Synthesis of a Human Urinary Metabolite of Prostaglandin D2

Article abstract of DOI:10.1021/acs.orglett.9b03983

A chemical synthesis of the major human metabolite of prostaglandin D₂, tricyclic-PGDM, is described. The synthetic route starts from iodocyclopentenone 1 (available from cyclopentadiene in 6 steps) and requires 13 synthetic transformations. The synthetic route takes advantage of a contrasteric allylation to establish the 1,2-cis relationship between the ring hydroxyl group and side chain. A second key sequence is the application of Fu's copper-catalyzed C-H insertion of a diazoacetate followed by an alkyne semihydrogenation to introduce the unsaturated side chain.

Full text of DOI:10.1021/acs.orglett.9b03983

Letter
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Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Synthesis of a Human Urinary Metabolite of Prostaglandin D2
Jennifer R. Kimbrough,† Zachary Austin,† Ginger L. Milne,‡,§ and Gary A. Sulikowski*,†,‡,§
†Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37232, United States
‡Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, United States
§Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37232, United States
S
* Supporting Information
ABSTRACT: A chemical synthesis of the major human
metabolite of prostaglandin D2, tricyclic-PGDM, is described.
The synthetic route starts from iodocyclopentenone 1
(available from cyclopentadiene in 6 steps) and requires 13
synthetic transformations. The synthetic route takes advantage
of a contrasteric allylation to establish the 1,2-cis relationship
between the ring hydroxyl group and side chain. A second key
sequence is the application of Fu’s copper-catalyzed C−H
insertion of a diazoacetate followed by an alkyne semihydrogenation to introduce the unsaturated side chain.
rostaglandins are key lipid mediators produced as an
PGDM in human fluid samples by LC-MS and as a biomarker
for inflammation.2a,4 The Eicosanoid Core Laboratory at
Vanderbilt University offers this assay, as it held a supply of
tricyclic-PGDM prepared by total synthesis in 1988 by Taber
and co-workers.5 A resupply of PGDM by total synthesis was
recently needed, as the current supply became exhausted. To
this end, we aimed to develop an efficient route to tricyclic-
PGDM.
P
inflammatory response to potentially harmful stimuli and
serve as a hallmark of many human diseases.1 Due to their
rapid metabolism, direct detection of prostaglandins is not
useful as a diagnostic tool but instead detection and
quantification of downstream metabolites is used as an indirect
method of analysis.2
In 1985, Liston and Roberts identified 9α,11β-dihydroxy-15-
oxo-tetranorprost-5-ene-1,20-dioic acid (PGDM) (Figure 1) as
The total synthesis of prostaglandins and their metabolites
has remained of great interest to the synthetic community for
over 50 years.6 The concise synthesis of these arachidonic acid
metabolites is of importance due to scarcity of prostaglandins
from natural resources, relevance to human health and
presentation of stereochemistry within their core structure.
Control of stereochemistry is central to the design of synthetic
pathways leading to prostaglandins and their metabolites,
requiring establishment of up to four contiguous stereocenters
within the cyclopentane core structure. In this regard, the
Corey lactone has served very well as a starting material for
many syntheses of prostaglandins, analogs, and metabolites.6b
Indeed, this was the starting material used in the Taber total
synthesis of tricyclic-PGDM (2, Scheme 1).5 In the early
1980s, 4-hydroxy-2-cyclopentenone emerged as a useful
starting material for the synthesis of prostaglandins.7 Stereo-
selective functionalization of the prochiral enone, often under
control of the C4 stereocenter, provides access to various
relative stereochemistry within the cyclopentane ring as
presented in prostaglandins A−F and congeners. Two- and
three-component couplings starting from 4-oxygenated
cylopentenones have been effective in providing access to a
variety of prostaglandins and derivatives.6 Our synthesis of
Figure 1. PGD2 metabolic pathway leading to tricycic-PGDM.
