Backbone modifications in somatostatin analogues: relation between conformation and activity.

Twenty cyclic and linear analogues of somatostatin have been compared with respect to their conformational behavior and biological activity. It appears that all active compounds have in common a well defined, predominant backbone conformation. For linear peptides, this conformation can only be detected at low (-80 degrees C) temperature by NMR measurements. Selectivity is suggested to be determined by the nature and topology of the side chains linked to this common backbone conformation. The side chain conformation is also only accessible for NOE measurements in the low temperature range.