Stereocontrolled synthesis of highly functionalised tetrahydrofurans,

Polysubstituted tetrahydrofurans appear in a large variety of bioactive structures of both natural and unnatural origin. The stereochemistry of the substituents has a profound effect on function; therefore, the development of new methodology for the stereoselective construction of tetrahydrofuran rings is very attractive. A tandem methodology for the stereoselective synthesis of 2,3,5-trisubstitutedtetrahydrofurans is reported here. This involves a catalytic C-H insertion of diazocarbonyl acetal templates followed by the stereoselective reductive cleavage of the resultant bicyclic acetals. A key area of this project is the formation and reaction of diazoketones. The diazoketones were prepared in good yields (70-85%) by acylation of diazomethane with a mixed anhydride, which involves the initial activation of the acid group of the corresponding acid acetal precursors. Alternatives to the use of diazomethane have been examined but proved to be less efficient. Two routes towards the synthesis of the acid acetals have been examined. A one-pot process involving the treatment of 1,3- and 2,2-disubstitutedpropane- 1,3-diols with pyruvic acid gave poor yields (30-38%). A two-step procedure involving the initial synthesis of pyruvate ester acetals, by ketalisation of 2-substitutedpropane- 1,3-diols followed by their hydrolysis, led to the formation of acid acetals in good yield (~ 75% after 2 steps). Rhodium (II) acetate is an efficient catalyst for the decomposition of diazoketones leading to transition metal-carbenoids (or metallocarbenes), reactive intermediates susceptible to insertion into a C-H bond. Determination of the optimum conditions for the C-H insertion process has been achieved and electronic effects of the substituents on the C-H insertion process have been examined. The reaction was regioselective, occurring at the C-H bond a to the oxygen, and a variety of bicyclic ketones were prepared in moderate but reproducible yields. The bicyclic core intermediate, present in naturally occurring bioactive molecules, is also a target for synthesis. An attempt to synthesize sordidin, an aggregation pheromone released by male banana weevils, is reported. Finally, the reductive cleavage of these bicyclic ketones, upon Et3SiH/Lewis Acid treatment, has been examined. In all cases, the reactions were stereoselective leading to 2,3-anti-3,5-cis-trisubstituted tetrahydrofurans. The stereoselectivity increased with the size of the OR group at C-3

Interaction of immunostimulants and stress on innate defence mechanisms of rainbow trout, Oncorhynchus mykiss

This study investigated the use of non-specific immunostimulants to alleviate stress-mediated suppression of defence mechanisms and subsequent susceptibility to bacterial pathogens in rainbow trout (Oncorhynchus mykiss). One yeast (1-3),)1-6)-β-glucan and a bacterial peptidoglycan were selected as immunostimulants from a panel of test substances on the basis of enhanced intracellular superoxide generation by kidney macrophages stimulated in vitro. Kidney macrophage effector activity was not affected after 1, 2, 3 or 4 weeks of in-feed treatment with 0.05% or 5% of glucan or peptidoglycan. However, production of bactericidal superoxide by inflammatory peritoneal macrophages did increase significantly after four weeks of oral treatment with 0.05% peptidoglycan. Although a single confinement of fish (93% reduction of water volume for five minutes) caused a physiological stress response, as indicated by hyperglycaemia in plasma, kidney and inflammatory macrophage activities were only affected after six daily confinements. Phagocytosis, intracellular superoxide production and killing of Aeromonas salmonicida in vitro by kidney macrophages were significantly reduced. Conversely, production of extracellular superoxide, which may be associated with damage to self, was enhanced. Peritoneal macrophages displayed a similar but less marked respiratory burst response after repeated confinement. Some of the alterations in macrophage function caused by daily confinement were prevented by feeding 0.05% peptidoglycan four weeks before the first confinement. The increase in kidney macrophage extracellular superoxide production caused by repeated confinement was significantly alleviated by in-feed peptidoglycan. Similarly, the decrease in intracellular production by peritoneal macrophages caused by repeated confinement was prevented by in-feed treatment with peptidoglycan. Neither peptidoglycan nor repetitive confinement had any effect on complement lytic activity. These results indicate that dietary peptidoglycan was able to reduce, by regulating macrophage function, the impact of stress on certain bactericidal defences and potential damage to self. However, there was no significant difference in the persistence of viable A. salmonicida in the spleen or blood of infected fish in any of the experimental treatments

The impact of foreign direct investment in poverty reduction in Ethiopia: a time series analysis.

This paper examines the impact of foreign direct investment on poverty reduction in Ethiopia. The study seeks to test the hypothesis that foreign direct investment has no contribution in economic growth and has no direct effect on poverty reduction in Ethiopia. The methodology involves estimating error correction model using time series data for the period 1981-2010. The results indicate that foreign direct investment has significant positive effect on economic growth as well as on the poverty reduction of Ethiopia. Domestic economic conditions such as domestic investment and infrastructure have significant positive effect on both human development index and economic growth, where as openness has a positive effect merely on economic growth. The study recommended that effort should be made to encourage the inflow of foreign direct investment. Even if, foreign direct investment contributes to poverty reduction, parts of the revenues from the investment, which are collected through tax revenue, rental fees, and export and import activities, should be used to promote further economic activities, safety nets as well as investment in infrastructure. Key words; Foreign direct investment, Poverty reduction, Economic growth, Ethiopia, Error correction modelJimma Universit

Rabbi David Rosen

This article was originally published in Shabbat Shalom Vol. 42 #2, 199

When pressure sinks performance: evidence from diving competitions

Tournaments are designed to enhance participants’ effort and productivity. However, ranking near the top may increase psychological pressure and reduce performance. We empirically study the impact of interim rank on performance using data from international diving tournaments. We find that competitors systematically underperform when ranked closer to the top, despite higher incentives to perform well