Synthesis of Oxasmaragdyrin–Amino Acid Conjugates

Abstract

A series of covalently linked oxasmaragdyrin‐amino acid and BF2‐oxasamaragdyrin–amino acid conjugates were synthesized by treating oxasmaragdyrin or its BF2 complex that contain a benzylhydroxyl group at one of the meso positions with an appropriate fluorenylmethyloxycarbonyl‐protected amino acid in CH2Cl2 in the presence of 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide·HCl/hydroxybenzotriazole under basic conditions at room temperature. The conjugates are stable, highly soluble in all organic solvents, and confirmed by HRMS. 1D and 2D NMR spectroscopic techniques were used to characterize the oxasmaragdyrin–amino acid conjugates. Absorption, fluorescence, and electrochemical studies of conjugates indicate that the conjugates strongly absorb and emit in visible‐NIR region with decent quantum yields, singlet state lifetimes and are stable under electrochemical conditions. Furthermore, the conjugates showed minimal change in their spectral and electrochemical properties relative to that of the unconjugated oxasmaragdyrin or its BF2 complex suggest that the characteristic features of the oxasmaragdyrin and its BF2 complex is retained in the conjugates, which will be a useful feature for Near‐IR fluorescence imaging and other applications.