Multifunctional anchors

Cleavage a) Strong acid or hydrogenolysis a) TMG b) Photolysis or thiophenoxide-ions b) Photolysis + nBu4NCN Product after cleavage a) Carboxylic acid a) Carboxylic acid b) O-Methylphenyl-acetic acid ester b) Carboxylic acid 

The use of stronger acids (TFA. TfOH) for cleavage leads to decomposition. 

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Stannaries have become prominent in multifunctional anchoring groups. A polymer-bound tin hydride 41 has been used to hydrostannylate alkynes under the action of palladium-catalysis to give polymer-bound alkenylstannanes 42. These alkenyl stannanes have been employed in intermolecular [45] and intramolecular Stille reactions [46]. Alkenylstannanes can also undergo protonation to give alkenes 44 in a traceless fashion. This linker is therefore multifunctional (Scheme 6.1.12). 

Stannanes have become prominent members in the field of multifunctional anchoring groups. Nicolaou et al. [358] used polymer-bound tin hydride 693 to hydrostannylate alkynes 694 under palladium-catalysis to give polymer-bound alkenyl stannanes. Alternatively, the latter ones can be prepared from a polymer-bound tin chloride and an alkenyl-Hthium or -magnesium halide reagent. These alkenyl stannanes were employed in intermolecular as well... 

Platelet membrane phosphatidylserine is critical to the formation of the tenase complex since on its surface activated factor VIII (Villa) generates a high-afflnity binding site for activated factor IX (IXa) in the presence of calcium. Subsequently, this complex activates factor X (2, 13). Platelet membrane phosphatidylserine similarly anchors activated factor V (Va), favoring the calcium-dependent binding of activated factor X (Xa). The prothrombinase complex is generated on the surface of the anionic platelet membrane phosphatidylserine when factor Va binds prothrombin. The prothrombinase complex cleaves prothrombin to produce thrombin, which has a multifunctional role (14). 

Multifunctional Linkers as an Efficient Tool for the Synthesis of Diverse Small Molecule Libraries The Triazene Anchors... 

Literature precedence for multifunctional linkers can be found among various types of anchoring groups (Fig. 3). 

Scheme 6.1.36. Electrophilic selenium anchors as multifunctional linkers.

An anchor for traceless linking might also have a safety-catch function or be suitable for multifunctional cleavage. Linker systems enable the introduction of certain atoms or molecule fragments and will play an important role in the development of diverse organic substance libraries. It is important to point out that the final diversity is achieved on cleavage, and not in an additional solution phase re-... 

A substrate functionalized with proper molecules can be used to anchor particles on its surface via surface exchange reaction, leading to controlled assembly of the particles. This self-assembly technique is known as molecule-mediated self-assembly and is commonly used for constructing various composite nanostructures [49-55]. Due to their excellent adhesion capability to various substrates, multifunctional polymers are routinely applied as templates to mediate the assembly of the particles. The assembly is carried out as follows a substrate is immersed into a polymer solution, and then rinsed, leading to a functionalized substrate. Subsequently, this substrate is dipped into the nanoparticle dispersion and then rinsed, leaving one layer of nanoparticles on the substrate surface. By repeating this simple two-step process in a cyclic fashion, a layer-by-layer assembled poly-mer/nanoparticle multilayer can be obtained. 

Dextrins are hydrolyzed by a membrane-bound enzyme, isomaltase, which occurs in the same polj eptide chain as sucrase, the enzyme that hydrolyzes sucrose. Two active sites (catalytic sites) reside on one polypeptide chain. The entire protein is called sucrase-isomaltase. Enzymes containing more than one active site on one polypeptide chain are called multifunctional. The orientation of sucrase-isomaltase in the gut cell, or enterocyte, is shown in Figure 2.43. Both active sites are situated in the lumen of the gut the N-terminal region is anchored in the membrane. Each of the active sites of sucrase-isomaltase is capable of hydrolyzing maltose. Perhaps a better, although cumbersome, name for the enzyme would be sucrase/maltase-isomaltase/maltase. The isomaltase catalytic site is closest to the membrane, whereas the sucrase site is the C-terminal portion of the enzyme. 

Van Deurs, B., K. Roepstorff, A. Hommelgaard, and K. Sandvig. 2003. Caveolae anchored multifunctional platforms in the lipid ocean. Trends Cell Biol. 13 92-100. 

An active carbonate resin 2a has also been prepared from Wang resin and used to anchor a multifunctional benzylamine derivative for a combinatorial application. Final products were cleaved using TFA-CH2CI2 (1 1)... 

Type of Active Sites. - In heterogeneous catalysis the following type of actives sites can be distinguished (i) metallic, (ii) acid-base, (iii) red-ox type, and (iv) anchored metal-complex. The catalytic sites may contain one of the above types of active sites or can include several types of sites. In case of different type of sites the catalysts are bifunctional or multifunctional. For instance, Pt/Al203 and Pt/mordenite are typical bifunctional catalysts containing both metallic and acidic types of active sites. On the other hand, Pt or Pd supported on silicon carbide, nitride, or Pt/L-zeolite are mono-functional catalysts. There are important industrial reactions, such as isomerization and aromatization of linear hydrocarbons, which requires bifunctional catalysts, such as chlorinated... 

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