New synthetic approach to benzo/f/- and benzo/g/- phthalazines

Benzo/f/- and benzo/g/- phthalazine derivatives were synthesised from 2-naphthaldazine by means of a Lewis acid mediated cyclization with elimination of naphthalene.     

Accrediting PT/EQA providers to ISO/IEC 17043

After many years and having several different attempts for the accreditation of proficiency testing provider (PT provider), there is finally one stand-alone standard defining the requirements for the competence of PT providers and therefore an internationally harmonised basis for the accreditation of proficiency test providers. Since February 2010, the ISO/IEC 17043:2010 has replaced ISO/IEC Guide 43:1997 and ILAC G 13:2007. The philosophy of the standard about subcontracting work is different to this of the standards mostly used for accreditation like ISO/IEC 17025:2005 or ISO/IEC 17020:2004, etc. Besides the planning of the proficiency tests (PT), the performance evaluation and the authorisation of the PT reports the ISO/IEC 17043:2010 allows subcontracting for the rest of the work when providing PTs. This is a challenge for the assessors to judge about the competence of a PT provider. In numerous paragraphs, the standard sets very detailed requirements. Nevertheless, there is room for interpretation. For these cases, for example, contracts for subcontractors, procedure for the advisory board, minimum requirements for PT certificates, etc., some proposals are given to enable harmonised approach for the assessment of PT providers.     

Cycloartenol to Buxus alkaloids

Cycloartenol, a pentacyclic triterpene alcohol, has emerged as an obligatory intermediate in the biosynthesis of sterols in higher plants and algae. Cycloartenol has also been implicated in the biosynthesis of steroidal alkaloids. TheBuxus alkaloids, which have a pregnane-type framework, are considered to arise from cycloartenol by catabolic processes with nitrogen incorporation at an appropriate stage, although no biosynthetic studies appear to have been carried out. Thus, cycloartenol is an important substrate in nature for elaborating a rather large group of secondary metabolites. In an effort to mimic some of these processes in the laboratory, we have carried out transformations of cycloartenol intoBuxus alkaloids. New routes for side-chain degradation of cycloartenol and cyclolaudenol have been developed. A novel method for functionalization at C-16 has been worked out and a new strategy for regioselective oxygenation of 4-methyl has been exploited. Synthesis of buxandonine, cycloprotobuxine-F, cycloprotobuxine-A, cyclobuxophyllinine-M and 31-norcyclolaudenone have been achieved.     

Stereoselective approach to C-glycosylasparagines

In this paper we describe a simple and efficient approach to N-glycopeptide analogues that incorporate a ketomethylene unit in place of a native amide link. Key CC bond forming steps involve the stereocontrolled addition of a functionalised allylsilane to activated sugar derivatives and the asymmetric phase-transfer alkylation of a glycine imine. Utility of this chemistry is demonstrated by the synthesis of a C-analogue of the glycopeptide core found in nephritogenoside. Regioselective ozonolysis of a 1,5-diene is also described.     

Guide to Semi-Quantitative Non-Targeted Screening Using LC/ESI/HRMS

Non-targeted screening (NTS) with reversed phase liquid chromatography electrospray ionization high resolution mass spectrometry (LC/ESI/HRMS) is increasingly employed as an alternative to targeted analysis; however, it is not possible to quantify all compounds found in a sample with analytical standards. As an alternative, semi-quantification strategies are, or at least should be, used to estimate the concentrations of the unknown compounds before final decision making. All steps in the analytical chain, from sample preparation to ionization conditions and data processing can influence the signals obtained, and thus the estimated concentrations. Therefore, each step needs to be considered carefully. Generally, less is more when it comes to choosing sample preparation as well as chromatographic and ionization conditions in NTS. By combining the positive and negative ionization mode, the performance of NTS can be improved, since different compounds ionize better in one or the other mode. Furthermore, NTS gives opportunities for retrospective analysis. In this tutorial, strategies for semi-quantification are described, sources potentially decreasing the signals are identified and possibilities to improve NTS are discussed. Additionally, examples of retrospective analysis are presented. Finally, we present a checklist for carrying out semi-quantitative NTS.     

