Studies on the Biosynthesis of Spirostaphylotrichin A

Incorporation of ¹⁴C-labelled acetate and amino acids as well as of [1-¹³C]-, [2-¹³C]-, and [1,2-¹³C₂] acetate, L -[methyl¹³C] methionine, [2,3-¹³C₂] succinate, and L -[2,3-¹³C₂] aspartate into spirostaphylotrichin A ( 1 ) by Staphylotrichum coccosporum demonstrates that the building blocks of 1 are 5 units of acetate/malonate, 1 unit of methionine, and a C₄-dicarboxylic acid. The latter is most likely aspartate and derived from the citric-acid cycle. Using [2-¹³C, 2-²H₃] acetate as a precursor, the starter unit of the polyketide chain was identified.     

Simultaneous Determination of Lipophilic Vitamin Esters Using Square-wave Voltammetry at the Glassy Carbon Electrode

Simple and rapid voltammetric method for simultaneous determination of all-trans-retinyl acetate (RAc) or all-trans-retinyl palmitate (RPa) and α-tocopheryl acetate (α-TOAc) has been proposed. The respective method was based on the anodic oxidation of the compounds of interest by square-wave voltammetry in acetone with 0.1 mol L⁻¹ LiClO₄ at the glassy carbon electrode. The procedure was also beneficial with respect to simple dissolution of sample directly in the supporting electrolyte. The all-trans-retinyl acetate could be quantified in two linear ranges (3.1–140 μmol L⁻¹ and 140–400 μmol L⁻¹) and α-tocopheryl acetate in linear range 5.3–400 μmol L⁻¹ with detection limits of 0.9 μmol L⁻¹ RAc (or 0.8 μmol L⁻¹ RPa) and of 1.6 μmol L⁻¹ α-TOAc. Selected commercial cosmetic products were analysed achieving satisfactory recoveries.     

Presence of an N-6 acetate group shifts the alkylation site of the ambident nucleophile sodium 1-N-methylisoguanide

Inclusion of an N-6 acetate into the ambident nucleophile, sodium 1-N-methylisoguanide, resulted in a shift in alkylation preference from N-9 to N-3. The preparation of the N-6 acetate of 1-N-methylisoguanine, 9-N-acetyl-1-N-methylisoguanine (4) , and related acetate analogs are described and evidence presented for their structural determination. Analysis of long range ¹³C-¹H coupling data facilitated the structural elucidation of the predominant alkylation products and provided evidence for the unusual N-7 hydrogen tautomeric form in one of them, 3-N-benzyl-6-N-acetyl-1-N-methylisoguanine (8).     

Insights into the Synthesis of Steroidal A‐Ring Olefins

The classical synthesis, followed by purification of the steroidal A‐ring Δ¹‐olefin, 5α‐androst‐1‐en‐17‐one ( 5 ), from the Δ¹‐3‐keto enone, (5α,17β)‐3‐oxo‐5‐androst‐1‐en‐17‐yl acetate ( 1 ), through a strategy involving the reaction of Δ¹‐3‐hydroxy allylic alcohol, 3β‐hydroxy‐5α‐androst‐1‐en‐17β‐yl acetate ( 2 ), with SOCl₂, was revisited in order to prepare and biologically evaluate 5 as aromatase inhibitor for breast cancer treatment. Surprisingly, the followed strategy also afforded the isomeric Δ²‐olefin 6 as a by‐product, which could only be detected on the basis of NMR analysis. Optimization of the purification and detection procedures allowed us to reach 96% purity required for biological assays of compound 5 . The same synthetic strategy was applied, using the Δ⁴‐3‐keto enone, 3‐oxoandrost‐4‐en‐17β‐yl acetate ( 8 ), as starting material, to prepare the potent aromatase inhibitor Δ⁴‐olefin, androst‐4‐en‐17‐one ( 15 ). Unexpectedly, a different aromatase inhibitor, the Δ^3,5‐diene, androst‐3,5‐dien‐17‐one ( 12 ), was formed. To overcome this drawback, another strategy was developed for the preparation of 15 from 8 . The data now presented show the unequal reactivity of the two steroidal A‐ring Δ¹‐ and Δ⁴‐3‐hydroxy allylic alcohol intermediates, 3β‐hydroxy‐5α‐androst‐1‐en‐17β‐yl acetate ( 2 ) and 3β‐hydroxyandrost‐4‐en‐17β‐yl acetate ( 9 ), towards SOCl₂, and provides a new strategy for the preparation of the aromatase inhibitor 12 . Additionally, a new pathway to prepare compound 15 was achieved, which avoids the formation of undesirable by‐products.     

