Synthesis and evaluation of a novel Rhodamine B pyrene [2]rotaxane as an intracellular delivery agent for doxorubicin.

A novel Rhodamine B-derivatized host [2]rotaxane, containing a dibenzyl-24-crown-8 (DB24C8) ring as the wheel and a pyrene as another fluorophore blocking group, was designed, synthesized and structurally characterized. A comparison of the (1)H NMR spectra of RhBPy [2]rotaxane with those of and DB24C8, nuclear Overhauser effect spectroscopy (NOESY), mass spectrometry and fluorescence spectroscopy confirmed the interlocked nature of RhBPy [2]rotaxane. The temperature dependence of the rotaxane studied by (1)H NMR spectroscopy further demonstrated that RhBPy [2]rotaxane can be applied as a molecular switch. RhBPy [2]rotaxane has also been demonstrated to be an efficient transport agent for delivering the cancer drug doxorubicin (DOX) into tumor cells. Indeed, DOX delivered by RhBPy [2]rotaxane could effectively inhibit tumor cell growth.