Design of peptides with alpha,beta-dehydro residues: a dipeptide with a branched beta-carbon dehydro residue at the (i+1) position, methyl N-(benzyloxycarbonyl)-alpha,beta-didehydrovalyl-L-tryptophanate.

The structure of the title peptide, C(25)H(27)N(3)O(5), has been determined and its conformation analysed. Values of the standard peptide torsion angles are phi(1) = -44.2 (3) degrees, psi(1) = 135.9 (2) degrees, phi(2) = -141.6 (2) degrees and psi(2)(T) = 168.0 (2) degrees. The crystal structure is stabilized by an intermolecular hydrogen bond, with an N...O distance of 2.919 (3) A, which is formed between screw-axis-related NH and CO groups of dehydrovaline residues.