470) and The School of Pharmacy
is acknowledged for a scholarship to J. E. T., J. D. received funding
from the European Research Council (ERC) under the European
Union’s Horizon 2020 research and innovation program (grant
no: 677542) and the Barts Charity (grant no: MGU0343). J. D. is
also supported by a Sir Henry Dale Fellowship jointly funded by
the Wellcome Trust and the Royal Society (grant 107613/Z/15/Z).
C. N. S is supported by the National Institutes of Health GM Grant
PO1GM095467 and continuous financial support is gratefully
acknowledged
Appendix A. Supplementary data
Copies of 1H and 13C NMR spectra for intermediates and charac-
terization data (UV/VIS spectra, HPLC chromatograms and LC/MS-
MS spectra from matching experiments) of 2 as well as experimen-
tal procedures. Supplementary data to this article can be found
online at https://doi.org/10.1016/j.tetlet.2019.151510.
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
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j.tetlet.2019.151510