Emission spectra of the radical cations of hexa-, penta-, tetra-, and tri-fluorobenzenes

Emission spectra of the radical cations of the title fluorobenzenes were excited in the gaseous phase by electron impact. The spectra, vibrational fine structure discernible and the threshold energy of the emission are discussed in relation to the photoelectron spectra of the fluorobenzenes.     

Synthesis of jasplakinolide analogues containing a novel omega-amino acid

The synthesis of the omega-amino acid 4 is described utilizing a two-dimensional synthesis strategy combined with an enzymatic differentiation of homotopic ester groups. The amino acid 4 features two non-bonded interactions that result in conformational constraints on a cyclic construct. This amino acid was incorporated into the four macrolactams 17, 22, 31, and 37. The ring in 17 and 22 is 18-membered, whereas 31 and 37 have a 19-membered ring. The pairs with the same ring size differ in a N-methyl group. For the larger macrolactams (31 and 37) conformational analysis showed that the macrocyclic rings are somewhat more rigid than in the natural lead, the depsipeptide jasplakinolide. Nevertheless, their conformations are comparable to the natural product. There are no intramolecular hydrogen bonds, neither is the cis-rotamer populated in the N-methyl compound 37. Due to the increased flexibility of the smaller macrolactams 17 and 22 and signal overlap, a distinct solution structure could not be obtained for these compounds. The amino acid 4 should be useful for restricting the conformation of other small peptides.     

Development of pork fat reference material for OCPs BCR-CRM 430

Summary A pork fat sample was prepared and tested as candidate reference material for 10 organochlorine pesticides and metabolites (OCPs): hexachlorobenzene, -, - and -HCH, -heptachlor epoxide, dieldrin, endrin, p,p'-DDT, p,p'-TDE and p,p'-DDE. Preparation and testing for homogeneity and stability of the OCPs in the pork fat are discussed. The coefficient of variation of pesticide determinations carried out to test the between-ampoule homogeneity ranged from 2.4–5.8% and was found to be very similar to that for the analytical method (2.5–4.9%). This means that the homogeneity is very good. Stability data over 12 months do not show any trends that suggest lack of stability.     

Formation of protonic defects in perovskite-type oxides with redox-active acceptors: case study on Fe-doped SrTiO(3)

The thermodynamics of water incorporation into Fe-doped SrTiO(3) was investigated by thermogravimetric measurements. Changes in valence states of redox-active dopant ions (Fe(3+)/Fe(4+)) with water vapor pressure were taken into account in the defect chemical analysis. The proton solubility was significantly enhanced by the presence of the redox centers. The hydration enthalpies and entropies were -60 kJ mol(-1) and -122 J mol(-1) K(-1). The defect chemical model was applied to describe the water vapor dependence of the electrical conductivity in mixed ionic and electronic conducting Fe-doped SrTiO(3) single crystals.     

Use of epoxidation and epoxide opening reactions for the synthesis of highly functionalized 1-oxaspiro[4.5]decan-2-ones and related compounds

Epoxidation of ethyl 3-(6-hydroxycyclohex-1-en-1-yl)propanoate (11) provided the syn epoxide 12. By invoking chelation controlled epoxide opening the triol derivatives 13 and 14 or the spiro lactone 25 could be obtained. Elimination of HBr from the bromides 26 and 27 produced the spiro cyclohexenones 28 and 29. Epoxidation of the double bond occurred in a diastereoselective manner to give epoxides 30 and 31, respectively. Treatment of the epoxide 31 with LiBr/AcOH gave the bromo hydrin 38. In a ‘merry go round’ fashion 38 was further functionalized on the cyclohexane ring by elimination, epoxidation, and epoxide opening resulting in the bromo hydrin 43. Other cyclohexane derivatives that were produced during these studies include the cyclohexenone 19 and the cyclohexanediol 23. In addition, enolate azidation of the spiro lactone 29 proceeded in a diastereoselective manner providing the α-azido lactone 32.     

BIOSYNTHESIS OF PTERIDINES IN Neurospora crassa,Phycomyces blakesleeanus AND Euglena gracilis: DETECTION AND CHARACTERIZATION OF BIOSYNTHETIC ENZYMES*,†

Abstract— Occurrence, biosynthesis and some functions of tetrahydrobiopterin (H₄biopterin) in animals are well known. The biochemistry of H₄biopterin in other organisms than animals was hitherto not widely investigated. Recently H₄biopterin was found in the phytoflagellate Euglena gracilis, in the zygomycete Phycomyces blakesleeanus and in the ascomycete Neurospora crassa. In Euglena, Neurospora and Phycomyces the enzymatic activities of GTP cyclohydrolase I, 6-pyruvoyl tetrahydropterin synthase and sepiapterin reductase are detectable and the biosynthesis follows the same steps as were shown for animals. The biosynthetic enzymes, however, show a much lower sensitivity to those inhibitors that act on vertebrate enzymes. 2,4-Diamino-6-hydroxypyrimidine as inhibitor of GTP cyclohydrolase I and N-acetylserotonin or N-methoxyacetylserotonin as inhibitors of sepiapterin reductase can decrease pteridine biosynthesis significantly, in vitro and in vivo. The apparent K_mvalues are in general higher when compared with the respective animal enzymes. In Neurospora, the conversion of GTP to dihydroneopterin triphosphate was closely associated with subsequent production of 6-hydroxymethyl-7, 8-dihydropterin due to the high activity of dihydroneopterin aldolase, different from all other tested organisms. Investigations involving inhibition of pteridine synthesis might be a useful tool for evaluating the hypothesis that pteridines in fungi and plants are co-chromophores of various blue light-dependent, flavin-containing phototrcptors.     

Synthesis of chimeric oligonucleotides containing phosphodiester, phosphorothioate, and phosphoramidate linkages

[reaction: see text] H-Phosphonate monomers of 2'-O-(2-methoxyethyl) ribonucleosides have been synthesized. Oxidation of oligonucleotide H-phosphonates has been optimized to allow the synthesis of oligonucleotides containing either 2'-deoxy or 2'-O-(2-methoxyethyl) ribonucleoside residues combined with three different phosphate modifications in the backbone, i.e., phosphodiester (PO), phosphorothioate (PS), and phosphoramidate (PN). Phosphodiester linkages were introduced by oxidation with a cocktail of 0.1 M Et(3)N in CCl(4)/Pyr/H(2)O (5:9:1) without affecting phosphorothioate or phosphoramidate linkages. For the synthesis of phosphoramidate-modified oligonucleotides, N(4)-acetyl deoxycytidine-3'-H-phosphonate monomers were used to avoid transamination during the oxidation step.     

Zur Biosynthese des Strychnins. 135. Mitteilung über Alkaloide

From the feeding of young plants of Strychnos nux-vomica with [¹⁴C]-1-and [¹⁴C]-2-acetate it could be deduced that the C-atoms 22 and 23 were derived from acetate. [¹⁴C]-2-mevalonate, [¹⁴C]-2-geraniol and [¹⁴C]-2-geranyl pyrophosphate were also incorporated into strychnine. The distribution of radioactivity in the «mevalonate-strychnine» was in agreement with the monoterpenoid hypothesis. Feeding experiments especially with [¹⁴C]-tryptophane showed that the main production centre of the alkaloid lay in the roots and that only a small part of it was carried to the leaves. Tritium labelled WIELAND GUMLICH aldehyde as well as N_(a)-[¹⁴C]-1-acetyl WIELAND GUMLICH aldehyde were not converted into strychnine by S. nux-vomica.