Reactions of β-nitrostyrenes with tert-butylmercury halides in the presence of lodide lon

Photolysis of t-BuHgCl/KI with PhC(R²)C(R¹)NO₂ forms PhC(R²)C(R¹)Bu-t when R¹ = R² = H or in low yield when R¹ = H, R² = Ph. When R¹ ≠ H, or when R² = Ph, reactions with t-BuHgI/KI/hv proceed mainly via PhC(R²)C(R¹)NO₂·-, PhC(R²)C(R¹)N(OBu-t)O⁻HgX⁺, PhC(R²)C(R¹)NO and PhC(R²)C(R¹)N(OBu-t)HgX to form a variety of novel products including the dimeric bisnitronic esters ( 6 ) with R¹ = Me or Ph and R² = H; PhCH(R²)C(R¹) = NOBu-t with R¹ = Me or Ph and R² = H or R¹ = H and R² = Ph; PhC(R²)(OBu-t)C(R¹)NOH with R¹ = H or Me and R² = Ph; and 3-phenyl-2-R¹-indoles with R¹ = H, Me, Ph, PhS or t-BuS and R² = Ph. Nitrosoaromatics react with t-BuHgX in the dark to form ArN(OBu-t)(OBu-t)HgX⁺ which condenses with ArNO to form the azoxy compound. tert-Butyl radicals will add to RNO₂ [R = Ph, Ph₂CCH, Ph₂CC(Ph)] in the presence of t-BuHgI₂⁻ to form products derived from RN(OBu-t)O⁻HgI⁺.     

Radiosynthesis of New Carbon-11-labeled Nimesulide Analogs as Potential PET SAER Tracers for Imaging of Aromatase Expression in Breast Cancer

Carbon-11-labeled nimesulide analogs, N-[¹¹C]methyl-N-(2-benzyloxy-4-nitrophenyl)methanesulfonamide ([¹¹C]4a), N-[¹¹C]methyl-N-[2-(4′-methylbenzyloxy)-4-nitrophenyl]methanesulfonamide ([¹¹C]4b), N-[¹¹C]methyl-N-[2-(4′-fluorobenzyloxy)-4-nitrophenyl]methanesulfonamide ([¹¹C]4c), N-[¹¹C]methyl-N-[2-(4′-nitrobenzyloxy)-4-nitrophenyl]methanesulfonamide ([¹¹C]8a), N-[¹¹C]methyl-N-[2-(β-naphthylmethoxy)-4-nitrophenyl]methanesulfonamide ([¹¹C]8b), and N-[¹¹C]methyl-N-[2-(2′-phenylbenzyloxy)-4-nitrophenyl]methanesulfonamide ([¹¹C]8c), have been synthesized as new potential positron emission tomography (PET) selective aromatase expression regulator (SAER) radiotracers for imaging of aromatase expression in breast cancer. The target tracers were prepared by N-[¹¹C]methylation of their corresponding precursors using [¹¹C]CH₃OTf under basic conditions (NaH) and isolated by reversed-phase high-pressure liquid chromatography (HPLC) method in 30–50% radiochemical yields decay corrected to end of bombardment (EOB) with 25–30 min overall synthesis time and 111–148 GBq/μmol specific activity at end of synthesis (EOS).     

Photofragmentation of alpha-oxocarboxylic acids in aqueous solution. An EPR study. Formation of semidione radicals by decarboxylative substitution of alpha-oxocarboxylic acids by acyl radicals--II. Oxaloacetic acid (oxosuccinic acid).

Abstract— –On in situ photolysis (Λ= 250–400 nm) of aqueous oxaloacetic acid solutions, between pH 5 and 10, the radicals ^-O₂CCH₂C(O^->=C(O⁺)CH₂CO₂^- and ^-O₂CCH₂C(OH)CO₂ are identified. With acetone present, CH₂CO₂, CH₃C(OH)CO^-₂, CH₃C(O^-)=C(O)CH₂CO₂ and -O₂CCHCOCO₂ are also observed. CO₂ and CO are identified as reaction products. The experimental results are explained in terms of α-cleavage of the electronically excited keto-isomer dianion of oxaloacetic acid to yield O₂CCH₂CO and CO₂^-. ^-O₂CCH₂CO adds to the keto-isomer of oxaloacetic acid and to pyruvic acid, which is formed from oxaloacetic acid by thermal decarboxylation, to yield ^-O₂CCH₂C(O^-)= C(O^-)CH₂C0^- and CH₃C(O^-)=C(O)CH₂CO^-₂, respectively, via a decarboxylase substitution reaction. CH₂CO₂ is derived from ^-O₂CCH₂CO by decarbonylation. CO₂^- is scavenged by oxaloacetic acid and pyruvic acid to yield O₂CCH₂C(OH)CO₂ and CH₃C(OH)CO₂^-, respectively.     

