17392-83-5Relevant articles and documents
A model for the enatioselective hydrogenation of pyruvate catalysed by alkaloid-modified platinum
Simons, K. E.,Meheux, P. A.,Griffiths, S. P.,Sutherland, I. M.,Johnston, P.,et al.
, p. 465 - 474 (1994)
A LEED and XPS study of the adsorption of naphthalene, quinoline, and 10,11-dihydrocinchonidine on Pt(111) at 300K has shown that only naphthalene forms an ordered ad-layer, and that quinoline and the alkaloid adsorb in a disordered state and without decomposition.These experiments do not support the hypothesis of ordered adsorption of alkaloid that forms the basis of the template model for the interpretation of enantioselectivity in Pt-catalysed pyruvate hydrogenation.The model is accordingly reviewed.Molecular modelling studies show that a highly specific 1:1 interaction between cinchonidine (or cinchonine) and pyruvate interprets the observed sense of the enantioselectivity, provided relative energy relationships derived for purely intermolecular interactions are valid for the same molecules in the absorbed state.Moreover, the 'product' of this 1:1 interaction is a satisfactory precursor to the H-bonded state considered responsible for the greatly enhanced rate that always accompanies enantioselective reaction over cinchona-modified Pt.The previously published dependencies of optical yield on (a) surface concentration of adsorbed cinchonidine modifier, and (b) modifier composition for mixtures of quinine and quinidine, are shown to be in quantitative agreement with the proposed 1:1 interaction model and at variance with the ordered adsorption model.Catalysts modified and used under strictly anaerobic conditions show negligible activity and enantioselectivity demonstrating that oxygen plays a crucial role in successful catalyst preparation.XPS experiments confirm that adsorption of cinchonidine from air-saturated ethanolic solution on Pt(111) provides an adlayer containing both alkaloid and adsorbed oxygen. (S)-(-)-1-benzyl-pyrrolidine-2-methanol, various configurations of ephedrine, D- and L-histidine and the methyl esters of D- and L-tryptophan have been examined as modifiers for supported Pt.Although there is evidence that these compounds can provide chiral direction to pyruvate hydrogenation, rate enhancement is slight and enantioselectivity is correspondingly low.
High enantioselectivity in the asymmetric hydrogenation of ketones by a supported Pt nanocatalyst on a mesoporous modified MCM-41 support
Basu, Susmit
, p. 634 - 638 (2015)
Catalysts containing metal nanotubes were prepared by the adsorption of platinum metal nanotubes onto functionalized and modified silica surfaces (MCM-41 and fumed silica). (3-Chloropropyl)trimethoxysilane and cinchonidine were used for functionalization and modification, respectively. Potassium chloroplatinate was used as the metal precursor to impregnate platinum metal nanotubes on the pretreated functionalized and modified silica surfaces. The solid catalysts were characterized by ESEM, TEM, EDAX, and XPS. The MCM-41 supported platinum nanotube catalyst showed >98% to ～100% enantioselectivity towards the hydrogenation of a range of pharmaceutically important chemicals such as methyl pyruvate, ethyl pyruvate, and acetophenone with nearly full conversion.
Asymmetric hydrogenation of α-ketoesters over finely dispersed polymer-stabilized platinum clusters
Zuo, Xiaobin,Liu, Hanfan,Liu, Manhong
, p. 1941 - 1944 (1998)
Finely dispersed polyvinylpyrrolidone-stabilized platinum clusters (PVP-Pt) modified with cinchonidine catalyze the asymmetric hydrogenation of α-ketoesters, giving enantiomeric excesses in favour of R-(+)-methyl lactate up to 97.6%. The reaction is demonstrated to be structure insensitive and runs best over a tiny cluster with a mean size of 1.4 nm, which is quite different from conventional supported catalysts.
Synthesis of alkyl (R)-lactates and alkyl (S,S)-O-lactyllactates by alcoholysis of rac-lactide using Novozym 435
Jeon, Nan Young,Ko, Sung-Jin,Won, Keehoon,Kang, Han-Young,Kim, Bum Tae,Lee, Yeon Soo,Lee, Hyuk
, p. 6517 - 6520 (2006)
Enzymatic alcoholysis of rac-lactide for kinetic resolution was carried out in organic solvents. Effects of organic solvent, reaction temperature, and alcohol as a nucleophile were also investigated in Novozym 435-catalyzed alcoholysis of rac-lactide. Both alkyl (R)-lactate and alkyl (S,S)-O-lactyllactate were simultaneously obtained in high yields (>45%) and high enantiopurities (>97% ee) through Novozym 435-catalyzed ring-opening of rac-lactide and subsequent enantioselective alcoholysis of the resultant alkyl O-lactyllactate.
New insights into the relationship between conversion and enantioselectivity for the asymmetric hydrogenation of alkyl pyruvate
Li, Xiabao,Wells, Richard P.K.,Wells, Peter B.,Hutchings, Graham J.
