CONFORMATIONAL STUDIES OF OXYTOCIN ANALOGS

Oxytocin(OT) has two intrisic chromophores: the phenol ring of Tyr2 an d the Cys1-Cys6 disulphide bridge. Their emission and absorption chara cteristics indicate that tyrosyl fluorescence is attenuated by fluores cence-energy transfer to the disulphide bridge what can be used to cal culate an average inter-chromophore distance in the cyclic-hexapeptide fragment of oxytocin. Apart from the conformation of the cyclic part, we are interested in the structure of the acyclic tripeptide and its interaction with the cyclic fragment. We therefore prepared oxytocin ( 1), [Trp9]OT (II) and [Val2, Phe(p-F)9]OT (III) for the purpose of det ermination of the average distance between the chromophores Tyr2 and T rp9 (analogue II) and Phe-(p-F)9 and the disulphide bridge (analogue I II). The inter-chromophore distances determined by fluorescence spectr oscopy are similar to those obtained from molecular mechanics calculat ions.