1. HPLC enantiomeric resolution of novel aromatase inhibitors on cellulose- and amylose-based chiral stationary phases under reversed phase mode
H Y Aboul-Enein, I Ali, G Gübitz, C Simons, P J Nicholls Chirality. 2000 Nov;12(10):727-33. doi: 10.1002/1520-636X(2000)12:103.0.CO;2-T.
The chiral resolution of seven aromatase inhibitors (four triazole derivatives (Ia, Ib, Ic, and Id) and three tetrazole derivatives (IIa, IIb, and IIc)) was achieved on Chiralcel OJ-R [cellulose tris (4-methyl benzoate)], Chiralcel OD-RH [cellulose tris (3,5-dimethylphenyl carbamate)], and Chiralpak AD-RH [amylose tris (3,5-dimethylphenyl carbamate)] chiral stationary phases. The mobile phases used were A: 2-PrOH-MeCN (90:10, v/v); B: 2-PrOH-MeCN (50:50, v/v); C: MeCN-H(2)O (50:50, v/v); D: MeCN-H(2)O (80:20, v/v); and E: MeCN-H(2)O (95:05, v/v). The flow rate was 0.5 mL/min for all the mobile phases. The resolution capability of these chiral stationary phases were in the order Chiralpak AD-RH > Chiralcel OD-RH > Chiralcel OJ-R. The values of alpha and Rs of the resolved enantiomers of the aromatase inhibitors varied from 1.02-5.63 and 1. 12-6.72, respectively.
2. Normal phase chiral HPLC of methylphenidate: comparison of different polysaccharide-based chiral stationary phases
Hassan Y Aboul-Enein, Imran Ali Chirality. 2002 Jan;14(1):47-50. doi: 10.1002/chir.10028.
A comparison of the enantiomeric resolution of (+/-)-threo-methylphenidate (MPH) (Ritalin) was achieved on different polysaccharide based chiral stationary phases. The mobile phase used was hexane-ethanol-methanol-trifluoroacetic acid (480:9.75:9.75:0.5, v/v/v/v). Benzoic acid and phenol were used as the mobile phase additives for the enantiomeric resolution of MPH on Chiralcel OB column only. The alpha values for the resolved enantiomers were 1.34, 1.29, 1.30, and 1.24 on Chiralpak AD, Chiralcel OD, Chiralcel OB (containing 0.2 mM benzoic acid in mobile phase), and Chiralcel OB (containing 0.2 mM phenol in mobile phase) columns, respectively. The R(s) values were 1.82, 1.53, 1.19, and 1.10 on Chiralpak AD, Chiralcel OD, Chiralcel OB (containing 0.2 mM benzoic acid in mobile phase), and Chiralcel OB (containing 0.2 mM phenol in mobile phase), respectively. The role of benzoic acid and phenol as mobile phase additives is discussed.
3. Comparative studies between covalently immobilized and coated chiral stationary phases based on polysaccharide derivatives for enantiomer separation of N-protected alpha-amino acids and their ester derivatives
Jing Yu Jin, Su Kyoung Bae, Wonjae Lee Chirality. 2009 Nov;21(10):871-7. doi: 10.1002/chir.20680.
Liquid chromatographic enantiomer separation of several N-benzyloxycarbonyl (CBZ) and N-tert-butoxycarbonyl (BOC) alpha-amino acids and their corresponding ethyl esters was performed on covalently immobilized chiral stationary phases (CSPs) (Chiralpak IA and Chiralpak IB) and coated-type CSPs (Chiralpak AD and Chiralcel OD) based on polysaccharide derivatives. The solvent versatility of the covalently immobilized CSPs in enantiomer separation of N-CBZ and BOC-alpha-amino acids and their ester derivatives was shown and the chromatographic parameters of their enantioselectivities and resolution factors were greatly influenced by the nature of the mobile phase. In general, standard mobile phases using 2-propanol and hexane on Chiralpak IA showed fairly good enantioselectivities for resolution of N-CBZ and BOC-alpha-amino acids and their esters. However, 50% MTBE/hexane (v/v) for resolution of N-CBZ-alpha-amino acids ethyl esters and 20% THF/hexane (v/v) for resolution of N-BOC-alpha-amino acids ethyl esters afforded the greatest enantioselectivities on Chiralpak IA. Also, liquid chromatographic comparisons of the enantiomer resolution of these analytes were made on amylose tris(3,5-dimethylphenylcarbamate)-derived CSPs (Chiralpak IA and Chiralpak AD) and cellulose tris(3,5-dimethylphenylcarbamate)-derived CSPs (Chiralpak IB and Chiralcel OD). Chiralpak AD and/or Chiralcel OD showed the highest enantioselectivities for resolution of N-CBZ-alpha-amino acids and esters, while Chiralpak AD or Chiralpak IA showed the highest resolution of N-BOC-alpha-amino acids and esters.
