Highly Enantioselective Synthesis of 1,2,3‐Substituted Cyclopropanes by Using α‐Iodo‐ and α‐Chloromethylzinc Carbenoids

Herein, we report the enantio‐ and diastereoselective formation of trans‐iodo‐ and trans‐chlorocyclopropanes from α‐iodo‐ and α‐chlorozinc carbenoids by using a dioxaborolane‐derived chiral ligand. The synthetically useful iodocyclopropane building blocks were derivatized by an electrophilic trapping of the corresponding cyclopropyl lithium species or a Negishi coupling to give access to a variety of enantioenriched 1,2,3‐substituted cyclopropanes. The synthetic utility of this method was demonstrated by the formal synthesis of an HIV‐1 protease inhibitor. In addition, the related stereoselective bromocyclopropanation was also investigated. New insights about the relative electrophilicity of haloiodomethylzinc carbenoids are also presented.     

Single-detector micro-electro-mechanical scanning grating spectrometer

A compact, robust grating spectrometer based on an optimised micro-electro-mechanical grating mirror component has been developed, built, and characterised. The application of an oscillating reflection grating micro-mirror component as scanning dispersive element in a modified Czerny–Turner monochromator layout enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. Designed for a wavelength range between 1200 and 1900 nm, the spectrometer features a spectral resolution of 10 nm with wavelength stability better than ±0.5 nm. One-hundred scan spectra can be acquired in less than one second, or spectral changes can be monitored at time a resolution of less than 10 ms. In combination with a fibre-optic interface and a typical weight of less than 1 kg, this makes this novel type of fully portable micro-electro-mechanical near-IR scanning spectrometer an interesting alternative to existing spectrometers and opens a range of new applications, in particular the detection of major and minor components in the near-IR. MEMS SG spectrometer prototype     

Use of photolithography to encode cell adhesive domains into protein microarrays

Protein microarrays are rapidly emerging as valuable tools in creating combinatorial cell culture systems where inducers of cellular differentiation can be identified in a rapid and multiplexed fashion. In the present study, protein microarraying was combined with photoresist lithography to enable printing of extracellular matrix (ECM) protein arrays while precisely controlling "on-the-spot" cell-cell interactions. In this surface engineering approach, the micropatterned photoresist layer formed on a glass substrate served as a temporary stencil during the microarray printing, defining the micrometer-scale dimensions and the geometry of the cell-adhesion domains within the printed protein spots. After removal of the photoresist, the glass substrates contained micrometer-scale cell-adhesive regions that were encoded within 300 or 500 microm diameter protein domains. Fluorescence microscopy and atomic force microscopy (AFM) were employed to characterize protein micropatterns. When incubated with micropatterned surfaces, hepatic (HepG2) cells attached on 300 or 500 mum diameter protein spots; however, the extent of cell-cell contacts within each spot varied in accordance with dimensions of the photoresist stencil, from single cells attaching on 30 microm diameter features to multicell clusters residing on 100 or 200 microm diameter regions. Importantly, the photoresist removal process was shown to have no detrimental effects on the ability of several ECM proteins (collagens I, II, and IV and laminin) to support functional hepatic cultures. The micropatterning approach described here allows for a small cell population seeded onto a single cell culture substrate to be exposed to multiple scenarios of cell-cell and cell-surface interactions in parallel. This technology will be particularly useful for high-throughput screening of biological stimuli required for tissue specification of stem cells or for maintenance of differentiated phenotype in scarce primary cells.     

Equilibrium Formation of Stable All‐Silicon Versions of 1,3‐Cyclobutanediyl

Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c‐Si₃Tip₄ (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c‐[(CR₂CH₂)(NtBu)₂]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c‐(CH)₂(NtBu)₂Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate.     

Dibenzotetraaza crown ethers: a new family of crown ethers based on o-phenylenediamine

Dibenzotetraaza (DBTA) crown ethers possess two o-phenylenediamine moieties. They are homologues of dibenzo crown ether phase-transfer catalysts and were prepared from the condensation of benzimidazoles with oligo(ethyleneglycol) dichlorides and oligo(ethyleneglycol) ditosylates. Compounds with ring sizes ranging from 18-crown-6 to 42-crown-14 were prepared. In addition, various altered benzimidizoles were used to produce DBTA crown ethers with modified substituents and ether bridges, as well as benzimidazolidine crown ethers. The synthetic approach presented here proved to be a convenient route to a new family of crown ethers with overall yields of up to 48% based on the benzimidazole. Yields for the ring-closing step were generally high, ranging from 51% to 94%, without the need for high-dilution conditions. Reaction of the DBTA crown ethers with alkyl and benzyl halides was found to be a facile way to obtain the corresponding tetra(N-organyl) compounds. Picrate extraction studies were carried out to determine phase-transfer catalytic capabilities. Extraction efficiencies for alkali-metal ions were lower than those for dibenzo-18-crown-6. Efficiencies were higher for other metal ions, with some selectivity for Pb(2+). Tetra(N-methyl) DBTA-18-crown-6 generally exhibited higher extraction efficiencies than its N-H analogue, but the selectivity was lower.