Abstract
Four new Aib-containing cyclopentapeptides have been synthesized by cyclization of the corresponding linear pentapeptides using the diethyl phosphorocyanidate (DEPC)/EtN(iPr)2 method. The linear precursors were prepared via the 'azirine/oxazolone method', i.e., the Aib units were introduced by the reaction of amino acids or peptide acids with a 2,2-dimethyl-2H-azirin-3-amine, followed by selective hydrolysis of the terminal amide function. Most remarkably, cyclo[(Aib)5] exists in CDCl3 solution in a symmetrical conformation, i.e., no intramolecular H-bonds are detectable.
Arnhold, Franziska S