A one-pot oxidation/allylation/oxidation sequence for the preparation of β,γ-unsaturated ketones directly from primary alcohols

A one-pot oxidation/allylation/oxidation procedure has been developed for the conversion of primary alcohols into β,γ-unsaturated ketones. The methodology has been applied to a range of alcohols, and in some cases, isomerisation to produce the corresponding α,β-unsaturated ketones has been carried out.     

Combined effect of stacking and solvation on the spontaneous mutation in DNA

In DNA, base pairs are involved in two reciprocal interactions: interbase hydrogen bonds and stacking. Furthermore, base pairs also undergo the effects of the external entities present in the biological environment, such as water molecules and cations. In this contribution, the double spontaneous mutation has been studied with hybrid theoretical tools in a DNA-embedded guanine-cytosine model accounting for the impact of the first hydration shell. According to our findings, the combination of the neighboring base pairs and surrounding water molecules plays a crucial role in the double proton transfer. Indeed, as a consequence of these interactions, the double proton transfer (DPT) mechanism is altered: on the one hand, stacking and hydration strongly affect the geometry of base pairs, and, on the other hand, vicinal water molecules may play an active role in the tautomeric equilibrium by catalyzing the proton transfer reaction.     

Myosin-cross-reactive antigen (MCRA) protein from <Emphasis Type="Italic">Bifidobacterium breve</Emphasis> is a FAD-dependent fatty acid hydratase which has a function in stress protection

Background  

The aim of this study was to determine the catalytic activity and physiological role of myosin-cross-reactive antigen (MCRA) from Bifidobacterium breve NCIMB 702258. MCRA from B. breve NCIMB 702258 was cloned, sequenced and expressed in heterologous hosts (Lactococcus and Corynebacterium) and the recombinant proteins assessed for enzymatic activity against fatty acid substrates.     

Asymmetric copper-catalysed intramolecular C-H insertion reactions of α-diazo-β-keto sulfones

Asymmetric copper-catalysed intramolecular C-H insertion reactions of a series of α-diazo-β-keto sulfones are reported. Enantioselectivities of up to 82% ee were achieved in moderate to good yield. These results represent the highest level of enantiocontrol achieved to date for a copper-catalysed cyclopentanone synthesis via C-H insertion.     

The intramolecular aryl embrace: from light emission to light absorption

6-(1-Methylpyrrol-2-yl)-2,2'-bipyridine, 3, and 6-(selenophene-2-yl)-2,2'-bipyridine, 4, have been prepared and characterized in solution and by structural determinations. Copper(I) complexes [CuL(2)][PF(6)] in which L is 2,2'-bipyridine substituted in the 6-position by furyl, thienyl, N-methylpyrrolyl, selenopheneyl, methyl or phenyl, (L = 1-6) have been synthesized. The complexes have been characterized by electrospray mass spectrometry, and solution NMR and UV-VIS spectroscopies. The single crystal structures of [Cu(1)(2)][PF(6)], [Cu(2)(2)][PF(6)], [Cu(3)(2)][PF(6)], [Cu(5)(2)][PF(6)] and [Cu(6)(2)][PF(6)] have been determined. In those compounds containing an aromatic substituent attached to the bpy unit, the substituent is twisted with respect to the latter. In [Cu(3)(2)][PF(6)] and [Cu(5)(2)][PF(6)], this results in intra-cation π-stacking between ligands which is very efficient in [Cu(3)(2)](+) despite the steric requirements of the N-methyl substituents. Face-to-face stacking between the ligands in the [Cu(2)(2)](+) ion is achieved by complementary substituent twisting and elongation of one Cu-N bond, but there is no analogous intra-cation π-stacking in [Cu(1)(2)](+). Ligand exchange reactions between [CuL(2)][PF(6)] (L = 1-6) and TiO(2)-anchored ligands 7-10 (L' = 2,2'-bipyridine-based ligands with CO(2)H or PO(OH)(2) anchoring groups) have been applied to produce 24 surface-anchored heteroleptic copper(i) complexes, the formation of which has been evidenced by using MALDI-TOF mass spectrometry and thin layer solid state diffuse reflectance electronic absorption spectroscopy. The efficiencies of the complexes as dyes in DSCs have been measured, and the best efficiencies are observed for [CuLL'] with L' = 10 which contains phosphonate anchoring groups.     

Characterization of procyanidin B2 oxidation products in an apple juice model solution and confirmation of their presence in apple juice by high-performance liquid chromatography coupled to electrospray ion trap mass spectrometry

Procyanidins (i.e. condensed tannins) are polyphenols commonly found in fruits. During juice and cider making, apple polyphenol oxidase catalyzes the oxidation of caffeoylquinic acid (CQA) into its corresponding o-quinone which further reacts with procyanidins and other polyphenols, leading to the formation of numerous oxidation products. However, the structure and the reaction pathways of these neoformed phenolic compounds are still largely unknown. Experiments were carried out on a model system to gain insights into the chemical processes occurring during the initial steps of fruit processing. Procyanidin B2 was oxidized by caffeoylquinic acid o-quinone (CQAoq) in an apple juice model solution. The reaction products were monitored using high performance liquid chromatography (HPLC) coupled to ultraviolet (UV)-visible and electrospray tandem mass spectrometry (ESI-MS/MS) in the negative mode. Oxidative conversion of procyanidin B2 ([M-H](-) at m/z 577) into procyanidin A2 at m/z 575 was unambiguously confirmed. In addition, several classes of products were characterized by their deprotonated molecules ([M-H](-)) and their MS/MS fragmentation patterns: hetero-dimers (m/z 929) and homo-dimers (m/z 1153 and 705) resulting from dimerization involving procyanidin and CQA molecules; intramolecular addition products at m/z 575, 573, 927, 1151 and 703. Interestingly, no extensive polymerization was observed. Analysis of a cider apple juice enabled comparison with the results obtained on a biosynthetic model solution. However, procyanidin A2 did not accumulate but seemed to be an intermediate in the formation of an end-product at m/z 573 for which two structural hypotheses are given. These structural modifications of native polyphenols as a consequence of oxidation probably have an impact on the organoleptic and nutritional properties of apple juices and other apple-derived foods.     

Phosphites as ligands in ruthenium-benzylidene catalysts for olefin metathesis

The use of phosphites in second generation, ruthenium-based olefin metathesis pre-catalysts leads to an improvement in catalyst stability and activity at low catalyst loadings.     

First substoichiometric version of the catalytic enantioselective addition of an alkyllithium to an aldehyde

A substoichiometric enantioselective version of the extremely fast nucleophilic addition of Alk-Li to RCHO is made possible thanks to a thorough analysis of the aggregation phenomena involved in the reaction: calculated quantities of LiCl must be added to the medium at the right time to keep the catalytic cycle running.     

Use of alkyl 2,4,6-triisopropylbenzoates in the asymmetric homologation of challenging boronic esters

(-)-Sparteine induced lithiation of primary 2,4,6-triisopropylbenzoates and subsequent homologation of boronic esters is reported. A comparative study with lithiated N,N-diisopropylcarbamates has demonstrated the superiority of the hindered benzoate.