Non-canonical amino acids bearing thiophene and bithiophene: synthesis by an Ugi multicomponent reaction and studies on ion recognition ability

Novel thienyl and bithienyl amino acids with different substituents were obtained by a multicomponent Ugi reaction between a heterocyclic aldehyde, an amine, an acid and an isocyanide. Due to the presence of the sulphur heterocycle at the side chain, these unnatural amino acids are highly emissive and bear extra electron donating atoms so they were tested for their ability to act as fluorescent probes and chemosensors in the recognition of biomedically relevant ions in acetonitrile and acetonitrile/water solutions. The results obtained from spectrophotometric/spectrofluorimetric titrations in the presence of organic and inorganic anions, and alkaline; alkaline-earth and transition metal cations indicated that the bithienyl amino acid bearing a methoxy group is a selective colorimetric chemosensor for Cu2+, while the other (bi)thienyl amino acids act as fluorimetric chemosensors with high sensitivity towards Fe3+ and Cu2+ in a metal-ligand complex with 1:2 stoichiometry. The photophysical and ion sensing properties of these amino acids confirm their potential as fluorescent probes suitable for incorporation into peptidic frameworks with chemosensory ability.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 (F-COMP-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.info:eu-repo/semantics/publishedVersio

Novel alanines bearing an heteroaromatic side chain: synthesis and studies on fluorescent chemosensing of metals cations with biological relevance

A family of novel thienyl-benzoxazol-5-yl-L-alanines, consisting of an alanine core bearing a benzoxazole at the side chain with a thiophene ring at position 2, substituted with different (hetero)aryl substituents, was synthesised in order to study the tuning of the photophysical and chemosensory properties of the resulting compounds. These novel heterocyclic alanines and a series of structurally related bis-thienyl-benzoxazolyl-alanines 3g-j were evaluated for the first time in the recognition of selected metal cations with environmental, medicinal and analytical interest such as Co2+, Cu2+, Zn2+ and Ni2+, in acetonitrile solution, with the heterocycles at the side chain acting simultaneously as the coordinating and reporting units, via fluorescence changes. This behaviour can be explained by the involvement of the electron donor heteroatoms in the recognition event, through complexation of the metal cations. The spectrofluorimetric titrations showed that thienyl-benzoxazolyl-alanines 3a-j and 4a,b were non-selective fluorimetric chemosensors for the above mentioned cations, with the best results being obtained for the interaction of Cu2+ with bis-alanine 3j and deprotected alanines 4a,b. The encouraging photophysical and metal ion sensing properties of these thienyl-benzoxazolyl-alanines suggest that they can be used to obtain bioinspired fluorescent reporters for metal ion such as peptides/proteins with chemosensory/probing ability.Thanks are due to Fundação para a Ciência e Tecnologia (FCT) for a PhD grant to R. C. M. Ferreira (SFRH/BD/86408/2012), and FEDER (European Fund for Regional Development)-COMPETEQREN-EU for financial support through the Chemistry Research Centre of the University of Minho (Ref. UID/QUI/00686/2013 and UID/QUI/0686/2016). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT.info:eu-repo/semantics/publishedVersio