Chiral stationary phases vancomycin

Biaryl structures are wide-spread in many of naturally occuring products including alkaloids, lignans, terpenes, flavonoids, tannins, as well as polyketides, coumarins, peptides, glycopeptides, etc. For example, vancomycin (1) is a basic structure of several related glycopeptide antibiotics [1] balhimycin, actinoidin A, ristocetin A, teicoplanin A2-2, complestatin, etc which are important in medicinal chemistry or as a HPLC chiral stationary phases (vancomycin) [2]. 

The chirobiotic chiral stationary phases (103,104) are based on macrocycHc antibiotics such as vancomycin (4) and teicoplanin (5). 

Vancomycin was the first macrocyclic antibiotic evaluated as selector for the synthesis of HPLC chiral stationary phases (CSPs) [7], along with rifamycin B (among ansamycins) and thiostrepton (among polypeptides). 

Ghassempour, A. et al., Crystalline degradation products of vancomycin as a new chiral stationary phase for liquid chromatography, Chromatographia, 61, 151, 2005. 

Donnecke, J. et ah. Evaluation of a vancomycin chiral stationary phase in packed capillary supercritical fluid chromatography, J. Microcol. Sep., 11, 521, 1999. 

Svensson, L.A. et ah. Vancomycin-based chiral stationary phases for micro-column liquid chromatography. Chirality, 11, 121, 1999. 

Wikstrom, H. et ah. Immobilisation and evaluation of a vancomycin chiral stationary phase for capillary electrochromatography, J. Chromatogr. A, 869, 395, 2000. 

Kang, W. et ah. Analysis of benidipine enantiomers in human plasma by liquid chromatography—mass spectrometry using a macrocyclic antibiotic (vancomycin) chiral stationary phase column, J. Chromatogr. B, 814, 75, 2005. 

Pihlainen, K. and Kostiainen, R., Effect of the eluent on enantiomer separation of controlled drugs by liquid chromatography-ultraviolet absorbance detection-electrospray ionisation tandem mass spectrometry using vancomycin and native fi-cyclodextrin chiral stationary phases, J. Chromatogr. A, 1033, 91, 2004. 

Lehotay, J. et al.. Chiral separation of enantiomers of amino acid derivatives by HPLC on vancomycin and teicoplanin chiral stationary phases, Pharmazie, 53, 863, 1998. 

Aboul-Enein, H.Y. and Serignese, V., Enantiomeric separation of several cyclic imides on a macrocyclic antibiotic (vancomycin) chiral stationary phase under normal and reversed phase conditions, Chirality, 10, 358, 1998. 

Bosikova, Z., Klouhkova, 1., and Tesafova, E., Study of the stability of promethazine enantiomers by liquid chromatography using a vancomycin-bonded chiral stationary phase, J. Chromatogr. B, 770, 63, 2002. 

Lehotay, J. et al.. Separation of enantiomers of some 1,4-piperazine derivatives of aryloxy-aminopropanols on a vancomycin chiral stationary phase, Pharmazie, 54, 743, 1999. 

Hefnawy, M.M. and Aboul-Enein, H.Y., A validated LC method for the determination of vesamicol enantiomers in human plasma using vancomycin chiral stationary phase and sohd phase extraction, J. Pharm. Biomed. Anal, 35, 535, 2004. 

Armstrong et al. ° first introduced chiral stationary phases based on macrocyclic antibiotics. Vancomycin, ristocetin A, teicoplanin, avoparcin, rifamycin B and thiostrepton are used as chiral selectors. They posses a broad enantiorecognition range, similar to protein based CSPs. However, CSPs based on macrocyclic antibiotics show higher stability and capacities.Underivatized amino acids, N-derivatized amino-acids, acidic compounds, neutrals, amides, esters and amines can be separated.The first four of the above-mentioned chiral selectors appear to have the largest enantiorecognition range.The selectors can also be derivatized to obtain different enantioselectivities. 

Temperature is also an important parameter for controlling the resolution of enantiomers in HPLC. The enthalpy and entropy control of chiral resolution on antibiotic CSPs is similar to the case of polysaccharide-based CSPs (Chapter 2). Armstrong et al. [1] have studied the effect of temperature on the resolution behavior of proglumide, 5-methyl-5-phenylhydantoin and A-carbamyl-D-pheny-lalanine on the vancomycin column. The experiments were carried out from 0°C to 45°C. These results are given in Table 6 for three chiral compounds. It has been observed that the values of k, a, and Rs for the three studied molecules have decreased with the increase in temperature, indicating the enhancement of chiral resolution at low temperature. In another work, the same workers [22] have also studied the effect of temperature on the resolution of certain amino acid derivatives on the teicoplanin chiral stationary phase. They further observed poor resolution at ambient temperature, whereas the resolution increased at low... 

