Alicja Wzorek

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.

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. We demonstrate that, in sharp contrast to amides, the substitution of the sulphur atom for the oxygen in the acyl group, strongly reduced the observed magnitude of the SDE. These results clearly indicate the importance of the hydrogen bonding for the formation of homo/hetero-chiral association responsible for manifestation of the SDE phenomenon.

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.

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.

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.

Preparation of partially functionalised resorcinarene derivatives

The conditions for synthesis of mono-, di- and trifunctionalised resorcinarenes by catalysed Mannich reaction are described. A series of these compounds are functionalised with different functional groups.

Synthesis and Structure of Tetratosyl Bora Derivatives of Resorcinarenes From l-Proline and l-Prolinol

Organoboron compounds play an important role in asymmetric synthesis. In particular, the oxazaborolidines are highly useful as excellent chiral catalysts for the asymmetric reduction of prochiral ketones as well as for the other enantioselective reactions.1–4 Formation of strong intramolecular coordinate bonds between the nitrogen and the boron atoms provides many possibilities for the synthesis of new heteroor macrocyclic compounds.5–9 In addition, some of these compounds have been recognized as biologically active substances.10 Examples of the synthesis of chiral boron derivatives of resorcinarene have been reported.11–14 Herein we describe the synthesis of new chiral di-boron derivatives of resorcinarenes from tetratosylresorcinarene, l-proline and l-prolinol. The reaction of resorcinarene 1 with tosyl chloride in the presence of triethylamine gave the tetratosyl derivative of resorcinarene 2 in good yields (67%),15 as shown in Scheme 1, that is consistent with the literature data.

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. This shortcoming is easily remedied though by defining a fixed ranking for a particular ligand in the system under study, eg, the ligand at which the change has occurred. The configurations are then expressed as iR or iS, akin to the R and S descriptors, for sp3 -hybridized tetrahedral chiral structures and similarly, as ire and isi faces, akin to the re and si descriptors, for sp2 -hybridized trigonal prochiral structures. All in all, the notation can be considered as an auxiliary to extend the usefulness of the R/S system. Thus, the proposed iR/iS notation could find profitable use in comparative studies where there is a need to avoid confusion arising from changing assignments due to priority rules or to expedite the ease of comprehension. Moreover, in the current digital age, the facile retrieval of stereochemically clear data by machines is highly desirable-something that the iR/iS notation is readily amenable to.

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

Abstractα-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. As well as thioacylation, attention was paid to the effect of altering the R group of the ester functionality, the side chain, or that of the acyl group attached to the amide nitrogen, whereby it was found that electron-withdrawing groups in the latter moiety had a pronounced effect on the magnitude and behavior of the resulting SDE phenomenon. Intriguingly, in the case of N-fluoroacylated derivatives, by favoring the formation of dimeric associates and effecting a strong bias toward homochiral associates over heterochiral associates, the SDE magnitude was greatly reduced contrary to intuitive expectations. Energy estimates resulted from DFT calculations.

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. This podands under appropriate conditions can thus form a sufficiently long cavity to accommodate more than one metal ion inside without disturbance of the axial symmetry like an ion channel. Podand with shorter arms, obtained from ethylene glycol form complexes with 1:1 stoichiometry and also readily dimers or trimers. In the presence of alkali metal cations this podand selectively binds cesium ions. The significant affinity of synthesized podands for the biologically important alkali metal ions may affect living organisms. Antibacterial activities were tested with series of Gram-positive and Gram-negative bacteria.