Chain side group

X-Amino acids ate ampholytic compounds. The chemical reactions of amino acids can be classified according to their carboxyl, amino, and side-chain groups. Most of the reactions have been well known for a long time the details of these reactions have been reviewed (77). 

For 3-acetylthiotetronic acid the same type of tautomerization process (90 91, 92 93 as a result of prototropy between internal tautomers 90, 91 92, 93, rotation of the side-chain group, between external tautomers) was observed as for the corresponding 3-acetyl-tetronic acids ( H NMR, NMR) [76JHC533 78BCJ651 79JCS (P2)1605],... 

Because side-chain groups can be easily introduced in the polymer backbone, polymers synthesized via transition metal coupling are usually soluble in common... 

The second step introduces the side chain group by nucleophilic displacement of the bromide (as a resin-bound a-bromoacetamide) with an excess of primary amine. Because there is such diversity in reactivity among candidate amine submonomers, high concentrations of the amine are typically used ( l-2 M) in a polar aprotic solvent (e.g. DMSO, NMP or DMF). This 8 2 reaction is really a mono-alkylation of a primary amine, a reaction that is typically complicated by over-alkylation when amines are alkylated with halides in solution. However, since the reactive bromoacetamide is immobilized to the solid support, any over-alkyla-tion side-products would be the result of a cross-reaction with another immobilized oligomer (slow) in preference to reaction with an amine in solution at high concentration (fast). Thus, in the sub-monomer method, the solid phase serves not only to enable a rapid reaction work-up, but also to isolate reactive sites from... 

The Liskamp group also examined the ability of peptoid-peptide hybrids to be bound by the MHC Class II receptor, an important component of the human immune system [39]. Two of three peptoid substitutions in the 14-residue peptide caused substantial decreases in binding affinity, despite the fact that these were solvent-exposed residues. These results were attributed to a loss of hydrogen-bond contacts as well as to steric clashes caused by unfavorable positioning of the new side chain groups. 

Covalent modification of side-chain groups in the Ca -ATPase... 

DM Oh, PJ Sinko, GL Amidon. Characterization of the oral absorption of P-lactam Effect of the cx-amino side chain group. J Pharm Sci 82 897-900, 1993. 

The use of highly fluorinated side-chain groups that are insulated from reaction centers in order to exploit their unique influence upon the solubility properties of the molecule without affecting the chemistry of the functional groups has spawned a new subfield of fluorine chemistry... 

Polyesters Having Reactive (Hydrophilic) Side-Chain Groups... 

To design amphiphilic and/or reactive copolymers containing aliphatic polyesters, one of the most promising approaches is copolymerization with functional monomers having protected reactive side-chain groups. Some kinds of monomers having reactive (hydrophilic) side-chain groups have been reported (Fig. 3). Recently, the synthesis of various types of functional polyesters has been reviewed [15-19],... 

Fig. 3 Examples of monomer units having reactive side-chain groups, which can be copolymerized with polyesters (a) a-malic acid, (b) [S-malic acid, (c) a-carboxyl- -caprolactone, (d) carboxy lactic acid, (e) trimethylene carbonate derivative, and (1) depsipeptide...

Copolymers of a-hydroxy acids and a-amino acids are one type of poly(ester-amide)s and are called polydepsipeptides (PDPs) [17]. Since some of natural occurring a-amino acids, typically Asp, Glu, lysine (Lys), cysteine (Cys), serine (Ser), and threonine (Thr), possess reactive (hydrophilic) side-chain groups, PDPs... 

Fig. 4 Synthesis of polydepsipeptides and poly(depsipeptide-co-lactide)s having reactive side-chain groups...

Figure 1.19 Tyrosine and phenylalanine residues can undergo oxidation to modify their phenyl side-chain groups. Tyrosine can form covalent dimers that link two side chains together via a radical reaction. Both tyrosine and phenylalanine can be modified by oxidation to add oxygen-containing groups directly to their aromatic ring.

Figure 4.33 Benzidine can be diazotized with sodium nitrite and HC1 for reaction with proteins through their tyrosine, histidine, or lysine side-chain groups.

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