The allylic amination of acetates and carbonates affords dehydro-beta-aminoesters, which are useful precursors of biologically active compounds. The uncatalyzed reaction proceeds via a S(N)2' mechanism. On the other hand, under palladium-catalyzed conditions, the reaction shows a strong solvent-dependent regiocontrol, affording exclusively one of the two possible regioisomers with complete transfer of chirality from the substrates to the products.
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Synthesis of α/β dipeptides containing linear or cyclic α-dehydro-β-amino acids as scaffolds for bioactive compounds.
Amino Acids
November 2019
Department of Chemistry "G. Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy.
The synthesis of α/β dipeptides containing linear or cyclic α-dehydro-β-amino acids has been performed starting from alkylidene acetacetamides, which were obtained from α-amino esters via Ir-catalyzed allylic amination. Differently hindered carbonates were synthesized via a protocol involving chemoselective Luche's reduction, acylation, and allylic amination. Depending on the nature of the selected α-amino acid, we observed strong influence on the product regiochemistry due to the carbonate size and the amino-acid side chain.
View Article and Find Full Text PDFModulation of αvβ₃- and α₅β₁-integrin-mediated adhesion by dehydro-β-amino acids containing peptidomimetics.
Eur J Med Chem
August 2013
Department of Chemistry G.Ciamician, University of Bologna, Via Selmi 2, 40126 Bologna, Italy.
A novel class of low molecular weight ligands of αvβ₃ and α₅β₁ integrins, that possess a dehydro-β-amino acid as conformationally constrained core, linked to the pharmacophoric moieties mimicking the RGD recognition sequence, have been synthesized through a very simple protocol. Cell adhesion assays and integrin-mediated signaling activation experiments suggested a good affinity of these compounds toward both integrin receptors. Moreover, further elongation with two glycine units allowed to obtain an excellent dual inhibitor.
View Article and Find Full Text PDFA straightforward route to enantiopure 2-substituted-3,4-dehydro-β-proline via ring closing metathesis.
Amino Acids
August 2011
Department of Chemistry, G. Ciamician, University of Bologna, Via Selmi 2, 40126, Bologna, Italy.
The synthesis of unusual cyclic amino acids, that may be envisaged as proline analogs, is an area of great interest for their potential applications as scaffolds for the design of bioactive peptidomimetics or units for the creation of novel foldamers. We have carried out the preparation of cyclic dehydro-β-amino acids starting from allylic carbonates via a two-step allylic amination/ring closing metathesis (RCM) protocol. The introduction of the allylamino moiety has been carried out either without a catalyst, through an S(N)2' reaction, or in the presence of iridium complexes.
View Article and Find Full Text PDFSynthesis of dehydro-beta-amino esters via highly regioselective amination of allylic carbonates.
Org Lett
June 2008
Department of Chemistry G Ciamician, University of Bologna, Bologna, Italy.
The allylic amination of acetates and carbonates affords dehydro-beta-aminoesters, which are useful precursors of biologically active compounds. The uncatalyzed reaction proceeds via a S(N)2' mechanism. On the other hand, under palladium-catalyzed conditions, the reaction shows a strong solvent-dependent regiocontrol, affording exclusively one of the two possible regioisomers with complete transfer of chirality from the substrates to the products.
View Article and Find Full Text PDFRh-catalyzed asymmetric hydrogenation of prochiral olefins with a dynamic library of chiral TROPOS phosphorus ligands.
Chemistry
November 2005
Dipartimento di Chimica Organica e Industriale, Centro di Eccellenza C.I.S.I. Università degli Studi di Milano, Istituto di Scienze e Tecnologie Molecolari del CNR, Via G. Venezian 21, 20133 Milano, Italy.
A library of 19 chiral tropos phosphorus ligands, based on a flexible (tropos) biphenol unit and a chiral P-bound alcohol (11 phosphites) or secondary amine (8 phosphoramidites), was synthesized. These ligands were screened, individually and as a combination of two, in the rhodium-catalyzed asymmetric hydrogenation of dehydro-alpha-amino acids, dehydro-beta-amino acids, enamides and dimethyl itaconate. ee values up to 98% were obtained for the dehydro-alpha-amino acids, by using the best combination of ligands, a phosphite [4-P(O)2O] and a phosphoramidite [13-P(O)2N].
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