Recognition of metallic ions by unnatural amino acids bearing nitrogen and oxygen heterocycles : synthesis and interaction studies with relevant metals

Abstract

Molecular recognition phenomena play important roles in a variety of physical, chemical, and biological events, and are a field of convergence of knowledge from organic, inorganic, analytical and physical chemistry. Therefore, in recent years there have been considerable efforts on the design, synthesis and application of novel fluorescent molecular probes that selectively and specifically respond to the presence of specific analytes (ions and neutral molecules), as fluorescence allows the highest sensitivity (up to detection of single molecules) in sensory applications [1]. Metal ions are key parts in all aspects of human life, and recently amino acids have attracted great interest for constructing bio-analogous metal-organic frameworks materials since amino acid residues are the origin for the highly selective substrate- binding ability of proteins [2]. Metal coordination to amino acids and peptides could give rise to metal-organic frameworks in which amino acid residues may offer flexible hydrogen bonding to induce molecular recognition. The design of peptides that coordinate metals, by incorporation of modified amino acids, has potential applications in the study of protein-protein interactions mediated by metals, protein binding to nanoparticles and metal surfaces, and the development of selective chemosensors for metals for use in vitro and in vivo [3]. Bearing these facts in mind and following our research interests that include the synthesis and application of fluorimetric probes for metallic ions based on heterocycles and amino acids [4], we now report the synthesis and evaluation of unnatural alanine derivatives as fluorimetric chemosensors for the recognition of metallic ions through the introduction of five-membered nitrogen and oxygen heterocycles as coordinating/reporting units in a benzoxazolyl-alanine core in order to obtain new chemosensors