Dansyl-DL-amino acids

MECC has also been reported to be an effective method for the separation of enantiomers [269, 270]. Tsai et al. [271] reported y-cyclodextrin-modified micellar capillary electrophoresis technique for the separation of dansylated-DL-amino acids. 

Bile salts are natural and chiral anionic surfactants which form helical micelles of reversed micelle conformation. The first report on enantiomer separation by MEKC using bile salts was the enantioseparation of dansylated DL-amino acids (Dns-o,L-AAs) and, since then, numerous papers have been available. Nonconjugated bile salts, such as sodium cholate (SC) and sodium deoxycholate (SDC), can be used at pH > 5, whereas taurine-conjugated forms, such as sodium taurocholate (STC) and sodium taurodeox-ycholate (STDC), can be used under more acidic conditions (i.e., pH > 3). Several enantiomers, such as diltiazem hydrochloride and related compounds, carboline derivatives, trimetoquinol and related compounds, binaphthyl derivatives, Dhs-dl-AAs, mephenytoin and its metabolites, and 3-hydroxy-l,4-benzodiazepins have been successfully separated by MEKC with bile salts. In general, STDC is considered as the the most effective chiral selector among the bile salts used in MEKC. 

Bhushan, R. and Thiong o, G.T., Separation of the enantiomers of dansyl-DL-amino acids by normal-phase TLC on plates impregnated with a macrocyclic antibiotic, J. Planar Chromatogr., 13, 33-36, 2000. 

Lepri, L. et al.. Reversed phase planar chromatography of dansyl DL amino acids with bovine serum albumin in the mobile phase, Chromatographia, 36 297,1993. 

Cyclodextrins have been used mainly as mobile phase additives for chiral resolutions of a number of racemates, including amino acids and their derivatives, but Alak and Armstrong [25] used fi-CD bounded to silica gel for resolution of dansyl derivatives of DL-amino acid enantiomers, by forming areversible inclusion complex of different stability. Dansyl DL-amino acids were better separated on fi-CDs layers than nonderivatized amino acids, because they have additionally two or more carbohydrogen rings. 

Armstrong and co-workers [466] studied the retention of the DL isomers of dansyl-substituted amino acids on both (R)- and (5)-(naphthylethyl)carbamoyl-modified -cyclodextrin column. The A and a values for nine amino acids with a wide range of substituents added to the terminal amine group were tabulated. The mobile phase compositions used were analyte-dependent but ranged fiom 99/1 ethanol/acetic acid to 25/75 ethanol/acetonitrile (-H% acetic acid) with a 50/50 ethanol/acetonitrile (-1-1% acetic acid) composition being most fi-equently used. 

Also macrocyclic antibiotics, erythromycin and vancomycin, were successfully employed as the chiral selectors [23,24] for separation of dansyl derivatives of DL-amino acids. It was shown that such chromatographic system is very sensitive especially to changes of pH and temperature, owing to possibility of ionization of functional groups or changing conformational structure of the antibiotic molecule. 

Appllca.tlons. Various A/-derivatives of amino acids (qv) are resolvable on BSA columns. These /V-amino acid derivatives include ben2enesulfonyl-, phthalimido-, S-dimethylarnino-l-naphthalenesulfonyl- (DANSYL-), 2,4-dinitrophenyl- (DNP-), and 2,3,6-trinitrophenyl- (TNP-) derivatives (30). Amines such as Prilocain, ( )-2-(prop5lamino)-(9-propiono-toluidide, a local anesthetic (Astra Pharm. Co.), are also resolved on BSA. The aromatic amino acids DL-tryptophan, 5-hydroxy-DL-tryptophan, DL-kynurenine [343-65-7] C qH 2N 2 3 3-hydroxy-DT.-kynurenine [484-78-6] and dmgs... 

In Reference 55, several positively charged CDs, i.e., 6 mono-6-alkylimidazolium p-CDs, 2 mono-6-aIkylammo-nium p-CDs, mono-6-amino-p-CD hydrochloride, and 2-amino-p-CD hydrochloride, and mono-6-substituted a- and y-CDs with alkylimidazolium, alkylammonium, and amino moieties, were successfully applied for the separation of 14 derivatized AAs, 8 hydroxyl acids, and 14 carboxyl acids. Phosphate buffers and acetate buffers both with a concentration of 50 mM, were used for basic and acidic compounds, respectively. The optimum buffer pH varied for the different CDs. For example, 2-amino-p-CD hydrochloride (20-mM BGE) could baseline resolve a mixture of 8 dansyl (Dns)-amino and hydroxyl acids, i.e., Dns-DL-a-caprylic acid, Dns-DL-a-aminobutyric acid, Dns-oL-glutamic acid,... 

Retention (hRfi, hRf2) Resolution (u, Rs) Data of DL-Dansyl-Amino Acids (Dns-AA) on Silanized Silica Gel Precoated Plates (RP-18 Merck) Impregnated with the Copper (II) Complex of Various Chiral Selectors... 

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