Amino trifunctional

FIGURE 1 Schematic representation of the use of trifunctional amino acids as monomeric starting materials for the synthesis of pseudopoly-(amino acids), (a) Polymerization via the C terminus and the side chain R. (b) Polymerization via the N terminus and the side chain R. (c) Polymerization via the C terminus and the N terminus. The wavy line symbolizes any suitable nonamide bond. See text for details. ... 

A convenient molecule from which to build trifunctionals is the amino acid, L-lysine. Its three functional groups, a-carboxy, a-amino, and e-amino, can be derivatized independently to contain three arms. Each arm can be designed to terminate in a complexing group able to participate in a particular type of conjugation reaction or affinity interaction. 

Interest in Fixing Agent P (7.123) has been revived in the context of nucleophilic aminoalkyl dyes of the 7.129 and 7.131 types. Nylon pretreated with this symmetrical trifunctional reactant contains residual acryloyl sites that will undergo an addition reaction with nucleophilic dye molecules [145]. Although in theory each N-terminal amino group in the fibre can give rise to two acryloyl sites (Scheme 7.73), crosslinking between two N-... 

TRIFUNCTIONAL AMINO ACIDS WITH TWO DIFFERENT PROTECTORS... 

FIGURE 6.30 Approaches for the synthesis of monosubstituted trifunctional amino acids. (A) Monoesterification of dicarboxylic acids. (B) Aa-Alkoxycarbonylation of lysine through the e-benzylidene derivative [Bezas Zervas, 1963]. (C) SelectiveN -detritylation of ditrityl derivatives.138 (D) A- AI ko x y met hy 1 at 10 n of histidine by displacement of AP-substituents.137 Cbz-His(CH2OR)-OMe are obtained from Cbz-His(xAc)-OMe. = Acylating reagent. 

Dicyclohexylamine (10) is a base employed as counter ion for crystallizing acid-sensitive -protected amino acids and /V-protected amino acids that do not crystallize as the acids. Its use allows removal of unreacted substrate after /V-methylation of trifunctional amino acid derivatives (see Section 8.13). 

Collagen cross-links. Besides amide bonds between amino acids in the same a chain, bonds between amino acid side chains of different a chains can form "cross-links". These bonds originate from enzymatically-oxidized side chains of lysine and hydroxylysine residues. The oxidized residues react with other lysine and hydroxylysine residues, forming difunctional products. Reactions of such products with oxidized lysine or hydroxylysine yield trifunctional cross-links (Reiser et al., 1992). 

Suyama K, Yamazaki K and Nakamura P (1995) Gyclopentenosine, trifunctional crosslinking amino acid of elastin and collagen, characterization and distribution. Spec Publ - R Soc Chem 151, 425. 

The nomenclature of the RP is not consequent. The RP most often used contains octyl (RP C8) or octadecyl (RP C18) groups. There is no differentiation even when two methyl groups are introduced additionally with the silane (as with monofunctional silanes) or only one (difunctional) or none (trifunctional silane). Some manufacturer use silanes with bulky side groups (e.g., isopropyl groups) to improve the hydrolytic stability of the bonded phases, but here also, only the longest alkyl group is used in nomenclature. RP C8 and RP C18 are the work horses in HPLC. Shorter chains (RP4) are used in protein separations, and special selectivity can be obtained with bonded phenyl, cyano, amino or fluoro groups. 

Taking advantage of the side-chain linkage of C-terminal trifunctional amino acids to solid supports, related iV-mono(alkyl)amides or Ai-bis(alkyl)amides serve for the production of C-terminally lipidated peptides. So far, this approach has been reported only for the synthesis of a C-terminally mono-alkylated peptide.1 1 ... 

PG1 = 1st order protecting group PG2 = 2nd order protecting group PG3 = 3rd order protecting group R1,R2 = side-chain of trifunctional amino acid... 

Aspartame, discovered by Mazur in 1969 (5), is 200 times sweeter than sucrose. Aspartame has a large commercial market as an artificial sweetening agent. It is apparent that the sweetness exhibited by aspartame requires amino (AH, electropositive) and carboxyl (B, electronegative) groups of aspartic acid moiety and the hydrophobic side chain (X) of the phenylalanine moiety (4). The sweetness of aspartame is exhibited by the trifunctional units AH, B, and X. It is thought that when the trifunctional units of aspartame, X, AH, and B, fit the corresponding receptor sites, a sweet taste is produced. 

Polyfunctional OH Components (Crosslinkers). For crosslinking, trifunctional alcohols are used mainly. Some are of the same type as the difunctional prepolymers—e.g., polyethers derived from trifunctional initiators (glycerol, trimethylolpropane, 1,2,6-hexanetriol) and propylene or butylene oxide—and are preferred. Low molecular weight alcohols are used also. Examples are the ones listed above and glycerol monoricinole-ate, glycerol triricinoleate and amino alcohols like triethanolamine. 

Polymers of different isomeric structures were prepared on the basis of 2,4,6-triaminotoluene (TAT) - the simplest TNT derivative [48]. As this compound is trifunctional, at least one amino group must be blocked before the polycondensation reaction to avoid gelation. Preparation of the polyimides was carried out using the following approaches ... 

RIS theory, in the form appropriate for branched molecules, is used to calculate the mean-square unperturbed radius of gyration, < s2>0, for cross-linked polyglycine, poly(L-alanine),poly(L-proline),poly(i-alanyl-D-alanine),poly(i.-prolyl-L-pro lylglycine),poly(L-prolyl-i.-alanylglycine ,poly(glycyl-L-alanyl-L-pro line), andpoly(L-aianyl-L-alanylgIycine).Thecentral amino acid residue in each polypeptide chain is replaced by the L-cysteinyl residue involved in cross-link formation. Each cross-linked molecule is considered to contain two trifunctional branch points, the a-carbon atoms of the two... 

Tropoelastin molecules are crosslinked in the extracellular space through the action of the copper-dependent amine oxidase, lysyl oxidase. Specific members of the lysyl oxidase-like family of enzymes are implicated in this process (Liu etal, 2004 Noblesse etal, 2004), although their direct roles are yet to be demonstrated enzymatically. Lysyl oxidase catalyzes the oxidative deamination of e-amino groups on lysine residues (Kagan and Sullivan, 1982) within tropoelastin to form the o-aminoadipic-6-semialdehyde, allysine (Kagan and Cai, 1995). The oxidation of lysine residues by lysyl oxidase is the only known posttranslational modification of tropoelastin. Allysine is the reactive precursor to a variety of inter- and intramolecular crosslinks found in elastin. These crosslinks are formed by nonenzymatic, spontaneous condensation of allysine with another allysine or unmodified lysyl residues. Crosslinking is essential for the structural integrity and function of elastin. Various crosslink types include the bifunctional crosslinks allysine-aldol and lysinonorleucine, the trifunctional crosslink merodes-mosine, and the tetrafunctional crosslinks desmosine and isodesmosine (Umeda etal, 2001). 

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