Synthesis of boron dipyrromethene fluorescent probes for bioorthogonal labeling

Seven 5-substituted 3-hydrazinyl derivatives of 3a, 4a-diaza-4,4-difluoro-8-phenyl boron dipyrromethene (BODIPY) were prepared for use as bioorthogonal fluorescent labels of aldehydes and ketones. The absorption energies can be tuned to absorb visible light over a large span of wavelengths by changing the nature of the 5-substituent. Optical properties of the hydrazones formed with these molecules are affected by the nature of the electrophile such that aliphatic and aromatic hydrazones can be differentiated from each other and from unreacted fluorophore.