Thin-layer chromatography of steroisomeric 2,4-dinitrophenylhydrazones of aliphatic aldehydes.
Abstract The stereoisomeric forms of 2,4-dinitrophenylhydrazones (2,4-DNP) of some aliphatic aldehydes and unsymmetrical detones were separated by several reverse phase thin-layer chromatographic procedures. Evidence indicated that the reaction to produce the 2,4-DNP produces both the syn and anti form, but that repeated recrystallization in ethanol yielded the pure syn crystalline form. Racemizaton of the crystalline syn form could be stimulated by dissolving it in chloroform or by the addition of a small amount of hydrochloric acid to an acetone or methanol solution. Certain thin-layer chromatographic systems separated the homologous series to the greatest extent and the isomers the least (undecane/75% methanol-25% water). Another system separated the isomers to a considerable extent but was not too effective in separating the homologous series (dimethylformamide/heptane). Combinations of these systems should be of value in resolving mixtures of syn and anti forms of mixtures of aliphatic aldehyde 2.4-DNP.
The HPLC resolution of N-2,4-dinitrophenylated amino acids and peptides stereoisomers on naphthylethylcarbamate-β-cyclodextrin bonded phase using the acetonitrile-based mobile phase: evidence for the chiral recognition pattern
Summary.A facile method of enantioresolving a variety of α-amino acids and peptides on naphthylethylcarbamate-β-cyclodextrin bonded phases (i.e., SN- and RN-β-CDs) under the elution of acetonitrile-based mobile phase makes use of 2,4-dinitrofluorobenzene (DNFB) as the tagging reagent, which undergoes nucleophilic substitution by the free amino group in alkaline medium to give a N-2,4-dinitrophenyl (DNP) derivative. The resolution is better obtained on RN-β-CD phase and fails to reproduce on the intact β-cyclodextrin bonded phase under the same chromatographic conditions, which strongly suggests that the observed resolution should be due to the interaction of analyte with naphthylethylcarbamate moiety, not with the residual secondary hydroxyl groups on the β-cyclodextrin.
Liquid state 1H high field NMR in food analysis.
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