On the generation of novel anticancer drugs by recombinant DNA technology: the use of combinatorial biosynthesis to produce novel drugs

Chemotherapeutic drugs for cancer treatment have been traditionally originated by the isolation of natural products from different environmental niches, by chemical synthesis or by a combination of both approaches thus generating semisynthetic drugs. In the last years, a number of gene clusters from several antitumor biosynthetic pathways, mainly produced by actinomycetes and belonging to the polyketides family, are being characterized. Genetic manipulation of these antitumor biosynthetic pathways will offer in the near future an alternative for the generation of novel antitumor derivatives and thus complementing current methods for obtaining novel anticancer drugs. Novel antitumor derivatives have been produced by targetted gene disruption and heterologous expression of single (or a few) gene(s) in another hosts or by combining genes from different, but structurally related, biosynthetic pathways ("combinatorial biosynthesis"). These strategies take advantage from the "relaxed substrate specificity" that characterize secondary metabolism enzymes.     

Recherches sur la structure électronique et les caractéristiques des différentes formes tautomères de la purine

Résumé Les caractéristiques électroniques (énergie, charges , géométrie, moment dipolaire, énergie de transition) des quatre formes tautomères de la purine et des phényl-8 N(1)H et N(3)H purines ont été déterminées par la méthode LCAO améliorée. La forme 9 est trouvée la plus stable à l'état isolé. Une interprétation nouvelle des bandes d'absorption est proposée.

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Researches on the electronic structure and the characteristics of various tautomer forms of Purine

The electronic characteristics (energy, charge , geometry, dipole moment, transition energy) of the four tautomeric forms of the purine and of the phenyl-8 N(1)H and N(3)H purines have been determined by the improved LCAO method. The form 9 is considered as the most stable at the isolated state. A new interpretation of the absorption bands is proposed.

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Zusammenfassung Die elektronischen Charakteristiken (Energie, Ladung , Geometrie, Dipolmoment, Übergangsenergie) der vier Tautomerformen des Purins und der Phenyl-8 N(1)H und N(3)H Purine sind durch die verbesserte LCAO-Methode bestimmt worden. Die Form 9 ist, zum isolierten Stand, als am meisten beständig zu betrachten. Eine neue Erklärung der Absorptionsbänder ist vorgeschlagen.

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Les auteurs remercient le Professeur B. Pullmann (Paris) de l'intérêt qu'il a porté à ce travail, ainsi que Madame H. Feilchenfeld (Jérusalem) pour les résultats inédits qu'elle a bien voulu leur communiquer.     

Xylanase production by Trichoderma reesei rut C-30 on rice straw

Xylanase production of Trichoderma reesei Rut C-30 was examined at different initial pH values (4.8, 5.9, and 7.0) on rice straw in shake flasks, and in a fermentor, for the best pH condition. Enzyme performance was tested on ammonia-treated dwarf elephant grass. The maximum xylanase activities, 92 and 122 IU/mL, were obtained at pH 4.8 in the shake flasks and fermentor, respectively, in which good growth of the fungus was observed during the first 24 h and consumption of proteins dissolved from the rice straw caused the pH to rise later to values between 6.4 and 6.7 (optimal for xylanase production). The xylanases from T. reesei were as effective as Multifect XL, a commercial enzyme preparation, in hydrolyzing ammonia-treated elephant grass.     

Kinetics and mechanism of ligand interchange in the [RuIII(edta)L] complexes; L=Cysteine and related thiolates

Complexes of the [RuIII(edta)SR]n series, with SR–= deprotonated cysteine, N- acetylcysteine, 2–mercaptoethanol, glutathione and penicilamine, were prepared from [Ru(edta)H2O]– and the corresponding RSH thiols, at pH=5.5. The complexes exhibit intense visible absorption bands at ca. 520nm (3500M–1 cm–1), associated with LMCT from the sulfur ligands bound to RuIII. The kinetics of the formation reactions were first order in [RuIII(edta)H2O]– and thiol reactants, with k1 values ca. 1–5×102 M–1s–1 (25°C) for all the sulfur ligands except penicilamine, which reacted slower by a factor of 10. Activation parameters suggest an associative mechanism, as for the coordination of other S- and N-bound ligands to [RuIII(edta)H2O]–. A reactivity decrease is apparent at low and high pH's (ranges 1–3 and 8–10, respectively), associated with acid-base equilibria involving the less reactive [RuIII(Hedta)H2O] and [RuIII(edta)OH]2– species. A significant rate increase was found for cysteine and penicilamine at ca. pH=8.0, because the thiol reactants deprotonate. The equilibrium constants for all the ligands showed that robust complexes were formed, with K=ca. 1×105 M–1 (25°C). The dissociation rate constants, k–1, were in the 10–3–10–4 s–1 range. The influence of nucleophilic and steric effects increasing and decreasing the formation rates, respectively, is discussed for the thiolate ligands, with adequate comparisons with other L species bound to [RuIII(edta)H2O]–.     

