Synthesis and Structure-Activity Relationship Studies of Anti-Inflammatory Epoxyisoprostane Analogues

Article abstract of DOI:10.1021/acs.orglett.8b01042

The lactone derivative of the epoxyisoprostane EC is a highly effective inhibitor of the secretion of the proinflammatory cytokine IL-6. Herein, a modular synthesis of analogues is described, allowing flexible variations of the cyclic side chain of the parent lactone. A structure-activity relationship study identified a lactam analogue that retains the high activity. Furthermore, the exocyclic allylic alcohol was shown to be crucial for the observed effect.

Full text of DOI:10.1021/acs.orglett.8b01042

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Synthesis and Structure−Activity Relationship Studies of Anti-
Inflammatory Epoxyisoprostane Analogues
Helene Wolleb,‡ Seiji Ogawa,‡ Michael Schneider,‡ Andrej Shemet,‡ Jonathan Muri,† Manfred Kopf,†
and Erick M. Carreira*,‡,⧧
‡Laboratory of Organic Chemistry, ETH Zurich, HCI H335, Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland
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†Institute of Molecular Health Sciences, ETH Zurich, HPL G12, Otto-Stern-Weg 7, 8093 Zurich, Switzerland
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⧧Competence Center for Systems Physiology and Metabolic Diseases, ETH Zurich, 8093 Zurich, Switzerland
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* Supporting Information
ABSTRACT: The lactone derivative of the epoxyisoprostane EC is a highly effective inhibitor of the secretion of the
proinflammatory cytokine IL-6. Herein, a modular synthesis of analogues is described, allowing flexible variations of the cyclic
side chain of the parent lactone. A structure−activity relationship study identified a lactam analogue that retains the high activity.
Furthermore, the exocyclic allylic alcohol was shown to be crucial for the observed effect.
xidized phospholipids (OxPLs) constitute a class of
biomolecules generated upon exposure of biological
future anti-inflammatory therapeutics. While our previous
studies showed that the endo- and the exocyclic enone as
well as the allylic epoxide in EC (1) are crucial for the observed
O
membranes to reactive oxygen species (ROS).1 These natural
products have been recognized as active compounds in
inflammation. Intriguingly, while a majority of investigations
suggest proinflammatory effects of OxPLs via interaction with
pattern recognition receptors of the innate immune system,2
anti-inflammatory properties have also been observed.3
Recently, we have shown that epoxyisoprostane EC (1, Figure
1), as well as to a lesser extent its phosphatidylcholine
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high activity, the role of the side chain in lactone 2 vis-a-vis its
anti-inflammatory effects has not been investigated. Therefore,
a structure−activity relationship study was initiated. In this
regard, the presence of a lactone in 2 creates ambiguity with
respect to the generation of seco-acid; therefore, key structures
targeted for synthesis include replacements for the lactone, such
as lactams (3, Figure 1), sultams, and other rings.6
The general strategy to access the targeted analogues
involved late-stage coupling of previously described cyclo-
pentenone 4 with various side chains as the corresponding
aldehydes 5 via aldol condensation reactions to afford dienones
6 (Scheme 1, I). This approach allowed for a modular synthesis
of a variety of different target structures. The synthesis of
lactam 3 commenced with sulfinimine 7 (Scheme 1, II).7
Grignard addition proceeded with dr = 10:1, and the desired
sulfinamide 8 was isolated in 69% yield.8 Oxidative cleavage of
the alkene in 8 led to the corresponding methyl ester, which
following I2-mediated auxiliary removal with concomitant
amide bond formation furnished lactam 9.9 Aldehyde 11 was
subsequently prepared in four steps and appended to 4 as
described above to give lactam 3. All other analogues described
in this work were accessed employing closely related
approaches (see the Supporting Information).
Figure 1. Structures of EC (1), lactone 2, and lactam 3.
derivative PECPC, act in an anti-inflammatory fashion.4 This
was demonstrated by the observed reduced secretion of the
proinflammatory cytokines IL-6 and IL-12 by bone-marrow-
derived dendritic cells (BMDCs). Furthermore, during studies
aimed at understanding the underlying mechanisms for the
action of these epoxyisoprostanes, we discovered lactone 2
derived from EC (1) as the most potent anti-inflammatory
