Polymer-supported protective groups

Frechet, J. M. J., Synthesis Using Polymer-Supported Protecting Groups, Chap. 6 in Polymer-Supported Reactions in Organic Synthesis, P. Hodge and D. C. Sherrington, eds., Wiley, New York, 1980a. 

While our reaction was a solid-liquid-solid reaction, Hcylge s involved the use of concentrated aqueous sodium hydroxide and tetrabutyl ammonium hydroxide. It is noteworthy that the final polymer (IV) is much more effective in its use as a polymer-supported protecting group for carbonyl compounds (Ref. 29) than a somewhat similar polymer-bound diol prepared under standard conditions (Ref. 30, 31). 

There is a large range of resins available for SPOS. These resins are derivatised polymer supports with a range of linkers. The roles of linkers are (i) to provide point(s) of attachment for the tethered molecule, akin to a solid supported protecting group(s), (ii) to provide distance from the polymeric backbone in order to minimise interactions with the backbone, (iii) to enable cleavage of product molecules under conditions compatible with the stability of the molecules and the reaction conditions employed for chemical transformations. Hence in order to... 

In contrast to oligosaccharide synthesis on polymer supports, the use of polymers as protecting groups in carbohydrate chemistry appears to be a more promising proposition and should be given attention as a convenient alternative to the solution method. 

Soluble supports (W = 6000 g mol ) of the following structure have been used with 4-<2-nitrovinyl)benzoic acid as terminal group (loading capacity 86%) [93]. The loading capacity of the latter POE-derivative was 75% (0.25 mmol g ). Such solubilizing polymer-based protecting groups are of considerable interest for the synthesis of cysteine peptides. 

One widely used method of formation of protected compounds involves polymer-supported reagents, with the advantage of simple workup by filtration and automated syntheses, especially of polypeptides. Polymer-supported reagents are used to protect a terminal — COOH group as a polymer-bound ester (RCOOR —( ) during peptide syntheses, to protect primary alcohols as... 

The first, and still widely used, polymer-supported ester is formed from an amino acid and a chloromethylated copolymer of styrene-divinylbenzene. Originally it was cleaved by basic hydrolysis (2 N NaOH, FtOH, 25°, 1 h). Subsequently, it has been cleaved by hydrogenolysis (H2/Pd-C, DMF, 40°, 60 psi, 24 h, 71% yield), and by HF, which concurrently removes many amine protective groups. Monoesterification of a symmetrical dicarboxylic acid chloride can be effected by reaction with a hydroxymethyl copolymer of styrene-divinylbenzene to give an ester a mono salt of a diacid was converted into a dibenzyl polymer. ... 

Polymer supported reagents, catalysts, protecting groups, and mediators can be used in place of the corresponding small molecule materials (Sherrington, 1991 Sundell and Nasman, 1993). The reactive species is tightly bound to a macromolecular support which immobilizes it. This generally makes toxic, noxious, or corrosive materials much safer. The use of polystyrene sulfonic acid catalyst for the manufacture of methyl r-butyl... 

Polymer-supported esters are widely used in solid-phase peptide synthesis, and extensive information on this specialized protection is reported annually. Some activated esters that have been used as macrolide precursors and some that have been used in peptide synthesis are also described in this chapter the many activated esters that are used in peptide synthesis are discussed elsewhere. A useful list, with references, of many protected amino acids (e.g., -NH2, COOH, and side-chain-protected compounds) has been compiled/ Some general methods for the preparation of esters are provided at the beginning of this chapter conditions that are unique to a protective group are described with that group/ Some esters that have been used as protective groups are included in Reactivity Chart 6. 

Polymer-NH(CH2),NH2, (jc = 2, 4, 6), BuOH, 85°, 92-96% yield. The polymer-supported amine helps in the final purification of oligosacchar-rides that have used the TCP group for —NH2 protection. ... 

---