Novel N-(2,2-dimethyl-2H-azirin-3-yl)-L-prolinates as Aib-Pro synthons

The syntheses of phenacyl N-(2,2-dimethyl-2H-azirin-3-yl)-L-prolinate and allyl N-(2,2-dimethyl-2H-azirin-3-yl)-L-prolinate are reported. Reactions of these 2H-azirin-3-amine derivatives with Z-protected amino acids have shown them to be suitable synthons for the Aib-Pro unit in peptide synthesis. After incorporation into the peptide by means of the 'azirine/oxazolone method', the C-termini of the resulting peptides were deprotected selectively with Zn in AcOH or by a mild Pd-0-promoted procedure, respectively.