The Conformations of 17β-Estradiol (E2) and 17α-Estradiol as Determined by Solution NMR

The conformational structures of the hormone 17β-estradiol (E2) and the epimeric 17α-estradiol determined by solution NMR spectroscopy and restrained molecular dynamics calculations found a single low energy conformation.     

Saturation molalities and standard molar enthalpies of solution of α-d-xylose(cr) in H2O(l); standard molar enthalpies of solution of 1,4-β-d-xylobiose(am), and 1,4-β-d-xylotriose(am) in H2O(l)

The saturation molality of α-d-xylose(cr) in water was measured by using HPLC and is m(sat) = (8.43 ± 0.42) mol · kg⁻¹ at T = 298.15 K. It was also established that the anhydrous form of α-d-xylose(cr) is the crystalline form that is in equilibrium with the aqueous solution at T = 298.15 K. Solution calorimetry was used to measure the following standard molar enthalpies of solution at T = 298.15 K: ${\mathrm{\Delta }}_{\text{sol}}{H}_{\text{m}}^{\circ }$ = (12.10 ± 0.12) kJ · mol⁻¹ for α-d-xylose(cr); ${\mathrm{\Delta }}_{\text{sol}}{H}_{\text{m}}^{\circ }$ = −(8.1 ± 2.7) kJ · mol⁻¹ for 1,4-β-d-xylobiose(am); and ${\mathrm{\Delta }}_{\text{sol}}{H}_{\text{m}}^{\circ }$ = −(24.1 ± 6.4) kJ · mol⁻¹ for 1,4-β-d-xylotriose(am). It was observed that both 1,4-β-d-xylobiose(am) and 1,4-β-d-xylotriose(am) were amorphous substances and that they form thick gels in water in which no solid phase is present. Consequently, it is not possible to measure m(sat) for these two substances. All substances were carefully characterized by using both HPLC and Karl Fischer analysis. NMR was used to measure the anomeric purity of the α-d-xylose(cr). Thermodynamic network calculations were used to calculate standard molar formation properties for the aforementioned substances.     

Temperature dependent absorption spectra of Br(-), Br2(•-), and Br3(-) in aqueous solutions

The absorption spectra of Br(2)(?-) and Br(3)(-) in aqueous solutions are investigated by pulse radiolysis techniques from room temperature to 380 and 350 °C, respectively. Br(2)(?-) can be observed even in supercritical conditions, showing that this species could be used as a probe in pulse radiolysis at high temperature and even under supercritical conditions. The weak temperature effect on the absorption spectra of Br(2)(?-) and Br(3)(-) is because, in these two systems, the transition occurs between two valence states; for example, for Br(2)(-) we have (2)Σ(u) → (2)Σ(g) transition. These valence transitions involve no diffuse final state. However, the absorption band of Br(-) undergoes an important red shift to longer wavelengths. We performed classical dynamics of hydrated Br(-) system at 20 and 300 °C under pressure of 25 MPa. The radial distribution functions (rdf's) show that the strong temperature increase (from 20 to 300 °C) does not change the radius of the solvent first shell. On the other hand, it shifts dramatically (by 1 ?) the second maximum of the Br-O rdf and introduces much disorder. This shows that the first water shell is strongly bound to the anion whatever the temperature. The first two water shells form a cavity of a roughly spherical shape around the anion. By TDDFT method, we calculated the absorption spectra of hydrated Br(-) at two temperatures and we compared the results with the experimental data.     

Transport numbers of H+ and O2- in the electrochemical system (H2 + H2O),Me/BaCe0.9Nd0.1O3-α/Me,(H2 + H2O)

In the temperature range 873–1123 K, transport numbers of oxygen ions and protons are determined in the system (H₂ + H₂O), Me/BaCe_0.9Nd_0.1O_3-α/Me,(H₂ + H₂O), where Me = Ag, Au, Pt, Ni, by the emf and current methods. The determined transport numbers are independent of the determination method, the electrode material, the current direction (anodic and cathodic polarization of the electrode), polarizability of electrodes, and the partial water (hydrogen) pressure in the gas phase. This unambiguously suggests that the transport numbers refer to the solid electrolyte, and not the electrochemical system as a whole. It also follows that partial currents of the hydrogen ionization and the oxygen ion discharge are determined by the transport numbers of protons and oxygen ions in the electrolyte. At a constant temperature, their ratio is affected by neither the electrode potential nor the gas phase composition, i.e., both electrode reactions have a common limiting step (or steps). Deceased.     

