Solid-supported Purification Processes

Unfortunately, many reactions do not occur with quantitative conversion and in near absolute purity. The work-up and purification of most chemical processes probably takes up most of a bench chemists time. Therefore techniques that simplify and accelerate these operations not only free up valuable time, but allow greater creativity and increased levels of output. Here again, supported systems can be used to aid the chemist in the guise of scavengers, quenching agents and catch and release systems. 

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An important difference between combinatorial or parallel DOS and, for example, total synthesis is the high number of synthesized compounds, which renders conventional purification procedures such as flash chromatography impractical, at least if they have to be performed after every step. Synthesis on solid support avoids these problems to some extent if high conversions can be achieved with excess reagent or selective release strategies (see above). To do solution phase DOS, selective, high yield reactions or selective purification processes are required. 

In contrast to reactions in solution, solid-phase synthesis has the advantage that excess amounts of reactants can be used and the yields thus increased. Work-up and purification processes - which often prove difficult in homogeneous solution - are rationalised as straightforward washing or filtration. Recycling of the support material after cleavage of the product from the solid phase also has cost benefits. 

Solid-phase extraction (SPE) is a purification technique based on the extraction of a compound (or a mixture of compounds) from a solution through absorption on a solid support The main physical principles involved in the extraction process are ionic interactions between acidic and basic species, and polar and/or nonpolar... 

Combined with expedient purification techniques (e.g., scavengers, reagents on solid support, and solid phase extraction techniques) [ 14], microwave-assisted synthesis is leading the way towards genuine high-throughput chemistry that will hopefully ease the chemistry-related bottleneck in the drug development process. 

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