Cover Picture: Angew. Chem. Int. Ed. 20/2002

The cover picture shows a series of ¹⁹F NMR spectra taken every hour during the monitoring of a time‐course experiment after addition of 5′‐fluoro‐5′‐deoxyadenosine (5′‐FDA) to a cell‐free extract of Streptomyces cattleya. This bacterium has the unusual capacity to biosynthesise organofluorine compounds from inorganic fluoride. The ¹⁹F NMR spectra illustrate that 5′‐FDA is a true intermediate in the biosynthesis of fluoroacetate and 4‐fluorothreonine. Other intermediates such as fluoroacetaldehyde are also observed for the first time. In a separate experiment, inorganic fluoride was converted into fluoroacetate, thus indicating that all of the enzymes involved in the fluoroacetate biosynthesis pathway are active in the cell‐free extract. These experiments report the first cell‐free biotransformations of inorganic fluoride into fluoroacetate, the most ubiquitous organic fluorine natural product, and pave the way for a biotechnological approach to organofluorine synthesis. Full details are described by O'Hagan and co‐workers on p. 3913 ff.     

Comment on "Adsorption of naphthalene on zeolite from aqueous solution" by C.F. Chang, C.Y. Chang, K.H. Chen, W.T. Tsai, J.L. Shie, Y.H. Chen

A paper contributes not only by its originality and creativity, but also by its continuity and development toward subsequent research. Referencing and quotation accuracy are an important part of a scientific article. This study presents a literature review concerning the precision of 50 first authors' publications, which originally cited Ho's pseudo-second-order kinetic expression paper in kinetics model for solute sorption on various sorbents. This model applies to a range of solid-liquid systems such as metal ions, dyestuffs, herbicides, oil, and organic substances in aqueous systems onto various sorbents. In addition, citations of Lagergren and Elovich rate equations are also discussed. This comment offers information for citing the original idea of Ho's pseudo-second-order kinetic expression and Lagergren's pseudo-first-order kinetic equation. It is also suggested that the cited paper should be accurately quoted.     

Quantum molecular similarity. 3. QTMS descriptors.

Building on the ideas of a previous paper [part 1, J. Phys. Chem. A 1999, 103, 2883] we present a new molecular similarity method based on the topology of the electron density. This method is directly applicable to QSARs and is called quantum topological molecular similarity (QTMS). It has been tested for five sets of carboxylic systems including para- and meta-benzoic acid, para-phenylacetic acid, 4-X-bicyclo[2.2.2]octane-1-carboxylic acids, and polysubstituted benzoic acids. In combination with the partial least squares (PLS) procedure QTMS is able to produce excellent and statistically valid regressions. It is shown that QTMS avoids certain challenges of traditional Carbó-like similarity indices. Finally, QTMS is able to suggest a molecular fragment that contains the active center or the part of the molecule that is responsible for the QSAR.     

Cover Picture: Angew. Chem. Int. Ed. 6/2002

The cover picture shows the electric eel, Electrophorus electricus, a source for commercially available acetylcholinesterase. In an experiment described by K. B. Sharpless and M. G. Finn and co‐workers on pp. 1053–1057, a femtomolar inhibitor was assembled by the enzyme from a collection of building blocks containing azide and alkyne functional groups, shown floating in solution. The templated 1,3‐dipolar cycloaddition reaction, producing the inhibitor, is represented by the flare of light at the center of the image.     

Triaziridine. 6. Mitteilung. Substituententransformationen an Triaziridinen

Substituent Transformations on Triaziridines Several novel triaziridines were prepared by substituent transformations starting from the known dialkyl-triaziridine-carboxylates 1a – c , with the aim to study the influence of the substitution pattern on the properties of the triaziridine ring. The dialkyl-triaziridines 2a – c were obtained by (t-BuO^?)-mediated demethylation and decarboxylation and the dialkyl-triaziridine-methanols 4a – c by LiAlH₄ reduction. Further reduction of the tosylates of 4a , b with LiAlH₄ gave the methyl-dialkyl-triaziridines 3a , b . The dialkyl-triaziridines 2a , c could not be N-methylated directly with CH₃I, but the anions 10a , c , obtained from 2a, c with CH₃Li, yielded 3a , c . N-Methylation of 2a with (CH₃)₃OBF₄ did not afford 3a but rather the methyl-triaziridinium salt 11 . The dialkyl-triaziridine 2c has pK_a > 14, its protonated species < 2. A concept that the electron pairs on the triaziridine N-atoms are more strongly localized than on amine N-atoms explains (a) that the dialkyl-triaziridine 2c is hardly basic, (b) that the LiAlH₄ reductions of the esters 1 stop at the stage of the methanols 4 , and (c) that the methanols 4a , b do not cleave like aminomethanols.     

