Stereospecific C-Glycosylation by Mizoroki-Heck Reaction: A Powerful and Easy-to-Set-Up Synthetic Tool to Access α- and ß-Aryl-C-Glycosides.

A stereospecific Mizoroki-Heck cross-coupling of differently substituted glycals with haloarenes resulting in the exclusive formation of either α- or ß-aryl-C-glycosides depending solely on the configuration at C3 was achieved. The reaction was easy to set up because no specific precautions were required concerning moisture or oxygen, and it proceeded by a chirality transfer from C3 to C1. After optimization of cross-coupling conditions, various prepared glycals (7 examples) and arenes (10 examples) were tested, leading stereospecifically to the corresponding aryl-C-glycosides with a carbonyl group at C3, thus opening up new horizons for the total synthesis of glycosylated natural products.

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step.

In this paper, a new access to several chiral 3-aminoglycals as potential precursors for glycosylated natural products is reported from a common starting material, (-)-methyl-L-lactate. The stereodivergent strategy is based on the implementation of a ring-closing metathesis of vinyl ethers as key step of reaction sequences developed.

Function-Oriented Synthesis toward Peloruside A Analogues.

A convergent and rapid synthesis of original C2,C3-unsaturated, C11,C13-keto-enol macrocycles with a peloruside A skeleton has been developed. These original unsaturated macrocycles constitute valuable platforms to access peloruside A analogues with high diversity. The four-fragment strategy implemented features two aldol-type couplings with the central C12-C14 building block TES-diazoacetone and a late-stage ring-closing metathesis. Enantiopure analogue 18ab showed antiproliferative activity in the low micromolar range on NCI and MCF7 tumor cell lines.

Mitochondrial fusion in human cells is efficient, requires the inner membrane potential, and is mediated by mitofusins.

Mitochondrial fusion remains a largely unknown process despite its observation by live microscopy and the identification of few implicated proteins. Using green and red fluorescent proteins targeted to the mitochondrial matrix, we show that mitochondrial fusion in human cells is efficient and achieves complete mixing of matrix contents within 12 h. This process is maintained in the absence of a functional respiratory chain, despite disruption of microtubules or after significant reduction of cellular ATP levels. In contrast, mitochondrial fusion is completely inhibited by protonophores that dissipate the inner membrane potential. This inhibition, which results in rapid fragmentation of mitochondrial filaments, is reversible: small and punctate mitochondria fuse to reform elongated and interconnected ones upon withdrawal of protonophores. Expression of wild-type or dominant-negative dynamin-related protein 1 showed that fragmentation is due to dynamin-related protein 1-mediated mitochondrial division. On the other hand, expression of mitofusin 1 (Mfn1), one of the human Fzo homologues, increased mitochondrial length and interconnectivity. This process, but not Mfn1 targeting, was dependent on the inner membrane potential, indicating that overexpressed Mfn1 stimulates fusion. These results show that human mitochondria represent a single cellular compartment whose exchanges and interconnectivity are dynamically regulated by the balance between continuous fusion and fission reactions.

Membrane topology and mitochondrial targeting of mitofusins, ubiquitous mammalian homologs of the transmembrane GTPase Fzo.

Two human Fzo-homologs, mitofusins Mfn1 and Mfn2, are shown by RT-PCR and western blot to be ubiquitous mitochondrial proteins. Protease digestion experiments reveal that Mfn2 is an outer membrane protein with N-terminal and C-terminal domains exposed towards the cytosol. The transmembrane and C-terminal domains of Mfn2 (Mfn2-TMCT) are targeted to mitochondria and deletion of these domains leads to the cytosolic localization of truncated Mfn2 (Mfn2-NT). Mfn2 is targeted to the endoplasmic reticulum or to mitochondria when the C-terminal domain is replaced by short stretches of neutral/hydrophobic (Mfn2-IYFFT) or polar/basic (Mfn2-RRD) amino acids. The coiled-coil domains of Mfn2, upstream and downstream of the transmembrane domain, are also important for mitochondrial targeting: Mfn2-mutants deleted of any of its coiled-coil domains are only partially targeted to mitochondria and significant protein amounts remain cytosolic. We show that these coiled-coil domains interact with each other: mistargeted Mfn2-NT or Mfn2-IYFFT localize to mitochondria if co-expressed with Mfn2-TMCT. This relocalization is abolished when the coiled-coil domain is deleted in any of the co-transfected molecules. We also found that Mfn2 can cluster active mitochondria in the perinuclear region independently of the cytoskeleton, bring mitochondrial membranes into close contact and modify mitochondrial structure, without disturbing the integrity of the inner and outer membrane.

Organization and dynamics of human mitochondrial DNA.

Heteroplasmic mutations of mitochondrial DNA (mtDNA) are an important source of human diseases. The mechanisms governing transmission, segregation and complementation of heteroplasmic mtDNA-mutations are unknown but depend on the nature and dynamics of the mitochondrial compartment as well as on the intramitochondrial organization and mobility of mtDNA. We show that mtDNA of human primary and immortal cells is organized in several hundreds of nucleoids that contain a mean of 2-8 mtDNA-molecules each. Nucleoids are enriched in mitochondrial transcription factor A and distributed throughout the entire mitochondrial compartment. Using cell fusion experiments, we demonstrate that nucleoids and respiratory complexes are mobile and diffuse efficiently into mitochondria previously devoid of mtDNA. In contrast, nucleoid-mobility was lower within mitochondria of mtDNA-containing cells, as differently labeled mtDNA-molecules remained spatially segregated in a significant fraction (37%) of the polykaryons. These results show that fusion-mediated exchange and intramitochondrial mobility of endogenous mitochondrial components are not rate-limiting for intermitochondrial complementation but can contribute to the segregation of mtDNA molecules and of mtDNA mutations during cell growth and division.