Poly liquid phase peptide

A barbell-like ABA-type triblock copolymer, comprised of poly(L-lysine) (PLL) dendrimers (A) and poly(ethylene glycol) connector (B) has been reported [202], The synthetic route involved the use of an a, poly(ethylene glycol) as the polymeric supporter, for the attachment of - NH2 protected lysine via an amidation reaction. The PLL den-drimer was generated at both ends of A by repeated liquid-phase peptide synthesis, as shown in Scheme 111. The intermediate products along with the final copolymers were characterized by MALDI-TOF MS. The results revealed that narrow molecular weight copolymers were synthesized having low molecular weights. 

Several polymers have been studied for this purpose, including both polystyrene and poly(ethylene glycol). However, for reasons enumerated below, poly(ethylene glycol) is the polymer support of choice in these liquid phase peptide syntheses. 

Automation of liquid phase peptide synthesis is also possible. However, as the size of the peptide attached to the poly(ethylene glycol) support increases, the properties of the... 

These issues can be avoided by performing the synthesis on linear polymers such as poly(ethylene glycol) (PEG) (64,65), as PEG is soluble in a wide range of organic solvents and, when linked to polypeptides, enhances solubilization. Furthermore, Bayer demonstrated that during coupling reactions, PEG-linked amino acids had the same kinetic properties as amino acid esters (66). However, the main problem in liquid-phase peptide synthesis is the separation of linear PEG from the final polypeptide after cleavage. 

In 1977, E. Bayer s group in Tubingen synthesized for the first time a heme group embedded iil a polymer network (241). The structure is shown in Fig. 6.4 and was obtained from poly [ethylene glycol bis(glycine ester)] and polyurethanes from polyethylene glycols and diisocyanates as the basic polymers, using the procedure of liquid-phase peptide synthesis. At the end... 

Table 11. Poly (ethylene glycol) derivatives (POE-R) for liquid-phase peptide synthesis... 

Frank and Hagenmaier suggested an alternative to both solid- and liquid-phase peptide synthesis by creating the solid-liquid-phase method in order to overcome the problem of failure and truncated sequences [105, 106], To this end, poly(ethylene glycol) monoalkyl ethers were used as carboxy protecting poups. The principle of this method is depicted in Scheme 2. 

Linear polystyrene can be functionalized by various methods . The functional group capacity in these polymers diould not be too high otherwise, steric complications may arise. Poly(ethylene ycol) has been found to be most suitable for liquid-phase synthesis. This linear polyether and the block copolymers with functional groups at defined distances are chemically stable and soluble in a large number of solvents including water and can be precipitated selectively. Partially hydrolyzed poly(vinylpyrrolidone) and its copolymers with vinyl acetate were successfully applied in peptide synthesis. Poly(acrylic acid), poly(vinyl alcdiol), and poly-(ethylenimine) are less suitable for the sequential type synthesis because of the... 

The Liquid-Phase Method (LPS) developed by Mutter and Bayer combines the advantages of a polymer-supported technique with those of a synthesis carried out under homogmeous reaction conditions. The C-terminal amino acid is coupled to a mono- or bifiinctional poly(ox thyl )e) (POE-M, POE), and the extension of the peptide towards the N-terminus takes place step by step. Unlike the solid-phase method, the LPS aisures coupling and deprotection in homogeneous solution. Excess low-molecular reagents are removed by precipitation of the POE-peptide with diethyl ether ch- by crystallization from ethanol or methanol. 

Beyond these three main concepts, the inverse bioconjugation approach offers another strategy to connect peptides or proteins with synthetic polymers. Using a solid support, which is preloaded with a polymer block, the biological molecule can be assembled in a stepwise fashion through solid-phase synthesis. Mutter and coworkers first showed the attachment of PEO to a poly(styrene) resin via a benzyl ether linker. This concept was finally developed further by Bayer and Rapp leading to a commercially available PAP resin, which is widely applied in solid-phase peptide synthesis. In a similar approach. Lutz, Borner, and coworkers demonstrated the preparation of cleavable and non-cleavable soluble polystyrene supports by ATRP for the liquid-phase synthesis of peptide-polymer conjugates. ... 

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. 

Studies by Bayer et al. [22] and Mutter [69] have shown that liquid-phase synthesis of peptides exhibits kinetic behaviour analogous to classic peptide synthesis. The reaction rates of both methods are of the same order of magnitude, and using poly(ethylene glycol) esters, the polymer reaction proceeds at an even higher rate than the reaction involving the corresponding low-... 

Several different analytical and ultra-micropreparative CEC approaches have been described for such peptide separations. For example, open tubular (OT-CEC) methods have been used 290-294 with etched fused silicas to increase the surface area with diols or octadecyl chains then bonded to the surface.1 With such OT-CEC systems, the peptide-ligand interactions of, for example, angiotensin I-III increased with increasing hydrophobicity of the bonded phase on the capillary wall. Porous layer open tubular (PLOT) capillaries coated with anionic polymers 295 or poly(aspartic acid) 296 have also been employed 297 to separate basic peptides on the inner wall of fused silica capillaries of 20 pm i.d. When the same eluent conditions were employed, superior performance was observed for these PLOT capillaries compared to the corresponding capillary zone electrophoresis (HP-CZE) separation. Peptide mixtures can be analyzed 298-300 with OT-CEC systems based on octyl-bonded fused silica capillaries that have been coated with (3-aminopropyl)trimethoxysilane (APS), as well as with pressurized CEC (pCEC) packed with particles of similar surface chemistry, to decrease the electrostatic interactions between the solute and the surface, coupled to a mass spectrometer (MS). In the pressurized flow version of electrochromatography, a pLC pump is also employed (Figure 26) to facilitate liquid flow, reduce bubble formation, and to fine-tune the selectivity of the separation of the peptide mixture. 

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