Total Synthesis of Mycinolide IV and Path‐Scouting for Aldgamycin N

Proof‐of‐concept is provided that a large estate of 16‐membered macrolide antibiotics can be reached by a “unified” approach. The key building block was formed on scale by an asymmetric vinylogous Mukaiyama aldol reaction; its alkene terminus was then converted either into the corresponding methyl ketone by Wacker oxidation or into a chain‐extended aldehyde by catalyst‐controlled branch‐selective asymmetric hydroformylation. These transformations ultimately opened access to two structurally distinct series of macrolide targets. Notable late‐stage maneuvers comprise a rare example of a ruthenium‐catalyzed redox isomerization of an 1,3‐enyne‐5‐ol into a 1,3‐diene‐5‐one derivative, as well as the elaboration of a tertiary propargylic alcohol into an acyloin by trans‐hydrostannation/Chan‐Lam‐type coupling. Moreover, this case study illustrates the underutilized possibility of forging complex macrolactone rings by transesterification under essentially neutral conditions

North Atlantic western boundary currents are intense dissolved organic carbon streams

In the North Atlantic, there are two main western boundary currents related to the Atlantic Meridional Overturning Circulation (AMOC): the Gulf Stream flowing northward and the Deep Western Boundary Current (DWBC) flowing southward. Here we analyze data from the OVIDE section (GO-SHIP A25 Portugal-Greenland 40-60 degrees N) that crosses the DWBC and the northward extension of the Gulf Stream, the North Atlantic Current. We show that North Atlantic western boundary currents play a key role in the transport of dissolved organic matter, specifically dissolved organic carbon (DOC). Revisited transports and budgets of DOC with new available data identify the eastern Subpolar North Atlantic (eSPNA) as an important source of locally produced organic matter for the North Atlantic and a key region in the supply of bioavailable DOC to the deep ocean. The East Greenland Current, and its upstream source the East Reykjanes Ridge Current on the eastern flank of the mid-Atlantic ridge, are export pathways of bioavailable DOC toward subtropical latitudes. The fast overturning and subsequent remineralization of DOC produced in the autotrophic eSPNA explains up to 38% of the total oxygen consumption in the deep North Atlantic between the OVIDE section and 24 degrees N. Carbon budgets that do not take into account this organic remineralization process overestimates the natural uptake of carbon dioxide (CO2) from the atmosphere by one third. The inclusion of DOC transports in regional carbon budgets reconciles the estimates of CO2 uptake in the North Atlantic between model and observations.FCT: UID/Multi/04326/2019/ CEECINST/00114/2018.info:eu-repo/semantics/publishedVersio

Stereoselective cis -Vinylcyclopropanation via a Gold(I)-Catalyzed Retro-Buchner Reaction under Mild Conditions

A highly stereoselective gold(I)-catalyzed cis-vinylcyclopropanation of alkenes has been developed. Allylic gold carbenes, generated via a retro-Buchner reaction of 7-alkenyl-1,3,5-cycloheptatrienes, react with alkenes to form vinylcyclopropanes. The gold(I)-catalyzed retro-Buchner reaction of these substrates proceeds by simple heating at a temperature much lower than that required for the reaction of 7-aryl-1,3,5-cycloheptatrienes (75 °C vs 120 °C). A newly developed Julia−Kocienski reagent enables the synthesis of the required cycloheptatriene derivatives in one step from readily available aldehydes or ketones. On the basis of mechanistic investigations, a stereochemical model for the cis selectivity was proposed. An unprecedented gold-catalyzed isomerization of cis– to trans-cyclopropanes has also been discovered and studied by DFT calculations

The GEOVIDE cruise in May-June 2014 reveals an intense Meridional Overturning Circulation over a cold and fresh subpolar North Atlantic

The GEOVIDE cruise was carried out in the subpolar North Atlantic (SPNA) along the OVIDE section and across the Labrador Sea in May-June 2014. It was planned to clarify the distribution of the trace elements and their isotopes in the SPNA as part of the GEOTRACES international program. This paper focuses on the state of the circulation and distribution of thermohaline properties during the cruise. In terms of circulation, the comparison with the 2002-2012 mean state shows a more intense Irminger Current and also a weaker North Atlantic Current, with a transfer of volume transport from its northern to its central branch. However, those anomalies are compatible with the variability already observed along the OVIDE section in the 2000s. In terms of properties, the surface waters of the eastern SPNA were much colder and fresher than the averages over 2002-2012. In spite of negative temperature anomalies in the surface waters, the heat transport across the OVIDE section estimated at 0.56±0.06PW was the largest measured since 2002. This relatively large value is related to the relatively strong Meridional Overturning Circulation measured across the OVIDE section during GEOVIDE (18.7±3.0Sv). By analyzing the air-sea heat and freshwater fluxes over the eastern SPNA in relation to the heat and freshwater content changes observed during 2013 and 2014, we concluded that on a short timescale these changes were mainly driven by air-sea heat and freshwater fluxes rather than by ocean circulation

