Pseudopeptide fragments and local structures induced by an α-aminoxy acid in a dipeptide

An α-aminoxy acid residue has been introduced by liquid-phase procedures in a model dipeptide, by means of the amidoxy (CO–NH–O), oxime (CHN–O) and hydroxylamine (CH2–NH–O) pseudopeptide link. The structural properties induced by the three amide surrogates, which are not protonated at the physiological pH, have been studied in organic solution. In all three cases, the α-oxygen interacts with the adjacent amide NH to close a five-membered cycle. The amidoxy link gives rise to a very stable γ-like folded structure and the cis-oxime link to a β-like folded structure.