A. Sadownik, J. Stefely, S. Regen
Nov 1, 1986
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0
Influential Citations
52
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Journal
Journal of the American Chemical Society
Abstract
This paper describes an efficient synthesis of 1 ,2-bis[ t2-(lipoyloxy)dodecanoyl]-sn-glycero-3-phosphocholine (1) and its use in the construction of highly stable polymerized liposomes under extremely mild conditions. Esterification of glycerophosphorylcholine with 12-(tetrahydropyranyloxy)dodecanoic acid affords the corresponding phosphatidylcholine; subsequent deprotection furnishes 1,2-bis( 12-hydroxydodecanoyl)-sn-glycero-3-phosphocholine (2). Esterification of 2 with DL1,2-dithiolane-3-pentanoic (lipoic) acid anhydride produces a 43% overall yield of 1. Injection of an ethanolic solution of 1 into 10 mM borate buffer (pH 8.5) and treatment with 10 mol % dithiothreitol at 27 O C yields polymerized liposomes which are completely stable in the presence of 1% sodium dodecylsulfate. Over the past 6 years, substantial synthetic effort has focused on the preparation of polymerized forms of lipid bilayer vesicle^.^ Phospholipid-based systems (liposomes4), in particular, have attracted special attention because of their close structural relationship to biological membranes5 In order to maximize their utility for biomechanistic studies (membrane modeling) and for biomedical applications (drug delivery), polymerized liposomes should be prepared under the mildest conditions possible, so that sensitive comembrane and entraped components can be incorporated. We have recently shown that 1,2-bis(l I-mercaptoundecanoyl)-sn-glycero-3-phosphocholine can be polymerized in vesicle form via oxidation with hydrogen peroxide.6 We have also shown that its macrocyclic disulfide analogue is polymerized in the vesicle state through ring-opening polymerization, initiated by using a catalytic amount of dithiothreitol (DTT).' In both cases, polymerization proceeds to completion within 4 h at 50 OC, affording linear polymers having a maximum number average degree of polymerization of 28. While polymerization results in improved vesicle shelf life, it does not yield membranes that can withstand lysis by sodium dodecylsulfate (SDS).6 In this paper we report an efficient synthesis of 1,2-bis[12(lipoyloxy)dodecanoy1]-sn-glycero-3-phosphocholine (1) and demonstrate its utility in the formation of polymerized liposomes. On the basis of its ease of synthesis, its ability to form highly stable polymerized liposomes under extremely mild conditions, and its potential biodegradability, 1 promises to become the polymerizable lipid of choice for a wide variety of mechanistic and practical applications. Results and Discussion Synthesis of 1. Scheme I summarizes the synthetic route which has been employed in the preparation of 1. Esterification of the (1 ) Supported by PHS Grant CA 42065 awarded by the National Cancer Institute and by The National Science Foundation. (2) On leave from the Institute of Chemistry, Agricultural University of Warsaw, Poland. (3) For recent reviews, see: (a) Bader, H.; Dorn, Hashimoto, K.; Hupfer, B.; Petropoulm, J. H.; Ringsdorf, H.; Sumimoto, H. In Polymeric Membranes; Gordon, M., Ed.; Springer Verlag: Berlin, 1985; p 1. (b) Fendler, J. H.; Tundo, P. Arc. Chem. Res. 1984, 17, 3. (c) Palms, C. M. Chem. Soc. Rev. 1985, 1 4 , 4 5 . (d) Hayward, J. A.; Johnston, D. S.; Chapman, D. Ann. N. Y. Acad. Sci. 1985, 446, 267. (e) OBrien, D. F.; Klingbiel, R. T.; Specht, D. P.; Tyminski, P. N. Ibid. 1985, 446, 282. (f) Regen, S. L. Ibid. 1985, 446, 296. (g) Fendler, J. H. Ibid. 1985, 446, 308. (4) ,In this manuscript, we adopt the definition of a liposome as a vesicle comprised of naturally occurring or synthetic phospholipids: Fendler, J. H. Membrane Mimetic Chemistry; Wiley-Interscience: New York, 1982; p 113. ( 5 ) Regen, S . L. Ann. N . Y. Acad. Sci. 1985,446,296 and references cited therein. (6) Samuel, N. K. P.; Singh, M.; Yamaguchi, K.; Regen, S. L. J. Am. Chem. SOC. 1985, 107.42. Regen, S. L.; Yamaguchi, K.; Samuel, N. K. P.; Singh, M. Ibid. 1983, 105, 6354. (7) Regen, S. L.; Samuel, N. K. P.; Khurana, J. M. J. Am. Chem. Sor. 1985, 107, 5804. 0002-7863/86/lSO8-7789$01 .SO10 Scheme I