Molecular tubes for lipid sensing: tube conformations control analyte selectivity and fluorescent response.

Two fluorescent sensors for lipids have been prepared and tested for detection of a number of hydrophobic compounds of varying shape and size. The data suggest that the two sensors have a different mode of fluorescent response. Yet, the two sensors are only different in the bridging group--one having a flexible amide and one having a rigid allyl bridge. The fluorescence data are explained based on a difference in conformation of the two sensors in aqueous solution.

Total Synthesis of Propolisbenzofuran B.

The first total synthesis of propolisbenzofuran B, a bioactive natural product isolated from honeybee propolis resin, is reported. The convergent synthesis makes use of a silicon-tether controlled oxidative ketone-ketone cross-coupling and a novel benzofuran-generating cascade reaction to deliver the core structure of the natural product from readily prepared precursors.

Triflimide-catalysed sigmatropic rearrangement of N-allylhydrazones as an example of a traceless bond construction.

The recognition of structural elements (that is, retrons) that signal the application of specific chemical transformations is a key cognitive event in the design of synthetic routes to complex molecules. Reactions that produce compounds without an easily identifiable retron, by way of either substantial structural rearrangement or loss of the atoms required for the reaction to proceed, are significantly more difficult to apply during retrosynthetic planning, yet allow for non-traditional pathways that may facilitate efficient acquisition of the target molecule. We have developed a triflimide (Tf(2)NH)-catalysed rearrangement of N-allylhydrazones that allows for the generation of a sigma bond between two unfunctionalized sp(3) carbons in such a way that no clear retron for the reaction remains. This new 'traceless' bond construction displays a broad substrate profile and should open avenues for synthesizing complex molecules using non-traditional disconnections.

Diastereoselective oxidative carbon-carbon bond formation via silyl bis-enol ethers.

Diisopropylsilyl bis-enol ethers are shown to be powerful intermediates for the diastereoselective dimerization and cross-coupling of cyclic ketones. The trends observed for the oxidative coupling of a range of different dialkylsilyl bis-enol ethers derived from cyclohexanone are rationalized by invoking a stereochemical model based on a Thorpe-Ingold effect.

Shape-selective sensing of lipids in aqueous solution by a designed fluorescent molecular tube.

The design, synthesis, and recognition properties of two isomeric calixnaphthalene-type molecular tubes is described. The anti isomer showed strong fluorescence quenching upon titration with various simple lipid guests in water, in which the more hydrophobic guests associated with higher affinity. The syn isomer bound long straight-chain guests tightly with a similar fluorescence-quenching response. However, the syn isomer was more selective, giving an increase in fluorescence upon titration of guests which could not thread through the tube. Thus, the syn isomer is a selective fluorescent sensor for long straight-chain lipids.