The stability of two-component liposomes composed of the polymerizable 1,2-bis-[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphati dylcholine (SorbPC) and either a phosphatidylethanolamine (PE) or a phosphatidylcholine (PC) were examined via fluorescence leakage assays. Ultraviolet light exposure of SorbPC-containing liposomes forms poly-SorbPC, which phase separates from the remaining monomeric lipids. If the nonpolymerizable lipids are PE's, then the photoinduced polymerization destabilizes the liposome with loss of aqueous contents. The permeability of the control dioleoylPC/SorbPC membranes was not affected by photopolymerization of SorbPC. The photodestabilization of dioleoylPE/SorbPC (3:1) liposomes required the presence of oligolamellar liposomes. NMR spectroscopy of extended bilayers of dioleoylPE/SorbPC (3:1) showed that the photopolymerization lowers the temperature for the appearance of 31P NMR signals due to the formation of isotropically symmetric lipid structures. These observations suggest the following model for the photoinduced destabilization of liposomes composed of PE/SorbPC; photopolymerization induced phase separation with the formation of enriched domains of PE, which allows the close approach of apposed regions of enriched PE lamellae and permits the formation of an isotropically symmetric structure between the lamellae. The formation of such an interlamellar attachment (ILA) between the lamellae of an oligolamellar liposome provides a permeability pathway for the light-stimulated leakage of entrapped water-soluble reagents.

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The polymerization of lipid bilayer vesicles (liposomes) is an effective method to enhance the long-term colloidal and chemical stability of the aqueous suspensions.1 A host of methods to polymerize vesicles have been described since the first reports in the early 1980s.2 It was soon recognized that the polymerization of two-component vesicles, where only one component was polymerizable, resulted in phase separation of the lipids into polymeric and monomeric domains.3"5 The polymerizable lipids form

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Due to the reactivity of the chromophore halogens removal of the toluoyl residues by sodium methoxide resulted in rapid displacement of the chloro substituents which prevented the isolation of the free deoxyriboside of 3b and led to the 2,4-dimethoxynucleoside 7. As shown by the conversion of 5a into 2, regioselective displacement of the halogen in position 4 can be accomplished under conditions which maintain the protecting groups of the sugar moiety.In einer von uns unlangst durchgefuhrten Untersuchung konnten wir zeigen, daB 2,CDichlor-7H-pyrrolo[2,3-d]pyrimidin (3 b) in guter Ausbeute regioselektiv an N-7 mit l-Brom-2,3,5-tri-Obenzylarabinofuranose glycosyliert werden kann. Das dabei entstehende Arabinonucleosid besitzt ein hohes Potential fur die Synthese von Nucleosiden'). Im folgenden versuchen wir den Chromophor 3b auch fur die Darstellung von P-~-2'-Desoxynucleosiden, hier speziell fur die Synthese von 7-Desaza-2'-desoxyxanthosin (1 a) und 7-Desaza-2'-desoxyspongosin (2) einzusetzen.Die Purin-Stammnucleoside von 1 a und 2 sind seit langerem bekannt. 2'-Desoxy-2-methoxyadenosin2) wurde von Broom et. al. 3, aus einem 2,4-Dichlorpurin-P-~-2'-desoxyribosid durch selektiven Halogenaustausch erhalten, wahrend 2'-Desoxyxanthosin enzymatisch mittels Purinnucleosid-Phophorylase aus Xanthin und Desoxyrib~se-l-phosphat~~~) hergestellt wurde.

In THF at room temperature, 1 reacts with less reactive dienophiles such as 7 -11 (Table 1) to give the cycloadducts 12[61 in high yield; intermediate radical ions are not detected. The adducts 12a -12d split off two equivalents of dimethylamine at 140-160°C under acid catalysis with formation of the compounds 13a-13d (yield 50-70%).

Ein geschlossenes Gefäß molekularer Dimension, das durch Ansäuern geöffnet werden kann, besteht aus einer synthetischen Vesikel, deren Poren reversibel mit einem „Stopfen”︁ aus 1 verschlossen werden könne. Eine Voraussetzung für das Verschließen war die Verwendung einer Membran aus einem ungeladenen Bola‐Amphiphil und dem Kanalbildner Monensinpyromellitat.