Conformation of tert-butoxy­carbonyl­glycyl-dehydro­alanyl-glycine methyl ester in the crystalline state and calculated in the gas phase

tert-Butoxy­carbonyl­glycyl-dehydro­alanyl-glycine methyl ester (systematic name: methyl {2-[(tert-butoxycarbonylamino)­acetamido]prop-2-enamido}acetate) (Boc⁰-Gly¹-ΔAla²-Gly³-OMe), C₁₃H₂₁N₃O₆, has been structurally characterized by single-crystal X-ray diffraction and by density functional theory (DFT) calculations at the B3LYP/6–311+G** level. The peptide chain in both the solid-state and calculated structures adopts neither β nor γ turns. All amino acid residues in the tripeptide sequence are linked trans to each other. The bond lengths and valence angles of the amino acid units in the crystal structure and gas phase are comparable. However, the conformation of the third glycyl residue (Gly³) is different in the crystalline state and in the gas phase. It is stabilized in the calculated structure by an additional intra­molecular short contact between Gly³ NH and methyl ester COMe groups.