An efficient method for the determination of enantiomeric purity of racemic amino acids using micellar chromatography, a green approach

Abstract

A simple, sensitive and green micellar liquid chromatographic method (RP-HPLC) was developed for enantioseparation of four racemic amino acids, namely, (RS)-selenomethionine, (RS)-methionine, (RS)-cysteine and (RS)-penicillamine. An aqueous solution of sodium dodecyl sulfate and Brij-35 was prepared and used as mobile phase for HPLC analysis. Activated esters of (S)-ibuprofen, (S)-ketoprofen and (S)-levofloxacin were synthesized by reacting them with N-hydroxybenzotriazole. These esters were characterized by UV, IR, 1 HNMR, HRMS and elemental analysis. These chiral reagents (activated esters) were used for the synthesis of diastereomeric derivatives of the chosen amino acids. The diastereomeric derivatives were separated on a C 18 column by micellar liquid chromatography. Chromatographic conditions were optimized by varying concentration of surfactant in aqueous solution, and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (78, an excellent green method score). In addition, density functional theory calculations were performed, using Gaussian 09 rev. A.02 and hybrid density functional B3LYP with a 6-31G* basis set program, in order to develop lowest energy optimized structures of diastereomeric derivatives. The method was validated according to International Conference on Harmonization guidelines and the retention factor (k), selectivity factor (α), resolution factor (R S) and limit of detection (0.295 ng ml −1) and limit of quantification (0.896 ng ml −1) were calculated.

Micellar liquid chromatographic green enantioseparation of racemic amino alcohols and determination of elution order

“…Enantiomers, in the chiral environment, exhibit different activities (e.g., pharmacological, toxicity, and metabolism), because of which, in many countries, regulatory agencies demand complete information on pharmacodynamics and pharmacokinetics of a new chiral/racemic drug before permitting it to the market. Because of the increasing demand for a single pure enantiomer as a pharmaceutical, nowadays, the chromatographic development, especially the enantioseparation of racemic compounds, has gained huge attention (Alwera, Alwera, & Sehlangia, 2020; Alwera & Bhushan, 2016a). The chromatographic method developers always aim to develop new, sensitive, inexpensive, and efficient methods for the detection of enantiopurity of a wide variety of racemic pharmaceuticals under different conditions.…”