1,721,317 research outputs found
Formal total synthesis of eleutherobin
No full textEleutherobin is a cytotoxic agent with microtubule stabilizing properties. A formal total synthesis of eleutherobin was accomplished by accessing a key-intermediate reported by Danishefsky and co-workers in their 1998 synthesis of the natural product. The key-step of our strategy, used for obtaining the [8.4.0] fused bicyclic ring system, is a ring-closing metathesis (RCM) reaction of a densely functionalized diene under forcing conditions, using Grubbs' second-generation catalyst
A formal total synthesis of eleutherobin and synthesis of simplified analogues using the ring-closing-metathesis reaction (RCM)
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Natural products with Taxol®-like anti-tumour activity: Synthetic approaches to the Sarcodictyins and Eleutherobin
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Supramolecular Catalysis: Investigation of Acid-Base Interactions to Promote the Assembly of Monodentate P-Ligands
No full textIn recent years, monodentate phosphorus ligands have held center stage in asymmetric catalysis, thanks to their outstanding activity, selectivity and convenient, fast and practical synthesis. Bidentate ligands are of course still very important, even though their synthesis is usually more tedious and expensive. Supramolecular bidentate ligands, based on the assembly of monodentate ligands possessing complementary functionalities, combine the essential features of bidentate ligands (preorganization and rigidity) with the advantages of monodentate ligands (practicality). Metal-ligands interactions (Reek, van Leeuwen, Takacs), hydrogen bonds (Breit, Reek, Nishibayashi), and ionic interactions (van Leeuwen) have been so far the main non-covalent forces used to promote the recognition of monodentate ligands.1
Here we report two new approaches for the assembly of monodentate phosphites in Rh-complexes: i) arene - interactions, using a binary combination of an electron-poor (with a perfluroarene or dinitroarene unit) and an electron-rich ligand (with a methoxyarene unit); ii) acid-base interactions, using a binary combination of an acidic (bearing a carboxylic acid) and a basic (bearing a tertiary amine) chiral binaphtholic phosphite.
The preferential formation of the Rh-heterocomplexes was investigated by 31P-NMR and the ligand binary combinations were also tested in the Rh-catalyzed asymmetric hydrogenation of functionalized olefins (methyl acetamidoacrylate and dimethyl itaconate). In both cases, enhanced ee’s (up to 99 %) were obtained using selected heterocobinations with respect to the corresponding homocombinations.
We thank MiUR for a postdoctoral fellowship (to L. Pignataro, PRIN prot. 2006030449), the European Commission [RTN Network (R)Evolutionary Catalysis MRTN-CT-2006-035866] for financial support and for a predoctoral fellowship (to B. Lynikaite) and a postdoctoral fellowship (to J. Cvengroš). C. Gennari gratefully acknowledges Merck Research Laboratories for the Merck's Academic Development Program Award
Synthesis of the C15-C23 fragment of dictyostatin using a highly stereoselective Carreira alkynylation
No full textA straightforward synthesis of the C15–C23 fragment of dictyostatin has been achieved by a highly stereoselective Carreira
alkynylation between alkyne 1 and aldehyde 2, followed by three chemoselective reductions
Aspetti regolatori dei radiofarmaci
No full textLegislative decree 219/06 defines radiopharmaceuticals as «any medicinal product which, when ready for use, contains one or more radionuclides (radioactive isotopes) included for a medicinal purpose». Nowadays it is possible to make a distinction, regulatory wise, between radiopharmaceuticals compounded in hospitals and radiopharmaceuticals produced in industries. Many open and controversial issues must be faced to allow compliance with the current European and national legislation. Among them it is important to underline the high number of radiopharmaceuticals on the market from before 1992, did not yet receive the Marketing Authorization (MA); the production of some radiopharmaceuticals in hospitals with cyclotron, like for example 18-FDG, as officinal formula; the difficulties of the nuclear medicines centres in fulfilling the national Good Compounding Practice of radiopharmaceuticals preparations; a still confused scenario for experimental radiopharmaceuticals
A highly stereoselective synthesis of the C10-C23 fragment of (-)-dictyostatin
No full textA highly stereoselective synthesis of the C10–C23 fragment of (-)-dictyostatin has been achieved using a Carreira alkynylation and a Marshall-Tamaru allenylzinc addition as key-steps
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