Apparent Molar Volume and Isentropic Compressibility for the Binary Systems {Methyltrioctylammonium Bis(trifluoromethylsulfonyl)imide + Methyl Acetate or Methanol} and (Methanol + Methyl Acetate) at <Emphasis Type="Italic">T</Emphasis>=298.15, 303.15, 308.15 and 313.15 K and Atmospheric Pressure

The densities and speeds of sound for binary mixtures containing the solute ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]⁺[Tf₂N]⁻), solute/solvent methanol, and solvent methyl acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K at atmospheric pressure. The binary mixtures studied are ([MOA]⁺[Tf₂N]⁻ + methyl acetate or methanol), and (methanol + methyl acetate). The apparent molar volume, V _φ and the apparent molar isentropic compressibility, k _φ , have been evaluated from the experimental density and speed of sound data, respectively. The parameters of a Redlich–Mayer type equation were fitted to the apparent molar volume and apparent molar isentropic compressibility data. The apparent molar volume and apparent molar isentropic compressibility at infinite dilution, V_f⁰V_{\phi}^{0} and k_f⁰k_{\phi}^{0}, respectively, of the binary solutions have also been calculated at each temperature. The infinite dilution apparent molar volume indicates that intermolecular interactions for (IL + methyl acetate) mixtures are stronger than for (IL + methanol) mixtures at all temperatures except at 298.15 K, and that V_f⁰V_{\phi}^{0} for the (IL + methyl acetate or methanol) binary systems increases with an increase in temperature. For the (methanol + methyl acetate) system the intermolecular interaction are weaker and V_f⁰V_{\phi}^{0} also increases with an increase in temperature. Values of the infinite dilution apparent molar expansibility, E_f⁰E_{\phi}^{0}, indicate that the interaction between (IL + methyl acetate) is greater than for (IL + methanol) and (methanol + methyl acetate).     

Densities and Viscosities of the Ternary Mixture (Benzene + 1-Propanol + Ethyl Acetate) at 298.15 K

Abstract

Densities and viscosities of the ternary mixture (benzene + 1-propanol + ethyl acetate) and the corresponding binary mixtures (benzene + 1-propanol, benzene + ethyl acetate and 1-propanol + ethyl acetate) have been measured at the temperature 298.15 K. From these measurements excess volumes, V^E , excess viscosities, η^E, and excess Gibbs energies of activation for viscous flow, G*^E , have been determined. The equation of Redlich-Kister has been used for fitting the excess properties of binary mixtures. The excess properties of the ternary system were fitted to Cibulka's equation.     

Characterisation of phenolic compounds of the ethyl acetate fraction from Tabernaemontana catharinensis and its potential antidepressant-like effect

This study evaluates the antidepressant-like effect and analysed the qualitative and quantitative 74 phenolic standards of ethyl acetate fraction from Tabernaemontana catharinensis leaves. Acute administration of fraction in mice reduced the immobility time in forced swimming and tail suspension tests confirming its antidepressant-like activity. The anti-immobility effect elicited by this fraction was prevented by the pretreatment of mice with PCPA (100 mg kg^?1), ketanserin (5 mg kg^?1), SCH 23,390 (0.05 mg kg^?1) or yohimbine (1 mg kg^?1). A sub effective dose of the fraction produced a synergistic effect with fluoxetine (5 mg kg^?1). Chromatographic analysis identified 4-hydroxybenzoic and p-coumaric acids in the ethyl acetate fraction from T. catharinensis. Capillary electrophoresis presented 7.34 ± 0.02 mg g^?1 of p-coumaric acid concentration in the fraction. Therefore, it is possible that antidepressant-like effect elicited by ethyl acetate fraction from T. catharinensis be dependent on the p-coumaric acid.     

