Azopeptides: Synthesis and Pericyclic Chemistry.

Azopeptides possess an imino urea as an amino amide surrogate in the sequence. Azopeptides were synthesized by oxidation of aza-glycine residues and employed in pericyclic chemistry. Diels-Alder cyclizations and Alder-ene reactions on azopeptides enabled construction of constrained aza-pipecolyl and reactive aza-allylglycyl residues. X-ray crystallographic analyses of azopeptide 16a and azapeptides 30a and 35a provided insight into imino urea configuration and conformational affects of cycloalkane side chains at the semicarbazide α- and β-nitrogen, respectively.