Synthesis of [2‐p‐Fluorophenylalanine]oxytocin and its Desamino Analogue Using the S‐Acetamidomethyl Protecting Group

Abstract [2‐ p ‐Fluorophenylalanine]oxytocin ( 1a ), desamino‐[2‐ p ‐fluorophenylalanine]oxytocin ( 1b ), and desamino‐oxytocin ( 2 ) have been synthesised via intermediates containing S‐acetamidomethyl‐cysteine. The protected linear peptides were built up using both stepwise and fragment‐condensation procedures, and the S‐protecting groups were removed by iodine with simultaneous formation of the disulfide bridge. The uterotonic activities in vitro of the analogues have been determined. The close similarity of the 19 F‐NMR. spectra indicates that the p ‐fluorbenzyl side chain is freely exposed to the solvent in the disulfide‐bridged hormone analogues as well as in their S‐protected, acyclic precursors.