The Intramolecular Asymmetric Pauson-Khand Cyclization as a
`Novel and General Stereoselective Route to Benzindene
`Prostacyclins: Synthesis of UT-15 (Treprostinil)
`
`Robert M. Moriarty,*,† Neena Rani,‡ Livia A. Enache,§ Munagala S. Rao,§ Hitesh Batra,‡
`Liang Guo,‡ Raju A. Penmasta,‡ James P. Staszewski,‡ Sudersan M. Tuladhar,‡ Om Prakash,†
`David Crich,† Anca Hirtopeanu,†,| and Richard Gilardi⊥
`Department of Chemistry (M/C 111), University of Illinois at Chicago, Chicago, Illinois 60607,
`United Therapeutics, Chicago, Illinois 60612, deCODE Genetics, Inc., Chicago, Illinois 60612,
`Institute of Organic Chemistry, C.D. Nenitescu, Bucharest, Romania, and Laboratory for the Stucture of
`Matter, Naval Research Laboratory, Washington, DC 20375
`
`Received June 5, 2003
`
`A general and novel solution to the synthesis of biologically important stable analogues of
`prostacyclin PGI2, namely benzindene prostacyclins, has been achieved via the stereoselective
`intramolecular Pauson-Khand cyclization (PKC). This work illustrates for the first time the
`synthetic utility and reliability of the asymmetric PKC route for synthesis and subsequent
`manufacture of a complex drug substance on a multikilogram scale. The synthetic route surmounts
`issues of individual step stereoselectivity and scalability. The key step in the synthesis involves
`efficient stereoselection effected in the PKC of a benzoenyne under the agency of the benzylic
`OTBDMS group, which serves as a temporary stereodirecting group that is conveniently removed
`via benzylic hydrogenolysis concomitantly with the catalytic hydrogenation of the enone PKC
`product. Thus the benzylic chiral center dictates the subsequent stereochemistry of the stereogenic
`centers at three carbon atoms (C3a, C9a, and C1).
`
`Prostacyclin (PGI2) (1) is an important physiological
`prostanoid and occurs as a major metabolic product from
`arachidonic acid throughout the vasculature and is
`produced in the endothelium and in smooth muscles.1a-r
`PGI2 is the most potent endogenous vasodilator in both
`
`* To whom correspondence should be addressed.
`† Department of Chemistry (M/C 111), University of Illinois at
`Chicago, 845 W. Taylor St., Room 4500.
`‡ United Therapeutics.
`§ deCODE Genetics, Inc..
`| Institute of Organic Chemistry, C.D. Nenitescu.
`⊥ Naval Research Laboratory.
`(1) (a) Moncada, S.; Gryglewski, R.; Bunting, S.; Vane, J. R. Nature
`1976, 263, 663-665. (b) Johnson, R. A.; Morton, D. R.; Kinner, J. H.;
`Gorman, R. R.; McGuire, J. C.; Whittaker, N.; Bunting, S.; Salmon,
`J.; Moncada, S. Prostaglandins 1976, 12, 915-928. (c) Vane, J. R.;
`Bergstrom, S., Eds. Prostacyclin; Raven Press: New York, 1979. (d)
`Moncada, S.; Vane, J. R. Pharmacol. Rev. 1979, 30, 293-331. (e)
`Bunting, S.; Gryglewski, R.; Moncada, S.; Vane, J. R. Prostaglandins
`1976, 12, 897-913. (f) Moncada, S.; Herman, A. G.; Higgs, E. A.; Vane,
`J. R. Thromb. Res. 1977, 11, 323-344. (g) Marcus, A. J.; Weksler, B.
`B.; Jaffe, E. A. Biol. Chem. 1978, 253, 7138-7141. (h) Weksler, B. B.;
`Marcus, A. J.; Jaffe, E. A. Proc. Natl. Acad Sci. U.S.A. 1977, 74, 3922-
`3926. (i) MacIntyre, D. E.; Pearson, J. D.; Gordon, J. L. Nature 1978,
`271, 549-551. (j) Nakagawa, O.; Tanaka, I.; Usui, T.; Harada, M.;
`Sasaki, Y.; Itoh, H.; Yoshimasa, T.; Namba, T.; Narumiya, S.; Nakao,
`K. Circulation 1994, 90, 1643-1647. Syntheses of PGI2: (k) Corey, E.
`J.; Keck, G. E.; Szekely, I. J. Am. Chem. Soc. 1977, 99, 2006-2008. (l)
`Johnson, R. A.; Lincoln, F. H.; Thompson, J. L.; Nidy, E. G.; Mizsak,
`S. A.; Axen, U. J. Am. Chem. Soc. 1977, 99, 4182-4184. (m) Johnson,
`R. A.; Lincoln, F. H.; Nidy, E. G.; Schneider, W. P.; Thompson, J. L.;
`Axen, U. J. Am. Chem. Soc. 1978, 100, 7690-7705. (n) Corey, E. J.;
`Pearce, H. L.; Szekely, I.; Ishiguro, M. Tetrahedron Lett. 1978, 19,
`1023-1026. (o) Tomoskozi, I.; Galambos, G.; Simonidez, V.; Kovacs,
`G. Tetrahedron Lett. 1977, 18, 2627-2628. (p) Tomoskozi, I.; Galambos,
`G.; Kovacs, G.; Gruber, L. Tetrahedron Lett. 1979, 20, 1927-1930. (q)
`Nicolaou, K. C.; Barnette, W. F.; Gasic, G. P.; Magolda, R. L.; Sipio,
`W. J. J. Chem. Soc., Chem. Commun. 1977, 630-631. (r) Fried, J.;
`Barton, J. Proc. Natl. Acad. Sci. U.S.A. 1977, 74, 2199-2203.
