Alanine, isomers

Most non-protein aromatic amino acids are derived from L-phenylglycine (2-47), L-phenylalanine (2-4) or L-tyrosine (2-4). For example, various plants contain 3-carboxyphenylalanine, which is accompanied by 3-carboxyphenyltyrosine. Legumes of the genus Vigna (Fabaceae) contain 4-aminophenylalanine, the P-phenyl-fS-alanine isomer of phenylalanine (2-47) occurs in different types of beans Phaseolus spp.). 

Fig. 15 Simultaneous separations of five CBZ-derivatized brivanib alaninate isomers on a 25-cm X 4.6-mm Chiralcel OJ-RH column in reversed phase (a) and an OJ-H column in polar oiganic phase (b). Mobile phase (a) 50 50 20 mM NH40Ac ACN (b) MeOH [166]. The arrows link the enantiomeric pairs (adapted from [166])...

Figure 2.8 Using d- and L-glyceraldehyde to assign other chirai molecules as d or l. It is helpful to remember that L-glyceraldehyde has the OH group on the left in the Fisher projection when the aldehyde is at the top of the structure. The glyceric acid enantiomer shown has the OH on the right with the acid group on top and is assigned as o-gly-ceric acid, whereas the alanine isomer has the amino group on the left with the acid on top and so is i-alanine.

Alitame (trade name Adame) is a water-soluble, crystalline powder of high sweetness potency (2000X, 10% sucrose solution sweetness equivalence). The sweet taste is clean, and the time—intensity profile is similar to that of aspartame. Because it is a stericaHy hindered amide rather than an ester, ahtame is expected to be more stable than aspartame. At pH 2 to 4, the half-life of aUtame in solution is reported to be twice that of aspartame. The main decomposition pathways (Fig. 6) include conversion to the unsweet P-aspartic isomer (17) and hydrolysis to aspartic acid and alanine amide (96). No cyclization to diketopiperazine or hydrolysis of the alanine amide bond has been reported. AUtame-sweetened beverages, particularly colas, that have a pH below 4.0 can develop an off-flavor which can be avoided or minimized by the addition of edetic acid (EDTA) [60-00-4] (97). 

RS- P-Aminoisobutyric acid (a-methyl-P-alanine) [10569-72-9] M 103.1, m 176-178 , 178-180 , 181-182 , R -(-)- isomer [144-90-1] m 183 , [a] -21 (c 0.43, HjO), pKes,(,) 3.7, pKEst(2) 10.2. Colorless prisms from hot H O, were powdered and dried in vacuo. The purity is checked by paper chromatography (Whatman 1) using ninhydrin spray to visualise the amino acid Rp values in 95% MeOH and n-PrOH/5N HCOOH (8 2) are 0.36 and 0.50 respectively. [Kupiecki and Coon Biochem Prep 7 20 7960 Pollack J Am Chem Soc 65 1335 7943.] The R-enantiomer, isolated from iris bulbs or human urine was crystd from H2O and sublimed in vacuo [Asen et al. J Biol Chem 234 343 7959]. The RS-hydrochloride was recrystd from EtOH/Et20 m 128-129 , 130° [Bbhme et al. Chem Ber92 1258, 1260, 1261 7959]. 

In all the amino acids shown in Table 23.3 except glycine, the a-carbon is chiral. This means that these compounds are optically active. With alanine, for example, there should be two optical isomers ... 

The Separation of the Isomers of Methadone, Norphenylephrine and t-boc-Alanine by Mixed Retention... 

The phosphotriesterase from Pseudomonas diminuta was shown to catalyze the enantioselective hydrolysis of several racemic phosphates (21), the Sp isomer reacting faster than the Rp compound [65,66]. Further improvements using directed evolution were achieved by first carrying out a restricted alanine-scan [67] (i.e. at predetermined amino acid positions alanine was introduced). Whenever an effect on activity/ enantioselectivity was observed, the position was defined as a hot spot. Subsequently, randomization at several hot spots was performed, which led to the identification of several highly (S)- or (R)-selective mutants [66]. A similar procedure was applied to the generation of mutant phosphotriesterases as catalysts in the kinetic resolution of racemic phosphonates [68]. 

When the substrate is availabT in either the d- or 1-racemic form, it is preferable to use the appropriate isomer rather than its mixture In a case of transaminase assays for GOT and GPT activity, for example, the initial assays used the d-1 amino acid as substrate, and a marked improvement in activity and linearity was found by Henry and co-workers when they used 1-aspartate or 1-alanine, respectively (28) ... 

A simple and rapid method of separating optical isomers of amino acids on a reversed-phase plate, without using impregnated plates or a chiral mobile phase, was described by Nagata et al. [27]. Amino acids were derivatized with /-fluoro-2,4-dinitrophenyl-5-L-alanine amide (FDAA or Marfey s reagent). Each FDAA amino acid can be separated from the others by two-dimensional elution. Separation of L- and D-serine was achieved with 30% of acetonitrile solvent. The enantiomers of threonine, proline, and alanine were separated with 35% of acetonitrile solvent and those of methionine, valine, phenylalanine, and leucine with 40% of acetonitrile solvent. The spots were scraped off the plate after the... 

