Crossed intramolecular Rauhut−Currier-type reactions via dienamine activation

Trabajo presentado como póster al 3.Tag der Chemie celebrado en Dortmund (Alemania) en 2010.The intramolecular Rauhut−Currier reaction creates a carbon−carbon bond between two tethered Michael acceptors. Previous asymmetric versions have relied on 1,4-additions of chiral nucleophilic catalysts. Herein, we investigate a novel strategy that involves the formation of electron rich dienamines as key intermediates. Our methodology provides an efficient entry to the iridoid framework.Financial support was provided by the DFG (SPP1179), the Fonds der Chemischen Industrie (Dozentenstipendium to M. C.), the Alexander von Humboldt Foundation (fellowship to E. M.-L.) and the Aragón I+D Foundation and the Spanish Ministry of Science and Innovation (Programa Nacional de Movilidad de Recursos Humanos del Plan Nacional de I-D+I 2008-2011) and CSIC (PIE 200880I260) (R. P. H.).Peer Reviewe

Diversity of Color Vision: Not All Australian Marsupials Are Trichromatic

Color vision in marsupials has recently emerged as a particularly interesting case among mammals. It appears that there are both dichromats and trichromats among closely related species. In contrast to primates, marsupials seem to have evolved a different type of trichromacy that is not linked to the X-chromosome. Based on microspectrophotometry and retinal whole-mount immunohistochemistry, four trichromatic marsupial species have been described: quokka, quenda, honey possum, and fat-tailed dunnart. It has, however, been impossible to identify the photopigment of the third cone type, and genetically, all evidence so far suggests that all marsupials are dichromatic. The tammar wallaby is the only Australian marsupial to date for which there is no evidence of a third cone type. To clarify whether the wallaby is indeed a dichromat or trichromatic like other Australian marsupials, we analyzed the number of cone types in the “dichromatic” wallaby and the “trichromatic” dunnart. Employing identical immunohistochemical protocols, we confirmed that the wallaby has only two cone types, whereas 20–25% of cones remained unlabeled by S- and LM-opsin antibodies in the dunnart retina. In addition, we found no evidence to support the hypothesis that the rod photopigment (rod opsin) is expressed in cones which would have explained the absence of a third cone opsin gene. Our study is the first comprehensive and quantitative account of color vision in Australian marsupials where we now know that an unexpected diversity of different color vision systems appears to have evolved

Enantioselective rauhut-currier-type cyclizations via dienamine activation: scope and mechanism

This Feature Article describes our mechanistic studies in organocatalytic Rauhut-Currier-type reactions and some applications in target-oriented synthesis. The developed approach involves the cyclization of two tethered Michael acceptors via dienamine intermediates and leads to highly functionalized cycloalkenes. The utility of these intermediates is further demonstrated by the synthesis of biologically important targets, such as optically active iridoid derivatives. 1 Introduction 2 Organocatalytic Cyclization of Tethered α,β-Unsaturated Carbonyl Compounds; Synthesis of Cyclopentene Derivatives 2.1 Mechanistic Proposal 2.1.1 ESI-HRMS Measurements 2.1.2 NMR Experiments 2.1.3 Complementary Reactivity 2.2 Synthetic Applications 3 Organocatalytic Cyclization of Tethered α,β-Unsaturated Carbonyl Compounds; Synthesis of Cyclohexene Derivatives 4 Conclusions. © Georg Thieme Verlag Stuttgart New York.We thank the Fonds der Chemischen Industrie for a Dozentenstipendium (M.C.), the DFG (Priority Program 1179 - Organocatalysis), Spanish Government (CTQ2010-19606-C02-01), the Humboldt Foundation (postdoctoral (E.M.-L.) and experienced researcher (R.P.H.) fellowships).Peer Reviewe

Crossed Intramolecular Rauhut−Currier-Type Reactions via Dienamine Activation

International audienceThe intramolecular Rauhut-Currier reaction creates a carbon-carbon bond between two tethered Michael acceptors. Previous asymmetric versions have relied on 1,4-additions of chiral nucleophilic catalysts. Herein, we investigate a novel strategy that involves the formation of electron rich dienamines as key intermediates. Our methodology provides an efficient entry to the iridoid framework

Polymorphisms in predator induced defences of coexisting Daphnia pulex and D. longispina

A comparison of juvenile predator-avoidance polymorphisms of Daphnia pulex and D. longispina in a shallow water body of Northern Italy is reported. The presence of the Chaoborus larvae resulted in juvenile adaptive predator-avoidance cyclomorphosis in both species. The frequency of induced morphotypes was higher in the small-sized D. longispina than in the large-sized D. pulex. Relative tail-spine size was higher in D. longispina than in D. pulex. D. longispina displayed much more responsiveness to Chaoborus than D. pulex. Both species showed at least 6 different defensive morphotypes that were classified according to the neckteeth number, the neckteeth position and the thickness of occipital epithelia under neckteeth. The frequencies of different morphotypes varied significantly between species. The developmental responses of Daphnia to the presence of predators are regulated at various levels, according to specific timelines of kairomone sensitive phases and developmental frame of defense trait formation. Variation of a specific timeline might be linked to flexibility in developmental responses of Daphnia to Chaoborus and seasonal variation in the frequencies of various morphotypes. Cyclomorphosis should not only be due to changes in environmental factors that directly affects risk, but also to ones that act as proxy signaling changes in predation risk