Peptide bond condensation reaction

Proteins are polymers formed from peptides in condensation reactions. Condensation of two amino acids means that the OH group of carboxyl of one peptide and a hydrogen of the amino group of the other expel a water molecule and form a peptide bond (Figure 9.4). Further condensation reactions lead to the protein. The sequence of peptides is referred to as the primary structure of the protein. The 20 amino adds composing natural proteins are given in Table 9.3. 

Figure 16.3 Conceptual illustration of two peptides before (left) and after (right) a chemical reaction with formaldehyde. The amino acids are represented as circles. In this particular peptide, a tyrosine (Y) is located within the epitope (shaded circles). An arginine (R) is located elsewhere in the peptide. Formaldehyde results in the formation of a covalent bond between the two residues, due to a Mannich condensation reaction, as shown on the right. The new configuration prevents antibodies from binding to the epitope on the left. 

The link between adjacent units or monomers in a polypeptide is formed in a condensation reaction between the amine group of one amino acid and the carboxylic acid group of another with the elimination of H20 molecules. These links are called peptide bonds. 

Successive amino acids are joined together during protein synthesis via a peptide (i.e. amide) bond (Figure 2.2). This is a condensation reaction, as a water molecule is eliminated during bond formation. Each amino acid in the resultant polypeptide is termed a residue , and the polypeptide chain will display a free amino (NH2) group at one end and a free carboxyl (COOH) group at the other end. These are termed the amino and carboxyl termini respectively. 

A condensation reaction joins two molecules and splits out a small molecule. The small molecule is usually water. The formation of a peptide bond is an example of a condensation reaction. The conditions necessary for a condensation reaction vary with the functional groups involved. In most cases, a catalyst will be present. The two most common catalysts are acids and enzymes. Two alcohols will condense to form an ether. A carboxylic acid condenses with an alcohol to form an ester. A carboxylic acid condenses with an amine to form an amide. 

Figure 4.1 The zwitterionic structure of two ot-amino acids, and the condensation reaction to form a dipeptide, linked by a peptide bond.

The peptide bond is fotmedby a condensation reaction between an amino group on one amino acid and the carboxyl group of another. 

Two molecules join together with the elimination of a H20. Condensation reactions are used when macromolecules are being formed. Amino acids are joined via peptide bonds and monosaccharides via glycosidic bonds, both of which are condensation reactions. 

An alternative to the synthesis of proteins by classical fragment synthesis in solution or by solid-phase synthesis on a support is the use of enzyme-catalyzed condensation of amino acids or peptides. This possibility was first demonstrated in 1938 91 with the synthesis of poorly soluble benzoyl-leucyl-leucine anilide by papain catalysis. After many years, this approach was extended to the preparation of peptide hormones such as Leu-enkephalin 92 and dynorphin(l -8).[93 This was made possible by the use of highly purified enzymes and by careful control of reaction conditions. The basic principles of protease-catalyzed peptide bond formation have been discussed.194 ... 

Amino acids and their derivatives undergo a wide range of reactions, e.g. racemization, peptide bond formation, ester hydrolysis, aldol-type condensation, Schiff base formation and redox reactions, which are catalyzed by coordination to a metal centre. A number of reviews are available which cover some of these reactions.48,69,70... 

The condensation reaction between two amino acid molecules, usually in the form of active esters, produces a dipeptide molecule (equation 16). The resulting amide bond (—CONH—) is often referred to as a peptide bond. This condensation reaction can be repeated to give a polypeptide chain (18). In naming the sequence of amino acid residues in the chain the customary habit of starting from the N-terminal (free amino) end will be adopted. Synthetic polypeptides made from a single amino acid type, i.e. R1 = R2 = R3 = = R" in (18), are known as homopolypeptides. Cyclic peptide molecules are also known and can occur naturally. 

In this section the synthesis of fluoroalkyl (Section 15.1.4.1.3), a,a-difluoroalkyl (Section 15.1.4.2.3), and trifluoromethyl- and perfluoroalkyl ketones are discussed collectively. The second most widely used method for synthesizing peptide fluoromethyl ketones is the Henry nitro-aldol condensation reaction, which involves the use of (3-nitro alcohols to build the fluoromethyl ketones. As with the modified Dakin-West procedure, the Henry reaction has also been used to synthesize mono-, di-, tri-, and extended fluoromethyl ketones, making it another extremely versatile synthetic method.19 12 19 27 29 33 341 However, similar to the Dakin-West procedure, the products of the Henry reaction are not chiral, since an achiral carbanion is involved in the crucial carbon bond forming step. 

Amino acids are the building blocks of proteins. A single protein consists of one or more chains of amino adds strung end to end by peptide bonds Hence the name polypeptide. You must be able recognize the structure of an amino acid and a polypeptide. A peptide bond creates the functional group known as an amide (an amine connected to a carbonyl carbon). It is formed via condensation of two amino acids. The reverse reaction is the hydrolysis of a peptide bond. 

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