Mycobacterium ulcerans infections (Buruli ulcer disease) have a long history that can be traced back 150 years. The successive discoveries of the mycobacteria in 1948 and of mycolactone A/B in 1999, the toxin responsible for this dramatic necrotic skin disease, resulted in a paradigm shift concerning the disease itself and in a broader sense, delineated an entirely new role for bioactive polyketides as virulence factors. The fascinating history, biology and chemistry of M. ulcerans infections are discussed in this review.
2013-02- Formation of NHC-Boryl Radicals through Electrochemical and Photochemical Cleavage of the B–S bond in N-Heterocyclic Carbene-Boryl Sulfides
Telitel, S.; Vallet, A.-L.; Schweizer, S.; Delpech, B.; Blanchard, N.; Morlet-Savary, F.; Graff, B.; Curran, D. P.; Robert, M.; Lacôte, E.; Lalevée, J. J. Am. Chem. Soc.2013, 135, 16938-16947.
The B–S bond in N-heterocyclic carbene (NHC)–boryl sulfides can be cleaved homolytically to NHC–boryl or NHC–thioboryl and thiyl radicals using light, either directly around 300 nm or with a sensitizer at a longer wavelength (>340 nm). In contrast, the electrochemical reductive cleavage of the B–S bond is difficult. This easy photolytic cleavage makes the NHC–boryl sulfides good type I photopolymerization initiators for the polymerization of acrylates under air.
2013-03- Taming sulfur dioxide: a breakthrough for its wide utilization in chemistry and biology
Bisseret, P.; Blanchard, N. Org. Biomol. Chem.2013, 11, 5393-5398.
Although sulfur dioxide (SO2) has been used as a reagent for organic chemistry for more than one hundred years, being endowed with quite a distinct and varied reactivity profile, which allows the synthesis of a large range of compounds, its notorious toxicity as well as its gaseous state have impeded its frequent utilization by chemists. We summarize recent studies in this emerging area aimed at stimulating its utilization in organic (including organometallic) chemistry thanks to the development of innocuous, bench-stable reliable SO2 donors. Proof-of-concept experiments have also been recently performed in biology with the design of organic SO2 donors having controlled release profiles under physiological conditions, either active against mycobacteria or used for clarifying the role of endogenously produced SO2 in living cells.
2013-04- Mechanistic and Preparative Studies of Radical Chain Homolytic Substitution Reactions of NHeterocyclic Carbene Boranes and Disulfides
Pan, X.; Vallet, A.-L.; Schweizer, S.; Dahbi, K. J.-L.; Delpech, B.; Blanchard, N.; Graff, B.; Geib, S. J.; Curran, D. P.; Lalevée, J.; Lacôte, E. J. Am. Chem. Soc.2013, 135, 10484-10491.
Reactions of 1,3-dimethylimidazol-2-ylidene–borane (diMe-Imd-BH3) and related NHC–boranes with diaryl and diheteroaryl disulfides provide diverse NHC–boryl monosulfides (diMe-Imd-BH2SAr) and NHC–boryl disulfides (diMe-Imd-BH(SAr)2). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC–borane in the primary NHC–boryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC–boryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible.
2013-05- BODIPY derivatives and boranil as new photoinitiating systems of cationic polymerization exhibiting a tunable absorption in the 400–600 nm spectral range
Novel photoinitiators based on the BODIPY and boranil chromophores being able to photosensitize the iodonium salt decomposition are proposed for the cationic polymerization of epoxy, epoxy-silicone and vinyl ether monomers under exposure to laser diodes at 405, 457, 473 and 532 nm. They allow an interesting tunability of the absorption in the 400–600 nm wavelength range. Quite excellent polymerization profiles are recorded with final conversions up to 90%. Addition of N-vinylcarbazole (NVK) can also greatly enhance the performance. ESR and steady state photolysis experiments show the generation of aryl radicals and cation radicals. The observed mechanisms are discussed.
2013-06- Soft Photopolymerizations initiated by Dye-Sensitized Formation of NHC-Boryl Radicals under Visible Light
Telitel, S.; Schweizer, S.; Morlet-Savary, F.; Graff, B.; Tschamber, T.; Blanchard, N.; Fouassier, J. P.; Lelli, M.; Lacôte, E.; Lalevée, J. Macromolecules2013, 46, 43-48.
A procedure for the production of N-heterocyclic carbene–boryl radicals (NHC-BH2•) upon visible light irradiation under soft conditions is presented. New acridine orange (dye)/diphenyl disulfide/NHC–BH3 and dye/sulfonium salt/NHC–BH3 three-component initiating systems are introduced for the efficient visible light photopolymerization of trimethylolpropane triacrylate. The new systems could be extendend to polymerization reactions in water (hydroxyethyl acrylate and hydroxyethyl methyl acrylate), which proceeded with strongly improved polydispersity. The chemical mechanisms are investigated through EPR and photolysis experiments.
