Valine polymer

The polymer-supported chiral oxazaborolidinone catalyst 5 prepared from valine was found by Ituno and coworkers to be a practical catalyst of the asymmetric Diels-Alder reaction [7] (Scheme 1.12). Of the several cross-linked polymers with a... 

Based on chiral functional monomers such as (15), MICSPs can be prepared using a racemic template. Thus, using racemic A-(3,5-dinitrobenzoyl)-a-methylbenzy-lamine (16) as template, a polymer capable of racemic resolution of the template was obtained [67]. Another chiral monomer based on L-valine (17), was used to prepare MIPS for the separation of dipeptide diastereomers [68]. In these cases the configu-... 

Similar to the work described by Spohn et al. [34], a trienzyme sensor was developed recently for the determination of branched-chain amino acids (L-valine, L-leucine, and L-isoleucine). Leucine dehydrogenase, NADH oxidase, and peroxidase were coimmobilized covalently on tresylate-hydrophylic vinyl polymer beads and packed into a transparent PILL tube (20 cm X 1.0 id), which was used as flow cell. The sensor was free of interferences from protein and NH4+ and it was stable for 2 weeks. The sensor system was applied to the determination of branched-chain amino acids in plasma with recoveries ranging from 98 to 100% [36],... 

Fig. 5. Structure and biological activities of Kiessling s initial carbohydrate-substituted polymers generated by ROMP. Relative inhibitory potency the saccharide residue concentration needed to inhibit the agglutination of red blood cells mediated by the protein concana-valin A... 

Their studies involved the partial polymerization of NCAs of mixtures of specific amino adds having known e.e.s, followed by determination of the e.e.s of the amino adds in both the resulting polypeptides and in the residual unreacted NCA monomers. [94] In a typical experiment it was found that when an optically impure leucine NCA monomer having an l > d e.e. of 31.2% was polymerized to the extent of 52 % to the helical polyleucine peptide, the e.e. of the polymer was enhanced to 45.4 %, an increase of 14.2 %. In the same experiment the e.e. of the unreacted leucine NCA monomer was depleted to a similar extent. Analogous experiments with valine NCAs of known e.e.s, however, led to a reverse effect, namely, the preferential incorporation of the racemate rather than one enantiomer into the growing polyvaline peptide. This finding was interpreted to be the result of the fact that polyvaline consists of (3-sheets rather than a-helices, emphasizing that the Wald mechanism applies only to a-helix polymers. At about the same time Brach and Spach [95] showed that, under proper conditions, (3-sheet polymers could also be implicated in the amplification of amino add e.e.s. 

The H- and C-NMR spectroscopic data support the proposed primary structure of poly(Lys-25). The amide carbonyl resonances are particularly informative as these signals are well resolved in the C-NMR spectrum of poly(Lys-25) (Figure 4). An amide carbonyl resonance is observed at 174.9 ppm for poly(Lys-25) that does not appear in the spectrum of poly(Val-Pro-Gly-Val-Gly) [13]. The position and relative intensity of this resonance are consistent with a lysine amide carbonyl group within a peptide bond [14]. Moreover, the resonances of the amide carbonyl groups for other residues in the pentapeptide repeat are split due to the substitution of a lysine residue at position 4 in every fifth pentapeptide in Lys-25. In addition, the absence of splitting in amide carbonyl group of valine in position 4 (174.5 ppm) supports this assignment, as this residue is replaced by lysine in the fifth pentapeptide of the Lys-25 repeat. The presence of other resonances attributable to the lysine residue can be detected in the H- and C-NMR spectra of the Lys-25 polymer at levels commensurate with its... 

The effect of chain length on surface tension arises from the fact that, as the hydrophobicity increases with each -CH2- group, the amphiphile molecule adsorbs more at the surface. This will thus be a general trend in more complicated molecules also, such as proteins and other polymers. In proteins, the amphiphilic property arises from the different kinds of amino acids (25 different amino acids). Some amino acids have lipophilic groups (such as phenylalanine, valine, leucine, etc.), while others have hydrophilic groups (such as glycine, aspartic acid, etc.) (Figure 3.4). 

Valine and tert-leucine derived cyclohexanone imines were hydrolyzed with 5% aqueous citric acid in an ice bath under vigorous stirring for 25 minutesi-17. From the acidic layer 67% of the chiral auxiliary was recovered3. Aldimines13. acyclic ketimines10, and cyclic polymer-... 

