Macrocyclic peptides II. Synthesis and structure of a novel dipeptide, (2S,3′S)‐2‐(2′‐oxo‐3′‐methylpiperazin‐1′‐yl)‐propanoic acid, and its use as the unit of cyclic peptides

A new cyclic compound [(2S,3′S)‐2‐(2′‐oxo‐3′‐methylpiperazin‐1′‐yl)‐propanoic acid] obtained using (2S,7S)‐2,7‐dimethyl‐3,6‐diazaoctanedioic acid as a starting material was derived from N‐t‐butyloxycarbonyl‐(2S,3′S)‐2‐(2′‐oxo‐3′‐methylpiperazin‐1′‐yl)‐propanoic acid in order to determine the molecular structure by X‐ray crystal analysis. Two new macrocyclic peptides were prepared using the above cyclic compound and sarcosine as peptide units.