Chiral linker 5: scope and limitations of arylsubstituted m-hydrobenzoins as solid supported open chain chiral auxiliaries for diastereoselective syntheses

The applicability of five aryl substituted m-hydrobenzoin ethers already tested in the L-Selectride^® mediated stereoselective reduction of phenylglyoxylates as open chain chiral auxiliaries was further investigated via the α-alkylation of propionates, the addition of n-BuZnCl to phenylglyoxylates and the Diels–Alder reaction of acrylates with cyclopentadiene as model reactions. As up to 90% de could be achieved in the solution phase, two optimized auxiliary structures were immobilized on commercially available Wang-resin and applied as a reusable solid supported chiral auxiliaries in the same type of reactions.     

Short Syntheses of (±)-Grandisol and (±) Lineatin via,a common Intermediate

A 6-step synthesis of (±)-grandisol ( 1 ) is presented, which involves dichloroketene addition to 3-methyl-3-butenyl acetate ( 4 ), reductive dechlorination of the adduct 6 to the ketone 7 and saponification to 8 , aldolization of 7 or 8 with acetone and cyclization to the bicyclic ketone 9 , Wolff-kishner, reduction to 14 , and finally ring opening to 1. Since 9 is a known intermediate of the synthesis of (±)-lineatin ( 2 ), the latter can now be obtained in 6 steps.     

Micro-fabricated metal nozzle plates used for water-in-oil and oil-in-water emulsification

In this paper the fabrication and use of micro-structured metal nozzle plates as emulsification devices is investigated and discussed. These structured metal nozzle plates were fabricated via two distinct routes. Laser ablation, performed with a femtosecond laser, was used to drill micrometer-sized holes into stainless steel and aluminum foils. Also a conventional steel mesh with an average pore size of 2.4 μm fabricated by weaving and roll compaction of micrometer-sized steel wires was investigated. The perforated metal nozzle plates were used for oil-in-water and after hydrophobization with alkylchlorosilanes for water-in-oil emulsification as well. In both cases, two types of drop formation processes were observed. The first one is the shear-induced drop formation well known for cross-flow membrane emulsification. The second is the spontaneous drop formation known from microchannel emulsification.     

Phosphorylated serine and threonine residues promote site‐specific fragmentation of singly charged,arginine‐containing peptide ions

In order to investigate gas‐phase fragmentation reactions of phosphorylated peptide ions, matrix‐assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) tandem mass (MS/MS) spectra were recorded from synthetic phosphopeptides and from phosphopeptides isolated from natural sources. MALDI‐TOF/TOF (TOF: time‐of‐flight) spectra of synthetic arginine‐containing phosphopeptides revealed a significant increase of y ions resulting from bond cleavages on the C‐terminal side of phosphothreonine or phosphoserine. The same effect was found in ESI‐MS/MS spectra recorded from the singly charged but not from the doubly charged ions of these phosphopeptides. ESI‐MS/MS spectra of doubly charged phosphopeptides containing two arginine residues support the following general fragmentation rule: Increased amide bond cleavage on the C‐terminal side of phosphorylated serines or threonines mainly occurs in peptide ions which do not contain mobile protons. In MALDI‐TOF/TOF spectra of phosphopeptides displaying N‐terminal fragment ions, abundant b–H₃PO₄ ions resulting from the enhanced dissociation of the pSer/pThr–X bond were detected (X denotes amino acids). Cleavages at phosphoamino acids were found to be particularly predominant in spectra of phosphopeptides containing pSer/pThr–Pro bonds. A quantitative evaluation of a larger set of MALDI‐TOF/TOF spectra recorded from phosphopeptides indicated that phosphoserine residues in arginine‐containing peptides increase the signal intensities of the respective y ions by almost a factor of 3. A less pronounced cleavage‐enhancing effect was observed in some lysine‐containing phosphopeptides without arginine. The proposed peptide fragmentation pathways involve a nucleophilic attack by phosphate oxygen on the carbon center of the peptide backbone amide, which eventually leads to cleavage of the amide bond. Copyright © 2009 John Wiley & Sons, Ltd.     

The Euler multiplicity and addition-deletion theorems for multiarrangements

The addition–deletion theorems for hyperplane arrangements,which were originally shown by Terao [J. Fac. Sci. Univ. TokyoSect. IA Math. 27 (1980) 293–320.], provide useful waysto construct examples of free arrangements. In this article,we prove addition–deletion theorems for multiarrangements.A key to the generalization is the definition of a new multiplicity,called the Euler multiplicity, of a restricted multiarrangement.We compute the Euler multiplicities in many cases. Then we applythe addition–deletion theorems to various arrangements,including supersolvable arrangements and the Coxeter arrangementof type A₃, to construct free and non-free multiarrangements.