Total synthesis of infectopyrone,aplysiopsenes A–C,ent-aplysiopsene D,phomapyrones A and D, 8,9-dehydroxylarone,and nectriapyrone

The total synthesis of the 2-pyrone natural products nectriapyrone, aplysiopsenes A–C, ent-aplysiopsene D, phomapyrones A and D, and of 8,9-dehydroxylarone were achieved by Wittig olefination starting with vermopyrone. Infectopyrone was synthesized by Horner–Wadsworth–Emmons reaction starting with phomapyrone D. Racemic phomapyrone C methyl ether was obtained by hydrogenation of nectriapyrone. The total syntheses were achieved starting from commercially available 3,5-heptanedione and led to the desired natural products in 18–46% over 5–6 steps, whereupon all five-step syntheses were carried out with a single chromatographic workup. The total synthesis of infectopyrone, aplysiopsenes A–D, of phomapyrones A and D, and of 8,9-dehydroxylarone were achieved for the first time, giving unambiguous proof for the proposed structures of these natural products.     

Applying a dynamic method to the measurement of ion mobility

A dynamic method is applied to measure the mobility of gas-phase ions in the dual ion funnel interface of the electrospray source of a quadrupole orthogonal time-of-flight mass spectrometer. In a new operational mode, a potential barrier was formed in the second ion funnel of the mass spectrometer and then progressively increased. In this region, a flow of gas drags the ions into the mass spectrometer while the electric force applied by the potential barrier decelerates them. Ions with lower mobility can be carried by the gas flow more easily than those with high mobility. Thus, electrical forces can block the more mobile ions more easily. Hence, the electric barrier formed in the ion funnel permits only ions below a certain mobility threshold to enter the mass spectrometer. When the barrier voltage is increased, this threshold moves from high to low mobilities. Ions with mobilities above the threshold cannot enter the mass spectrometer, and their signal decreases to zero. Thus, in a barrier voltage scan, mass spectrometric signals of ions sequentially disappear. Differentiation of these decreasing ion signal curves produces peaks from which an ion mobility spectrum can be reconstructed. Blocking voltages, i.e., the positions of the peaks on the barrier voltage scale are directly related to the mobility of these ions. An internal calibration using ions with known mobility values helps determine the unknown ion mobilities and allows calculation of ionic cross sections.     

Application of displacement chromatography for the proteome analysis of a human plasma protein fraction

It was the aim of this study to compare the performance of displacement chromatography with gradient elution chromatography both applied as the cation-exchange separation step for a proteome analysis in a bottom-up approach using multidimensional chromatography for the separation of tryptic peptides prior to their mass spectrometric analysis. The tryptic digest of the human Cohn fraction IV-4 served as a sample. For both chromatography modes commonly used operating parameters were chosen thus ensuring optimal separation results of equal sample amounts for each mode. All resulting fractions were analyzed with an HPLC-chip–LC–MS system. The eluate of the HPLC-chip column was ionized by electrospray ionization (ESI) and analyzed with an ion-trap mass spectrometer. For guaranteeing high confidence concerning the identity of the peptides, the mass spectrometric data were processed by different bioinformatic tools applying stringent criteria. By the displacement approach the total amount of identified proteins (78) was significantly higher than in the gradient mode (58). The results showed that displacement chromatography is a well suited alternative in comparison to gradient elution separation for analysis of proteomes via the bottom-up approach applying multidimensional chromatography, especially in those cases when larger quantities of proteins are available.     

Raman and Infrared Spectroscopic Investigation of Speciation in BeSO<Subscript>4</Subscript>(aq)

