No abstract

The peptide N-benzyloxycarbonyl-L-valyl-L-tyrosine methyl ester or NCbz-Val-Tyr-OMe (where NCbz is N-benzyloxycarbonyl and OMe indicates the methyl ester), C(23)H(28)N(2)O(6), has an extended backbone conformation. The aromatic rings of the Tyr residue and the NCbz group are involved in various attractive intra- and intermolecular aromatic π-π interactions which stabilize the conformation and packing in the crystal structure, in addition to N-H...O and O-H...O hydrogen bonds. The aromatic π-π interactions include parallel-displaced, perpendicular T-shaped, perpendicular L-shaped and inclined orientations.

The title tripeptide, C17H23N3O6, contains a nonproteinogenic C-terminal amino acid residue, norvaline, which is an isomer of the amino acid valine. Norvaline, unlike valine, has an unbranched side chain. The mol­ecule has a Gly–Gly segment which adopts an extended conformation. The norvaline residue also adopts an extended backbone conformation while its side chain has a g + t conformation. In the crystal lattice, N—H⋯O and O—H⋯O hydrogen bonds stabilize the packing. Mol­ecules translated along the crystallographic a axis associate through an N—H⋯O hydrogen bond. The remaining three hydrogen bonds are between mol­ecules related by a 2 1 screw axis.

The title peptide, N-benzyl­oxycarbonyl-β-glycylglycylglycine benzyl ester, C22H25N3O6, contains a non-proteinogenic amino acid residue, β-glycine, which is a homologated analogue of glycine. In the mol­ecular structure, β-glycine adopts an extended conformation with a trans conformation about its Cβ—Cα bond. The second glycine residue adopts an extended conformation while the third glycine residue adopts a helical conformation. In the crystal, three N—H⋯O hydrogen bonds, two involving the same carbonyl O atom as acceptor, results in an infinite two-dimensional network parallel to the bc plane.