Synthesis and biological evaluation of oxytocin analogues containing l-α- t-butylglycine [Gly(Bu t)] in positions 8 or 9

We report the solid phase synthesis and some pharmacological properties of seventeen new oxytocin (OT) analogues. Basic modification at positions 8 and/or 9 (introduction of l-α- t-butylglycine [Gly(Bu t )]) was combined with d-Cys 6, d-Tyr(Et) 2, Mpa 1 or Pen 1 modifications and their various combinations. We also present properties of two previously reported re-synthesized analogues ([Gly(Bu t ) 8]OT and [Mpa 1, Gly(Bu t ) 8]OT). The analogues were tested for rat uterotonic activity in vitro, in the rat pressor assay and for binding affinity to human OTR.