title: Helical screw-sense preferences of peptides based on chiral, Cα-tetrasubstituted α-amino acids.
abstract: The preferred helical screw senses of chiral α-amino acids with a C(α)-tetrasubstituted α-carbon atom, as determined in the crystal state by X-ray diffraction analyses on derivatives and peptides, are reviewed. This survey covers C(α)-methylated and C(α)-ethylated α-amino acids, as well as α-amino acids cyclized on the α-carbon, including those characterized by the combination of lack of chirality at the α-carbon with either side-chain or axial chirality. Although, in general, chiral C(α)-tetrasubstituted α-amino acids show a less pronounced bias toward a single helical screw sense than their proteinogenic (C(α)-trisubstituted) counterparts, our analysis highlights significant differences in terms of magnitude and direction of such a bias among the various sub-families of residues, and between individual amino acids within each sub-family as well. The experimental findings can be rationalized, at least in part, on the basis of steric considerations.
authors.affiliation: Institute of Biomolecular Chemistry, Padova Unit, CNR, 35131, Padova, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Crisma
authors.forename: Claudio
authors.initials: C
authors.lastname: Toniolo
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D000596:Amino Acids; D010455:Peptides
keywords: Cα-tetrasubstituted α-amino acids; X-ray diffraction crystallography; chirality; handedness; helical structures; peptides