Resolut of 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosylisothiocyanate derivatives of α-methyl amino acid enantiomers by high-performance liquid chromatography

A Universal HPLC-MS Method to Determine the Stereochemistry of Common and Unusual Amino Acids

The determination of the stereochemistry of common and unusual amino acids is important in food chemistry, archeology, medicine, and life sciences including such diverse areas as marine biology and extraterrestrial chemistry and has greatly contributed to our current knowledge in these fields.To determine the stereochemistry of amino acids, many chromatographic methods have been developed and refined over the last decades. Here we describe a state-of-the-art indirect chromatography-based LC-MS method. Diastereomers were formed from amino acids that were reacted with chiral derivatizing agents such as Marfey's reagent (FDAA), GITC, S-NIFE, and OPA-IBLC and separated on a reversed phase column using mass spectrometry compatible buffers.

A universal HPLC-MS method to determine the stereochemistry of common and unusual amino acids

The determination of the stereochemistry of common and unusual amino acids is important in food chemistry, archeology, medicine, and life sciences, including such diverse areas as marine biology and extraterrestrial chemistry and has greatly contributed to our current knowledge in these fields.To determine the stereochemistry of amino acids, many chromatographic methods have been developed and refined over the last decades. Here, we describe a state-of-the-art indirect chromatography-based LC-MS method. Diastereomers were formed from amino acids that were reacted with chiral derivatizing agents, such as Marfey's reagent (FDAA), GITC, S-NIFE, and OPA-IBLC and separated on a reversed phase column using mass spectrometry compatible buffers.

Chiral separation of beta-blockers after derivatization with a new chiral derivatization agent, GATC

A new chiral derivatization agent with sugar moiety, 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl isothiocyanate (GATC) was synthesized. Several beta-blockers were investigated for the possible separation of the enantiomers by reversed-phase HPLC after derivatization with this new chiral derivatization agent (GATC). GATC was reacted readily with beta-blockers at room temperature and the reaction mixture could directly be injected into the HPLC system. The corresponding diastereomers were well resolved on an ODS column with acetonitrile-ammonium acetate buffer as a mobile phase and monitored at UV 254 nm. The optimization of the derivatization procedure (concentration of GATC, reaction temperature and time) and HPLC conditions (pH and ionic strength of mobile phase) were investigated and compared with GITC.

Chirality determination of unusual amino acids using precolumn derivatization and liquid chromatography-electrospray ionization mass spectrometry

Unusual amino acids such as beta-methoxytyrosine (beta-MeOTyr), allo-threonine (allo-Thr) and allo-isoleucine (allo-Ile) were derivatized with N-alpha-(2,4-dinitro-5-fluorophenyl)-L-alaninamide (FDAA), 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (GITC), (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester (S-NIFE), or o-phthalaldehyde/isobutyryl-L-cysteine (OPA-IBLC), and then separated via reversed-phase high-performance chromatography followed by UV and electrospray ionization mass spectrometry detection. FDAA generally showed the highest enantioselectivity but the lowest sensitivity among the chiral derivatizing agents (CDAs) investigated. The detection limit of FDAA-derivatized amino acids was in the low picomolar range. Although the enantioselectivity of FDAA derivatives was generally quite high, its selectivity among beta-MeOTyr isomers was poor. The best separation of beta-MeOTyr stereoisomers was achieved with S-NIFE. Due to the complex relationships between the investigated CDAs, stereochemical analyses using a combination of two or more of the CDAs gave the most reliable results for a given separation problem. In general, the methods described are selective and reliable, and are being applied to the analysis of unusual amino acids as they occur in marine peptides.

High-performance liquid chromatographic separation of the enantiomers of unusual alpha-amino acid analogues

The direct and indirect stereochemical resolution of the enantiomers of ring- and alpha-methyl-substituted phenylalanines and phenylalanine amides was attempted by high-performance liquid chromatographic methods. The direct separation was carried out on two chiral stationary phases, the crown-ether-based Crownpak CR(+), and the teicoplanin-based Chirobiotic T, while the indirect resolution was performed by applying pre-column derivatization with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (GITC) and Nalpha-(2,4-dinitro-5-fluorophenyl)-L-alanine amide (Marfey's reagent, FDAA). The Chirobiotic T column was efficient in the separation of ring- and alpha-methyl-substituted phenylalanine analogues, but was ineffective for the amides of these analogues. The Crownpak CR(+) column separated the ring-substituted phenylalanines and amides, whereas the alpha-methylated analogues were coeluted. Of the two indirect methods, GITC derivatization seemed more effective than FDAA derivatization.

Enantiomeric derivatization for biomedical chromatography

Derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers are reviewed, with emphasis on the literature published in the last 10 years. Three main aspects of chiral derivatization are discussed. (a) Enantiomers containing suitable functional groups (amino, carboxyl, hydroxyl, epoxy, etc.) are transformed into covalently bonded diastereomeric derivatives using homochiral derivatizing agents. The diastereomers formed (esters, amides, urethanes, urea and thiourea, etc., derivatives) can be separated on achiral stationary phases. The derivatization reactions often afford further advantages, such as the improvement of chromatographic properties and the detectability of the solutes using UV and fluorimetric detectors. (b) Covalent but achiral derivatization is often necessary even with the use of chiral stationary phases enabling in principle direct enantioseparations (Pirkle-type columns, cyclodextrin-bonded phases, glycoprotein column and functionalized cellulose columns). The main goals of these derivatization reactions (which are analogous to those discussed above), are to introduce functional groups into the molecule of the enantiomers that improve the possibilities for chiral interactions or block functional groups to avoid non-specific interactions. (c) In the broader sense, the dynamic formation of diastereomers using chiral mobile phase additives (cyclodextrins, various reagents to form diastereomeric ion pairs, adducts, mixed metal complexes) can also be considered to be chiral derivatization reactions and is therefore briefly discussed also.

Resolution of enantiomers of amino acids by HPLC

Application of HPLC as a prime tool in the area of enantiomeric resolution has opened doors of success and varied interest. Use of chiral reagents either indirectly (as derivatization reagent) or directly (added to stationary or mobile phase) has led to achieve resolution of a wide range of compounds. Amino acids, being important molecules with simple structure and easy availability, have been extensively studied. A bibliographic survey on HPLC resolution of amino acids and derivatives along with a brief discussion on general methods of enantiomeric separation has been presented.

Synthesis of optically pure C alpha-methyl-arginine

Optically pure L-(+)-C alpha-methyl-arginine and D-(-)-C alpha-methyl-arginine were synthesized. Experimental results indicated that DL-C alpha-methyl-arginine methyl ester could be resolved by trypsin, but workup posed a technical difficulty. Chemical resolution at the stage of DL-C alpha-methyl-ornithine, followed by selective guanidination using N,N'-di-Cbz-S-methylisothiourea and hydrogenolysis provided a effective and practical method for the synthesis of optically pure C alpha-methyl-arginine.