Monoclinic polymorph of 3,7-dimethyl-1-(5-oxohex­yl)-3,7-dihydro-1H-purine-2,6-dione

The structure of the title compound, pentoxifylline, C13H18N4O3, has been previously characterized as a triclinic polymorph [Pavelčík et al. (1989 ▶). Acta Cryst. C45, 836–837]. We have discovered the monoclinic form. There are no strong hydrogen bonds in the crystal structure, rather, moderate C—H⋯O hydrogen bonds are present, which serve to stabilize the three-dimensional architecture

Combined Use of Structure Analysis, Studies of Molecular Association in Solution, and Molecular Modelling to Understand the Different Propensities of Dihydroxybenzoic Acids to Form Solid Phases

The arrangement of hydroxyl groups in the benzene ring has a significant effect on the propensity of dihydroxybenzoic acids (diOHBAs) to form different solid phases when crystallized from solution. All six diOHBAs were categorized into distinctive groups according to the solid phases obtained when crystallized from selected solvents. A combined study using crystal structure and molecule electrostatic potential surface analysis, as well as an exploration of molecular association in solution using spectroscopic methods and molecular dynamics simulations were used to determine the possible mechanism of how the location of the phenolic hydroxyl groups affect the diversity of solid phases formed by the diOHBAs. The crystal structure analysis showed that classical carboxylic acid homodimers and ring-like hydrogen bond motifs consisting of six diOHBA molecules are prominently present in almost all analyzed crystal structures. Both experimental spectroscopic investigations and molecular dynamics simulations indicated that the extent of intramolecular bonding between carboxyl and hydroxyl groups in solution has the most significant impact on the solid phases formed by the diOHBAs. Additionally, the extent of hydrogen bonding with solvent molecules and the mean lifetime of solute–solvent associates formed by diOHBAs and 2-propanol were also investigated

Crystal structure of 3,6,6-trimethyl-4-oxo-1-(pyridin-2-yl)-4,5,6,7-tetrahydro-1H-indazol-7-aminium chloride and its monohydrate

The title compounds, C15H19N4O+·Cl− and C15H19N4O+·Cl−·H2O, obtained in attempts to synthesize metal complexes using tetrahydroindazole as a ligand, were characterized by NMR, IR and X-ray diffraction techniques. The partially saturated ring in the tetrahydroindazole core adopts a sofa conformation. An intramolecular N—H...N hydrogen bond formed by the protonated amino group and the N atom of the pyridyl substituent is found in the first structure. In the hydrochloride, the organic moieties are linked by two N—H...Cl− hydrogen bonds, forming a C(4) graph-set. In the hydrate crystal, a Cl− anion and a water molecule assemble the moieties into infinite bands showing hydrogen-bond patterns with graph sets C(6), R64(12) and R42(8). Organic moieties form π–π stacked supramolecular structures running along the b axis in both structures

{(3aR,5S,6R,6aR)-5-[(R)-1,2-Dihydroxyethyl]-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-yl}methyl methanesulfonate

In the title compound, C11H20O8S, the furanose ring has a pseudorotation phase angle equal to 31.3° and assumes a 3T4 conformation, with deviations of 0.297 (4) and −0.152 (4) Å for the corresponding C atoms. The dioxolane ring adopts an envelope conformation. One of the O atoms is at the flap and deviates from the least-squares plane formed by the other four ring atoms by 0.405 (2) Å. The dihedral angle between the planar fragments of the rings is 63.53 (8)°. In the crystal, molecules are associated into sheets perpendiculer to the b axis by means of O—H...O hydrogen bonds. A few weak C—H...O interactions are also observed

Crystallographic Study of Solvates and Solvate Hydrates of an Antibacterial Furazidin

In this study we present a detailed crystallographic analysis of multiple solvates of an antibacterial furazidin. Solvate formation of furazidin was investigated by crystallizing it from pure solvents and solvent-water mixtures. Crystal structure analysis of the obtained solvates and computational calculations were used to identify the main factors leading to the intermolecular interactions present in the solvate crystal structures and resulting in formation of the observed solvates and solvate hydrates. Furazidin forms pure solvates and solvate hydrates with solvents having large hydrogen bond acceptor propensity and with a hydrogen bond donor and acceptor formic acid. In solvate hydrates the incorporation of water allows formation of additional hydrogen bonds and results in more efficient hydrogen bond network in which water is “hooking” the organic solvent molecule, and this slightly reduces the cut-off of solvent hydrogen bond acceptor propensity required for obtaining a solvate. The crystal structures of all pure solvates are formed from molecule layers and in almost all structures solvent is hydrogen bonded to the furazidin, but the packing in each solvate is unique. In contrast, the hydrogen bonding and packing in most solvate hydrates are nearly identical

SnAr Reactions of 2,4-Diazidopyrido[3,2-d]pyrimidine and Azide-Tetrazole Equilibrium Studies of the Obtained 5-Substituted Tetrazolo[1,5-a]pyrido[2,3-e]pyrimidines

A straightforward method for the synthesis of 5-substituted tetrazolo[1,5-a]pyrido[2,3-e]pyrimidines from 2,4-diazidopyrido[3,2-d]pyrimidine in SnAr reactions with N-, O-, and S- nucleophiles has been developed. The various N- and S-substituted products were obtained with yields from 47% to 98%, but the substitution with O-nucleophiles gave lower yields (20–32%). Furthermore, the fused tetrazolo[1,5-a]pyrimidine derivatives can be regarded as 2-azidopyrimidines and functionalized in copper(I)-catalyzed azide-alkyne dipolar cycloaddition (CuAAC) and Staudinger reactions due to the presence of a sufficient concentration of the reactive azide tautomer in solution. In total, seven products were fully characterized by their single crystal X-ray studies, while five of them were representatives of the tetrazolo[1,5-a]pyrido[2,3-e]pyrimidine heterocyclic system. Equilibrium constants and thermodynamic values were determined using variable temperature 1H NMR and are in agreement of favoring the tetrazole tautomeric form (ΔG298 = −3.33 to −7.52 (kJ/mol), ΔH = −19.92 to −48.02 (kJ/mol) and ΔS = −43.74 to −143.27 (J/mol·K)). The key starting material 2,4-diazidopyrido[3,2-d]pyrimidine presents a high degree of tautomerization in different solvents

2,6-Dichloro-9-(2′,3′,5′-tri-O-acetyl-β-d-ribofuranosyl)-9H-purine

The title synthetic analog of purine nucleosides, C16H16Cl2N4O7, has its acetylated β-furanose ring in a 3′β-envelope conformation, with the corresponding C atom deviating by 0.602 (5) Å from the rest of the ring. The planar part of the furanose ring forms a dihedral angle of 65.0 (1)° with the mean plane of the purine bicycle. In the crystal, molecules form a three-dimensional network through multiple C—H...O and C—H...N hydrogen bonds and C—H...π interactions