Xiuzhu Xu

Enantioseparation of Seven Amino Alcohols on Teicoplanin Chiral Column

Abstract Under the polar organic mode, seven amino alcohols, propranolol, metoprolol, bisoprololfumarate, atenolol, salbutamol, isoprenaline, metoprolol and labetalol, were enantioseparated on teicoplanin chiral stationary phase (CSP), using methanol as mobile phase and acetic acid (HOAc) and triethylamine (TEA) as mobile phase additives. When the proportion of HOAc and TEA was 1:1, the retention factors and the resolutions of seven amino alcohols decreased with the increase of HOAc/TEA concentration, and the separation factors being kept constant. The excessive acid increased the polarity of mobile phase, and therefore the eluting ability was increased. Without HOAc additive, the retention factors of the amino alcohols decreased with the increase of the amount of TEA, with the separation factors being kept constant except labetalol. The polarity of mobile phase increased with the increasing of TEA concentration; therefore, the hydrogen bonding between solutes and CSPs decreased. All the results showed that the proportion of HOAc and TEA did not change the essentiality of chiral separation.

Comparative Enantioseparation of Seven Amino Alcohols on Teicoplanin‐Based Chiral Stationary Phases

Abstract The macrocyclic antibiotics represent a relatively new class of chiral selectors in separation science and teicoplanin‐based chiral stationary phases (CSP) have been used successfully in a number of applications in high‐performance liquid chromatography. In the present studies, we self‐prepared two bonded CSPs–teicoplanin (TE) and teicoplanin phenyl isocyanate (TE‐Phe). Seven amino alcohols, propranolol, bisoprolol fumarate, atenolol, salbutamol, isoproterenol, metoprolol, and labetalol were enantioseparated on both self‐made CSPs using methanol as mobile phase and acetic acid (HOAc) and triethylamine (TEA) as mobile phase additives. On both CSPs, the different enantioseparation behavior of analytes with different structure was compared. The influence of the concentration of mobile phase additives (HOAc and TEA) on the enantioseparation was investigated. In all conditions, the retention factors (k′) of seven analytes on TE‐Phe CSP were larger than that on TE CSP. However, the separation factors (α) and resolutions (Rs) on TE‐Phe CSP were smaller than that on TE CSP. The results indicated that the derivatized TE‐Phe CSP is not efficient as original teicoplanin CSP. Our observations also suggested that, for teicoplanin‐based CSPs, π‐π interactions and dipole‐dipole between solutes and CSPs mainly contribute to the retention of solutes on CSPs while hydrogen bonding and steric interactions play important roles in the chiral recognition for teicoplanin‐based CSPs.

Study of optical isomer separation of chiral antifungal drugs tetramisole, miconazole, and paclobutrazol on two chiral stationary phases

Abstract The optical isomer separation of chiral antifungal drugs tetramisole, miconazole, and paclobutrazol on Pirkle‐type (S,S)‐Whelk O1 chiral column in three‐component normal phase mode was described. When the polar modifier in hexane mobile phase was iso‐propanol, ethanol, and n‐butanol, respectively, the chiral separation of each solute was investigated. Then on self‐prepared cellulose tris (3,5‐dimethylphenylcarbamate) (CDMPC) chiral column, comparative study of chiral separation was made, to discuss the different chiral recognition mechanisms between the solutes and the two different types of chiral stationary phases. We thank Prof. Dr. Kinkel in Georg‐Simon‐Ohm University of Applied Science (Nürnberg, Germany) for providing (S,S)‐Whelk‐O1 chiral column.

