Tyrosine-derived polycarbonates: backbone-modified "pseudo"-poly (amino acids) designed for biomedical applications

Area of Science:

• Polymer Chemistry
• Biomaterials Science
• Organic Synthesis

Background:

• L-tyrosine derivatives are valuable building blocks for functional polymers.
• Understanding structure-property relationships is crucial for designing advanced materials.

Purpose of the Study:

• To synthesize novel polycarbonates from modified L-tyrosine-based dipeptides.
• To investigate the impact of N- and C-terminus protecting groups on polymer properties.
• To identify promising polymer candidates for biomedical applications.

Main Methods:

• Synthesis of four model dipeptides: desaminotyrosine-tyramine (Dat-Tym), Z-tyrosine-tyramine (Z-Tyr-Tym), desaminotyrosine-tyrosine hexyl ester (Dat-Tyr-Hex), and Z-tyrosine-tyrosine hexyl ester (Z-Tyr-Tyr-Hex).
• Polymerization of dipeptides using phosgene or triphosgene to form polycarbonates.
• Characterization of polymer molecular weights (105,000–400,000 Da) using gel permeation chromatography.
• Evaluation of physicomechanical properties including solubility, mechanical strength, glass transition temperature, decomposition temperature, and processibility.

Main Results:

• Polycarbonates were successfully synthesized with varying molecular weights.
• N-terminus protection (urethane bond) decreased solubility, ductility, and processibility, likely due to hydrogen bonding.
• C-terminus alkyl ester protection enhanced solubility and processibility.
• The polycarbonate derived from Dat-Tyr-Hex (C-terminus protected) exhibited the most favorable properties for biomedical use.

Conclusions:

• The nature of terminal protecting groups significantly influences polycarbonate properties.
• C-terminus protection is key to improving solubility and processibility for potential biomedical applications.
• The findings are consistent with related polyiminocarbonate studies, suggesting general validity of structure-property correlations.