`
`1890
`
`J. Org. Chem. 2004, 69, 1890-1902
`
`systemic and pulmonary circulation. It exerts effects on
`vascular smooth muscle cells and inhibits both platelet
`aggregation and adhesion.2a-f These biological activities
`are relevant to a broad range of cardiovascular diseases
`including congestive heart failure, peripheral vascular
`disease, myocardial ischemia, and pulmonary hyperten-
`sion.3a-r Use of PGI2 as a drug for coronary disease has
`not been fruitful because of the fleeting half-life of this
`compound (∼10 min at pH 7.6 at 25 °C).4 The ability to
`inhibit platelet aggregation in plasma samples is lost
`within 5 min.5 Application of PGI2 to disease therapy
`presents a typical drug delivery challenge that is dealt
`with either mechanically by an appropriate pharmaceuti-
`cal device or chemically by synthesizing a hydrolytically
`stable analogue that retains the biological activity. The
`first option currently is used for the treatment of pulmo-
`nary hypertension in which an aqueous solution of PGI2
`sodium salt (chemical name, epoprostenol; trade name
`Flolan) is pumped continuously and intravenously through
`a catheter permanently placed in the patient’s chest via
`a portable external pump. PGI2 is light sensitive and
`must be stored between 15 and 25 °C, and the formula-
`tion in a buffer solution must be prepared by the patient
`on a daily basis.6 The PGI2 is thereby introduced directly
`
`(2) (a) Tateson, J. E.; Moncada, S.; Vane, J. R. Prostaglandins 1977,
`13, 389-397. (b) Higgs, E. A.; Moncada, S.; Vane, J. R.; Caen, J. P.;
`Michel, H.; Tobelem, G. Prostaglandins 1978, 16, 17-22. (c) Flower,
`R. J.; Cardinal, D. C.; Prostacyclin; Vane, J. R.; Bergstrom, S., Eds.
`Raven Press: New York, 1979; pp 211-216. (d) Gorman, R. R.;
`Bunting, S.; Miller, O. V. Prostaglandins 1977, 13, 377-388. (e)
`Ubatuba, F. B.; Moncada, S.; Vane, J. R. Thromb. Haemostasis 1979,
`41, 425-434. (f) Cooper, B.; Schafer, A. I.; Puchalsky, D.; Handin, R.
`I. Prostaglandins 1979, 17, 561-571.
`
`10.1021/jo0347720 CCC: $27.50 © 2004 American Chemical Society
`Published on Web 02/19/2004
`
`See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
`
`Downloaded via SAN JOSE STATE UNIV on March 24, 2020 at 16:20:54 (UTC).
`
`Liquidia - Exhibit 1009 - Page 1
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`

`

`Synthesis of Treprostinil
`
`into the pulmonary arterial system. This is a difficult
`therapy and one can appreciate the strong motivation to
`discover an active, stable analogue that could be admin-
`istered in a less invasive manner either orally or sub-
`cutaneously. From a chemical viewpoint one can readily
`understand the hydrolytic lability of PGI2 on the basis
`of the presence of the Z-vinyl ether group. Protonation
`of 1 yields the oxonium ion 2 followed by ring opening of
`the derived hemiketal to yield 6-keto-PGF1R (3).7a Ad-
`ditional driving force for the rapid hydrolysis has been
`proposed to involve the carboxylate form of 24 and proven
`in an elegant kinetic study.7b
`
`Syntheses of stable analogues as potential drugs have
`used this mechanism as a point of departure. Thus
`substitution of geminal fluorine atoms at C7 destabilizes
`
`(3) (a) Gimson, A. E. S.; Langley, P. G.; Hughes, R. D.; Canalese,
`J.; Mellon, D. J.; Williams, R.; Woods, H. F.; Weston, M. J. Lancet 1980,
`1, 173-175. (b) Braude, S.; Gimson, A. S.; Williams, R. Intensive Care
`Med. 1981, 7, 101-103. (c) Woods, H. F.; Ash, G.; Weston, M. J.;
`Bunting, S.; Moncada, S.; Vane, J. R. Lancet 1978, 2, 1075-1077. (d)
`Turney, J. H.; Williams, L. C.; Fewell, M. R.; Parsons, V.; Weston, M.
`J. Lancet 1980, 2, 219-222. (e) Zusman, R. M.; Rubin, R. H.; Cato, A.
`E.; Cocchetto, D. M.; Crow, J. W.; Tolkoff-Rubin, N. N. Engl. J. Med.
`1981, 304, 934-939. (f) Longmore, D. B.; Bennett, G.; Gueirrara, D.;
`Smith, M.; Bunting, S.; Moncada, S.; Reed, P.; Read, N. G.; Vane, J.
`R. Lancet 1979, 1, 1002-1005. (g) Longmore, D. B.; Bennett, J. G.;
`Hoyle, P. M.; Smith, M. A.; Gregory, A.; Osivand, T.; Jones, W. A.
`Lancet 1981, 1, 800-803. (h) Walker, I. D.; Davidson, J. F.; Faichney,
`A.; Wheatly, D. J.; Davidson, K. G. Br. J. Haematol. 1981, 49, 415-
`423. (i) Radegran, K.; Aren, C.; Teger-Nilsson, A.-C. J. Thorac.
`Cardiovasc. Surg. 1982, 83, 205-211. (j) Sinzinger, H.; O’Grady, J.;
`Cromwell, M.; Hofer, R. Lancet 1983, 1, 1275-1276. (k) Szczeklik, A.;
`Nizankowski, R.; Skawinski, S.; Szczeklik, J.; Gluszko, P.; Gryglewski,
`R. J. Lancet 1979, 1, 1111-1114. (l) Lewis P. J.; O’Grady, J., Eds.