N-Bromosuccinimide-dibenzoyl peroxide/azabisisobutyronitrile: a reagent for Z- to E-alkene isomerization

N-Bromosuccinimide-dibenzoyl peroxide/azobisisobutyronitrile is used to carry out several types of Z- to E-alkene isomerizations. The NBS-bromination conditions are sufficient for both allylic bromination and alkene isomerization. When the allylic hydrogens are not available in substrates, only the isomerization of the alkene takes place. The present conditions for isomerization of carbon-carbon double bonds are mild and efficient.     

One-minute full-gradient HPLC/UV/ELSD/MS analysis to support high-throughput parallel synthesis

High-throughput parallel synthesis of library compounds for early drug discovery requires high-throughput analytical methods to confirm synthesis, identify reaction products, and determine purity. An ultrafast 1.0-min HPLC/UV/ELSD/MS method was developed and compared to our standard 2.5- and 5.0-min methods in order to determine if the faster method was appropriate to evaluate compound synthesis and determine purity. In addition to using standard test mixtures, a 400-member library produced by high-throughput parallel synthesis was used for comparing the various methods. Mass spectrometric detection was used for compound identification, while UV and ELSD data offered purity assessment. Compared to our longer separations, chromatographic separation achieved using the 1.0-min method was sufficient for compound evaluation and purity assessment. This ultrafast 1.0-min HPLC/UV/ELSD/MS method is expected to increase analytical throughput tremendously, provide important information faster, and reduce the overall cycle time from synthesis to screening.     

Efficient access to disubstituted exo-glycals. Application to the preparation of C-glycosyl compounds

Efficient methods of preparation of disubstituted exo-glycals by palladium cross-coupling reaction on the readily available dibromo exo-glycal and methoxycarbonyl exo-glycal have been developed. Hydrogenation of these new monosubstituted and disubstituted exo-glycals proceeded with a high stereocontrol and led to original C-glycosyl compounds.     

Methanol dehydration to produce dimethyl ether over g-Al2O3

Summary The kinetic data of about 150 points for methanol dehydration were obtained at the temperature of 240~270^oC, the GHSV of 25,000~120,000 (mL/g_cat./h) and under atmospheric pressure. The data were fitted into six plausible equations. The kinetic equation derived from the molecular adsorption of methanol on two sites fit the kinetic data best, however, that from the dissociative adsorption of methanol could not be safely ruled out. The activation energy of 114.7 kJ/mol for methanol dehydration on γ-Al₂O₃ was obtained from the kinetic analysis.     

Response functions of CaSO4/Dy/ and BaSO4/Dy/ thermoluminescent detectors to gamma radiation

The authors synthesized BaSO₄/Dy/ phosphors and measured the energy dependence of their sensitivity.     

Oxidation process of MoOxCy to MoO3: kinetics and mechanism

A non-isothermal kinetic study of the oxidation of “carbon-modified MoO₃” in the temperature range of 150-550°C by simultaneous TGA-DTA was investigated. During the oxidation process, two thermal events were detected, which are associated with the oxidation of carbon in MoO_xC_y and MoO₂ to MoO₃. The model-free and model-fitting kinetic approaches have been applied to TGA experimental data. The solid state-kinetics of the oxidation of MoO_xC_y to MoO₃ is governed by F1 (unimolecular decay), which suggests that the reaction is of the first order with respect to oxygen concentration. The constant (Ea)_α value (about 115±5 kJ/mol) for this first stage can be related to the nature of the reaction site in the MoO₃ matrix. This indicates that oxidation occurs in well-defined lattice position sites (energetically equivalent). On the other hand, for the second stage of oxidation, MoO₂ to MoO₃, the isoconversional analysis shows a complex (Ea)_α dependence on (α) and reveals a typical behavior for competitive reaction. A D2 (two-dimensional diffusion) mechanism with a variable activation energy value in the range 110-200 kJ/mol was obtained. This can be interpreted as an inter-layer oxygen diffusion in the solid bulk, which does not exclude other simultaneous mechanism reactions.     

