Christian G. Bochet

Bio: Christian G. Bochet is an academic researcher from University of Fribourg. The author has contributed to research in topics: Cycloaddition & Protecting group. The author has an hindex of 27, co-authored 108 publications receiving 3680 citations. Previous affiliations of Christian G. Bochet include University of Geneva & Imperial College London.

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Abstract: The review covers the knowledge on photoremovable protecting groups and includes all relevant chromophores studied in the time period of 2000–2012; the most relevant earlier works are also discussed.

Absolute configuration of chirally deuterated neopentane.

Abstract: A molecule is 'chiral' when it cannot be superimposed on its mirror image; this property is of decisive importance throughout nature, as DNA, proteins, and many small molecules are chiral. Anomalous X-ray scattering has become the definitive method for determining the absolute configuration of a molecule, but this approach cannot be used unless the molecule contains a 'heavy' atom (for example, bromine). Haesler et al. now show that instrumental advances in Raman optical activity, combined with quantum chemical computations, have made it possible to determine the absolute configuration of molecules that do not contain a heavy atom — in this case, a specially synthesized chirally deuterated version of neopentane that represents the archetype of all molecules that are chiral as a result of a dissymmetric mass distribution. The unequivocal spectroscopic determination of the absolute configuration of this molecule presented a major challenge, one that was at the very limit of what is possible. Decisive instrumental advances in Raman optical activity (ROA), combined with quantum chemical computations, make it possible to determine the absolute configuration of (R)-[2H1, 2H2, 2H3]-neopentane. The relationship between macroscopic chirality and chirality on the molecular level was unequivocally established in 1951 through anomalous X-ray scattering1. Although this technique became the definitive method for determining the absolute configuration of a molecule, one important limitation of the approach is that the molecule must contain ‘heavy’ atoms (for example, bromine). The direct determination of absolute configurations for a wider range of molecules has recently become possible by measuring a molecule’s vibrational optical activity2,3. Here we show that instrumental advances in Raman optical activity4,5, combined with quantum chemical computations6,7,8, make it possible to determine the absolute configuration of (R)-[2H1, 2H2, 2H3]-neopentane9. This saturated hydrocarbon represents the archetype of all molecules that are chiral as a result of a dissymmetric mass distribution. It is chemically inert and cannot be derivatized to yield molecules that would reveal the absolute configuration of the parent compound. Diastereomeric interactions with other molecules, optical rotation, and electronic circular dichroism are, in contrast to the well-known case of bromochlorofluoromethane10,11,12, not expected to be measurable. Vibronic effects in the vacuum ultraviolet circular dichroism might reveal that the molecule is chiral, but the presence of nine rotamers would make it extremely difficult to interpret the spectra, because the spatial arrangement of the rotamers’ nuclei resembles that of enantiomers. The unequivocal spectroscopic determination of the absolute configuration of (R)-[2H1, 2H2, 2H3]-neopentane therefore presented a major challenge, one that was at the very limit of what is possible.

The ABC transporter BcatrB from Botrytis cinerea exports camalexin and is a virulence factor on Arabidopsis thaliana

Abstract: Arabidopsis thaliana is known to produce the phytoalexin camalexin in response to abiotic and biotic stress. Here we studied the mechanisms of tolerance to camalexin in the fungus Botrytis cinerea, a necrotrophic pathogen of A. thaliana. Exposure of B. cinerea to camalexin induces expression of BcatrB, an ABC transporter that functions in the efflux of fungitoxic compounds. B. cinerea inoculated on wild-type A. thaliana plants yields smaller lesions than on camalexin-deficient A. thaliana mutants. A B. cinerea strain lacking functional BcatrB is more sensitive to camalexin in vitro and less virulent on wild-type plants, but is still fully virulent on camalexin-deficient mutants. Pre-treatment of A. thaliana with UV-C leads to increased camalexin accumulation and substantial resistance to B. cinerea. UV-C-induced resistance was not seen in the camalexin-deficient mutants cyp79B2/B3, cyp71A13, pad3 or pad2, and was strongly reduced in ups1. Here we demonstrate that an ABC transporter is a virulence factor that increases tolerance of the pathogen towards a phytoalexin, and the complete restoration of virulence on host plants lacking this phytoalexin.

Wavelength-Selective Caged Surfaces: How Many Functional Levels Are Possible?

Abstract: The possibility of wavelength-selective cleavage of seven photolabile caging groups from different families has been studied. Amine-, thiol-, and carboxylic-terminated organosilanes were caged with o-nitrobenzyl (NVOC, NPPOC), benzoin (BNZ), (coumarin-4-yl)methyl (DEACM), 7-nitroindoline (DNI, BNI), and p-hydroxyphenacyl (pHP) derivatives. Caged surfaces modified with the different chromophores were prepared, and their photosensitivity at selected wavelengths was quantified. Different pairs, trios, and quartets of chromophore combinations with wavelength-selective photoresponse were identified. Our results show, for the first time, the possibility of generating surfaces with up to four different and independently addressable functional levels. In addition, this manuscript presents the first systematic comparison of the photolytic properties of different photolabile groups under different irradiation conditions.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Abstract: Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Abstract: The review covers the knowledge on photoremovable protecting groups and includes all relevant chromophores studied in the time period of 2000–2012; the most relevant earlier works are also discussed.

Visible-Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Abstract: Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.