3 research outputs found
A γ‑Amino Acid That Favors 12/10-Helical Secondary Structure in α/γ‑Peptides
H-bonded helices in conventional
peptides (containing exclusively
homochiral α-amino acid residues) feature a uniform H-bonding
directionality, N-terminal side Cî—»O to C-terminal side NH.
In contrast, heterochiral α-peptides can form helices in which
the H-bond directionality alternates along the backbone because neighboring
amide groups are oriented in opposite directions. Alternating H-bond
directions are seen also in helices formed by unnatural peptidic backbones,
e.g., those containing β- or γ-amino acid residues. In
the present study, we used NMR spectroscopy and crystallography to
evaluate the conformational preferences of the novel γ-amino
acid (1<i>R</i>,2<i>R</i>,3<i>S</i>)-2-(1-<i>a</i>mino<i>p</i>ropyl)-<i>c</i>yclo<i>h</i>exanecarboxylic acid (APCH), which is constrained by a
six-membered ring across its Cα–Cβ bond. These
studies were made possible by the development of a stereoselective
synthesis of N-protected APCH. APCH strongly enforces the α/γ-peptide
12/10-helical secondary structure, which features alternating H-bond
directionality. Thus, APCH residues appear to have a conformational
propensity distinct from those of other cyclically constrained γ-amino
acid residues
Evaluation of a Cyclopentane-Based γ‑Amino Acid for the Ability to Promote α/γ-Peptide Secondary Structure
We report the asymmetric synthesis
of the γ-amino acid (1<i>R</i>,2<i>R</i>)-2-aminomethyl-1-cyclopentane carboxylic
acid (AMCP) and an evaluation of this residue’s potential to
promote secondary structure in α/γ-peptides. Simulated
annealing calculations using NMR-derived distance restraints obtained
for α/γ-peptides in chloroform reveal that AMCP-containing
oligomers are conformationally flexible. However, additional evidence
suggests that an internally hydrogen-bonded helical conformation is
partially populated in solution. From these data, we propose characteristic
NOE patterns for the formation of the α/γ-peptide 12/10-helix
and discuss the apparent conformational frustration of AMCP-containing
oligomers
Evaluation of a Cyclopentane-Based γ‑Amino Acid for the Ability to Promote α/γ-Peptide Secondary Structure
We report the asymmetric synthesis
of the γ-amino acid (1<i>R</i>,2<i>R</i>)-2-aminomethyl-1-cyclopentane carboxylic
acid (AMCP) and an evaluation of this residue’s potential to
promote secondary structure in α/γ-peptides. Simulated
annealing calculations using NMR-derived distance restraints obtained
for α/γ-peptides in chloroform reveal that AMCP-containing
oligomers are conformationally flexible. However, additional evidence
suggests that an internally hydrogen-bonded helical conformation is
partially populated in solution. From these data, we propose characteristic
NOE patterns for the formation of the α/γ-peptide 12/10-helix
and discuss the apparent conformational frustration of AMCP-containing
oligomers