Synthesis and Spectroscopic Properties of Rosamines with Cyclic Amine Substituents

There is a close structural similarity between rosamines A and rhodamines B, yet a diversity of structures in the rosamine class and their spectral properties have yet to be explored in depth. This manuscript describes a concise, scalable, solution-phase method to obtain rosamines 1-5 and 12-15, which include some water-soluble derivatives. In one test case (for 15) an illustrative protein conjugate was also formed. Throughout these products were isolated and purified, and the syntheses were found to be scalable. Further, the rosamines with these cyclic amine substituents display solvent-dependent fluorescence intensities, and high quantum yields in chlorinated hydrocarbons. In some cases the nature of the cyclic amine substituent was shown to modulate the fluorescence of the parent molecules in pH-dependent ways. The ring size of those amine substituents also correlated with some of their spectroscopic properties. Several water-soluble rosamines were prepared from some of the addition products 1-5, and one of these, 15, was efficiently conjugated to avidin via an amide linkage. The spectroscopic properties of 15 and 15-avidin in aqueous media were very similar.