Gear effect—10 : Conformational aspects of the positive or negative buttressing effects of methyl groups: polymethylpyridines

The effect of the shape of a methyl group on reactivity, which cannot be accounted for by considering a methyl group as a spherical substituent with the appropriate van der Waals radius, was considered in kinetics of alkylalion of substituted pyridines and barriers to rotation and ground state conformations of an isopropyl group attached to a planar framework. The perturbation of a methyl group by an o-methyl group is accounted for by a unique conformational explanation which involves the polyhedral shape of the methyl group.     

The gold(III) tetra­chloride salt of L‐cocaine

The title salt, methyl (1R,2R,3S,5S,8S)‐3‐benzoyl­oxy‐8‐methyl‐8‐aza­bicyclo­[3.2.1]octane‐2‐carboxyl­ate tetra­chloro­aurate(III), (C₁₇H₂₂NO₄)[AuCl₄], has its protonated N atom intra­molecularly hydrogen bonded to the O atom of the methoxy­carbonyl group [N⋯O = 2.755 (6) Å and N—H⋯O = 136°]. Two close inter­molecular C—H⋯O contacts exist, as well as five C—H⋯Cl close contacts. The [AuCl₄]⁻ anion was found to be distorted square planar.     

An Efficient Synthesis of 2-Cyclohexene-1-Carboxylic Acid and 2-Cyclopentene-1-Carboxylic Acid

A simple and efficient synthesis of the title compounds by modified Grignard methodology is described.     

Carbophilic 3‐Component Cascades: Access to Complex Bioactive Cyclopropyl Diindolylmethanes

Naturally occurring indole‐3‐carbinol and 3,3‐diindolylmethane show bioactivity in a number of disparate disease areas, including cancer, prompting substantial synthetic analogue activity. We describe a new approach to highly functionalised derivatives that starts from allene gas and proceeds via the combination of a three‐component Pd⁰‐catalysed cascade with a one‐pot, three‐component carbophilic Pt^II cascade linked to a stereoselective acid‐catalysed Mannich–Michael reaction that generates complex cyclopropyl diindolylmethanes which show selective activity against prostate cancer cell lines.     

The combi-CLEA approach: enzymatic cascade synthesis of enantiomerically pure (S)-mandelic acid

Enantiomerically pure (S)-mandelic acid was synthesised from benzaldehyde by sequential hydrocyanation and hydrolysis in a bienzymatic cascade at starting concentrations up to 0.25 M. A cross-linked enzyme aggregate (CLEA) composed of the (S)-selective oxynitrilase from Manihot esculenta and the non-selective nitrilase from Pseudomonas fluorescens EBC 191 was employed as the biocatalyst. The nitrilase produces approx. equal amounts of (S)-mandelic acid and (S)-mandelic amide from (S)-mandelonitrile under standard conditions, but we surprisingly found that high (up to 0.5 M) concentrations of HCN induced a marked drift towards amide production. By including the amidase from Rhodococcus erythopolis in the CLEA we obtained (S)-mandelic acid as the sole product in 90% yield and >99% enantiomeric purity.     

Multi-Residue Analysis by Liquid Chromatography-Mass Spectrometry Coupling. Application to Drinking and River Waters

Abstract

The coupling between liquid chromatography and mass spectrometry with an APCI or ESI interface (in positive or negative mode) is used here for multi-residue analyses in natural waters, covering basic and neutral pesticides as well as acid pesticides. The methods developed are applied to drinking and, river waters after the samples are concentrated by liquid-liquid extraction or solid phase extraction on C18 cartridges. Comparisons are made between UV detection and mass spectrometry and between two chromatographic methods for acid substances. The quantitation limits range from 0.01 to 0.1 μg/l according to the substance.     

On the problem of the stability of pyramidal structures on bombarded copper surfaces

The morphological evolution of pyramids, developed on bombarded copper surfaces, as a function of consecutive doses of 12 keV Kr—ions from 2.4 × 10¹⁶ up to 3 × 10¹⁶ ions/cm², has been studied. In disagreement with many previous studies, apparently based on a limited choice of doses which were sometimes not in sequence, we found that the pyramids disappeared at high enough doses. Pyramids are therefore not an equilibrium structure.