A one-step synthetic procedure for the radical CH alkylation of BODIPY dyes has been developed. This new reaction generates alkyl radicals through the oxidation of boronic acids or potassium trifluoroborates and allows the synthesis of mono-, di-, tri-, and tetraalkylated fluorophores in a good to excellent yield for a broad range of organoboron compounds. Using this protocol, multiple bulky alkyl groups can be introduced onto the BODIPY core thus creating solid-state emissive BODIPY dyes.

We report a synthetic route to BODIPY–cholesterol conjugates in which the key steps were Suzuki or Liebeskind–Srogl cross-coupling of cholesterol phenyl moieties with structurally diverse BODIPY scaffolds. All conjugates feature single-bonded and hydrophobic linkages between the fluorophore and sterol that are devoid of heteroatoms. Using HeLa cells, we show that these BODIPY–cholesterol analogues can be used simultaneously with the parent BODIPY–cholesterol for cell imaging and flow cytometry. The BODIPY–cholesterol analogues exhibit similar cellular localization in HeLa cells and show similar cholesterol efflux properties from THP-1 cells to HDL acceptors. These results demonstrate that the red-shifted BODIPY–cholesterol analogues behave in a manner similar to unlabeled cholesterol and are useful probes for simultaneous visualization of intracellular cholesterol pools and for monitoring cholesterol efflux from cells to extracellular acceptors.