Solanum-alkaloide—SCVI: Synthese von solafloridin und 25-iso-solafloridin

3β,16α-Diacetoxy-20-(5-methyl-2-pyridyl)-pregna-5,20-diene (2) available from 3β-acetoxy-pregna-5,16-dien-20-one (1) was transformed into solafloridine (11) and 25-iso-solafloridine (13).     

Investigation of the mechanism of polymerization of butadiene by π-allylic nickel complexes

Various π-allylic nickel complexes were synthesized by reacting bis(1,5-cyclooctadiene)-nickel with an allylic ester of trifluoroacetic acid. A study of the stereospecific polymerization of 1,3-butadiene initiated by these catalysts showed the strong influence of the initial substitution in the π-allylic ligand as well as of the solvent used for synthesis of the catalysts on the course of the reaction, i.e., on both the polymerization rate and the stereospecificity. Moreover, new catalytic species were isolated by adding electron-accepting or electron-donating ligands to some of the π-allylic complexes. In that way, we were able to modify the behavior of the catalysts and, in some cases, to enhance catalytic activity considerably.     

Thermodynamics of hydrogen-isotope-exchange reactions. Proton solvation inn-hexanol and water

This paper reports our results for the direct experimental determination of the equilibrium constant for the hydrogen-isotope-exchange reaction, 1/2D₂(g)+HCl(hexOH)=1/2H₂(g)+DCl(hexOD), where hexOH isn-hexanol and hexOD isn-hexanol with deuterium substitution in the alcohol function. The reaction was studied in electrochemical double cells without liquid junction for which the net cell reaction is the above isotope-exchange reaction. The experimentally determined value of ε° (296.0°K) for this cell is 4.03±0.95 mV (strong electrolyte standard states, mole-fraction composition scale); the value of the equilibrium constant for the reaction is 1.17±0.05. The contributions of isotope-exchange and transfer effects to the magnitude of the standard Gibbs energy change for the above reaction and for the analogous reaction 1/2D₂(g)+HCl(aq)=DCl(daq)+1/2H₂(g) are considered. Our results support the conclusion of Heinzinger and Weston that the formulation of the solvated proton in water as H₃O⁺, as opposed to H₉O₄ ⁺, is sufficient for the interpretation of the thermodynamics of hydrogen-isotope-exchange reactions in water. We also find that the formulation of the solvated proton inn-hexanol as ROH ₂ ⁺ is sufficient for the interpretation of our results on the thermodynamics of hydrogen-isotope-exchange inn-hexanol.     

Synthesen von Heterocyclen, 85. Mitt.: Über die α-Acyllactonumlagerung von 5-Benzoyl-dehydracetsäure

Zusammenfassung Die vonButt undElvidge aufgefundenen Isomeren, 4-Hydroxy-5-acetyl-6-phenyl-pyron-(2) (1) und 4-Hydroxy-5-ben-zoyl-6-methyl-pyron-(2) (2), ergeben bei der Umsetzung mit POCl₃ und Eisessig 5-Benzoyl-dehydracetsäure (3). Im Gegensatz zur Dehydracetsäure² reagiert 5-Benzoyl-dehydracetsäure (3) in alkohol. HCl zum 2,6-Dimethyl-3-äthoxycarbonyl-5-benzoyl-pyron-(4) (6). Die Struktur dieser Verbindung wird auf chemischem und physikalischem Wege abgeleitet.Mit wäßr. HCl läßt sich3 in 2,6-Dimethyl-5-benzoyl-pyron-(4) (5) umwandeln.

---

The isomeric compounds¹ 4-hydroxy-5-acetyl-6-phenyl-pyron-2 (1) and 4-hydroxy-5-benzoyl-6-methyl-pyron-2 (2) yield 5-benzoyl-dehydroacetic acid (3) if with glacial acetic acid and POCl₃. In contrast to dehydroacetic acid² 5-benzoyl-dehydroacetic acid (3) reacts in ethanolic HCl to 2,6-dimethyl-3-carbethoxy-5-benzoyl-pyron-(4) (6).However, with aquenous HCl3 is converted to 2.6-dimethyl-5-benzoyl-pyron-(4) (5).

     

Reactivity of [Fe4S4(SR)4]2-,3- clusters with sulfonium cations: analogue reaction systems for the initial step in biotin synthase catalysis

