Solid supports crowns

However, other polymer composite materials also popular in solid-phase synthesis, such as polyethylene or polypropylene tea bags , lanterns, crowns, or plugs, are generally less suitable for high-temperature reactions (>160 °C). Therefore, micro-wave irradiation is typically not a very suitable tool to speed up reactions that utilize these materials as either a solid support or as containment for the solid support. 

It is not necessary to weigh the solid support when setting up reactions because the scale of the reaction is determined by the crown loading. 

Another kind of solid support that has gained more popularity is the surface-modified polypropylene, such as the Multipin crown and Microtubes. Reaction 3 was carried out on lightly and highly cross-linked polystyrene resins (1 % and >20% divinylbenzene, respectively), poly sty rene-PEG resin, and a surface-functionalized Microtube reactor.12 The reaction kinetics on these supports is compared in Figures 7.4 and 7.5. The reaction on the highly cross-linked polystyrene resin was shown to be slower than on other supports and the reaction on Microtube was faster than on polystyrene resins. 

The same principle of moderating the acidity in order to achieve a greater selectivity for the oxidation of unsaturated alcohols is applied in the use of PCC in a CH2C12 solution containing 2% of 3,5-dimethylpyrazole (DMP),141 complexes of -butylammonium chlorochromate (BACC) with 18-crown-6,142 and the solid support-bound 1-aminoimidazolium chlorochromate. 143... 

Lambert and co-workers49 (University of Melbourne) synthesized a library of cyclic thioether peptides with a pendant 9-aminoacridine moiety as a DNA-binding agent 81. Diversity in the library was achieved by assembling every permutation of four amino acid residues within the cyclic peptide (Scheme 24). The linear peptides 80 were synthesized in parallel with standard Fmoc chemistry on SynPhase Crowns functionalized with a Rink linker. The acridine moiety was incorporated onto the C-terminal lysine side chain using 9-phenoxyacridine. Cysteine deprotection and peptide cy-clization also took place under the acidic conditions used for the cleavage of 80 from the solid support. The library of cyclic thioether peptides 81 was obtained in high yields and purity (11 of 12 members had purities >95%). 

In a subsequent study [30], cholesteryl-substituted 18C6 derivative 11 and diaza [18]crown-6 12 (Scheme 6) were used to create solid-supported bilayer lipids. The liquid crystalline crown derivatives 11,12 were dissolved in chloroform and mixed with squalene or squalene saturated with cholesterol. The solid-supported bilayers were prepared in freshly cut stainless steel wires. A 10-4 to 10-1 mol L-1 solution of MCI (M = Li, Na, K, Rb, Cs) or MgCl2 was used as aqueous phase. Measurement of the membrane potential revealed a Nemst response to the concentration of M+ in solution. It was possible to differentiate between the different cations which might be used for the preparation of new ion sensors. For the detection of K+ and Rb+, aza crown derivative 12 proved to be the most selective. A problem was the presence of traces of Fe2+/3+ that made the measurements difficult. It was also not... 

The CSPs based on chiral crown ethers were prepared by immobilizing them on some suitable solid supports. Blasius et al. [33-35] synthesized a variety of achiral crown ethers based on ion exchangers by condensation, substitution, and polymerization reactions and were used in achiral liquid chromatography. Later, crown ethers were adsorbed on silica gel and were used to separate cations and anions [36-39]. Shinbo et al. [40] adsorbed hydrophobic CCE on silica gel and the developed CSP was used for the chiral resolution of amino acids. Kimura et al. [41-43] immobilized poly- and bis-CCEs on silica gel. Later, Iwachido et al. [44] allowed benzo-15-crown-5, benzo-18-crown-6 and benzo-21-crown-7 CCEs to react on silica gel. Of course, these types of CCE-based phases were used in liquid chromatography, but the column efficiency was very poor due to the limited choice of mobile phases. Therefore, an improvement in immobilization was realized and new methods of immobilization were developed. In this direction, CCEs were immobilized to silica gel by covalent bonds. 

Furthermore, the internal reflection spectra of these reactions are much less distorted by the absorption bands of the solid support than are the transmission spectra recorded from KBr pellets made of polystyrene or TentaGel beads. In Fig. 3 the spectra of polystyrene resin (upper curve) and of a polystyrene Mega Crown (lower curve), both loaded with adipinic acid monoamide, are shown. The disturbing polystyrene bands are marked P. ... 

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