Preparative Chromatography - The Preparative Separation of the Enantiomers of Chlorokynurenine > Page 69

It also contains two sugar moieties and has a molecular weight of 1449. This material has multimodal capabilities, great stability and high chromatographic capacity for preparative work. It is complimentary in chiral selectivity to the antibiotics Teicoplanin and Ristocetin. An example of the use of Vancomycin in preparative chromatography is demonstrated in the separation of the enantiomers of Nicardipine. Nicardipine is a cerebral and coronary dilator with calcium blocking activity. It chemical name is 1,4-dihydro2,6-dimethyl4-[3-nitrophenol]3,5-pyridine dicarboxylic methyl2-[methyl (phenylmethyl)amino]ester. It exists in two isomeric forms the (a) form M.Pt.168-173˚C and the (b) form M.Pt. 179-181˚C.

The chromatographic properties of the enantiomers of nicardipine on the phase system selected for their preparative separation is shown in figure 38. It is seen that the solvent system selected elutes both isomers at fairly low capacity ratios (cf. 0.64 and 0.97) but the separation ratio is still relatively high (cf. 1.51) which will allow considerablecolumn overload. These advantageous retentive properties are afforded by he unique character of chirobiotic stationary phase. The mobile phase (termed by the manufacturers as elution by the polar organic mode) is strongly polar so the major retentive mechanism is likely to be predominantly dispersive in nature modified by the selective interactions afforded by the chiral centers of the Vancomycin (see The Mechanism of Chromatographic Retention ).


Courtesy of ASTEC Inc.


Figure 38. The Chromatographic Properties of the Enantiomers of Nicardipine when Retained on the Chirobiotic Vancomycin