Amino Acids and Dipeptides

Crystal stmctures of complexes of copper(II) with aromatic amine ligands and -amino acids " " and dipeptides" have been published. The stmctures of mixed ligand-copper complexes of L-tryptophan in combination with 1,10-phenanthroline and 2,2 -bipyridine and L-tyrosine in combination with 2,2 -bipyridine are shown in Figure 3.2. Note the subtle difference between the orientation of the indole ring in the two 1,10-phenanthroline complexes. The distance between the two... 

FIGURE 8.5 SEC of aromatic amino acids and dipeptides. Column Same as Fig. 8.1. Flow rate 0.6 ml/min. Mobile phase 50 m/VI formic acid. Detection Ajj, = 0.5 AUFS. 

In the case of simple amino acids and dipeptides, esterification of the carboxyl groups occurs on heating in toluene with the appropriate bis(triorganotin) oxide or triorganotin hydroxide 481, 482), the water being removed azeotropically. 

PepTl gene by selective amino acids and dipeptides in the diet [81]. It has also been reported that the integrated response to certain stimuli may increase PepTl activity by translocation from a preformed cytoplasm pool [52]. 

When Linus Pauling and Robert Corey carried out their pioneering X-ray crystallographic studies on a number of amino acids and dipeptides in the 1930s and 1940s, they... 

Kinetic data for release of p-nitrophenol from amino acid and dipeptide ester salt substrates in the presence of the macrocyclic reagent [3271 ... 

Isopropylidene methoxymethylenemalonate (420) was reacted with amino esters, amino acids, and dipeptides at 95-100°C to give rise to the corresponding isopropylidene aminomethylenemalonates (424) in 54-85% yields (85MI3 86YZ154). 

The chapter is divided into three sections the first part is concerned with the derivation of 3D-LogP descriptor and the selection of suitable parameters for the computation of the MLP values. This study was performed on a set of rigid molecules in order, at least initially, to avoid the issue of conformation-dependence. In the second part, both the information content and conformational sensitivity of the 3D-LogP description was established using a set of flexible acetylated amino acids and dipeptides. This initial work was carried out using log P as the property to be estimated/predicted. However, it should be made clear that, while the 3D-LogP descriptor can be used for the prediction of log P, this was not the primary intention behind its the development. Rather, as previously indicated, the rationale for this work was the development of a conformationally sensitive but alignment-free lipophilicity descriptor for use in QSAR model development. The use of log P as the property to be estimated/predicted enables one to establish the extent of information loss, if any, in the process used to transform the results of MLP calculations into a descriptor suitable for use in QSAR analyses. 

Experimental and Estimated log P0ct/water Values for a Set of 49 Acetylated Amino Acids and Dipeptides... 

Comet, M. and Bousset, J. (1999). Free amino acids and dipeptides in porcine muscles Differences between red" and "white" muscles. Meat Sci. 51, 215-219. 

Fonteh, A. N., Harrington, R. J., Tsai, A., Liao, P., and Harrington, M. G. (2007). Free amino acid and dipeptide changes in the body fluids of Alzheimer s disease subjects. Amino Acids 32, 213-224. 

An example of the above mentioned cascade complexation of carboxylates by macrocyclic receptors containing metal ionic centers is the inclusion of oxalate by the dien dicobalt complex 9 (Martell, Mitsokaitis) [12]. Similarly, the -cyclodextrin (jS-CD) 10, modified with a zinc cation bound by a triamine side chain, encapsulates anions like 1-adamantylcarboxylate in its cavity, fixing them by combined electrostatic and hydrophobic interactions [13], Zinc s group achieved the enantioselective transport of the potassium salts of N-protected amino acids and dipeptides by making use of the cation affinity of... 

Free amino acids and dipeptides are taken up by the intestinal epithelial cells. There, the dipeptides are hydrolyzed in the cytosol to amino acids before being released into the portal system. Thus, only free amino acids are found in the portal vein after a meal containing protein. These amino acids are either metabolized by Ihe liver or released into the general circulation. 

In the small intestine, proteases released by the pancreas as zymogens become active. Each has a different specificity for the amino acid R-groups adjacent to the susceptible peptide bond. Examples of these enzymes are trypsin, chymotrypsin, elastase, and car-boxypeptidase A and B. The resulting oligopeptides are cleaved by aminopeptidase found on the luminal surface of the intestine. Free amino acids and dipeptides are then absorbed by the intestinal epithelial cells. 

Trimethyl orthoformate has been used as a solvent by Campbell and co-workers for site-selective monoalkylation in SPPSi1 % Trimethyl orthoformate was previously shown to be a highly efficient dehydrating solvent for the formation of imines. 112 Thus, dividing the reductive alkylation step into two separate substeps of (1) imine formation followed by solvent removal and (2) reduction, resulted in on-resin monoalkylation of various amino acids and dipeptides (Scheme 26). 

Modification of the peptide backbone, including C -alkyl a-amino acids, a, 3-didehydro a-amino acids, and Na<->C and C° Ca cyclized a-amino acids and dipeptides, may influence the conformational properties of the resulting pseudopeptide molecules while preserving the mandatory side-chain substituents. 

K Stulik, V Pacakova, H Wang. High-performance liquid chromatography of amino acids and dipeptides on new ion exchangers of the HEMA series. J Chromatogr 552 439-448, 1991. 

K Shimada, K Hirakata. Retention behavior of derivatized amino acids and dipeptides in high-performance liquid chromatography using cyclodextrin as a mobile phase additive. J Liq Chromatogr 15 1763-1771, 1992. 

Efficient asymmetric hydrogenation of alkenes other than the amino acid and dipeptide precursors described above has met with only limited success. This appears to be at least in part due to the inability of many alkenes to function as bidentate chelates. Ethyl 2-acetoxyacrylate was hydrogenated with an enantiomer excess of 89% using [Rh(cod)(R,R-DIPAMP)]+, giving the S-enantiomer (equation 53). The ligands CHIRAPHOS, PROPHOS, DIOP, BPPM and CAMP were less effective.266... 

Stereoselectivity in the metal complexes of amino acids and dipeptides has been reviewed by Pettit and Hefford,87 and will not be discussed further here. 

Baurain, R., M. Masquelier, D. Deprez-De Campeneere, and A. Trouet. 1980. Amino acid and dipeptide derivatives of daunorubicin. 2. Cellular pharmacology and antitumor activity on L1210 leukemia cells in vitro andin vivo. J. Med. Chem23 1171-1174. 

Wang,T. S. C., Chen, J.-H., and Hsiang, W.-M. (1985). Catalytic synthesis of humic acids containing various amino acids and dipeptides. Soil Sci. 140, 3-10. 

Aside from gastrointestinal and renal metabolism, the liver may also contribute substantially to the metabolism of peptide and protein drugs. Proteolysis usually starts with endopeptidases that attack in the middle part of the protein, and the resulting oligopeptides are then further degraded by exopeptidases. The ultimate metabolites of proteins, amino acids and dipeptides, are finally reutilized in the endogenous amino acid pool. The rate of hepatic metabolism is largely dependent on specific amino acid sequences in the protein. 

CSF, plasma, urine AD patients (n = 8), healthy subjects (n = 8) Metabolic profiling of amino acids and dipeptides HPLC-MS2 (87)... 

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