Separation of negatively charged carbohydrates by capillary electrophoresis

Capillary electrophoresis (CE) has recently emerged as a highly promising technique consuming an extremely small amount of sample and capable of the rapid, high-resolution separation, characterization, and quantitation of analytes. CE has been used for the separation of biopolymers, including acidic carbohydrates. Since CE is basically an analytical method for ions, acidic carbohydrates that give anions in weakly acid, neutral, or alkaline media are often the direct objects of this method. The scope of this review is limited to the use of CE for the analysis of carbohydrates containing carboxylate, sulfate, and phosphate groups as well as neutral carbohydrates that have been derivatized to incorporate strongly acidic functionality, such as sulfonate groups.     

Size control and catalytic activity of bio-supported palladium nanoparticles

The development of nanoparticles has greatly improved the catalytic properties of metals due to the higher surface to volume ratio of smaller particles. The production of nanoparticles is most commonly based on abiotic processes, but in the search for alternative protocols, bacterial cells have been identified as excellent scaffolds of nanoparticle nucleation, and bacteria have been successfully employed to recover and regenerate platinum group metals from industrial waste. We report on the formation of bio-supported palladium (Pd) nanoparticles on the surface of two bacterial species with distinctly different surfaces: the gram positive Staphylococcus sciuri and the gram negative Cupriavidus necator. We investigated how the type of bacterium and the amount of biomass affected the size and catalytic properties of the nanoparticles formed. By increasing the biomass:Pd ratio, we could produce bio-supported Pd nanoparticles smaller than 10nm in diameter, whereas lower biomass:Pd ratios resulted in particles ranging from few to hundreds of nm. The bio-supported Pd nanoparticle catalytic properties were investigated towards the Suzuki-Miyaura cross coupling reaction and hydrogenation reactions. Surprisingly, the smallest nanoparticles obtained at the highest biomass:Pd ratio showed no reactivity towards the test reactions. The lack of reactivity appears to be caused by thiol groups, which poison the catalyst by binding strongly to Pd. Different treatments intended to liberate particles from the biomass, such as burning or rinsing in acetone, did not re-establish their catalytic activity. Sulphur-free biomaterials should therefore be explored as more suitable scaffolds for Pd(0) nanoparticle formation.     

Ex situ generation of stoichiometric and substoichiometric 12CO and 13CO and its efficient incorporation in palladium catalyzed aminocarbonylations

A new technique for the ex situ generation of carbon monoxide (CO) and its efficient incorporation in palladium catalyzed carbonylation reactions was achieved using a simple sealed two-chamber system. The ex situ generation of CO was derived by a palladium catalyzed decarbonylation of tertiary acid chlorides using a catalyst originating from Pd(dba)(2) and P(tBu)(3). Preliminary studies using pivaloyl chloride as the CO-precursor provided an alternative approach for the aminocarbonylation of 2-pyridyl tosylate derivatives using only 1.5 equiv of CO. Further design of the acid chloride CO-precursor led to the development of a new solid, stable, and easy to handle source of CO for chemical transformations. The synthesis of this CO-precursor also provided an entry point for the late installment of an isotopically carbon-labeled acid chloride for the subsequent release of gaseous [(13)C]CO. In combination with studies aimed toward application of CO as the limiting reagent, this method provided highly efficient palladium catalyzed aminocarbonylations with CO-incorporations up to 96%. The ex situ generated CO and the two-chamber system were tested in the synthesis of several compounds of pharmaceutical interest and all of them were labeled as their [(13)C]carbonyl counterparts in good to excellent yields based on limiting CO. Finally, palladium catalyzed decarbonylation at room temperature also allowed for a successful double carbonylation. This new protocol provides a facile and clean source of gaseous CO, which is safely handled and stored. Furthermore, since the CO is generated ex situ, excellent functional group tolerance is secured in the carbonylation chamber. Finally, CO is only generated and released in minute amounts, hence, eliminating the need for specialized equipment such as CO-detectors and equipment for running high pressure reactions.     

An expedient synthesis of the fibril binding compound FSB via sequential Pd-catalyzed coupling reactions

The styryl benzene derivative (E, E)-1-fluoro-2,5-bis(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (FSB), well-known for its binding to beta-amyloid peptide fibrils, was synthesized in an efficient manner exploiting two sequential palladium(0)-catalyzed coupling reactions in a 34% overall yield. This is a substantial improvement to the previously reported synthesis of FSB in 1.1%.     

Palladium-catalyzed double carbonylation using near stoichiometric carbon monoxide: expedient access to substituted 13C2-labeled phenethylamines

A novel and general approach for (13)C(2)- and (2)H-labeled phenethylamine derivatives has been developed, based on a highly convergent single-step assembly of the carbon skeleton. The efficient incorporation of two carbon-13 isotopes into phenethylamines was accomplished using a palladium-catalyzed double carbonylation of aryl iodides with near stoichiometric carbon monoxide.