Conformationally Restricted Analogues of Substance P

The three-dim-nsional structure of a peptide deduced from conformational analyses (nuclear magnetic resonance and circular dichroism spectroscopies) and/or from energy calculations should provide an insight into the structural requirements of the binding protein, if this structure has any relevance to the conformation which interacts with the binding protein. A decisive contribution to overcome this problem has been the design of constrained analogues of the peptide which simulate the predicted conformers. Indeed such rigidified analogues, if active, must contribute to a more accurate description of the bioactive conformation[l]. We have established, using NMR and CD spectroscopies, that the three-dimensional structure of SP is strongly influenced by its environment. The main features of the conformation model we have proposed are the flexibility of the N-terminal Arg-ProLys, the a-helical folding of the core of SP, Pro-Gln-Gln-Phe-Phe, and the folding of the C-terminal carboxamide towards the primary amides of Gin⁵ and Gln⁶ [2] The validity of this model has been checked by the means of constrained cyclic analogues of SP. Therefore, we have synthesized two groups of disulfide bridged analogues of SP.