New boron-based coumarin fluorophores for bioimaging applications

Abstract

The synthesis and characterisation of five new boron-based coumarin fluorophores are reported, with key structural variations involving the linker at the C3-position (hydrazone or imine) of the 7-(diethylamino)-coumarin (7DEAC) core and the terminal boron moiety (i.e. boronic acid or closo-1,2-carborane). All the coumarin derivatives were found to display significant bathochromic shifts relative to the parent 7DEAC, with conjugate ICCb displaying the greatest overall shift. Confocal microscopy studies with A549 lung cancer cells showed clear differences in the observed intra-cellular distributions of the fluorophores. The polar boronic acid species (HCoBA, HCmBA and HCpBA) were found to localise in the endoplasmic reticulum. In contrast, the lipophilic closo-1,2-carborane derivatives (HCCb and ICCb) were found to localise within lipid droplets (LDs), showcasing the future potential for these probes to be utilised as stains for LD observations by means of confocal microscopy.