Stereodiversified Modular Synthesis of Non‐planar Five‐Membered Cyclic N‐Hydroxylamidines: Reactivity Study and Application to the Synthesis of Cyclic Amidines
| A modular, stereodiversified and scalable synthesis of 5‐membered cyclic N‐hydroxylamidines endowed with three contiguous stereogenic centres is reported. The synthesis utilizes 2‐cyano‐3‐aryl‐4‐nitro‐alkynoates as key building blocks, which are provided by a novel 3‐component Knoevenagel ‐Michael addition manifold carried out as an aqueous emulsion (on water). The key building blocks are obtained as separable mixtures of two series of diastereomers: 2,3,4‐syn,syn and 2,3,4‐syn,anti. Both series were separately transformed into the corresponding 5‐membered 3,4,5‐trisubstituted N‐hydroxylamidines by a tandem hydrogenation cyclization reaction (stereodiversification phase). These N‐hydroxylamidines are functionalized at C3‐methinic position of the ring (alpha to the amidine function) by a robust and unprecedented N‐amidinoxyl radical‐mediated auto‐oxidation process (hydroxylation), or by a diastereoselective enamine‐based C−C bond forming manifold (creation of an all‐carbon quaternary centre). The outcome of the latter is biased by the relative disposition of substituents in the ring, affording C3‐quaternized 5‐membered cyclic N‐hydroxylamidines or 2,9‐diazabicyclo[4.3.0]non‐1‐en motives. Finally, the Ti(III)‐reduction of these quaternized N‐hydroxylamidines generates the corresponding amidines in excellent yields. |
Prieto-Ramírez, Mary Cruz; Fernández, Israel; Da Silva, Ivan; González-Platas, Javier; Armas, Pedro de; García-Tellado, Fernando
Global geographic patterns in the colours and sizes of animal-dispersed fruits
[Aim] Fruit colours attract animal seed dispersers, yet the causes of fruit colour diversity remain controversial. The lack of knowledge of large-scale spatial patterns in fruit colours has limited our ability to formulate and test alternative hypotheses to explain fruit colour, fruit size and fruit colour diversity. We describe spatial (especially latitudinal) variation in fruit colour, colour diversity and length, and test for correlations between fruit colour, length and plant habit. [Location] Global. [Time period] Present day. [Major taxa studied] Seed plants. [Methods] We assembled a database of fruit traits for 13,178 fleshy fruited plant species spanning 136 sites around the world. To assess whether fruit colour categories correspond with spectral reflectances, we tested for clustering of hue, chroma and saturation for 236 species for which we had reflectance data. We then quantified latitudinal gradients in fruit colour, fruit length and fruit colour diversity while controlling for the effects of plant habit and whether colour categories varied with respect to average fruit size. [Results] Colour categories corresponded well with reflectance data. The tropics show high colour diversity, while red fruits progressively constitute a higher proportion of the fleshy-fruited plant community towards high latitudes. All mammal-associated colours (green, orange, brown and yellow) are more common in the tropics than at high latitudes. Fruit length also increases towards the tropics. [Main conclusions] Tropical communities tend to have diverse fruit colours, including many mammal-associated fruit colours, while high latitude communities contain a higher percentage of red-fruited species. The correlation between colour and size is strong, and some latitudinal patterns may be partly driven by changes in fruit size. Differences in geography and in the history of plant lineages in the Southern versus the Northern Hemisphere may help to explain some biogeographic patterns, but alternative hypotheses related to fruit defence, development and metabolic costs are plausible.
Sinnott-Armstrong, Miranda A.; Downie, Alexander E.; Federman, Sarah; Valido, Alfredo; Jordano, Pedro; Donoghue, Michael J.
Sustainable tourism and social value at World Heritage Sites: Towards a conservation plan for Altamira, Spain
This study aims to identify the factors that constitute the social value of heritage in relation to sustainable tourism. To do so, this paper provides a theoretical contribution by unifying the fields of heritage management and sustainable tourism through a mixed-method approach. It showcases the social dimension of the World Heritage Site of Altamira, Spain, combining qualitative and quantitative techniques. Research findings provide information about the multiple factors determining the social value of heritage, namely: existential, aesthetic, economic, and legacy values and the risks associated with underestimating the contemporary social value. Ultimately, this research paves the way for improving normative approaches toward sustainable tourism and, offers practical solutions to the challenges faced by the Altamira and other World Heritage Sites.
