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Biomedical subjects

Oscar Pàmies

Publications and source records attributed to Oscar Pàmies.

13 recordsLinked to original sources
PubMed2007

First chiral phosphoroamidite-phosphite ligands for highly enantioselective and versatile Pd-catalyzed asymmetric allylic substitution reactions.

[reaction: see text] A series of phosphite-phosphoroamidite ligands, derived from readily available d-xylose, has been successfully applied for the first time in the Pd-catalyzed allylic substitution of several substrates with different steric and electronic properties, with high enantioselectivities (ee's up to 98) and activities in standard conditions.

Journal Article↗
PubMed2006

Screening of a modular sugar-based phosphite ligand library in the asymmetric nickel-catalyzed trialkylaluminum addition to aldehydes.

We synthesized a modular sugar-based phosphite ligand library for the Ni-catalyzed trialkylaluminum addition to aldehydes. This library has been designed to rapidly screen the ligands to uncover their important structure features and determine the scope of the phosphite ligands in this catalytic reaction. After systematic variation of the sugar backbone, the substituents at the phosphite moieties, and the flexibility of the ligand backbone, the monophosphite ligand 1,2:5,6-di-O-isopropylidene-3-O-((3,3';5,5'-tetra-tert-butyl-1,1'-biphenyl-2,2'-diyl)phosphite)-alpha-D-glucofuranose 1c was found to be optimal, yielding high activities and enantioselectivities (ee's up to 94%) for several aryl aldehydes.

Journal Article↗
PubMed2005

Chiral phosphite-oxazolines: a new class of ligands for asymmetric Heck reactions.

[chemical reaction: see text]. A series of phosphite-oxazoline ligands, derived from readily available D-glucosamine, have been used for the first time in the palladium-catalyzed Heck reaction of several substrates with high regio- and enantioselectivities (ee's up to 99%) and improved activities in standard conditions.

Catalysis↗
PubMed2005

Palladium-diphosphite catalysts for the asymmetric allylic substitution reactions.

[structure: see text] We have designed a series of diphosphite ligands to study the effect of the backbone, the size of the chelate ring, and the substituents of the biphenyl moieties and to determine the scope of this type of ligand in the Pd-catalyzed asymmetric substitution reactions of different types of substrates. Good-to-excellent activities and enantioselectivities have been obtained for disubstituted linear substrate 11 (TOF's up to >2000 mol x (mol x h)(-1), ee values up to 99%) and cyclic substrate 14 (TOF up to 285 mol x (mol x h)(-1), ee values up to 92%). However, these ligands are inadequate for the Pd-catalyzed allylic alkylation of monosubstituted linear substrates because they provide low enantioselectivities.

Journal Article↗
PubMed2005

Kinetic resolution and chemoenzymatic dynamic kinetic resolution of functionalized gamma-hydroxy amides.

[reaction: see text] An efficient kinetic resolution of racemic gamma-hydroxy amides 1 was performed via Pseudomas cepacia lipase (PS-C)-catalyzed transesterification. The enzyme PS-C tolerates both variation in the chain length and different functionalities giving good to high enantioselectivity (E values of up to >250). The combination of enzymatic kinetic resolution with a ruthenium-catalyzed racemization led to a dynamic kinetic resolution. The use of 2,4-dimethyl-3-pentanol as a hydrogen source to suppress ketone formation in the dynamic kinetic resolution yields the corresponding acetates in good yield and good to high enantioselectivity (ee's up to 98%). The synthetic utility of this procedure was illustrated by the practical synthesis of the versatile intermediate gamma-lactone (R)-5-methyltetrahydrofuran-2-one.

Journal Article↗
PubMed2005

New phosphite-oxazoline ligands for efficient Pd-catalyzed substitution reactions.

We have designed and synthesized a new family of readily available highly modular phosphite-oxazoline ligands for the Pd-catalyzed asymmetric allylic substitution reactions. The introduction of a pi-acceptor flexible bulky biphenyl phosphite moiety in the ligand design is highly adventitious in the product outcome. Thus, this ligand series affords excellent reaction rates (TOF's up to >2400 mol.(mol.h)-1) and enantioselectivities (ee's up to >99%) and, at the same time, shows a broad scope for different substrate types.

Journal Article↗
PubMed2004

Chemoenzymatic dynamic kinetic resolution.

During the past decade a new concept has appeared in asymmetric catalysis involving the combination of a biocatalyst and a chemocatalyst in one 'pot' leading to efficient deracemization via dynamic kinetic resolution (DKR). Here, we outline the different strategies that have been developed for efficient chemoenzymatic DKR, in particular the powerful combination of an enzyme and a metal catalyst.

Biotransformation↗
PubMed2003

An efficient route to chiral alpha- and beta-hydroxyalkanephosphonates.

Enzymatic kinetic resolution of alpha- and beta-hydroxyphosphonates in combination with ruthenium-catalyzed alcohol isomerization led to a successful dynamic kinetic resolution. A variety of racemic hydroxyphosphonates were efficiently transformed to the corresponding enantiomerically pure acetates (ee up to 99% and yield up to 87%).

Journal Article↗
PubMed2003

Combined metal catalysis and biocatalysis for an efficient deracemization process.

Driven by the demand to enhance the economic balance of chemical processes, the transformation of a racemate into a single stereoisomer (the deracemization process) is one of the most important areas of research. The recent development of the combined use of enzyme and metal catalysis has led to efficient deracemization processes. Dynamic kinetic resolution and cyclic deracemization processes have shown particular promise in this area.

Alcohols↗
PubMed2002

Chemoenzymatic dynamic kinetic resolution of beta-halo alcohols. An efficient route to chiral epoxides.

Enzymatic resolution of beta-chloro alcohols in combination with ruthenium-catalyzed alcohol isomerization led to a successful dynamic kinetic resolution (conversion up to 99% and ee up to 97%). The efficiency of the DKR is dramatically reduced when beta-bromo alcohols are used. The presence of the bromo substituent causes decomposition of the ruthenium catalysts, which triggers the progressive deactivation of the enzyme. The synthetic utility of this procedure has been illustrated by the practical synthesis of different chiral epoxides.

Journal Article↗
PubMed2002

Enzymatic kinetic resolution and chemoenzymatic dynamic kinetic resolution of delta-hydroxy esters. An efficient route to chiral delta-lactones.

A successful kinetic resolution of a racemic mixture of delta-hydroxy esters 1 was obtained via lipase-catalyzed transesterification (E value up to 360). The combination of the enzymatic kinetic resolution with a ruthenium-catalyzed alcohol racemization led to an efficient dynamic kinetic resolution (ee up to 99% and conversion up to 92%). The synthetic utility of this procedure was illustrated by the practical syntheses of delta-lactones (R)-6-methyl- and (R)-6-ethyl-tetrahydropyran-2-one and (S)-5-(tert-butyldimethylsiloxy)heptanal. The former are important building blocks in the synthesis of natural products and biologically active compounds, and the latter is a key intermediate in the synthesis of widely used commercial insecticide Spinosyn A.

Aspergillus↗