Molecular umbrella-assisted transport of glutathione across a phospholipidmembrane

A di-walled molecular umbrella (1a) has been synthesized by acylation of th e terminal amino groups of spermidine with cholic acid, followed by condens ation with bis{3-O-[N-1.2,3-benzotriazin-4(3H)-one]yl}- 5,5 ' -dithiobis-2- nitrobenzoate (BDTNB), anti displacement with glutathione (gamma -Glu-Cys-G ly, GSH). Replacement of the sterol hydroxyls with sulfate groups, prior to displacement with GSH, afforded a hexasulfate analogue 1b. Both conjugates have been found to enter large unilamellar vesicles (200 nm diameter, extr usion) of l-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and to r eact with entrapped GSH to form oxidized glutathione (GSSG). Evidence for v esicular entry has come from the formation of oxidized glutathione (GSSG) w ithin the interior of the vesicle, the appearance of the thiol form of the umbrella (USH), and the absence of release of GSH into the external aqueous phase. Results that have been obtained from monolayer experiments, togethe r with the fact that the heavily sulfa :ed conjugate is able to cross the p hospholipid bilayer, have yielded strong inferential evidence for an "umbre lla-like" action of these molecules as they cross the lipid bilayer.