Conjugation of a phenanthrene‐imidazole fluorophore with the chondroitin sulfate generated from Escherichia coli K4 polysaccharide

Escherichia coli K4 expressed a fructosylated chondroitin (K4), which had a chondroitin structure after the defructosylation treatment. Polysaccharide K4 as a preferred precursor was modified to produce chondroitin sulfate A (CSA). Here, glycosaminoglycans including K4, defructosylated K4, and CSA were conjugated with fluorophore A, which were optimized under three reaction conditions to give the maximum DS of 2.9, 6.5, and 8.5%, respectively. All of conjugates displayed luminescence response linearly to concentration. And they exhibited good storage stability in luminescence and dispersion within 24 h. The conjugate CSA‐A with substituted degree of 6.4% was chosen for the bioimaging study in vitro. CSA‐A showed nontoxic to astrocytes with concentrations lower than 100  μ g/ml. It was internalized effectively by astrocytes after incubation for 24 h.