Biosynthesis of cytochalasans. Part 4. The mode of incorporation of common naturally-occurring carboxylic acids into cytochalasin D1.

Utilization of sodium [1-¹⁴C]-, [2–¹⁴C]-, and [1,2-¹³C]-acetates, [1-¹⁴C]-, [1-¹³C]-, or [2-¹⁴C]-propionates, [1-¹⁴C]-or [2-¹⁴C]-malonates, of [1-¹⁴C]- or of [1-¹⁴C]-myristic acid, or of [1-¹⁴C]- and [1-¹⁴C]-palmitic acid in the biosynthesis of cytochalasin D ( 1 ) by Zygosporium masonii was determined by degradation studies or by carbon magnetic resonance spectroscopy. The precursors were incorporated primarily via the acetate-malonate pathway to generate 1 from nine intact acetate units, eight of which are coupled in a head to tail fashion to form the C₁₆-polyketide moiety.     

On the biosynthesis of dendrolasin, a body constituent of the ant Lasius fuliginosus Latr

By feeding the ant Lasius fuliginosus LATR . with [¹⁴C]-1-acetate, [¹⁴C]-2-acetate, [¹⁴C]-2-mevalonate, [¹⁴C]-2-mevalonate, [¹⁴C]-1-glucose and [¹⁴C]-U-glucose, incorporation ratios of 10^?4 – 0,15% were obtained in the sesquiterpenoid dendrolasin. It was shown by analysis of the labelling pattern in dendrolasin that the insertions were spread over the whole molecule in exactly the manner that would be expected from terpene biosynthesis.     

Gallium “Shears” for C=N and C=O Bonds of Isocyanates

Digallane [L¹Ga−GaL¹] ( 1 , L¹=dpp-bian=1,2-[(2,6-iPr₂C₆H₃)NC]₂C₁₂H₆) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C−N−Ga fragments to afford [L¹(O=C−NR)Ga−Ga(RN−C=O)L¹] (R=Ph, 3 ; R=Tos, 4 ). The reactions with both isocyanates result in new C−C and N−Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C−N−Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga−N bond of the same fragment to afford compound [L¹Ga−Ga(AllN− C=O)₂L¹] ( 5 ) (All=allyl). In the presence of Na metal, the related digallane [L²Ga−GaL²] ( 2 ; L²=dpp-dad=[(2,6-iPr₂C₆H₃)NC(CH₃)]₂) is converted into the gallium(I) carbene analogue [L²Ga:]⁻ ( 2 A ), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂(THF)₅]{L²Ga[EtN−C(O)]₂GaL²} ( 6 ), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂]₂[L²Ga(p-MeC₆H₄)(N−C(O))₂−N(p-MeC₆H₄)]₂ ( 7 ), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃]₂[L²Ga-(μ-O)₂-GaL²] ( 8 ), and generation of the further addition product [Na₂(THF)₅][L²Ga(CyNCO₂)]₂ ( 9 ). Complexes 3 – 9 have been characterized by NMR (¹H, ¹³C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.     

The influence of the temperature on the formation of samarium nitrato complexes

The stability constants of the Sm(NO₃)²⁺ complex were determined at three temperatures, using the solvent extraction method. It was found that:K ₁ ⁰ =63.6 at 17°C, 30.3 at 35°C, 20.1 at 50°C. This corresponds with the formation of a Sm(H₂O)(NO₃)²⁺ complex at 17°C and a Sm(H₂O)₂(NO₃)²⁺ complex at 50°C.

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Der Einfluß der Temperatur auf die Bildung von Samarium Nitrato Komplexen

Zusammenfassung Die Stabilitätskonstanten von Sm(NO₃)²⁺ Komplexen wurden mittels der Lösungsmittelextraktionsmethode bei drei Temperaturen bestimmt. Dabei ergab sichK ₁ ⁰ =63.6 bei 17°C, 30.3 bei 35°C und 20.1 bei 50°C. Das entspricht der Bildung eines Sm(H₂O)(NO₃)²⁺ Komplexes bei 17°C und eines Sm(H₂O)₂(NO₃)²⁺ Komplexes bei 50°C.