How does internal motion influence the relaxation of the water protons in Ln(III)DOTA-like complexes?

Taking advantage of the Curie contribution to the relaxation of the protons in the Tb(III) complex, and the quadrupolar relaxation of the 17O and 2H nuclei on the Eu(III) complex, the effect of the internal motion of the water molecule bound to [Ln(DOTAM)(H2O)]3+ complexes was quantified. The determination of the quadrupolar coupling constant of the bound water oxygen chi(Omicron)(1 + eta(Omicron)2/3)1/2 = 5.2 +/- 0.5 MHz allows a new analysis of the 17O and 1H NMR data of the [Gd(DOTA)(H2O)]- complex with different rotational correlation times for the Gd(III)-O(water) and Gd(III)-H(water) vectors. The ratio of the rotational correlation times for the Ln(III)-H(water) vector and the overall rotational correlation time is calculated tau(RH)/tau(RO) = 0.65 +/- 0.2. This could have negative consequences on the water proton relaxivity, which we discuss in particular for macromolecular systems. It appears that the final effect is actually attenuated and should be around 10% for such large systems undergoing local motion of the chelating groups.     

Anthill Earth as a Gold Occurrence Indicator,and Gold Determination by Solid Sampling Flame Atomic Absorption Spectrometry

With the aim of avoiding cumbersome sample treatment, we present a device for the introduction of solid soil samples into AAS-flames for gold determination, as well as the proposition of earth from anthills as a gold occurrence indicator. A previous ground sample of anthill earth (0.50 mg) was weighed directly into a small recipient of polyethylene which was then connected to a sampling boronsilicate glass chamber. The sample was carried by an airflow (5 L min⁻¹) to a quartz cell positioned between the burner top and the optical beam. The generated atomic vapor produced a transient signal which was totally integrated in three seconds. The performance was compared with conventional flame atomic absorption spectrometry after proper sample digestion. No significant differences were observed between both procedures (mean deviation ±1.90%), and a LOQ of 0.03 μg Au was achieved using the proposed method. The anthill earth was found to be very suitable for indication of gold occurrence in soils and related materials.     

Magnetic properties on holmium iron garnet in high magnetic field. Optical absorption spectra in the infra-red region

On single crystals of holmium iron garnet (HoIG), magnetic properties have been studied in magnetic field up to 150kOe applied parallel to the main crystallographic directions in the 4.2–300K temperature range. Above 130 K, the magnetization is isotropic and linear magnetic field dependent as previously found in polycrystals and predicted by Néel's ferrimagnetic theory. Nevertheless the paramagnetic Curie temperature is much higher than the polycrystal value. Below 130K, due to the onset of the umbrella structure, the ferrite magnetization presents a non linear field variation with [111] as easy direction. The field evolutions of the anisotropy constants (K ₁ andK ₂) were calculated. Optical absorption measurements of both 5₈5I ₆ and 5I ₈5I ₇ transitions are reported and compared to the results of the literature in terms of inequivalent magnetic sites.     

Dérivés de la dihydro-2,4 triazole-1,2,4 thione-3 et de l'amino-2 thiadiazole-1,3,4 à partir de nouvelles thiosemicarbazones d'esters

A new general synthesis of 4,5-disubstituted 2,4-dihydro-1,2,4-triazole-3-thiones is proposed. These heterocycles are obtained by the action of primary amines, arylhydrazines or aroylhydrazines on the thiosemicarbazones of eaters. These last compounds are prepared by action of chlorhydrates of iminoethers on thiosemicarbazide in dimethylformamide. These thiosemicarbazones react also with strong acids, acid anhydrides and chlorides; by thermolysis and they give 2-amino-1,3,4-thiadiazole derivatives. Also, two derivatives of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole have been prepared.     

First enantioselective total synthesis of (-)-Centrolobine

[structure: see text] The first enantioselective total synthesis of (-)-Centrolobine is described. The key reaction is the synthesis of the cis-disubstituted tetrahydropyran framework by intramolecular cyclization of the enantiopure hydroxyketone 3 with Et3SiH and TMSOTf. The stereoselective reduction of the beta-ketosulfoxide 4 is the source of chirality. Revision of the absolute configuration of (-)-Centrolobine is proposed.     

Effects of Alkylamines on the Percolation Phenomena in Water/AOT/Isooctane Microemulsions

We carried out an investigation on the influence of several alkylamines, frequently present in reactions carried out in microemulsions, on the properties of the water/AOT/isooctane system. The presence of alkylamines has an important effect on the electrical percolation phenomena. This effect of amines on the electrical percolation of microemulsions of AOT/isooctane/water can be explained by taking into account the ability of these substrates to associate with the AOT film in the microemulsion, the basicity of the amine, and the different solubility of the amine in the three pseudophases of the system. Copyright 2000 Academic Press.