PubMed Health⌕ Search

PubMed · 12355522

New efficient iterative approaches to polycyclic ethers.

Abstract

The imposing structures of the marine polyether ladder toxins have inspired synthetic chemists to develop many clever methods for assembling these complex skeletons. One intriguing strategy is to use a short and reliable sequence of reactions to build successive rings in an iterative fashion. The ideal approach should tolerate variation in ring size and substitution at the bridgehead positions. This paper offers an overview of recent progress in this field.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Fredrik P Marmsäter, Frederick G West. 2002-10-04. New efficient iterative approaches to polycyclic ethers.. https://doi.org/10.1002/1521-3765(20021004)8%3A19%3C4346%3A%3Aaid-chem4346%3E3.0.co%3B2-s

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Targeted cytoplasmic irradiation induces bystander responses.

The observation of radiation-induced bystander responses, in which cells respond to their neighbors being irradiated, has important implications for understanding mechanisms of radiation action particularly after low-dose exposure. Much of this questions the current dogma of direct DNA damage driving response in irradiated systems. In this study, we have used a charged-particle microbeam to target individual helium ions ((3)He(2+)) to individual cells within a population of radioresistant glioma cells cultured alone or in coculture with primary human fibroblasts. We found that even when a single cell within the glioma population was precisely traversed through its cytoplasm with one (3)He(2+) ion, bystander responses were induced in the neighboring nonirradiated glioma or fibroblasts so that the yield of micronuclei was increased by 36% for the glioma population and 78% for the bystander fibroblast population. Importantly, the yield of bystander-induced micronuclei was independent of whether the cytoplasm or nucleus of a cell was targeted. The bystander responses were fully eliminated when the populations were treated with 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide or filipin, which scavenge nitric oxide (NO) and disrupt membrane rafts, respectively. By using the probe 4-amino-5-methylamino-2',7'-difluorofluorescein, it was found that the NO level in the glioma population was increased by 15% after 1 or 10 cytoplasmic traversals, and this NO production was inhibited by filipin. This finding shows that direct DNA damage is not required for switching on of important cell-signaling mechanisms after low-dose irradiation and that, under these conditions, the whole cell should be considered a sensor of radiation exposure.

Biological Factors↗

Nickel-catalyzed reductive cyclizations and couplings.

For over 50 years, nickel catalysis has been applied in cycloaddition processes. Nickel-catalyzed reductive couplings and cyclizations, however, have only recently attracted a high level of interest. This group of new reactions allows a broad range of multicomponent couplings involving two or more pi components with a main-group or transition-metal reagent. These processes allow the assembly of important organic substructures from widely available reaction components. Multiple contiguous stereocenters, polycyclic ring systems, and novel arrays of complex functionality may often be prepared from simple, achiral, acyclic precursors. With three or more reactive functional groups participating in the catalytic processes, many mechanistic questions abound, including the precise timing of bond constructions and the nature of reactive intermediates. This Review is thus aimed at providing a critical evaluation of recent progress in this rapidly developing field.

Biological Factors↗