Peptides Constrained to Type VI beta-Turns. 1. Evidence for an Exceptionally Stable Intramolecular Hydrogen Bond

Area of Science:

• Chemical synthesis and structural analysis of peptide mimetics.
• Conformational analysis of peptides and their analogs.

Background:

• Peptide secondary structures, like beta-turns, are crucial for protein function.
• Understanding the stability of different peptide conformations is essential for drug design and protein engineering.

Purpose of the Study:

• To synthesize and analyze conjugates of amino acids with a type VI beta-turn dipeptide mimic.
• To investigate the conformational preferences and stability of these conjugates, particularly regarding intramolecular hydrogen bonding.

Main Methods:

• Synthesis of novel dipeptide mimics and their conjugation with amino acids.
• Spectroscopic analysis using Infrared (IR) and Nuclear Magnetic Resonance (NMR) spectroscopy.
• Conformational analysis through assessment of intramolecular hydrogen bond formation and stability in various solvents.

Main Results:

• Conjugates formed stable intramolecular hydrogen bonds, mimicking type VI beta-turns.
• IR and NMR data confirmed hydrogen bonding between the amino acid amide hydrogen and the carbamate carbonyl.
• The hydrogen-bonded conformation (type VIa) was found to be more stable than the non-hydrogen-bonded conformation (type VIb).

Conclusions:

• The synthesized dipeptide mimic effectively promotes the formation of type VI beta-turns.
• Intramolecular hydrogen bonding significantly enhances the conformational stability of peptides.
• These findings have implications for designing stable peptide-based therapeutics and understanding protein folding.