N-terminus FITC labeling of peptides on solid support: the truth behind the spacer

Abstract Fluorescein isothiocyanate(FITC) is an amine reactive derivative of fluoresceindye that has wide ranging application in biochemistry. It has been extensively used to label peptides and proteins. However, its use in solid phase peptide synthesisis restricted. Indeed, in acidic conditions required for linker cleavage, N-ter FITC-labeled peptides undergo a cyclization leading to the formation of a fluoresceinwith subsequent removal of the last amino acid. This can be avoided when a spacer such as amino hexanoic acidis used or if non-acidic cleavage is operated to release targeted peptidefrom the resin.