4-amino-1,8-naphthalimide azetidine fluorescent indicators and cellular imaging agents

Three 4-amino-1,8-naphthalimides appended with azetidine and substituted at the imide position with methyl 1 , dimethylaminoethylene 2 and methyleneferrocene 3 were synthesised. Compounds 2 and 3 were designed as photoinduced electron transfer switches for protons and oxidants while 1 is a model dye. The fluorescent indicators were studied by UV–visible absorbance, fluorescence and circular dichroism spectroscopy in aqueous methanol. The circular dichroism of 2 exhibits a significant change in the ellipticity of calf-thymus DNA while no change was observed with 1 and 3 . The DNA binding constant of 2 was determined by absorption and fluorescence spectroscopy. The cytotoxicity and cellular fluorescent imaging properties were tested on four human breast cancer cells MCF-7, T47D, MDA-MB-231 and MDA-MB-468 by phase contrast and confocal fluorescence microscopy. Incubation of 1 and 2 within MCF-7 cells reveals localization in the nucleus. Phase contrast images of incubated MDA-MB-468 cells did not reveal any distortion in the morphology of the cells. Moderate cytotoxicity was observed with 2 across all cell lines while no antiproliferation activity was observed with 1 and 3 confirming the significance of the dimethylaminoethylene towards cytotoxicity, and the non-cytotoxic character of the azetidine moiety. • A series of 4-amino-1,8-naphthalimide azetidine dyes were synthesised. • The dyes emit a green emission in solution and within living cells. • The dimethylaminoethylene moiety increases cytotoxicity while the azetidine moiety is non-cytotoxic. • fluorescent imaging was performed in MCF-7 and MDA-MB-468 cancer cells.