Enantiomeric amino acids

One of the most useful applications of chiral derivatization chromatography is the quantification of free amino acid enantiomers. Using this indirect method, it is possible to quantify very small amounts of enantiomeric amino acids in parallel and in highly complex natural matrices. While direct determination of free amino acids is in itself not trivial, direct methods often fail completely when the enantiomeric ratio of amino acid from protein hydrolysis must be monitored in complex matrices. 

Chiral discrimination between enantiomeric amino-acid />-nitrophenyl ester hydrobromides in addition to enhanced rate of transacylation were reported by Chao and Cram (1976) for chiral 3,3 -Ws(mercaptomethyl)dinaphthyl-20-crown-6 [323]. Compared with a non-cyclic reference compound (5)-[324] the rates for a series of amino-acid esters are enhanced by factors of 102 to 103, except for L-proline. This once more demonstrates that reaction takes place in... 

T Kinoshita, Y Kasahara, N Nimura. Reversed-phase high-performance liquid chromatographic resolution of non-esterified enantiomeric amino acids by derivatization with 2,3,4,6-tetra-O-acetyl-P-D-glucopyranosyl isothiocyanate and 2,3,4 tri-O-acetyl-a-D-arabinopyranosyl isothiocyanate. J Chromatog 210, 77, 1981. 

Shinkai and coworkers prepared numerous novel amphiphilic crowns (Shinkai, 1990) and incorporated them into membranes, formed membranes from them, or used them in liquid crystalline assemblies to control properties (He et al., 1990). Interest in this area continues. Four chiral amphiphilic crown ethers were recently reported that recognize enantiomeric amino acids when examined as Langmuir films (Badis et al., 2004). Finally, it is interesting to note that liposomes formed from amphiphiles (e.g., crown ethers) having neutral headgroups (i. e., niosomes) have been studied as drug delivery vehicles (Uchegbu and Vyas, 1998). 

We analyzed several organic and inorganic phases identified from the Murchison and Murray meteorites [100] in order to determine whether they contain any possible chirality besides the enantiomeric amino acids [98]. Asymmetric autocatalysis is a method capable of revealing chiral imbalances in various media, therefore, we employed this method as a possible chiral sensor for the meteorites. 

Perez, M.T., Pausz, C., and Hemdl, GJ. (2003) Major shift in bacterioplankton utilization of enantiomeric amino acids between surface waters and the ocean s interior. Limnol. Oceanogr. 48, 755-763. 

Similarly, reversed-phase HPLC can be used as an Eilternative to the racemization test for amino acids as developed by Manning and Moore (115). Rivier and Burgus (109) have suggested the use of L-phenylalanine, coupled via the N-carboxyanhydride method to a hydrolysate, to monitor racemization during synthesis, although other hydrophobic L-amino acids should also prove equally effective. The use of /eri-butyloxycarbonyl-L-amino acid-Af-hydroxysuccinimide esters in the separation of enantiomeric amino acids and diastereoisomeric peptides has been described (110). Ultimately, these methods may not prove as versatile as the use of chiral stationary phases made by stereoselective control of the bonding process or, alternatively, with surface-active reagents similar to the D-... 

Fitznar, H. P., Lobbes, J. M., and Kattner, G. (1999). Determination of enantiomeric amino acids with high-performance liquid chromatography and pre-column derivatization with ophthaldiadehyde and N-isobutyrylcysteine in seawater and fossil samples (moUusks). l. Chrom. A 832, 123—132. 

R) -configuration indicates that the attack of the nitrogen atom took place from the re-face of the double bond of (E)-237. The (5)-configured trichloroacetamide (5)-238 was formed from the (Z)-olefin as the only detectable product via an approach of nitrogen from the ii-face of the double bond of (Z)-237. The enantiomeric amino acids D-alanine (R)-239 and L-alanine... 

Resolution of Enantiomeric Amino Acids and Their Derivatives... 

The D-enantiomeric amino acids form by nonprotein synthesis inside bacteria in the form of peptide antibiotics. Although proteins predominate in today s DNA world, one assumes that proteins were in a minority at the beginning of the RNA world. It is likely that several pathways independently produced the first smaller peptides early on. Many essential coenzymes consist not only of nucleotide derivatives but also amino acids Coenzyme A, NADH+, S-adenosyl-methionine, tetrahydrofolate, and many more, see below. 

