title: 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-Phe(1)-cyclo(Cys(2)-Tyr(3)-D-Trp(4)-Lys(5)-Thr(6)-Xxx(7))-Thr(8)- NH2 (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 position-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 -Tyr(3)-D-Trp(4)-Lys(5)-Thr(6)-. However, the disulfide conformation differs in the analogs, with 1 and 3 having a left-handed and 4 a right-handed disulfide chirality.
mesh_terms: D000595:Amino Acid Sequence; D004220:Disulfides; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D010396:Penicillamine; D011487:Protein Conformation; D011957:Receptors, Opioid / Q000378:metabolism*; D013004:Somatostatin / Q000031:analogs & derivatives*; D013329:Structure-Activity Relationship
chemical_list: D004220:Disulfides; D011957:Receptors, Opioid; D013004:Somatostatin; D010396:Penicillamine