Characterization of Cu-ZnO-Cr2O3/SiO2 catalysts and application to dehydrogenation of 2-butanol to 2-butanone

The Cu-ZnO-Cr₂O₃/SiO₂ catalysts were prepared by impregnation method, which exhibited high activity for the dehydrogenation of 2-butanol to 2-butanone. These catalysts were characterized by means of XRD, EPR and BET. The experimental results indicated that (i) the valence states of copper play a key role, (ii) groups of copper atoms were the main active sites in this reaction, and (iii) copper oxide would lead to the condensation product of 5-methyl-3-heptanone.     

Nitrogen cold plasma treatment stabilizes Cu0/Cu+ electrocatalysts to enhance CO2 to C2 conversion

Cu-based materials are ideal catalysts for CO₂ electrocatalytic reduction reaction(CO₂RR) into multicarbon products.However,such reactions require stringent conditions on local environments of catalyst surfaces,which currently are the global pressing challenges.Here,a stabilized activation of Cu⁰/Cu⁺-onAg interface by N₂ cold plasma treatment was developed for improving Faradaic efficiency(FE) of CO₂RR into C2 products.The resulta...     

AuCl3/AgSbF6-catalyzed rapid epoxide to carbonyl rearrangement

An efficient epoxide to carbonyl rearrangement using catalytic AuCl₃/AgSbF₆ has been presented. The reactions are fast and high yielding. β-Hydrogen migration takes place exclusively when hydrogen and methyl or substituted methyl groups are present at β-carbon of epoxide. When phenyl/acetyl/benzoyl and hydrogen are available at same carbon atom, migration of the former is preferred over the latter.     

Highly Z/E stereoselective approach to β-iodo aza Morita-Baylis-Hillman adducts

A multicomponent reaction between sulfonyl-protected imines, magnesium iodide, and acetylenic esters or ketones is described. The resulting β-iodo aza Morita-Baylis-Hillman adducts were obtained in good yields and excellent Z/E stereoselectivities. The reaction showed good tolerance for sulfonyl protecting groups, as well as for acetylenic ketones and esters. This work presents the first synthetic approach to β-iodo aza Morita-Baylis-Hillman adducts.     

A convenient synthesis of iminosugar-C-glycosides via organometallic addition to N-benzyl-N-glycosylhydroxylamines

N-Benzyl-N-glycosylhydroxylamines were prepared in very good yield via condensation of furanoses and pyranoses with N-benzylhydroxylamine at 110°C for 30 min under solvent-free conditions. These anomeric sugar-hydroxylamines exist in equilibrium with the open-chain nitrone form. In fact upon treatment with various organometallic reagents, the corresponding adducts were obtained with good to high diastereoselectivity. These adducts were converted into iminosugar-C-glycosides by reductive dehydroxylation and intramolecular cyclization.     

Sequential Pd/Ru-catalysed allenylation/olefin metathesis/1,3-dipolar cycloaddition route to novel heterocycles

A novel sequential palladium/ruthenium-catalysed four component process is described involving carbonylation of an aryl/heteroaryl iodide followed by allenylation to generate (π-allyl) palladium species which are intercepted by nitrogen nucleophiles to afford 1,6-dienes. Subsequent Ring-Closing Metathesis (RCM) affords C-acyl-N-heterocycles in good yield. These heterocycles proved to be active dipolarophiles in sequential and cascade 1,3-dipolar cycloaddition reactions (1,3-DC) as exemplified by reactions with nitrones and azomethine ylides.