A Stereoselective Oxidative Dimerization En Route to (-)-Lomaiviticin A.

We describe a stereoselective synthesis of the dimeric diazofluorene , a potential precursor to the cytotoxic -symmetric bacterial metabolite (-)-lomaiviticin A (). An efficient route was developed to convert the tetracyclic diol to the diketone (five steps, 30% overall). Oxidative dimerization of the enoxysilane provided the -symmetric dimeric diazofluorene in 56% yield and with 15:1:0 diastereoselectivity.

Design and Semisynthesis of Biselectrophile-Functionalized Ubiquitin Probes To Investigate Transthioesterification Reactions.

Ubiquitin (Ub) regulates a wide array of cellular processes through post-translational modification of protein substrates. Ub is conjugated at its C-terminus to target proteins via an enzymatic cascade in which covalently bound Ub thioesters are transferred from E1 activating enzymes to E2 conjugating enzymes, and then to certain E3 protein ligases. These transthioesterification reactions proceed via transient tetrahedral intermediates.

Structure Elucidation of Secondary Metabolites: Current Frontiers and Lingering Pitfalls.

Analytical methods allow for the structure determination of submilligram quantities of complex secondary metabolites. This has been driven in large part by advances in NMR spectroscopic capabilities, including access to high-field magnets equipped with cryogenic probes. Experimental NMR spectroscopy may now be complemented by remarkably accurate carbon-13 NMR calculations using state-of-the-art DFT software packages.

Dementia's Unique Burden: Function and Health Care in the Last 4 Years of Life.

Background: Dementia is a terminal illness marked by progressive cognitive decline. This study characterized trajectories of functional status and health care use for people with and without dementia at the end of their life.

Methods: We used the Health and Retirement Study linked with Medicare claims to generate a series of generalized linear models.