The first step in catalysis by a class of iron-sulfur enzymes that includes biotin synthase is the one-electron reductive cleavage of the obligatory cofactor S-adenosylmethionine by an [Fe(4)S(4)](+) cluster to afford methionine and the deoxyadenosyl radical (DOA*). To provide detailed information about the reactions of sulfonium ions with [Fe(4)S(4)](2+,+) clusters, the analogue reaction systems [Fe(4)S(4)(SR')(4)](2)(-)(,3)(-)/[PhMeSCH(2)R](+) (R' = Et (4, 6), Ph (5, 7); R = H (8), COPh (9), p-C(6)H(4)CN (10)) were examined by (1)H NMR spectroscopy. Sulfonium ions 8-10 react completely with oxidized clusters 4 and 5 to afford PhSMe and R'SCH(2)R in equimolar amounts as a result of electrophilic attack by the sulfonium ion on cluster thiolate ligands. Reactions are also complete with reduced clusters 6 and 7 but afford, depending on the substrate, the additional products RCH(3) (R = PhCO, p-C(6)H(4)CN) and the ylid PhMeS=CHR or (p-NCC(6)H(4)CH(2))(2). Redox potentials of 9 and 10 allow electron transfer from 6 or 7. The reaction systems 6/9,10 and 7/9,10 exhibit two reaction pathways, reductive cleavage and electrophilic attack, in an ca. 4:1 ratio inferred from product distribution. Cleavage is a two-electron process and, for example in the system 6/9, is described by the overall reaction 2[Fe(4)S(4)(SR')(4)](3)(-) + 2[PhMeSCH(2)R](+) --> 2[Fe(4)S(4)(SR')(4)](2)(-) + PhSMe + RCH(3) + PhMeS=CHR. This and other reactions may be summarized as [PhMeSCH(2)R](+) + 2e(-) + H(+) --> PhSMe + RCH(3); proposed reaction sequences parallel those for electrochemical reduction of sulfonium ions. This work demonstrates the intrinsic ability of [Fe(4)S(4)](+) clusters with appropriate redox potentials to reductively cleave sulfonium substrates in overall two-electron reactions. The analogue systems differ from the enzymes in that DOA* is generated in a one-electron reduction and is sufficiently stabilized within the protein matrix to abstract a hydrogen atom from substrate or an amino acid residue in a succeeding step. In the present systems, the radical produced in the initial step of the reaction sequence, [Fe(4)S(4)(SR')(4)](3)(-) + [PhMeSCH(2)R](+) --> [Fe(4)S(4)(SR')(4)](2)(-) + PhSMe + RCH(2)*, is not stabilized and is quenched by reduction and protonation.     

Supramolecular framework adducts constructed of hexamethylenetetramine,aquated alkali metal cationic clusters,and hexacyanoferrates(II/III)

The reaction of alkali metal hexacyanoferrate(II/III) with (CH₂)₆N₄ (hexamethylenetetramine, abbreviated HMT) in an acidic medium yielded crystalline compounds of stoichiometries HK₂[Fe¹¹¹(CN)₆]·2HMT·4H₂O, H₂K₂[Fe¹¹(CN)₆]·2HMT·4H₂O, and HNa₂[Fe¹¹¹(CN)₆]· 2HMT·5H₂O. Their crystal structures are based on a packing of three molecular components: neutral and/orprotonated HMT, hexacyanoferrate, and an alkali metal ion-water cluster. The resulting three-dimensional supramolecular framework is constructed from the coordination of the alkali metal ion by aqua ligands as well as [Fe(CN)₆]{n–} and HMT units, and further stabilization is achieved by hydrogen bonding between water molecules and the noncoordinated nitrogen atoms of HMT and hexacyanoferrate.     

Expert system for precision testing in validation of liquid chromatographic methods

After a liquid chromatographic method has been developed, it must be validated to establish its limitations in daily use. Method validation is becoming increasingly important as stricter rules are applied by regulatory authorities. Precision testing is a vital step in this validation; both intralaboratory testing and interlaboratory testing are needed. In an intralaboratory test, repeatability and ruggedness tests are usually done. Expert systems are available for both tests. Here they are integrated to form an intralaboratory precision-testing expert system; special integration architecture is described. Important features of the integrated system are a supervisor containing planning knowledge about the tests and a common data structure containing all the objects necessary for an expert system in this area.     

Interaction of globular proteins with mixed lipid vesicles

Vesicles of charged (Phosphatidic Acid) and neutral (Phosphatidylcholine) lipids were used as membranes model to examine the lateral phase separation induced by a globular protein, namely lysozyme. The ability of the positively charged protein, adsorbed onto vesicles surfaces, to induce the formation of micro-domains richer in the charged lipid component has been investigated by calorimetric measurements, using a DSC instrument. The protein adsorption, rate of denaturation and lipid micro-domains formation were affected bypH and salt concentration variations showing the deep influence of the electric charges in modulating this phenomena.Some of the present results have been rationalized on the basis of a theoretical model recently developed by the authors.     

Solvatochromism and piezochromism of dicyano-, tricyano-, and tetracyano-diimine-iron(II) complexes

The solvatochromism of several dicyano-bis-diimine-iron(II) complexes in various binary aqueous solvent mixtures has been established, at 25 °C. A solvent sensitivity scale has been developed for these complexes. The solvatochromic properties of two tricyano-terdentate ligand iron(II) complexes in several solvents have also been determined, as have those of a series of tetracyano-diimine complexes in DMSO–water media. These results have been analysed and systematic but varied trends of solvation were demonstrated. Piezochromic parameters for two complexes have been obtained and are discussed in the context of a solvatochromism/piezochromism correlation.     

2,5-Dichloro-4,4-ethylenedioxy-3-phenylsulfonyl-2-cyclopentenone in Nucleophilic Substitution and Addition Reactions

2,5-Dichloro-4,4-ethylenedioxy-3-phenylsulfonyl-2-cyclopentenone reacts with diethyl malonate potassium salt according to the Ad_NE pattern with replacement of chlorine atoms at the double C=C bond, while the reaction of the same substrate with allylcuprate is not selective, and it follows several pathways.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 4, 2005, pp. 562–566.Original Russian Text Copyright © 2005 by Ivanova, Usmanova, Miftakhov.