Distinct rhodamine B derivatives exhibiting dual effect of anticancer activity and fluorescence property

Abstract

Design and application of novel Rhodamine B amide derivatives achieved especially with simple secondary amines, and furthermore exhibiting fluorescence property and anticancer activity is not reported elsewhere. Further functionalization of rhodamine B at the carboxylic acid group with selected secondary amines generated amides, avoiding cyclization and simultaneously sustaining fluorescence. Currently, we have designed and developed three well defined novel rhodamine B amide derivatives by reacting rhodamine B (RHB) with thiomorpholine, bis-(2-chloroethyl) amine and morpholine (the side chains of several anticancer drugs) via rhodamine B acid chloride which resulted in fluorophores namely rhodamine B thiomorpholine amide (1), rhodamine B bis(2-chloroethyl)amine amide (2) and rhodamine B morpholine amide (3). All the three RHB amides were thoroughly characterized using analytical techniques like FT-IR, Mass, 1H NMR, 13C NMR spectroscopy and HPLC. Obtained compounds displayed molecular material attributes as well as anticancer activity. The wavelength of maximum absorption and emission of solutions occurred at ~560 nm and ~583 nm. Quantum yields (Φf = 0.40) and average fluorescence decay (~1.60 ns) of amides was comparable to RHB (1.72 ns). Optical bandgap of solids revealed semiconducting property (~ 2.9 eV). Acquired rhodamine B amides were found to be insensitive over a wide range of pH i.e. from 2 to 10 suggesting their plausible utility in biological labeling, moreover, showed potential anticancer activity against B16F10 (murine melanoma cells), MDA-MB231 (human breast cancer cells), A549 (human lung cancer cells) while they displayed less toxicity to normal HEK 293 (human embryonic kidney) cells. Interestingly, the cellular uptake study manifested that more quantity of the compound were taken up by the cancer cells compared to normal cells which indicate that these amides might become potential candidates to be developed as theranostic agents.