Reduction of Nitrobenzene to Aniline with Carbon Monoxide and Water in the Presence of the PdCl2/Fe/I2 System

A study of modified catalyst systems composed of palladium or its chloride and a co-catalyst such as metallic Fe-powder, iodine, and pyridine was used in the reduction of nitrobenzene to aniline with carbon monoxide and water at 180°C and 2.5-4 MPa pressure. The reaction is complete in 2 h with a nitrobenzene conversion of 98-100% and a 100% selectivity with respect to aniline.     

Calibration of somatic cell count in milk based on near-infrared spectroscopy

A PLS model for prediction of somatic cell count (SCC) based on near-infrared (NIR) spectra of unhomogenized milk is presented in the study. Samples of raw milk were collected from cows in the early lactation period (from 7th to 29th day after parturition). The NIR spectra were measured in the region 400–1100 nm. As reference method a fluoro-opto-electronic method was applied. Different preprocessing methods were investigated. The robust version of PLS regression was applied to handle outliers present in the dataset and the uninformative variable elimination–partial least squares (UVE–PLS) method was used to eliminate uninformative variables. The final model is acceptable for prediction of SCC in raw milk.     

Determination of the absolute configurations using electronic and vibrational circular dichroism measurements and quantum chemical calculations

The stereochemistry of products obtained via a chemical reaction may not always be obvious from the reaction scheme utilized. The identification of convenient methods to determine the stereochemistry in such cases is highly desirable. To identify these methods, we considered a substituted 4-vinyl-1-azabicyclo[3.2.0]hept-3-en-7-one that undergoes spontaneous oxidation in the atmosphere at room temperature, yielding an epoxide with unknown absolute configuration. To determine the absolute configuration of the resulting epoxide, three different approaches have been utilized: (a) experimental NOE measurements; (b) experimental electronic circular dichroism (ECD) spectroscopic measurements and their analysis using corresponding quantum chemical predictions at the B3LYP/aug-cc-pVDZ level; (c) experimental vibrational circular dichroism (VCD) spectroscopic measurements and their analysis using corresponding quantum chemical predictions at the B3LYP/aug-cc-pVDZ level. It was found that the NOE data could not provide enough proof for assigning the absolute configuration, while ECD data could not provide enough discrimination to distinguish between the two possible stereoisomers. On the other hand, VCD spectroscopic analysis provided enough discrimination to distinguish between the two possible stereoisomers, and the absolute configuration could be assigned with confidence.     

Rethinking Carbohydrate Synthesis: Stereoretentive Reactions of Anomeric Stannanes

In this Concept article, recent advances are highlighted in the synthesis and applications of anomeric nucleophiles, a class of carbohydrates in which the C1 carbon bears a carbon–metal bond. First, the advantages of exploiting the carboanionic reactivity of carbohydrates and the methods for the synthesis of mono- and oligosaccharide stannanes are discussed. Second, recent developments in the glycosyl cross-coupling method resulting in the transfer of anomeric configuration from C1 stannanes to C-aryl glycosides are reviewed. These highly stereoretentive processes are ideally suited for the preparation of carbohydrate-based therapeutics and were demonstrated in the synthesis of antidiabetic drugs. Next, the application of the glycosyl cross-coupling method to the preparation of Se-glycosides and to glycodiversification of small molecules and peptides are highlighted. These reactions proceed with exclusive anomeric control for a broad range of substrates and tolerate carbohydrates with free hydroxyl groups. Taken together, anomeric nucleophiles have emerged as powerful tools for the synthesis of oligosaccharides and glycoconjugates and their future applications will open new possibilities to incorporate saccharides into small molecules and biologics.