NMR frequency and magnetic dipole moment of (3)He nucleus

We present new gas-phase NMR spectra which relate the resonance frequency of (3)He nucleus to the resonance frequency of the proton in tetramethylsilane (TMS). We discuss the dependence of (3)He resonance frequency on the density of the solvent gas, and we consider in detail the absolute shielding scales of both nuclei. Finally, we analyse the accuracy of the results, using the relationship between the resonance frequencies, absolute shielding constants and magnetic dipole moments of (1)H and (3)He nuclei.     

The simplest synthesis of 5,5-disubstituted and spiranic methyl 4-amino-2,2-dioxo-2,5-dihydro-1,2λ6-oxathiole-3-carboxylates

We report the short and the simplest strategy for the synthesis of methyl 4-amino-2,2-dioxo-2,5-dihydro-1,2λ⁶-oxathiole-3-carboxylates bearing aliphatic substituents at the 5th position. A number of cyanohydrins were forced to react with methyl 2-(chlorosulfonyl)acetate to give the interim methyl 2-[(cyanomethoxy)sulfonyl]acetates that upon Et₃N-mediated conditions underwent the CSIC [Carbanion mediated Sulfonate (Sulfonamido) Intramolecular Cyclization] reaction yielding the 5,5-disubstituted and spiranic methyl 4-amino-2,2-dioxo-2,5-dihydro-1,2λ⁶-oxathiole-3-carboxylates.     

3-Fluoroalkyl (CF3, CHF2, CH2F) Cyclobutane-Derived Building Blocks for Medicinal Chemistry: Synthesis and Physicochemical Properties

Synthesis and physicochemical characterization of all possible cis- and trans-1,3-disubstituted cyclobutane-derived amines and carboxylic acids bearing mono-, di- and trifluoromethyl groups at the C-3 position is disclosed. Tetramethylammonium fluoride (TMAF)- or morpholinosulfur trifluoride (Morph-DAST)-mediated nucleophilic fluorination of appropriate cis- and trans-diastereomeric substrates was used as the key step for the preparation of CH₂F- and CHF₂-substituted derivatives. To obtain the corresponding cis- and trans-isomeric CF₃-substituted derivatives, resolution of known 3-(trifluoromethyl)cyclobutanecarboxylic acid (obtained as a mixture of diastereomers) was applied. The proposed procedures were suitable for the preparation of corresponding fluoroalkyl-substituted cyclobutane-derived amines and carboxylic acids on up to 50 g scale. All 12 building blocks obtained were characterized by measuring dissociation constants (pK_a) and lipophilicities (LogP, for model derivatives) to evaluate the effect of the fluoroalkyl substituents on their physicochemical properties relevant to further drug discovery applications.     

Revisiting the properties of delafossite CuCrO2: A single crystal study

Platelet-like single-crystals of delafossite CuCrO₂ have been successfully grown and characterised by X-ray diffraction and pole figures, scanning electron and atomic force microscopy. Transport measurements reveal that the resistivity is highly anisotropic, with a ratio of about 35 at 300 K between the in- and out-of-plane directions, reflecting the layered crystal structure. The magnetization and specific heat data show that CuCrO₂ undergoes a unique antiferromagnetic transition at T_N=24.0 K, in contrast to a recent report on CuCrO₂ single-crystals [16] showing the existence of two magnetic transitions, T_N1=24.2 K and T_N2=23.6 K, depending on the orientation of the applied magnetic field along and perpendicular to c, respectively.