Ristocetin-type glycopeptides

In addition to the vancomycin and teicoplanin CSPs, ristocetin A (Chirobiotic R) [289] and recently avoparcin [280] have been evaluated as novel chiral SOs and CSPs. It turned out that within the large family of macrocyclic antibiotics complementarity of enantioselectivity exists for different glycopeptides. As a consequence, very often it is possible to obtain a complete resolution by switching to a congeneric antibiotic CSP, if after optimization no baseline, but partial. separation can be achieved on a certain macrocyclic antibiotic type CSP (see Fig. 9.22). It can be expected that the enantioselectivity potential of closely related antibiotics will be further exploited in the future leading to an increase in the number of macrocyclic antibiotic type CSPs. 

Tesarova and Bosakova [58] proposed an HPLC method for the enantio-selective separation of some phenothiazine and benzodiazepine derivatives on six different chiral stationary phases (CSPs). These selected CSPs, with respect to the structure of the separated compounds, were either based on b-CD chiral selectors (underivatized (J>-CD and hydroxypropyl ether (3-CD) or on macrocyclic antibiotics (vancomycin, teicoplanin, teicoplanin aglycon and ristocetin A). Measurements were carried out in a reversed-phase separation mode. The influence of mobile phase composition on retention and enantio-selective separation was studied. Enantioselective separation of phenothiazine derivatives, including levopromazine (LPZ), promethazine and thioridazine, was relatively difficult to achieve, but it was at least partly successful with both types of CSPs used in this work (CD-based and glycopeptide-based CSP), except for levomepromazine for which only the [CCD-based CSP was suitable. 

Fig. 7.15 Chemical structures of the glycopeptide-type antibiotics vancomycin, teicoplanin and ristocetin A. For teicoplanin the prevalent derivative (A2-2, 85%) of the teicoplanin complex is shown.

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