The co-polymerization of D-alanine-derived A-propargylamide 22, L-valine-derived 23, and pyrene-based monomer 24 gives helical poly(22 -< o-23-c -24) carrying pyrene. The secondary structure of the co-polymer is tunable by the composition of the optically active amino acid units and solvent, which makes it possible to control the direction of the pyrene groups in the side chain. The interaction between the pyrene groups is small when the co-polymer takes a helical structure. The pyrene groups are regularly positioned in the polymer side chain. The co-polymer emits weak... 

Similarly, good results were obtained with poly-(L)-alanine, poly-(L)-leucine and poly-(L)-isoleucine, whereas with poly-(L)-valine or random copolymers reduced chemical yields as well as asymmetric induction were obtained. Chemical and optical yields are closely related in all cases. The enantiomeric excesses obtained increased as the average chain length of the catalyst increased varying from 10 to 30 amino acids (ee values between 50 to 99%). For high ee values it seems to be essential that the polymer chain is at least 10 units154. The degree of asymmetric induction decreases as the temperature is raised. The amount of catalyst only influences the chemical yield, not the optical yield of... 

The synthesis and characterization of water-soluble "random" copolymers containing t-valine with either A -O-hydroxypropyD-L-glutamine or / -(A-hydroxybutyD-L-glutamine are described, and the thermally induced helix-coil transitions of these copolymers in water are studied. The incorporation of /.-valine is found to decrease the helix content of the polymer at low temperatures and increase it at high temperatures. The Zimm-Bragg parameters o and s for the helix-coil transition in poly(t-valine) in water are deduced from an analysis of the melting curves of the copolymers. The values of s, computed for o = 1 x 1CI-4, are s 0.85 (273 K), 0.93 (293 K), 1.00 (313 K), 1.06 (333 Kl. 

A second enzyme (of mass 100 kDa) is needed for activation of phenylalanine. It is apparently the activated phenylalanine (which at some point in the process is isomerized from l- to D-phenylalanine) that initiates polymer formation in a manner analogous to that of fatty acid elongation (Fig. 17-12). Initiation occurs when the amino group of the activated phenylalanine (on the second enzyme) attacks the acyl group of the aminoacyl thioester by which the activated proline is held. Next, the freed imino group of proline attacks the activated valine, etc., to form the pentapeptide. Then two pentapeptides are joined and cyclized to give the antibiotic. The sequence is absolutely specific, and it is remarkable that this relatively small enzyme system is able to carry out each step in the proper sequence. Many other peptide antibiotics, such as the bacitracins, tyrocidines,215 and enniatins, are synthesized in a similar way,213 216 217 as are depsipeptides and the immunosuppresant cyclosporin. A virtually identical pattern is observed for formation of polyketides,218 219 whose chemistry is considered in Chapter 21. 

A template polymer complex, which incorporates N-benzyl-D-valine with almost 100 % stereospecificity, has been synthesized by copolymerization of A-P2-[Co (R,R )-A, /V -bis(4-(vinylbenzyloxy)salicylidene]-l,2-diaminocyclohexane -(A-benzyl-D-valine)], styrene, and divinylbenzene, followed by dissociation of the coordinated amino acid 115). 

Several polyamides and polyurethanes have been synthesized by condensation polymerization and used as the precursors for the preparation of different CSPs. These CSPs showed different chiral recognition properties than those of addition polymers. AUenmark and Andersson [67] prepared a CSP containing silica gel supported by v-triazinc derivatives of L-valine isopropyl esters (Fig. 14) and the... 

FIGURE 14 Structure of polyamide-based CSP (.s-triazi ne derivative of L-valine isopropyl ester) (condensation polymer). (From Ref. 37.)... 

The Raillard group at Affymax developed a multigram synthesis of a 2,5-diketopiperazine and other heterocyclic systems by employing a high-load Merri-field resin transformed into polymer-supported valine, which was used as the amino component in an Ugi-4CR to gave the target diketopiperazine 137 after cleavage of 136 from the resin [77] (Scheme 2.49). 

Wamsley, A., Jasti, B., Phiasivongsa, P., and Li, X. Synthesis of random terpolymers and determination of reactivity ratios of IV-carboxyanhydrides of leucine, (1-benzyl aspartate, and valine. J. Polymer Sci. [A] Polymer Chem. 42 317—325, 2004. 

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