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"Smith, Martin D."
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Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation
Axially chiral biaryls, as exemplified by 1,1′-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in enantioenriched form through metal-mediated cross coupling,
de novo
construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed
O
-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective
O
-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to
C
2
-symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective
O
-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.
A chiral ammonium salt mediates a dynamic kinetic resolution of racemic α-aryl ketones by atropselective
O
-alkylation. Oxidation with DDQ gives access to
C
2
-symmetric and non-symmetric BINOL derivatives in high yields and with high enantioselectivity.
Journal Article
X-Men: Legion : Shadow King rising
David Haller is no ordinary mutant. Son of Charles Xavier, founder of the X-Men, David's incredible mental powers fractured his mind and now, each of his personalities controls a different ability! And they're not all friendly, as Xavier and the New Mutants find out the hard way! But as Legion struggles to control the chaos in his head, he attracts the attention of one of Xavier's oldest and most malevolent foes: Amahl Farouk, the Shadow King, who's secretly been stalking and manipulating the X-Men and their allies. When the Shadow King sinks his hooks deep into David's mind, will two teams of X-Men be enough to defeat him -- or will David be the key to the villain's ultimate victory? Includes the Muir Island Saga storyline.
BOOK
The Dynamic Efficiency Costs of Common-Pool Resource Exploitation
We conduct the first empirical investigation of common-pool resource users' dynamic and strategic behavior at the micro level using real-world data. Fishermen's strategies in a fully dynamic game account for latent resource dynamics and other players' actions, revealing the profit structure of the fishery. We compare the fishermen's actual and socially optimal exploitation paths under a time-specific vessel allocation policy and find a sizable dynamic externality. Individual fishermen respond to other users by exerting effort above the optimal level early in the season. Congestion is costly instantaneously but is beneficial in the long run because it partially offsets dynamic inefficiencies.
Journal Article
Infinity wars
What does Infinity hold for the Marvel Universe? As the Infinity Stones come to Earth, so too comes the war for control over them. But none who wield the stones truly understand the power they contain...or comprehend what it would take to bring them to their end! The nature of the cosmos itself hangs in the balance as we learn the answer to the question on everyone's lips: Who is Requiem? The ramifications of this story will be felt throughout Infinity for years to come! As cosmic war begins to rage, Gerry Duggan and Mike Deodato Jr. gaze into the Infinite - and bring the truth to light!
Book
Less Is More: An Adaptive Branch-Site Random Effects Model for Efficient Detection of Episodic Diversifying Selection
Over the past two decades, comparative sequence analysis using codon-substitution models has been honed into a powerful and popular approach for detecting signatures of natural selection from molecular data. A substantial body of work has focused on developing a class of “branch-site” models which permit selective pressures on sequences, quantified by the ω ratio, to vary among both codon sites and individual branches in the phylogeny. We develop and present a method in this class, adaptive branch-site random effects likelihood (aBSREL), whose key innovation is variable parametric complexity chosen with an information theoretic criterion. By applying models of different complexity to different branches in the phylogeny, aBSREL delivers statistical performance matching or exceeding best-in-class existing approaches, while running an order of magnitude faster. Based on simulated data analysis, we offer guidelines for what extent and strength of diversifying positive selection can be detected reliably and suggest that there is a natural limit on the optimal parametric complexity for “branch-site” models. An aBSREL analysis of 8,893 Euteleostomes gene alignments demonstrates that over 80% of branches in typical gene phylogenies can be adequately modeled with a single ω ratio model, that is, current models are unnecessarily complicated. However, there are a relatively small number of key branches, whose identities are derived from the data using a model selection procedure, for which it is essential to accurately model evolutionary complexity.
Journal Article
Interrogating the configurational stability of atropisomers
Atropisomers are molecules whose stereogenicity arises from restricted rotation about a single bond. They are of current importance because of their applications in catalysis, medicine and materials science. The defining feature of atropisomeric molecules is that their stereoisomers are related to one another by bond rotation: as a result, evaluating their configurational stability (i.e., the rate at which their stereoisomers interconvert) is central to any work in this area. Important atropisomeric scaffolds include C–C linked biaryls, such as the ligand BINAP and the drug vancomycin, and C–N linked amine derivatives such as the drug telenzepine. This article focuses on the three most widely used experimental methods that are available to measure the rate of racemization in atropisomers, namely: (i) kinetic analysis of the racemization of an enantioenriched sample, (ii) dynamic HPLC and (iii) variable-temperature NMR. For each technique, an explanation of the theory is set out, followed by a detailed experimental procedure. A discussion is also included of which technique to try when confronted with a new molecular structure whose properties are not yet known. None of the three procedures require complex experimental techniques, and all can be performed by using standard analytical equipment (NMR and HPLC). The time taken to determine a racemization rate depends on which experimental method is required, but for a new compound it is generally possible to measure a racemization rate in <1 d.
