First ever observation of the intermediate of phosphonium salt and ylide hydrolysis: P-hydroxytetraorganophosphorane

P-Hydroxytetraorganophosphorane, the long-postulated intermediate in phosphonium salt and ylide hydrolysis, has been observed and characterised by low temperature NMR, finally definitively establishing its involvement in these reactions. The results require modification of the previously accepted mechanism for ylide hydrolysis: P-hydroxy-tetraorganophosphorane is generated directly by 4-centre reaction of ylide with water

Impact of dynamic sub-populations within grafted chains on the protein binding and colloidal stability of PEGylated nanoparticles

Polyethylene glycol grafting has played a central role in preparing the surfaces of nano-probes for biological interaction, to extend blood circulation times and to modulate protein recognition and cellular uptake. However, the role of PEG graft dynamics and conformation in determining surface recognition processes is poorly understood primarily due to the absence of a microscopic picture of the surface presentation of the polymer. Here a detailed NMR analysis reveals three types of dynamic ethylene glycol units on PEG-grafted SiO2 nanoparticles (NPs) of the type commonly evaluated as long-circulating theranostic nano-probes; a narrow fraction with fast dynamics associated with the chain ends; a broadened fraction spectrally overlapped with the former arising from those parts of the chain experiencing some dynamic restriction; and a fraction too broad to be observed in the spectrum arising from units closer to the surface/graft which undergo slow motion on the NMR timescale. We demonstrate that ethylene glycol units transition between fractions as a function of temperature, core size, PEG chain length and surface coverage and demonstrate how this distribution affects colloidal stability and protein uptake. The implications of the findings for biological application of grafted nanoparticles are discussed in the context of accepted models for surface ligand conformation

Biotransformation of fluorophenyl pyridine carboxylic acids by the model fungus Cunninghamella elegans

1. Fluorine plays a key role in the design of new drugs and recent FDA approvals included two fluorinated drugs, tedizolid phosphate and vorapaxar, both of which contain the fluorophenyl pyridyl moiety. 2. To investigate the likely phase-I (oxidative) metabolic fate of this group, various fluorinated phenyl pyridine carboxylic acids were incubated with the fungus Cunninghamella elegans, which is an established model of mammalian drug metabolism. 3. 19F NMR spectroscopy established the degree of biotransformation, which varied depending on the position of fluorine substitution, and gas chromatography–mass spectrometry (GC–MS) identified alcohols and hydroxylated carboxylic acids as metabolites. The hydroxylated metabolites were further structurally characterised by nuclear magnetic resonance spectroscopy (NMR), which demonstrated that hydroxylation occurred on the 4′ position; fluorine in that position blocked the hydroxylation. 4. The fluorophenyl pyridine carboxylic acids were not biotransformed by rat liver microsomes and this was a consequence of inhibitory action, and thus, the fungal model was crucial in obtaining metabolites to establish the mechanism of catabolism

Investigations on the operation of stereochemical drift in the Wittig reaction by NMR and variable-temperature NMR spectroscopy of oxaphosphetane intermediates and their quench products

Within the currently accepted mechanism of the Li‐salt‐free Wittig reaction, the phenomenon of stereochemical drift remains the one remaining “loose end” in an otherwise internally consistent explanation of a large body of diverse observations. The term describes the nonstereospecific decomposition of the oxaphosphetane (OPA) intermediate in reactions of certain alkylides with certain aldehydes. In this paper, it is shown that the previous examples in which drift occurs are not merely isolated aberrations from the observed norm, but rather that there is a general phenomenon in reactions of ethylides with benzaldehydes. Variable‐temperature NMR (VTNMR) spectroscopy was used to establish that the amount and diastereomeric ratio of the OPA intermediates do not change below a certain temperature. At and above the temperature at which OPA decomposition to alkene and phosphine oxide begins to occur, the alkene shows a different diastereomeric ratio to the OPA, which indicates the occurrence of stereochemical drift. In one example, owing to an apparent remarkable coincidence of rates, the diastereomeric ratio of the OPA does not change above the decomposition temperature, even though stereochemical drift occurs in the formation of the alkene product. An alternative mechanism for drift involving its catalysis by aldehyde was not confirmed. Drift was also shown not to occur in similar Wittig reactions of structurally related longer‐chain alkylides by stereospecific decomposition of OPA intermediates generated from β‐hydroxyphosphonium salts (β‐HPSs). The extremely useful (and generally applicable) NMR techniques, 1H–31P HMBC and selective 1H{31P}, which we have utilised to establish kinetic diastereomeric ratios, are described in full for the first time. Details of the determination of the relative stereochemistry of two β‐HPSs (derived from acid quenching of OPAs) by X‐ray crystallography are also given

Synthèse et réactivité de complexes manganèse-propynylidène dérivés du méthylcymantrène

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

First ever observation of the intermediate of phosphonium salt and ylide hydrolysis: P-hydroxytetraorganophosphorane

P-Hydroxytetraorganophosphorane, the long-postulated intermediate in phosphonium salt and ylide hydrolysis, has been observed and characterised by low temperature NMR, finally definitively establishing its involvement in these reactions. The results require modification of the previously accepted mechanism for ylide hydrolysis: P-hydroxy-tetraorganophosphorane is generated directly by 4-centre reaction of ylide with water

Synthesis of a conformationally constrained delta-amino acid building block

Conformationally restricted amino acids are important components in peptidomimetics and drug design. Herein, we describe the synthesis of a novel, non-proteinogenic constrained delta amino acid containing a cyclobutane ring, cis-3(aminomethyl)cyclobutane carboxylic acid (ACCA). The synthesis of the target amino acid was achieved in seven steps, with the key reaction being a base induced intramolecular nucleophilic substitution. A small library of dipeptides was prepared through the coupling of ACCA with proteinogenic amino acids.Author has checked copyrightAMS. The delta sign is in the article title rather that the word delta. Not sure where to find this

Biotransformation of fluorophenyl pyridine carboxylic acids by the model fungus Cunninghamella elegans

1.Fluorine plays a key role in the design of new drugs and recent FDA approvals included two fluorinated drugs, tedizolid phosphate and vorapaxar, both of which contain the fluorophenyl pyridyl moiety. 2.To investigate the likely phase-I (oxidative) metabolic fate of this group, various fluorinated phenyl pyridine carboxylic acids were incubated with the fungus Cunninghamella elegans, which is an established model of mammalian drug metabolism. 3.19F NMR spectroscopy established the degree of biotransformation, which varied depending on the position of fluorine substitution, and gas chromatography–mass spectrometry (GC–MS) identified alcohols and hydroxylated carboxylic acids as metabolites. The hydroxylated metabolites were further structurally characterised by nuclear magnetic resonance spectroscopy (NMR), which demonstrated that hydroxylation occurred on the 4′ position; fluorine in that position blocked the hydroxylation. 4.The fluorophenyl pyridine carboxylic acids were not biotransformed by rat liver microsomes and this was a consequence of inhibitory action, and thus, the fungal model was crucial in obtaining metabolites to establish the mechanism of catabolism.European Commission - Seventh Framework Programme (FP7

Design and Synthesis of Pyrrolidinyl Ferrocene-Containing Ligands and Their Application in Highly Enantioselective Rhodium-Catalyzed Olefin Hydrogenation

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions and excellent levels of enantioselectivities of up to >99.9% ee and 97.7% ee, respectively, using a BINOL-substituted phosphine-phosphoaramidite ligand which possesses planar, central, and axial chirality elements