Preparation Of Pure Enantiomers Research Articles

Light-assisted preparation of vancomycin chiral stationary phase based on diazotized silica and its enantioseparation evaluation by high-performance liquid chromatography

Owing to enantiomers’ identical physical and chemical properties, separation work in the chiral environments is still a great challenge.and chemical properties. Chromatographic techniques employing chiral stationary phases (CSPs) have been developed as powerful tools for the chiral analysis and preparation of pure enantiomers. Here we report a facile synthesis of vancomycin stationary phase based on diazotized silica. Monodisperse silica particles were synthesized by a modified Stöber method. The obtained silica particles were modified by self-assembly photosensitive diazoresin (DR) and vancomycin on the surface. After treatment with UV light, the ionic bonding was converted into covalent bonding through a unique photochemistry reaction of DR. Baseline separation of chiral drugs was achieved by using the vancomycin@SiO2 particles as packing materials in high performance liquid chromatography (HPLC). The effects of separation parameters including elution mode, flow rate and analyte mass on the enantioselectivity of the CSP were investigated in detail. Due to the replacement of highly toxic and moisture sensitive silane agent by water soluble non-toxic DR in the modification of silica microspheres, this method provides a green and easy way to manufacture packing materials for chromatography applications.

Memory of Chiral Molecules Define Their Interactions and the Results of Resolution Processes

The preparation of pure enantiomers has an increasing demand both for academic and industrial (pharmaceutical) practice. This is not surprising, because the active ingredients of a main part of medicines (about 70-80%) are pure enantiomers. Several selective methods are known for preparation of pure enantiomers but the more economical and usual method is the resolution, when the pure enantiomers are obtained from diastereomeric salts formed due the reaction of the racemic compound and resolving agent in adequate conditions (solvent, temperature crystallization time). Since the first resolution effectuated by Pasteur the researchers have tried to explain what is happening during resolution, but this has not yet been fully accomplished, it is still a mystery. In this paper is described our proposal for resolution’s mechanism, based on systematization of our results and observations made during the resolution, taking into consideration the principal characteristics of enantiomeric mixtures, namely the eutectic composition and their helicity. We suppose that the enantiomers have a memory and they used it during the resolution processes, tending to form their stable symmetric conformation.

Engineering Cyclodextrin Clicked Chiral Stationary Phase for High-Efficiency Enantiomer Separation.

The separation of racemic molecules is of crucial significance not only for fundamental research but also for technical application. Enantiomers remain challenging to be separated owing to their identical physical and chemical properties in achiral environments. Chromatographic techniques employing chiral stationary phases (CSPs) have been developed as powerful tools for the chiral analysis and preparation of pure enantiomers, most of which are of biological and pharmaceutical interests. Here we report our efforts in developing high-performance phenylcarbamated cyclodextrin (CD) clicked CSPs. Insights on the impact of CD functionalities in structure design are provided. High-efficiency enantioseparation of a range of aryl alcohols and flavanoids with resolution values (Rs) over 10 were demonstrated by per(3-chloro-4-methyl)phenylcarbamated CD clicked CSP. Comparison study and molecular simulations suggest the improved enantioselectivity was attributed to higher interactions energy difference between the complexes of enantiomers and CSPs with phenylcarbamated CD bearing 3-chloro and 4-methyl functionalities.

Supramolecular Host-Guest Asymmetric Induction In Organic Synthesis

In past decades, the pharmacopoeia was dominated by racemates, but since the emergence of new technologies in the 1990s that allowed the preparation of pure enantiomers in significant quantities, the awareness and interest in the stereochemistry of drug actions have increased. In this short review, the implementation of several hosts, guests, building blocks and methods in host-guest supramolecular chemistry was outlined with an emphasis on the synthetic aspects, catalyst libraries and molecular recognition. Solid-state host-guest interactions, intra- and intermolecular host-guest photoreactions in solution and in the solid state, molecular and supramolecular self-assembly and molecular recognition between host and guests, and some specific and important reactions, such as aldol and Michael reactions, were reviewed. Keywords: Asymmetric, catalyst libraries, chiral auxiliary, combinatorial chemistry, host-guest, photochirogenesis, self-assembly, supramolecular

Papain-Assisted Resolution of Natural and Xenobiotic α-Amino Acid

Abstract A new and convenient method for the preparation of pure enantiomers of α-amino acids is described. Industrial papain, catalyzes the synthesis of L-Z-amino acid ethyl esters in ethanolic medium, with good yields. These esters are obtained from DL-Z-amino acids with 100% optical purity. Unreactive D-Z-amino acids are readily isolated from reaction medium. Physical constants of natural and xenobiotic L-Z-amino acid esters and D-Z-amino acids are described.

Enantioselective photodeconjugation of conjugated esters and lactones

Abstract