Spectroscopic Characterization of a Coumarin-Labelled Therapeutic Tetrapeptide

The labelling of biomolecules with organic fluorophores is widely used for analytical applications and for the study of the dynamics of living systems. Coumarins are well known fluorophores that have been reported as fluorescent labels and probes, due to their extended spectral range, high fluorescence quantum yields, good photostability and solubility in common solvents. More recently, they have also been applied in the synthesis of photolabile protecting groups to release relevant biomolecules by UV and visible light irradiation.As most amino acids are poor UV-absorbing, fluorescence labelling is often employed in peptides and, for example, a peptide or protein bound to a fluorescent moiety may be an important tool for conformational studies of protein-protein and ligand-receptor interactions. The tetrapeptide H-Ala-Ala-Pro-Val-NH₂ (AAPV) is an important inhibitor of the enzyme human neutrophil elastase, and a few studies have been conducted for the use of this peptide as a therapeutic agent for transdermal delivery.Considering these facts, the present work describes the synthesis of the tetrapeptide labeled at the C-terminus with 7-methoxycoumarin and its spectroscopic characterization by UV-vis and fluorescence spectroscopy in different organic solvents and mixtures with aqueous HEPES solution, in order to simulate physiological conditions. Acknowledgements: Thanks are due to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for financial support to the NMR Portuguese network (PTNMR, Bruker Avance III 400-Univ. Minho), FCT and FEDER (European Fund for Regional Development)-COMPETE-QREN-EU for financial support to Research Centre of Chemistry, CQ/UM [PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302)].