Peptide Synthesis Combined with Polymerization

Alternative total solid phase-based strategies for the preparation of polymer-peptide block copolymers were based on the polymerization of the synthetic polymer block from the supported peptide segment using either nitroxide-mediated radical polymerization (NMP) or ATRP (Fig. 15) [64,65]. 

Becker et al. [64] functionalized a peptide, based on the protein transduction domain of the HIV protein TAT-1, with an NMP initiator while on the resin. They then used this to polymerize f-butyl acrylate, followed by methyl acrylate, to create a peptide-functionahzed block copolymer. Traditional characterization of this triblock copolymer by gel permeation chromatography and MALDI-TOF mass spectroscopy was, however, comphcated partly due to solubility problems. Therefore, characterization of this block copolymer was mainly hmited to ll and F NMR and no conclusive evidence on molecular weight distribution and homopolymer contaminants was obtained. Difficulties in control over polymer properties are to be expected, since polymerization off a microgel particle leads to a high concentration of reactive chains and a diffusion-limited access of the deactivator species. The traditional level of control of nitroxide-mediated radical polymerization, or any other type of controlled radical polymerization, will therefore not be straightforward to achieve. 

In a second article the same approach was used to synthesize a peptidic polymer containing the peptide Tritrpticin, a 13 residue antimicrobial peptide (Fig. 16) [66]. This time they initiated the polymerization of f-butyl acrylate, followed by styrene to produce a triblock copolymer, which clearly formed micelles in solution. Interestingly, the antimicrobial activity of the peptide was enhanced relative to the free peptide and the detrimental side effects normally associated with antimicrobial peptides, such as a high hemolytic activity, were reduced, highhghting the benefits of using peptide polymer hybrids in place of peptides alone. 

The addition of an a-bromo ester or amide to the end of a molecule is a strategy which is commonly used to create a wide range of functional 

A similar approach was followed by Couet et al. [69] who fimctionahzed peptide Ghadiri rings on 3 sites with ATRP initiators, which were subsequently used for the polymerization of N-isopropyl acrylamide. These hybrid polymer peptide structures were capable of forming peptide nanotubes, which were homogeneously covered by the attached polymer. 

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The combination of sohd phase peptide synthesis with polymer chemistry has proven to be a versatile method for the preparation of polymer-peptide hybrids. Introduction of native ligation methods even allows the synthesis of polymer modified polypeptides and proteins via an entire organic chemistry approach. In the field of polymer chemistry—besides the advances in NCA polymerization, which will be discussed by others and is therefore not part of the scope of this review—controlled radical polymerization has been shown to be a robust technique, capable of creating well-defined biofunctional polymer architectures. Through protein engineering, methods have been estabhshed that enable the construction of tailor-made proteins, which can be functionalized with synthetic polymer chains in a highly defined manner. 

Peptide synthesis [19] A TFA salt of a peptide was dissolved in chloroform (10 mL mmol ). A 40% excess of the polymeric activated ester of the amino acid to be coupled and 2 equiv. of dry triethylamine were added. Shaking was continued until complete consumption of the starting material, as determined by TLC. The polymer was washed with chloroform and the combined washings were extracted with aqueous sodium hydrogencarbonate solution and dried. 

Interesting new block copolymers are accessible through the combination of peptides prepared by solid phase synthesis or polypeptides prepared by polymerization of the corresponding A-carboxyanhydride with other polymers. The different methods for NCA synthesis and their combination with methods for preparing mostly flexible coil polymers have been reviewed. Among the numerous synthetic... 

In this chimeric peptide construct the aim was to combine the carrier function and immunstimulatory activity of tuftsin derivatives with an epitope derived from HSV gD to achieve an increased antibody response. Tuftsin is a well-known natural tetrapeptide (TKPR) that has a pronounced effect on the immune system (28,29). Polymerized tuftsin (polytuftsin) is also considered as a carrier molecule that increased antibody levels against attached epitopes in mice (30,31). New, sequential oligopeptides based on repeated tuftsin derivatives (H-[Thr-Lys-Pro-Lys-Gly]n-NH2, where n = 2,4,6,8) were developed in our laboratory to eliminate the drawbacks of tuftsin derivatives produced by polymerization. These new, nontoxic, nonimmunogenic compounds have immunostimulatory activity and a minor chemoattractant effect on monocytes (32). An oligotuftsin derivative was used in this study for the synthesis of a peptide chimera containing an HSV peptide epitope. 

This review presents a survey on functional soluble polymers in view of their use as supports for liquid-phase synthesis. The gen al aspects of syntheas in homogeneous media as well as analytical and separation problems are discussed, focussing on the role of the polymer in the synthetic cycle and the problems associated with polymer-supported reactions. A survey of polymeric carriers in respect of their functional groups and badcbones is provided with an emphasis on poly(oxyethylene), polystyrene, and poly(vinyl alcohol) suf rts. Combined methods using solid and sduble supports are al highli ted. Ihe polymeric carriers are discussed and evaluated for their use in peptide and nudeotide synthesis. Finally an outlook into future developments is attempted. 

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