Crystal Structure of the C-Terminal Tetrapeptide of Oxytocin

WE have determined the crystal structure of the protected, C-terminal tetrapeptide of oxytocin S-benzyl-L-cysteinyl-L-prolyl-L-leucyl-glycine amide as well as of its virtually isomorphous seleno-analogue. The crystal structure analyses of these two peptides were undertaken because of our interest in the conformation of the tetrapeptide in isolation as well as when attached to the ring in the complete oxytocin molecule. The seleno-analogue provided an opportunity to compare sulphur and selenium stereochemistry.