Synthesis and Solid State Conformation of Tetrapeptide Amides Containing two Aib and two (αMe)Phe Residues – Use of Enantiomerically Pure 2‐Benzyl‐2‐methyl‐2H‐azirin‐3‐amines as (αMe)Phe‐Synthons

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A series of tetrapeptide amides containing two aminoisobutyric acids (Aib) and two α ‐methylphenylalanine (( α Me)Phe) units were prepared through the ‘azirine/oxazolone method’. New 2‐benzyl‐2‐methyl‐2 H ‐azirin‐3‐amines have been used for the selective introduction of ( S )‐ and ( R )‐( α Me)Phe, respectively. The solid‐state conformations of five tetrapeptide amides were determined by X‐ray crystallography. In all cases, two β ‐turns stabilize 3 10 ‐helical conformations and it was confirmed that, in contrast to proteinogenic amino acids, the configuration of ( α Me)Phe does not determine the screw sense of the helix.