Chiral phases amyloses

Aboul-Enein and Ali [78] compared the chiral resolution of miconazole and two other azole compounds by high performance liquid chromatography using normal-phase amylose chiral stationary phases. The resolution of the enantiomers of ( )-econazole, ( )-miconazole, and (i)-sulconazole was achieved on different normal-phase chiral amylose columns, Chiralpak AD, AS, and AR. The mobile phase used was hexane-isopropanol-diethylamine (400 99 1). The flow rates of the mobile phase used were 0.50 and 1 mL/min. The separation factor (a) values for the resolved enantiomers of econazole, miconazole, and sulconazole in the chiral phases were in the range 1.63-1.04 the resolution factors Rs values varied from 5.68 to 0.32. 

Aboul-Enein, H.Y. Ali, I. HPLC enantiomeric resolution of nebivolol on normal and reversed amylose based chiral phases, Pharmazie, 2001, 56, 214-216. 

As mentioned previously, cellulosic phases as well as amylosic phases have also been used extensively for enantiomeric separations more recently (89,90). Most of the work ia this area has been with various derivatives of the native carbohydrate. The enantioresolving abiUties of the derivatized cellulosic and amylosic phases are reported to be very dependent on the types of substituents on the aromatic moieties that are appended onto the native carbohydrate (91). Table 3 fists some of the cellulosic and amylosic derivatives that have been used. These columns are available through Chiral Technologies, Inc. and J. T. Baker, Inc. 

An hplc assay was developed suitable for the analysis of enantiomers of ketoprofen (KT), a 2-arylpropionic acid nonsteroidal antiinflammatory dmg (NSAID), in plasma and urine (59). Following the addition of racemic fenprofen as internal standard (IS), plasma containing the KT enantiomers and IS was extracted by Hquid-Hquid extraction at an acidic pH. After evaporation of the organic layer, the dmg and IS were reconstituted in the mobile phase and injected onto the hplc column. The enantiomers were separated at ambient temperature on a commercially available 250 x 4.6 mm amylose carbamate-packed chiral column (chiral AD) with hexane—isopropyl alcohol—trifluoroacetic acid (80 19.9 0.1) as the mobile phase pumped at 1.0 mL/min. The enantiomers of KT were quantified by uv detection with the wavelength set at 254 nm. The assay allows direct quantitation of KT enantiomers in clinical studies in human plasma and urine after adrninistration of therapeutic doses. 

Ferretti et al. (1988) used an amino column coupled to a derivatized amylose column (Chiralpak AS) operated in the reverse-phase mode to separate the enantiomers of the antifungal agent voriconazole from several chiral impurities and one achiral impurity. Three of the chiral impurities are the other enantiomer and corresponding diastereomers of voriconazole. More chiral impurities result from a chlorinated voriconazole. Additionally, this multidimensional method could baseline separate all but two of the chiral impurities into their respective enantiomers. These separations are shown in Figure 14.5. 

Okamoto et al [85] performed the optical resolution of primaquine and other racemic drugs by high performance liquid chromatography using cellulose and amylose tris-(phenylcarbamate) derivatives as chiral stationary phases. Primaquine and other compounds were effectively resolved by cellulose and/or amylose derivatives having substituents such as methyl, tertiary butyl, or halogen, on the phenyl groups. 

Amylose inclusion compounds, 14 168 Amylosic phases, for chiral separations, 6 88-89... 

These polysaccharide-based stationary phases appear to be the most useful in organic, bio-organic and pharmaceutical analysis. Of the above-mentioned derivatives three of them, namely cellulose tris-(3,5-dimethylphenylcarbamate), amylose tris-(3,5-dimethylphenylcarbamate) and cellulose tris-(4-methylbenzoate), have very complementary properties and numerous publications have demonstrated that they have been able to achieve the chiral resolution of more than 80% of the drugs currently available on the market. " These CSPs are known under the commercial names, Chiralcel OD-H , Chiralpak AD and Chiralcel OJ , respectively (Figure 4). Their very broad enantiorecognition range is also the... 

Musshoff et al. [35] developed a method for the enantiomeric separation of the synthetic opioid agonist tramadol and its desmethyl metabolite using a Chiralpak AD column containing amylose tris-(3,5-dimethylphenylcarbamate) as chiral selector and a n-hexane/ethanol, 97 3 v/v (5mM TEA) mobile phase nnder isocratic conditions (1 mL/min). After atmospheric pressure chemical ionization (APCI), detection was carried out in positive-ion MS-MS SRM mode. The method allowed the confirmation of diagnosis of overdose or intoxication as well as monitoring of patients compliance. 

TABLE 5 Effects of Flow Rate and Substituents on Chiral Resolution of Imidazole Antifungal Agents on Amylose CSPs Using Hexane-2-Propanol-Diethylamine (400 99 1, v/v/v) as the Mobile Phase... 

Recently, Aboul-Enein and Ah [100] carried out certain studies on the chiral resolution of methylphenidate on derivatives of cellulose and amylose. They observed that %-% interactions are also the important binding forces for the chiral resolution of aromatic racemates. The best resolution of methylphenidate (MPH) on a Chiralcel OB column was achieved when phenol or benzoic acid, separately, was used as the mobile phase additive. Phenol (benzoic acid) forms the MPH-phenol (MPH-benzoic acid) pair in which the possibility of %-% interaction between one of these pairs and CSP is greater than the possibility of 7t—7t interactions between MPH and CSP. Therefore, the resolution of MPH enantiomers was improved when phenol or benzoic acid served as the mobile... 

In sub-FC, a detailed study of the influence of mobile phase additives on the chiral resolution of isoxazoline-based Ilb/IIIb receptor antagonists was carried out by Blackwell [145] on Chiralcel OD-H CSPs. The different mobile phase additives used were acetic acid, trifluoroacetic acid, formic acid, water, triethylamine, triethanolamine, n-hexylamine, trimethyl phosphate, and tri-w-butyl phosphate. In general, n-hexylamine and tri-/ -butyl phosphate mobile phase additives resulted in better resolution. The chiral separation of four 1,3-dioxolane derivatives on an amylose-based column has been described [151]. The effects of mobile phase composition, temperature, and pressure have been investigated. The nature of the modifier is the main parameter it has the highest impact on chiral resolution and is more important than the polarity of the mobile phase. Therefore, the organic modifier that gave the best enantiomeric separation was different for each compound. 

Balmer et al. [60] separated the two enantiomers of omeprazole on three different stationary phases with immobilized protein, viz, Chiral-AGP with a-1 acid glycoprotein, Ultron ES-OVM with ovomucoid, and BSA-DSC with BSA cross-linked into 3-aminopropyl silica using N-suc-cinimidyl carbonate. The mobile phase (1 ml/min) was phosphate buffer solution with 3—10% 2-propanol as the organic modifier. The enantiomers of omeprazole were separated on Chiralpak AD, an amylose-based chiral stationary phase, with ethanol-hexane (1 4) as mobile phase (1 ml/min). 

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