Enantioseparation and Chiral Recognition Mechanism of Two Novel Organic Phosphonate Derivatives on Chiral Stationary Phases

Abstract Direct enantiomeric resolution of two synthesized organic phosphonate derivatives [(2‐Chloro‐phenylamino)‐(2‐hydroxy‐phenyl)‐methyl]‐phosphonic acid diethyl ester (compound 1) and [(2‐Chloro‐phenyl)‐(4‐fluoro‐phenylamino)‐methyl]‐phosphonic acid diethyl ester (compound 2) has been achieved using hexane as the mobile phase with various alcohols as modifiers. The influence of the mobile phase composition and solute structure on the chiral separation was studied. It was found that compound 1 achieved good separation on (S,S)‐Whelk‐O1, cellulose tris(3,5‐dimethylphenylcarbamate) (CDMPC) and cellulose trisphenylcarbamate (CTPC) chiral stationary phases, while compound 2 could be separated on (R,R)‐3,5‐dinitrobenzoyl‐1,2‐diphenylethane‐1,2‐diamine((R,R)‐DNB‐DPEDA) and CDMPC chiral stationary phases. Interestingly, on cellulose derivative chiral stationary phases (CSPs), acidic additive was necessary for enantioseparation of compounds 1 and 2. The chiral recognition mechanism of (S,S)‐Whelk‐O1, (R,R)‐DNB‐DPEDA and cellulose derivative CSPs was explored. On (S,S)‐Whelk‐O1‐CSP, hydrogen‐bonding interactions play an important role in chiral recognition. On (R,R)‐DNB‐DPEDA‐CSP, the dipole‐dipole interactions and π‐π stacking are important to chiral discrimination. On (S,S)‐Whelk‐O1‐CSP and (R,R)‐DNB‐DPEDA‐CSP, a correlation is concluded between elution order and absolute configuration of the analytes. On cellulose CSPs, the inclusion and fitness of solute shape in the chiral cavity significantly contributed to the enantioseparation of solutes. Furthermore, as for the enantioseparation of compound 1, the hydrogen‐bonding interactions play an important role on CTPC, but play a minor role on CDMPC.

Enantioseparation of Four Aryloxyphenoxypropionic Acid Herbicides by HPLC on CDMPC and (S,S)-Whelk-O 1

Abstract This article reported the enantioseparation of diclofop, fluazifop, quizalofop-P and fenoxaprop using self-prepared cellulose derivative CDMPC and (S,S)-Whelk-O 1 columns. The influence of the mobile phase composition and solute structure on the chiral separation was studied. And their chiral recognition mechanism was discussed. The experiment results showed that fenoxaprop obtained the best resolution on (S,S)-Whelk-O 1, while the other three solutes obtained the best separation on CDMPC. It was concluded that the four aryloxyphenoxypropionic acid herbicides obtained excellent separation and the chiral recognition mechanisms of CDMPC and (S,S)-Whelk-O 1 are different from each other. And the structure of solutes and CSP play a key role in the chiral recognition.

Comparative Study of the Enantioseparation of Uniconazole and Imazalil by HPLC on Various Cellulose Chiral Columns

Abstract This paper reported the enantioseparation of uniconazole and imazalil using four different self‐prepared cellulose derivative columns, namely, CTB, CTMB, CTPC, and CDMPC. The mobile phase composition including the type of the alcohol modifier and the ethanol concentration in hexane changed, and the influence on the retention factor (k′); for each enantiomer, the separation factor (α) and the resolution (RS) was studied. The influence of the structures of the analytes on the chiral separation was investigated. The results showed that uniconazole obtained the best resolution of 2.16 on CTPC, while imazalil obtained the best separation on CTMB, with the maximal resolution of 4.83. It was concluded that the structure of solutes and CSP play a key role in the chiral recognition. And the chiral attraction between them is the predominant factor.

Enantioseparation of Benazepril Intermediates by High‐Performance Liquid Chromatography on Chiral CDMPC Column

Abstract A HPLC method was developed for resolutions of two benazepril intermediates. The separation was achieved on CDMPC. The influence of kinds of alcoholic modifiers, concentration of n‐butanol and column temperature was studied for the optimization of resolutions. The best separation was achieved using 10% n‐butanol as modifier and at 25°C with α‐value of 1.84 for BTB‐C and 1.34 for BTB. The chiral recognition mechanism of CDMPC was explored. Hydrogen‐bonding interaction and inclusion and fitness of solute in the chiral cavity significantly play an important role influencing the chiral separation, and the polarities of the alcohols have effect on the stereoselectivity too.