Efficient Synthesis of Molecular Precursors for Para‐Hydrogen‐Induced Polarization of Ethyl Acetate‐1‐13C and Beyond

A scalable and versatile methodology for production of vinylated carboxylic compounds with ¹³C isotopic label in C1 position is described. It allowed synthesis of vinyl acetate‐1‐¹³C, which is a precursor for preparation of ¹³C hyperpolarized ethyl acetate‐1‐¹³C, which provides a convenient vehicle for potential in vivo delivery of hyperpolarized acetate to probe metabolism in living organisms. Kinetics of vinyl acetate molecular hydrogenation and polarization transfer from para‐hydrogen to ¹³C via magnetic field cycling were investigated. Nascent proton nuclear spin polarization (%P_H) of ca. 3.3 % and carbon‐13 polarization (%P_13C) of ca. 1.8 % were achieved in ethyl acetate utilizing 50 % para‐hydrogen corresponding to ca. 50 % polarization transfer efficiency. The use of nearly 100% para‐hydrogen and the improvements of %P_H of para‐hydrogen‐nascent protons may enable production of ¹³C hyperpolarized contrast agents with %P_13C of 20–50 % in seconds using this chemistry.     

Preparations of regioselectively methylated cellulose acetates and their 1H and 13C NMR spectroscopic analyses

Seven possible regioselectively methylated cellulose acetates (RS‐MCAs)—2,3,6‐tri‐O‐methyl cellulose acetate, 3,6‐di‐O‐methyl cellulose acetate, 2,6‐di‐O‐methyl cellulose acetate, 2,3‐di‐O‐methyl cellulose acetate, 6‐O‐methyl cellulose acetate, 3‐O‐methyl cellulose acetate, and 2‐O‐methyl cellulose acetate—were prepared for the first time from chemically synthesized cellulose derivatives obtained by cationic ring‐opening polymerization and then were analyzed by ¹H and ¹³C NMR spectroscopy. The chemical shifts of ring protons and carbons were influenced by substituent groups (methyl or acetyl) and clearly reflected the pattern of substituent distribution in anhydroglucose units. These data may conveniently be used for the determination of the substituent distribution of methyl cellulose. The synthesized RS‐MCAs also may be used for the elucidation of the structure–property relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4167–4179, 2002     

Biosynthesis of the cytochalasans. Part III. C-NMR. of cytochalasin B (phomin) and cytochalasin D. Incorporation of [1-13C]- and [2-13C]-sodium acetate

Sequential single frequency decoupling and partially relaxed Fourier transform (PRFT) are used to assign the natural abundance ¹³C-NMR. spectra of cytochalasin B (phomin) ( 1 ) and cytochalasin D ( 2 ). Cultures of Phoma spec. S 298 were fed [2-¹³C]-sodium acetate, and the distribution of this precursor in cytochalasin B (phomin) ( 1 ) was determined by ¹³C-NMR. spectroscopy. Likewise, the labelling patterns in cytochalasin D (zygosporin A) ( 2 ) from Zygos-posium masonii could be identified after incorporation of [2-¹³C]-sodium acetate and [l-¹³C]-sodium acetate. The results confirm previous proposals for the biogenesis of the cytochalasans from phenylalanine, methionine, and a C₁₈, or C₁₆, polyketide part.     

Determination of the reactivity parameters for the copolymerization of butyl acrylate with vinyl acetate

The composition of vinyl acetate–butyl acrylate copolymers obtained with batch emulsion polymerization have been studied by ¹H-NMR. Using the integrated copolymerization Meyer–Lowry equation, the apparent reactivity ratios of the two monomers were calculated as 10.67 for r₁, the reactivity ratio of butyl acrylate (BA), and 0.024 for r₂, the reactivity ratio of vinyl acetate (VAC). These results were compared with those obtained by other methods.     

Kinetics of the reactions of OH radicals with selected acetates and other esters under simulated atmospheric conditions

The relative hydroxyl radical reaction rate constants from the simulated atmospheric oxidation of selected acetates and other esters have been measured. Reactions were carried out at 297 ± 2 K in 100-liter FEP Teflon®-film bags. The OH radicals were generated from the photolysis of methyl nitrite in pure air. Using a rate constant of 2.63 × 10^?11 cm³ molecule^?1 s^?1 for the reaction of OH radicals with propene, the principal reference organic compound, the rate constants (×10¹² cm³ molecule^?1 s^?1) obtained for the acetates and esters used in this study are:

Influence of Cu(II) Ions on the Mechanism of the Ring Transformation of S‐(2‐Oxotetrahydrofuran‐3‐yl)‐N‐(4‐methoxyphenyl)isothiouronium Bromide

