Sugar balls:: Synthesis and supramolecular assembly of [60]fullerene glycoconjugates

The synthesis and characterization of fully deprotected C-60 glycoconjugates 4 and 17 is reported. Bis(U-D-mannopyranosyl)malonamide 4 was obtained by using nucleophilic cyclopropanation chemistry, which in general is a very versatile method for fullerene functionalization. Fullerene sugar 17 contains two dendritic alpha-D-mannopyranosides that are connected through two adjacent imino bridges to the all-carbon framework. In this adduct-type of C-60, which represents a 1,9-dihydro-1a-aza-1(2)a-homo(C-60-I-h)[5,6]fullerene derivative, the entire 60-pi-electron system of the fullerene core is retained. This architecture allows the basic cleavage of the acetyl protection groups of precursor adduct 16 without destruction of the core structure of the fullerene sugar. Dendritic glycoconjugate 17 containing six deprotected sugar building blocks is very soluble in water. The amphiphilic nature of 17 with its cone-shaped structure forces the formation of small supramolecular aggregates in aqueous solutions to shield the hydrophobic fullerene units from the water sub-phase. DOSY NMR spectroscopy and TEM investigation reveal micellar sugar balls with an extremely narrow size distribution of around 4 nm. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).