EN
The crystal structure of Ac-ΔVal-NMe2 (ΔVal = a,β-dehydrovaline) was determined by X-ray crystallography. The found angles φ = -60o and Ψ = 125° correspond exactly to the respective values of the (i + 1)th residue in idealised yS-turn II/VIa. Ab initio/DFT studies revealed that the molecule adopts the angle Ψ restricted only to about |130° | and very readily attains the angle φ about -50°. This is in line with its solid-state conformation. Taken together, these data suggest that the ΔVal residue combined with a C-terminal tertiary amide is a good candidate at the (i + 1)th position in a type II/VIa β-turn.