Parga Dans, Eva; Alonso González, Pablo
Under which humidity conditions are moss spores released? A comparison between species with perfect and specialized peristomes
Dispersal is a fundamental biological process that can be divided into three phases: release, transportation, and deposition. Determining the mechanisms of diaspore release is of prime importance to understand under which climatic conditions and at which frequency diaspores are released and transported. In mosses, wherein spore dispersal takes place through the hygroscopic movements of the peristome, the factors enhancing spore release has received little attention. Here, we determine the levels of relative humidity (RH) at which peristome movements are induced, contrasting the response of species with perfect (fully developed) and specialized (reduced) peristomes. All nine investigated species with perfect peristomes displayed a xerochastic behavior, initiating a closing movement from around 50%–65% RH upon increasing humidity and an opening movement from around 90% RH upon drying. Five of the seven species with specialized peristomes exhibited a hygrochastic behavior, initiating an opening movement under increasing RH (from about 80%) and a closing movement upon drying (from about 90%). These differences between species with hygrochastic and xerochastic peristomes suggest that spore dispersal does not randomly occur regardless of the prevailing climate conditions, which can impact their dispersal distances. In species with xerochastic peristomes, the release of spores under decreasing RH can be interpreted as an adaptive mechanism to disperse spores under optimal conditions for long-distance wind dispersal. In species with hygrochastic peristomes, conversely, the release of spores under wet conditions, which decreases their wind long-distance dispersal capacities, might be seen as a safe-site strategy, forcing spores to land in appropriate (micro-) habitats where their survival is favored. Significant variations were observed in the RH thresholds triggering peristome movements among species, especially in those with hygrochastic peristomes, raising the question of what mechanisms are responsible for such differences.
Zanatta, Florian; Vanderpoorten, Alain; Hedenäs, Lars; Johansson, Victor; Patiño, Jairo; Lönnell, Nikas; Hylander, Kristoffer
Contrasting effects of invasive rabbits on endemic plants driving vegetation change in a subtropical alpine insular environment
Alpine ecosystems on islands are among the most isolated on Earth, leading to very high rates of endemism. Endemic species on oceanic islands are particularly vulnerable to invasive herbivores. In the alpine zone of Tenerife, which harbors a unique endemic flora, the dominance pattern of the two most dominant species in our days (Spartocytisus supranubius and Pterocephalus lasiospermus) has shifted in the last few decades, which may be a result of increasing rabbit pressure. In this study we explore how rabbits affect the population structure, soil nutrient composition and regeneration of our two target endemics within Teide National Park. For this purpose, we established 90 plots at 30 locations. Within 13 locations we sampled permanent exclosure plots that were established between 7 and 12 years before sampling, applying three treatments (full herbivory, rabbit herbivory and no herbivory). At one site we collected 80 soil samples to evaluate changes in soil chemistry and plant growth using a greenhouse experiment. Our results show that rabbits have a negative effect on the population structure of S. supranubius, while the contrary occurs with P. lasiospermus. Rabbit presence alters soil chemistry leading to a decline in nitrogen, which affects growth in both species. The presence of rabbits leads to a dominance shift in these two keystone endemic species, altering dominance patterns in the summit scrub of Tenerife. The decline of S. supranubius could represent the example of many endemic species of this system. Thus, we call for an immediate control of rabbit population (<0.5 rabbits/ha) to protect this unique alpine endemic flora.
Cubas, Jonay; Martín-Esquivel, José Luis; Nogales, Manuel; Severin, D. H. Irl; Hernández-Hernández, Raquel; López-Darias, Marta; Marrero-Gómez, Manuel; Arco Aguilar, Marcelino del; González-Mancebo, Juana María
Iron-Catalyzed Prins-Peterson Reaction for the Direct Synthesis of δ4-2,7-Disubstituted Oxepenes
A direct iron(III)-catalyzed Prins-Peterson reaction involving α-substituted γ-triphenylsilyl bis-homoallylic alcohols and aldehydes is described. Thus, cis--2,7-disubstituted oxepenes were synthesized in a diastereoselective reaction using sustainable catalytic conditions (3-5 mol %). This highly productive process is the result of a cascade of three chemical events with the concomitant formation of a C-O bond, a C-C bond, and a endocyclic double bond, through a Prins cyclization followed by a Peterson-type elimination. This tandem reaction is chemoselective vs the classical Prins cyclization.
