Synthetic and conformational studies on dehydrovaline-containing model peptides

Abstract

To explore the conformational preferences of αs-dehydrovaline (ΔVal) residue, three model dipeptide N-methylamides containing ΔVal were synthesized. Conformational investigations using 300 MHz NMR spectroscopy were based on delineation of intramolecularly hydrogen-bonded NH groups and Nuclear Overhauser Effect (NOE) studies. Temperature and solvent dependence studies in (CD3)2SO and CDC13-(CD3)2SO mixtures showed the absence of any intramolecular hydrogen bonding which suggests that all the three peptides have an extended conformation in solution. Dilution studies in CHC13 conducted using IR spectroscopy further supported the above conclusions. NOE studies also ruled out the existence of any type of discernible secondary structure for these peptides. Conformational behaviour of these dehydrovaline peptides is in contrast with corresponding peptides containing ΔzPhe and ΔzLeu, both of which stabilize s-turn (type-II) structure. These results highlight the importance of steric factors in deciding the conformational properties of dehydropeptides.