the major urinary metabolite of prostaglandin D2 (PGD2) in
humans, isolated in its tricyclic form (tricyclic-PGDM).3 The
metabolic pathway leading to PGDM is shown in Figure 1,
starting with reduction of PGD2 to 11β-PGF2α. A series of
oxidations, followed by double bond reduction (Δ13-reductase)
and cyclodehydration, leads to tricyclic-PGDM, a stable and
readily detectable metabolite.2b An 18O-labeled derivative of
PGDM has served in clinical assays for quantification of
Received: November 7, 2019
© XXXX American Chemical Society
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DOI: 10.1021/acs.orglett.9b03983
Org. Lett. XXXX, XXX, XXX−XXX

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Scheme 1. Taber Route to PGDM and Present Work
Scheme 3. Preparation of Cyclopentenone 9
tricyclic-PGDM methyl esters started from racemic 2-iodo-4-
hydroxy-2-cyclopentenone (1, Scheme 1).8
Two key synthetic disconnections of tricyclic-PGDM are
shown in Scheme 2. First, a contrasteric allyl metal addition to
Scheme 2. Key Disconnections and Stereoselective cis- and
trans-Allylation
isomeric allyl addition products, separable by flash chromatog-
raphy, plus annulation product 11 in <5% yield (Scheme 4).15
Scheme 4. Stereoselective Allylation of α-Substituted
Cyclopentenones
a 2-substituted-4-siloxycylopentenone and, second, a C−H
insertion of a diazoacetate followed by a semihydrogenation of
the alkyne. Danishefsky described the former transformation in
two publications employing γ-oxygenated cyclopent- and
cyclohexenones, but devoid of α-substitution.9 We repeated
the titanium tetrachloride promoted cis-selective allylation in
parallel with a trans-selective allyl cupration both starting from
4-siloxy-2-cyclpentenone 3 (Scheme 2). The 1H and 13C NMR
spectra of cis- and trans-4 revealed differences in the C4 proton
and carbon chemical shifts (Scheme 2) useful in stereo-
chemical assignment of intermediates en route to tricyclic-
PGDM (vide infra).10 We next turned to incorporation of the
required α-substituent, and its application in the key
contrasteric allylation reaction en route to tricyclic-PGDM.
α-Functionalization of 2-iodoenone 1 by way of cross-
coupling reactions has provided access to a variety of 2-
substituted enones.11 We required incorporation of a protected
3-keto side chain terminating in a carboxylate group. We
identified allylic acetate 7 as a potential cross-coupling partner,
a substrate uniquely harboring the central keto and terminal
carboxylate group. Acetate 7 was prepared by silver-mediated
cycloisomerization of alkynyl carboxylic acid 6,12 the latter
readily prepared from 4-pentynol in four steps (Scheme 3).
While iodoenone 1 failed to couple with allylic acetate 7
directly, we were pleased to observe 7 smoothly underwent a
Stille coupling with stannane 8 to afford enone 9.13 Analysis of
the 1H NMR of 7 and 9 suggested inconsequential inversion of
enol ester double bond geometry occurred in the course of the
cross-coupling reaction.14
As the chemical shifts of the C4 proton and carbon were nearly
identical, the isomers were assigned epimeric at C2 (trans,cis-
10 and cis,cis-10). The stereochemical assignment was further
supported by allylation of keto ester 12 to afford trans,cis-13
and cis,cis-13. Acidic methanolysis of trans,cis-10 afforded
trans,cis-13 while acidic methanolysis of cis,cis-10 resulted in
enone formation by way of a rapid β-elimination of the C4
siloxy group.
Cyclopentanone trans,cis-10 was carried forward to tricyclic-
PGDM methyl ester (Scheme 5). Chemoselective reduction of
the keto group over the enol-lactone was achieved using a t-
BuNH2·BH3 complex in dichloromethane. Reduction of
ketone 10 produced a near 1:1 mixture of secondary alcohol
isomers. Selectivity was improved by removal of the bulky TBS
group to give the less sterically encumbered ketone 14.
Reduction of 14 with t-BuNH2·BH3 now afforded trans-1,3-
diol 15 as the major product (3:1 dr). Upon treatment with
TFA, diol 15 underwent stereoselective spirocyclization to
afford spiroacetal 16. The acetal carbon emerged as a single
isomer, assigned the configuration shown in Scheme 5, based
on favored axial orientation of the lactone oxygen in order to
benefit from the anomeric effect. Following TBS protection of
the remaining alcohol, ozonolysis of alkene 17 provided
Treatment of enone 9 with titanium tetrachloride and
allyltrimethylsilane at −78 °C provided a near 1:1 mixture of
B
DOI: 10.1021/acs.orglett.9b03983
Org. Lett. XXXX, XXX, XXX−XXX

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Scheme 5. Completion of Tricyclic-PGDM Methyl Ester
REFERENCES
■
(1) (a) Nittner-Marszalska, M.; Cichocka-Jarosz, E.; Sanak, M.;
Wujczyk, M.; Dor-Wojnarowska, A.; Lis, G.; Liebhart, J. 9α, 11β-
PGF2, a Prostaglandin D2 Metabolite, as a Marker of Mast Cell
Activation in Bee Venom-allergic Patients. Arch. Immunol. Ther. Exp.