The FeS world is a still incomplete model for building up a primitive metabolism and other pathways to enlarge the repertoire of biogenic compounds. Although limited because of the missing enantiomeric amino acids, any FeS scenario is open-ended... 

The enantiomeric products can be obtained by use of the enamines derived from enantiomeric amino acids. Alternatively, the enantiomeric cyclohexanone can be obtained by chemical interconversion Sone, T. Terashima, S. Yamada, S. Synthesis 1974, 725-726. 

Cyanuric chloride on monosubstitution with nucleophiles such as methanol or 4-amino-azobenzene followed by displacement of a second chlorine with alanine amide gave compounds which are used for precolumn derivatization of amino acids. The diastereoisomers formed are resolved by reverse-phase HPLC <92MI 6l2-0i>. Enantiomeric amino acids are separated by HPLC on bis[carbamoyl(alkyl)methylamino]-6-chloro-l,3,5-triazine derived stationary phases <93JC277>. 

Chiral differentiation between enantiomeric amino acid / -nitrophenyl ester hydrobromines was observed [9,73] in transacylations catalysed by the chiral 3,3-... 

Melittin, a toxin in bee venom, is a pentacationic peptide composed of 26 amino acids. Four of the basic residues occur in a cluster near the C-terminus. The retromer made of the enantiomeric amino acids in a reversed sequence (Scheme 9.6.1) forms helices in water containing 20% hexafluoro-2-propanol as a cosolvent. The CD spectra of L-melittin and retroenantio melittin (retro d-melittin) are approximately mirror images, but both are equally effective in their antibacterial activity. The toxic action of melittin can therefore not function via a (protein) receptor or enzyme-type action. The only other possibility is formation of ion-conducting pores by self-aggregation (Juvvadi, 1997). 

The racemic N-benzoyl-alanine is resolved with brucine or strychnine. If brucine is used, it is the brucine salt of D-alanine that is less soluble. If strychnine is used, the strychnine salt of L-alanine crystallizes. Acidification of the salts yields the D-and L-enantiomers of N-benzoylalanine. Basic hydrolysis then gives the pure enantiomeric amino acids. The process is outlined schematically as follows ... 

Fig. 9.7. Separation of a mixture of enantiomeric amino acids on a reversed phase column with a chiral agent added to the mobile phase. Chromatographic conditions column, Spherisorb/LC-18 (5 pm, 150x4.6 mm I.D.) mobile phase, water chiral additive, Cu(jV,A -di- r-propyl-L-alanine) flow rate, 0.2 ml/min temperature, ambient.

NAD(P)H-dependent enzyme systems] membrane enantiomeric amino acids... 

Lepri, L, L Boddi, M Del ubba and A Cincinelli (2001). Reversed-phase planar chromatography of some enantiomeric amino acids and oxazolidinones. Biomedical Chromatography, Special Issue Chiral Resolution, 15(3), 196-201. 

R. H. Buck and K. Krummen, High-performance liquid chromatographic determination of enantiomeric amino acids and amino alcohols after derivatization with o-phthaldialdehyde and various chiral mercaptans Application to peptide hydrolysates,/. Chromatogr., A, 1987,357, 255-265. 

Pedrazzoli (1957) catalytically reduced (VII) (Fig. 17) to unequal amounts of diastereomeric products which yielded nearly optically pure amino acids when hydrolyzed. Catalytic hydrogenation of the (—)-bornyl ester corresponding to (VII), however, yielded almost equal amounts of enantiomeric amino acids. Also, Yamada et al. (1962) hydrogenated (VIII) and obtained nearly... 

RESOLUTION OF ENANTIOMERIC AMINO ACID AND THEIR DERIVATIVES... 

The D-enantiomer of such bidentate compounds was generally retained more than L-enantiomer. Mixtures of methanol/acetonitrile/water or dichloromethane/methanol were often used as eluents. Chiral recognition based on CLEC was also involved in the enantiomer separation of amino acids and (3-adrenergic blocking agents on silica gel plates coated with the copper(II) complex of enantiomeric amino acids (L-proline, L-arginine, and lR,3R,5R-2-azobicyclo [3.3.0]octan-3-carboxylic acid). 

---