On the Synthesis,Characterization and Reactivity of N‐Heteroaryl–Boryl Radicals,a New Radical Class Based on Five‐Membered Ring Ligands

The synthesis and physical characterization of a new class of N‐heterocycle–boryl radicals is presented, based on five membered ring ligands with a N(sp²) complexation site. These pyrazole–boranes and pyrazaboles exhibit a low bond dissociation energy (BDE; B?H) and accordingly excellent hydrogen transfer properties. Most importantly, a high modulation of the BDE(B?H) by the fine tuning of the N‐heterocyclic ligand was obtained in this series and could be correlated with the spin density on the boron atom of the corresponding radical. The reactivity of the latter for small molecule chemistry has been studied through the determination of several reaction rate constants corresponding to addition to alkenes and alkynes, addition to O₂, oxidation by iodonium salts and halogen abstraction from alkyl halides. Two selected applications of N‐heterocycle–boryl radicals are also proposed herein, for radical polymerization and for radical dehalogenation reactions.     

Acylation of Sugar Hydroxyl Groups with N-BOC Amino Acid N-Carboxyanhydrides (Boc-NCAs). Synthesis of Amino Acid-Saccharide Conjugates

Boc-NCAs cleanly react with a series of free or protected sugars to give mono-or poly-amino acid conjugates in good yields. Trifluoroacetic acid in methylene chloride only cleaves the N-Boc protecting group. Treatment with aqueous trifluoroacetic acid removes the remaining isopropylidene protecting groups and leads to free glycoconjugates.     

Effect of Lewis base coordination on boryl radical reactivity: investigation using laser flash photolysis and kinetic ESR

The effect of Lewis base coordination on boryl radical reactivity (L→BH where L is triethylamine, 2‐picoline, 4‐dimethylaminopyridine, quinoline and diphenyl phosphine) is examined. Direct detection of the different boryl radicals, their transient absorption spectra, their interaction with double or triple bonds, oxygen, oxidizing agent, alkyl halides and their hydrogen lability have been studied using laser flash photolysis (LFP), kinetic ESR (KESR), ESR spin trapping and MO calculations. For example, a strong decrease of both the bond dissociation energy (BDE)(B? H) (33.8 kcal mol^?1) and the addition rate constant to MA (1300 10⁵ to >10⁵ M^?1 s^?1) was noted when going from the triethylamine borane to the quinoline borane complex, in line with the spin delocalization (1.04 vs. 0.19). These structures are also proposed as new highly efficient co‐initiators for the acrylate photopolymerization. Copyright © 2009 John Wiley & Sons, Ltd.     

A diverted total synthesis of mycolactone analogues: an insight into Buruli ulcer toxins

Mycolactones are complex macrolides responsible for a severe necrotizing skin disease called Buruli ulcer. Deciphering their functional interactions is of fundamental importance for the understanding, and ultimately, the control of this devastating mycobacterial infection. We report herein a diverted total synthesis approach of mycolactones analogues and provide the first insights into their structure-activity relationship based on cytopathic assays on L929 fibroblasts. The lowest concentration inducing a cytopathic effect was determined for selected analogues, allowing a clear picture to emerge by comparison with the natural toxins.     

New boryl radicals derived from N-heteroaryl boranes: generation and reactivity

Recently, boryl radicals have been the subject of revived interest. These structures were generated by hydrogen-abstraction reactions from the corresponding boranes (i.e., from amine or phosphine boranes). However, the classical issue remains their high B--H bond-dissociation energy (BDE), thereby preventing a very efficient hydrogen-abstraction process. In the present paper, new N-heteroaryl boranes that exhibiting low B--H BDE are presented; excellent hydrogen-transfer properties have been found. Both the generation and the reactivity of the associated boryl radicals have been investigated through their direct observation in laser flash photolysis. The boryl radical interactions with double bonds, oxygen, oxidizing agent, and alkyl halides have been studied. Some selected applications of N-heteroaryl boryl radicals as new polymerization-initiating structures are proposed to evidence their high intrinsic reactivity.     

Short total syntheses of the avenaciolide family of natural products

The avenaciolide family of natural products are small α-methylene bis-γ-lactones that exhibit a wide variety of biological activities. Herein we report concise syntheses of five members of this family of natural products along with the synthesis of one non-natural analogue. The syntheses proceed in five or six steps from simple, commercially available compounds and feature a key oxidative cyclization/lactonization reaction that likely occurs via a radical mechanism.     

Cannabinoid Receptor 2 Alters Social Memory and Microglial Activity in an Age-Dependent Manner

Physiological brain aging is characterized by gradual, substantial changes in cognitive ability, accompanied by chronic activation of the neural immune system. This form of inflammation, termed inflammaging, in the central nervous system is primarily enacted through microglia, the resident immune cells. The endocannabinoid system, and particularly the cannabinoid receptor 2 (CB₂R), is a major regulator of the activity of microglia and is upregulated under inflammatory conditions. Here, we elucidated the role of the CB₂R in physiological brain aging. We used CB₂R^−/− mice of progressive ages in a behavioral test battery to assess social and spatial learning and memory. This was followed by detailed immunohistochemical analysis of microglial activity and morphology, and of the expression of pro-inflammatory cytokines in the hippocampus. CB₂R deletion decreased social memory in young mice, but did not affect spatial memory. In fact, old CB₂R^−/− mice had a slightly improved social memory, whereas in WT mice we detected an age-related cognitive decline. On a cellular level, CB₂R deletion increased lipofuscin accumulation in microglia, but not in neurons. CB₂R^−/− microglia showed an increase of activity markers Iba1 and CD68, and minor upregulation in tnfa and il6 expression and downregulation of ccl2 with age. This was accompanied by a change in morphology as CB₂R^−/− microglia had smaller somas and lower polarity, with increased branching, cell volume, and tree length. We present that CB₂Rs are involved in cognition and age-induced microglial activity, but may also be important for microglial activation itself.     

狄氏型关于狄氏型的扰动

本文在狄氏型扰动的经典意义基础上，首次提出了狄氏型关于狄氏型的扰动的概念，并得到了若干使得扰动后的狄氏型具有拟正则性的条件，最后给出了一些应用。