Abstract
Structural and dynamic properties of [8‐arginine]vasopressin and a class of highly potent vasopressin V1 antagonists which contain 3‐mercepto‐3, 3‐cyclopentamethylene propionic acid (Mca) in position 1 of the vasopressin sequence have been determined. On the basis of two‐dimensional NMR experiments in dimethyl sulfoxide solution, interproton distances were derived according to which model conformations were built and refined using molecular dynamics simulations. The antagonistic property was found to be related to an inversed chirality of the disulfide bridge. In all investigated molecules, characteristic β‐turn structure elements were found for the backbone conformation of the endocyclic residues Tyr2–Asn5. For this portion of the peptide sequence, various conformational equilibria were detected which matched different time scales. For [Arg8]vasopressin, averaged NMR parameters were obtained which could be explained by rapid interconversion between different β‐turn geometries, whereas multiple slowly exchanging conformations were observed for the V1 antagonists. V1 antagonists containing sarcosine in position 7 exhibited multiple spectral patterns for the exocyclic part attributed tocis/trans isomerization. The X‐ray structure of deamino‐oxytocin [Wood, S. P., Tickle, I. J., Treharne, A. M., Pitts, J. E., Mascarenhas, Y., Li, J. Y., Husain, J., Cooper, S., Blundell, T. L., Hruby, V. J., Buku, A., Fischman, A. J. & Wyssbrod, H. R. (1986) Science 232, 633–636] was found to represent one sample of the conformational space covered by the multiple conformations found for [Mca1, Arg8]vasopressin.