A novel scalable and stereospecific synthesis of 3α- and 3β-amino-5α-androstan-17-ones and 3α- and 3β-amino-5α-pregnan-20-ones

A novel scalable stereoselective synthesis of 3α- and 3β-amino-5α-androstan-17-ones and 3α- and 3β-amino-5α-pregnan-20-ones has been developed using phthalimide based Mitsunobu chemistry. In all four cases, the products were isolated as single diastereoisomers in high chemical yield and purity without the need for chromatography at any stage in their syntheses.     

Infrared spectral evidence for tricarbonyldinitrosylchromium,Cr(CO)3(NO)2—A re-examination

The evidence for the d⁸ carbonyl—nitrosyl Cr(CO)₃(NO)₂ is re-examined. Making use of ligand effect constants, to calculate energy-factored force constants and ν(CO) frequencies, we conclude that Cr(CO)₃(NO)₂ does not have the D_3h structure suggested by Satija et al. [Inorg. Chem. 17, 1737 (1978)]. We find that it has a C_2v structure, with the NO groups occupying two equatorial positions of a trigonal bipyramid.The hitherto unidentified complex Cr(CO)₄(NO), which was formed in low yield in Satija et al.'s experiments, appears to have a C_4v structure that is very similar to the isoelectronic molecule Mn(CO)₅.     

First Total Synthesis of 3α,4α-Oxidoagarofuran and (-)-3β,4α-Dihydroxy-β-dihydroagarofuran

The first stereoselective total synthesis of (–)-3β, 4α-dihydroxy-β-dihydroagarofuran (1) and 3α, 4α-oxidoagarofuran (2) has been described. The key step is the epoxidation of α-agarofuran (6) with dimethyldioxirane.     

Infrared and Raman spectra of CuCl2·2(H,D)2O and K2CuCl4·2(H,D)2O. Vibrational modes,assignment and coupling of the water librations

The i.r. and Raman spectra of CuCl₂·2H₂O and K₂CuCl₄·2H₂O and of deuterated samples of these compounds are presented in the range 50–1700 cm⁻¹ at liquid helium, liquid nitrogen, and ambient temperatures. The spectra obtained are discussed and compared with the literature data in terms of both bonding structure of the water molecules and vibrational modes, assignment, intermolecular coupling, and combination bands of the H₂O, HDO, and D₂O librations. The i.r. and Raman bands of the librational modes of CuCl₂·2H₂O are very broad even at liquid helium temperature indicating orientational disorder of the water molecules.     

Spanning or looping? The order and conformation of bipolar phospholipids in lipid membranes using 2H NMR spectroscopy

Solid-state 2H NMR spectroscopy was used to study and characterize the conformation and order of bolaform lipid membranes. A series of 2H-labeled bolaform phosphatidylcholines has been synthesized and their properties compared to a [D4]dimyristoylphosphatidylcholine (DMPC) and a [D8]-32 macrocyclic phosphatidylcholine. 31P NMR measurements establish that the aqueous dispersions of these lipids adopt lamellar phases. Computational dePakeing was used to extract the spectrum of the oriented system from spectra consisting of a superposition of randomly oriented domains in an unoriented sample. A large (> 90 %) and constant value for the normalized segmental order parameter (Smol) was observed for all positions along the diacyl chain of the bolaform lipids and only a small population (< 10%) of a less ordered conformer was observed. The less ordered conformer is assigned to the looping conformation on the basis of comparison with the deuterated macrocyclic phospholipid which has an enforced loop in its diacyl chain. The predominant population(> 90%) of the bolaform lipids is assigned to a highly ordered, spanning conformer.     

Possible conformations and relative stability of the 7-membered ring in 1α,5β,6,7α(H)-and 1β,5α,6,7α(H)-guai-11(13)-en-6,12-olides

Stereoisomers of 1,5,6,7(H)- and 1,5,6,7(H)-guai-11(13)-en-6,12-olides are calculated using molecular mechanics. The possibility of forming various conformations in the 7-membered ring is examined as a function of the fusion to the 5-membered C-ring. The effect of the methyl orientation on the conformation of the 7-membered ring and the relative stability of the conformers are discussed.Insitute of Phytochemistry, Karaganda, fax (3212)-43-37-73. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 54–56, January–February, 2000.     