`Clinical Pharmacology of Prostacyclin; Raven Press: New York, 1981.
`(m) Belch, J. J.; Newman, P.; Drury, J. K.; McKenzie, F.; Capell, H.;
`Leiberman, P.; Forbes, C. D.; Prentice, C. R. Lancet 1983, 1, 313-
`315. (n) Belch, J. J.; McKay, A.; McArdle, B.; Leiberman, P.; Pollock,
`J. G.; Lowe, G. D.; Forbes, C. D.; Prentice, C. R. M. Lancet 1983, 1,
`315-317. (o) Rubin, L. J.; Groves, B. M.; Reeves, J. T.; Frosolono, M.;
`Handel, F.; Cato, A. E. Circulation 1982, 66, 334-338. (p) Yui, Y.;
`Nakajima, H.; Kawai, C.; Murakami, T. Am. J. Cardiol. 1982, 50, 320-
`324. (q) Gryglewski, R. J.; Nowak, S.; Kostka-Trabka, E.; Bieron, K.;
`Dembinska-Kiec, A.; Blaszczyk, B.; Kusmiderski, J.; Markowska, E.;
`Szmatola, S. Pharmacol. Res. Commun. 1982, 14, 879-908. (r) Vane,
`J.; O’Grady, J., Eds. Therapeutic Applications of Prostaglandins;
`Edward Arnold: London, UK, 1993.
`
`intermediate 2 and this compound is called APF-07 4.8
`Removal of the C5-6 double bond yields 6(cid:2)- and 6R-
`9a-e or formal removal of the oxygen atom and
`PGI1
`replacement by a methylene group generates the class
`of analogues called carbaprostacyclins.10a-f These ana-
`logues do not possess the reactive vinyl ether system and
`prominent examples are iloprost 5,11 cicaprost 5a,12 and
`eptaloprost 5b13a-d which are differentiated by variations
`in the side chains. Replacement of the oxygen atom by
`sulfur as well as nitrogen has been reported, e.g. (5Z)-
`6,9-thiaprostacyclin14a-d and 9-deoxy-9R-nitrilo-PGF1.15a,b
`Finally, the Z-vinyl ether can be embedded in an aryl
`ether motif as in beraprost (6)16a-e or UT-15 (7).17a-c UT-
`15 (7) belongs to a class of stable analogues of PGI2 called
`
`(4) Cho, M. J.; Allen, M. A. Prostaglandins 1978, 15, 943-954.
`(5) Whittle, B. J. R.; Moncada, S.; Vane, J. R. Prostaglandins 1978,
`16, 373-388.
`(6) Epoprostenol sodium is a Glaxo Smith Kline drug. For the
`synthesis of the sodium salt see: Whittaker, N. Tetrahedron Lett. 1977,
`32, 2805-2808.
`(7) (a) Johnson, R. A.; Morton, D. R.; Kinner, J. H.; Gorman, R. R.;
`McGuire, J. C.; Sun, F. F.; Whittaker, N.; Bunting, S.; Solomon, J.;
`Moncada, S.; Vane, J. R. Prostaglandins 1976, 12, 915-928. (b)
`Bergman, N. A.; Chiang Y.; Jansson, M.; Kresge, A. J.; Ya, Y. J. Chem.
`Soc., Chem. Commun. 1986, 1366-1368.
`(8) Nakano, T.; Makino, M.; Morizawa, Y.; Matsumura, Y. Angew.
`Chem., Int. Ed. Engl. 1996, 35, 1019-1021.
`(9) (a) Johnson, R. A.; Lincoln, F. H.; Nidy, E. G.; Schneider, W. P.;
`Thompson, J. L.; Axen, U. J. Am. Chem. Soc. 1978, 100, 7690-7705.
`(b) Togna, G.; Gandolfi, C.; Andreoni, A.; Fumagalli, A.; Passarotti,
`C.; Faustini, F.; Patrono, C. Pharmacol. Res. Commun. 1977, 9, 909-
`916. (c) Whittle, B. J. R.; Boughton-Smith, N. K.; Moncada, S.; Vane,
`J. R. J. Pharm. Pharmacol. 1978, 30, 597-599. (d) Nelson, N. A. J.
`Am. Chem. Soc. 1977, 99, 7362-7363. (e) Whittle, B. J. R.; Moncada,
`S.; Vane, J. R. In Medicinal Chemistry Advances; de las Heras, F. G.,
`Vega, S., Eds.; Pergamon Press: Oxford, UK, 1981; pp 141-158.
`(10) (a) Nicolaou, K.; Sipio, W. J.; Magolda, R. L.; Seitz, S.; Barnette,
`W. E. J. Chem. Soc., Chem. Commun. 1978, 1067-1068. (b) Kojima,
`K.; Sakai, K. Tetrahedron Lett. 1976, 17, 101-104. (c) Morton, D. R.;
`Brokaw, F. C. J. Org. Chem. 1979, 44, 2880-2887. (d) Ceserani, R.;
`Grossoni, M.; Longiave, D.; Mizzotti, B.; Pozzi, O.; Dembinska-Kiec,
`A.; Bianco, S. Prostaglandins Med. 1980, 5, 131-139. (e) Morita, A.;
`Mori, M.; Hasegawa, K.; Kojima, K.; Kobayashi, S. Life Sci. 1980, 27,
`695-701. (f) Whittle, B. J. R.; Steel, G.; Boughton-Smith, N. K. J.