Magnetic Recording of N.Q.R. spectra

This paper gives complete details of a unique system for Magnetically Recording the Analogue Spectral Signals from an N.Q.R. Spectrometer of the S.R.O./Marginal Oscillator type.This is a very low cost system, but producing a very high order of play-back resolution from recordings, using a normal domestic Cassette or Tape, Reel to Reel Recorder. Spectra can also be transmisted via telephone lines, fibre optic links or radio frequencies.This system has been used now for several years, and due to the design being based mainly om passive components, the order of reliability is extremely high, without any faults being encountered to dete!.     

Vertebrate collagenase inhibitor. II. Tetrapeptidyl hydroxamic acids.

To develop a potent and specific collagenase inhibitor, a series of tetrapeptidyl hydroxamic acids were synthesized, based on the previous findings with tripeptidyl derivatives (Chem. Pharm. Bull., 38, 1007-1011, 1990). Among the series of tetrapeptidyl derivatives synthesized, R-Gly-Pro-Leu-Ala-NHOH and R-Gly-Pro-D-Leu-D-Ala-NHOH were found to be highly specific and potent inhibitors against vertebrate collagenase with an IC50 of 10(-6) M order, where R stands for Boc or acyl group. Analysis of their structure-activity relationships showed a characteristic feature of the substrate-binding site of collagenase as follows: 1) the S1 subsite forms a shallow hydrophobic pocket, although glycine residue corresponds to the subsite of the natural collagen substrate: 2) the S2 subsite constitutes a bulky pocket with less requirement for hydrophobicity: 3) the S3 subsite preferentially accommodates Pro residue: and 4) the accommodation of the P4-P1 subsites of peptidyl collagenase inhibitor to the S4-S1 subsites is required to form a tight binding of its hydroxamic acid moiety to the zinc ion at the catalytic site of the enzyme. The introduction of an enantiometric dipeptide unit, D-Leu-D-Ala, to the P2-P1 subsites demonstrated an increased binding capacity to the extended S4-S1 subsites of collagenase, thus providing proteinase-resistant inhibitor.     

Structure investigations by P.A.C.

The perturbed angular correlation /P.A.C./ technique is employed to investigate the structures of barium ferrite and barium hexaferrite using radioactive¹³³Ba /10.7 Y/ as a probe. The quadrupole interaction frequencies /W_Q'S/ are found to be 9.68 and 12.02 Mrad sec^–1 for barium ferrite and barium hexaferrite, respectively, showing a drift from usual cubic structure.     

Interfacial polycondensation. I.

Interfacial polycondensation is a rapid, irreversible polymerization at the interface between water containing one difunctional intermediate and an inert immiscible organic solvent containing a complementary difunctional reactant. It is based on the Schotten-Baumann reaction in which acid chlorides are reacted with compounds containing active hydrogen atoms (—OH, —NH and —SH). A large number of polymers (heat-sensitive and infusible as well as stable and meltable) can be prepared. The method has been applied to the preparation of polyurethanes, polyamides, polyureas, polysulfonamides, and polyphenyl esters. Interfacial polycondensations are run in simple, open laboratory equipment with or without stirring. With suitable agitation granular or powdered polymers with high molecular weight are prepared at room temperature and isolated within a few minutes. The intermediates need not be absolutely pure or in balance nor is a quantitative yield needed in order to obtain high polymer. The major variables in the interfacial polycondensation process are discussed and the laboratory techniques and principles are contrasted with melt polycondensation.     

Azidinium-Salze. 23. Mitteilung. Photolyse heterocylischer Azidinium-Salze

Photolysis of Heterocyclic Azidinium Salts The photochemistry of some azidinium salts was investigated. Their photolusis led to a large variety of products which were isolated and identified. Reaction mechanisms involving singlet and triplet nitrene intermediates are discussed to explain the product formation.     

Die sterischen Bedingungen der Fragmentierungsreaktion. II. Teil. Stereoisomere 3-Aminocyclohexyl-p-toluolsulfonate. Fragmentierungsreaktionen, 15. Mitteilung

The solvolytic fragmentation of cis- and of trans-3-amino-cyclohexyl p-toluenesulfonates 8a and 9a and the corresponding N, N-dimethyl derivatives 8b and 9b has been studied. In 80% ethanol the cis-amino-tosylates 8a and 8b react faster than the homomorphous cis-3-alkyl-cyclohexyl tosylates 11a and 11b to yield fragmentation product exclusively or predominantly. The synchronous mechanism predictable on stereoelectronic grounds is therefore indicated.     

Stoffwechselprodukte von Mikroorganismen. 177. Mitteilung. Avilamycin C

From cultures of the Avilamycin (Avilamycin A) producing organism, Streptomyces viridochromogenes, strain ETH 23575, a second antibiotic, Avilamycin C, C₆₁H₉₀Cl₂O₃₂ could be isolated in crystalline form. Both Avilamycins belong to the group of the Orthosomycins. By IR., ¹H- and ¹³C-NMR. spectroscopy and by transformation to a common derivative it could be proven that Avilamycin A is a methyl ketone, Avilamycin C the corresponding methyl carbinol.     

