Aminomethyl polystyrene beads

Recently, various scavenger resin approaches have appeared in the literature. For the synthesis of 4000 ureas (400 pools of 10-compound mixtures) [47], a solid-supported amino nucleophile was used to quench the excess of isocyanates, yielding the desired products in good purity. A similar concept has been employed in the synthesis of 2-thioxo-4-dihydropyrimidinones using aminomethylated polystyrene beads to quench isothiocyanates as well as aldehydes [48]. To quench an excess of amine in the synthesis of 2,6,9-trisubstituted purines, formyl polystyrene beads were used to form the corresponding polymer-bound imine, which could be filtered off [49]. 

A dry 50 mL Schlenk reaction tube was flushed with nitrogen and charged with a mixture of 7 (527mg, l.Ommol), 1,3-dicyclohexylcarbodiimide (1.04g, 5mmol), pentafluorophenol (920 mg, 5 mmol), 4-(dimethylamino)pyridine as the catalyst and the aminomethylated polystyrene (930 mg, 1.07 mmol g ) in dry dichloromethane (20 mL). The mixture was stirred at room temperature for 24h under a N2 atmosphere. The polymer was filtrated, rinsed sequentially with CH2CI2 and acetone and dried at 50 °C in vacuo to yield the polymer-bound ligand 8 as pale yellow beads. 

Reusability is a characteristic of the sensitizers prepared by stirring Ceo-fullerene with aminomethylated poly(styrene/vinylbenzene). They have been used to promote the standard O2 oxidation processes such as ene and Diels-Alder reactions (Scheme 7), and catalysts suitable for photoxidations in water have been prepared from them by reaction with poly(allylamine). The same reactions have been carried out using a novel solvent-free procedure which involves loading a porphyrin into solvent-swollen polystyrene beads and carrying out the photo-oxidation in neat liquid substrate. The formation of the allylic hydroperoxide (89) from p-pinene, with complete conversion and in 84% yield, is particularly noteworthy, as the standard liquid-phase reaction can be problematic. It is suggested that the possibility of using this approach under solar conditions is further evidence of the sustainable, green chemistry potential of synthetic photochemistry. 

To improve the access to the functional groups, Lee and coworkers developed a process of placing most of the functional groups on the outer surface of the polystyrene beads [7]. This was done by surface aminomethylation of preformed cross-Unked commercially available polystyrene beads. Such bead usually range in size from 100 to 400 mesh (in.) in diameter and can be functionalized by surface reactions or by surface grafts. This yielded materials with a lower number of functional groups, but with the majority of them being accessible. Lee and coworkers then utilized the beads in a solid peptide synthesis [7]. 

Ogata et al. published several applications with graft copolymers of poly(7 benzyl-L-glutamate) onto suspension polymerized crosslinked polystyrene beads containing aminomethyl functions [39] (Scheme 6). 4- 7 7 3 benzyl ester group of the polypeptide side chain was converted either to benzyl amide by aminolysis or to free acid by hydrolysis and the effects... 

The potential of grafted polymers remained unrecognized until the use of PS-PTFE support was resurrected in the 1990s under the phosphoramidite method [168]. The aminomethylated and loaded with nucleoside 3 -succinate from 12.5 to 48pmol per g-PS-Teflon support has been employed successfully in the automated synthesis of oligodeoxyribonucleotides as long 143-mer, with stepwise efficiency of up to 99.8%, comparing favorably with such popular carriers as silica beads CPG-500 and macroporous polystyrene Primer Support (Pharmacia). 

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