`Pharm. Pharmacol. 1980, 32, 603-604.
`(11) Bursch, W.; Schulte-Hermann, R. In Prostacyclin and its Stable
`Analogue Iloprost; Gryglewski R. I., Stock, G., Eds.; Springer: Berlin,
`Germany, 1987; pp 257-268.
`(12) Skuballa, W.; Vorbrueggen, H. Angew. Chem. 1981, 93, 1080-
`1081.
`(13) (a) Shibasaki, M.; Torisawa, Y.; Ikegami, S. Tetrahedron Lett.
`1983, 24, 3493-3496. (b) Skuballa, W.; Schillinger, E.; Stuerzbecher,
`S.; Vorbrueggen, H. J. Med. Chem. 1986, 29, 313-315. (c) Ohno, K.;
`Nishiyama, H.; Nagase, H.; Matsumoto, K.; Ishikawa, M. Tetrahedron
`Lett. 1990, 31, 4489-4492. (d) Bartmann, W.; Beck, G. Angew. Chem.
`1982, 94, 767-780; Angew. Chem., Int. Ed. Engl. 1982, 21, 751.
`(14) (a) Nicolaou, K. C.; Barnette, W. E.; Magolda, R. L. J. Am. Chem
`Soc. 1981, 103, 3472-3480. (b) Gryglewski, R. J.; Nicolaou, K. C.
`Experientia 1978, 34, 1336-1338. (c) Lefer, A. M.; Trachte, G. J.;
`Smith, J. B.; Barnette, W. E.; Nicolaou, K. C. Life Sci. 1979, 25, 259-
`263. (d) Horii, D.; Kanayama, T.; Mori, M.; Shibasaki, M.; Ikegami, S.
`Eur. J. Pharmacol. 1978, 51, 313-316.
`(15) (a) Bundy, G. L.; Baldwin, J. M. Tetrahedron Lett. 1978, 19,
`1371-1374. (b) Lock, J. E.; Coceani, F.; Hamilton, F.; Greenaway-
`Coates, A.; Olley, P. M. J. Pharmacol. Exp. Ther. 1980, 215, 156-159.
`(16) (a) Kurihara, I.; Sahara, T.; Kato, H. Br. J. Pharmacol. 1990,
`99, 91-96. (b) Toda, N. Cardiovasc. Drug Rev. 1988, 6, 222-238. (c)
`Nishio, S.; Matsuura, H.; Kanai, N.; Fukatsu, Y.; Hirano, T.; Nish-
`ikawa, N.; Nameoka, K.; Umetsu, T. Jpn. J. Pharmacol. 1988, 47,
`1-10. (d) Umetsu, T.; Murata, T.; Tanaka, Y.; Osada, E.; Nishio, S.
`Jpn. J. Pharmacol. 1986, 43, 81-90. (e) Akiba, T.; Miyazaki, M.; Toda,
`N. Br. J. Pharmacol. 1986, 89, 703-711.
`(17) (a) Aristoff, P. A.; Harrison, A. W.; Aiken, J. W.; Gorman, R.
`R.; Pike, J. E. In Advances in Prostaglandin Thromboxane and
`Leukotriene Research; Samuelsson, B., Paoletti, R., Ramwell, P. W.,
`Eds.; Raven Press: New York, 1983; Vol. 11, pp 267-274. (b) UT-15
`has also been variously known as Uniprost, BW-15AU, LRX-15,
`U-62840, 15AU81, and finally Remodulin. (c) Sorbera, L. A.; Rabasseda,
`X.; Castaner, J. Drugs Future 2001, 26, 364-367.
`
`J. Org. Chem, Vol. 69, No. 6, 2004 1891
`
`Liquidia - Exhibit 1009 - Page 2
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`

`

`benzindene prostacyclins that are differentiated by the
`structure of their side chains.18a-c
`
`To date, UT-15 (7) has proven effective in the treat-
`ment of pulmonary hypertension, a debilitating and often
`fatal lung disease, for which Flolan mentioned above has
`been the main therapy available.19a-f UT-15 (7) has a
`longer biological half-life and is not degraded upon
`
`(18) (a) Shimoji, K.; Hayashi, M. Tetrahedron Lett. 1980, 21, 1255-
`1258. (b) Aristoff, P. A.; Harrison, A. W. Tetrahedron Lett. 1982, 23,
`2067-2070. (c) Aristoff, P. A.; Johnson, P. D.; Harrison, A. W. J. Am.
`Chem. Soc. 1985, 107, 7967-7974.
`(19) (a) Gaine, S. P.; Oudiz, R.; Rich, S.; Barst, R.; Roscigno, R. Am.
`J. Respir. Crit. Care Med. 157(3). (b) McLaughlin, V.; Barst, R.; Rich,
`S.; Rubin, L.; Horn, E.; Gaine, S.; Blackburn, S.; Crow, J. Eur. Heart
`J. 1999, 20 (Suppl.), Abst 2555. (c) Barst, R. J.; Horn, E. M.; Widlitz,
`A. C.; Goudie, S. M.; Kerstein, D.; Berman-Rosenzweig, E.; Blackburn,
`S. D. Eur. Heart J. 2000, 21 (Suppl.), Abst P1721. (d) McLaughlin, V.
`V.; Hess, D. M.; Sigman, J.; Blackburn, S.; Rich, S. Eur. Respir. J.
`2000, 16 (Suppl. 31), Abst P2830. (e) Barst, R. J.; Simonneau, G.; Rich,
`S.; Blackburn, S. D.; Naeije, R.; Rubin, L. J. Circulation 2000, 102
`(18, Suppl.), Abst 477. (f) Seetharam, T. A.; Anderson, L. W.; Crow, J.
