Polystyrene-Based Resins

Ion exchange resins are also useful for demineralising biochemical preparations such as proteins. Removal of metal ions from protein solutions using polystyrene-based resins, however, may lead to protein denaturation. This difficulty may be avoided by using a weakly acidic cation exchanger such as Bio-Rex 70. 

Yang, Y.-B., Harrison, K., and Kindsvater, J., Characterization of a novel stationary phase derived from a hydrophilic polystyrene-based resin for protein cation-exchange high-performance liquid chromatography, /. Chromatogr. A, 723, 1, 1996. 

Macroporous resin beads, due to their mode of preparation, consist of a macroporous internal structure and highly cross-linked areas (>5%). The latter impart the resin with rigidity, whereas the porous areas provide a large internal surface for functionalization, even in the dry state. These macroporous polystyrene-based resins are subsequently modified in various manners, which render them compatible with numerous organic solvents. Furthermore, they show high resistance toward osmotic shock, but can be brittle when not manipulated carefully. 

The mild conditions employed for the activation of sulfoxides, and the high reactivity of the glycosyl donor, suggested that the method might translate well to the solid phase. Moreover, the nonpolar nature of the sulfoxide, triflic anhydride, and DTBMP (solution-based reagents) should enable them to partition effectively into a non-polar, polystyrene-based resin. 

Last but not least, catechols are highly water-soluble (the water solubility of catechol is approximately 1 g per 2.3 mL of water), which makes it difficult to directly extract them in situ from reaction media with organic, water immiscible solvents. Nevertheless, extraction of catechols from aqueous systems with hydro-phobic polymers such as the polystyrene-based resin Amberlite XAD-4 is... 

We chose to employ PEGA1900 and PEG (polyacrylamide backbone with PEG spacer and amine functionalization) because its higher polarity allows water or buffer as solvent and better enzyme permeation with respect to classical polystyrene-based resins [99-100], while it is still compatible with a wide range of organic transformations and solvents. 

The leading solid phases are the 2-chlorotrityl chloride resins. Professor K. Barlos (University of Patras, Greece) has made the single most important contribntion to the development of these resins. They consist of a polystyrene-base resin crosslinked with a small amonnt of divinylbenzene and functionalized with 2-chlorotritiyl chloride. 

Overlap from resin signals, mentioned previously, can be overcome in several ways, and is particularly important when following reactions involving aromatic groups attached to polystyrene based resins. Spin echo MAS NMR was applied to follow the progress of a reduction of a resin-bound methyl benzoate to the alcohol.45 One-dimensional H as well as COSY and TOCSY spectra were used to elucidate the reaction products, although transformations were readily apparent in the ID spectra alone. 

Resin (polystyrene-based resin, 1% divinylbenzene, 100-200 mesh) substitution and amino acid deprotection were carried out in disposable... 

One major drawback of the current methods is the low atom economy45 of solid-supported chemistry with conventional resins in comparison to solution-phase synthesis. The low loadings are one important reason for excluding solid-supported methods from many resource-and cost-sensitive applications such as scale-up projects. Furthermore, polystyrene-based resins are restricted by solvent compatibility, thermal and chemical stability, and extensive adsorption of reagents. 

A key step in tin-based reductions on the solid phase is the washing procedure, which is used for the removal of residual tin salts. To be on the safe side, numerous washes with a very broad spectrum of solvents are recommended. In our experience good results are obtained with polystyrene-based resins when washes with warm DMF/water (1 1) are included. 

A 9-phenylfluoren-9-yl polystyrene-based resin has been described for the attachment of nitrogen and oxygen nucleophiles. Greater acid stability compared to the standard trityl resins that are widely used in solid-phase peptide synthesis make this solid support an interesting alternative in solid-phase organic synthesis. This resin can be used in Suzuki coupling reactions to furnish biaryls in good yields [100]. 

The methodology outlined in Scheme 10.50 has also been adopted to a corresponding stereoselective solid-phase approach to a-amino acids using the galactosylamine 160 immobilized on a polystyrene-based resin, enabling the combinatorial synthesis of stereoisomerically pure compounds (Figure 10.15) [123]. 

Macroreticular polystyrene-based resins with functional aminothiazole, imino-thiazole, or thiazoline groups exhibit a high selectivity for mercury(II). A thiazoline resin column has been used to concentrate mercury from sea water adjusted to pH 1 with hydrochloric acid. Maximum sorption capacity for mercury was found to be 2.8 mmole/g. The sorbed mercury is recovered quantitatively by eluting with 0.1 M HC1 containing 5 % thiourea 100). 

Also in 2000, attachment of the Jacobsen catalyst to polymeric supports such as poly(ethylene glycol) and different polystyrene-based resins through a glutarate spacer was described [28]. Soluble as well as insoluble polymer-bound complexes were employed as catalysts in the epoxidation of styrene, cfs-2-methylstyrene, and dihydronaphthalene with wx-CPBA/NMO. Results were similar to those achieved with the nonsupported catalyst. Catalyst recycling was shown to be possible either by filtration or by precipitation and one catalyst system could be used for three cycles without significant loss of activity and enantioselectivity. 

A keteneacetal, the Brassard diene, has also been bound to polystyrene-based resin (308). This has been achieved by the reaction of diketene with alcohol functions on polystyrene resin. The ketone function of the resulting acet-oacetate could readily be enolized by TMOF (trimethyl orthoformate) and a catalytic amount of H, giving the methyl enolate. The remaining ester function was then deprotonated with LDA and subsequently silylated with TBDMSCl. The resulting diene (311) was used in many hetero-Diels-Alder reactions (HDA) with aldehydes and ketones as dienophiles, giving a library... 

Polystyrene-based resins have been used widely as supports for metal complex catalysts and other reactive species. These polymers, however, have a drawback in their limited thermo-oxidative stability [1,2]. The scope for application is therefore restricted, particularly in polymer-supported transition metal complex oxidation catalysts [3]. Consequently there is a need for the development of polymer supports with a much higher intrinsic thermo-oxidative stability. Polybenzimidazoles and polyimides are likely candidates in this respect. 

---