Proton n.m.r. investigation of conformational influence of penicillamine residues on the disulfide ring system of opioid receptor selective Somatostatin derivatives

Abstract
Three cyclic disulfide analogs related to somatostatin, D-Phe1- Cys2-Tyr3-D-Trp4-Lys5-Thr6-Xxx7-Thr8NH2 (where Xxx = L-Pen 1; L-Cys 3; or D-pen 4) were examined in DMSO-d6 by one- and two-dimensional proton n.m.r. spectroscopy in order to analyze the conformational influence of the postion-7 residue on the 20-membered disulfide ring. From these studies it was concluded that all three analogs maintain a .beta. II'' turn solution conformation for the core tetrapeptide -Tyr3-D-Trp4-Lys5-Thr6-. However, the disulfide conformation differs in the analogs, with 1 and 3 having a left-handed and 4 a right-handed disulfide chirality.

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