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1.  Crystal structure of N-(tert-but­oxy­carbon­yl)phenyl­alanylde­hydro­alanine isopropyl ester (Boc–Phe–ΔAla–OiPr) 
In the crystal structure of the de­hydro­dipeptide (Boc-Phe-ΔAla-OiPr), the mol­ecule has a trans configuration of the N-methyl­amide group. Its geometry is different from saturated peptides but is in excellent agreement with other de­hydro­alanine compounds. In the crystal, an N—H⋯O hydrogen bond links the mol­ecules in a herringbone packing arrangement.
In the title compound, the de­hydro­dipeptide (Boc–Phe–ΔAla–OiPr, C20H28N2O5), the mol­ecule has a trans conformation of the N-methyl­amide group. The geometry of the de­hydro­alanine moiety is to some extent different from those usually found in simple peptides, indicating conjugation between the H2C=C group and the peptide bond. The bond angles around de­hydro­alanine have unusually high values due to the steric hindrance, the same inter­action influencing the slight distortion from planarity of the de­hydro­alanine. The mol­ecule is stabilized by intra­molecular inter­actions between the isopropyl group and the N atoms of the peptide main chain. In the crystal, an N—H⋯O hydrogen bond links the mol­ecules into ribbons, giving a herringbone head-to-head packing arrangement extending along the [100] direction. In the stacks, the mol­ecules are linked by weak C—H⋯O hydrogen-bonding associations.
doi:10.1107/S1600536814025197
PMCID: PMC4257372  PMID: 25553003
crystal structure; de­hydro peptides; α,β-de­hydro­amino acids; de­hydro­alanine; herringbone packing
2.  Crystal structure of N-(tert-but­oxy­carbon­yl)glycyl-(Z)-β-bromo­dehydro­alanine methyl ester [Boc–Gly–(β-Br)(Z)ΔAla–OMe] 
In a de­hydro­amino acid with a C=C bond between the α- and β-C atoms, the amino acid residues are linked trans to each other and there are no strong intra­molecular hydrogen bonds. The torsion angles indicate a non-helical conformation of the mol­ecule.
The title compound, C11H17BrN2O5, is a de­hydro­amino acid with a C=C bond between the α- and β-C atoms. The amino acid residues are linked trans to each other and there are no strong intra­molecular hydrogen bonds. The torsion angles indicate a non-helical conformation of the mol­ecule. The dipeptide folding is influenced by an inter­molecular N—H⋯O hydrogen bond and also minimizes steric repulsion. In the crystal, mol­ecules are linked by strong N—H⋯O hydrogen bonds, generating (001) sheets. The sheets are linked by weak C—H⋯O and C—H⋯Br bonds and short Br⋯Br [3.4149 (3) Å] inter­actions.
doi:10.1107/S1600536814025677
PMCID: PMC4257433  PMID: 25553002
crystal structure; β-bromo­dehydro­alanine; de­hydro­amino acid; non-helical conformation; hydrogen bonding
3.  Two penta­dehydro­peptides with different configurations of the ΔPhe residues 
Comparison of the crystal structures of two penta­dehydro­peptides containing ΔPhe residues, namely (Z,Z)-N-(tert-butoxy­carbonyl)­glycyl-α,β-phenyl­alanyl­glycyl-α,β-phenyl­alanyl­glycine (or Boc0–Gly1–ΔZPhe2–Gly3–ΔZPhe4–Gly5–OH) methanol solvate, C29H33N5O8·CH4O, (I), and (E,E)-N-(tert-butoxy­carbonyl)­glycyl-α,β-phenyl­alanyl­glycyl-α,β-phenyl­alanyl­glycine (or Boc0–Gly1–ΔEPhe2–Gly3–ΔEPhe4–Gly5–OH), C29H33N5O8, (II), indicates that the ΔZPhe residue is a more effective inducer of folded structures than the ΔEPhe residue. The values of the torsion angles ϕ and ψ show the presence of two type-III′ β-turns at the ΔZPhe residues and one type-II β-turn at the ΔEPhe residue. All amino acids are linked trans to each other in both peptides. β-Turns present in the peptides are stabilized by intra­molecular 4→1 hydrogen bonds. Mol­ecules in both structures form two-dimensional hydrogen-bond networks parallel to the (100) plane.
doi:10.1107/S0108270110003094
PMCID: PMC2855584  PMID: 20203407

Results 1-3 (3)