Preparation and Supramolecular Properties of Unadulterated Glycosyl Liposomes from a Bis(α-D-mannopyranosyl)[60]Fullerene Conjugate

The bis(alpha-D-mannopyranosyl)-[60]fullerene conjugate 3 was prepared by thermal coupling of C60 and either 2-azidoethyl 2,3,4,6-tetra-O-acetyl- or 2,3;4,6-di-O-isopropylidene-alpha-D-mannopyranoside (Scheme). Compound 3 was found to readily self-assemble. Dynamic-light-scattering (DLS) and atomic-force microscopy (AFM) experiments supported that the amphiphilic compound gives rise to nano-sized supramolecular structures during sugar deprotection (Ac-group removal) performed in MeOH/CH2Cl2 solution. Encapsulation studies with an aqueous suspension of 3 showed that the self-assembling structure envelopes Ba2+ and the fluorescent dye Acridine Red during its formation, which indicates that it resembles a bilayer vesicle or an unadulterated liposome with an inner hollow space. In addition to this notable property, the unique molecular geometry of the spatially arranged mannosyl surface residues of 3 gives rise to strong binding of the carbohydrate-recognizing lectin Con A. Hence, the polar amphiphilic end of 3 mimics the structure of 3,6-branched tri-alpha-D-mannoside (6; Fig. 3), a natural ligand of the Con A protein.