Simple synthetic methodology has been used to create biotinylated pyridyl cholate lipids that can undergo multiple self-assembly events when inserted into phospholipid vesicles; Pd(II) links cholates into transmembrane lipids, while avidin laterally clusters these complexes together and concomitantly assembles the vesicles into aggregates. The transmembrane assembly of cholates by Pd(II) "opened" the ion channels, whereas avidin addition produced vesicle aggregates, giving a system that mimicked both transmembrane transport and cellular adhesion. Complexation of these Pd(II)-linked cholates by avidin gave a measurable decrease in ion flow, suggesting some channels became blocked or were prevented from adopting the optimum geometry for ion conduction. This reflects the importance of spatially appropriate preorganisation when generating active supramolecular assemblies.
[reaction: see text] Enamine [2 + 2] cycloadditions can be achieved in useful yields simply by stirring a mixture of an aldehyde, diethylamine, a dialkyl fumarate, and potassium carbonate in acetonitrile at 25 degrees C, conditions that are compatible with the presence of a potential leaving group on the beta-position of the intermediate enamine. Methylation and elimination of the product cyclobutanes completes a mild nonphotochemical route to functionalized cyclobutenes.
Cyclobutane derivatives Q 0022Functionalized Cyclobutenes via Multicomponent Thermal [2 + 2] Cycloaddition Reactions. -The reaction of an aldehyde, a secondary amine and a fumarate (or maleate) affords 3-aminocyclobutane-1,2-dicarboxylates as single isomers or diastereomeric mixtures. The conversion into the desired cyclobutenes is performed via methylation and elimination reactions. Products (VIII) derived from (IV) undergo ring opening at elevated temperature to give (Z,E)-dienes (IX). In contrast, cyclobutenes derived from isomers (V) react spontaneously to afford (E,E)-dienes (XI). -(SHELDRAKE, H. M.; WALLACE*, T. W.; WILSON, C. P.; Org. Lett. 7 (2005) 19, 4233-4236; Sch. Chem., Univ. Manchester, Manchester M13 9PL, UK; Eng.) -Klein 02-066
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