Dorota K. Stępień

Towards a monomeric structure of phenylboronic acid: The influence of ortho-alkoxy substituents on the crystal structure

The structures of three ortho-alkoxyphenylboronic acids (2-methoxy-, 2-ethoxy-, 2-isobutoxy-), and three diortho-alkoxyphenylboronic acids (2,6-dimethoxy-, 2,6-diethoxy- and 2-isobutoxy-6-methoxy) were determined by single crystal X-ray diffraction. The study was undertaken with the intention of designing a novel boronic acid having a monomeric structure, which to date has been an unavailable building block for crystal engineering. This motif can be enhanced by involving two hydroxyl groups at the boron atom in intramolecular hydrogen bonds. Although monosubstituted systems form typical dimers in the crystal lattice, disubstituted species reveal a much bigger variety of possible interactions. Among the analyzed compounds, 2,6-dimethoxyphenylboronic acid and 2,6-diethoxyphenylboronic acid crystallize in two polymorphic forms each. The unprecedented packing with monomers as the dominant structural motif has been found in the crystal structure of 2-isobutoxy-6-methoxyphenylboronic acid and one of the polymorphs of both 2,6-dimethoxyphenylboronic acid and 2,6-diethoxyphenylboronic acid. This description of the molecular packing is also supported by the analysis of fingerprint 2-D plots based on the Hirshfeld surfaces. The variety of possible types of interactions either within a single moiety or between moieties in dimers were additionally analyzed on the basis of the interaction energies, which have been estimated by ab initio calculations at the MP2/6-31+G* and B3LYP/6-311+G** level of theory.

Unprecedented 1,3-Dipolar Cycloaddition: From 1,4,5,8-Naphthalene Bisimides to a New Heterocyclic Skeleton

1,4,5,8-Naphthalene bisimides react as dipolarophiles with in situ formed azomethine ylides. Double 1,3-dipolar cycloaddition is followed by unique ring rearrangement and leads to the formation of two six-membered rings. The formation of hexacyclic products is rationalized based on DFT calculations.

Synthesis and biological activity of novel series of heterocyclic compounds containing succinimide moiety

Abstract In the search for biological agents, a series of new N-substituted ethyl 11-ethyl-7-methyl-3,5,10-trioxo-4-azatricyclo[5.2.2.02,6]undecane-8-carboxylates 3, 9-methyl-3,5,8-trioxo-4-azatricyclo[5.2.1.02,6]dec-1-yl acetates 6 and 1,3-dioxo-4,5,6,7-tetraphenyl-2,3,3a,4,5,7a-hexahydro-1H-isoindole-4-carboxylic acids 9 were prepared. All compounds were characterized by 1H NMR, ESI-MS, and elemental analyses. Moreover, for intermediate products 2, 5, and 8, X-ray structural analyses were conducted. Compounds 3a–e, 6a, 6b, 9a–e were tested for their cytotoxic properties in K562 and HeLa cells.

Solid-state structure of N-o-, N-m-, and N-p-nitrophenyl-2,3,4-tri-O-acetyl-β-D-xylopyranosylamines.

Comprehensive structural analyses were performed for N-o-, N-m-, and N-p-nitrophenyl-2,3,4-tri-O-acetyl-β-D-xylopyranosylamines. Single-crystal X-ray diffraction data were collected and revealed that one compound under investigation undergoes temperature-dependent polymorph transitions (crystal structures of three polymorphs were obtained). The number of molecules in the independent part of the crystal unit cells was in agreement with the number of resonances in solid-state (13)C NMR spectra. Therefore, the compounds exist as single polymorphs at room temperature, as confirmed by powder X-ray diffraction measurements. Significant differences in (13)C chemical shifts between solution and solid-state NMR for selected carbon atoms confirmed the existence of intra- and/or intermolecular interactions.

Application of graph theory and topological models for the determination of fundamentals of the aromatic character of pi-conjugated hydrocarbons

Application of topological analysis and graph theory to benzenoid hydrocarbons leads to the determination of fundamentals of aromaticity: the Hückel rule and the Clar rule. The approach, based on a treatment of the adjacency matrix, allows resonance energy (RE)-like characteristics to be estimated with quite good accuracy, and magnetic aromaticity indices to be derived for both the individual rings and the whole molecules. It also allows an effective approach for interpreting ring current formation in molecules when exposed to an external magnetic field. The transformation of the perturbation matrix into a form describing the canonical structures allows their gradation and determination of their stabilizing/destabilizing character.