Conformational flexibility of dehydroalanine derivatives. Crystal and molecular structure of 2-N-acetyldehydrophenylalanyl-l-proline

The molecular structure of the title compound has been determined from three-dimensional X-ray data. C₁₆H₁₈N₂O₄·$\text{1}\text{2}$H₂O is monoclinic, space group C2, with Z=4 in a cell of dimensions: a = 18.508(3), b = 9.517(4), c = 10.538(4) Å, β = 120.00(3)°. One water molecule coordinates four molecules in a tetrahedral arrangement. The conformation of this molecular system is discussed also on the basis of the known structure of related compounds and previously reported theoretical results.