compound in the series.5 Herein, we report a structure−activity
relationship study that further investigates the effect of the
cyclic side chain in 2.
The promising activity of lactone 2 suggests this class of
epoxycyclopentenone derivatives as a potential scaffold for
Received: April 3, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b01042
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Access to Dienones 6 and Synthesis of Lactam 3
Figure 3. Comparison of the activity of lactone 2, sultams 13 and 14,
and ketone 15 in inhibiting secretion of the proinflammatory cytokine
IL-6.
In follow-up studies, structures incorporating simpler side-
chain surrogates of the lactone were examined. Additionally, the
significance of the allylic alcohol for activity was investigated. As
described in the Supporting Information, two deoxy derivatives
lactone 16 and lactam 17 were synthesized and tested for their
ability to inhibit IL-6 secretion (Figure 4).
Lactam 3 was tested together with its diastereomer 12 along
with EC (1) and 2 for comparative purposes for their ability to
inhibit IL-6 secretion by BDMCs (Figure 2). We were
Figure 2. Comparison of the activity of EC (1), lactone 2, and lactams
3 and 12 in inhibiting secretion of the proinflammatory cytokine IL-6.
delighted to observe that the substitution of the lactone for a
lactam resulted in a slightly more active epoxyisoprostane
analogue. Also, comparison with diastereomeric lactam 12
indicated that the stereogenic center in the six-membered ring
only had a minor impact on the activity.
With these results in hand, ester and amide surrogates were
further evaluated.10 To this end, diastereomeric sultams 13 and
14 as well as ketone 15 (all as single diastereomers; Figure 3)
were examined.11 When subjected to the IL-6 secretion assay,
sultam 13 displayed activity comparable to lactone 2; however,
cytotoxicity was observed at concentrations >1 μM. In contrast,
sultam 14 was slightly less active but not cytotoxic in the
observed concentration range. Interestingly, ketone 15 also
exhibited potent activity, whereby the observed cytotoxic effect
was observed at >2 μM.
Figure 4. Comparison of the activity of 2, 3, and 18 and their deoxy
analogues 16, 17, and 19 in inhibiting secretion of the proin-
flammatory cytokine IL-6.
Analysis of the data for 2 and 16 as well as for 3 and 17 in
Figure 4 clearly showed that the presence of the allylic alcohol
is crucial for potent activity. In order to further validate this
finding, the phenyl analogue 18 was tested along with its deoxy
derivative 19. Although allylic alcohol 18 exhibited noticeable
activity, 19 was virtually inactive.
Attention was next turned to the investigation of
homologated and truncated analogues (Figure 5). Both N-
substituted lactam 20 and γ-lactam 21 exhibited cytotoxicity at
>2 μM, but while the former was significantly less active, the
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DOI: 10.1021/acs.orglett.8b01042
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: carreira@org.chem.ethz.ch.
ORCID
Helene Wolleb: 0000-0002-0233-8449
Erick M. Carreira: 0000-0003-1472-490X
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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ETH Zurich is gratefully acknowledged for generous support
̈
through grant ETH-18 09-1. We thank Dr. N. Trapp and M.
Solar of the SMoCC (Small Molecule Crystallography Center)
facilities at ETH Zurich for X-ray crystallographic analysis and
̈
Dr. M.-O. Ebert, R. Arnold, S. Burkhardt, and R. Frankenstein
of the NMR Service at ETH Zurich. H.W. acknowledges the
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Stipendienfonds Schweizerische Chemische Industrie (SSCI).
REFERENCES
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In summary, we have described the convergent synthesis of
anti-inflammatory epoxyisoprostane analogues derived from
lactone 2 and analyzed their effect on the secretion of the
proinflammatory cytokine IL-6. We demonstrated that lactam 3
retained the high anti-inflammatory activity, and diastereomeric
lactam 12, sultam 13, ketone 15, as well as γ-lactam 21
displayed comparable activity. The study also highlighted the
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b01042.
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Experimental procedures and characterization data for all
new compounds (PDF)
Accession Codes
CCDC 1825895−1825896 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
C
DOI: 10.1021/acs.orglett.8b01042
Org. Lett. XXXX, XXX, XXX−XXX