2015, 63, 317−325. (b) Maeda, S.; Nakamura, T.; Harada, H.;
Tachibana, Y.; Aritake, K.; Shimosawa, T.; Yatomi, Y.; Murata, T.
Prostaglandin D2 Metabolite in Urine is an Index of Food Allergy. Sci.
Rep. 2017, 7. DOI: 10.1038/s41598-017-17798-w. (c) Pellefigues, C.;
Dema, B.; Lamri, Y.; Saidoune, F.; Chavarot, N.; Loheac, C.; Pacreau,
E.; Dussiot, M.; Bidault, C.; Marquet, F.; Jablonski, M.; Chemouny, J.
M.; Jouan, F.; Dossier, A.; Chauveheid, M. P.; Gobert, D.; Papo, T.;
Karasuyama, H.; Sacre, K.; Daugas, E.; Charles, N. Prostaglandin D2
Amplifies Lupus Disease through Basophil Accumulation in
Lymphoid Organs. Nat. Commun. 2018, 9, 1−14.
(2) (a) Tsikas, D. Application of Gas Chromatography Mass
Spectrometry and Gas Chromatography Tandem Mass Spectrometry
to Assess in Vivo Synthesis of Prostaglandins, Thromboxane,
Leukotrienes, Isoprostanes and related compounds in Humans. J.
Chromatogr., Biomed. Appl. 1998, 717, 201−245. (b) Song, W. L.;
Wang, M.; Ricciotti, E.; Fries, S.; Yu, Y.; Grosser, T.; Reilly, M.;
Lawson, J. A.; FitzGerald, G. A. Tetranor PGDM, an abundant
Urinary Metabolite reflects Biosynthesis of Prostaglandin D2 in Mice
and Humans. J. Biol. Chem. 2008, 283, 1179−1188.
(3) Liston, T. E.; Roberts, L. J. Metabolic-fate of Radiolabeled
Prostaglandin D2 in a Normal Human Male Volunteer. J. Biol. Chem.
1985, 260, 13172−13180.
(4) Milne, G. L. Lipid Biomarkers of Inflammation. Chronic
Inflammation: Molecular Pathophysiology, Nutritional and Therapeutic
Interventions; CRC Press: 2013; pp 275−286.
aldehyde 18. Alkynylation of 18 using the Seyferth−Gilbert16
reagent then provided alkyne 19 in 80% yield. Copper-
catalyzed coupling of alkyne 19 and methyl diazoacetate17
afforded alkynoate 20. Semihydrogenation of the alkyne group
proceeded smoothly following removal of the TBS protecting
(5) Prakash, C.; Saleh, S.; Roberts, L. J.; Blair, I. A.; Taber, D. F.
Synthesis of the Major Urinary Metabolite of Prostaglandin D2. J.
Chem. Soc., Perkin Trans. 1 1988, 1, 2821−2826.
(6) (a) Das, S.; Chandrasekhar, S.; Yadav, J. S.; Gree, R. Recent
Developments in the Synthesis of Prostaglandins and analogues.
Chem. Rev. 2007, 107, 3286−3337. (b) Peng, H. H.; Chen, F. E.
Recent Advances in Asymmetric Total Synthesis of Prostaglandins.
Org. Biomol. Chem. 2017, 15, 6281−6301.
(7) Roche, S. P.; Aitken, D. J. Chemistry of 4-Hydroxy-2-
cyclopentenone Derivatives. Eur. J. Org. Chem. 2010, 2010, 5339−
5358.
1
group, affording tricyclic-PGDM methyl ester. The H NMR
of the final product correlated with the reported spectrum of
tricyclic-PGDM methyl ester published by Taber.8
In summary, we have completed a chemical synthesis of the
tricyclic-PGDM methyl ester, the major urinary metabolite
produced from prostaglandin D2. The synthetic route is
concise and will be used for the preparation of isotopically
labeled tricyclic-PGDM for use as a quantifying standard in the
analysis of patient clinical samples.
