Synthesis and in vitro/in vivo Evaluation of the Antitrypanosomal Activity of 3-Bromoacivicin, a Potent CTP Synthetase Inhibitor

The first convenient synthesis of enantiomerically pure (alpha S,5S)-alpha-amino-3-bromo-4,5-dihydroisoxazol-5-yl acetic acid (3-bromoacivicin) is described. We demonstrate that 3-bromoacivicin is a CTP synthetase inhibitor three times as potent as its 3-chloro analogue, the natural antibiotic acivicin. Because CTP synthetase was suggested to be a potential drug target in African trypanosomes, the in vitro/in vivo antitrypanosomal activity of 3-bromoacivicin was assessed in comparison with acivicin. Beyond expectation, we observed a 12-fold enhancement in the in vitro antitrypanosomal activity, while toxicity against mammalian cells remained unaffected. Despite its good in vitro activity and selectivity, 3-bromoacivicin proved to be trypano-static and failed to completely eradicate the infection when tested in vivo at its maximum tolerable dos

A structural perspective on the enzymes that convert dTDP-D-glucose into dTDP-L-rhamnose

Bacteria have a rich collection of biochemical pathways for the synthesis of complex metabolites. These conversions often involve chemical reactions that are hard to reproduce in the laboratory. An area of considerable interest is in the manipulation and synthesis of carbohydrates. In contrast with amino acids, carbohydrates are densely functionalized (each carbon atom is attached to at least one heteroatom) and this holds out the prospect of discovering novel enzyme mechanisms. The results from the study of the biosynthetic dTDP-L-rhamnose pathway are discussed. dTDP-L-rhamnose is a key intermediate in many pathogenic bacteria, as it is the donor for L-rhamnose, which is found in the cell wall of important human pathogens, such as Mycobacteria tuberculosis and Salmonella typhimurium. All four enzymes have been structurally characterized; in particular, the acquisition of structural data on substrate complexes was extremely useful. The structural data have guided site-directed-mutagenesis studies that have been used to test mechanistic hypotheses. The results shed light on three classes of enzyme mechanism: nucleotide condensation, short-chain dehydrogenase activity and epimerization.</p

RmlC, a C3' and C5' carbohydrate epimerase, appears to operate via an intermediate with an unusual twist aoat conformation

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Measuring the realized niches of animals using stable isotopes: from rats to bears

© 2015 The Authors. Stable isotope analysis is a powerful method for estimating the impacts animals have on their environment (resource use), revealing their ecological niches. We demonstrated the use of a stable isotope mixing model for measuring the ecological niches of consumers. In particular, we used the model IsotopeR to estimate the resource use of two species with complex, omnivorous diets: invasive Norway rats from the Aleutian Islands, AK, and American black bears from Yosemite National Park, CA. Marginal posterior distributions for major food sources (for populations, groups and individuals) described the resource axes that partly define the realized niches of these omnivores. We used measures of these resource axes to inform resource management in the Aleutians and Yosemite. Results from our analyses confirm that coastal rats did not rely on marine birds on rat-infested islands in the Aleutians. Instead, rats foraged primarily on terrestrial plants and preferred amphipods when they were available. We also use stable isotopes to confirm that plants and acorns are the largest contributors to black bear nutrition in Yosemite and learned that female bears foraged for acorns and pine nuts more heavily than males. Although it is unclear if Norway rats can maintain viable populations in the Aleutians without access to marine-derived animal protein, results from our analyses suggest their dependence on such nutrients. In addition, sex-specific differences in foraging for high-fat acorns and pine nuts in Yosemite suggest black bear populations in the Sierra Nevada may be limited by the productivity and health of hard mast species. As demonstrated here, stable isotope analysis has wide applicability for investigating the resource use and ecological niches of animals. We anticipate and encourage its rapid development in this fundamental field of ecology