High-performance liquid chromatographic enantioseparation of unusual amino acid derivatives with axial chirality on polysaccharide-based chiral stationary phases

New Levan-Based Chiral Stationary Phases: Synthesis and Comparative HPLC Enantioseparation of (±)-trans-β-Lactam Ureas in the Polar Organic Mode

In this paper, the preparation of three new polysaccharide-type chiral stationary phases (CSPs) based on levan carbamates (3,5-dimethylphenyl, 4-methylphenyl, and 1-naphthyl) is described. The enantioseparation of (±)-trans-β-lactam ureas 1a-h was investigated by high-performance liquid chromatography (HPLC) on six different chiral columns (Chiralpak AD-3, Chiralcel OD-3, Chirallica PST-7, Chirallica PST-8, Chirallica PST-9, and Chirallica PST-10) in the polar organic mode, using pure methanol (MeOH), ethanol (EtOH), and acetonitrile (ACN). Apart from the Chirallica PST-9 column (based on levan tris(1-naphthylcarbamate), the columns exhibited a satisfactory chiral recognition ability for the tested trans-β-lactam ureas 1a-h.

Synthesis, resolution, and absolute configuration determination of a vicinal amino alcohol with axial chirality. Application to the synthesis of new box and pybox ligands

New racemic vicinal amino alcohol derivatives with 4‐benzylidenecyclohexane skeleton and axial chirality have been prepared. A preparatively easy and efficient protocol for resolution of the N‐benzoylamino alcohol is described. Using a 250 × 20 mm (L × ID) Chiralpak® IA column, and the appropriate mixture of n‐hexane/ethanol/chloroform as eluent, both enantiomers of N‐benzoylamino alcohol 3 are obtained with >99% enantiomeric excess (ee) by successive injections of a solution of the racemic sample in chloroform. The obtained axially chiral vicinal amino alcohol is used to synthesize structurally novel bisoxazoline ligands in high yields.

Polysaccharides as separation media for the separation of proteins, peptides and stereoisomers of amino acids

Reliable separation of peptides, amino acids and proteins as accurate as possible with the maximum conformation and biological activity is crucial and essential for drug discovery. Polysaccharide, as one of the most abundant natural biopolymers with optical activity on earth, is easy to be functionalized due to lots of hydroxyl groups on glucose units. Over the last few decades, polysaccharide derivatives are gradually employed as effective separation media. The highly-ordered helical structure contributes to complex, diverse molecular recognition ability, allowing polysaccharide derivatives to selectively interact with different analytes. This article reviews the development, application and prospects of polysaccharides as separation media in the separation of proteins, peptides and amino acids in recent years. The chiral molecules mechanism, advantages, limitations, development status and challenges faced by polysaccharides as separation media in molecular recognition are summarized. Meanwhile, the direction of its continued development and future prospects are also discussed.

High-performance liquid chromatographic enantioseparation of N-aryl-thioureidoalkylphosphonates and thiourylenedi(alkylphosphonates) on polysaccharide-based chiral stationary phases

The first successful enantioseparation of representative O,O-diphenyl-N-arylthioureidoalkylphosphonates, (±)-Ptc-Val^P (OPh)₂ & (±)-Ptc-Leu^P (OPh)₂ and thiourylenedi(isobutyl phosphonate), Tcm[Val^P (OPh)₂ ]₂ on analytical and semipreparative scale was achieved by high-performance liquid chromatography using polysaccharide-based chiral stationary phases (CPs). Atc-AA^P (OPh)₂ was obtained using modified tricomponent condensations of the corresponding aldehydes, N-arylthiourea and triphenyl phosphite whereas Tcm[Val^P (OPh)₂ ]₂ by the condensations of aldehydes, thiourea, and triphenyl phosphite. The prepared, racemic (±)-Atc-AA^P (OPh)₂ [(±)-Ptc-Val^P (OPh)₂ , (±)-Ptc-Leu^P (OPh)₂ , (±)-Ptc-Pgly^P (OPh)₂ and (±)-Ntc-Pgly^P (OPh)₂ ] and racemic (±)-Tcm[AA^P (OPh)₂ ]₂ [(±)-Tcm[Nva^P (OPh)₂ ]₂ & (±)-Tcm[Val^P (OPh)₂ ]₂ ] were adequately characterized and used for chromatographic separations on high-performance liquid chromatography-chiral stationary phases. The best results were obtained for (±)-Ptc-Val^P (OPh)₂ , (±)-Ptc-Leu^P (OPh)₂ and (±)-Tcm[Val^P (OPh)₂ ]₂ .

Functionalities tuned enantioselectivity of phenylcarbamate cyclodextrin clicked chiral stationary phases in HPLC

The mixed chloro- and methyl- functionalities can greatly modulate the enantioselectivities of phenylcarbamate cyclodextrin (CD) clicked chiral stationary phases (CSPs). A comparison study is herein reported for per(4-chloro-3-methyl)phenylcarbamate and per(2-chloro-5-methyl)phenylcarbamate β-CD clicked CSPs (i.e., CCC4M3-CSP and CCC2M5-CSP). The enantioselectivity dependence on column temperature was studied in both normal-phase and reversed-phase mode high performance liquid chromatography (HPLC). The thermodynamic study revealed that the stronger intermolecular interactions can be formed between CCC4M3-CSP and chiral solutes to drive the chiral separation. The higher enantioselectivities of CCC4M3-CSP were further demonstrated with the enantioseparation of 17 model racemates in HPLC.

Synthesis of substituted phenylcarbamates of N-cyclobutylformylated chitosan and their application as chiral selectors in enantioseparation

New CSPs exhibited high tolerability to common organic solvents, and most of them possessed excellent enantioseparation capability.