[en] Oxytocin a cyclic peptide whose sequence CYIQNCPLG was the first biologically relevant peptide to be synthesized. Synthesis by Boc strategy using p-methyl benzhydrylamine resin and also by Fmoc using Rink p-methyl benzhydrylamine resin was carried out with high yields. The crude peptide was cycled with 10% dimethylsulfoxide, characterized by mass spectrometry and nuclear magnetic resonance showing the presence of two isomers