Synthesis,thermal and spectral studies of oxoperoxo and dioxo complexes of vanadium(V), molybdenum(VI) and tungsten(VI) with 2-(α-hydroxyalkyl/aryl)benzimidazole

Reaction of 2-(-hydroxymethyl)benzimidazole or 2-(-hydroxyethyl)benzimidazole (LH) with the peroxovanadium(V) species, generated in situ by stirring V₂O₅, KOH and 30% aqueous H₂O₂, gives the corresponding complexes of formula K[VO(O₂)L₂]. Similar peroxo species of molybdenum and tungsten generated by stirring MoO₃ or WO₃·H₂O with an excess of 30% aqueous H₂O₂ readily react with 2-(-hydroxyethyl) benzimidazole in aqueous EtOH to give the peroxo complexes [MO(O₂)L₂] (M=Mo or W). The dioxo complexes of general formula [MO₂L₂] have also been isolated by the reaction of [MoO₂(acac)₂] or [WO₂- (acac)₂] (acacH=acetylacetone) with the above ligands and with 2-(-hydroxybenzyl)benzimidazole. The dioxo complexes are white, whereas peroxo complexes are light yellow to orange. The peroxo complexes generally decompose in two steps: (i) the decomposition of the peroxo group and (ii) the decomposition of the alkyl/aryl group followed by decomposition of the complete ligand. On the other hand, decomposition of the dioxo complexes follows only in a later step. All the peroxo complexes exhibit three i.r. active vibrational modes at ca. 860cm^–1, 760cm^–1 and 600cm^–1, characteristic of the ²-coordinated peroxo group. The dioxo complexes are dominated by the presence of two sharp bands in the 900cm^–1 region due to _sym(O=M=O) and _asym(O=M=O) modes. The (C=N) (ring) and (OH) shifts have also been measured in order to locate the coordination sites of the ligands. A broad band at ca. 400nm in the peroxovanadium(V) complexes, while the absorption at ca. 350nm in the peroxomolybdenum(VI) and tungsten(VI) complexes is assigned to the peroxo-metal charge transfer band.     

A Facile Synthesis of 4-(3β -Methoxy-5α-androstan-17β-YL)-3-pyrrolin-2-one

The title compound was prepared in 4 steps from 3β-methoxy-21-hydroxy-5α-pregnan-20-one (1). The required intermediate (4) was obtained using lithium enolate derived from t-butyl acetate. Interesting enough, p-tosyl chloride in pyridine quantitatively converted compound 1 into the α-chloro ketone derivative (2).     

Direct experimental evidence for the high chemical reactivity of α- and β-xylopyranosides adopting a (2,5)B conformation in glycosyl transfer

The effect of a (2,5)B boat conformation on xyloside reactivity has been investigated by studying the hydrolysis and glycosylation of a series of synthetic xyloside analogues based on a 2-oxabicyclo[2.2.2]octane framework, which forces the xylose analogue to adopt a (2,5)B conformation. The locked β-xylosides were found to hydrolyze 100-1200 times faster than methyl β-D-xylopyranoside, whereas the locked α-xylosides hydrolyzed up to 2×10(4) times faster than methyl α-D-xylopyranoside. A significant rate enhancement was also observed for the glycosylation reaction. The high reactivity of these conformers can be related to the imposition of a (2,5)B conformation, which approximates a transition state (TS) boat conformation. In this way, the energy penalty required to go from the chair to the TS conformation is already paid. These results parallel and support the observation that the GH-11 xylanase family force their substrate to adopt a (2,5)B conformation to achieve highly efficient enzymatic glycosidic bond hydrolysis.     

Synthesis of ( )-5α-Hydroxy-β-selinene and (-)-5β-Hydroxy-β-selinene

Eudesmanederivativeshavebeendrawingconsiderableattentionduetotheirwidespectrumofbiologicalproperties,particularlyantifeedant,cellgroWthinhibitoryandplantgroWthregulatingactivitiesl'2.Recently,twoepimericeudesmanederivatives( )-5a-hydroxy-6-selinene1and(-)-56-hydroxy-6-selinene2wereisolated3fromtheaerialpartsofCSubtraPicaFMell.,andtheirstructuresweredeterminedbyspectroscopicmethods.Herein,wereportafacilesynthesisofbothtwodiastereomers1and2from( )-dihydrocarvone3infivesteps,usingtheregioselect…     

Ab Initio Kinetics for Thermal Decomposition of CH(3)N(•)NH(2), cis-CH(3)NHN(•)H, trans-CH(3)NHN(•)H, and C(•)H(2)NNH(2) Radicals

