Synthesis and Investigation of Linker-Free BODIPY-Gly Conjugates Substituted at the Boron Atom.

An efficient synthesis of boron-functionalized cyclic BODIPY-Gly conjugates, using commercially available -protected glycine amino acids and a BF-BODIPY moiety as starting materials, is reported. The existence of two conformers (up and down) is revealed through comprehensive DFT calculations and H and B NMR analyses. The experimental and computational results indicate that all BODIPYs are stable in aqueous solutions at neutral pH and that Fmoc-BODIPY () is more stable than Ac-BODIPY () in the presence of trifluoroacetic acid (TFA). In part due to their enhanced rigidity, all BODIPY-Gly conjugates display increased fluorescence quantum yields (0.6 < Φ < 0.9) relative to the corresponding BF-BODIPY, making them excellent candidates for fluorescence imaging applications.