Lysine alkylation

In principle, the use of amino acid or peptide esters as nucleophilic components in protease-catalyzed synthesis is possible, but with a drastically decreased efficiency. However, acyl transfer to arginine or lysine alkyl esters in ice using a-chymotrypsin with regard to its strong preference for basic residues in the P/ position enabled synthesis of a N-protected tripeptide ester in high yield (Scheme 7, see Section 4.2.1.2.2). Furthermore, it was found to be the method of choice in synthesizing new potential protease substrates (for proteases with a preference for basic residues in the Pj position). Neither enzymatic synthesis at room temperature nor synthesis in organic solvents has been shown to proceed in a successful manner. 

Figure 15 Chemical structures of (a) poly(Qf,L-glutamic acid)-alkyltrimethylammonium cation complexes and (b) poly(L-lysine)-alkyl sulfate anion complexes.

Figure 18 Arrangement of the surfactant molecules within the lamellae of complexes of poly(L-lysine)-alkyl sulfates containing mixed alkyl chains. Figures in brackets indicate the composition of the system. (Taken from E.A. Ponomarenko, D.A. Tirrell, and W.J. MacKnight. Macromolecules 31 1584, 1998. With permission.)...

Caprolactam is an amide and, therefore, undergoes the reactions of this class of compounds. It can be hydrolyzed, Ai-alkylated, O-alkylated, nitrosated, halogenated, and subjected to many other reactions (3). Caprolactam is readily converted to high molecular weight, linear nylon-6 polymers. Through a complex series of reactions, caprolactam can be converted to the biologically and nutritionally essential amino acid L-lysine (10) (see Amino acids). 

A copper chelate selectively protects the -NH2 group in lysine. The chelate is cleaved by 2 AHCl or by EDTA, (H02CCH2)2NCH2CH2N(CH2C02H)2- This mode of protection is sufficient to allow alkylation of a copper-protected t50 osine at the phenol (75% yield). ... 

The amine containing side chains in lysine, arginine, and histidine typically are exposed on the surface of proteins and can be derivatized with ease. The most important reactions that can occur with these residues are alkylation and acylation (Figure 1.8). In alkylation, an active... 

More specific evidence came from affinity labeling with molecules which could react with specific amino acid group sat or adjacent to the substrate site. These labels were substrate analogues and competitive inhibitors. Substituted aryl alkyl ketones were used. TV-p-toluene-sulphonyl-L-phenylalanine chloromethyl ketone (TPCK) blocked the activity of chymotrypsin. Subsequent sequence analysis identified histidine 57 as its site of binding (see Hess, 1971, p 213, The Enzymes, 3rd ed.). Trypsin, with its preference for basic rather than aromatic residues adjacent to the peptide bond, was not blocked by TPCK but was susceptible to iV-p-toluenesulphonyl-L-lysine chloromethyl ketone (TLCK) (Keil, ibid, p249). 

Very detailed studies on the inhibition of alanine racemase by fluoroalanines have been conducted. This enzyme catalyzes the racemization of alanine to provide D-alanine, which is required for synthesis of the bacterial wall. This work has demonstrated that a more complex process than that represented in Figure 7.47 could intervene. For instance, in the case of monofluoroalanine, a second path (Figure 7.48, path b) occurs lysine-38 of the active site can also attack the Schiff base PLP-aminoacrylate that comes from the elimination of the fluorine atom. This enamine inactivation process (path b) has been confirmed by isolation and identification of the alkylation compound, after denaturation of the enzyme (Figure 7.48). ... 

The replacement of alanine residue by a lysine moiety leads to lisinopril (13-2) administered in this case as a free dicarboxylic acid this compound that is quite active orally in spite of its polarity. The synthesis is quite analogous to that above, involving reductive alkylation of tert-butoxycarbonyl protected lysilprohne (13-1) with ketoester (12-1). Separation of the desired diastereomer followed by the removal of the BOC group with triiluoroacetic acid and then saponification gives lisinopril (13-2) [14]. 

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