Janusz Jurczak

Resolution of some chiral mandelic acid derivatives into enantiomers by reversed-phase high-performance liquid chromatography via α- and β-cyclodextrin inclusion complexes

Abstract The resolution of mandelic acid derivatives (differing in the kind of functional group and in the position of its substitution in the aromatic ring) into enantiomers in a reversed-phase high-performance liquid chromatographic system via α- and β-cyclodextrin inclusion complexes was studied. Of the mandelic acid derivatives investigated (o-, m- and p-OH, o-CH3, o-OCH3, o- and m-Cl), only the chloro derivatives showed high enantioselectivity in the processes of complex formation with β- cyclodextrin (separation factors: αo-C1 = 1.8 at pH 2.1 and αo-Cl = 1.15 and αm-Cl = 1.15 at pH 6.8). In contrast, the enantioselectivity for complex formation between α-cyclodextrin and mandelic acid and the derivatives investigated was low.

A New Macrocyclic Polylactam-Type Neutral Receptor for Anions − Structural Aspects of Anion Recognition

A macrocyclic ligand containing four amide functionalities was synthesised and its complexes with various anions (F−, Cl−, AcO−, H2PO4−, and p-NO2C6H4O−) were investigated in solution and in the solid state. NMR titration experiments (carried out in [D6]DMSO), X-ray studies and electrospray mass spectrometry (ESI MS) were employed for determination of stoichiometry and selectivity. The results in solution indicated predominant formation of 1:1 complexes for all anions studied. However, the existence of a 2:1 complex of 1 with bidentate AcO− anion as a minor species was also detected. X-ray crystal structure determination provided evidence that the Cl− anion is too bulky to be included in the cavity of the 18-membered tetralactam ring [Kass(Cl−; DMSO) = 65 M−1], but that F− fits well [Kass(F−; DMSO) = 830 M−1]. The binding mode of AcO− anion consists of formation of four hydrogen bonds to only one of the carboxylate oxygen atoms (employing the syn-anti lone pairs of AcO−). The selectivity of the receptor towards AcO− anion [Kass(AcO−; DMSO) = 2640 M−1] is discussed in terms of a favourable arrangement of hydrogen-bond donors. The limited extent of formation of a 2:1 (1/AcO−) complex is attributed to unfavourable interactions between two receptor molecules.

Recognizing the Limited Applicability of Job Plots in Studying Host–Guest Interactions in Supramolecular Chemistry

Continuous variation method, known as Job plot, is the most commonly applied method for the determination of stoichiometry of complex chemical entities for over 100 years. Although, the method was proven successful in the analysis of very stable metal-ligand complexes, we demonstrate that its use in supramolecular chemistry often provides false results. We support this statement with multiple simulations as well as cases studies of several real host-guest systems. We propose an alternative, general method relying on the analysis of residual distribution in titration data fitting. The latter method is more convenient compared to the Job plot and unlike it gives correct results in all real cases studied.

Effective and mild method for preparation of optically active α-amino aldehydes via TEMPO oxidation

Abstract The TEMPO oxidation method is successfully applied to preparation of variously protected, optically active α-amino aldehydes without racemization and in very good yield.

Synthesis of chiral diaza-crown ethers incorporating carbohydrate units

Abstract A synthesis of a novel chiral diaza crown ethers derived from α-D-glucose, α-D-mannose, and α-D-galactose in two alternative pathways is described.

7,7'-Diureido-2,2'-diindolylmethanes: anion receptors effective in a highly competitive solvent, methanol.

Neutral, acyclic, indole-containing ligands bind anions with hydrogen bonds in pure methanol and form an unprecedented phosphate complex in the solid state.

Novel oxidative opening of 2,5-disubstituted furan ring

Abstract A new reaction of 2,5-disubstituted furans with bromine in an acetone - water solution afforded an efficient and mild method for opening of the furan ring, this leading to the respective enedione system. The reaction was successfully carried out under either basic or acidic conditions.

The resolution of some chiral compounds in reversed-phase high-performance liquid chromatography by means of β-cyclodextrin inclusion complexes

Summaryβ-Cyclodextrin is applied as the chiral component of the mobile phase in a systematic study of the resolution —into enantiomers — of mandelic acid and its derivatives by reversed-phase liquid chromatography. It is found that the stereoselectivity arising from inclusion in β-cyclodextrin molecules is significant (α=1.02÷1.05) only for the compounds showing at the asymmetric carbon atom the presence of first, an intact carboxylic group and second, a functional group capable of hydrogen bonding with the hydroxyl groups of β-cyclodextrin. Results are discussed in the light of the three-point attachment model of stereoselectivity as well as of the structure of the inclusion complexes.

B–Z DNA reversible conformation changes effected by high pressure

There are numerous data showing that a DNA molecule with alternate pirymidine‐purine sequence can adopt a left‐handed, double‐helical Z‐DNA conformation. Such structural changes of DNA occur as a consequence of environmental conditions (e.g. 4 M NaCl) or chemical modification (e.g. methylation or bromination of bases). In this paper, we found for the first time that high pressure (several kilobars) can change the DNA conformation from the B to the Z form. When the pressure is reduced to an atmospheric one, DNA conformation returns back to the B‐form. The Z‐DNA structure formation was confirmed by circular dichroism (CD) and ultraviolet (UV) measurements. However, we found, that the values of the ratio of absorbance at the wavelenghts 295 and 257 nm in the range of 0.3–0.4 is not a fully conclusive proof for the Z‐DNA conformation. Although the ratio is typical for Z‐DNA form, it is not obvious that the negative band in CD spectrum will be observed. On the other hand, methylated DNA does not undergo B→Z DNA transitions at the high pressure. These conformational changes of DNA molecules could be interpreted as the effect of different hydration of various DNA forms.

α-and β-cyclodextrin complexation as a tool for the separation of o-, m- and p-nitro-cis and trans-cinnamic acids by reversed-phase high-performance liquid chromatography

The capacity factors of o-, m- and p-nitro-cis- and trans-cinnamic acids on reversed-phase columns at various pH values of the mobile phase and concentrations of α- and/or β-cyclodextrin were determined. Attempts to calculate the stability constants, Ko and K−, as well as the capacity factors, k′, of all individual species (neutral and anionic, free and bound to β-cyclodextrin) were made on the basis of experimental data. It was found that β-cyclodextrin enhances the selectivity of the system towards m- and p-nitrocinnamic acids, of whether cis- or trans-configuration2. Under optimum conditions, attempts were made to separate all the compounds investigated.