Palladium catalysed [2 + 2 + 1] intramolecular cycloaddition for the preparation of bicyclo[3.3.0]octa-1.5-dien-3-ones from 1,6-diynes

Palladium catalysed [2 + 2 + 1] cycloaddition of 1,6-heptadiynes with CO (1 atm) furnishes bicyclo[3.3.0]octa-1,5-dien-3-ones in 30-74% yield.     

Assignment of the backbone resonances for microcrystalline ubiquitin

Site-specific assignments for the solid-state NMR spectra of uniformly 13C,15N-enriched ubiquitin are described. The assignments are derived from three three-dimensional 15N-13C-13C correlation spectra collected at 400 MHz on microcrystalline material. A few residues (the loop near Threonine 9 and the C-terminal fragment) were missing and correspond to regions previously reported to be mobile on the basis of X-ray crystallography and solution NMR studies. A few additional sites exhibit shifts that differ from previously reported solution NMR assignments. Nonetheless, these de novo assignments indicate close agreement between the chemical shifts observed in solution and those in microcrystalline or precipitated solids. The methods utilized are likely to be generally applicable for other noncrystalline, nonsoluble proteins.     

Separation of tetracycline and its related substances by capillary zone electrophoresis

Tetracycline was separated from its main impurities 4-epitetracycline, anhydrotetracycline, 4-epianhydrotetracycline, chlortetracycline, and demethyltetracycline by capillary electrophoresis. Systematic method development was performed in which following parameters were consecutively optimized: type and pH of the buffer, buffer concentration, type and concentration of organic modifier, voltage and temperature. Qualitative and quantitative aspects of the method are compared with liquid chromatography.     

Unperturbed dimensions of amylose tributyrate from viscosity data in non-ideal solvents

The unperturbed dimensions of amylose tributyrate have been estimated from viscosity measurements in non-ideal solvents. The validity of several methods of extrapolation has been assessed for this polymer. A small solvent dependence of the unperturbed dimensions has been observed and the characteristic ratio C_∞ has been found to vary between 5·6 and 6·8. One can conclude from this that the ester chain is only slightly more extended than the native amylose, assuming that the ring conformation in the backbone remains unaltered when the ester is formed.     

Method development and validation for the analysis of didanosine using micellar electrokinetic capillary chromatography

A selective MEKC method was developed for the analysis of didanosine in bulk samples. Successful separation of didanosine from 13 of its potential impurities, derived from the various synthetic preparation procedures, was achieved. As CZE gave poor separation selectivity, MEKC was preferable. The use of EKC allowed achievement of the separation in a significantly shorter time than conventional HPLC. An anionic long-chain surfactant, lithium dodecyl sulfate (LiDS), was used as the pseudostationary phase and sodium tetraborate buffer as the aqueous phase. In order to obtain the optimal conditions and to test the method robustness, a central composite response surface modeling experiment was performed. The optimized electrophoretic conditions include the use of an uncoated fused-silica capillary with a total length of 40 cm and an ID of 50 microm, a BGE containing 40 mM sodium tetraborate and 110 mM LiDS at pH 8.0, an applied voltage of 18.0 kV, and the capillary temperature maintained at 15 degrees C. The method was found to be robust. The parameters for validation such as linearity, precision, and sensitivity are also reported. Three commercial bulk samples were analyzed with this system.     

Chemical and Pharmacological Potential of Coccoloba cowellii,an Endemic Endangered Plant from Cuba

Coccoloba cowellii Britton (Polygonaceae) is an endemic and critically endangered plant that only grows in Camagüey, a province of Cuba. In this study, a total of 13 compounds were identified in a methanolic leaf extract, employing a dereplication of the UHPLC-HRMS data by means of feature-based molecular networking (FBMN) analysis in the Global Natural Products Social Molecular Network (GNPS), together with the interpretation of the MS/MS data and comparison with the literature. The major constituents were glucuronides and glycosides of myricetin and quercetin, as well as epichatechin-3-O-gallate, catechin, epicatechin and gallic acid, all of them being reported for the first time in C. cowellii leaves. The leaf extract was also tested against various microorganisms, and it showed a strong antifungal effect against Candida albicans ATCC {"type":"entrez-nucleotide","attrs":{"text":"B59630","term_id":"2614348"}}B59630 (azole-resistant) (IC₅₀ 2.1 µg/mL) and Cryptococcus neoformans ATCC {"type":"entrez-nucleotide","attrs":{"text":"B66663","term_id":"2640641"}}B66663 (IC₅₀ 4.1 µg/mL) with no cytotoxicity (CC₅₀ > 64.0 µg/mL) on MRC-5 SV2 cells, determined by the resazurin assay. Additionally, the extract strongly inhibited COX-1 and COX-2 enzyme activity using a cell-free experiment in a dose-dependent manner, being significantly more active on COX-1 (IC₅₀ 4.9 µg/mL) than on COX-2 (IC₅₀ 10.4 µg/mL). The constituents identified as well as the pharmacological activities measured highlight the potential of C. cowellii leaves, increasing the interest in the implementation of conservation strategies for this species.     

