Palladium-induced cyclizations for the synthesis of cis-2,5-disubstituted-3-methylenetetrahydrofurans: studies of the C7-C22 core of amphidinolide K

[formula: see text] The diastereoselective synthesis of cis-2,5-disubstituted-3-methylenetetrahydrofurans via Pd(0)-catalyzed cyclization of 2-methylene-1,4-diols is described. Investigations into the scope of the reaction and its application toward the synthesis of amphidinolide K is reported.     

THE EFFECTS OF PORPHYRIN STRUCTURE AND AGGREGATION STATE ON PHOTOSENSITIZED PROCESSES IN AQUEOUS AND MICELLAR MEDIA

The efficiency of several porphyrins at 10 μM and 83 μM as sensitizers of the photooxidation of 0.1 mM tryptophan and histidine via a singlet oxygen-mechanism was studied in pH 7.4-buffered aqueous solutions and in aqueous dispersions of Triton X-100 micelles. The porphyrins were either solubilized in the bulk aqueous medium or associated with the micellar phase, whereas the amino acids were always located in the aqueous phase. With those porphyrins, such as uroporphyrin I, meso-tetra (4-sulfonatophenyl)porphine, meso-tetra(4-carboxyphenyl)porphine and meso-tetra)N,N,N-trimethylanilinium)porphine, which are > 98% monomeric in both media, the efficiency of histidine photooxidation was independent of the site of O₂(¹Δ_g) generation, as shown by the closely similar values for the photooxidation rate constant and oxygen-consumption quantum yield in the presence and absence of Triton micelles; the same indications were provided by photokinetic experiments with tryptophan. Actually, laser flash photolysis studies showed that the micelle-incorporation of the above mentioned porphyrins brought about only minor changes in their photophysical properties, including the relative yield of O₂(¹Δ_g) generation. On the other hand, hematoporphyrin IX, its Zn²⁺-complex, and coproporphyrin III are largely aggregated in homogeneous aqueous solution; their incorporation into Triton micelles caused an increase of the triplet quantum yield and an enhancement of the oxygen-consumption quantum yield and photooxidation rate constant for both histidine and tryptophan. The lower photosensitizing efficiency of aggregated porphyrin species in comparison with the corresponding monomeric porphyrin was confirmed by measuring the initial rate and quantum yield of oxygen consumption upon irradiation of 1 mM histidine and tryptophan in the presence of different hematoporphyrin concentrations within the 0.3-100μM range.     

An electrochemical study of redox indicators : Part I. Substituted chrysoidines

The electrochemical oxidation of various substituted chrysoidines was studied by cyclic voltammetry, to determine which have stable oxidation products. Only 4-hydroxy-chrysoidine has a stable product; the apparent oxidation potential is 0.779 V vs. NHE. 4-Methoxy- and 4-ethoxy-chrysoidine rapidly lose methanol or ethanol, respectively, so that the 4-hydroxychrysoidine wave appears on subsequent scans. All the other chrysoidines studied are irreversible. The results indicate that a hydroxy group in the 4-position is necessary for stability; the 4-alkoxychrysoidines can achieve the stable quinoidal structure by cleavage of the alkoxy group after nucleophilic attack.     

Radiative lifetimes of ions measured with the photoelectron spectrometer

Using a modified photoelectron spectrometer the radiative lifetimes of some electronically excited diatomic and triatomic molecular ions have been determined. The method is based on measuring the time delay between the ejection of a photoelectron from a molecule and the emission of a photon from the resulting ion.     

Microstructure determination of poly-(1,3-pentadiene) by a combination of infrared, 60-MHz NMR, 300-MHz NMR,and X-ray diffraction spectroscopy

A quantitative procedure has been developed for characterizing the complete microstructure of polymers of 1,3-pentadiene, including the tacticity of any crystalline component. This can be accomplished by a combination of infrared spectroscopy, X-ray crystallinity, and 300-MHz NMR spectroscopy. A series of high structural purity polymers were synthesized with a series of previously unreported mixed microstructures. These samples were characterized by using the three techniques mentioned, including the previously unreported 300-MHz NMR data. With those results a 60-MHz NMR/IR method of spectroscopy was developed to determine the composition of poly(1,3-pentadiene)s in terms of percent cis-1,2-, cis-1,4-, trans-1,4-, and 3,4-pentadiene units.     

