Enantioselective Total Synthesis of (–)-Myrifabral A and B

A catalytic enantioselective approach to the Myrioneuron alkaloids (−)-myrifabral A and (−)-myrifabral B is described. The synthesis was enabled by a palladium-catalyzed enantioselective allylic alkylation, that generates the C(10) all-carbon quaternary center. A key N-acyl iminium ion cyclization forged the cyclohexane fused tricyclic core, while vinyl boronate cross metathesis and oxidation afforded the lactol ring of (−)-myrifabral A. Adaptation of previously reported conditions allowed for the conversion of (−)-myrifabral A to (−)-myrifabral B

Stringy K-theory and the Chern character

For a finite group G acting on a smooth projective variety X, we construct two new G-equivariant rings: first the stringy K-theory of X, and second the stringy cohomology of X. For a smooth Deligne-Mumford stack Y we also construct a new ring called the full orbifold K-theory of Y. For a global quotient Y=[X/G], the ring of G-invariants of the stringy K-theory of X is a subalgebra of the full orbifold K-theory of the the stack Y and is linearly isomorphic to the ``orbifold K-theory'' of Adem-Ruan (and hence Atiyah-Segal), but carries a different, ``quantum,'' product, which respects the natural group grading. We prove there is a ring isomorphism, the stringy Chern character, from stringy K-theory to stringy cohomology, and a ring homomorphism from full orbifold K-theory to Chen-Ruan orbifold cohomology. These Chern characters satisfy Grothendieck-Riemann-Roch for etale maps. We prove that stringy cohomology is isomorphic to Fantechi and Goettsche's construction. Since our constructions do not use complex curves, stable maps, admissible covers, or moduli spaces, our results simplify the definitions of Fantechi-Goettsche's ring, of Chen-Ruan's orbifold cohomology, and of Abramovich-Graber-Vistoli's orbifold Chow. We conclude by showing that a K-theoretic version of Ruan's Hyper-Kaehler Resolution Conjecture holds for symmetric products. Our results hold both in the algebro-geometric category and in the topological category for equivariant almost complex manifolds.Comment: Exposition improved and additional details provided. To appear in Inventiones Mathematica

Access to Functionalized Quaternary Stereocenters via the Copper-Catalyzed Conjugate Addition of Monoorganozinc Bromide Reagents Enabled by N,N-Dimethylacetamide

Monoorganozinc reagents, readily obtained from alkyl bromides, display excellent reactivity with β,β-disubstituted enones and TMSCl in the presence of Cu(I) and Cu(II) salts to synthesize a variety of cyclic functionalized β-quaternary ketones in 38–99% yields and 9:1–20:1 diastereoselectivities. The conjugate addition features a pronounced improvement in DMA using monoorganozinc bromide reagents. A simple one-pot protocol that harnesses in situ generated monoorganozinc reagents delivers comparable product yields

Temperature-induced viral resistance in Emiliania huxleyi (Prymnesiophyceae)

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 9 (2014): e112134, doi:10.1371/journal.pone.0112134.Annual Emiliania huxleyi blooms (along with other coccolithophorid species) play important roles in the global carbon and sulfur cycles. E. huxleyi blooms are routinely terminated by large, host-specific dsDNA viruses, (Emiliania huxleyi Viruses; EhVs), making these host-virus interactions a driving force behind their potential impact on global biogeochemical cycles. Given projected increases in sea surface temperature due to climate change, it is imperative to understand the effects of temperature on E. huxleyi’s susceptibility to viral infection and its production of climatically active dimethylated sulfur species (DSS). Here we demonstrate that a 3°C increase in temperature induces EhV-resistant phenotypes in three E. huxleyi strains and that successful virus infection impacts DSS pool sizes. We also examined cellular polar lipids, given their documented roles in regulating host-virus interactions in this system, and propose that alterations to membrane-bound surface receptors are responsible for the observed temperature-induced resistance. Our findings have potential implications for global biogeochemical cycles in a warming climate and for deciphering the particular mechanism(s) by which some E. huxleyi strains exhibit viral resistance.This study was supported by funding from the National Science Foundation (OCE-1061883 to KDB, BVM, and OCE-1061876 to GRD) and in part by grants from The Gordon and Betty Moore Foundation (to BVM and KDB)

Trade-offs between invertebrate fisheries catches and ecosystem impacts in coastal New Zealand

Invertebrate catches are increasing globally following the depletion of many finfish stocks, yet stock assessments and management plans for invertebrates are limited, as is an understanding of the ecosystem effects of these fisheries. Using an ecosystem modelling approach, we explored the trade-offs between invertebrate catches and their impacts on the associated ecosystem on the south coast of Wellington, New Zealand. We simulated exploitation of lobster (Jasus edwardsii), abalone (Haliotis australis, H. iris), and sea urchin (Evechinus chloroticus) over a range of depletion levels—fromno depletion to local extinction—to estimate changes in target catches and associated effects on other species groups, trophic levels, and benthic and pelagic components. Exploitation of lobster showed the strongest ecosystem effects, followed by abalone and urchin. In all three fisheries, the current exploitation rate exceeds that which producesmaximumsustainable yield, with considerable ecosystem effects. Interestingly, a reduced exploitation rate is predicted to increase target catches (and catch-per-unit-effort), thereby strongly reducing ecosystem effects, a win– win situation. Our results suggest that invertebrate exploitation clearly influences ecosystem structure and function, yet the direction and magnitude of responses depend on the target group and exploitation rate.Anecosystem-based fisheries management approach that includes the role of invertebrates would improve the conservation and management of invertebrate resources and marine ecosystems on broader scales

The CryoEM Method MicroED as a Powerful Tool for Small Molecule Structure Determination

In the many scientific endeavors that are driven by organic chemistry, unambiguous identification of small molecules is of paramount importance. Over the past 50 years, NMR and other powerful spectroscopic techniques have been developed to address this challenge. While almost all of these techniques rely on inference of connectivity, the unambiguous determination of a small molecule’s structure requires X-ray and/or neutron diffraction studies. In practice, however, X-ray crystallography is rarely applied in routine organic chemistry due to intrinsic limitations of both the analytes and the technique. Here we report the use of the electron cryo-microscopy (cryoEM) method microcrystal electron diffraction (MicroED) to provide routine and unambiguous structural determination of small organic molecules. From simple powders, with minimal sample preparation, we could collect high-quality MicroED data from nanocrystals (∼100 nm, ∼10^(–15) g) resulting in atomic resolution (<1 Å) crystal structures in minutes

Palladium-catalyzed α,β-dehydrogenation of acyclic ester equivalents promoted by a novel electron deficient phosphinooxazoline ligand

A unique example of Pd-catalyzed decarboxylative dehydrogenation of fully substituted N-acyl allyl enol carbonates is enabled by a new electron deficient phosphinooxazoline (PHOX) ligand. The reaction proceeds from the Z-enol carbonate to provide dehydrogenation products exclusively in high E/Z selectivity, while the E-enol carbonate provides the α-allylation product with only minor dehydrogenation. The reaction proceeds with a broad scope of Z-enol carbonates derived from N-acyl indoles to furnish acyclic formal α,β-unsaturated ester equivalents