`W.; Klein, K. B.; Whittle, B. J. European Patent Appl. EP 347,243,
`CA 1990, 113, 23513k.
`
`1892 J. Org. Chem., Vol. 69, No. 6, 2004
`
`Moriarty et al.
`
`passage through the lungs.20 In further contrast to
`Flolan, UT-15 is delivered subcutaneously via a micro-
`infusion device thus avoiding the risk of sepsis infection
`encountered with catheter delivery. UT-15 (7) retains all
`the biological activity of PGI2. UT-15 has been investi-
`gated for use in severe congestive heart failure,21a-c
`severe intermittent
`claudication,22a,b and immuno-
`suppresion.23a-c Furthermore, UT-15 has an antiprolif-
`erative effect on human pulmonary arterial smooth
`muscle cells.24 To meet the demands of producing mul-
`tikilogram quantities of UT-15 (7) needed in the course
`of drug development, an efficient and economical syn-
`thesis had to be devised. The essential requirements for
`any large-scale, multistep synthesis of a molecule of the
`complexity of UT-15 (7) are very high overall stereose-
`lectivity, high overall chemical yield, and scalability of
`individual steps to multigram quantities. Inspection of
`the structure of this molecule reveals the presence of five
`chiral centers and the molecule can be viewed as a benzo-
`annulated hydrindane with the BC ring system reminis-
`cent of the CD ring system of steroids.
`Benzindene prostacyclin UT-15 (7), [[(1R,2R,3aS,9aS)-
`2,3,3a,4,9,9a-hexahydro-2-hydroxy-1-[(3S)-3-hydroxy-
`octyl]-1-H-benz[f]inden-5-yl]oxy]acetic acid, has been syn-
`thesized previously by Upjohn chemists using an ap-
`proach in which the AB ring system is introduced in the
`form of 5-methoxy-2-tetralone (8), which is converted to
`racemic 9, followed by an intramolecular Wadworth-
`Emmons-Wittig cyclopentanone annulation using the
`homochiral side chain 10 with no stereochemical control
`in the creation of the C3a chiral center in 11.25 UT-15 (7)
`was synthesized in 14 steps following the route of Scheme
`1. Stereochemistry was introduced rather late in the
`synthesis in the form of the homochiral side chain 10 in
`this general route to benzindene prostacyclins differing
`in the C1 side chain. Unfortunately, this low level of
`control of stereochemistry in this route led to significant
`separation problems in obtaining the final product and
`could not be used to fulfill our scale-up needs for
`development of UT-15.
`Another early route to the benzindene prostacyclin
`system and UT-15 (7) used intramolecular alkylation of
`the phenolic ring for formation of the B-ring. Homochiral
`12 was made in a multistep synthesis and converted to
`13 with use of C6H5S(O)(NCH3)CH2MgBr (Scheme 2).
`Reductive elimination followed by hydroboration and
`
`(20) Remodulinsstable form of prostacyclin; United Therapeutics
`Corp. Web Site March 23, 2001.
`(21) (a) Patterson, J. H.; Adams, K. F., Jr.; Gheorghiade, M.; Bourge,
`R. C.; Sueta, C. A.; Clarke, S. W.; Jankowski, J. P.; Shaffer, C. L.;
`McKinnis, R. A. Am. J. Cardiol. 1995, 75, 26A-33A. (b) Adams, K. F.,
`Jr.; Patterson, H.; Gheorghiade, M.; Bourge, R. C.; Sueta, C. A.; Clarke,
`S. W.; Patel, J. D.; Shaffer, C. Circulation 1992, 86 (4, Suppl.), Abst
`1501. (c) Steffen, R. P.; de la Mata, M. Prostaglandins, Leucotrienes
`Essent. Fatty Acids 1992, 45, 83. (d) Fink, A. N.; Frishman, W. H.;
`Azidad, M.; Argarwal, Y. Heart Dis. 1999, 1, 29-40.
`(22) (a) Mohler, E. R., III; Klugherz, B.; Goldman, R.; Kimmel, S.
`E.; Wade, M.; Sehgal, C. M. Vasc. Med. 2000, 5, 231-237. (b) Mohler,
`E. R.; Klugherz, B.; Goldman, R.; Fishman, A. P.; Wade, M.; Sehgal,
`C. M. J. Am. Coll. Cardiol. 1999, 33 (2, Suppl. A), 277A.
`(23) (a) Dumble, L. J.; Gibbons, S.; Tejpal, N.; Chou, T.-C.; Redgrade,
`N. G.; Boyle, M. J.; Kahan, B. D. Transplantation 1993, 55, 1124-
`1128. (b) Boyle, M. J.; Dumble, L. J. Cell Transplant 1999, 8, 543-
`548. (c) Redgrave, N. G.; Francis, D. M. A.; Dumble, L. J.; Plenter, R.;
`Ruwart, M.; Birchall, I.; Clunie, G. J. A. Transplant Proc. 1992, 24,
`227-228.
`(24) Finney, P. A.; Tran, Q. S.; Tinker, A.; Clapp, L. H. Eur. Respir.
`J. 2000, 16, 1029.
`(25) Aristoff, P. A. EP 0159784, JP 1985208936, US 4683330.
