Regiospecific Hydrogenation of Bromochalcone by Unconventional Yeast Strains.

This research aimed to select yeast strains capable of the biotransformation of selected 2'-hydroxybromochalcones. Small-scale biotransformations were carried out using four substrates obtained by chemical synthesis (2'-hydroxy-2″-bromochalcone, 2'-hydroxy-3″-bromochalcone, 2'-hydroxy-4″-bromochalcone and 2'-hydroxy-5'-bromochalcone) and eight strains of non-conventional yeasts. Screening allowed for the determination of the substrate specificity of selected microorganisms and the selection of biocatalysts that carried out the hydrogenation of tested compounds in the most effective way.

Recommended Tests for the Self-Disproportionation of Enantiomers (SDE) to Ensure Accurate Reporting of the Stereochemical Outcome of Enantioselective Reactions.

The purpose of this review is to highlight the necessity of conducting tests to gauge the magnitude of the self-disproportionation of enantiomers (SDE) phenomenon to ensure the veracity of reported enantiomeric excess (ee) values for scalemic samples obtained from enantioselective reactions, natural products isolation, etc. The SDE always occurs to some degree whenever any scalemic sample is subjected to physicochemical processes concomitant with the fractionation of the sample, thus leading to erroneous reporting of the true ee of the sample if due care is not taken to either preclude the effects of the SDE by measurement of the ee prior to the application of physicochemical processes, suppressing the SDE, or evaluating all obtained fractions of the sample. Or even avoiding fractionation altogether if possible.

The self-disproportionation of enantiomers (SDE) via column chromatography of β-amino-α,α-difluorophosphonic acid derivatives.

This work presents the first study of the self-disproportionation of enantiomers via chromatography (SDEvC) of β-aminophosphonic acid esters, several of which have been synthesized for the first time. Three types of structures were examined, N-acetylated, dipeptide construction with N-Cbz glycine, and a free amine. In the latter case, this is the first time that SDEvC has been reported for free amine amino acids.

The self-disproportionation of enantiomers (SDE) of amino acids and their derivatives.

This review covers the phenomenon of the self-disproportionation of enantiomers (SDE) of amino acids and their derivatives in all its guises from phase transformations (recrystallization, sublimation, and distillation), to the application of force fields, through to chromatography including HPLC, MPLC, gravity-driven column chromatography, and SEC. The relevance of the SDE phenomenon to amino acid research and to marketed pharmaceuticals is clear given the potential for alteration of the enantiomeric excess of a portion of a scalemic sample. In addition, the possible contribution of the SDE phenomenon to the genesis of prebiotic homochirality is considered.

The self-disproportionation of enantiomers (SDE): The effect of scaling down, potential problems versus prospective applications, possible new occurrences, and unrealized opportunities?

This commentary discusses an important, though not widely appreciated, chiral phenomenon of molecular chirality that effectively always occurs whenever nonracemic samples are subjected to practically any physicochemical process (e.g., force field, recrystallization, sublimation, even distillation, etc.

The self-disproportionation of enantiomers (SDE) of α-amino acid derivatives: facets of steric and electronic properties.

α-Amino acids (α-AAs) are in extremely high demand in nearly every sector of the food and health-related chemical industries and continue to be the subject of intense multidisciplinary research. The self-disproportionation of enantiomers (SDE) is an emerging and one of the least studied areas of α-AA or enantiomeric properties, critically important for their production and application. In the present work, we report a detailed study of the SDE via achiral, gravity-driven column chromatography for a set of N-acylated, N-carbonylated, N-fluoroacylated, and N-thioacylated α-amino acid esters.

Internal chirality descriptors iR and iS and ire and isi. A proposed notation to extend the usefulness of the R/S system by retaining the sense of stereochemistry in cases of ligand ranking changes.

The R/S system, universally applied for indicating the absolute configuration of a structure, is extremely adept for conveying the absolute configuration unequivocally. However, it suffers from one limitation, viz that due to CIP priority rules the rankings of the ligands attached to an asymmetric center can be altered upon a change in a ligand leading to a change in the designated configuration even if bonds to the asymmetric center were not actually formed or broken. This means that the sense of stereochemistry in situations such as within a set of compounds where family relationships are of focus or where the sense of the stereochemical course of a reaction is of interest can be lost or confusion may occur.

The self-disproportionation of enantiomers (SDE): a menace or an opportunity?

Herein we report on the well-documented, yet not widely known, phenomenon of the self-disproportionation of enantiomers (SDE): the spontaneous fractionation of scalemic material into enantioenriched and -depleted fractions when any physicochemical process is applied. The SDE has implications ranging from the origins of prebiotic homochirality to unconventional enantiopurification methods, though the risks of altering the enantiomeric excess (ee) unintentionally, regrettably, remain greatly unappreciated. While recrystallization is well known as an SDE process, occurrences of the SDE in other processes are much less recognized, sublimation and even distillation.

