Synthesis of the sialic acid (-)-KDN and certain epimers from (-)-3-dehydroshikimic acid or (-)-quinic acid

(-)-3-Dehydroshikimic acid (3-DHS, 4), a C(7)-building block now available in large quantity from corn syrup, has been converted into the sialic acid (-)-KDN (3) as well as its C-7- and C-8-epimers. (-)-Quinic acid can be used for the same purpose. [structure: see text]     

Hybrid triple quadrupole-linear ion trap mass spectrometry in fragmentation mechanism studies: application to structure elucidation of buspirone and one of its metabolites

The use of a hybrid triple quadrupole-linear ion trap (QqQ(LIT)) mass spectrometer system for a comprehensive study of fragmentation mechanisms is described. The anxiolytic drug, buspirone, was chosen as a model compound for this study. With the advent of a QqQ(LIT) instrument, both the traditional quadrupole and the new linear ion trap scans (LIT) could be performed in a single LC run. In the past, a sample had to be run on two different instruments, namely, a triple quadrupole instrument (QqQ) and a 3D ion trap (3D IT) to obtain similar information. With the new QqQ(LIT) technology, collision-induced dissociation (CID) occur in a quadrupole collision cell, q2, and fragment ions are trapped and analyzed in Q3 operated in LIT mode. In this work, high-sensitivity product ion spectra of buspirone were obtained from the one-stage 'Enhanced Product Ion' scan (EPI) with rich product ions and no low mass cut-off. Furthermore, detailed fragmentation pathways were elucidated by further dissociation of each of the fragment ions in the EPI spectrum using MS(3) mode in the same run. The MS(3) scan was performed by incorporating CID in q2, and trapping, cooling, isolation, and resonance-excitation in Q3 when operating in LIT mode. This approach allowed unambiguous assignment of all fragment ions quickly with fewer experiments and easier interpretation than the previous approach. The overall sensitivity for obtaining complete fragment ion data was significantly improved for QqQ(LIT) as compared with that of QqQ and 3D IT mass spectrometers. This is beneficial for structure determination of unknown trace components. The method allowed structure determination of metabolites of buspirone in rat microsomes at 1 microM concentration, which was a 10-fold lower concentration than was needed for QqQ or 3D IT instruments. The QqQ(LIT) instrument provided a simple, rapid, sensitive and powerful approach for structure elucidation of trace components.     

Steady-state motion of a mode-III crack on imperfect interfaces

The aim of the present paper is to analyse the behaviour ofthe stress and displacement fields in the vicinity of the tipof a crack moving along a bi-material interface. For simplicity,we consider a straight interface of infinite extent. We assumethat the two phases are separated by a thin layer which is either‘soft’ or ‘stiff’ compared to the othertwo phases. We derive the transmission conditions which takeinto account the material properties of the layer and modelthe way the load is transferred across the layer from one phaseto the other. We assume that the point of interchange in theboundary/transmission conditions coincides with the crack tipthat moves along the interface boundary with a constant speed.We develop an integral equation formulation and derive asymptoticformulae for the out-of-plane displacement and the Mode-IIIstress intensity factor associated with such a motion of thecrack inside the interphase layer. The theoretical results areillustrated by numerical examples.     

Synthesis and Enzyme Inhibitory Activities of Highly Functionalized Pyridylmethyl-C-β-D-Glycosides

Several pyridylmethyl-C-β-D-glycosides (3a–3l, 6a, and 6h) were synthesized by refluxing 3-(β-D-glucopyranosyl)/(β-D-cellobiosyl)-propanones and dicyanobenzylidenes with ammonium acetate in anhydrous toluene in moderate to good yields. The reaction involves a C?C Michael addition of enamine, formed from glycosyl ketone and ammonium acetate, to the dicayanobenzylidene derivative; subsequent dehydrative cyclization; and oxidative aromatization. Two of these prototypes, compounds 3e and 3k, were deacetylated to the respective glucopyranosyl methyl pyridines 4e and 4k with NaOMe/MeOH. The synthesized compounds were screened for their in vitro α-glucosidase inhibitory activities and one of the compounds showed 20% inhibition as compared to standard drug acarbose displaying 39% inhibition.     

The acoustic emissions of cavitation bubbles in stretched vortices

Pairs of unequal strength, counter-rotating vortices were produced in order to examine the inception, dynamics, and acoustic emission of cavitation bubbles in rapidly stretching vortices. The acoustic signatures of these cavitation bubbles were characterized during their inception, growth, and collapse. Growing and collapsing bubbles often produced a sharp, broadband, pop sound. The spectrum of these bubbles, and the peak resonant frequency can generally be related to quiescent flow bubble dynamics and corresponding resonant frequencies. However, some elongated cavitation bubbles produced a short tonal burst, or chirp, with frequencies on the order of a few kilohertz. Theses frequencies are too low to be related to resonant frequencies of a bubble in a quiescent flow. Instead, the frequency content of the acoustic signal during bubble inception and growth is related to the volumetric oscillations of the bubble while it interacted with vortical flow that surrounds the bubble (i.e., the resonant frequency of the vortex-bubble system). A relationship was determined between the observed peak frequency of the oscillations, the highly stretched vortex properties, and the water nuclei content. It was found that different cavitation spectra could relate to different flow and fluid properties and therefore would not scale in the same manner.     

