Combinatorial Chemistry Review

TentaGel Resins

Poly (styrene-oxyethylene) graft copolymers, first reported by Bayer and Rapp, are another class of widely used supports for organic synthesis. As with the polyacrylamide resins, in order to produce a polar reaction milieu that is closer to the solvents generally used by solution synthetic chemists, grafted polymer beads have been prepared. The most pre-eminent of these is TentaGel resin which consists of polyethylene glycol attached to cross-linked polystyrene through an ether link, and combines the benefits of the soluble polyethylene glycol support with the insolubility and handling characteristics of the polystyrene bead. The resin was originally prepared by the polymerisation of ethylene oxide on cross-linked polystyrene already derives with tetraethylene glycol to give polyethylene glycol chains. (Figure) Poly (styrene-oxyethylene) graft copolymers beads display relatively uniform swelling in a variety of solvents from medium to high polarity ranging from toluene to water. The polymers are produced by grafting ethylene oxide from the polystyrene backbone creating long flexible chains that terminate with a reactive site spatially separated from the more rigid polystyrene backbone.

TentaGel resin onto a cross-linked polystyrene

Some disadvantages of Poly(styrene-oxyethylene) graft copolymers supports are:
- Relatively low functional group loading compared with GPS; the potential for the PEG chains to complex Lewis acids;
- The potential instability of PEG;
- The presence of linear PEG impurities found in the small molecule products after cleavage from the resin;
- The tendency for resins to become sticky and difficult to handle as the synthesis progress.