(8) Myers, A. G.; Dragovich, P. S. A Reaction Cascade Leading to
1,6-Didehydro[10]Annulene to 1,5-Dehydronaphthalene Cyclization
Initiated by Thiol Addition. J. Am. Chem. Soc. 1993, 115, 7021−7022.
(9) (a) Danishefsky, S. J.; Cabal, M. P.; Chow, K. Novel
Stereospecific Silyl Group Transfer-Reactions - Practical Routes to
the Prostaglandins. J. Am. Chem. Soc. 1989, 111, 3456−3457.
(b) Jeroncic, L. O.; Cabal, M. P.; Danishefsky, S. J.; Shulte, G. M.
On the Diastereofacial Selectivity of Lewis Acid-Catalyzed Carbon-
Carbon Bond Forming Reactions of Conjugated Cyclic Enones
Bearing Electron-Withdrawing Substituents at the Gamma-Position. J.
Org. Chem. 1991, 56, 387−395.
(10) Stothers, J. B.; Tan, C. T. C-13 Nuclear Magnetic-Resonance
Studies. 34. C-13 Spectra of Several Methylcyclopentanones and
Methylcyclohexanones. Can. J. Chem. 1974, 52, 308−314.
(11) (a) Johnson, C. R.; Braun, M. P. A 2-Step, 3-Component
Synthesis of PGE1 - Utilization of Alpha-Iodoenones in Pd(0)-
Catalyzed Cross-Couplings of Organoboranes. J. Am. Chem. Soc.
1993, 115, 11014−11015. (b) Gu, J. X.; Dirr, M. J.; Wang, Y. L.;
Soper, D. L.; De, B.; Wos, J. A.; Johnson, C. R. An Efficient Synthesis
of 3-hetero-13,14-dihydro prostaglandin F-1 alpha Analogues. Org.
Lett. 2001, 3, 791−794.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.9b03983.
Experimental procedures, characterization data, and
NMR spectra for new compounds (PDF)
AUTHOR INFORMATION
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Corresponding Author
*E-mail: gary.a.sulikowski@vanderbilt.edu.
ORCID
Gary A. Sulikowski: 0000-0002-1067-0767
Notes
(12) Pale, P.; Chuche, J. Silver Assisted Heterocyclization of
Acetylenic-Compounds. Tetrahedron Lett. 1987, 28, 6447−6448.
(13) Shipe, W. D.; Sorensen, E. J. A Convergent Synthesis of the
Tricyclic Architecture of the Guanacastepenes featuring a Selective
Ring Fragmentation. Org. Lett. 2002, 4, 2063−2066.
(14) Trost, B. M.; VanVranken, D. L. Asymmetric Transition Metal-
catalyzed Allylic Alkylations. Chem. Rev. 1996, 96, 395−422.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This research was supported by the National Institutes of
Health (5R01 GM115722).
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Letter
(15) (a) Danheiser, R. L.; Dixon, B. R.; Gleason, R. W. 5-Membered
Ring Annulation Via Propargylsilanes and Allylsilanes. J. Org. Chem.
1992, 57, 6094−6097. (b) Knolker, H. J.; Foitzik, N.; Goesmann, H.;
Graf, R. [3 + 2] Cycloadditions of Allylsilanes 0.2. A Versatile and
Efficient Synthesis of Annulated Cyclopentanes by Stereoselective [3
+ 2] Cycloaddition of Allylsilanes and Cycloalkenyl Methyl Ketones.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1081−1083.
(16) Gilbert, J. C.; Weerasooriya, U. Diazoethenes - Their
Attempted Synthesis from Aldehydes and Aromatic Ketones by
Way of the Horner-Emmons Modification of the Wittig Reaction - a
Facile Synthesis of Alkynes. J. Org. Chem. 1982, 47, 1837−1845.
(17) Suarez, A. S.; Fu, G. C. A Straightforward and Mild synthesis of
Functionalized 3-Alkynoates. Angew. Chem., Int. Ed. 2004, 43, 3580−
3582.
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DOI: 10.1021/acs.orglett.9b03983
Org. Lett. XXXX, XXX, XXX−XXX