A Synthetic,Structural, Spectroscopic and DFT study of ReI,CuI, RuII and IrIII Complexes Containing Functionalised Dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz)

The ligands 11‐cyanodipyrido[3,2‐a:2′,3′‐c]phenazine and 2‐(11‐dipyrido[3,2‐a:2′,3′‐c]phenazine)‐5‐phenyl‐1,3,4‐oxadiazole have been coordinated to Re^I, Cu^I, Ru^II and Ir^III metal centres. Single‐crystal X‐ray analyses were performed on fac‐chlorotricarbonyl(11‐cyanodipyrido[3,2‐a:2′,3′‐c]phenazine)rhenium (C₂₂H₉ClN₅O₃Re, a=6.509(5), b=12.403(5), c=13.907(5) Å, α=96.88(5), β=92.41(5), γ=92.13(5)°, triclinic, P , Z=2) and bis‐2,2′‐bipyridyl(2‐(11‐dipyrido[3,2‐a:2′,3′‐c]phenazine)‐5‐phenyl‐1,3,4‐oxadiazole)ruthenium triflate ? 2 CH₃CN (C₅₂H₃₆F₆N₁₂O₈RuS₂, a=10.601(5), b=12.420(5), c=20.066(5) Å, α=92.846(5), β=96.493(5), γ=103.720(5)°, triclinic, P , Z=2). The ground‐ and excited‐state properties of the ligands and complexes have been investigated with a range of techniques, including electrochemistry, absorption and emission spectroscopy, spectroelectrochemistry and excited‐state lifetime studies. Spectroscopic, time‐resolved and DFT studies reveal that the ligand‐centred (LC) transitions and their resultant excited states play an important role in the photophysical properties of the complexes. Evidence for the presence of lower‐lying metal‐to‐ligand charge‐transfer transitions is obtained from resonance Raman spectroscopy, but nanosecond transient Raman experiments suggest that once excited, the ³LC state is populated.     

On the relationship between GC content and the number of predicted microRNA binding sites by MicroInspector

MicroRNA GC content and length is believed to play a role in the prediction of putative microRNA targets. MicroInspector was evaluated to determine the extent to which these characteristics of microRNAs play a role in binding site predictive accuracy. A strong bias towards under predicting the number of expected bindings sites for low GC content sequences was observed, especially for microRNAs with <50% GC content. Researchers working with organisms with unusually low GC content should be aware of this bias.     

Turnover of hydrogen isotopes in lake sturgeon blood: implications for tracking movements of wild populations

Naturally occurring deuterium (²H) in biota can be used to trace movement, migration and geographic origin of a range of organisms. However, to evaluate movements of animals using δ²H measurements of tissues, it is necessary to establish the turnover time of ²H in the tissues and the extent of isotopic discrimination from different environmental ²H sources to those tissues. We investigated the turnover of ²H in lake sturgeon (Acipenser fulvescens) blood by manipulating both environmental water δ²H and diet δ²H over a four-month period. The half-life of deuterium in lake sturgeon blood was 37.9 days after an increase in the environmental water δ²H of +714?‰. However, no clear turnover in blood ²H occurred over the same period in a separate trial following a change of ?63.8?‰ or +94.2?‰ in diet. These findings suggest that environmental water ²H exchanges much faster with blood than diets and that blood δ²H values can be used to trace movements of sturgeon and other fish moving among isotopically distinct waters.     

Synthesis of chromium(III) bis(benzamidinate) complexes via single electron oxidation

Single-electron oxidation of the known Cr(II) bis(amidinate) Cr[(Me₃SiN)₂CPh]₂ (1) provides synthetic access to neutral Cr(III) complexes. The complexes Cr[(Me₃SiN)₂CPh]₂X were prepared by reaction of 1 with AgO₂CPh (X = O₂CPh, 2), of 1 with iodine in THF (X = I/THF, 3), or of 1 with iodine in pentane, followed by addition of 2-adamantanone (X = I/2-adamantanone, 4). Treatment of 2 or 3 with C₃H₅MgCl resulted in the thermally stable allyl complex (X = η³-C₃H₅, 5). A preliminary kinetics study of the reaction of 1 with excess allyl benzoate and allyl acetate was performed. The molecular structures of 2, 3 and 5 were confirmed by single crystal X-ray diffraction.