     

Production of highly enriched Carbon-13 by IR multiphoton dissociation of dichlorodifluoromethane mixed with hydrogen iodide

Isotope-selective IR multiphoton dissociation of CF₂C1₂ molecules in a mixture with HI was experimentally investigated. It was shown that irradiation of the CF₂C1₂-HI mixture leads to the successive buildup of the intermediates CF₂HC1 and CF₂HI, which also isotopically selectively dissociate simultaneously with the substrate to yield the final product CF₂H₂ enriched in¹³C up to 97% at an initial¹³C concentration of 1.1% in CF₂C1₂. When CF₂C1₂ preliminarily enriched in¹³C up to 12.3% was used, the attained¹³C concentration in CF₂H₂ was as high as ≥99%. Isotopic selectivity and dissociation yields of¹³C- and¹²C-containing components of the substrate CF₂C1₂ and both intermediate dissociation products, CF₂HC1 and CF₂HI, were measured, depending on experimental conditions. The¹³C distribution over the intermediate and final dissociation products was studied. The side products C₂F₄C1₂ and CF₂IC1 were detected.     

Thermodynamic properties of peptide solutions 4. Partial molar volumes and heat capacities of aqueous solutions of some glycyl dipeptides

Partial molar volumes, V ₂ ^o and partial molar heat capacities C _p,2 ^o have been determined in aqueous solution at 25°C for the dipeptides glycyl-L-asparagine, glycyl-DL-threonine, glycyl-DL-serine and glycyl-DL-phenylalanine. These results, along with those for some other dipeptides of sequence Gly-X, were used to estimate side chain contributions to V ₂ ^o and C _p,2 ^o . For these dipeptides both V ₂ ^o and C _p,2 ^o were found to be a linear function of the respective thermodynamic property for the amino acid X. The contributions of the glycyl units to V ₂ ^o and C _p,2 ^o of the dipeptide are discussed.     

Temperature dependence of second critical micelle concentration of dodecyldimethylbenzylammonium bromide in aqueous solution

The specific conductivity of dodecyldimethylbenzylammonium bromide (C12BBr) in aqueous solutions, in the temperature range of 15 to 40 °C, has been measured as a function of molality. The two breaks which were found on the conductivity against molality plots were attributed to the critical micelle concentration, cmc, and second critical micelle concentration, 2^nd cmc, respectively. The ratio of the slopes, S, of the three linear fragments on the plots, S2/S1 and S3/S1, was attributed to the degree of ionization of the micelles at cmc and 2^nd cmc respectively. It was shown that the values of the 2^nd cmc estimated above 27 °C are only apparent due to thermal disintegration of the micelles. In the temperature range of 15 to 27 °C, the values of the 2^nd cmc increase gradually and the plot of the 2^nd cmc against temperature is concave. The ratio of 2^nd cmc/cmc for C12BBr at 25 °C amounts to 15 and appears to be high compared to the literature values for other surfactants. For comparative purposes the cmc and 2^nd cmc values were also estimated conductometrically for decyldimethylbenzylammonium bromide (C10BBr) at 25 °C. The 2^nd cmc value for this surfactant is higher compared to the value for the C12 homologue by a factor of 2.6.The standard Gibbs free energies of micellization at cmc and at the 2^nd cmc were estimated from the experimental data for both surfactants at 25 °C.     

Reactions of carbethoxycarbene with enaminones. Formation of unexpected pyrroles

The reactions of carbethoxycarbene (:CH₂-CO₂Et, 2) with several acyclic enaminones (RCOCH=CR¹NHR², 3) lead to the unexpected formation of 2-Me, 3-CO₂Et, 4-H, 5-R¹-pyrroles 4 . Structural variations of the enaminones show that the structural fragments C(3)-CO₂Et and C(2)-Me are provided by 2 and that the fragment C(5)-R¹NHR² originates from the enaminones 3 , while the RCO group from 3 is eliminated during the course of reaction. Reactions with cyclic and nitrogen-hindered enaminones do not lead to pyrrole formation but occur by simple insertion of 2 to the Cα-H bond.     

Solid‐state nuclear magnetic resonance investigation of neurosteroid compounds and magnesium interactions