Organometallic polymers. XV. Synthesis and characterization of some ferrocene-containing oxysilane polymers from bis(dimethylamino)silanes

Three bis(dimethylamino)silane monomers have been polymerized with 1,1'-bis-(hydroxymethyl)ferrocene to give ferrocene-containing polyoxysilanes I and II. They were bis(dimethylamino)dimethylsilane (III), bis(dimethylamino)diphenylsilane (IV), and 1,4-bis(N,N-dimethylaminodimethylsilyl)benzene (V). Mixing of the diol and III or IV at O°C followed by heating resulted in polymerization to higher molecular weights than when the monomers were initially mixed at higher temperatures. At higher temperatures the formation of monomeric cyclic products seriously competed with polymerization, and the five atom bridged derivative, 3-sila-2,4-dioxa-3,3diphenyl[5]ferrocenophane (VI) was isolated in good yield. The use of silane V, where cyclization is not expected to compete, led to higher polymer yields and molecular weights. The polymers were low melting and I (R = C₆H₅) could be cast into films and weak fibers were drawn from its melt. The polymers were sensitive to hydrolytic decomposition; those containing Si-CH₃ linkages were completely hydrolyzed in refluxing THF-H₂O (10:1) in 1 hr. The polymers were characterized by viscosity studies, gel-permeation chromatography, and infrared and NMR spectroscopy.     

Detection of paralytic shellfish poison by rapid cell bioassay: antagonism of voltage-gated sodium channel active toxins in vitro

Although cytotoxicity assays provide several advantages over mouse bioassays, sodium channel-blocking marine toxins, such as those associated with paralytic shellfish poison (PSP), require prolonged incubation periods of 24-48 h. This is in marked contrast to in vitro detection of sodium channel-enhancing marine toxins such as ciguatoxins or brevetoxins which can be accomplished in as few as 4-6 h. We developed a modified PSP cell bioassay that is as rapid as in vitro methods for sodium channel-enhancing toxins. The cell bioassay is based on a saxitoxin-dependent antagonism of the rapid in vitro effects of brevetoxin or ciguatoxin. Comparative analysis of naturally incurred PSP residues by both antagonism cell bioassay and the mouse bioassay demonstrated significant correlation. The simplicity, sensitivity, and enhanced kinetics of the new antagonism cell bioassay format provide the basis for development of a practical alternative to conventional mouse testing for PSP.     

Titanium(IV) citrate speciation and structure under environmentally and biologically relevant conditions

The water-soluble complexes of Ti(IV) with citrate are of interest in environmental, biological, and materials chemistry. The aqueous solution speciation is revealed by spectropotentiometric titration. From pH 3-8, given at least three equivalents of ligand, 3:1 citrate/titanium complexes predominate in solution with successive deprotonation of dangling carboxylates as the pH increases. In this range and under these conditions, hydroxo- or oxo-metal species are not supported by the data. At ligand/metal ratios between 1:1 and 3:1, the data are difficult to fit, and are consistent with the formation of such hydroxo- or oxo- species. Stability constants for observed species are tabulated, featuring log beta-values of 9.18 for the 1:1 complex [Ti(Hcit)](+), and 16.99, 20.41, 16.11, and 4.07 for the 3:1 complexes [Ti(H(2)cit)(3)](2-), [Ti(H(2)cit)(Hcit)(2)](4-), [Ti(Hcit)(2)(cit)](6-), and [Ti(cit)(3)](8-), respectively (citric acid = H(4)cit). Optical spectra for the species are reported. The complexes exhibit similar yet distinct spectra, featuring putative citrate-to-Ti(IV) charge-transfer absorptions (lambda(max) approximately 250-310 nm with epsilon approximately 5000-7000 M(-)(1) cm(-1)). The prevailing 3:1 citrate/titanium ratio in solution is supported by electrospray mass spectrometry data. The X-ray crystal structure of a fully deprotonated tris-citrate complex Na(8)[Ti(C(6)H(4)O(7))(3)].17H(2)O (1) (or Na(8)[Ti(cit)(3)].17H(2)O) that crystallizes from aqueous solution at pH 7-8 is reported. Compound 1 crystallizes in the triclinic space group P, with a = 11.634(2) Angstroms, b = 13.223(3) Angstroms, c = 13.291(3) Angstroms, V = 1982.9(7) Angstroms(3), and Z = 2.     

Chelates formed by a constrained bis(diphenylphosphino)xylene; the crystal structures of [FeCl2(anphos)] and [RhCl(CO)(anphos-monoxide)]

The indan derived diphosphine, cis-1,3-(diphenylphosphino)indan (anphos) is synthesised by the addition of Ph₂P(BH₃)Li to cis-1,3-dibromoindan followed by deprotection with diethylamine. Anphos readily forms the bicyclic chelates [RhCl(CO)(anphos)], [PtCl₂(anphos)], [PtCl(Me)(anphos)] and [FeCl₂(anphos)]. The crystal structures of [FeCl₂(anphos)] and the monoxide complex, [RhCl(CO)(anphosO)] have been determined. Reaction of the diphosphine with [Rh(acac)(CO)₂] under moderate hydroformylation conditions catalysed the formation of 1-heptanal and branched aldehydes from 1-hexene in a ratio of 1.5:1.