Alanine, valine, and leucine, (amino-acids with alkyl substituents only) react in a manner very like that of glycine (49—53). All the reactions are rather slow and boiling solutions are normally employed in the preparative reactions. With the cis- and /raws-isomers of Pt(NHs)2Cl2 substitution of the chloride only occurs. Since the tfraws-labilising influence of the incoming groups of the amino-acids is very small, the —NH2 groups remain stable. Consequently chelated complexes are only formed by the amino-acids in the case of the cts-isomer. 

A similar reaction of A-toluenesulfonyl derivatives of (.S )-alanine, phenylalanine, and valine (188-190) with PhPCl2 gave 4-methyl, benzyl, and isopropyl derivatives of 2-phenyl-1-p-toluenesulfonyl-l, 3,2-oxazaphospholidin-5-one, 191-193 in high yields (Scheme 53) [84], The ratios of the (2.V,4.V)/(2/f,4.V) diastereomers (which were designated as cis/trans isomers) were 1 1, 2 1, and 10 1 for 191a,b, 192a,b, and... 

Shindo, H., T. Komai, and K. Kawai. Studies on the metabolism of D- and L-isomers of 3,4-dihydroxyphenyl-alanine (DOPA). V. Mechanism of intestinal absorption of D- and L-DOPA-14C in rats. Chem. Pharm. Bull. 1973, 21, 2031-2038. 

In order to obtain a compound labeled with a radioactive isotope for studies about the pancreas, p-2- and /i-3-sclenienyl alanine were prepared. Initially the synthetic route shown in Scheme 14, which allowed insertion of radioactive selenium as late in the synthesis as possible, was designed for the ji-2 isomer (116).149... 

Figure 10. Possibilities of degradation or polycondensation reactions of MAR Key a, MAP b, optical isomer c, DNP-alanine d, DNP-ethylamine e, 2-nitroso-4-nitroaniline f DNP-alanyl-(DNP) a amino-propanoate of methyl and g,l,4-bis(DNP)-3,6-dimethyl-2,5-dioxopiperazine. [(DNP) = 2,4-dinitro-...

Some times the sign and extent of rotation help in determining which isomer has which configuration. This happens because rotation of structurally related compounds of identical configuration undergoes analogous changes under the influence of temperature, solvent or other factors. Let us study the molecular rotations of L(+) lactic acid and alanine. 

The first reaction is p-elimination in cysteine, serine, phosphoserine, and threonine residues due to attack by hydroxide ion, leading to the formation of very reactive dehydroalanine (DHA). In a cystine residue, this results in rupturing of the disulfide bond and liberation of a sulfide ion and free sulfur (Figure 13.4). Nucleophilic additions of the s-amino group of the protein-bound lysine to the double bond of DHA residue causes crosslinking of the polypeptide chain. After hydrolysis, a mixture of L-lysino-L-alanine and L-lysino-D-alanine, with probably a small proportion of dl and dd isomers,... 

The cycloalkylamine salts of 5-cyano-l-uracilacetic acid and analogues, exemplified by (LI), are claimed to produce marked inhibition of gastric secretion with virtually no anticholinergic activity [378]. This activity is not inherent in the free acetic acid nor in the amine. There is no distinction between optical isomers of the longer chain acids. The pyrimidine portion can be prepared by the treatment of a-cyano-/3-ethoxy-A -(ethoxycarbonyl)acrylamide with alanine or related derivatives [301,302]. 

Amino-4-cyclopropylidenebutanoic acid (2S)-56, is a methylenecyclopro-pane substituted alanine which can be considered as a non-natural isomer of hypoglycine A 51. It has recently been synthesized racemic [61] and enantiome-rically pure [62]. Biological assays have shown that at relatively high concentration the 5,6-methanoamino acid 56 inhibits the metabolism of pyruvate into glucose, but 56 is not active in inducing the mitochondrial oxidation of fatty acids,Eq. (21) [63]. 

As noted above, with the exception of alanine, the addition of amino acids to form polypeptides allows for a large number of stereochemical isomers to be formed, even considering that all are of the L form. But nature does not allow for this diversity and rather selects only one configuration for a sequence to occur in its synthesis of structure-specific proteins such as those employed as enzymes. Even those employed for other activities such as muscle have a specific geochemistry. In fact, the cell produces only geometry-specific polypeptides. 

Levodopa Levodopa, (-)-3-(3,4-dihydroxyphenyl)-L-alanine (10.1.1), is a levorotatory isomer of dioxyphenylalanine used as a precursor of dopamine. There are a few ways of obtaining levodopa using a semisynthetic approach, which consists of the microbiological hydroxylation of L-tyrosine (10.1.1) [1,2], as well as implementing a purely synthetic approach. 

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