Die Anwendung des Derivatographen zur Gleichzeitigen Dilatometrischen und Differential-Thermischen Analyse von Gläsern

Simultaneous DTA and dilatometric measurements were made and the derivatives of the dilatometric curves were taken for three glasses by means of a derivatograph. Glass blocks were used as test pieces with a boring for the thermoelement. A maximum was observed in the rate of length change, which can be explained by overheating phenomena. A comparison with DTA curves of glass powders published by Yamamoto showed that the break points in the DTA curves of glass blocks do not coincide with the Tg points, but under identical conditions they can serve for the rapid characterization of the transformation range.     

Argentomctric coulomelric titration of thioacetamide

The coulometric determination of thioacetamide (TAA) with electrogenerated silver is described. The titration is done in a solution 0.1M in both ammonia and sodium hydroxide, and the end-point is detected potentiometncally with a silver-silver sulphide electrode. On repeat analyses of approx. 2-mg samples of TAA an average error of -04% (relative standard deviation 0.25%) was obtained. Important steps in the procedure include cleaning the silver generating electrode in nitric acid before each titration, purging well with nitrogen to remove oxygen, and not using too large a sample.     

An NQR study of the effects on the torsional oscillations of a molecular crystal due to uniaxial pressures

This work reports the experimental results of the uniaxial pressure dependence at various temperatures of the spin-lattice relaxation time, T₁, in paradichlorobenzene single crystals.The directionality of the pressure dependence, together the temperature dependence ot T₁ near room temperature, give us some information about the dependence of the molecular torsional frequencies and lifetimes of the oscillations ground levels with the intermolecular crystalline potential.     

Analytical and radioanalytical quality control of purity and stability of radiopharmaceutical compound [186gRe]Re-HEDP for bone metastases pain palliation

Summary The nuclear properties of ^186gRe make it a useful agent for radionuclide therapy and imaging. The coordination compound [^186gRe]Re-HEDP has proved to be a successful bone seeking agent for palliation of metastatic bone pain. Chemical, radiochemical and radionuclidic purity of commercial radiopharmaceutical [^186gRe]Re-HEDP have been checked by means by γ- and β-spectrometries, INAA and paper radio-chromatography. The results indicate a good radionuclidic purity, with levels of contamination from the short-lived ¹⁸⁸Re well below the required specifications. After injection of the radiopharmaceutical, the radiochemical measurements conducted in vivo, on biological matrices, blood, plasma and urine, have shown that, entering the systemic circulation, ^186gRe dissociates from the bis-phosphonate complex as hydrosoluble [^186gRe]ReO₄-, and the two chemical species follow different biokinetics.     

Application of capillary zone electrophoresis and reversed-phase high-performance liquid chromatography in the biopharmaceutical industry for the quantitative analysis of the monosaccharides released from a highly glycosylated therapeutic protein

Two assays for the quantitative determination of the neutral and amino-monosaccharides attached to a therapeutic glycoprotein were developed using capillary zone electrophoresis (CZE) and RP-HPLC. These assays meet the strict batch release requirements of the quality control in biopharmaceutical industry. The monosaccharides were released from the glycoprotein by hydrolysis with 2N trifluoroacetic acid. In the CZE assay the monosaccharides were reacetylated prior to derivatization with 8-aminopyrenesulfonic acid (APTS), reacetylation in the glycoprotein matrix was investigated in detail. The RP-HPLC method used pre-column derivatization with anthranilic acid in methanol-acetate-borate reaction medium; reacetylation was not necessary. However, epimerization of the different monosaccharides was observed and studied in detail. For the quantitative assay, separation of the amino-monosaccharide epimers had to be developed. The HPLC assay was validated.