Chiral sulfoxides: advances in asymmetric synthesis and problems with the accurate determination of the stereochemical outcome.

Chiral sulfoxides are in extremely high demand in nearly every sector of the chemical industry concerned with the design and development of new synthetic reagents, drugs, and functional materials. The primary objective of this review is to update readers on the latest developments from the past five years (2011-2016) in the preparation of optically active sulfoxides. Methodologies covered include catalytic asymmetric sulfoxidation using either chemical, enzymatic, or hybrid biocatalytic means; kinetic resolution involving oxidation to sulfones, reduction to sulfides, modification of side chains, and imidation to sulfoximines; as well as various other methods including nucleophilic displacement at the sulfur atom for the desymmetrization of achiral sulfoxides, enantioselective recognition and separation based on either metal-organic frameworks (MOF's) or host-guest chemistry, and the Horner-Wadsworth-Emmons reaction.

Possible Case of Halogen Bond-Driven Self-Disproportionation of Enantiomers (SDE) via Achiral Chromatography.

The major breakthrough reported in this work is the discovery of likely halogen bond-driven self-disproportionation of enantiomers (SDE). Taking into account that the halogen-bonding interactions can be rationally designed and can match, or even exceed, the strength of the more familiar hydrogen bond, this discovery clearly opens an unexpected new direction of research in the areas of molecular chirality and the SDE phenomenon.

Diastereoselective α-Alkylation of Metallo Enamines Generated from N-C Axially Chiral Mebroqualone Derivatives.

The reactions of various alkyl halides with the metallo enamines generated from racemic and optically pure N-C axially chiral mebroqualone derivatives were found to proceed with a synthetically attractive stereochemical outcome (up to 99% yield and up to dr = 26:1) allowing preparation of a structurally new type of pharmaceutically interesting compounds possessing elements of axial and central chirality.

Self-disproportionation of enantiomers via achiral gravity-driven column chromatography: A case study of N-acyl-α-phenylethylamines.

Herein we report a study of the self-disproportionation of enantiomers (SDE) via gravity-driven achiral column chromatography of a series of amides derived from 1-phenylethylamine. We demonstrated that structural and electronic factors of the substituents play an important role in the observed magnitude of the SDE. For the first time, the SDE phenomenon of amides with that of thioamides was compared.

Remarkable magnitude of the self-disproportionation of enantiomers (SDE) via achiral chromatography: application to the practical-scale enantiopurification of β-amino acid esters.

We report the best performance yet for the self-disproportionation of enantiomers (SDE) via achiral chromatography as typically used in laboratories for the isolated yield of the excess enantiomer using N-acetyl β-amino acid ethyl esters. The results are the most convincing ever demonstration of the capability of the SDE for practical-scale enantiopurification as comparable, or even superior for some systems, to that of recrystallization. For example, from a sample of 94.

Synthesis and complexing properties of diglycol resorcinarene podands.

Synthesis of new podands from resorcinarene and diethylene glycols are reported. The binding properties of these podands with alkali metal cations was studied by means of ESI-MS. The experimental results for podands with long diethylene glycol arms show the stable inclusion complexes with one or two metal cations and high affinity for sodium and potassium ions.

Introducing a new radical trifluoromethylation reagent.

Perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (PPFR) is a persistent radical stable at room temperature, but easily decomposes at 90 °C to produce a CF3 radical which is able to react with a variety of aromatic compounds to afford the corresponding trifluoromethyl derivatives, usually as mixtures of regioisomers in good to excellent overall yields.

The self-disproportionation of the enantiomers (SDE) of methyl n-pentyl sulfoxide via achiral, gravity-driven column chromatography: a case study.

This work explores the self-disproportionation of enantiomers (SDE) of chiral sulfoxides via achiral, gravity-driven column chromatography using methyl n-pentyl sulfoxide as a case study. A major finding of this work is the remarkable persistence and high magnitude of the SDE for the analyte. Thus, it is the first case where SDE is observed even in the presence of MeOH in the mobile phase.

Optical purifications via self-disproportionation of enantiomers by achiral chromatography: case study of a series of α-CF3-containing secondary alcohols.

This work demonstrates that self-disproportionation of enantiomers via achiral chromatography can be recommended as inexpensive and general method for optical purification of enantiomerically enriched compounds. In particular, the advantage of this approach over conventional recrystallization is that it can be used for both crystalline as well as liquid compounds.