Synthesis of Carbohydrates with an Anomeric Thiol Moiety for Elaboration into Metabolically Stable Thioglycosides

ABSTRACT

The synthesis of thioglycosides for use as metabolically stable biological probes is an area of continued interest. This paper describes the synthesis of functionalised carbohydrates which contain an anomeric thio group. During the course of this work we have examined the most viable route into compounds such as the specifically functionalised carbohydrates 36 and 37, and have also investigated the usefulness of disulfides as protecting groups for anomeric thiols.     

A systematic study of the solid state and solution phase conformational preferences of β-peptides derived from transpentacin

The solid state and solution phase conformational preferences of a homologous series of β-peptides derived from (S,S)-2-aminocyclopentanecarboxylic acid (transpentacin) have been investigated using a variety of spectroscopic and crystallographic techniques. These studies indicate that the hexamer and pentamer persist as a 12-helix in both the solid state and solution phase. Although the conformational traits of a 12-helix are exhibited by oligomers with as few as three residues in the solid state, in solution the trimer exists as an equilibrium of many alternative conformers whilst the tetramer has been shown to predominantly exist in either a 12-helix or a turn-type conformation.     

Asymmetric syntheses of 2,5-dideoxy-2,5-imino-d-glucitol [(+)-DGDP] and 1,2,5-trideoxy-1-amino-2,5-imino-d-glucitol [(+)-ADGDP]

The asymmetric syntheses of 2,5-dideoxy-2,5-imino-d-glucitol [(+)-DGDP] and 1,2,5-trideoxy-1-amino-2,5-imino-d-glucitol [(+)-ADGDP] were achieved via the ring-closing iodoamination of an enantiopure bishomoallylic amine, followed by functionalisation of the resultant iodomethyl substituted pyrrolidine. In the case of (+)-DGDP, formation of the corresponding aziridinium ion followed by regioselective ring-opening with H₂O gave the desired hydroxymethyl substituted pyrrolidine as a single diastereoisomer (>99:1 dr), with subsequent deprotection giving (+)-DGDP in good yield. Whereas in the case of (+)-ADGDP, displacement of iodide with NaN₃ proved to be optimal, giving (+)-ADGDP in good yield after reduction and deprotection.     

Analysis of the reactions used for the preparation of drug candidate molecules

The purpose of this perspective is to indicate the range of chemistries used in the manufacture of drug candidate molecules and to highlight certain gaps in current technologies. To do this a survey was carried out of chemical syntheses within the Process Chemistry R&D departments of GlaxoSmithKline, AstraZeneca and Pfizer.     

Pd-mBDPP-catalyzed regioselective internal arylation of electron-rich olefins by aryl halides

meso-2,4-Bis(diphenylphosphino)pentane (mBDPP) has proved to be an effective regiocontrolling ligand for palladium-catalyzed internal arylation by aryl bromides of electron-rich olefins in a common solvent DMSO with no need for any halide scavengers. The arylation of the benchmark electron-rich olefin butyl vinyl ether took place smoothly to afford exclusively alpha-arylated product with high isolated yields. The better performance of mBDPP, compared with that of the commonly used DPPP [1,3-bis(diphenylphosphino)propane], highlights the important but subtle effect of ligand on the regioselectivity of the Heck arylation reactions.     

A new hybrid electrospray Fourier transform mass spectrometer: design and performance characteristics

A new hybrid electrospray quadrupole Fourier transform mass spectrometry (FTMS) instrument design is shown and characterized. This instrument involves coupling an electrospray source and mass-resolving quadrupole, ion accumulation, and collision cell linear ion trap system developed by MDS Sciex with a home-built ion guide and ion cyclotron resonance (ICR) cell. The iterative progression of this design is shown. The final design involves a set of hexapole ion guides to transfer the ions from the accumulation/collision trap through the magnetic field gradient and into the cell. These hexapole ion guides are separated by a thin gate valve and two conduction limits to maintain the required <10(-9) mbar vacuum for FTICR. Low-attomole detection limits for a pure peptide are shown, 220 000 resolving power in broadband mode and 820 000 resolving power in narrow-band mode are demonstrated, and mass accuracy in the <2 ppm range is routinely available provided the signal is abundant, cleanly resolved, and internally calibrated. This instrument design provides high experimental flexibility, allowing Q2 CAD, SORI-CAD, IRMPD, and ECD experiments with selected ion accumulation as well as experiments such as nozzle skimmer dissociation. Initial top-down mass spectrometry experiments on a protein is shown using ECD.     

A method for the analysis of ginsenosides, malonyl ginsenosides, and hydrolyzed ginsenosides using high-performance liquid chromatography with ultraviolet and positive mode electrospray ionization mass spectrometric detection

A high-performance liquid chromatographic separation coupled to diode array absorbance and positive mode electrospray mass spectrometric detection has been developed for the analysis of ginsenosides, malonyl ginsenosides, and hydrolyzed ginsenosides in extracts of Asian ginseng (Panax ginseng) and American ginseng (P. quinquefolius). The method is capable of separating, identifying, and quantifying the predominant ginsenosides found in heated alcoholic extracts of Asian and American ginseng roots routinely sold as nutraceuticals. It also separates and identifies the malonyl ginsenosides often found in cold alcoholic extracts of ginseng root and has the potential to quantify these compounds if pure standards are available. Furthermore, it can separate and identify ginsenoside hydrolysis products such as those readily produced in situations mimicking gastric situations, including those used for dissolution studies (i.e., 0.1 N HCl, 37 degrees C).     

Mammalian laryngseal air sacs add variability to the vocal tract impedance: physical and computational modeling

Cavities branching off the main vocal tract are ubiquitous in nonhumans. Mammalian air sacs exist in human relatives, including all four great apes, but only a substantially reduced version exists in humans. The present paper focuses on acoustical functions of the air sacs. The hypotheses are investigated on whether the air sacs affect amplitude of utterances and/or position of formants. A multilayer synthetic model of the vocal folds coupled with a vocal tract model was utilized. As an air sac model, four configurations were considered: open and closed uniform tube-like side branches, a rigid cavity, and an inflatable cavity. Results suggest that some air sac configurations can enhance the sound level. Furthermore, an air sac model introduces one or more additional resonance frequencies, shifting formants of the main vocal tract to some extent but not as strongly as previously suggested. In addition, dynamic range of vocalization can be extended by the air sacs. A new finding is also an increased variability of the vocal tract impedance, leading to strong nonlinear source-filter interaction effects. The experiments demonstrated that air-sac-like structures can destabilize the sound source. The results were validated by a transmission line computational model.     

Design of an optimal tuned mass damper for a system with parametric uncertainty

Structural control is becoming an attractive alternative for enhanced performance of civil engineering structures subject to seismic and wind loads. However, in order to guarantee stability and performance of structures when implemented with a passive or active control technique, there is a need to include information of uncertainty in the structural models due to the fact that civil engineering structures are time variant and nonlinear. These variations in the structure are often due to parameters such as variable live loads and inelastic behavior and, in cases, may be modeled as parametric uncertainty. The design of an optimal tuned mass damper (TMD) for a one degree-of-freedom (SDOF) system with parametric uncertainty is presented in this paper. The optimization of the connection between the absorber and the primary structure is cast as a constant feedback problem which is solved using structured singular value, μ, synthesis with D-K iteration and decentralized H _∞ design. Results are presented of the TMD that minimize the harmonic response of the primary structure represented by a set of systems within an uncertainty set.