Ocean acidification in the subpolar North Atlantic:Rates and mechanisms controlling pH changes

Repeated hydrographic sections provide critically needed data on and understanding of changes in basin-wide ocean CO2 chemistry over multi-decadal timescales. Here, high-quality measurements collected at twelve cruises carried out along the same track between 1991 and 2015 have been used to determine long-term changes in ocean CO2 chemistry and ocean acidification in the Irminger and Iceland basins of the North Atlantic Ocean. Trends were determined for each of the main water masses present and are discussed in the context of the basin-wide circulation. The pH has decreased in all water masses of the Irminger and Iceland basins over the past 25 years with the greatest changes in surface and intermediate waters (between -0.0010 ± 0.0001 and -0.0018 ± 0.0001 pH units yr-1). In order to disentangle the drivers of the pH changes, we decomposed the trends into their principal drivers: changes in temperature, salinity, total alkalinity (AT) and total dissolved inorganic carbon (both its natural and anthropogenic components). The increase in anthropogenic CO2 (Cant) was identified as the main agent of the pH decline, partially offset by AT increases. The acidification of intermediate waters caused by Cant uptake has been reinforced by the aging of the water masses over the period of our analysis. The pH decrease of the deep overflow waters in the Irminger basin was similar to that observed in the upper ocean and was mainly linked to the Cant increase, thus reflecting the recent contact of these deep waters with the atmosphere

Quasi-synoptic transport, budgets and water mass transformation in the Azores–Gibraltar Strait region during summer 2009

We describe the circulation patterns in the Azores–Gibraltar Strait region (North-Eastern Atlantic) during the 2009 CAIBOX cruise on the basis of hydrographic and direct current velocity measurements. This study offers new data for a region where importation of central waters (subpolar and subtropical modes of Eastern North Atlantic Central Water) and exports of Mediterranean Water are strongly related to large-scale dynamics in the North Atlantic Ocean (Azores Current-Mediterranean Water system). The description is backed up quantitatively by the results of a box inverse model, which was used to obtain absolute water mass transport values consistent with thermal wind equations and with conservation of volume, salt and heat. The contributions of water masses were determined in an extended Optimum Multiparameter Analysis from a quasi-synoptic point of view, providing detail in addition to volume, salt and heat transport. The surface–subsurface large-scale current system in the region consists of the Azores Current (13.1 ± 2.5 Sverdrup [Sv], 1 Sv = 106 m3 s−1), the Azores Counter-Current (5.2 ± 2.1 Sv), the Portugal Current (4.5 ± 1.4 Sv) and the Canary Current (7.1 ± 1.1 Sv). Broadly speaking, central waters are imported into the CAIBOX region at a rate of 1.6 ± 0.9 Sv, and Mediterranean Water is exported at a rate of 1.5 ± 0.4 Sv. The downwelling of central waters west of Gibraltar Strait was quantified at 1.1 Sv. Not all this volume participates in MW formation, but 0.8 Sv of entrained central waters; of which 0.5 Sv are from central waters of subpolar origin and 0.3 Sv from subtropical central waters. Of the 4.9 Sv of subtropical central waters advected by the Azores Current, about 0.7 Sv would reach the Gulf of Cadiz region either to take part in central water entrainment or to flow across the Gibraltar Strait as part of the Atlantic inflow to the Mediterranean Sea

Genetic mixed stock analysis of an interceptory Atlantic salmonfishery in the Northwest Atlantic

Interceptory fisheries represent an ongoing threat to migratory fish stocks particularly when managed in the absence of stock specific catch and exploitation information. Atlantic salmon from the southern portion of the North American range may be subject to exploitation in the commercial and recreational salmon fisheries occurring in the French territorial waters surrounding St. Pierre and Miquelon off southern Newfoundland. We evaluated stock composition of Atlantic salmon harvested in the St. Pierreand Miquelon Atlantic salmon fishery using genetic mixture analysis and individual assignment with a microsatellite baseline (15 loci, 12,409 individuals, 12 regional groups) encompassing the species western Atlantic range. Individual salmon were sampled from the St. Pierre and Miquelon fishery over four years (2004, 2011, 2013, and 2014). Biological characteristics indicate significant variation among years in the size and age distribution. Nonetheless, estimates of stock composition of the samples showed consistent dominance of three regions (i.e., Southern Gulf of St. Lawrence, Gaspe Peninsula, and New-foundland). Together salmon from these regions accounted for more than 70% of annual harvest over the decade examined. Comparison of individual assignments and biological characteristics revealed a trend of declining fresh water age with latitude of assigned region. Moreover, locally harvested Newfoundland salmon were ten times more likely to be small or one sea winter individuals whereas Quebec and Gaspe Peninsula salmon were two-three times more likely to be harvested as large or two sea winter salmon.Estimates of region specific catch were highest for salmon from the southern Gulf of St. Lawrence region ranging from 242 to 887 individuals annually. This work illustrates how genetic analysis of interceptory marine fisheries can directly inform assessment and management efforts in highly migratory marines pecies