Polystyrylboronic acid

An early example of this concept, using polystyrylboronic acid for separating and purifying 1,2-cis diols from cist trans-mixtures, was presented by E. Seymour,... 

New resins more suitable for the preparation of libraries have recently been reported [17]. Polystyrylboronic acid can be prepared with high loading capacity even more importantly, a solvent mixture of acetone and water can be used to reduced the amount of impurities after the cleavage step. Polystyrylboronic acid has proven to be especially useful for coupling of thioglycosides, for which trichloroacetimidates give only modest results. 

The most classical examples of this application of crosslinked polymeric reagents were provided by Frichet and comprise the separation of cis and trans 1,2-diols (cf. Chapter 3) and the isolation of cis 1,3-diols from crude reaction mixtures using polystyrylboronic acid resin (Scheme 1.6.16). 

Separation of cis- and trans-/,2- and 1,3- ols. Polystyrylboronic acid resins react selectively with c/s-1,2- and 1,3-diols to form derivatives that can be cleaved to the diol by acetone-water to regenerate the polymer. The regenerated resins can be reused efficiently. ... 

Polystyrylboronic acid has similarly been used for the protection of hydroxyl groups in polyols. It has been claimed that the esters of the polymeric boronic acid are more stable to moisture and that the polymeric by-product is re-usable (Seymour and Frechet, 1976). Both the aldehyde polymer and boronic acid polymer have been used for simultaneous protection of C-4-0 and C-6-0 in derivatization reactions. A polymer incorporating a trityl group has also been used for protection of the C-6-0 group only (Frechet and Nuyens, 1976). 

Boons and coworkers have used the polystyrylboronic acid as a temporary polymeric support for oligosaccharide synthesis (Scheme 16.3). Polystyrylboronic acid 5, easily prepared from the corresponding bromide by treatment with trimethyl borate and n-BuLi in high loading capacity, was introduced on the 4,6-0 positions of the acceptor 6 by heating in pyridine. The immobilized boronate acceptor 7 was glycosylated with thioglycoside donor... 

Scheme 16.3. Synthesis using the polystyrylboronic acid linker.

Seyl976 Seymour, E. and Frechet, J.M.J., Use of Polymers as Protecting Groups in Organic Synthesis. IV. Applications of a Polystyrylboronic Acid Resin to the Selective Functionalization of Some Glycosides, Tetrahedron Lett., (1976) 1149-1152. 

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