Macrocyclic antibiotics such as teicoplanin and vancomycin have been used in chiral stationary phases separations of amino acids, drugs, and other species using HPLC and other separations methods. These applications have been reviewed in a number of recent sources, including a 2004 monograph on chiral separations. [97, 101-107]... 

Silica-base stationary phases have also been employed for enantiomeric separations in CEC [6,72-81]. In the initial work on chiral CEC, commercially available HPLC materials were utilized, including cyclodextrins [6,74,81] and protein-type selectors [73,75,80] such as human serum albumin [75] and ai-acid glycoprotein [73]. Fig. 4.9, for example, depicts the structure of a cyclodextrin-base stationary phase used in CEC and the separation of mephobarbital enantiomers by capillary LC and CEC in a capillary column packed with such a phase. The column operated in the CEC mode affords higher separation efficiency than in the capillary LC mode. Other enantiomeric selectors are also use in CEC, including the silica-linked or silica-coated macrocyclic antibiotics vancomycin [82,83] and teicoplanin [84], cyclodextrin-base polymer coated silicas [72,78], and weak anion-exchage type chiral phases [85]. Relatively high separation efficiency and excellent resolution for a variety of compounds have also been achieved using columns packed with naproxen-derived and Whelk-0 chiral stationary phases linked to 3 pm silica particles [79]. Fig. 4.10 shows the... 

Fig. 9.11. Enantiomer separation of thalidomide on a vancomycin chiral stationary phase by CEC under a slight overpressure (10 bar). Conditions 75 pm x 35.5 cm capillary mobile phase, methanol-acetonitrile-glacial acetic acid-triethylamine (80 20 2 0.2, v/v/v/v) 20 kV, UV detection, 220 nm. Reproduced from [52], with permission.

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. 

The chromatographic system chosen to examine was the chiral stationary phase Chirobiotic V (as already described, this is a macrocyclic glycopeptide called Vancomycin bonded to silica gel particles 5 pm in diameter) which was used in the normal phase mode (solute retention controlled largely by polar interactions), employing mixtures of hexane and ethanol as the mobile phase. 

This example, described by Chen et al. [13] demonstrates the complementary use of the two macrocyclic chiral stationary phases to separate a range of difficult chiral separations. It will be seen that where one type of chiral stationary phase fails to achieve a separation, the other can often succeed. Vancomycin and Teicoplanin were prepared in the manner described by Armstrong [14], and bonded to silica gel particles 5 nm in diameter and packed into columns 25 cm long and 4.6 mm I.D. The results that were obtained are shown in figure 11.17. All three racemates were developed under identical conditions. The mobile phase was methanol/1% triethylammonium acetate buffer, pH 4.1 1/90 v/v, used at a flow rate of 1 ml/minute. 

An additional example of the technique of recycling, which includes a procedure called peak shaving, is the preparative separation of the enantiomers of 5-methyl-5-phenylhydantoin. The recycling and peak shaving procedure is depicted in figure 12.8. The column was 30 cm long, 2 in. I.D., packed with 10 m particles carrying Vancomycin as the chiral stationary phase. The mobile phase was ethanol and the flow rate 100 ml/minute. The sample load was 400 mg dissolved in 5 ml of ethanol. 

Since first demonstration in 1994 of the potential use of macrocyclic antibiotics as chiral selectors in analysis, glycopeptide antibiotics have been successfully applied for enantiomer separations by liquid chromatography, as recognition components of chiral stationary phases, and by capillary electrophoresis (CE) as soluble chiral selec-tors. Four chiral stationary phases for chromatography with the selectors vancomycin, ristocetin, teicoplanin, and the teicoplanin aglycone are commercialized under the trade name Chirobiotic by Astec and Supelco. Various aspects of analytical applications of glycopeptide antibiotics have been extensively covered in the recent reviews cited above. As an example. Table 2 shows some representative results for CE enantioseparations with vancomycin, ristocetin A, and teicoplanin, which were taken from Ref. 39. 

---