Synthesis and Studies of Meso-Phenothiazinyl 3-Pyrrolyl BODIPY and Its Derivatives

Abstract

A fluorescent meso-phenothiazinyl 3-pyrrolyl BODIPY was synthesized in two steps. In the first step, 3formyl phenothiazine was condensed with pyrrole under acid-catalyzed conditions in CH₂Cl₂ to afford meso-phenothiazinyl dipyrromethane. In the second step, meso-phenothiazinyl dipyrromethane was oxidized with DDQ in CH 2 Cl 2 followed by the addition of pyrrole and subsequent complexation with BF 3 •OEt₂ afforded the fluorescent meso-phenothiazinyl 3-pyrrolyl BODIPY dye in 24% yield. The meso-phenothiazinyl 3-pyrrolyl BODIPY was oxidized with H 2 O 2 in CHCl 3 to afford another fluorescent dye, meso-phenothiazinyl-5,5 dioxide 3-pyrrolyl BODIPY (3.SO 2 ) in 89% yield. The mesophenothiazinyl 3-pyrrolyl BODIPY was formylated at the α-position of the appended pyrrole ring under Vilsmeier-Haack reaction conditions and the resulted α-formyl meso-phenothiazinyl 3-pyrrolyl BODIPY was reacted with two different diamines such as hydrazine hydrate (N 2 H 4 . H 2 O) and 1,4-diaminobenzene, in methanol at reflux to obtain the corresponding bis(meso-phenothiazinyl 3-pyrrolyl BODIPY)s in 75-89% yields. The meso-phenothiazinyl 3-pyrrolyl BODIPY and its derivatives were thoroughly characterized and studied by HR-MS, 1D & 2D NMR spectroscopy, absorption, fluorescence and theoretical techniques. The meso-phenothiazynyl 3-pyrrolyl BODIPY and its derivatives absorbs and emits strongly in the visible to NIR region with decent quantum yields. Biological evaluation of 3.SO 2 in A549 cells showed to stain cell membrane without permeabilization and lipid droplets in permeabilized cells. Cell morphology in presence of 3.SO 2 revealed no cytotoxic effect of the dye. Most importantly, comparison with commercial liphophilic dye, Dilinoleyl DiO (FAST DIO) revealed that 3.SO 2 is better suitable for fluorescence imaging in cells due to higher signal to noise ratio when tested at the same concentration. Finally, the most intense fluorescence signal was obtained with 561 nm excitation source making it suitable for complexing with green and far-red dyes for multiplex imaging.