The neurosteroid trans‐dehydroandrosterone (DHEA) and its analogs with slightly different modifications in the side chain attached to C17, that is, (3S)‐acetoxypregn‐5‐en‐20‐one ( 1 ) and (3S,20R)‐acetoxypregn‐5‐en‐20‐ol ( 2 ), have been synthesized to investigate DHEA–cation interactions. In this study, we applied solid‐state ¹H/¹³C cross‐polarization/magic‐angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy to a series of DHEA analog/Mg²⁺ mixtures at different Mg²⁺ concentrations. The high‐resolution ¹³C NMR spectra of 1 /Mg²⁺ mixtures exhibit two distinct ¹³C spectral patterns, one attributable to 1 free from Mg²⁺, and the other attributable to 1 with bound Mg²⁺. For 2 , the ¹³C NMR spectra exhibit three distinct spectral patterns; besides that of the free form, the other two can be assigned to Mg²⁺‐bound forms. Based on the analysis of the chemical shift deviations (CSDs), we conclude that both 1 and 2 might be subject to a cation–π interaction via the C5–C6 double bond, in contrast to that observed previously for DHEA. As demonstrated, DHEA possesses two Mg²⁺ binding sites, that is, C17–O and C5–C6 double bond, in which the binding affinity of the former is at least three times stronger than that of the latter. The solid‐state ¹³C NMR investigation allows better understanding of the underlying cation binding effects of neurosteroid molecules in vitro.     

Use of Dibutyl[14C]formamide as a Formylating Reagent in the Vilsmeier–Haack Reaction and Synthesis of a 14C‐Labeled Novel Phosphodiesterase‐4 (PDE‐4) Inhibitor

A simple, high‐yielding synthesis of dibutyl[¹⁴C]formamide ([¹⁴C]DBF; 1 ) from ¹⁴CO₂ was developed (Scheme 1): reaction of LiBEt₃H and ¹⁴CO₂ followed by aqueous workup gave H¹⁴CO₂H in high yield. Conversion of the [¹⁴C]formic acid to 1 was effected by a standard carbodiimide coupling procedure. The utility of 1 as an alternative to dimethyl[¹⁴C]formamide ([¹⁴C]DMF) in alkylation reactions and in the [¹⁴C]Vilsmeier–Haack reaction was demonstrated for several substrates (Table 2). A ¹⁴C‐labeled phosphodiesterase‐4 (PDE‐4) inhibitor, [¹⁴C]‐ 2 , was synthesized by application of this technology (Scheme 2).     

Alkylsilver(I) induced 1,5-substitution in functionally conjugated enynes. a novel route to cumulated trienes

Functionally conjugated enynes, H₂CC(R¹)CCCR²R₃OS(O)Me, undergo 1,5-substitution with alkylsilver(I) reagents, RAGG ☆ 3 LiBr. The purity of the produced alkylated butatrienes, RCH₂C(R¹)CCCR²R³ depends on the nature of R in RAg ☆ 3 LiBr and on the substituents R¹, R² and R³ in the substrate.     

Biosynthesis of the Verrucarins and Roridins. Part 1. The transformation of mevalonic acid into verrucarinic acid. Evidence for a hydrogen 1,2-shift. Verrucarins and roridins, 27th communication

Incorporation experiments using sodium [2-¹⁴C]-, [2-³H]-, (3R)-[5-¹⁴C]- and [2-³H, 2-¹⁴C]-mevalonates and with mevalonates stereospecifically tritiated at C(2) demonstrate the transformation of mevalonic acid ( 8 ) into verrucarinic acid ( 5 ). Degradation experiments showed that this transformation occurs with a hydrogen 1, 2-shift of the ‘pro-2R’ hydrogen atom of mevalonate to C(3) of verrucarinate. A possible mechanistic pathway is discussed.     

Stability constants for some divalent metal ion/crown ether complexes in methanol determined by polarography and conductometry

Stability constants in methanol at 25.0°C were evaluated for the complexes of the divalent cations Ca²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Mg²⁺, Co²⁺ and Cu²⁺ with the macrocyclic polyethers 15-crown-5 (15C5), 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6) and dibenzo-24-crown-8 (DB24C8). The log K values of the 1:1 complexes were generally in the range 2.1–4.2, which is low in comparison to the values of the corresponding crown ether/alkali metal ion complexes. M₂L complexes were observed for the systems Pb²⁺/18C6, Pb²⁺/DC18C6, Ca²⁺/DC18C6 and Cu²⁺/D18C6, whereas ML₂ complexes were found for Ca²⁺/18C6 and Cu²⁺/18C6. Within the series of complexes studied, there was no clear relationship between cation diameter and hole size.     

Selenoketene substitution structure

Microwave studies (26.5–40 GHz) of further isotopic species of selenoketene formed by pyrolysis of 1,2,3-selenodiazole (¹²CH₂¹²C^76,77,82Se, ¹²CH₂¹³C⁸⁰Se and ¹³CH₂¹²C⁸⁰Se) and by pyrolysis of 5-deuterio-1,2,3-selenodiazole (¹²CHD¹²C^78,80Se) are reported. In conjunction with earlier results for ¹²CH¹²C^78,80Se an r_s structure has been derived with distances SeC (1.706 Å), CC (1.303 Å), CH (1.0908 A) and a HCH bond angle of 119.7°. The geometry of the CH₂C moiety of selenoketene is closer to allene, CH₂CCH₂, than to ketene, CH₂CO.     

