## 1 Introduction  
Beta-blockers or -adrenergic antagonists are an important class of organic substances which are widely used to reduce the blood pressure of patients with corresponding cardiovascular diseases. The major structural fragment in typical -blockers is aryloxypropanolamine (see Table 1) containing at least one chiral centre. It is known that only one enantiomer of beta blockers exhibits pharmaceutical activity, so only half of a racemic active pharmaceutical ingredient (API) is effective and the rest is considered inactive, but not an absolutely non-harmful component. At present, commercially available -blockers are sold as racemic mixtures except for very few, e.g., timolol [1]. Emanitoseparation of APIs and preparative isolation of all possible isomers is a significant part of biomedical testing required for the medical approval of drugs. Determination of the optical purity of APIs at the production stage is also of great importance as optical isomers of one substance can produce diverse effects on humans. The application of various techniques including capillary zone electrophoresis (CZE) [2], capillary electrochromography (CEC) [3], supercritical fluid chromatography (SFC) [4], gas chromatography (GC [5], and thin layer chromatography (TLC) [6] have been reported for enantioseparation of -blockers. However, enantioselective or chiral high-performance liquid chromatography (HPLC) is commonly used for the separation and determination of optical isomers. The most practical separation of enantiomers includes the use of chiral stationary phases (CSPs)CSPs with immobilised macrocyclic antibiotics are well-known for their enantioselective properties towards -blockers. Enantioseparations of -blockers have been reported for silica-based CSPs with vancomycin [14; 19], rifamycinin B [20], teicoplanin [21], dalbavancin [22], eremomycin [23], ristocetin [24], and others used as chiral selectors. Elucidation of both chromatographic retention and enantioseparation mechanisms for these selectors is an important, but very complex, task due to the large numbers of chiral centres and functional groups available for various interactions. There are three options to obtain the required information. The most common option is a variation of eluent composition to suppress or increase certain interactions between enantiomers and a chiral selector. It could be a simple variation of eluent polarity to suppress hydrogen bonding [25], the addition of salts and pH regulation to change electrostatic interactions [26], blocking complexing groups with Cu\({}^{2+}\)[27], etc. A more difficult route is the analysis of datasets on retention and enantioselectivity values obtained for a large number of structurally similar racemates with a single CSP. Of course, this approach requires a representative collection of specially designed compounds [24]. The final option is a targeted modification of the chiral selector structure in CSPs and an analysis of corresponding changes in retention and enantioselectivity. This latter option is commonly used for the modification of glycoptide antibiotics and the preparation of new CSPs. There have been few attempts to improve the enantioselectivity of vancomycin-based phases by modifying their chemical structure. The structure of vancomycin and its structural analogues are shown in Figure 1. The family of modified vancomycin-based CSPs includes phases with immobilised vancomycin Edman degradation product (EDP) and with immobilised crystalline degradation product (CDP). The former differs from native vancomycin by N-terminus leucine residue converted into additional primary amino- group [28], and the latter by containing a second carboxylic acid group due to rearrangement in the structure [29]. Several other CSPs were also prepared by using antibiotics closely related to the vancomycin structure as chiral selectors. Chloroeremomycin, which is also known as an A82846B antibiotic, has eimeric disaccharide amino sugar and additional epi-vancosamine residue.