RAFT Synthesis of Peptide Based Block and Star Polymers

Author:Chen Chao

Supervisor:tang hua


Degree Year:2018





Peptide-polymer conjugates are unique constructs that combine the synthetic polymers and biological peptides via covalent linkage.This often leads to improved stabilities,solubilities and biological properties.As an interdisciplinary research field including chemistry and biology,it has attracted the attention of many researchers.The design and synthesis of novel peptide-polymer conjugates have a wide and long-term impact on the development of drug carriers,nanotechnology,tissue engineering and other fields.The advent and development of reversible addition-fragmentation chain transfer(RAFT)polymerization has greatly promoted the construction of complex polymer architectures(such as block copolymers,comb and star polymers).Star polymers consist of many linear polymers fused at a central core.Owing to its exclusive topological structure and some remarkable characteristics and properties,it has been widely studied by researchers since it emerged.In the present study,RAFT synthesized block copolymers and star polymers and peptides were combined for constructing a series of functional biomaterials.The detailed contents are listed as following:1.MARGD,a methacrylamide monomer containing pending RGD peptide was synthesized and obtained in high purity(≥ 90%)via an automated peptide synthesizer followed by a simple precipitation in diethyl ether.MARGD can be polymerized by reversible addition-fragmentation chain transfer(RAFT)polymerization to afford well-defined polymers containing RGD peptide group in controlled molecular weight,low dispersity(D<1.25),and precise chain end structure.In this study,linear pseudo-first-order kinetics and number average molecular weight dependence on conversion were observed during the RAFT polymerization.Diblock peptide-polymer conjugates were prepared using PMARGD as macro chain transfer agent or using MARGD as monomer,the resulting diblock conjugates all showed low dispersities.Cytotoxicity study using mouse fibroblast cells(L929)revealed that the bioconjugates are non-toxic up to high concentration.Furthermore,enhanced cell adhesion was observed when the bioconjugates immobilized on the glass slide surfaces.This study provides a novel and efficient strategy to access well-defined peptide-polymer conjugates with diversity for both peptides and polymers.2.RGD peptide was synthesized by solid phase peptide synthesis method followed by conjugation of 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid(CDTPA).Then the RGD peptide based RAFT agent(RGD-CTA)was cleaved by treatment with trifluoroacetic acid(TFA)cocktail.FT-IR,MS,NMR data confirmed the successful synthesis of RGD-CTA.Three sets of well-defined peptide-polymer conjugates were prepared by the effective RAFT polymerization.This study developed a novel and effective approach for construction of well-defined peptide-polymer conjugates.Additionally,our results have shown,for the first time,the stability of RAFT agent in TFA solution.3.RGD-CTA was used in RAFT polymerization of three monomers with markedly different properties,N,N-dimethylaminoethyl methacrylate(DMAEMA,cationic),n-butyl methacrylate(BMA,hydrophobic)and oligo(ethylene glycol)methyl ether methacrylate(OEGMA,hydrophilic)were conducted using RGD-CTA as chain transfer agent(CTA).With a disulphide dimethacrylate(DSDMA)redox-cleavable cross-linker and rhodamine B monomer,the above linear polymers were combined via arm-first technique to access miktoarm star(MAS)polymers containing peptide moeities.According to the GPC results,such method provided low dispersity(D≤1.30)MAS star polymers with high yield(>60%).Moreover,glutathione(GSH),dithiothreitol(DTT),Tributyl phosphine(TBP)were used as reductant to study the redox responsiveness of MAS polymers.In vitro cytotoxicity experiments of these MAS polymers(after quaternization)revealed excellent cyto-compatiblity.The cell imaging results of MAS polymers also indicated their potential application for excellent cell staining.4.In this research,a sequence-defined cell penetrating peptide(TP 10)based chain transfer agent(TP-CTA)is designed and synthesized.ESI-MS,NMR and Circular dichroism(CD)were used for characterization of TP-CTA.Kinetics study of oligo(ethylene glycol)methyl ether acrylate(OEGA)and n-butyl acrylate(BA)demonstrate the effective access to well-defined peptide-polymer conjugates via reversible addition-fragmentation chain transfer(RAFT)polymerization.Furthermore,rhodamine B labeled amphipathic block copolymer POEGA-b-PBA was synthesized using TP-CTA as CTA.Transmission electron microscopy(TEM)images reveal the formation of worm and vesicle morphology while the block copolymer self-assembled in water.Cytotoxicity study showed no obvious toxicity.Cell uptake was quantified via fluorescence intensity.Compared with the control sample,the TP10-containing copolymer has outstanding penetrability and cell uptake showed concentration dependent property.5.A series of linear and block polymers including POEGA,PDMAEMA,PBA and POEGMA-b-PDMAEMA were synthesized using CDTPA as CTA.Linear POEGA containing TP 10 was synthesized by RAFT polymerization.Star polymers were prepared by cross-linking the above two or three linear polymers using N,N’-Bisacrylylcystamine(BAC)as cross-linker.All the synthesis process was carried out in a high-throughput synthesizer(Chemspeed).Furthermore,the resulting star polymers were characterized by NMR and GPC.And the biodegradability and biocompatibility of the star polymers were investigated.