Synthesis and photophysical properties of phenyl-sulfanylated chlororophyll derivatives

Chlorophyll derivatives that possessed a phenylsulfanyl group at the C3¹- or C3²-position were synthesized and their optical properties were investigated. Methyl 3¹-phenylsulfanyl-mesopyropheophorbide-a was prepared by substitutions of the corresponding C3¹-hydroxy-chlorin, methyl bacteriopheophorbide-d, with thiophenol in the presence of zinc iodide or of the corresponding C3¹-bromo-chlorin with thiophenol. The regioisomeric C3²-phenylsulfanyl-chlorin was obtained by addition of thiophenol to the C3-vinyl group of methyl pyropheophorbide-a in the presence of AIBN. Both the synthetic compounds gave similar electronic absorption and emission spectra in chloroform, but fluorescence quantum yield of the C3¹-sulfanyl-chlorin (0.18) was ca. 30% smaller than those of the C3²-sulfanyl-chlorin (0.25) and the C3-ethyl-chlorin (0.24). These observations were consistent with their fluorescence lifetime data. It is suggested that the heavy atom effect of a sulfur atom at the C3¹-position can tune photophysical properties of the chlorophyll derivatives.     

Reactions of alkyl 4-hydroxybut-2-ynoates with arenes under superelectrophilic activation with triflic acid or HUSY zeolite: Alternative propargylation or allenylation of arenes,and synthesis of furan-2-ones

Reactions of alkyl 4-aryl(or 4,4-diaryl)-4-hydroxybut-2-ynoates [Ar(H or Ar')(OH)C⁴–C³≡C²–CO₂Alk] with arenes under the action of triflic acid TfOH or HUSY zeolite result in the formation of two main compounds, aryl substituted furan-2-ones or products of propargylation of electron rich arenes. Key reactive intermediates in these transformations are the corresponding O,O-diprotonated forms of starting butynoates, Ar(H or Ar')(⁺OH₂)C⁴–C³≡C²– C(=O⁺H)(OAlk), dehydration of which gives rise to mesomeric propargyl-allenyl cations Ar(H or Ar')(OH)⁴C⁺–C³≡C²–C(=O⁺H)(OAlk) ? Ar(H or Ar')(OH)⁴C = C³ = ²C⁺–C(=O⁺H)(OAlk), having two electrophilic centers on the carbons C4 and C2 respectively. Reactions of these species with arenes at C4 lead to products of arene propargylation, alternatively, reactions at C2 result in allenylation of arenes, followed by further transformation into furan-2-ones. Using quantum chemical calculations by the DFT method, it has been shown that the reactivity of such propargyl-allenyl cations is mainly explained by orbital factors. Plausible reaction mechanism is discussed.     

Conductometric study of complexation reaction between 15-crown-5 and Cr3+, Mn2+ and Zn2+ metal cations in pure and binary mixed organic solvents

The stability constants (K_f) for the complexation reactions of Cr³⁺, Mn²⁺ and Zn²⁺ metal cations with macrocyclic ligand, 15-crown-5 (15C5), in acetonitrile (AN), ethanol (EtOH) and also in their binary solutions (AN–EtOH) were determined at different temperatures, using conductometric method. 15C5 forms 1:1 complexes with Cr³⁺, Mn²⁺ and Zn²⁺ cations in solutions. A non-linear behaviour was observed for changes of logK_f of the metal ion complexes versus the composition of the mixed solvent. The order of stability of the metal–ion complexes in pure AN and in a binary solution of AN–EtOH (mol% AN?=?52) at 25?°C was found to be: (15C5Zn)²⁺?>?(15C5·Mn)²⁺?>?(15C5·Cr)³⁺, but in the case of pure EtOH at the same temperature, it changes to: (15C5·Zn)²⁺?>?(15C5·Cr)³⁺?>?(15C5·Mn)²⁺. The results also show that the stability sequence of the complexes in the other binary solutions of AN–EtOH (mol% AN?=?26 and mol% AN?=?76) varies in order: (15C5·Cr)³⁺?~?(15C5·Zn)²⁺?>?(15C5·Mn)²⁺. The values of the standard thermodynamic quantities (ΔH_C°, ΔS_C°) for formation of (15C15-Cr³⁺), (15C5-Mn²⁺) and (15C5-Zn²⁺) complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of complexation reactions is affected by nature and composition of the solvent systems and in most solution systems, the complexes are enthalpy stabilized but entropy destabilized.