Author: Andrea Hamza

0000000001302136

AUTHOR

Andrea Hamza

showing 14 related works from this author

Stereocontrol in Diphenylprolinol Silyl Ether Catalyzed Michael Additions : Steric Shielding or Curtin-Hammett Scenario?

2017

The enantioselectivity of amine-catalyzed reactions of aldehydes with electrophiles is often explained by simple steric arguments emphasizing the role of the bulky group of the catalyst that prevents the approach of the electrophile from the more hindered side. This standard steric shielding model has recently been challenged by the discovery of stable downstream intermediates, which appear to be involved in the rate-determining step of the catalytic cycle. The alternative model, referred to as Curtin-Hammett scenario of stereocontrol, assumes that the enantioselectivity is related to the stability and reactivity of downstream intermediates. In our present computational study, we examine th…

Steric effectsmechanismProtonation010402 general chemistry01 natural sciencesBiochemistryDFTCatalysisCatalysisColloid and Surface ChemistryComputational chemistryOrganic chemistryReactivity (chemistry)organocatalysista116stereocontrol010405 organic chemistryChemistryGeneral Chemistry0104 chemical sciencesCatalytic cyclekineticsElectrophileMichael reactionStereoselectivityESI-MS screening

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Stereoelectronic Requirements for Optimal Hydrogen-Bond-Catalyzed Enolization

2011

Protein crystallographic analysis of the active sites of enolizing enzymes and structural analysis of hydrogen-bonded carbonyl compounds in small molecule crystal structures, complemented by quantum chemical calculations on related model enolization reactions, suggest a new stereoelectronic model that accounts for the observed out-of-plane orientation of hydrogen-bond donors (HBDs) in the oxyanion holes of enolizing enzymes. The computational results reveal that the lone-pair directionality of HBDs characteristic for hydrogen-bonded carbonyls is reduced upon enolization, and the enolate displays almost no directional preference for hydrogen bonding. Positioning the HBDs perpendicular to the…

Models MolecularHydrogen bondOrganic ChemistryHydrogen BondingStereoisomerismOxyanionGeneral ChemistryCrystal structureKeto–enol tautomerismKetonesCarbon-Carbon Double Bond IsomerasesPhotochemistrySmall moleculeCatalysisMitochondriaCatalysischemistry.chemical_compoundCrystallographychemistryHumansThermodynamicsDensity functional theoryOxyanion holeAlgorithmsChemistry - A European Journal

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Mukaiyama–Michael Reactions with trans-2,5-Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions, Not from …

2013

The scope of the enantioselective Mukaiyama-Michael reactions catalyzed by trans-2,5-diphenylpyrrolidine has been expanded to include both α- and β-substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C-C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals…

chemistry.chemical_classificationSteric effectsStereochemistryOrganic ChemistryIntermolecular forceEnantioselective synthesisIminiumGeneral ChemistryCatalysisTransition statechemistryComputational chemistryOrganocatalysisNon-covalent interactionsStereoselectivityta116Chemistry: A European journal

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ChemInform Abstract: Mukaiyama-Michael Reactions with trans-2,5-Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent In…

2014

The 2,5-diphenylpyrrolidine-catalyzed enantioselective Mukaiyama—Michael reaction between substituted furans and enals is studied.

Steric effectschemistry.chemical_classificationAddition reactionChemistryOrganocatalysisEnantioselective synthesisNon-covalent interactionsGeneral MedicineCombinatorial chemistryCatalysisChemInform

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Folding Patterns in a Family of Oligoamide Foldamers

2015

A series of small, unsymmetrical pyridine-2,6-dicarboxylamide oligoamide foldamers with varying lengths and substituents at the end groups were synthetized to study their conformational properties and folding patterns. The @-type folding pattern resembled the oxyanion-hole motifs of enzymes, but several alternative folding patterns could also be characterized. Computational studies revealed several alternative conformers of nearly equal stability. These folding patterns differed from each other in their intramolecular hydrogen-bonding patterns and aryl-aryl interactions. In the solid state, the foldamers adopted either the globular @-type fold or the more extended S-type conformers, which w…

StereochemistryHydrogen bondChemistryOrganic Chemistrycrystal growthSolid-stateFoldamerGeneral ChemistryCatalysisoligomerizationCrystallographyLiquid stateIntramolecular forceprotein foldinghydrogen bondsMoleculeProtein foldingfoldamersConformational isomerismta116Chemistry: A European Journal

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