Several factors reduce the efficacy of natural peptides as drug candidates; chief among these is their rapid digestion by human proteases. Over the last few decades, a number of strategies have been employed to increase the enzymatic stability of peptides, including the introduction of non-natural amino acids. This study aims at the investigation of the effect of side chain fluorination on the stability of peptides in human blood plasma. Ten model peptides with different non-natural amino acids were designed, synthesized and subjected to enzymatic degradation in human blood plasma. The stability of the studied peptides was followed by HPLC analysis and compared to the control peptide built with only proteinogenic residues. Four main hydrolysis products were detected and identified by mass spectrometry, three of them being characteristic cleavage products of the serine protease Elastase. A final enzymatic study with isolated Elastase validated then the outcome of the plasma study. This case study contributes to the application of fluorinated amino acids in the design of proteolytically stable peptides and proteins with potential clinical relevance.
