[ D-Ala², D-Leu⁵]-Enkephalin Hydrochloride

The title compound, L-tyrosyl-D-alanyl-glycyl-L-phenyl­alanyl-D-leucine hydrochloride (C₂₉H₄₀N₅O₇⁺.Cl^-), co-crystallizes with 2-butanone (C₄H₈O). The structure reveals a slightly distorted type-I' β-bend conformation stabilized by one intramolecular hydrogen bond. This conformation is similar to that observed for other [Leu]-enkephalin analogues.

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