Amino Acid Polymerization

As noted in Section 23.2, molecules containing NH2 and COOH groups can undergo condensation polymerization. Amino acids contain both groups in the same molecule. Hence, two amino add molecules can combine by the reaction of the COOH group in one molecule with die NH2 group of the other molecule. If the adds involved are different, two different structural isomers are possible ... 

Amos. H. b., bvans, J. J., llimmelsbach. D. S., and Barton, F. li.. In vitro stability, in tivo hydrolysis, and absorption of lysine and methionine from polymerized amino acid preparations, J. Agric. Pood Chem.. 28, 1250. 1980 Chem. Abstr.. 93, 202990. 1980. 

Abstract This article summarizes recent developments in the synthesis of polypeptides and hybrid peptide copolymers. Traditional methods used to polymerize -amino acid-N-carboxyanhydrides (NCAs) are described, and limitations in the utility of these systems for the preparation of polypeptides are discussed. Recently developed initiators and methods are also discussed that allow polypeptide synthesis with good control over chain length, chain length distribution, and chain-end functionality. The latter feature is particularly useful for the preparation of polypeptide hybrid copolymers. The methods and strategies for the preparation of such hybrid copolymers are described, as well as analysis of the synthetic scope of the different methods. Finally, issues relating to obtaining these highly functional copolymers in pure form are detailed. 

Blaschke, G., Schwanghart, A. D. Investigation of chromatographic resolutions of racemates,VI. Polymeric amino acid derivatives as optically active adsorbents, Chem. Ber, 1976,109, 1967-1975. 

Another reaction where amino acids play a key role is the Julia-Golonna epoxidation of a,P-unsaturated ketones [52], which involves the use of a catalytic amount of polymeric amino acids, able to catalyze the Weitz-Scheffer epoxidation of chalcone using basic hydrogen peroxide, with high enantioselectivity (Scheme 8.17 Equation a). 

The large subunit contains the catalytic site for peptide bond formadon. The small subunit serves as a guide for the translation factors requited to regulate protein synthesis. Together the two subunits come together and form a molecular machine that polymerizes amino acids in a sequence specified by the base sequence in the mRNA molecule. 

The type III complex remained essentially inactive. Proof of an intermediate Cu2+-peroxy complex was shown by an absorption shoulder at 360 nm (189, 190). This biochemical reactivity was induced not only by ethylene diamine and its derivatives, but also by monomeric or polymeric amino acids or nucleotides. 

Proteins are formed by polymerizing amino acids. Each amino acid is joined to the next through the reaction of an amino group with a carboxylate group, resulting in the formation of a peptide bond and the elimination of water. 

Scheme 8.7. Nucleophilic epoxidation reactions of enones. (a) Epoxidation of chalcone using phase-transfer [32] or polymeric amino acid [33] catalysis.

Therefore not only parts of crystals can form active centers but certain small parts of large molecules as well, for instance, those of highly polymeric amino acids in enzymic catalysis, or separate X-ray-amor-phous fragments of a crystal lattice, containing for the sextets six... 

Similarly, poly-(.S )-leucine and other polymeric amino acids with definite chain length were prepared and used in the same way28. Poly-(5)-leucinc has also been used in enantioselective hydroesterifications (Section D. 1.5.8.). 

Polypeptide Polymerized amino acid molecules formed by enzymatically regulated stepwise polymerization in vivo between the carboxyl group of one amino add and the amino group of a second amino acid. 

The same group has developped a small library of supported chiral aminoalcohols from different amino acid [132]. The hydrochloride salt of different amino acid methyl esters 176 reacted with a chloromethylated polystyrene-divinylbenzene (1 mmol Cl/g, 1% DVB) under basic conditions to afford the polymeric amino acid ester 177. 

The benefit of microreaction systems is not limited to cationic or radical polymerization. Amino acid polymerization using a-amino acid V-carboxyanhydride (NCA) yielded better molecular weight distribution when performed in a microreactor [5]. Also, the average molecular weight could be controlled by changing the flow rates. 

I UP AC, Abbreviated nomenclature of synthetic polypeptides (polymerized amino acids) revised recommendations (1971), Biopolymers 11, 321-327 (1972). 

Three-letter codes have been developed for the amino acids and are very commonly used, especially when describing the polymeric amino acids known as peptides or in especially large examples, as proteins. A peptide is a molecule that is composed of two or more amino acids that are connected by an amide bond. The connecting amide bond is referred to as a peptide bond. A protein is just a long polypeptide chain. The boundary between the smaller peptides, or polypeptides, and the larger proteins is neither fixed nor always clear, and the terms are sometimes used interchangeably. More recently, an even shorter set of one-letter abbreviations... 

Proteins are polymeric amino acids and are the major component of dried living material. Some proteins are glycosylated (glycoproteins), still others are closely associated with lipids (membrane proteins, and lipoproteins). Each amino acid has a different chemical characteristic so that when they are assembled in a protein, they give the protein a unique series of chemical properties. Each protein varies by the... 

SCHEME 2 Schematic representation of polymeric amino acid and biopolymer/biopolymer derived structures. 

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