Amino acids and derivatives

A complex (-503 ppm) is readily formed when one acetate is replaced with the pyridyl functionality (2-Cyr). These complexes have octahedral coordination in the solid state, and unlike the complexes described above, this coordination is retained in aqueous solution [49], The ligand is complexed in a tetradentate fashion, and here, as similarly observed for the analogous amino alcohol complexes, the presence of pyridine in the coordination sphere has little influence on 51V NMR chemical shifts. Other complexes with similar tetradentate ligands have also been found to retain octahedral coordination when in aqueous medium [54], 

Picolinic acid (pyridine 2-carboxylic acid) is the prototype for this type of ligand. Pyridine itself does not react favorably with vanadate, nor do the 3 and 4 pyridine carboxylates. At first sight, one would expect that 2-hydroxypyridine would react favorably with vanadate, but this is not true. There are two likely explanations for this. First, the 2-hydroxypyridine exists predominantly as the keto tautomer, so the effective concentration of the hydroxylate is low. The keto form of the ligand can be expected to be much less reactive than the hydroxyl form. Second, the formation 

2-Hydroxybenzoic acid (salicylic acid) does form a complex, although its formation is not favored when compared to that of the picolinato ligand. Presumably this, at least to an extent, reflects the fact that the chelate formed with salicylate has a six-membered ring, and six-membered chelates are much less favored than the five-membered analogue. 

Unfortunately, a time course study was not reported in that work, so it is not known whether the crystalline compound corresponds to the -513 or -552 ppm signal of the solution study. However, it seems most likely that the -515 ppm signal corresponds to the bisligand compound of the crystal structure and the -554 ppm signal to the partially hydrolyzed product. Chemically, it seems likely that partial hydrolysis rather than isomerization occurs on dissolution. Additionally, isomerization of VL2 would be expected to provide three NMR signals not just two, whereas two signals would be expected from partial hydrolysis. 

Pyridine 2,6-dicarboxylic acid (dipic) also reacts favorably in a tridentate manner with vanadate to form a distorted trigonal bipyramidal complex [60], Multinuclear NMR studies of the complex in aqueous solution were consistent with the formation of only one complex (-533 ppm) that was monoanionic and had VL stoichiometry and a solution structure that corresponded to the crystalline compound [61], A pH variation study of a sample (10 mM in H20) prepared from the crystalline material showed that this complex is stable over a very wide pH range. Although it was almost fully dissociated at pH 7.3, the complex regenerated at lower pH and was almost fully formed at pH 6. At pH 0.4, it was partially dissociated to cationic vanadate but was still about half formed at pH 0.3 [61], One of the reasons for the extended range under strongly acidic conditions is the fact that the complex can be protonated and has a pKa very close to 0. This compound is a well-known insulin- 

Greene, P. G. M. Wuts, Protective Groups in Organic Synthesis, 2 ed., John Wiley Sons, New York (1991). 

Application of Amino Acid Esters and other Amino Acid Derivatives  

Vorbrueggen, K. Krolikiewicz, Tetrahedron 49 (1993) 9353. (+)-(S)-2-Amino-2-phenyl-ethanol 

Pouilhes, E. Uriarte, C. Kouklovsky, N. Langlois, Y. Langlois, A. Chiaroni, C. Riche, Tetrahedron Lett. 30 (1989) 1395. 

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Anderson, D.M. and Hsiao, H.-H. (1992) In Biocatalytic Production of Amino Acids and Derivatives (eds D. Rozzell and F. Wagner), Hanser, Munich,... 

T Wieland, H Bernhard. On the synthesis of peptides. Part 3. The use of anhydrides of N-acylated amino acids and derivatives of inorganic acids. Ann Chem 572, 190, 1951. 

CHROMATOGRAPHIC APPLICABILITY SPECTRUM 1.8.1 Analysis of Amino Acids and Derivatives... 

Pll The asymmetric synthesis of a-amino acids and derivatives is an important topic as a result of their extensive use in pharmaceuticals and agrochemicals and as chiral ligands. Many highly enantioselective approaches have been reported. Industrial production of a-amino acids via the Strecker reaction is historically one of the most versatile methods to obtain these compounds in a cost-effective manner, making use of inexpensive and easily accessible starting materials. (From Boesten et al., 2001)... 

Kempe M, Mosbach K. Chiral recognition of N alpha-protected amino acids and derivatives in non-covalently molecularly imprinted polymers. Int J Peptide Protein Res 1994 44 603 -606. 

Monsigny, M., Quetard, C., Bourgerie, S., Delay, D., Pichon, C., Midoux, P. et al. (1998) Glycotargeting the preparation of glyco-amino acids and derivatives from unprotected reducing sugars. Biochimie, 80, 99-108. 

Amino acids (and derivatives) Carbowax 600 diethylene glycol succinate (stabilized) Ethofat (on chromosorb T) ethylene glycol succinate neopentyl glycol adipate SE-30 XE-60 (methyl silicone phases)... 

Caprio, J., Olfaction and taste in the channel catfish an electrophysiological study of the responses to amino acids and derivatives, J. Comp. Physiol. A, 123, 357, 1978. 

Carlton, G. J. The Enzymatic Production of L-Aspartic Acid. In Biocatalytic Production of Amino Acids and Derivatives, Rozzell, J. D., Wagner, F. Eds., Hanser Publishers, 1992, p. 4. 

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