Synthesis and cellular properties of Near-IR BODIPY–PEG and carbohydrate conjugates

A series of red and near-IR fluorescent BODIPY conjugates, containing either one or two indolylstyryl groups at the 3- and/or 5-positions and a low molecular weight PEG or carbohydrate group, were synthesized using a Cu(I)-catalyzed azide–alkyne Huisgen cycloaddition (‘click’ reaction). All BODIPY conjugates show emission and fluorescence quantum yields in the ranges of 642–732 nm and 0.24–0.56, respectively, and Stokesʹ shifts of ca. 30 nm. In vitro cellular investigations using human carcinoma HEp2 cells showed that all BODIPYs are non-toxic, both in the absence and presence of light (1 J/cm2), up to 100 μM concentrations. The PEG and galactose conjugates were more efficient at cell internalization than the unconjugated BODIPYs. The mono-indolylstyryl–BODIPYs showed higher cellular uptake (about five-fold) compared with the di-indolylstyryl–BODIPYs, and higher fluorescence quantum yields.