Specific aggregations of alanine tetrapeptide derivatives as studied by nuclear magnetic resonance.

By use of high resolution nuclear magnetic resonance and infrared spectroscopy, we have found evidence for specific folded forms for the methoxyethoxyethoxyacetyl-blocked alanine tetramer ethyl ester. It appears that this tetrapeptide derivative exists in a folded form which is in rapid equilibrium with an extended structure (i.e., below 1% w/v). At high concentrations (i.e., above 1% w/v in chloroform) the folded form is stabilized by an association of the alanine tetrapeptide derivative into a side-by-side dimer which contains specific hydrogen bonds between the amine terminal regions of the two folded structures.