Ping-An Wang

Enantioselective separation of chiral vicinal diols in capillary electrophoresis using a mono‐6A‐aminoethylamino‐β‐cyclodextrin as a chiral selector

This paper describes an improved access to mono-6(A)-aminoethylamino-beta-CD (beta-CDen), a very efficient cationic chiral selector for CZE in the separation of eight chiral aromatic vicinal diols. The beta-CDen concentration has a strong influence on the efficiency of enantioseparation. The effects of the pH and concentration of the BGE, the capillary temperature, and the applied voltage on the resolution and separation selectivity have been studied. Excellent chiral resolution was achieved under the optimal conditions of beta-CDen 10 mM, pH 10, 200 mM borate buffer at 15 kV and 20 degrees C within 20 min. Moreover, the developed method was successfully applied to the determination of the enantiomeric purity of the catalytic asymmetric dihydroxylation (AD) reaction products.

Selectivity differences between alkyl and polar-modified alkyl phases in reversed phase high performance liquid chromatography.

Compared to conventional C18 phases, polar-modified phases have distinct differences with regards to chromatographic behavior. In the present study, ODS phases and polar-modified phases were synthesized. The columns containing these new packings demonstrated satisfactory stability under both acidic (pH 1.5) and basic (pH 10) conditions. We evaluated the selectivity differences between alkyl and polar-modified alkyl RP columns by using a range of neutral analytes. The polar-modified alkyl phases showed excellent peak shapes for almost all compounds. We also compared the selectivity differences between them for separating nucleotides by using 100% aqueous mobile phase and tricyclic antidepressants in the intermediate pH mobile phases. The results demonstrated that polar-modified phases display a significantly reduced hydrophobic nature and a significantly reduced silanol activity compared to the conventional C18 phases.

Ferrocene as a Privileged Framework for Chiral Organocatalysts

Ferrocene (Fc) as a privileged framework for chiral organocatalysts (Orgcat) has been developed rapidly in recent years. Herein, five categories have been summarized, including Fc‐based nucleophilic, bifunctional, Brønsted acid, hydrogen‐bonding organocatalysts and Fc‐based frustrated Lewis pairs. Their applications in enantioselective transformations were also highlighted and discussed in this Minireview.

Efficient synthesis of unnatural dipeptides based on cis-2,5-disubstituted pyrrolidine

The well-defined unnatural dipeptides based on cis-2,5-disubstituted pyrrolidine backbone were synthesized from commercially available starting materials meso-diethyl-2,5-dibromoadipate, (S)-(−)-1-phenylethylamine, and phenylalanine. The configurations of all the chiral centers in these unnatural dipeptides are confirmed by X-ray crystal diffraction analysis.

1-(4-Amino-3,5-dichloro-phen-yl)ethanol.

The asymmetric unit of the title compound, C8H9Cl2NO, contains two crystallographically independent molecules which are connected via an N—H⋯O hydrogen bond . There is aromatic π–π stacking in the crystal, with a centroid–centroid distance between benzene rings of 3.48 (2)Å. The crystal packing is stabilized by intermolecular hydrogen bonds.

2,2-Dichloro-1-(4-methyl­phen­yl)ethanone

The molecule of the title compound, C9H8Cl2O, is almost planar: the dihedral angle between the benzene ring and the plane defined by the carbonyl O and ethane C atoms is 15.5 (2)°. The crystal packing is stabilized by intermolecular C—H⋯O hydrogen bonds.

(S)-1-Ferrocenyl-3-hy-droxy-3-phenyl-propan-1-one.

In the title compound, [Fe(C5H5)(C14H13O2)], the dihedral angle between the phenyl ring and the unsubstituted cyclopetadienyl ring is 85.0 (2)°while that between the phenyl ring and the substituted cyclopetadienyl ring is 83.6 (2)°. The dihedral angle between the two cyclopenta-1,3-diene rings of the ferrocene unit is 2.2 (2)°. The molecules are stabilized by intermolecular O—H⋯O hydrogen-bonding interaction within the crystal lattice.

Ethyl 4-benzamido-5-phenyl-4H-1,2,4-triazole-3-carboxyl-ate monohydrate.

In the title compound, C18H16N4O3·H2O, the dihedral angles between the triazole ring and the phenyl rings are 84.8 (4) and and 39.8 (4)°. The phenyl rings make a dihedral angle of 84.5 (9)°. In the crystal, the molecules are linked by N—H⋯O and O—H⋯N hydrogen bonds. An intramolecular O⋯N interaction also occurs [2.827 (3) Å]