Cruz, Daniel A.; Sinka, Victoria; Martín, Víctor S.; Padrón, Juan I.
The toxic benthic dinoflagellate Prorocentrum maculosum Faust is a synonym of Prorocentrum hoffmannianum Faust
Three strains of the toxic benthic dinoflagellate Prorocentrum hoffmannianum were isolated in the Canary Islands (north-east Atlantic Ocean, Spain). The identity of the strains was determined by phylogenetic analyses of partial LSU rDNA (D1-D2 regions) but their morphology based on SEM images corresponded to P. maculosum. Their toxin profiles were analyzed by liquid chromatography and high resolution mass spectrometry analysis (LC–HRMS) on cell extracts and culture media. Okadaic acid and three analogs were detected in all strains. Rather, in culture media the detected compounds were variable among strains, two of them being okadaic acid analogs not found on cell extracts. As a result, the taxonomy of the species was revised and P. maculosum is proposed as a junior synonym of P. hoffmannianum whose description is emended.
Rodríguez, Francisco; Riobó, Pilar; Crespín, Guillermo D.; Daranas, Antonio H.; De Vera, Caterina R.; Norte, Manuel; Fernández, José J.; Fraga, Santiago
Identification and quantification, by NMR and LC-MS, of sterols isolated from the marine sponge Aplysina aerophoba
Aplysterol, several didehydroaplysterols, and their acetylated derivatives were isolated from samples of the marine sponge Aplysina aerophoba, which had been collected on the coast of the Canary Islands, and were identified by chromatography and H-and C-NMR spectroscopy. A quantitative analysis was done, based on the relative intensities of the signals corresponding to the olefinic quaternary carbons from the C-NMR spectrum at 125 MHz. Finally, the results described were confirmed by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS).
Ferriol, Pere; Toledo Marante; Francisco J.; Brouard, Ignacio; Santana Rodríguez, José J.; Guedes Alonso, Rayco; González Benkovics, Alba; Mioso, Roberto
Studies on the sesquiterpene lactones from Laurus novocanariensis lead to the clarification of the structures of 1-epi-tatridin B and its epimer tatridin B
The germacranolide 1-epi-tatridin B has been isolated from the aerial parts of Laurus novocanariensis. We have observed that the identification of this lactone and its epimer tetradin B in the scientific literature is confusing and contradictory. We have therefore studied this issue clarifying errors and contributing to the structural elucidation of other related products. Moreover, we have isolated from this plant a lactone with an 1,5-ether bridge, previously obtained from Austrolabium candidum. We have now named it austroliolide, reassigned its C NMR spectrum and compared its structure with that of badgerin. In addition, we have also isolated from L. novocanariensis the known germacranolides artemorin, costunolide, tatridin A, tulirinol and verlotorin, the eudesmanolides β-cyclopyrethrosin, 1β-hydroxy-arbusculin A, magnoliaolide and reynosin, and the guaianolide dehydrocostus lactone.
Fraga, Braulio M.; Terreno, David; Cabrera, Inmaculada; Reina, Matías
Why the COI barcode should be the community DNA metabarcode for the metazoa
Metabarcoding of complex metazoan communities is increasingly being used to measure biodiversity in terrestrial, freshwater and marine ecosystems, revolutionizing our ability to observe patterns and infer processes regarding the origin and conservation of biodiversity. A fundamentally important question is which genetic marker to amplify, and although the mitochondrial cytochrome oxidase subunit I (COI) gene is one of the more widely used markers in metabarcoding for the Metazoa, doubts have recently been raised about its suitability. We argue that (a) the extensive coverage of reference sequence databases for COI; (b) the variation it presents; (c) the comparative advantages for denoising protein-coding genes; and (d) recent advances in DNA sequencing protocols argue in favour of standardizing for the use of COI for metazoan community samples. We also highlight where research efforts should focus to maximize the utility of metabarcoding.
Andújar, Carmelo; Arribas, Paula; Yu, Douglas W.; Vogler, Alfried P.; Emerson, Brent C.