, p. 653 - 656 (2004)
The initial transient period in the enantioselective hydrogenation of alkyl pyruvate esters is probed using the sequential reactions of ethyl and methyl pyruvate. The reaction of methyl pyruvate, subsequent to the hydrogenation of ethyl pyruvate, led to a higher e.e. when compared to the coreaction of these reactants, or prehydrogenation with methyl pyruvate followed by reaction of ethyl pyruvate. The initial transient effect, in which e.e. increases with conversion, is observed in both periods of the sequential reaction and the origin of this effect is discussed.
New diphosphinite ligands derived from mannitol for rhodium catalyzed enantioselective hydrogenation of ketones
Naili, Said,Suisse, Isabelle,Mortreux, André,Agbossou, Francine,Ait Ali, Mustapha,Karim, Abdallah
, p. 2867 - 2870 (2000)
We have developed new electron rich chiral bisphosphinites from mannitol. The new ligands have been found to be efficient chiral auxiliaries for rhodium catalyzed hydrogenation of functionalized ketones leading to hydroxy compounds in up to 86% ee. (C) 2000 Elsevier Science Ltd.
Enhancing Effect of Residual Capping Agents in Heterogeneous Enantioselective Hydrogenation of α-keto Esters over Polymer-Capped Pt/Al2O3
Chung, Iljun,Song, Byeongju,Kim, Jeongmyeong,Yun, Yongju
, p. 31 - 42 (2021)
Heterogeneous enantioselective catalysis is considered a promising strategy for the large-scale production of enantiopure chemicals. In this work, polymer-capped Pt nanocatalysts having a uniform size were synthesized using poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) and supported on γ-Al2O3. After a facile heat treatment process, their catalytic performance for enantioselective hydrogenation of α-keto esters, a structure-sensitive reaction, was investigated. The presence of residual capping agents on the Pt surface often perturbs the adsorption of reacting species and reduces performance in structure-sensitive reactions. However, the 1 wt % PVP-Pt/Al2O3 catalyst exhibited an enhancement in both activity and enantioselectivity compared to a reference Pt/Al2O3 catalyst prepared by wet impregnation. Under optimized reaction conditions, the cinchonidine-modified PVP-Pt/Al2O3 gave an enantiomeric excess of 95% for the enantioselective hydrogenation of methyl pyruvate despite the low Pt loading. We demonstrate that depending on the type of polymers, the residual capping agents can lead to site-selective blockage of the Pt surface, that is, defects or terraces. Quantitative and qualitative analyses also show that the noticeable improvement in enantioselectivity is attributed to the stable adsorption of chiral modifiers on selectively exposed Pt terrace sites. The findings of this work provide a promising strategy to prepare metal nanoparticles having selectively exposed sites and offer insights into the enhancing effect of residual capping agents on the catalytic properties in structure-sensitive reactions.
Molecular Insights into the Ligand-Reactant Interactions of Pt Nanoparticles Functionalized with α-Amino Acids as Asymmetric Catalysts for β-Keto Esters
?ulce, Anda,Mitschke, Nico,Azov, Vladimir,Kunz, Sebastian
, p. 2732 - 2742 (2019/05/15)
The asymmetric hydrogenation of ?-keto esters over α-amino acid-functionalized Pt nanoparticles was explored in order to expand our understanding of ligand-reactant interactions underlying the chiral induction. A comprehensive investigation aimed at the quantification of the nonlinear effects demonstrated that for most of the ligands and reactants enantiodifferentiation is determined by 1 : 1 ligand-reactant interaction. However, attachment of phenyl substituents to the ligands or reactants likely involves the formation of more intricate intermediate complexes. We have shown that the asymmetric bias is sensitive to even small changes in the geometry of the ligand. Additionally, we have found that alkali metal cations, which balance the negative charge of the ligand's carboxyl group and originate from the metal hydroxide used for ligand functionalization, play a key role in the process of chiral induction. As the nature of the cation can be varied by simply changing the metal hydroxide used during functionalization, this finding opens an additional possibility to control the stereoselectivity by tuning the ligand-reactant interaction.
One-Pot Absolute Stereochemical Identification of Alcohols via Guanidinium Sulfate Crystallization
Brummel, Beau R.,Lee, Kinsey G.,McMillen, Colin D.,Kolis, Joseph W.,Whitehead, Daniel C.
supporting information, p. 9622 - 9627 (2019/12/02)
A novel technique for the absolute stereochemical determination of alcohols has been developed that uses crystallization of guanidinium salts of organosulfates. The simple one-pot, two-step process leverages facile formation of guandinium organosulfate single crystals for the straightforward determination of the absolute stereochemistry of enantiopure alcohols by means of X-ray crystallography. The strong hydrogen bonding network drives the stability of the crystal lattice and allows for a diverse range of organic alcohol substrates to be analyzed.
