[en] Oximation of 20-hydroxyecdysone oxo derivatives proceeds regio- and stereoselectively and provides (E)-configured oximes in quantitative yields. The Ni-Ra-catalyzed hydrogenation of the oximes affords novel α-aminoecdysteroids with the unchanged 14α-hydroxy-7-en-6-on native chromophore of ecdysteroids. The structures of synthesized compounds were confirmed by the means of homo- and heteronuclear one-dimensional and two-dimensional ¹H and ¹³C NMR spectroscopy and X-ray crystallography. (author)

[en] The synthesis of tetrabenzo[a,c,g,i]fluorenyl (Tbf) yttrium dialkyl complexes, (Tbf)Y(CH₂SiMe₃)₂(L) (L = tetrahydrofuran (THF), 1; L = bipy, 2), by direct protonolysis of the tris(alkyl) complex, Y(CH₂SiMe₃)₃(THF)₂, are reported. The X-ray crystal structures of 1 and 2 display the helical twisting typically observed for the Tbf ligand. Dynamic nuclear magnetic resonance (NMR) studies on 1 show a barrier to Tbf helical inversion (epimerization or 'wagging') of 38.1 ± 0.5 kJ mol^-1. The reaction of 1 with acidic hydrocarbons such as 1,3-bis(trimethylsilyl)cyclopentadiene or trimethylsilylacetylene results in protonolysis to form the mixed Cp derivative [(Tbf){C₅H₃(SiMe₃)₂}Y(CH₂SiMe₃)(THF)] (3) or [(Tbf)Y(CCSiMe₃)₂(THF)]_n (4), respectively. In the case of 4, a small amount of the trinuclear cluster (Tbf)Y₃(μ³-CCSiMe₃)₂(μ²-CCSiMe₃)₃(CCSiMe₃)₃(THF)₂ (5) was isolated and characterized by X-ray crystallography. Dialkyl 1 undergoes smooth insertion of trimethylsilyl isocyanate to afford [(Tbf)Y{κ²-(N,O)-Me₃SiN(Me₃SiCH₂)CO}₂(THF)] (6) but it does not react with alkenes. Treating 1 with [Ph₃C]⁺[B(C₆F₅)₄]^- in bromobenzene generates a moderately active ethylene polymerization catalyst (36 kg mol^-1 h^-1 bar^-1). (author)

[en] The recognition of neutral aromatic substrates by different neutral calix[4]arene receptors 1, 2, and 3 was studied by NMR spectroscopy. The stoichiometry is 1:1 in all cases as was confirmed by jobs plot. Owing to the deep cavity, 1 affords stronger binding abilities for substrate 4 and 5, while all receptors remained inert for substrates 6 and 7. The binding constants determined by ¹H NMR titration show that the recognition of substrate 4 by 1 gives strongest complexation (K_a of 9.8 x 10² M^-1)

[en] The new nitroisofalvones 2a-k were synthesized via nitration of the corresponding isoflavones 1a-f using NH4NO3/TFAA in acetonitrile. The aminoisoflavones 3a-g, also new, were produced by selective reduction of the corresponding nitroisoflavones with SnCl2.2H2O. The nitro- and aminoisoflavones, tested in vitro concerning their effects on the proliferation of endothelial cells showed modest activities. All the new products are fully characterized and the nitro compounds analyzed thoroughly by NMR to allow complete assignment of the proton and carbon resonance and to establish the orientation of nitration. (author)

[en] To minimize the variance in the quantification of solid-state phases in powder samples, gently placing polycrystalline samples one next to another directly in a sample holder is better than trying to mix them homogeneously prior to transferring to a sample holder. However, the solid-state cross polarization-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy results demonstrated that it is essential in this sampling method to place all the samples in the location of consistent signal sensitivity. The same sampling method may be employed in other spectroscopic quantification techniques of solid-state phases if the method to limit the sample to the location with uniform signal sensitivity in the sample holder is adapted to each technique

[en] The first general procedure is described for the synthesis of novel bisarylmethylidenes of 2-methoxy-2-methyl1,3-dioxan-5-one 1. Thus, several derivatives of 3 are obtained rapidly in high yields by reacting 1 with different aldehydes in the presence of catalytic quantities of pyrrolidine in EtOH at room temperature. Upon completion of the reactions, products are obtained directly by spontaneous precipitation avoiding time consuming and expensive chromatographic separations. All products were characterized by proton and carbon NMR spectroscopy methods, and in one case, the proposed structure was elucidated by X-ray crystallography, confirming the Z stereochemistry for the olefinic C=C bonds. Due to showing different colours in solid and solution states, products were studied for their photophysical properties as well. (author)

[en] It has been found that thermal regrouping of 3-allyl-2-allyloxy- and 3-allyl-4-allyl oxybenzonitrile is a suitable method for obtaining of 3,5-diallyl-2-hydroxy- and 3,5-diallyl-4-hydro oxybenzonitrile. (author)

[en] Highlights: • Clean determination of homonuclear couplings. • Pure shift acquisition delivers pure absorption 2D lineshapes. • Zero quantum coherence suppression filters out artefacts. Analysis of proton NMR spectra has been a key tool in structure determination for over 60 years. A classic tool is 2D J-spectroscopy, but common problems are the difficulty of obtaining the absorption mode lineshapes needed for accurate results, and the need for a 45° shear of the final 2D spectrum. A novel 2D NMR method is reported here that allows straightforward determination of homonuclear couplings, using a modified version of the PSYCHE method to suppress couplings in the direct dimension. The method illustrates the need for care when combining pure shift data acquisition with multiple pulse methods.

[en] Full text: Many drugs are poorly soluble in water, which is a challenge for the discovery of clinically useful pharmaceutical formulations due their low and erratic bioavailability. Therefore, to overcome these drawbacks, there is the need to design novel drug delivery systems to improve the bioavailability of poorly soluble drugs. An advantageous strategy is using polysaccharide hydrogels, such as dextran. In this study, we evaluated the effects of hydrogels containing 148 kDa and 70 kDa dextran (DEX-70 and DEX-148) in different proportions on the release profile of praziquantel (PZQ), a drug that is poorly soluble in water. Three formulations were prepared and characterized. IR and NMR spectra revealed the interactions between praziquantel and the polymers that changed the release profile, contributing to its modulation. Hydrogel swelling also contributed to the modulation of the release profile of praziquantel. These results show that hydrogels with different proportions of 70 kDa and 148 kDa dextran are capable of modulating the release of drugs with poor water solubility and can be used as a novel platform technology for drug delivery system development. (author)

[en] Almost all the elements in the periodic table have at least one natural isotope active in NMR. Although the same principles apply to all of them, accessing to the NMR information greatly depends on the properties of each nucleus. This article describes these issues as the starting point to show the breath of applications derived from the multinuclear approach of this spectroscopic technique across the periodic table based on representative selected examples in solution.