The effect of additional Cu(II) ions on the rate of transformation of S‐(2‐oxotetrahydrofuran‐3‐yl)‐N‐(4‐methoxyphenyl)isothiouronium bromide ( 1 ) into 5‐(2‐hydroxyethyl)‐2‐[(4‐methoxyphenyl)imino]‐1,3‐thiazolidin‐4‐one ( 2 ) has been studied in aqueous buffer solutions. The reaction acceleration in acetate buffers is caused by the formation of a relatively weakly bonded complex (K_c = 600 L·mol^?1) of substrate with copper(II) acetate in which the Cu(II) ion acts as a Lewis acid coordinating the carbonyl oxygen and facilitating the intramolecular attack, leading to the formation of intermediate T^±. The formation of the complex of copper(II) acetate with free isothiourea in the fast preequilibrium (K_c) is followed by the rate‐limiting transformation (k_Cu) of this complex. At the high concentrations of the acetate anions, the reaction is retarded by the competitive reaction of these ions with copper(II) acetate to give an unreactive complex [Cu(OAc)₄]^2?_. The influence of Cu(II) ions on the stability of reaction intermediates and the leaving group ability of the alkoxide‐leaving group compared to the Cu(II)‐uncatalyzed reaction is also discussed.     

Photoinduced Double Addition of Acetylene to 3-Oxocyclopent-1-ene-1-carbonitrile or 3-oxocyclopent-1-enyl acetate leading to 2,3-dihydro-1H-inden-1-one and other rearranged products

UV Irradiation of 3-oxocyclopent-1-enyl acetate ( 17 ) and acetylene in MeCN at 0° gives, besides the product of normal enone-alkyne [2 + 2] cycloaddition (cis-4-oxobicyclo[3.2.0] hept-6-en-1-yl acetate, 18 ) and its product of oxa-di-π-methane rearrangement (5-oxotricyclo[4.1.0.0^2,7]hept-2-yl acetate, 19 ), unexpected products of further addition of a molar equivalent of acetylene. These are indanone ( = 2,3-dihydro-1H-inden-1-one, 16 ), in 21% yield, cis-1-cisoid-1,2-cis-2- ( 20 ) and cis-1-transoid-1,2-cis-2-7-oxotricyclo[4.3.0.0^2,5]non-3-en-1-yl acetate ( 21 ), 4-oxo-7-‘exo’-vinyltricyclo[3.2.0.0^2,6]hept-2-yl acetate ( 22 ), cis-4-oxo-6-‘endo’- ( 23 ) and cis-4-oxo-6-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate ( 24 ), and cis-4-oxo-7-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate ( 25 ). At least in part, indanone must be formed via intermediates 20 and 21 . In fact, on heating a 9:1 mixture 20/21 , indanone is obtained quantitatively. With 3-oxocyclopent-1-ene-1-carbonitrile ( 15 ) in place of 17 , indanone is formed in lower (8%) yield besides much tars.     

Kinetics and mechanism of the atmospheric oxidation of Ethyl tertiary butyl ether

Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10^?13 cm³ molecule^?1 s^?1 at 298 K. The primary products and molar yields for the OH reaction with ETBE in the presence of NO_x were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.     

Thermal degradation of vinyl alcohol/vinyl acetate copolymers. III. Study of the reaction products

The thermal decomposition of vinyl alcohol/vinyl acetate copolymers have been studied at p = 10⁻²–10⁻⁴ Torr and T = 0–600°C. The decomposition products (solids, liquids, and gases) have been characterized by infrared (IR) and ultraviolet (UV) spectroscopy, gas chromatography, vapor pressure osmometry, and elemental analysis. It has been ascertained on the basis of the obtained data that the decomposition mechanism of the vinyl alcohol/vinyl acetate copolymers depends on the chemical composition and sequence distribution of comonomers.     