This protocol describes how to measure the rate of racemization in atropisomers by (i) kinetic analysis of the racemization of an enantioenriched sample, (ii) dynamic HPLC and (iii) variable-temperature NMR.
Key points
Stereoisomers of atropisomeric molecules interconvert by rotation of a single bond. If the interconversion rate is slow enough, the atropisomers can be separated by HPLC. After enrichment of one isomer, the kinetics of racemization can be determined.
At increasing rates of interconversion, analytical HPLC shows two peaks, a ‘Batman’ profile (dynamic HPLC) or a single peak.
For molecules with faster interconversion, variable-temperature NMR can be performed.
Journal Article
RELAX: Detecting Relaxed Selection in a Phylogenetic Framework
Relaxation of selective strength, manifested as a reduction in the efficiency or intensity of natural selection, can drive evolutionary innovation and presage lineage extinction or loss of function. Mechanisms through which selection can be relaxed range from the removal of an existing selective constraint to a reduction in effective population size. Standard methods for estimating the strength and extent of purifying or positive selection from molecular sequence data are not suitable for detecting relaxed selection, because they lack power and can mistake an increase in the intensity of positive selection for relaxation of both purifying and positive selection. Here, we present a general hypothesis testing framework (RELAX) for detecting relaxed selection in a codon-based phylogenetic framework. Given two subsets of branches in a phylogeny, RELAX can determine whether selective strength was relaxed or intensified in one of these subsets relative to the other. We establish the validity of our test via simulations and show that it can distinguish between increased positive selection and a relaxation of selective strength. We also demonstrate the power of RELAX in a variety of biological scenarios where relaxation of selection has been hypothesized or demonstrated previously. We find that obligate and facultative γ-proteobacteria endosymbionts of insects are under relaxed selection compared with their free-living relatives and obligate endosymbionts are under relaxed selection compared with facultative endosymbionts. Selective strength is also relaxed in asexual Daphnia pulex lineages, compared with sexual lineages. Endogenous, nonfunctional, bornavirus-like elements are found to be under relaxed selection compared with exogenous Borna viruses. Finally, selection on the short-wavelength sensitive, SWS1, opsin genes in echolocating and nonecholocating bats is relaxed only in lineages in which this gene underwent pseudogenization; however, selection on the functional medium/long-wavelength sensitive opsin, M/LWS1, is found to be relaxed in all echolocating bats compared with nonecholocating bats.
Journal Article
Fish Is Food - The FAO’s Fish Price Index
World food prices hit an all-time high in February 2011 and are still almost two and a half times those of 2000. Although three billion people worldwide use seafood as a key source of animal protein, the Food and Agriculture Organization (FAO) of the United Nations-which compiles prices for other major food categories-has not tracked seafood prices. We fill this gap by developing an index of global seafood prices that can help to understand food crises and may assist in averting them. The fish price index (FPI) relies on trade statistics because seafood is heavily traded internationally, exposing non-traded seafood to price competition from imports and exports. Easily updated trade data can thus proxy for domestic seafood prices that are difficult to observe in many regions and costly to update with global coverage. Calculations of the extent of price competition in different countries support the plausibility of reliance on trade data. Overall, the FPI shows less volatility and fewer price spikes than other food price indices including oils, cereals, and dairy. The FPI generally reflects seafood scarcity, but it can also be separated into indices by production technology, fish species, or region. Splitting FPI into capture fisheries and aquaculture suggests increased scarcity of capture fishery resources in recent years, but also growth in aquaculture that is keeping pace with demand. Regionally, seafood price volatility varies, and some prices are negatively correlated. These patterns hint that regional supply shocks are consequential for seafood prices in spite of the high degree of seafood tradability.
Journal Article
Global markets and the commons: the role of imports in the US wild-caught shrimp market
The commons literature focuses heavily on rules and the behavior of resource users but places less emphasis on the returns to individual effort. However, for most resource settings, market conditions and associated resource prices are key drivers of exploitation effort. In a globalized world, import competition can strongly influence the incentives for individual resource users, a topic largely unexplored in the commons literature. Import competition is especially salient for seafood, one of the most internationally traded food groups. We analyze the US shrimp market, which was once dominated by domestic catches but is now mostly supplied by imports. For domestic producers (users of the commons), lower revenues result, while US consumers eat more shrimp at lower prices. Globalization changed the sources of price risk and compensation that domestic producers face and altered incentives to exploit the commons. In a market dominated by domestic supply shocks, the price response to a shock moderates the effect on revenue and effort. In a market dominated by imports, domestic shocks are buffered by import adjustments, while price movements are determined by global shocks. Despite losses for the domestic fishery, globalization creates new incentives to coordinate effort and capture price premiums determined in the global market.
Journal Article