Solution-phase combinatorial chemistry suffers from one main disadvantage. To drive reactions to completion, more than one equivalent of reagent is frequently necessary, but the use of excess reagents is often prohibitive because their removal causes in most cases severe problems. Two new techniques were established to overcome these difficulties: polymer-supported reagents and scavenger resins. The latter are functional group-specific, reactive resins, e.g. polystyrene-bound iso-cyanates which react selectively with primary and secondary amines. Thus excess reagents are first used to drive reactions to completion. Subsequently, scavenger resins are added to the reaction mixture. After selective coupling of the resin to the excess starting material the insoluble material is removed by filtration and the product remains in pure form (Fig. 2.6).
Also the second approach to simplify solution-phase chemistry relies on the separation of insoluble material from the reaction mixture and combines the benefits of solid- and solution-phase chemistry (Fig. 2.7): instead of immobilizing the starting material on the support, only the employed reagents are polymer supported. Again, the work-up and purification are reduced to a simple filtration.
Furthermore, different polymer-supported reagents do not interfere with each other, making one-pot reactions possible that would not work in classic solution
Was this article helpful?