A class of novel nitronyl nitroxide labeling basic and acidic amino acids : Synthesis, application for preparing ESR optionally labeling peptides, and bioactivity investigations

Abstract Aimed at optional ESR label 2-(4′-hydroxyl)phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl was introduced into the guanido of l -Arg-OH, the ω-amino group of l -Lys-OH with methylcarboxyl as a linker, and into the β-carboxyl of l -Asp-OH and the γ-carboxyl of l -Glu-OH with ethylamino as a linker. It was explored that the synthetic 30 novel ESR labeling amino acid derivatives were stable enough to the reaction conditions of peptide synthesis. Their incorporation led to 12 novel ESR optionally labeling PAK, RGDS, RGDV, and ECG. A series of NO related chemical tests, the in vitro and in vivo assays of these peptides confirmed that this strategy was practical.