Olga V. Hordiyenko

Remarkably strong polarization of amidine fragment in the crystals of 1-imino-1H-isoindol-3-amine

Results of the X-ray diffraction studies of 1-imino-1H-isoindol-3-amine and its derivatives reveal unusual distribution of bond lengths within the NH2–C=N amidine fragment in the considered crystals. In the crystal phase, single C–N bond is shorter or at most has the same length as double C=N bond, while in isolated molecules both these bonds have expected lengths, according to the calculations by MP2/6-311G(d,p) and MP2/cc-pvtz methods. It is demonstrated that so unusually strong polarization of the amidine fragment is induced by polar environment in solid state. This effect stabilizes the amino-imino tautomer of 1-imino-1H-isoindol-3-amine, which becomes more stable than the diimino tautomer possessing the lowest energy in the gas phase.

Methyl N-(3-cyano-picolino-yl)-l-tryptophanate.

In the title compound, C19H16N4O3, the stereocenter has an l configuration; l-tryptophan methyl ester hydrochloride being used as a starting material. The indole ring system and the pyridine ring are inclined to one another by 13.55 (14)°. In the crystal, adjacent molecules are linked via N—H⋯O hydrogen bonds, forming chains propagating along the c-axis direction.

Conformational studies of new pseudotripeptide with pyrazine amidoxime motif and simplified analogs using IR, NMR spectroscopy, and molecular dynamic simulations

Solution structures of new pyrazine-based pseudotripeptide with amidoxime function and simplified pseudodipeptide analogs were determined by a combination of IR and NMR spectroscopic studies and molecular dynamic simulations using explicit chloroform as a solvent. It was found that proline-phenylalanine dipeptide residue and amidoxime moiety in o-position are essential for intramolecular hydrogen bonding including a seven-membered γ-turn formation. In addition, a cis/trans equilibrium study was present for prolyl amides in polar solvents (D2O and DMSO). A phenylalanine substituent was found to exhibit profound effect on thermodynamic parameters in prolyl peptides. The presence of intramolecular hydrogen bonds dramatically increases the amount of trans isomer in non-hydrogen-bonding CHCl3 and significantly favor cis isomer in hydrogen-bonding solvents such as DMSO and D2O. All molecules are not cytotoxic therefore they can be further studied in relation to potent biological activities.

Methyl esters of 2-(N-hydroxycarbamimidoyl)benzoyl-substituted α-amino acids as promising building blocks in peptidomimetic synthesis: a comparative study

An efficient and simple synthetic protocol for the synthesis of a number methyl esters of 2-(N-hydroxycarbamimidoyl)benzoyl-substituted (S)-α-amino acids via subsequent coupling and hydroxyamination of 2-cyanobenzamide derivatives has been developed. Comparative analysis of three pseudopeptide series based on 2-cyano- and 2-amidoxime-substituted benzoic acid and its pyridine and pyrazine counterparts has been provided and it has revealed a practical advantage of the benzoic acid derivatives due to their greater availability. The impact of the nitrogen atom in the aromatic ring on the trans/cis-amide equilibrium in the proline derivatives is discussed.Graphical abstract

Crystal structure of 4-tert-butyl-2-{2-[N-(3,3-dimethyl-2-oxobut­yl)-N-iso­propyl­carbamo­yl]phen­yl}-1-isopropyl-1H-imidazol-3-ium perchlorate

Bulky isopropyl substituents introduce steric hindrance within the molecule. The organic cation and perchlorate anion are linked by N—H⋯O hydrogen bonding. In the crystal, molecules form separated layers resulting in a low crystal density of 1.18 Mg m−1.