Synthesis, optical properties and binding interactions of a multivalent glycocluster based on a fluorescent perylene bisimide derivative

A water-soluble fluorescent perylene bisimide derivative, PBI-CI-Man, grafted with six mannose groups was synthesized. Its optical properties were investigated by UV-vis and fluorescence spectra, which indicated that compound PBI-CI-Man exists in the monomer state at low concentrations and exhibits high fluorescence with a fluorescence quantum yield of 59.9% in water. Furthermore, the binding interactions of PBI-CI-Man with Con A were studied by fluorescence spectra, CD spectra, turbidity assays and ELLA experiments. The almost complete quenching of the fluorescence upon binding with Con A was observed, with a binding constant of 2.4 x 10(7) M-1 (4.0 x 10(6) M-1 for monomeric mannose, valency corrected), nearly 3 orders of magnitude higher than that of monovalent mannose ligands (alpha-MMP). The ELLA experiments indicated that PBI-CI-Man, as a multivalent glycocluster, exhibits a strong binding interaction with Con A with an IC50 value of 34 mu M (204 mu M, valency corrected), 7 times stronger than that of the reference compound (alpha-MMP).