New Polymorph of Dehydroepiandrosterone Obtained via Cryomodification

A new anhydrous polymorph of dehydroepiandrosterone (DHEA) is detected in cryomodified powder samples and designated as form VII. The crystal structure of form VII is determined from multiphase X-ray powder diffraction (XRPD) data. Additionally, the unknown crystal structures of anhydrous form III and the new monohydrated DHEA form designated as form S5 are also determined from multiphase XRPD data. To validate the crystal structures III, VII, and S5, energy minimization with dispersion-corrected density functional theory is performed in VASP. An extended list of the DHEA forms with the known crystal structures, which now covers anhydrous forms I, II, III, VI, and VII and solvated forms S1, S2, S4 and S5, allows quantification of DHEA solid-state transformations to be carried out

Synthesis and Structural Characterization of a Series of Novel Zn(II)-based MOFs with Pyridine-2,5-dicarboxylate Linkers

A series of novel metal–organic frameworks comprised of Zn–O–Zn dinuclear units and multidentate pyridine-2,5-dicarboxylate linkers were synthesized under mild conditions. The crystal structure and composition of the novel phases were established from synchrotron powder diffraction data. Small variations in the parameters of the synthesis led to formation of the metal–organic systems of different topologies, either 3D metal–organic frameworks (MOFs) or a 0D molecular complex. The novel MOFs feature a permanent porosity. The excess hydrogen uptake measured for the selected MOF sample was about 0.9 wt % at 77 K and 1 bar. Structural examinations indicated the phase transformation in several samples caused by the absorption of the atmospheric water molecules. The thermal stability and guest-molecule content in the pores of the novel MOFs were also characterized by TGA-DSC

Synthesis and Structural Characterization of a Series of Novel Zn(II)-based MOFs with Pyridine-2,5-dicarboxylate Linkers

A series of novel metal–organic frameworks comprised of Zn–O–Zn dinuclear units and multidentate pyridine-2,5-dicarboxylate linkers were synthesized under mild conditions. The crystal structure and composition of the novel phases were established from synchrotron powder diffraction data. Small variations in the parameters of the synthesis led to formation of the metal–organic systems of different topologies, either 3D metal–organic frameworks (MOFs) or a 0D molecular complex. The novel MOFs feature a permanent porosity. The excess hydrogen uptake measured for the selected MOF sample was about 0.9 wt % at 77 K and 1 bar. Structural examinations indicated the phase transformation in several samples caused by the absorption of the atmospheric water molecules. The thermal stability and guest-molecule content in the pores of the novel MOFs were also characterized by TGA-DSC

Diversity Oriented Synthesis of Polycyclic Heterocycles through the Condensation of 2‑Amino[1,2,4]triazolo[1,5‑<i>a</i>]pyrimidines with 1,3-Diketones

The acid-catalyzed condensation between 2-aminosubstituted [1,2,4]­triazolo­[1,5-<i>a</i>]­pyrimidines and their analogues with various saturation of the pyrimidine ring and 1,3-diketones or 1,1,3,3-tetramethoxypropane was evaluated as a new approach for the synthesis of diversely substituted polycyclic derivatives of triazolopyrimidine. The reaction of 4,5,6,7-tetrahydro- or aromatic aminotriazolopyrimidines results in selective formation of the corresponding [1,2,4]­triazolo­[1,5-<i>a</i>:4,3-<i>a</i>′]­dipyrimidin-5-ium salts, and the condensation of substrates containing the 4,7-dihydro-[1,2,4]­triazolo­[1,5-<i>a</i>]­pyrimidine fragment is accompanied by a cascade rearrangement with unusual recyclization of the dihydropyrimidine ring to yield partially hydrogenated [1,2,4]­triazolo­[1,5-<i>a</i>:4,3-<i>a</i>′]­dipyrimidin-5-ium or pyrimido­[1′,2′:1,5]­[1,2,4]­triazolo­[3,4-<i>b</i>]­quinazolin-5-ium salts. The proposed methodology exhibits a wide scope, providing rapid access to polycondensed derivatives of the [1,2,4]­triazolo­[1,5-<i>a</i>]­pyrimidine scaffold. DFT calculations of the Gibbs free energies of possible isomers were performed to rationalize the experimentally observed reactivity and selectivity

Two Anhydrous and a Trihydrate Form of Tilorone Dihydrochloride: Hydrogen-Bonding Patterns and Reversible Hydration/Dehydration Solid-State Transformation

During the polymorph screening of an active pharmaceutical ingredient tilorone dihydrochloride (chemical name 2,7-bis­[2-(diethylamino)­ethoxy]-9-fluorenone dihydrochloride) two new polymorphic modifications  <b>III</b> and <b>IV</b>  were obtained. The crystal structures of both polymorphs were established from X-ray powder diffraction. An interesting phenomenon has been observed at ambient conditions for <b>III</b>, which transforms into a novel hydrated form <b>IIIh</b> during 2–3 h when the humidity in the storage room increases to 70% or more. As soon as the relative humidity falls to 30% or less, <b>IIIh</b> transforms into the parent anhydrous form <b>III</b> within an hour. Form <b>IIIh</b> has been identified as a trihydrate of tilorone dihydrochloride, and its crystal structure has been established from X-ray powder diffraction. On the basis of the crystal structures and hydrogen-bonding patterns, a mechanistic model of reversible hydration/dehydration solid-state transformation <b>III</b> ↔ <b>IIIh</b> depending on the relative humidity is proposed