The thermal decomposition of the CH(3)N(?)NH(2), cis-CH(3)NHN(?)H, trans-CH(3)NHN(?)H, and C(?)H(2)NNH(2) radicals, which are the four radical products from the H-abstraction reactions of monomethylhydrazine, were theoretically studied by using ab initio Rice-Ramsperger-Kassel-Marcus (RRKM) transition-state theory and master equation analysis. Various decomposition pathways were identified by using either the QCISD(T)/cc-pV∞Z//CASPT2/aug-cc-pVTZ or the QCISD(T)/cc-pV∞Z//B3LYP/6-311++G(d,p) quantum chemistry methods. The results reveal that the β-scission of NH(2) to form methyleneimine is the predominant channel for the decomposition of the C(?)H(2)NNH(2) radical due to its small energy barrier of 13.8 kcal mol(-1). The high pressure limit rate coefficient for the reaction is fitted by 3.88 × 10(19)T(-1.672) exp(-9665.13/T) s(-1). In addition, the pressure dependent rate coefficients exhibit slight temperature dependence at temperatures of 1000-2500 K. The cis-CH(3)NHN(?)H and trans-CH(3)NHN(?)H radicals are the two distinct spatial isomers with an energy barrier of 26 kcal mol(-1) for their isomerization. The β-scission of CH(3) from the cis-CH(3)NHN(?)H radical to form trans-diazene has an energy barrier of 35.2 kcal mol(-1), and the β-scission of CH(3) from the trans-CH(3)NHN(?)H radical to form cis-diazene has an energy barrier of 39.8 kcal mol(-1). The CH(3)N(?)NH(2) radical undergoes the β-scission of methyl hydrogen and amine hydrogen to form CH(2)═NNH(2), trans-CH(3)N═NH, and cis-CH(3)N═NH products, with the energy barriers of 42.8, 46.0, and 50.2 kcal mol(-1), respectively. The dissociation and isomerization rate coefficients for the reactions were calculated via the E/J resolved RRKM theory and multiple-well master equation analysis at temperatures of 300-2500 K and pressures of 0.01-100 atm. The calculated rate coefficients associated with updated thermochemical property data are essential components in the development of kinetic mechanisms for the pyrolysis and oxidation of MMH and its derivatives.     

Use of 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide and graphene oxide for separation and preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ) ions in different samples

A simple and selective method using a column packed with graphene oxide(GO) as a solid phase extractant has been developed for the multi-element preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ)ions prior to flame atomic absorption spectrometric determinations.The method is based on the sorption of mentioned ions on synthesized GO using 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide as a chelating agent.Several parameters on the extraction and complex formation were optimized.Under the optimized conditions(pH 6,flow rate 9 mL/min),metal ions were retained on the column,then quantitatively eluted by HNO3solution(5 mL,3.0 mol/L).The preconcentration factor was calculated as250.The detection limits for the analyte ions of interest were found in the range of 0.11 ng/mL(Ni2+) to0.63 ng/mL(Cu2+).The column packed with GO was adequate for metal ions separation in matrixes containing alkali,alkaline earth,transition and heavy metal ions.     

Functionalization of Testosterone at Position 7α and Synthesis of 7α-(3-Methoxypropyl)-4-androsten-17β-ol-3-one

An efficient transformation of the terminal alkene function of 7α-allyltestosterone is reported along with the stereospecific synthesis of 7α-(3-methoxypropyl)-4-androsten-17β-ol-3-one.     

Synthesis of α-fluoro-α,β-unsaturated esters monitored by 1D and 2D benchtop NMR spectroscopy

For optimization and control of pharmaceutically and industrially important reactions, chemical information is required in real time. Instrument size, handling, and operation costs are important criteria to be considered when choosing a suitable analytical method apart from sensitivity and resolution. This present study explores the use of a robust and compact nuclear magnetic resonance (NMR) spectrometer to monitor the stereo-selective formation of α-fluoro-α,β-unsaturated esters from α-fluoro-β-keto esters via deprotonation and deacylation in real time. These compounds are precursors of various pharmaceutically active substances. The real-time study revealed the deprotonation and deacylation steps of the reaction. The reaction was studied at temperatures ranging from 293 to 333 K by interleaved one-dimensional ¹H and ¹⁹F and two-dimensional ¹H–¹H COSY experiments. The kinetic rate constants were evaluated using a pseudo first-order kinetic model. The activation energies for the deprotonation and deacylation steps were determined to 28 ± 2 and 63.5 ± 8 kJ/mol, respectively. This showed that the deprotonation step is fast compared with the deacylation step and that the deacylation step determines the rate of the overall reaction. The reaction was repeated three times at 293 K to monitor the repeatability and stability of the system. The compact NMR spectrometer provided detailed information on the mechanism and kinetics of the reaction, which is essential for optimizing the synthetic routes for stepwise syntheses of pharmaceutically active substances.