Molecular and crystal structure of a dehydroalanine dipeptide

The molecular and crystal structure of the synthetic, terminally blocked, model dipeptide t-Boc-L-Val-ΔAla-OMe (1) was determined by single-crystal X-ray diffraction. Crystal data for 1 are: C14H24N2O5, hexagonal, space group P65 (no.170), a = 10.8000(2) Å, c = 27.077(2) Å, and Z = 6. The crystal structure was solved by direct methods. The least-squares refinement led to R and Rw values of 0.077 and 0.075, respectively, for 1298 reflections F ≥ 5 σ(F). The conformation of the Val residue is partially extended, while that of ΔAla residue is trans, cis. The N-terminal protecting groups is in the trans, trans disposition