Measurements have been made of the Raman spectra of aqueous solutions of Be(ClO₄)₂, BeCl₂, (NH₄)₂SO₄ and BeSO₄ to 50 cm⁻¹. In some cases low concentrations (0.000770 mol⋅kg⁻¹) have been used and two temperatures (23 and 40 °C) were studied. In BeSO₄(aq), the ν ₁-SO₄^2-\mathrm{SO}_{4}^{2-} mode at 980 cm⁻¹ broadens with increasing concentration and shifts to higher wavenumbers. At the same time, a band at 1014 cm⁻¹ is detectable with this mode being assigned to [BeOSO₃], an inner-sphere complex (ISC). Confirmation of this assignment is provided by the simultaneous appearance of stretching bands for the Be²⁺-OSO₃^2-\mathrm{Be}^{2+}\mbox{-}\mathrm{OSO}_{3}^{2-} bond of the complex at 240 cm⁻¹ and for the BeO₄ skeleton mode of the [(H₂O)₃BeOSO₃] unit at 498 cm⁻¹. The ISC concentration increases with higher temperatures. The similarity of the n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} Raman bands for BeSO₄ in H₂O and D₂O is further strong evidence for formation of an ISC. After subtraction of the ISC component at 1014 cm⁻¹, the n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} band in BeSO₄(aq) showed systematic differences from that in (NH₄)₂SO₄(aq). This is consistent with a n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} mode at 982.7 cm⁻¹ that can be assigned to the occurrence of an outer-sphere complex ion (OSCs). These observations are shown to be in agreement with results derived from previous relaxation measurements. Infrared spectroscopic data show features that are also consistent with a beryllium sulfato complex such as the appearance of a broad and weak n₁-SO₄^2-\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-} mode at ∼1014 cm⁻¹, normally infrared forbidden, and a broad and asymmetric n₃-SO₄^2-\nu_{3}\mbox{-}\mathrm{SO}_{4}^{2-} band contour which could be fitted with four band components (including n₃-SO₄^2-(aq)\nu_{3}\mbox{-}\mathrm{SO}_{4}^{2-}(\mathrm{aq})). The formation of ISCs in BeSO₄(aq) is much more pronounced than in the similar MgSO₄(aq) system studied recently.     

Molecular structure and fracture properties of ZrO<Subscript>X</Subscript>/Epoxysilane hybrid films

The mechanical reliability of hybrid films depends critically on their fracture properties which are controlled largely by the film composition and molecular structure. We have investigated the adhesive and cohesive fracture properties of hybrid films processed from 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetra n-propoxyzirconium (TPOZ), for which the roles of molecular structure and composition have not been well established. The influences of film Zr/GPTMS ratio, silane crosslinking, and substrate composition on fracture resistance were quantified in terms of the critical strain energy release rate, G_C Film fracture energy was found to increase, then decrease with increasing Zr/GPTMS ratio. Removal of the epoxy rings of GPTMS from the film was found to drastically decrease the cohesive fracture energy of the film as well as the adhesive fracture energy of the film/epoxy interface. Finally, films deposited on silicon had much higher fracture energies compared to those deposited onto aluminum and titanium from identical sols. FTIR, XPS, and AFM were used to characterize the film structure and fracture surfaces. The molecular-scale mechanisms responsible for the observed trends are discussed. These results provide new insights into the interaction between the substrate chemistry, molecular structure, and mechanical reliability of hybrid sol-gel films.     

Efficient Aerobic Wacker Oxidation of Styrenes Using Palladium Bis(isonitrile) Catalysts

The palladium‐catalyzed aerobic oxidation of alkenes and especially styrenes (Wacker oxidation) by using chiral pseudo C₂‐symmetrical bis(isonitrile) ligands in the absence of further cocatalysts gives rise to methyl ketones in a highly chemoselective manner. The palladium bis(isonitrile) catalyst was characterized by NMR spectroscopy and X‐ray structure analysis, revealing a dissymmetric coordination of palladium by the two isonitrile moieties.     

Cyclization of Propargylic Amides: Mild Access to Oxazole Derivatives

The substrate scope, the mechanistic aspects of the gold‐catalyzed oxazole synthesis, and substrates with different aliphatic, aromatic, and functional groups in the side chain were investigated. Even molecules with several propargyl amide groups could easily be converted, delivering di‐ and trioxazoles with interesting optical properties. Furthermore, the scope of the gold(I)‐catalyzed alkylidene synthesis was investigated. Further functionalizations of these isolable intermediates of the oxazole synthesis were developed and chelate ligands can be obtained. The use of Barluenga’s reagent offers a new and mild access to the synthetically valuable iodoalkylideneoxazoles from propargylic amides, this reagent being superior to other sources of halogens.