`
`Liquidia - Exhibit 1009 - Page 3
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`

`Synthesis of Treprostinil
`
`SCHEME 1
`
`SCHEME 2
`
`SCHEME 3
`
`mesylation gave 14 that underwent intramolecular alky-
`lation (14 f 15).26a-cA related approach in which the
`B-ring of a benzindene prostacyclin was formed by
`intramolecular alkylation coupled with conjugate addi-
`tion to a vinyl sulfone has also been reported (16 f 17)
`(Scheme 3).27a-dReductive cleavage of the phenyl sulfone
`group in 17 yielded the cis/trans ring fused product in a
`1.9/1 ratio.
`These routes, although conceptually appealing, were
`deemed inadequate to the task of producing kilogram
`quantities of UT-15 (7), and accordingly a novel synthetic
`route was required. The principal requirement envisioned
`was production of an enantiopure intermediate early in
`the synthesis, ideally at the tricyclic stage. In principle,
`
`(26) (a) Aristoff, P. A. US 4306075. (b) Aristoff, P. A. US 4349689.
`(c) Aristoff, P. A.; Kelly, R. C.; Nelson, N. A. CH 648017, CH 655308,
`FR 2484413, GB 2070596, JP 1990167248, JP 1994145085.
`(27) (a) Hardiger, S. A.; Jakubowski, J. A.; Fuchs, P. L. Bioorg. Med.
`Chem. Lett. 1991, 1, 79-82. (b) Nevill, C. R., Jr.; Braish, T. F.;
`Jakubowski, J. A.; Fuchs, P. L. Biomed. Chem. Lett. 1991, 1, 77-78.
`(c) Hardinger, S. A.; Jakubowski, J. A.; Fuchs, P. L. Biomed. Chem.
`Lett. 1991, 1, 79-82. (d) Nevill, C. R., Jr.; Jakubowski, J. A.; Fuchs,
`P. L. Biomed. Chem. Lett. 1991, 1, 83-86.
`
`the intramolecular asymmetric Pauson-Khand cycliza-
`tion (PKC) of enynes to cyclopentenones could fulfill both
`these requirements.28a-s An enyne of type 18 appeared
`to be relatively readily accessible and the powerful
`stereodirecting influence of an R-propargylic substituent
`at C9 in the intramolecular asymmetric PKC has been
`amply demonstrated and productively used in stereose-
`lective synthesis.29a-q In the present example the C1 S
`configuration of the substituent would create the requi-
`site C3a(cid:2)-configuration of the hydrogen atom in UT-
`15.30a-c Thus, an advanced tricyclic enantiopure inter-
`mediate could potentially be obtained from a relatively
`simple homochiral precursor. Furthermore, additional
`
`(28) (a) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem.
`Rev. 1996, 96, 635-662. (b) Khand, I. U.; Knox, G. R.; Pauson, P. L.;
`Watts, W. E.; Foreman, M. I. J. Chem Soc., Perkin Trans. 1 1973, 977-
`981. (c) Pauson, P. L. Tetrahedron 1985, 41, 5855-5860. (d) Pauson,
`P. L. In Organometallics in Organic Synthesis, Aspects of a Modern
`Interdisciplinary Field; de Meijere A., Tom Diek, H., Eds; Springer-
`Verlag: Berlin, Germany, 1988; p, 233. (e) Schore, N. E. Chem. Rev.
`1988, 88, 1081-1119. (f) Schore, N. E. Org. React. 1991, 40, 1-90. (g)
`Schore, N. E. In Comprehensive Organic Synthesis; Trost B. M.,
`Fleming, I., Eds., Pergamon Press Ltd.: Oxford, UK, 1991; Vol. 5, p
`1037. (h) Schore, N. E. In Comprehensive Organometallic Chemistry
`II; Abel, E. W., Stone, F. A., Wilkinson, G., Eds.; Elsevier: New York,
`1995; Vol. 12, p 703. (i) Geis, O.; Schmalz, H. G. Angew. Chem., Int.
`Ed. 1998, 37, 911-914. (j) Ingate, S. T.; Marco-Contelles, J. Org. Prep.
`Proced. Int. 1998, 30, 121-143. (k) Jeong, N. In Transition Metals in
`Organic Synthesis; Beller M., Molm, C., Eds.; Wiley-VCH: Weinhem,
`Germany, 1998; Vol. 1, p 560. (l) Chung, Y. K. Coord. Chem Rev. 1999,
`188, 297-341. (m) Buchwald, S. L.; Hicks, F. A. In Comprehensive
`Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
`Springer Verlag: Berlin, Germany, 1999; Vol. II, p 491. (n) Brummond,
`K. M.; Kent, J. L. Tetrahedron 2000, 56, 3263-3283. (o) Khand, I. U.;
`Pauson, P. L. J. Chem. Soc., Perkin Trans. 1 1976, 30-32. (p) Pauson,
`P. L.; Khand, I. U. Ann. N.Y. Acad. Sci. 1977, 295, 2-14. (q) Bladon,
`P.; Khand, I. U.; Pauson, P. L. J. Chem. Res. Miniprint 1977, 146. (r)
`Khand, I. U.; Pauson, P. L. J. Chem. Res. Miniprint 1980, 3501. (s)
`Fruhauf, H.-W. Chem. Rev. 1997, 97, 523-596.
`
`J. Org. Chem, Vol. 69, No. 6, 2004 1893
`
`Liquidia - Exhibit 1009 - Page 4
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`

`

`benefits accrue from this approach: cis-stereochemistry
`is expected in the heterogeneous catalytic hydrogenation
`
`Moriarty et al.
`
`ence of a catalytic amount of CuI to yield (S)-1-chloro-2-
`heptanol (37), which was then converted to the diaster-
`eomeric tetrahydropyranyl derivative 38. This compound
`was then treated with lithio 1-trimethylsilyl-1-propyne
`formed with use of butyllithium at -20 °C and at a
`reaction temperature of 0 °C (38 f 39). Cleavage of the
`TMS group yielded 5-S-tetrahydropropanoxy-1-decyne
`(25).
