Valine, 490 Table

In 1980, Kelly Rein began an investigation into the use of an oxazoline chiral auxiliary to effect ditistereoseleetive additions of Grignard reagents based on the Seebaeh discovery. The initial effort 46 used an oxazoline auxiliary derived from valine (Table 53, entry 5), one that we had used previously in studies of asymmetric alkylations of... 

Other examples are glycine — formaldehyde, alanine — acetaldehyde, valine — isobutyraldehyde, phenylalanine — phenylacetaldehyde, and methionine — methional (106). Products such as dried skim milk, dried eggs, and dehydrated vegetables and fmits are particularly susceptible to deteriorative flavor changes ascribed to this reaction (Table 10). 

Many kinds of amino acids (eg, L-lysine, L-omithine, t-phenylalanine, L-threonine, L-tyrosine, L-valine) are accumulated by auxotrophic mutant strains (which are altered to require some growth factors such as vitamins and amino acids) (Table 6, Primary mutation) (22). In these mutants, the formation of regulatory effector(s) on the amino acid biosynthesis is genetically blocked and the concentration of the effector(s) is kept low enough to release the regulation and iaduce the overproduction of the corresponding amino acid and its accumulation outside the cells (22). 

The IPNS enzyme has also been shown to recognize modified tripeptides. The synthesis of a range of tripeptides, other than aminoadipoyl cysteinyl valine (ACV) (Table 6), has given rise to a selection of modified penicillins using IPNS as a means of cyclizing the tripeptide (58). 

Fig. 4. Structures of DNA interactive agents are given in Table 3. In structure (38) L-MeVal is 1-/V-metby1 valine.

However, the use of a HPLC separation step enabled a remarkable acceleration of the deconvolution process. Instead of preparing all of the sublibraries, the c(Arg-Lys-O-Pro-O-P-Ala) library was fractionated on a semipreparative HPLC column and three fractions as shown in Fig. 3-2 were collected and subjected to amino acid analysis. According to the analysis, the least hydrophobic fraction, which eluted first, did not contain peptides that included valine, methionine, isoleucine, leucine, tyrosine, and phenylalanine residues and also did not exhibit any separation ability for the tested racemic amino acid derivatives (Table 3-1). 

Table 8-2. Singe column (3.9 g ChiraLig ) loading curve of 24 mM D-methyl ester valine versus 25 mM L-methyl ester valine in 3 M LiClO and 0.1 M HCIO at a flowrate of 0.4 ml min . ...

Table 1.11 based 80. Chiral induction through the use of the valine ... 

Otto et al. studied asymmetric Diels-Alder reactions in the presence of the copper salts of glycine, L-valine, L-leucine, L-phenylalanine, L-tyrosine, l-tryptophan, and /V-a-L-tryptophan (L-abrine). The copper salt of L-abrine gave the highest enantioselectivity. Table 5 3 compares the solvent effect in this reaction, and clearly water is the best solvent among the solvent systems studied. 

The amounts of single amino acids excreted in urine in the conjugated form, as determined independently by Stein and Muting, are given in Tables 1 and 2. According to Stein, glycine, glutamic acid, aspartic acid, histidine, and proline are quantitatively the most important amino acids liberated in the course of urine hydrolysis. Serine, lysine, tyrosine, cysteine and cystine, threonine, alanine, valine, phenylalanine, and leucine are... 

As noted by the original authors (Dorovska et al., 1972), and cited by Fersht (1985), there is an excellent linear correlation between log/ccat/KM and the Hansch hydrophobicity parameters (v) of the side chains (Fig. 9, A), except for the two branched side chains (valine and isoleucine residues). However, since the ku values for the esters do vary somewhat (Table A6.8), the values of pKrs do not correlate as strongly with ir (Fig. 9, B). Moreover, the plot shows distinct curvature which probably indicates the onset of a saturation effect due to the physical limits of the Sj binding pocket, adjacent to the enzyme s active site. Still, the points for valine and isoleucine deviate below the others, suggesting that the pocket has a relatively narrow opening. 

Fig. 9 Correlation of (A) the second order rate constants (k2 = kcatIKM) and (B) the transition stabilization (pATS) with the hydrophobicity (it) of the substituent of the amino acid residue for the cleavage of /V-acetylamino acid methyl esters by a-chymotrypsin. The open symbols are for the points for two branched residues (valine and isoleucine). Data from Table A6.8.

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