Aspartic acid resolution

In the best cases it was possible to achieve [(R, S) glutamic acid and (S) lysine (R, S)-threonine + (S) glutamic acid (R,S) asparagine + (S) aspartic acid] resolution with quantitative enantiomeric excess. The growth of the affected crystals in these instances was delayed up to several days with respect to that of the unaffected ones. In all of the systems investigated it could be demonstrated that the additive is occluded throughout the bulk of the affected crystals in amounts ranging typically from 0.05 to 1.5% w/w of substrate it was found in much smaller amounts, if any, in the crystals of the enantiomorph. 

The improvements in resolution achieved in each deconvolution step are shown in Figure 3-3. While the initial library could only afford a modest separation of DNB-glutamic acid, the library with proline in position 4 also separated DNP derivatives of alanine and aspartic acid, and further improvement in both resolution and the number of separable racemates was observed for peptides with hydrophobic amino acid residues in position 3. However, the most dramatic improvement and best selectivity were found for c(Arg-Lys-Tyr-Pro-Tyr-(3-Ala) (Scheme 3-2a) with the tyrosine residue at position 5 with a resolution factor as high as 28 observed for the separation of DNP-glutamic acid enantiomers. 

Fumaric acid to L-aspartic acid, L-aspartic acid to L-alanine Enzymatic resolution of methyl ester of (+/-) trans 4- methoxy-... 

The method is limited in the scope as it has been successfully tried only in two amino acids, glutamic acid and aspartic acid. In others it has resulted only in partial resolution. Harada has now (1965) succeded in resolving free amino acids by inoculation. 

A contemporaneous study on the same subject utilized a chemical correlation method where (—)-A-benzylargemonine chloride, obtained by sequential optical resolution and quatemization of ( )-7V-methylpavine (5), underwent a multistep degradative process to furnish (-)-A,A-dimethyl-di-H-propyl aspartate. Comparison of this final product with L-aspartic acid of known chirality led to the absolute configuration of (—)-5 (115,158). (—)-Eschscholtzine (9) was assigned the same absolute configuration by correlation of its ORD curve and optical rotation with those of (—)-argemonine (775). 

In all tRNAs the bases can be paired to form "clover-leaf" structures with three hairpin loops and sometimes a fourth as is indicated in Fig. 5-30.329 331 This structure can be folded into the L-shape shown in Fig. 5-31. The structure of a phenylalanine-carrying tRNA of yeast, the first tRNA whose structure was determined to atomic resolution by X-ray diffraction, is shown.170/332 334 An aspartic acid-specific tRNA from yeast,335 and an E. coli chain-initiating tRNA, which places N-formyl-methionine into the N-terminal position of proteins,336,337 have similar structures. These molecules are irregular bodies as complex in conformation as globular proteins. Numerous NMR studies show that the basic... 

FIGURE 11 The effects of phosphate buffer concentration (ionic strength) on the chiral resolution of (a) rf-ephedrine ( ), /-ephedrine ( ), (/-norephedrine ( ), and /-norephedrine (O) and (b) the dansyl amino acids aspartic acid (A), glutamic acid (O), serine ( ), and phenylalanine (V) on /1-CD columns. (From Refs. 65,70.)... 

In addition to resolution approaches, there are three main methods to prepare amino acids by biological methods addition of ammonia to an unsaturated carboxylic acid the conversion of an a-keto acid to an amino acid by transamination from another amino acid, and the reductive animation of an a-keto acid. These approaches are discussed in Chapter 19 and will not be discussed here to avoid duplication. The use of a lyase to prepare L-aspartic acid is included in this chapter as is the use of decarboxylases to access D-glutamic acid. 

Historically, L-aspartic acid was produced by hydrolysis of asparagine, by isolation from protein hydrolysates, or by the resolution of chemically synthesized d,L-aspartate. With the discovery of aspartase (L-aspartate ammonia lyase, EC 4.3.1.1),57 fermentation routes to L-aspartic acid quickly superseded the initial chemical methods. These processes are far more cost effective than the fermentation routes, and aspartate is now made exclusively by enzymatic methods that use variations of the general approach outlined in Scheme 2.19.53-57-65... 

Other resolving agents are readily prepared from inexpensive chiral starting materials such as glucose, aspartic acid, or glutamic acid. A literature example is the use of /V-methylglucamine 6, obtained by reductive amination of D-glucose, in the resolution of naproxen (Chapter 6).13... 

A number of decarboxylase enzymes have been described as catalysts for the preparation of chiral synthons, which are difficult to access chemically (see Chapter 2).264 The amino acid decarboxylases catalyze the pyridoxal phosphate (PLP)-dependent removal of C02 from their respective substrates. This reaction has found great industrial utility with one specific enzyme in particular, L-aspartate-P-decarboxylase (E.C. 4.1.1.12) from Pseudomonas dacunhae. This biocatalyst, most often used in immobilized whole cells, has been utilized by Tanabe to synthesize L-alanine on an industrial scale (multi-tons) since the mid-1960s (Scheme 19.33).242-265 Another use for this biocatalyst has been the resolution of racemic aspartic acid to produce L-alanine and D-aspartic acid (Scheme 19.34). The cloning of the L-aspartate-P-decarboxylase from Alcaligenes faecalis into E. coli offers additional potential to produce both of these amino acids.266... 

Although DTPAMP is a suitable ligand for this reaction as well, the industrial process uses the diphosphine DNNP. Unfortunately, the product is initially obtained in rather modest enantiomeric excess (83%), but recrystallization improves this to 97%. In the manufacture of aspartame, coupling with natural (and therefore 100% ee) aspartic acid turns the 1.5% of the minor enantiomer into a diastereoisomeric impurity that can be removed by crystallization (essentially a resolution). 

Figure 3 shows a comparison of the membrane topologies of the En. hirae CopB copper ATPase and the Ca " -ATPase of sarcoplasmic reticulum. The three-dimensional structure of the latter has recendy been derived to a resolution of 2.6 A (Toyoshima et al., 2000). The residue that has been demonstrated to be phosphorylated is the aspartic acid in the conserved sequence DKTGT (given in single-letter amino acid code. 

Using amphoteric, isoelectric buffers at pH close to their isoelectric points (p7), at which the electrolytes have a net charge of zero, is an efficient way to decrease the BGE conductivity and apply extremely high field strength. Thus the separation time can be reduced to the order of a few minutes, and high resolution is achieved as a result of minimal diffusion-driven peak spreading. Several acidic isoelectric buffers, such as cysteic acid (p7 1.85), iminodiacetic acid (p7 2.23), aspartic acid (p7 2.77), and glutamic acid (p7 3.22), all at 50 mM concentra-... 

The synthesis of various phosphonate analogues of aspartic acid, glutamic acid and their homologues and serine phosphate have been reported. The kynurenine phosphinic acid analogue 217 and the corresponding phosphinate 218 have been synthesised from iV-protected 2-amino P-propiolactone (Scheme 27). Kinetic resolution was achieved by esterase-selective hydrolysis of the carboxylate group in the diester. 

---