`
`of the double bond of the enone, resulting in the required
`C9a (cid:2)-configuration; and benzylic hydrogenolysis expect-
`edly would remove the unneeded benzylic group while
`the carbonyl group at C2 remains available for reduction
`to the C2 R-hydroxyl group. All of these preconceptions
`proved valid in the synthesis of UT-15 (7) as summarized
`in Scheme 4. Individual steps will be discussed in turn.
`
`Results and Discussion
`Synthesis of Enyne (1,1-Dimethylethyl)[[(1S,6S)-
`1-[3-methoxy-2-(2-propenyl)phenyl]-6-[(tetrahydro-
`2H-pyran-2-yl)oxy]-2-undecynyl]oxy]dimethyl-
`silane (29). The key feature of enyne 29 is the benzylic
`C1 S stereochemistry because this group influences the
`creation of the chiral center formed in the PKC at C3a in
`the requisite S configuration. It had been shown earlier
`that the tert-butyldimethyl silyl ether is a particularly
`useful group as the R-propargyl substituent in the PKC.29i
`Aldehyde 24 was produced in a straightforward manner.
`3-Methoxybenzyl alcohol 20 was protected as the TBDMS
`derivative and ortho-allylated (20 f 21 f 22). Depro-
`tection and Swern oxidation gave 2-allyl-3-methoxy-
`benzaldehyde (24) (22 f 23 f 24).
`The further synthesis of enyne involves Grignard
`addition of side chain 25 to aldehyde 24 to yield 26. The
`diastereomeric side chain 5-S-tetrahydropropanoxy-1-
`decyne (25) was synthesized by using an adaptation of
`the method of Takano et al.31 (S)-(-)-Epichlorohydrin (36)
`was reacted with butylmagnesium chloride in the pres-
`
`(29) (a) Mukai, C.; Uchiyama, M.; Sakamoto, S.; Hanaoka, M.
`Tetrahedron Lett. 1995, 36, 5761-5764. (b) Xestobergsterol D and E
`rings: Krafft, M. E.; Chirico, X. Tetrahedron Lett. 1994, 35, 4511-
`4514. (c) Krafft, M. E.; Juliano, C. A.; Scott, I. L.; Wright, C.; McEachin,
`M. D. J. Am. Chem. Soc. 1991, 113, 1693-1703. (d) Krafft, M. E. J.
`Am. Chem. Soc. 1988, 110, 968-970. (e) Krafft, M. E. Tetrahedron Lett.
`1988, 29, 999-1002. (f) (+)-Epoxydicylmene: Jamison, T. F.; Sham-
`bayati, S.; Crowe, W. E.; Schreiber, S. L. J. Am. Chem. Soc. 1994, 116,
`5505-5506. Jamison, T. F.; Shambayati, S.; Crowe, W. E.; Schreiber,
`S. L. J. Am. Chem. Soc. 1997, 119, 4353-4363. (g) (-)-R-Kainic acid:
`Yoo, S.; Lee, S. H. J. Org. Chem. 1994, 59, 6968-6972. (h) Pental-
`enene: Schore, N. E.; Rowley, E. G. J. Am. Chem. Soc. 1988, 110,
`5224-5225. (i) Pentalenic acid, pentalenene: Rowley, E. G.; Schore,
`N. E. J. Organomet. Chem. 1991, 413, C5-C9. (j) Siliphene: Rowley,
`E. G.; Schore, N. E. J. Org. Chem. 1992, 57, 6853-6861. (k) Kal-
`manol: Paquette, L. A.; Borrelly, S. J. Org. Chem. 1995, 60, 6912-
`6921. (l) Dendrobine: Cassayre, J.; Zard, S. Z. J. Am. Chem. Soc. 1999,
`121, 6072-6073. (m) Coriolin: Exon, C.; Magnus, P. J. Am. Chem.
`Soc. 1983, 105, 2477-2478. (n) 9-cis-Retinoic acid: Murray, A.;
`Hansen, J. B.; Christensen, B. V. Tetrahedron 2001, 57, 7383-7390.
`(o) Quadrone: Magnus, P.; Principe, L. M.; Slater, M. J. J. Org. Chem.
`1987, 52, 1483-1486. (p) Hirsuitic acid: Magnus, P.; Exon, C.;
`Albaugh-Robertson, P. Tetrahedron 1985, 41, 5861-5869. (q) Carba-
`cyclins: Mulzer, J.; Graske, K. D.; Kirste, B. Liebigs Ann. Chem. 1988,
`891-897.
`(30) (a) Magnus, P.; Principe, L. M. Tetrahedron Lett. 1985, 26,
`4851-4854. (b) Schore, N. E. Pauson-Khand Reaction. In Compre-
`hensive Organic Synthesis; Trost, B. M., Ed., Pergamon Press: Oxford,
`UK, 1991. (c) Jeong, N.; Lee, B. Y.; Lee, S. M.; Chung, Y. K.; Lee, S. G.
`Tetrahedron Lett. 1993, 34, 4023-4026.
`
`1894 J. Org. Chem., Vol. 69, No. 6, 2004
`
`3-Methoxy-2-(2-propenyl)-R-[(5S)-5-[(tetrahydro-2H-py-
`ran-4-yl)oxy]-1-decynyl]benzenemethanol
`intermediate
`(26), which results from the addition of 25-MgBr to 24,
`possesses three chiral centers, one of which is fixed, i.e.,
`the S-configuration of the C6 carbon atom. The benzylic
`carbon atom and the chiral carbon atom of the THP group
`are individually heterochiral. In agreement with expecta-
`tion a chiral chromatogram (Daicel Chiralpak AD Col-
`umn) of 26 showed four peaks. Diastereomeric 26 was
`oxidized with pyridinium chlorochromate to the diaster-
`eomeric ketone 27.
