1,720,998 research outputs found
Methylsulfinyl (Dimsyl) Anion as Umpolung Catalyst for the Chemoselective Cross Benzoin Reaction of α-Diketones with Aldehydes
No full textMicroreattori monolitici polistirenici funzionalizzati con carbeni N‐eterociclici per lo studio di reazioni di unpolung stereoselettive
No full textOxidative coupling of aldehydes with alcohol for the synthesis of esters promoted by polystyrene-supported N-Heterocyclic Carbene: Unravelling the solvent effect on the catalyst behavior using NMR relaxation
Full text linkHeterogeneous organocatalysts hold great potential as they offer practical advantages in terms of purification and reusability compared with the homogeneous counterpart. A puzzling aspect is the solvent effect on their catalytic performance. Here we propose a new approach whereby T1/T2 NMR relaxation measurements are used to evaluate the strength of solvent–surface interactions in the polystyrene-supported N-heterocyclic carbene-promoted oxidation of aldehydes. The results reveal that solvents with high surface affinity lead to a decrease in catalyst activity
Derivatization of biomass-derived 5-(hydroxymethyl)furfural through heterogeneous NHC oxidative catalysis
No full textNucleophilic and electrophilic double aroylation of chalcones with benzils promoted by the dimsyl anion as a route to all carbon tetrasubstituted olefins.
No full textSupported organocatalysis as a greener alternative in the production of fine chemicals
No full textOrganocatalysis is a useful tool for organic synthesis and plays a key role in many sectors of the chemical business, most notably in the pharmaceutical industry and drug discovery, as well as for the production of many modern commodities in the food, agrochemical and cosmetic businesses. Since the use of potentially toxic metal species is intrinsically avoided, organocatalysis can lead to more sustainable processes. The majority of organocatalytic processes currently being investigated are run as homogeneous catalytic reactions, whereby the catalyst is dissolved in the reactive mixture. The major drawback of this approach is in the laborious, expensive and energy-intensive procedures needed to separate the catalyst from the reaction products which, in many cases, is unfeasible or may lead to catalyst degradation with consequent waste of valuable material, with impact on process sustainability.
In this work we show a promising way to carry out organocatalytic processes by adopting an approach whereby the organocatalyst is immobilised onto a solid support, hence made insoluble, which has advantages both in terms of avoiding energy-intensive distillation procedures as well as enabling catalyst recycling and reuse and potentially use of such materials for fixed-bed continuous processes. We show that in some cases the activity of the immobilised organocatalyst is comparable to that of the homogeneous counterpart. The results reported here have important implication for the development of greener and more sustainable routes for the production of fine and specialty chemicals, which may pave the way to new developments, especially in the pharmaceutical industry
Phenyl-substituted aminomethylene-bisphosphonates inhibit human P5C reductase and show antiproliferative activity against proline-hyperproducing tumour cells
No full textIn certain cancers, such as breast, prostate and some lung and skin cancers, the gene for the enzyme catalysing the second and last step in proline synthesis, δ1-pyrroline-5-carboxylate (P5C) reductase, has been found upregulated. This leads to a higher proline content that exacerbates the effects of the so-called proline-P5C cycle, with tumour cells effectively using this method to increase cell survival. If a method of reducing or inhibiting P5C reductase could be discovered, it would provide new means of treating cancer. To address this point, the effect of some phenyl-substituted derivatives of aminomethylene-bisphosphonic acid, previously found to interfere with the catalytic activity of plant and bacterial P5C reductases, was evaluated in vitro on the human isoform 1 (PYCR1), expressed in E. coli and affinity purified. The 3.5-dibromophenyl- and 3.5-dichlorophenyl-derivatives showed a remarkable effectiveness, with IC50 values lower than 1 μM and a mechanism of competitive type against both P5C and NADPH. The actual occurrence in vivo of enzyme inhibition was assessed on myelogenous erythroleukemic K562 and epithelial breast cancer MDA-MB-231 cell lines, whose growth was progressively impaired by concentrations of the dibromo derivative ranging from 10−6 to 10−4M. Interestingly, growth inhibition was not relieved by the exogenous supply of proline, suggesting that the effect relies on the interference with the proline-P5C cycle, and not on proline starvation
One-pot, two-step desymmetrization of symmetrical benzils catalyzed by the methylsulfinyl (Dimsyl) anion
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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