铵梯脲混合炸药中改性硝酸脲和硝酸铵含量的测定

论述了铵梯脲混合炸药中改性硝酸脲和硝酸铵组分含量的一种快速准确的化学分析测定方法。该法在研制和生产铵脲类炸药的过程中,对选择最佳配比,控制生产和质量把关等有着重要的指导作用。同时笔者对测定方法,反应原理,影响因素等作了深入的探讨与研究。     

Cover Picture: Angew. Chem. Int. Ed. 13/2002

The cover picture shows benzoborirene, the product of the crossed‐molecular‐beam reaction between benzene molecules and boron atoms, displayed above the three‐dimensional plot of the angular‐ and translational‐energy‐dependent flux of the benzoborirene molecules in the center‐of‐mass system. As the reaction conditions preclude secondary collisions, the intermediate initially formed from the reactive collision decays by ejection of a hydrogen atom. The structure of the benzoborirene depicted is based on a DFT computation, which, combined with results of highly accurate coupled‐cluster calculations has been used to assign the reaction product by comparing experimental and theoretical reaction energies. Details are described by R. I. Kaiser and H. F. Bettinger on p. 2350 ff.     

Hetero-Cope-Umlagerungen. 4. Mitteilung. Regiokontrollierte Indolsynthesen

Hetero-Cope-Rearrangements, Regio-Controlled Synthesis of Indoles The reaction of O-deprotonated N-phenylhydroxylamines 1 with various electron-deficient allenes 2 , 14 , 16 gives, via Michael addition and Cope-rearrangement, substituted anilines 5 , which are easily convertible into indoles 6 . In this manner, sulfoxides 17 , serve as equivalents of 2-vinylindoles. Diels-Alder reaction with this 2-vinylindole equivalent followed by indolisation affords isoquinuclidine derivative 21 which may be a useful precursor for the preparation of Iboga alkaloids.     

Strahlungschemie von Kohlenwasserstoffen. 17. Mitteilung. Hexan-NO

The influence of NO on the radiolysis of hexane at ?70°C has been studied. The results allow the following interpretations: The bimolecular part of the hydrogen production is in contrary to N₂O efficiently quenched by NO. This part involves non-thermal hydrogen atoms and has a G-value of about 1.4. All olefins are suppressed, probably in a secondary chain reaction with NO. The radical yield is drastically reduced by very low concentrations of NO, but by higher concentrations this decrease is slowed down. A reaction scheme proposed by BURRELL is able to explain these results.     

Anti-inflammatory drugs. X.

In the solid-state structure of the title compound, C₄H₁₀N⁺·C₁₄H₁₀Cl₂NO₂⁻·H₂O, the asymmetric unit contains one cation, one anion and a water mol­ecule. There is a network of hydrogen bonds which is similar to that found in the hydrated diethyl­ammonium diclofenac salt. A comparison is made of the molecular conformation of the anions in the two related structures.     

13C-NMR. Spectroscopy of naturally occurring substances. XLV. Iboga alkaloids.

The carbon shifts of the Iboga-type alkaloids catharanthine, voacangine, coronaridine, ibogaine, dihydrocatharanthine and epiibogamine were recorded and correlated with the conformation of the natural bases. A ¹³C-NMR. analysis of heyneanine determined its C(19) configuration and a similar study of epiheyneanine proved its structure.     

An E.P.R. study of peptides after U.V. irradiation

Abstract— Various peptides of Gly, Ala, Phe, Tyr, and Trp have been irradiated with U.V. light in the solid state or in frozen aqueous solution. The radicals produced were studied by E.P.R. spectroscopy at low temperature and at room temperature. Radicals seem to occur preferentially on Gly or Ala when in the C-terminal position and there is evidence for a photosensitization of these amino acids by aromatic amino acids.     

Polysulfonylamines. CXXXII.

The crystal structure of the title compound, C₅H₇N₂⁺·C₁₂H₁₀NO₄S₂⁻, consists of two independent cation–anion pairs, A and B. Within each pair, the H—N—C—N*—H grouping (N*—H is the pyridinium function) and one N—S—O moiety of the anion are linked by N*—H⃛N and N—H⃛O hydrogen bonds to form an antidromic ring motif of type R²₂(8). The remaining amino donors give rise to N—H⃛O hydrogen bonds, connecting the ion pairs into A–B–A–B– chains. The structure testifies to the persistence of the R²₂(8) motif in question, which was previously detected as a highly robust supramolecular synthon in a series of onium di(methane­sulfonyl)­amidates. The structure is pseudosymmetric; the anion positions correspond to space group P2₁/n, but those of the cations do not.