Dansyl-norleucine

Fig. 9 Electropherograms showing the change in enantioselectivity obtained before and after blocking of the sugar amino groups. Conditions buffer, 40 mM sodium phosphate buffer pH 6.0 with 2 mM chiral selector. Analyte dansyl-norleucine. The selector is indicated on each electropherograms. Reprinted by permission of the American Chemical Society [29]...

Whatman RP diphenylsiloxane-bonded silica gel plates have 8.5% carbon loading and 10-14 /rm average particle size they are endcapped but still contain a relatively high concentration of silanol groups [27]. These layers were used with the macrocyclic antibiotic, vancomycin, as a mobile phase additive to resolve 6-aminoquinolyl-Ai-hydroxysuccinimidyl carbamate (AQC) derivatized amino acids, racemic drugs, and dansyl amino acids. The mobile phase was acetonitrile-0.6 M NaCl-1% triethylammonium acetate buffer (pH 4.1) with 0.025-0.08 M vancomycin in various ratios. The development distance was 10 cm, development time 1-3 h, and detection by fluorescence at 245 and 365 nm. Typical Rf values were bendroflumethiazide (0.02/0.06), AQC-a//o-isoleucine [0.14 (l)/0.21 (d)], and dansyl-norleucine [0.04 (l)/0.16 (d)] [40]. 

Fig. S6. Separation of D,L-dansyl amino acids. Conditions 0.65 oiAf L 2>isopropyl-dien-Zn(II) 0.17 A NH,Ac to pH 9.0 with aqueous NI 35/65 CH,CN/H,0 T - 30 flowrate 2 tnl/min column 15 cm by 4.6 mm i.d. S iun Hypersil C solutes CySO H -cysteic acid Ser - serine Trp - tryptophan thr - threonine Norval - norvaline Leu w leucine Norleu - norleucine Phe phenylalanine. Detection at 254 nm. Reprinted with permission from LePage ef at. C246), Am/. Chem. Copyright 1979 by the American Chemical Society.

Reagents. Certified A.C.S. spectroanalyzed methanol, phenol, m-nitrophenol, benzene, naphthalene, sodium acetate, and acetic acid were obtained from Fisher Scientific and were used as received. The e-CD, dansyl-DL-leucine, dansyl-DL-norleucine (all from Signal Chemical Co., St. Louis, MO), o-chlorophenol, m-chlorophenol, p-chlorophenol, o-nitrophenol (all from Eastman Kodak Co., Rochester, NY), p-nitrophenol, and biphenyl (from MCB, South Plainfield, NJ) were all used as received. 

The conventional C-18 and the CD columns do interact differently with solutes of certain classes of isomers. For example, C-18 columns cannot separate enantiomers unless special additives are introduced into the mobile phase. The cyclodextrin bonded phases, however, can easily separate enantiomeric species as illustrated in Figure 9. The D and L enantiomers of dansyl-DL-leucine and of dansyl-DL-norleucine are resolved using a beta-CD column, but attempts to separate these isomers were unsuccessful using a C-18 column. The nature of the interactions between enantiomers and the cyclodextrin cavity has been described elsewhere (20. 21). 

Figure 9. Separation of (A) dansyl-DL-leucine and (B) dansyl-DL-norleucine enantiomers column, Cyclobond I ( -CD) (25 cm X 4.6 nm i.d.) mobile phase, 45/55 methanol-water with 0.05 M acetate buffer (pH 4.6 flow rate 1.0 mL/min detector range, 0.08 a.u.f.s.

Eleven dansylated amino acid isomers were separated on a -cyclodextrin column (A = 254nm) using methanol/water (0.2 M ionic strength phosphate buffer at pH 6.5) mobile phases [465]. The level of methanol needed to generate a separation varied fiom 15% to 25%. At 15% methanol, four sets of enantiomers (glutamine, serine, norvaline, norleucine) are partially resolved in <30 min. The aufliors claim that water is an essential component of the mobile phase, but the next study clearly argues against this statement. 

Dansyl-D,L-norvaline Dansy I-D, L-asparagine Dansyl-D,L-glutamic acid Dansy I-D, L-valine Dansyl-D,L-tryptophan Dansyl-D,L-threonine Dansyl-D, L-pheny lalaninc Dansyl-D,L-methionine Dansyl-D,L-norleucine Dansyl-D,L-threonine Dansyl-D,L-serine... 

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