`For the subsequent stereoselective Pauson-Khand
`cyclization, we required the S-configuration of the ben-
`zylic (propargylic) carbon bearing the hydroxyl group.
`The stereochemistry was obtained by using a stoichio-
`metric Corey-type asymmetric reduction of 27 employing
`commercially available R-methyloxazaborolidine, borane-
`dimethyl sulfide complex, and ketone 27 at -30 °C.32a
`The S stereochemical result is in agreement with the
`results of Parker and Ledeboer using the same system.32b
`Chiral chromatographic analysis of 28 showed the pres-
`ence of two diastereomers.
`For the Pauson-Khand cyclization, 28 was converted
`to the corresponding TBDMS protected alcohol 29 and
`subjected to either stoichiometric or catalytic Co2(CO)8
`cyclization33 to yield the tricyclic enone 30 in 89% yield.
`For assessment of the stereoselectivity of the reaction,
`the crude product prior to chromatography was analyzed
`with HPLC, which revealed that over 99% of the product
`consisted of two peaks of equal intensity corresponding
`to >99% creation of the new chiral center at C3a in one
`configuration. The two peaks result from the THP dia-
`stereomeric center -O-CH-O-.
`Two points are noteworthy in connection with the
`Pauson-Khand cyclization of 29. The first is the high
`
`(31) Takano, S.; Yanase, M.; Takahashi, M.; Ogasawara, K. Chem.
`Lett. 1987, 2017-2020.
`(32) (a) Helal, C. J.; Magriotis, P. A.; Corey, E. J. J. Am. Chem. Soc.
`1996, 118, 10938-10939. (b) Parker, K. A.; Ledeboer, M. W. J. Org.
`Chem. 1996, 61, 3214-3217.
`(33) Pagenkopf, B. L.; Livinghouse, T. J. Am. Chem. Soc. 1996, 118,
`2285-2286.
`
`Liquidia - Exhibit 1009 - Page 5
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`

`

`Synthesis of Treprostinil
`
`SCHEME 4
`
`J. Org. Chem, Vol. 69, No. 6, 2004 1895
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`Liquidia - Exhibit 1009 - Page 6
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`

`

`SCHEME 5
`
`Moriarty et al.
`
`chemical yield (89%) and the high degree of chiral
`induction of almost 100%. Since these yields are the same
`in both the stoichiometric and the catalytic reaction the
`results must be mechanistically controlled with steric
`effects being determinant. Two factors are operative. The
`first is that the phenyl ring forces the enyne system into
`the most favorable orientation for annulation by restrict-
`ing rotational conformations (18 S 18a). It has been
`observed that (cid:2)-positioned geminal dialkyl enynes give
`relatively higher yields of cyclized products due to a
`Thorpe-Ingold-type effect.34a-d This cisoid orientation of
`the alkyne Co(CO)6 group and the alkene in 40 is further
`enhanced by the ortho CH3O group steric interaction with
`the alkyl system.
`According to the mechanism proposed by Magnus and
`applied by others, the stereochemical course follows from
`the relative energy difference of the transition states
`leading to the two diastereomeric metallocycle intermedi-
`ates 40 and 42 (Scheme 5) with the latter possessing a
`destabilizing 1,3-diaxial interaction that disfavors this
`course of reaction.29a-p,30a,b This effect is amplified because
`of the large steric bulk of the benzylic TBDMS group.
`Catalytic hydrogenation 30 f 31 removed the now
`superfluous stereodirecting benzylic TBDMS ether and
`the thermodynamically more stable cis-hydrindanone is
`formed.35a,b The side chain at C1 existed in both the R-
`and (cid:2)-configurations. Formation of the cis-hydrindanone
`appears to concur with expectation; indeed the catalytic
`heterogeneous hydrogenation of hydrindenones has been
`studied in great detail because of its relationship to the
`CD ring of steroids.36 Basically the problem is that the
`desired stereochemistry for the CD ring system of ste-
`roids is trans but invariably the undesired cis-fused
`product is formed by catalytic reduction. Stork and Kahne
`
`(34) (a) De Tar, D. F.; Luthra, N. P. J. Am. Chem. Soc. 1980, 102,
`4505-4512. (b) Kirby, A. J. Adv. Phys. Org. Chem. 1980, 17, 208. (c)
`Eliel, E. L. Stereochemistry of Carbon Compounds; McGraw-Hill: New
`York, 1962; pp 106-202. (d) The majority of the syntheses involve
`cyclization of 1,6-enynes to yield bicyclo[3.3.0]octene-3-ones. Applica-
`tions to form bicyclo[4.3.0]octene-ones are known: Quattropani, A.;
`Anderson, G.; Bernardinelli, G.; Kuendig, E. P. J. Am. Chem. Soc. 1997,
`119, 4773-4774 and references therein.
`(35) (a) Boyce, C. B. C.; Whitehurst, J. S. J. Chem. Soc. 1960, 4547-
`4553. (b) Baggaley, K. H.; Brooks, S. G.; Green, J.; Redman, B. T. J.
`Chem. Soc. C 1971, 2671-2678.
`(36) Hajos, Z. H.; Parrish, D. P. J. Org. Chem. 1973, 38, 3239-3243.
`
`1896 J. Org. Chem., Vol. 69, No. 6, 2004
`
`found this to be the case