Synthesis and Ion Recognition Studies of Novel Benzimidazol-5-yl-L-Alanines

Some natural amino acids can be the precursors for unnatural amino acids by suitable synthetic transformations. Modification in the side chain is the basis for the synthesis of new amino acids, allowing functional interaction between the new modified amino acids and other compounds, by altering their chemical and photophysical properties, to have a wide variety of applications. Heteroaromatic systems containing in its structure potential chelating groups have the ability to act both in the recognition of ions and in the signaling of the recognition event because, when complexed, variation of their fluorescent properties may occur. Benzimidazole and its derivatives have been studied in ion recognition systems that display color changes or fluorescence quenching or enhancement upon binding. Furan and thiophene are also known for their very interesting photophysical properties, which enable their application as sensors and/or fluorescent markers. Therefore, new amino acids containing these associated units could be potential fluorimetric sensors for ions with improved photophysical properties. We now report the synthesis and photophysical characterization of novel benzimidazol-5-yl-L-alanines, by formation of an imidazole ring fused to the phenyl ring at the side chain of phenylalanine, to give a benzimidazole, with different five membered heterocycles as substituents. An interaction study with biologically important ions was carried out through spectrofluorimetric titrations.Acknowledgements: Thanks are due to Fundação para a Ciência e Tecnologia (FCT-Portugal) and FEDER-COMPETE for financial support through Centro de Química [PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302] and a PhD grant to C.I.C. Esteves (SFRH/BD/68360/2010). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER.