Natural products containing tetronic acid or tetramic acid moieties continue to attract the interest of chemists, biologists,
and physicians due to their challenging structures and to the wide range of biological activities they display. This review
portrays the structural varieties of tetronic and tetramic acids and the spectrum of possible therapeutically relevant effects
in man for exemplary derivatives. Their biosynthetic origin from α-amino and α-hydroxy acids is briefly discussed as is the
relationship between their structures and their modes of interaction with biochemical effectors such as metal cations or enzymes.
A short overview of laboratory syntheses of the heterocyclic core structures of tetramic and tetronic acids is provided with
an emphasis on those emulating the biosynthesis. A synthesis from the α-amino or α-hydroxy esters and the cumulated phosphorus
ylide Ph3PCCO based upon a domino addition–intra-Wittig alkenation sequence is presented with applications to the preparation of the
antibiotics reutericyclin and tenuazonic acid, the cytotoxic melophlin B, and the enzyme inhibitor RK-682. Procedural advantages
of immobilizing either starting component by attaching it to a resin and its exploitation in the parallel synthesis of libraries
of potential drug candidates are described. The basic domino reaction can even be extended by further C–C bond forming steps
when starting from suitable α-hydroxy or α-amino allyl esters. Depending on the chosen reaction conditions, bioactive intermediates
of formally three to seven step long cascades can be obtained. Among them, herbicidal 3-alkyltetronic acids and lactone endoperoxides
with antiplasmodial activity exceeding that of the natural antimalarial lead artemisinin. Hence, this domino reaction gives
access to diversely functionalized derivatives of tetronic and tetramic acids. As it can also be ported to solid phase, it
is ideally suited for parallel and combinatorial processing. Future developments might include running such domino sequences
in continuous mode in arrays of “labs on microchips”. 相似文献
Mit impr?gnierten Filtermaterialien ist es m?glich, die Schwermetalle Blei, Kupfer und Nickel sowie Arsen durch Sorption bzw.
chemische Bindung aus Wasser zu entfernen. Bei 24stündiger Einwirkungszeit wurden Reduktionsraten von 97% bis>99,9% erreicht. 相似文献
Mixed contamination by organic and inorganic compounds in soil is a serious problem for remediation. Most laboratory studies and field-scale trials focused on individual contaminant in the past. For concurrent bioremediation by biodegradation and bioleaching processes, we tested metal-reducing microorganism, Geobacter metallireducens. In order to prove the feasibility of the coupled process, multiple-contaminated soil was prepared. Mineralogical analyses have shown the existence of labile forms of As(V) as amorphous and/or weakly sorbed phases in the secondary Fe oxides. In the biotic experiment using G. metallireducens, biodegradation of toluene and bioleaching of As by bacteria were observed simultaneously. Bacteria accelerated the degradation rate of toluene with reductive dissolution of Fe and co-dissolution of As. Although there have been many studies showing each individual process, we have shown here that the idea of concurrent microbial reaction is feasible. However, for the practical use as a remediation technology, more details and multilateral evaluations are required in future studies.
In a lysimeter experiment, topsoils were polluted with filter dust from a non-ferrous metal smelter and then planted with trees. Sequential extractions were used to follow the changes in metal fractionation of Cu, Zn, Cd, and Pb over 42 months. Plant-free and uncontaminated soils served as reference. In the contaminated and planted soils, the largest changes in speciation occurred within the first 6 months. The relative amounts of certain metal fractions were linearly related to each other, indicating systematic redistribution between fractions. The results indicate that under natural conditions with high heterogeneity in total metal contents spatial differences are more important than temporal variations in determining the fractionation and solubility of metals in contaminated soils. In the absence of plants soils exhibited a completely different fractionation 30 months after pollution, with much higher proportions in the more refractory phases. This suggests that plant activity kept the metals in a more soluble form. 相似文献
Nudibranchs (Mollusca, Gastropoda) feeding on tentacles and polyps of Cnidaria thereby ingest both latent and discharged nematocysts
(NCs) along with the food mass. In eolid nudibranchs (Opisthobranchia, Aeolidacea), many of the undischarged NCs are transported
to terminal cnidosacs in their body appendages (cerata) and incorporated as kleptocnidae for defense. In the present report,
the occurrence and fate of NCs in the digestive tracts of eolids is compared with hydrozoan-feeding dendronotacean nudibranchs
(Opisthobranchia, Dendronotacea), which may show more basic stages in the evolution of cnidosacs. Tomographic reconstructions
of the distal tips of cerata were composed from series of semithin light microscopic sections, utilizing 3D-surface rendering
software. Doto acuta (Dendronotacea, Dotidae) does not have cnidosacs; transmission electron micrographs show that the NCs are digested in lysosomes
of digestive gland cells. In contrast, species of the genus Hancockia (Dendronotacea, Hancockiidae) have several small cnidosacs in each ceras; they accumulate NCs in the digestive cells, as
well as in the cnidosacs. Many of the cnidosacs were found open to the exterior with NCs in the process of expulsion. These
and other structural details suggest assigning a function of expelling the NCs to the Hancockia spp. cnidosacs. It is proposed that cnidosacs similar to those of Hancockia spp. provide a clue to understanding how the defensive function of eolid cnidosacs may have evolved.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献