Resins support materials

Another report demonstrates the capability of providing quantitative information on the extent of conversion of a solid-phase material. This method may be applicable to a wide range of reaction chemistries and resin-supported materials. These authors use NMR to quantify the extent of the derivatization of functionalized polymeric material with a fluorinated substrate. Thus the rate of the reaetion of Merrifield resin with 2-lluo-rophenol was examined. At various time intervals portions of the reacting resins were removed and were exhaustively reacted with excess 4-lluo-rophenol. Analysis of the resin samples shows two signals (Scheme 2.9), one for the 2-fluoro derivative at -134 ppm and the other for the 4-fluoro derivative at -124ppm. Quantitative information on the extent of the reaction was obtained by measuring the relative intensities of the resin bound fluorine and a known concentration of an internal standard in solution, such as fluorobenzene. It was noted that there needed to be a sufficient time delay between the RF pulses so that the solid-phase and solution-phase nuclei would be similarly relaxed in the F NMR spectra. This method provided excellent correlation for resin-bound F atom content in samples containing 30 mg resin samples blended to various extents with 100% 2-fluorophenyl Merrifield ether and unfunctionalized Merrifield resin. This fluorophenol based assay was then used to optimize the attaehment of an epoxide to the Merrifield resin (Scheme 2.10). The alkylation reaetion was monitored at... 

Depending on the technical requirements such as corrosion resistance, pressure and temperature stability, industrial scale azo pigment synthesis is carried out in appropriate equipment. Suitable materials include cast iron, stainless steel, steel lined with rubber, acid-proof brick, enamel, synthetic resins supported by glass fiber, and wood. 

Despite the current success and popularity of polymer reagents, the availability of functional resins has been a severe limitation in recent years. For many synthetically important transformations, reliable reagents were not available. Moreover, polymer-assisted synthesis was usually restricted to small scale apphcations, and also suffered from the inherent limitations of the standard support material (e.g., cross-linked polystyrene) such as solvent incompatibihty, adsorption of reagents,14 or the chemical reactivity of the resin backbone. 

Subramanian and coworkers developed polymeric sorbents using different support materials (such as Merrifield chloromethylated resin, Amberlite XAD 16) and complexing ligands (amides, phosphonic acids, TTA), and evaluated their binding affinity for U(VI) over other diverse ions, even under high acidities. The practical utility of these sorbents was demonstrated using simulated waste solutions (220-222). Shamsipur et al. reported the solid-phase extraction of ultra trace U(VI) in natural waters using octadecyl silica membrane disks modified by TOPO (223). The method was found satisfactory for the extraction and determination of uranium from different water samples. 

The strong interaction of dextran sulfates with cationic functions in porous support materials is exploited to create new highly charged surfaces for adsorption of proteins. It was revealed that new and strong ionic exchange resins are accessible by simple and rapid deposition of dextran sulfates on commercial DEAE- or MANAE-agarose. The material is characterised by an increased charge density on the porous surface of the support, which can perfectly bind protein material, as demonstrated in Fig. 15 [153]. 

Phase-switching strategy was applied to the multistep synthesis of isoxazolines 45-47. The approach exploits the boronic acid functionality as a phase-tag which can be easily immobilized on diethanolaminomethyl polystyrene (DEAM-PS) resin and then released by treatment with wet THF. Each reaction step was carried out in solution and the products were purified by addition of the scavenging resin, followed by filtration, washing of the supported material, hydrolytic release and evaporation. Finally, the boronic acid could be used to introduce additional substituents on the molecule. For example, 46 was converted into the biaryl-containing isoxazoline 47 by a Suzuki cross-coupling reaction <07JCO193>. 

The second approach, named many compounds per bead (Fig. 7.3), starts by coupling the solid support in a single reaction vessel with an equimolar mixture of the 100 amines (step a) then the mixture is reduced (step b) and the resin-bound amines are reacted with an equimolar mixture of the 100 acylating agents (step c). The 10,000-member library is obtained as a single 50-g pool of resin, and each bead contains similar quantities of each library individual. A bead has typically 10 " -10 reaction sites, so that each bead will contain an average of lO -lO copies of each library individual. The library synthesis could technically be considered successful if all the monomers react properly and the 10,000 compounds are acmally present, but the identification of positives from this library for any specific application is not feasible. In fact, the cleavage of resin-bound materials produces an equimolar mixture of all the components, whose activity, if any, is the activity of a 10,000-member unresolved mixmre. As a consequence of this major limitation, this SPS approach is not used for library synthesis. 

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