Two Anhydrous and a Trihydrate Form of Tilorone Dihydrochloride: Hydrogen-Bonding Patterns and Reversible Hydration/Dehydration Solid-State Transformation

During the polymorph screening of an active pharmaceutical ingredient tilorone dihydrochloride (chemical name 2,7-bis­[2-(diethylamino)­ethoxy]-9-fluorenone dihydrochloride) two new polymorphic modifications  <b>III</b> and <b>IV</b>  were obtained. The crystal structures of both polymorphs were established from X-ray powder diffraction. An interesting phenomenon has been observed at ambient conditions for <b>III</b>, which transforms into a novel hydrated form <b>IIIh</b> during 2–3 h when the humidity in the storage room increases to 70% or more. As soon as the relative humidity falls to 30% or less, <b>IIIh</b> transforms into the parent anhydrous form <b>III</b> within an hour. Form <b>IIIh</b> has been identified as a trihydrate of tilorone dihydrochloride, and its crystal structure has been established from X-ray powder diffraction. On the basis of the crystal structures and hydrogen-bonding patterns, a mechanistic model of reversible hydration/dehydration solid-state transformation <b>III</b> ↔ <b>IIIh</b> depending on the relative humidity is proposed

Two Anhydrous and a Trihydrate Form of Tilorone Dihydrochloride: Hydrogen-Bonding Patterns and Reversible Hydration/Dehydration Solid-State Transformation

During the polymorph screening of an active pharmaceutical ingredient tilorone dihydrochloride (chemical name 2,7-bis­[2-(diethylamino)­ethoxy]-9-fluorenone dihydrochloride) two new polymorphic modifications  <b>III</b> and <b>IV</b>  were obtained. The crystal structures of both polymorphs were established from X-ray powder diffraction. An interesting phenomenon has been observed at ambient conditions for <b>III</b>, which transforms into a novel hydrated form <b>IIIh</b> during 2–3 h when the humidity in the storage room increases to 70% or more. As soon as the relative humidity falls to 30% or less, <b>IIIh</b> transforms into the parent anhydrous form <b>III</b> within an hour. Form <b>IIIh</b> has been identified as a trihydrate of tilorone dihydrochloride, and its crystal structure has been established from X-ray powder diffraction. On the basis of the crystal structures and hydrogen-bonding patterns, a mechanistic model of reversible hydration/dehydration solid-state transformation <b>III</b> ↔ <b>IIIh</b> depending on the relative humidity is proposed

Two Anhydrous and a Trihydrate Form of Tilorone Dihydrochloride: Hydrogen-Bonding Patterns and Reversible Hydration/Dehydration Solid-State Transformation

During the polymorph screening of an active pharmaceutical ingredient tilorone dihydrochloride (chemical name 2,7-bis­[2-(diethylamino)­ethoxy]-9-fluorenone dihydrochloride) two new polymorphic modifications  <b>III</b> and <b>IV</b>  were obtained. The crystal structures of both polymorphs were established from X-ray powder diffraction. An interesting phenomenon has been observed at ambient conditions for <b>III</b>, which transforms into a novel hydrated form <b>IIIh</b> during 2–3 h when the humidity in the storage room increases to 70% or more. As soon as the relative humidity falls to 30% or less, <b>IIIh</b> transforms into the parent anhydrous form <b>III</b> within an hour. Form <b>IIIh</b> has been identified as a trihydrate of tilorone dihydrochloride, and its crystal structure has been established from X-ray powder diffraction. On the basis of the crystal structures and hydrogen-bonding patterns, a mechanistic model of reversible hydration/dehydration solid-state transformation <b>III</b> ↔ <b>IIIh</b> depending on the relative humidity is proposed

Nature Chooses Rings: Synthesis of Silicon-Containing Macrocyclic Peroxides

The reactions of 1,2-bis­(dimethylchlorosilyl)­ethane (<b>1</b>), 1,2-bis­(dimethylchlorosilyl)­ethene (<b>6</b>), and 1,2-bis­(dimethylchlorosilyl)­ethyne (<b>7</b>) with <i>gem</i>-bis­(hydroperoxides) <b>2a</b>–<b>h</b> and 1,1′-bis­(hydroperoxy)­bis­(cycloalkyl)­peroxides <b>4a</b>–<b>c</b> were found to proceed in an unusual way. Thus, the reactions do not give the expected polymeric peroxides; instead, they produce cyclic silicon-containing peroxides containing 2, 4, or 6 silicon atoms in the ring: 9- (<b>3a</b>–<b>h</b>), 12- (<b>5a</b>–<b>c</b>), 18- (<b>8</b>,<b> 12</b>), 24- (<b>9</b>, <b>10</b>), 27- (<b>13</b>), and 36-membered (<b>11</b>) compounds. The size of the rings produced in the reactions increases in the series 1,2-bis­(dimethylchlorosilyl)­ethane < 1,2-bis­(dimethylchlorosilyl)­ethene < 1,2-bis­(dimethylchlorosilyl)­ethyne. The resulting 9- and 12-membered cyclic peroxides are stable under ambient conditions. These compounds were isolated by chromatography and characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy, X-ray diffraction, elemental analysis, and high-resolution mass spectrometry. The yields vary from 77 to 95%. Structures of the larger-size rings (18-, 24-, 27-, and 36-membered peroxides) were confirmed by ¹H, ¹³C, and ²⁹Si NMR spectroscopy using 2D (COSY, HSQC, and HMBC), 2D DOSY ¹H, 3D ¹H–²⁹Si HMBC-DOSY NMR experiments, and elemental analysis