Immobilization of pyrene - adorned N - heterocyclic carbene complexes of rhodium (I) on reduced graphene oxide and study of catalytic activity

Twopyrene-tagged N-heterocyclic carbene (NHC) complexes of rhodium(I) wereobtained and characterized. Thetwo complexes were supported onto reduced graphene oxide (rGO), generating two new materials in which the molecular complexes are immob ilized by p–p stacking interactions onto the surfaceofthe solid. The catalytic activity of both complexes and solid hybrid materials were studied in the 1,4-addition of phenylboronic acid to cyclohex-2-one, and in the hydrosilylation of terminal alkynes. The studies showed that for both reactions,the dimetallic complex displayed better catalytic performances than the monometallic one. This accounted for both the reactions performed in homogeneous conditions and for the reactions performed with the solid. In the case of the addition of phenylboronic acid to cyclohexanone,the solid containing the dimetallic catalystcould be effectively recycled up to five times, with negligible loss of activity,whereas the monometallic catalyst rapidlybecame inactive. In the hydrosilylation of terminal alkynes, the selectivity towards the b-(Z)-vinylsilane was improved if the immobilized dimetallic catalyst was used, although the catalyst startedtolose activity after the second run

Phospholane-phosphite ligands for Rh catalyzed enantioselective conjugate addition : unusually reactive catalysts for challenging couplings

We would like to thank the University of St Andrews, and the EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT) for financial support [Ph.D. studentship to SG; Grant code: EP/L016419/1], and the EPSRC for funding of JAF (EP/M003868/1).The use of Rh catalysts derived from a phospholane-phosphite ligand were found to be more productive than the classic rhodium/BINAP system in enantioselective conjugate additions. These catalysts enable the use of lower amounts of aryl boronic acid in an asymmetric arylation reaction that required an impractical excess of nucleophile. This catalyst was also found to enable the coupling of a poorly reactive Michael acceptor, N-CBz-2-3-dehydro-4-piperidone, or the coupling of poorly reactive 2-furyl boronic acids at ambient or near temperatures.Publisher PDFPeer reviewe

How can natural products serve as a viable source of lead compounds for the development of new/novel anti-malarials?

Malaria continues to be an enormous global health challenge, with millions of new infections and deaths reported annually. This is partly due to the development of resistance by the malaria parasite to the majority of established anti-malarial drugs, a situation that continues to hamper attempts at controlling the disease. This has spurred intensive drug discovery endeavours geared towards identifying novel, highly active anti-malarial drugs, and the identification of quality leads from natural sources would greatly augment these efforts. The current reality is that other than compounds that have their foundation in historic natural products, there are no other compounds in drug discovery as part of lead optimization projects and preclinical development or further that have originated from a natural product start-point in recent years. This paper briefly presents both classical as well as some more modern, but underutilized, approaches that have been applied outside the field of malaria, and which could be considered in enhancing the potential of natural products to provide or inspire the development of anti-malarial lead compounds

Natural products in modern life science

With a realistic threat against biodiversity in rain forests and in the sea, a sustainable use of natural products is becoming more and more important. Basic research directed against different organisms in Nature could reveal unexpected insights into fundamental biological mechanisms but also new pharmaceutical or biotechnological possibilities of more immediate use. Many different strategies have been used prospecting the biodiversity of Earth in the search for novel structure–activity relationships, which has resulted in important discoveries in drug development. However, we believe that the development of multidisciplinary incentives will be necessary for a future successful exploration of Nature. With this aim, one way would be a modernization and renewal of a venerable proven interdisciplinary science, Pharmacognosy, which represents an integrated way of studying biological systems. This has been demonstrated based on an explanatory model where the different parts of the model are explained by our ongoing research. Anti-inflammatory natural products have been discovered based on ethnopharmacological observations, marine sponges in cold water have resulted in substances with ecological impact, combinatory strategy of ecology and chemistry has revealed new insights into the biodiversity of fungi, in depth studies of cyclic peptides (cyclotides) has created new possibilities for engineering of bioactive peptides, development of new strategies using phylogeny and chemography has resulted in new possibilities for navigating chemical and biological space, and using bioinformatic tools for understanding of lateral gene transfer could provide potential drug targets. A multidisciplinary subject like Pharmacognosy, one of several scientific disciplines bridging biology and chemistry with medicine, has a strategic position for studies of complex scientific questions based on observations in Nature. Furthermore, natural product research based on intriguing scientific questions in Nature can be of value to increase the attraction for young students in modern life science

Les trifluoro(organo)borates de potassium : nouvelles perspectives pour la formation de liaisons carbone-carbone à l'aide de complexes du rhodium

This manuscript describes the use of potassium trifluoro(organo)borates in rhodiumcatalyzed carbon-carbon bond forming reactions. These easy to purify and very stable reagents turned out to constitute a valuable alternative to other boron reagents commonly used in transition metal catalyzed reactions. Asymmetric rhodium-catalyzed 1,4-additions of trifluoroborates were developed with the use of a chiral diphosphine which allowed a good control of the enantioselectivity. Under neutral conditions Michael adducts were obtained from various acceptors in nearly quantitative yield avoiding the use of a large excess of organometallic reagent. A new catalytic method for 1,2-addition allowed an easy and straightforward access to various alcohols. This general reaction proceeds under very mild conditions and was applied to the synthesis of substituted carbinols. Finally, a new cross-coupling reaction between organometallic reagents (boron and tin derivatives) and aldehydes has been discovered. This C-H bond activation has allowed an easy access to dissymmetric ketones using nonfunctionalized derivatives.Ce manuscrit présente l'utilisation de trifluoro(organo)borates de potassium dans des réactions de formation de liaisons carbone-carbone catalysées par des complexes du rhodium. Ces composés très stables, faciles à préparer et à purifier constituent une alternative intéressante aux dérivés du bore trivalent habituellement utilisés en catalyse. Un système catalytique général a été développé pour réaliser des additions de Michael asymétriques. L'emploi d'une diphosphine chirale assure un bon contrôle de l'énantiosélectivité et de bonnes conversions sont obtenues en milieu neutre sans ajout d'un large excès d'organométallique. Une nouvelle méthode catalytique d'addition-1,2 a permis d'obtenir des alcools dans des conditions très douces. Cette réaction très générale peut être appliquée à la synthèse de carbinols diversement substitués. Enfin, une réaction de couplage entre un aldéhyde et un organométallique a été découverte. L'activation formelle d'une liaison C-H permet ainsi un accès facile à de nombreuses cétones non symétriques à partir de dérivés peu fonctionnalisés