3-amino-2H-azirines undergo a number of ring opening reactions. The cleavage of the azirine-N(1), C(3) double bond leads thereby to synthons which can be considered as amino acid equivalents. The reaction of 3-amino-2H-azirines with carboxylic acids yields N-acyl amino acid amides, which can be converted by a selective amide cleavage to the corresponding N-acyl amino acids. 2-Oxazolin-5-ones are intermediates of this amide cleavage. This reaction sequence has been used for the extension of peptide chains as well as for a number of heterocycle syntheses. Likewise, the described synthesis of cyclic depsipeptides and lactones by direct amide cyclization proceeds via 2-oxazolin-5-one intermediates. The selective amide cleavage was also applied to a novel method for the resolution of enantiomeric amino acid derivatives.