Polyethylene glycol (PEG) as polymeric support and phase-transfer catalyst in the soluble polymer liquid phase synthesis of α-amino esters

Asymmetric Epoxidation of Enones: Effect of Surfactants, Radical Scavengers and Morphology of Catalysts on Reaction Rates, Chemical Yields and Enantioselectivities in Phase-Transfer Catalysis

Highly enantioselective epoxidation of enones has been accomplished with asymmetric phase-transfer catalysis (PTC) using cinchona alkaloid-derived meta-dimer catalysts. An intensive study of structure-reactivity relationships among catalysts and oxidants in terms...

Progress, challenges and future directions of heterocycles as building blocks in iterative methodologies towards sequence-defined oligomers and polymers

Heterocyclic building blocks for iterative methodologies leading to sequence-defined oligomers and polymers are reviewed. Solid- as well as solution-phase methods, challenges surrounding these systems and potential future directions are presented.

A Novel Microwave-Activated Sonogashira Coupling Reaction and Cleavage using Polyethylene Glycol as Phase-Transfer Catalyst and Polymer Support

Under microwave-activation polyethylene glycol bound 4-iodobenzoic acid could be readily reacted with various terminal alkynes in excellent yields and purity using polyethylene glycol (PEG) as a solid-liquid phase-transfer catalyst and polymer support; the cleavage could be dramatically accelerated under microwave activation.

Asymmetric synthesis of highly functionalized tetrahydropyran DPP-4 inhibitor

A practical synthesis of a highly functionalized tetrahydropyran DPP-4 inhibitor is described. The asymmetric synthesis relies on three back-to-back Ru-catalyzed reactions. A Ru-catalyzed dynamic kinetic resolution (DKR) reduction establishes two contiguous stereogenic centers in one operation. A unique dihydropyran ring is efficiently constructed through a preferred Ru-catalyzed cycloisomerization. Hydroboration followed by a Ru-catalyzed oxidation affords the desired functionalized pyranone core scaffold. Finally, stereoselective reductive amination and subsequent acidic deprotection afford the desired, potent DPP-4 inhibitor in 25% overall yield.

Ultrasounds in melted poly(ethylene glycol) promote copper-catalyzed cyanation of aryl halides with K(4)[Fe(CN)(6)]

Melted poly(ethylene glycols) (PEGs) were used for the first time as solvent for the sonochemically promoted cyanation of aryl halides employing inexpensive and safe K4[Fe(CN)6] and a relatively low amount of Cu-based catalyst. The Mw (weight-average polymer molecular weight) of PEG proved to notably influence the substrate conversion, which is indicative of a strong dependence of the sonication efficacy on solvent properties. Gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) contributed to the characterization of the polymer and the elucidation of the catalytic system.

SENSASS NMR: New NMR techniques for enhancing the sensitivity and the spectral resolution of polymer supported chemicals

The use of polyethylene glycols (PEGs) as organic polymer soluble supports for synthesis has been receiving growing interest. The main advantages of using PEGs as support are related to their non-toxicity, their commercial availability and their solubility properties allowing easy recovery and analysis of compounds linked to the polymer. The NMR characterization of PEG-branched products could however be difficult due to the presence of huge signals of the polymeric support. In order to overcome this problem, we developed new NMR experiments named SENSitivity increAsed and resolution enhanced by Signal Suppression or SENSASS NMR. These experiments implement either semi-selective pulses or Water Gate sequences for reducing signals of the polymer as well as fast pulsing techniques optimizing the recycling delay for enhancing the sensitivity of signals. They have been successfully implemented in classical NMR characterization experiments namely, COSY, HSQC and HMBC experiments.

Phosphine-free palladium acetate catalyzed Suzuki reaction in water

Pd(OAc)(2) in a mixture of water and poly(ethylene glycol) (PEG) is shown to be an extremely active catalyst for the Suzuki reaction of aryl iodides and bromides. The reaction can be conducted under mild conditions (50 degrees C) without the use of a microwave or phosphine ligand in high yields. The isolation of the products is readily performed by the extraction of diethyl ether, and the Pd(OAc)(2)-PEG can be reused without significant loss in activity.

A poly(ethylene glycol)-supported quaternary ammonium salt: An efficient, recoverable, and recyclable phase-transfer catalyst

A quaternary ammonium salt readily immobilized on a soluble poly(ethylene glycol) polymer support efficiently catalyzes different reactions carried out under phase-transfer catalysis conditions; the catalyst, easily recovered by precipitation and filtration, shows no appreciable loss of activity when recycled three times.

Some of the amino acid chemistry going on in the Laboratory of Amino Acids, Peptides and Proteins

Some of the chemistry of amino acids going on in our laboratory (Laboratoire des Amino acides Peptides et Protéines) is described as well as some mass spectrometry methodology for their characterization particularly on solid supports. Several aspects are presented including: (i) the stereoselective synthesis of natural and unnatural amino acids using 2-hydroxypinan-3-one as chiral auxiliary; (ii) the stereoselective synthesis of natural and unnatural amino acids by deracemization of alpha-amino acids via their ketene derivatives; (iii) the synthesis of alpha-aryl-alpha-amino acids via reaction of organometallics with a glycine cation; (iv) the diastereoselective synthesis of glycosyl-alpha-amino acids; (v) the synthesis of beta-amino acids using alpha-aminopyrrolidinopiperazinediones as chiral templates; (vi) the reactivity of urethane-N-protected N-carboxyanhydrides. To characterize natural and non natural amino acids through their immonium ions by mass spectrometry, some methodology is also described.

Chemical reactivity in matrix-assisted laser desorption/ionization mass spectrometry

During the control of a multistep organic synthesis on a soluble polymer (PEG) by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, a chemical reactivity was encountered when the matrix was acidic, for the samples where the amino moiety of the anchored compounds was protected as a Schiff base. Such imine hydrolysis was proven to be solely mediated by the acidic matrix during analyses since the expected protected structures were detected when the experiments were duplicated with a non-acidic matrix. Even if MALDI mass spectrometry was found to be more convenient than electrospray ionization mass spectrometry for the monitoring of liquid phase organic syntheses, the chemical reactivity imparted by the use of a matrix must be taken into account to avoid erroneous spectra interpretations. Copyright 1999 John Wiley & Sons, Ltd.