Synthesis and characterization of water-soluble C 60 -peptide conjugates.

With the aim of developing biocompatible and water-soluble C 60 derivatives, three types of C 60 -peptide conjugates consisting of hydrophilic oligopeptide anchors (oligo-Lys, oligo-Glu, and oligo-Arg) were synthesized. A previously reported Prato reaction adduct of a biscarboxylic acid-substituted C 60 derivative was subjected to a solid phase synthesis for amide formation with N - terminal amines of peptides on resin to successfully provide C 60 -peptide conjugates with one C 60 and two peptide anchors as water-soluble moieties. Among three C 60 -peptide conjugates prepared, C 60 -oligo-Lys was soluble in water at neutral pH, and C 60 -oligo-Glu was soluble in buffer with a higher pH value, but C 60 -oligo-Arg was insoluble in water and most other solvents. C 60 -oligo-Lys and C 60 -oligo-Glu were characterized by 1 H and 13 C NMR. Photoinduced 1 O 2 generation was observed in the most soluble C 60 -oligo-Lys conjugate under visible light irradiation (527 nm) to show the potential of this highly water-soluble molecule in biological systems, for example, as a photosensitizer in photodynamic therapy.