Block copolymers of amino acids. I. Synthesis and structure of copolymers of L-alanine or L-phenylalanine with D,L-Lysine-d7 or D,L-lysine

One-Shot Synthesis of Peptide Amphiphiles with Applications in Directed Graphenic Assembly

High molecular weight, synthetic block copolypeptides that self-assemble are in high demand for biomedical applications. The current standard method for synthesis of block copolypeptides is the controlled ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydride (NCA) monomers, where block architectures can be created by sequential NCA monomer addition. Recently, researchers have focused on developing reaction conditions and initiation systems that make NCA ROP more convenient, particularly for interdisciplinary labs without designated polypeptide facilities. In an effort to further simplify and increase the convenience of polypeptide synthesis, we developed a one-shot copolymerization strategy that allows access to block copolypeptides by capitalizing on the inherently faster reactivity of NCA monomers, compared to NTA (N-thiocarboxyanhydride) monomers. For the first time, we combine an NCA and NTA monomer in one reaction to kinetically promote block copolypeptide formation, providing a convenient alternative to sequential monomer addition. The controlled nature of this copolymerization technique is supported by a molecular weight that is modulated by the concentration of the initiator and low dispersities. We used this one-shot copolymerization to synthesize p(lysine)-b-p(leucine), a known peptide amphiphile (PA). Our one-shot PAs are antimicrobial and can spontaneously form ordered, micron-scale assemblies. Covalent conjugation of one-shot PAs to a graphenic backbone results in a functional graphenic material (FGM) with a self-assembled morphology, paving the way for creation of sophisticated FGM scaffolds with polypeptide-templated, hierarchical order. Overall, we demonstrate that this novel, one-shot copolymerization strategy produces functional copolypeptides with macroscopic sequence control.

Synthesis of polypeptides by ring-opening polymerization of α-amino acid N-carboxyanhydrides

This chapter summarizes methods for the synthesis of polypeptides by ring-opening polymerization. Traditional and recently improved methods used to polymerize α-amino acid N-carboxyanhydrides (NCAs) for the synthesis of homopolypeptides are described. Use of these methods and strategies for the preparation of block copolypeptides and side-chain-functionalized polypeptides are also presented, as well as an analysis of the synthetic scope of different approaches. Finally, issues relating to obtaining highly functional polypeptides in pure form are detailed.

Living polypeptides

Block copolypeptides, which combine the self-assembly of block copolymers and the highly ordered 3D structures of proteins, are potential candidates for novel supramolecular structures and biotech applications, such as biosensors, tissue engineering, and selective drug delivery. The synthesis of model block copolypeptides through living nucleophilic/basic polymerization of alpha-amino acid N-carboxyanhydrides (NCAs) has been a challenge for more than fifty years, most probably due to traces of impurities in the system. This problem has been overcome, using high vacuum techniques in order to create and maintain the conditions necessary for the living polymerization of NCAs with primary amines. This method is a general one and opens avenues leading to novel, well-defined polypeptides with various architectures.

Methodologies for preparation of synthetic block copolypeptides: materials with future promise in drug delivery

This article summarizes recent developments in the synthesis of copolypeptides, focusing on the realization of living polymerizations that allow preparation of materials with excellent attributes for drug delivery. Traditional methods used to polymerize alpha-amino acid-N-carboxyanhydrides (NCAs) are described, and limitations in the utility of these systems for the preparation of polypeptides are discussed. A system utilizing transition metal catalysis for polypeptide synthesis is described that allows preparation of materials that begin to rival biologically produced counterparts in terms of complexity and purity. Overall, new developments in NCA and beta-lactam polymerizations hold tremendous promise now that block copolypeptides of controlled dimensions (molecular weight, sequence, composition, and molecular weight distribution) can be prepared. Such well-defined polymers should greatly assist in the development of new drug carriers with increased function.

Facile synthesis of block copolypeptides of defined architecture

Many natural polymeric materials (particularly structural proteins) display a hierarchy of structure over several length scales. Block copolymers are able to self-assemble into ordered nanostructures, but the random-coiled nature of their polymer chains usually suppresses any further levels of organization. The use of components with regular structures, such as rigid-rod polymers, can increase the extent of spatial organization in self-assembling materials. But the synthesis of such polymeric components typically involves complicated reaction steps that are not suitable for large-scale production. Proteins form hierarchically organized structures in which the fundamental motifs are generally alpha-helical coils and beta-sheets. Attempts to synthesize polypeptides with well-defined amino-acid sequences, which might adopt similar organized structures, have been plagued by unwanted side reactions that give rise to products with a wide range of molecular weights, hampering the formation of well-defined peptide block copolymers. Here I describe a polymerization strategy that overcomes these difficulties by using organonickel initiators which suppress chain-transfer and termination side reactions. This approach allows the facile synthesis of block copolypeptides with well-defined sequences, which might provide new peptide-based biomaterials with potential applications in tissue engineering, drug delivery and biomimetic composite formation.