This material can also be bonded to 5 mm silica gel particles by multiple covalent linkages. Teicoplanin contains 20 chiral centers surrounding four molecular 'pockets' or 'cavities'. Neighboring groups are strongly polar and aromatic rings provide ready polarizability. The proposed structure of Teicoplanin is shown in figure 51. This stationary phase is claimed to be complementary to the Vancomycin phase and can be used with the same types of mobile phase, one often providing chiral selectivity, when the other does not. Teicoplanin can be used in a reversed phase mode using strongly

nbsp; The column used was 25 cm long, 4.6 mm I.D., packed with Chirobiotic T. The mobile phase was methanol containing acetic acid and triethylamine in the concentrations shown in figure 52. The column was operated at room temperature and at a flow rate of 2 ml/min. Teicoplanin is stable over a pH range of 3.8 to 6.5 although it can be used for limited periods of time outside this range. By suitable choice of mobile phase, Teicoplanin can be used in the reversed phase mode. Another macrolytic glycopeptide that has been used as a chiral stationary phase, is the glycopeptide, Avoparcin [40]. This stationary phase is available as CHIROBIOTIC A. Avoparcin is an antibiotic complex produced by Streptomysces candidus. In particular, it is used to prevent

phase. Consequently, the remaining dominant retentive forces will be polar or ionic. In the second case, the mobile phase is predominantly water and thus provides strong polar interactions with the solute but weak dispersive interactions. It also follows, that the dispersive forces will dominate in the stationary phase. These two examples demonstrate the useful flexibility of Vancomycin. Another macrolytic glycopeptide used in chiral chromatography is the amphoteric glycopeptide Teicoplanin which is commercially available under the trade name of  CHIROBIOTIC T. A, B, C and D are inclusion cavities. Molecular weight 1885. Chiral centers 20, Sugar moieties 3, and R is CH3-decanoic acid Courtesy of ASTEC Inc. Figure 51. The Proposed Structure of Teicoplanin

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