Facile synthesis of polymer-peptide conjugates via direct amino acid coupling chemistry

Amphiphilic bromelain-synthesized oligo-phenylalanine grafted with methoxypolyethylene glycol possessing stabilizing thermo-responsive emulsion properties

A thermo-responsive amphiphile was developed from oligo-phenylalanine [oligo(Phe)]. The hydrophobic moiety of the amphiphile, oligo(Phe) was synthesized via reverse hydrolysis catalyzed by bromelain in dimethyl sulfoxide and dioxane solutions. The production of oligo(Phe) increased by 80.7% by screening suitable reaction conditions. The average degree of polymerization of oligo(Phe) was determined to be four by ¹H NMR. By grafting with aldehyde-ended methoxypolyethylene glycol (mPEG), oligo(Phe) was converted to amphiphilic oligo(Phe)-mPEG. The surface tension of oligo(Phe)-mPEG solution increased with decreasing chain length of the mPEG moiety. Cytotoxicity studies showed oligo(Phe)-mPEGs are biocompatible. On varying temperature, a reversible phase transition of oligo(Phe)-mPEG solutions could be observed. N-octane-in-water emulsions and 0.5% beta-carotene containing squalene-in-water emulsions stabilized by oligo(Phe)-mPEGs occurred at 25 °C but de-emulsification took place at >40 °C. Emulsification could be restored once the separated mixture cooled and re-homogenized. The emulsification/de-emulsification cycling could be repeated many times. The time required for de-emulsification decreased with elevated temperature but increased with a reduced concentration of oligo(Phe)-mPEGs and a reduction in the chain length of the mPEG moiety.

Poly(Ethylene glycol)-based backbones with high peptide loading capacities

Polymer-peptide conjugates are a promising class of compounds, where polymers can be used to overcome some of the limitations associated with peptides intended for therapeutic and/or diagnostic applications. Linear polymers such as poly(ethylene glycol) can be conjugated through terminal moieties and have therefore limited loading capacities. In this research, functionalised linear poly(ethylene glycol)s are utilised for peptide conjugation, to increase their potential loading capacities. These poly(ethylene glycol) derivatives are conjugated to peptide sequences containing representative side-chain functionalised amino acids, using different conjugation chemistries, including copper-catalysed azide-alkyne cycloaddition, amide coupling and thiol-ene reactions. Conjugation of a sequence containing the RGD motif to poly(allyl glycidyl ether) by the thiol-ene reaction, provided a conjugate which could be used in platelet adhesion studies.

"Bio"-macromolecules: polymer-protein conjugates as emerging scaffolds for therapeutics

Polymer-protein conjugates are biohybrid macromolecules derived from covalently connecting synthetic polymers with polypeptides. The resulting materials combine the properties of both worlds: chemists can engineer polymers to stabilize proteins, to add functionality, or to enhance activity; whereas biochemists can exploit the specificity and complexity that Nature has bestowed upon its macromolecules. This has led to a wealth of applications, particularly within the realm of biomedicine. Polymer-protein conjugation has expanded to include scaffolds for drug delivery, tissue engineering, and microbial inhibitors. This feature article reflects upon recent developments in the field and discusses the applications of these hybrids from a biomaterials standpoint.