A low frequency assignment for infrared and Raman spectra of (+) bornyl acetate using related compounds and deuterated derivatives

Twenty-one fundamentals of (+)-bornyl acetate and nine deuterium substituted modifications (2-d₁; 3,3-d₂; 2,3,3-d₃; acetate-d₃; 2-d₁ acetate-d₃; 3,3-d₂ acetate-d₃; 2,3,3-d₃ acetate-d₃; 10-d₁; 10,10,10-d₃) as well as (−)-isobornyl-1-10,10.10-d₃ acetate have been assigned between 200 and 850cm⁻¹. These results supplement the previous assignment of nineteen fundamentals of (−)-isobornyl acetate and seven deuterium substituted modifications (2-d₁,; 3,3-d₂; 2,3,3-d₃; acetate-d₃; 2-d₁ acetate-d₃; 3,3-d₂ acetate-d₃; 2,3,3-d₃ acetate-d₃) between 200 and 900cm⁻¹ [8]. These fundamentals are: skeletal vibrations of the quaternary carbons, ring breathing, bending, and twisting vibrations, and vibrations of the acetate group. Key model compounds used in this analysis are norbornane, neopentane, methyl acetate, cyclopentanol, and the (−)-isobornyl acetate system. A series of related compounds (norbornane, bornane, endo-norbomyl acetate, 1-methyl-endo-norbornyl acetate, apobornyl acetate, and (+)-bornyl acetate) is used to identify frequencies associated with the quaternary carbon and the acetate group. Raman spectra are more useful for the quaternary carbon frequencies and i.r. spectra are more useful for acetate group frequencies. Four exo stereoisomer alcohols (1-methyl-exo-norborneol, 1-methy d₃-exonorborneoI, apoisoborneol, (−)-isoborneol) and three endo stereoisomer alcohols (1-methyl-endo-norborneol, apoborneol, (+)-borneol) serve as model compounds for a modification of the earlier assignment [8] for the skeletal stretching of the quaternary carbons in the (−)-isobornyl acetate system and extension of this modified assignment to the (+)-bornyl acetate system. Quaternary carbon symmetric skeletal stretching is believed to be responsible for prominent Raman bands between 580 and 680cm⁻¹ in the 36 bicyclic ring compounds investigated to date. Fermi resonance is proposed as the explanation for a number of unexpected intensity patterns observed in the i.r. and Raman spectra.     

Kinetics and mechanism of the atmospheric oxidation of tertiary amyl methyl ether

Tertiary-amyl methyl ether (TAME) is proposed for use as an additive to increase the oxygen content of gasoline as stipulated in the 1990 Clean Air Amendments. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of TAME. The kinetics of the reaction of OH with TAME was examined by using a relative rate technique in which photolysis of methyl nitrite or nitrous acid was used as the source of OH. The OH rate constant for TAME and two major products (t-amyl formate and methyl acetate) were measured and yields for ten products were determined as primary products from the reaction. Values determined for the rate constants for the reaction with OH were 5.48 × 10^?12 (TAME), 1.75 × 10^?12 (t-amyl formate), and 3.85 × 10^?13 cm³ molec^?1 s^?1 (methyl acetate) at 298 ± 2 K. The primary products (with corrected yields where required) from the OH + TAME that have been observed include (1) t-amyl formate (0.366), methyl acetate (0.349), acetaldehyde (0.43, corrected), acetone (0.036), formaldehyde (0.549), t-amyl alcohol (0.026), 3-methyoxy-3-methyl-butanal (0.044, corrected), t-amyloxy methyl nitrate (0.029), 3-methyoxy-3-methyl-2-butyl nitrate (0.010), and 2-methoxy-2-methyl butyl nitrate (0.004). Mechanisms leading to these products involve OH abstraction from each of the four different hydrogen atoms of TAME. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization thesulphides type ZnS(1-x)MSx

ZnS_(1-x)MS_x(x=0.01 and M=Mn²⁺, Cu²⁺ and Eu²⁺) compounds have been obtained by precipitation from homogeneous solutions of zinc, copper, manganese and europium salts, with S^2- as the precipitating anion, formed by the decomposition of thioacetamide. The thermal study of the milled zinc acetate, thioacetamide, copper acetate, manganese acetate and europium nitrate, respectively, was studied for thermal analyis TG/DSC. XRD respect exhibits a zinc blend crystal structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

New Highlights in the Synthesis of 4‐Aryl‐1,4‐dihydropyrazines

The 4‐aryl‐1,4‐dihydropyrazines were prepared via the cyclization of N,N‐bisalkylated anilines with ammonium acetate. These reactions were aided by improvements in the synthesis of N,N‐bisalkylated anilines which were alkylated with anilines using ethyl 2‐diazo acetoacetate in a reaction catalyzed by rhodium acetate in the absence of oxygen. A possible mechanistic route is postulated on the basis of the isolation of the N‐alkylation intermediates, which were determined to be N‐aryloxamates by ¹H NMR data and X‐ray diffraction.