A general modular approach for the solubility tagging of BODIPY dyes

We describe a general and practical strategy for the direct one-step incorporation of a tunable solubility module at the boron atom of F-BODIPY dyes. The tethering reaction uses easy-to-handle reagents, has broad functional group compatibility and proceeds under mild conditions without requiring any pre-functionalization of the starting F-BODIPY to yield the solubility-tagged O-BODIPY derivative in 51–86% yield. The module can be introduced at the end of the synthetic route without perturbing the fluorophore scaffold, thus minimizing difficulties in product isolation. Its orthogonal geometrical arrangement with respect to the plane of the BODIPY chromophore hampers intermolecular aggregation processes that quench fluorescence, while the covalent attachment to the boron atom has a minimal effect on the absorption properties. Fully water-soluble and hydrolytically stable BODIPYs were prepared by incorporating either neutral (tetra- and octaethylene glycol chains) or zwitterionic (sulfobetaine) hydrophilic tags in the module. The new dyes are valuable live cell imaging probes that ameliorate the undesired partitioning into lipophilic compartments that is often observed for standard BODIPYs. This strategy can be readily adapted to the general and highly practical post-synthetic introduction of new functionalities into F-BODIPY dyes, including phase-tagging, by appropriately choosing the nature of the chemical tags attached to the module.