Search results for "MERIS"

Enantioselective transformation of fluoxetine in water and its ecotoxicological relevance

2017

European legislation focusing on water quality is expected to broaden to encompass several pharmaceuticals as priority hazardous substances. This manuscript aims to challenge current regulatory approaches that do not recognize stereochemistry of chiral pharmaceuticals by testing the hypothesis that environmental transformation and effects of chiral pharmaceuticals are stereoselective. Our experiments revealed that, while degradation of chiral fluoxetine (FL) in river water occurs via non-enantioselective photochemical and mildly-enantioselective microbial processes favoring the (R)-enantiomer, a pronounced enantioselectivity favoring (S)-FL (leading to the formation of (S)-NFL (norfluoxetin…

Conformational studies into N-methylation of alanine diamide models: A quantitative approach

2006

Abstract A systematic theoretical analysis was performed on N -acetyl- l -alanine N ′-methylamide (Ac- l -Ala-NHMe) and the analogues methylated on the N-terminus (Ac- l -(Me)Ala-NHMe), C-terminus (Ac- l -Ala-NMe 2 ), and both N/C-termini (Ac- l -(Me)Ala-NMe 2 ), to evaluate the influence of methylation of the amide group on the conformational properties of the affected residues. The ϕ , ψ potential energy surfaces were calculated at the B3LYP/6-31+G**//HF/3-21G level of theory with inclusion of the solvent (water) effect (SCRF method). The conformers localised were fully optimised at the B3LYP/6-31+G** in vacuo. The accessible areas of the potential energy surfaces; the number of conformer…

Phase selection of calcium carbonate through the chirality of adsorbed amino acids.

2007

Catalytic Diastereo- and Enantioselective Synthesis of Tertiary Trifluoromethyl Carbinols through a Vinylogous Aldol Reaction of Alkylidenepyrazolone…

2022

A diastereo- and enantioselective organocatalytic aldol reaction between alkylidenepyrazolones and trifluoromethyl ketones leading to chiral tertiary alcohols bearing a trifluoromethyl group is presented. The methodology is based on the use of a bifunctional organocatalyst in order to activate the γ-hydrogen atoms of the alkylidenepyrazolone nucleophile and the carbonyl group of the trifluoromethylarylketone providing highly functionalized trifluoromethyl alcohols with moderate yields, excellent diastereoselectivity, and moderate to good enantioselectivity. Experiments monitoring the conversion by 1H NMR and the enantiomeric excess by HPLC with the reaction time showed that full conversion …

Stereoselective anti aldol reactions of erythrulose derivatives. Functionalized chiral d3 and d4 synthons.

2004

An improved procedure for the synthesis of anti aldols from protected erythrulose derivatives is reported. The preparation of functionalized d3 and d4 synthons with various stereochemical arrays by means of this methodology is described and subsequently applied to a stereoselective formal synthesis of the natural metabolite goniothalesdiol.

Bis(oxazoline) Lewis Acid Catalyzed Aldol Reactions of PyridineN-Oxide Aldehydes—Synthesis of Optically Active 2-(1-Hydroxyalkyl)pyridine Derivatives…

2006

A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro-chiral pyridine-N-oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1-oxypyridine-2-carbaldehyde derivatives catalyzed by chiral copper(II)-bis(oxazoline) complexes gave optically active 2-(hydroxyalkyl)- and 2-(anti-1,2-dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities-up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.

Diastereoselective Synthesis of 2-Phenylselenenyl-1,3-anti-Diols and 2-Phenylselenenyl-1,3-anti-Azido-Alcohols via Hydroxy- and Azido-Selenenylation …

2005

A method to synthesize 2-phenylselenenyl-1,3-anti-diols and 2-phenyl- selenenyl-1,3-anti-azidoalcohols via hydroxy- or azido-selenenylation of trans-allylic alcohols is reported. Moreover, the first example of hydroxyl-selenenylation of an allylic azide is presented. Yields ranging from moderate to good and diastereomeric ratios up to 95:5 are achieved.

Unsaturated syn- and anti-1,2-Amino Alcohols by Cyclization of Allylic Bis-trichloroacetimidates. Stereoselectivity Dependence on Substrate Configura…

2014

Disubstituted allylic bis-imidates undergo Lewis acid catalyzed or spontaneous cyclization to oxazolines, which are precursors of unsaturated amino alcohols. Stereoselectivity of the cyclization is mainly determined by the substrate configuration. Highly selective cis-oxazoline formation is achieved starting from anti-E-bis-imidates while trans-oxazoline predominantly forms from anti-Z-bis-imidates. On the basis of DFT calculations, the stereoselectivity trends can be explained by the formation of the energetically most stable carbenium ion conformation, followed by the cyclization via most favorable bond rotations.

Design, Synthesis, and Biological Evaluation of Novel Fluorinated Ethanolamines

2011

The preparation of novel fluorinated allylamines and their use as key fragments for the stereoselective synthesis of hydroxyethyl secondary amine (HEA)-type peptidomimetics is described. Our strategy employs chiral sulfinyl imines as synthesis intermediates, by treatment of hemiaminal precursors with two equivalents of vinylmagnesium bromide. The subsequent oxidation of the allylic amines to the corresponding epoxides was achieved by treatment with methyl(trifluoromethyl)dioxirane. Finally, epoxide ring opening with a range of nitrogen nucleophiles provided a library of HEA-derived peptidomimetics with a phenyldifluoromethylene moiety. The biological evaluation of these derivatives revealed…

Novel Approach for Asymmetric Synthesis of Fluorinated β-Amino Sulfones and Allylic Amines

2003

[reaction: see text] Enantiomerically pure gamma-fluoroalkyl beta-amino sulfones are readily synthesized in three steps starting from fluorinated imidoyl chlorides and arylmethyl sulfones. A complementary two-step sequence starting from chiral fluorinated beta-amino sulfoxides has also been developed. To illustrate the application of this procedure, a new method for the synthesis of alpha-fluoroalkyl allylic amines in optically pure form involving a Julia methylenation-desulfonylation reaction is presented.