Reactive block copolymer scaffolds

Block copolymers with sequences of differential reactivity were synthesized, and the step-wise and selective derivatization to form a new block copolymer was demonstrated.     

Catalytic enantioselective diboration, disilation and silaboration: new opportunities for asymmetric synthesis

This article summarizes recent developments in the area of catalytic enantioselective reactions of unsaturated organic substrates with diboron, silylboron, and disilane reagents. These reactions provide new routes to the functionalization of prochiral substrates and therefore offer new strategies in asymmetric organic synthesis.     

Application of the statistical test of equivalent pathways (STEP) method to the triple quadrupole mass spectrometer

Recently, we demonstrated a new method, STEP (Statistical Test of Equivalent Pathways) analysis, which differentiates first-generation product ions (primary product ions) from second-generation product ions (secondary product ions) obtained in tandem mass spectrometric (MS/MS) experiments on a quadrupole ion trap mass spectrometer. The study presented here defines how to adapt the STEP method to a more routinely used mass analyzer, the triple quadrupole. New ion activation conditions were developed to adapt the STEP method to the triple quadrupole mass spectrometer using peptides and carbohydrates. The application of this method to the triple quadrupole is useful because it provides an efficient approach to differentiate primary and secondary ions on this instrument. Out of the total number of ions that were subjected to the STEP analysis, this method correctly identified 96% of ions as primary or secondary, indicating that this analysis is effective for carbohydrates and peptides undergoing collision-induced dissociation (CID) on a triple quadrupole mass spectrometer.     

Development, mechanism, and scope of the palladium-catalyzed enantioselective allene diboration

In the presence of a chiral phosphoramidite ligand, the palladium-catalyzed diboration of allenes can be executed with high enantioselectivity. This reaction provides high levels of selectivity with a range of aromatic and aliphatic allene substrates. Isotopic-labeling experiments, stereodifferentiating reactions, kinetic analysis, and computational experiments suggest that the catalytic cycle proceeds by a mechanism involving rate-determining oxidative addition of the diboron to Pd followed by transfer of both boron groups to the unsaturated substrate. This transfer reaction most likely occurs by coordination and insertion of the more accessible terminal alkene of the allene substrate, by a mechanism that directly provides the eta3 pi-allyl complex in a stereospecific, concerted fashion.     

Small molecule inhibitors of the MDM2-p53 interaction discovered by ensemble-based receptor models

Five nonpeptide, small-molecule inhibitors of the human MDM2-p53 interaction are presented, and each inhibitor represents a new scaffold. The most potent compound exhibited a Ki of 110 +/- 30 nM. These compounds were identified using our multiple protein structure (MPS) method which incorporates protein flexibility into a receptor-based pharmacophore model that identifies appropriate hotspots of binding. Docking the inhibitors with an induced-fit docking protocol suggested that the inhibitors mimicked the three critical binding residues of p53 (Phe19, Trp23, and Leu26). Docking also predicted a new orientation of the scaffolds that more fully fills the binding cleft, enabling the inhibitors to take advantage of additional hydrogen-bonding possibilities not explored by other small molecule inhibitors. One inhibitor in particular was proposed to probe the hydrophobic core of the protein by taking advantage of the flexibility of the binding cleft floor. These results show that the MPS technique is a promising advance for structure-based drug discovery and that the method can truly explore broad chemical space efficiently in the quest to discover potent, small-molecule inhibitors of protein-protein interactions. Our MPS technique is one of very few ensemble-based techniques to be proven through experimental verification of the discovery of new inhibitors.     

A Series of Collaborations between Various Pharmaceutical Companies and Regulatory Authorities Concerning the Analysis of Biomolecules Using Capillary Electrophoresis: Additional Instruments/Buffer

An international project team (including members from US, Canada and UK) was formed from a number of interested biopharmaceutical companies and regulatory authorities to conduct a cross-organisation collaboration exercise. The results of the first comparison with eight different organisations that used instruments of the same equipment model, the same reagents, and the same methodology has been reported previously [1]. This report represents the addition of other instruments using a different run buffer. The relative migration times were different, as expected, prohibiting a direct comparison between companies. The within-organisation variability was low for both relative migration time (<0.34% RSD% for all companies save one) and the peak area (<5% RSD% for all companies save one) when measuring the purity of a representative IgG sample. The apparent molecular weight of bovine serum albumin was measured with good precision (less than 10% RSD% across all companies) to the theoretical value when all data is utilized (67.5 kDa compared to 66.4 kDa). For a representative IgG sample, the three main components, IgG Light Chain, IgG Non-glycosylated Heavy Chain, and IgG Heavy Chain, could not be separated, specifically the IgG Non-glycosylated Heavy Chain and IgG Heavy Chain. When the IgG Non-glycosylated Heavy Chain and IgG Heavy Chain were combined for all organisations, the fractional peak area for the IgG Light Chain and IgG Non-glycosylated Heavy Chain + IgG Heavy Chain peak also showed excellent agreement, with less than 7.5 and 3.5% RSD%, respectively. The value of this exercise is in demonstrating the reliability of CE for the determination of apparent size of biopharmaceutical proteins. This underpins the appropriate use of such CE data in support of regulatory submissions.

     

Strategies for interfacing solid-phase microextraction with liquid chromatography

Solid-phase microextraction (SPME) techniques are equally applicable to both volatile and non-volatile analytes, but the progress in applications to gas-phase separations has outpaced that of liquid-phase separations. The interfacing of SPME to gas chromatographic equipment has been straight-forward, requiring little modification of existing equipment. The requirement of solvent desorption for non-volatile or thermally labile analytes has, however, proven challenging for interfacing SPME with liquid-phase separations. Numerous options to achieve this have been described in the literature over the past decade, with applications in several different areas of analysis. To date, no single strategy or interface device design has proven optimal. During method development analysts must select the most appropriate interfacing technique among the options available. Out of these options three general strategies have emerged: (1) use of a manual injection interface tee; (2) in-tube SPME; and (3) off-line desorption followed by conventional liquid injection. In addition, there has been interest in coupling SPME directly to electrospray ionisation and matrix-assisted laser desorption ionisation (MALDI) for mass spectrometry. Several examples of each of these strategies are reviewed here, and an overview of their use and application is presented.