One equivalent of carbonyldiimidazol was added to provide the activated acid which was subsequently reacted with one equivalent of amine 2. After extraction with 0.5M H₂SO₄, H₂O and 1M K₂CO₃ (basic compounds H₂O and 1M K₂CO₃) the ethyl acetate was allowed to evaporate and the crude products were purified by FlashTube chromatography as follows:

TLC analysis showed that the neutral products had Rf values ranging from 0.1 to 0.6 in ethyl acetate/heptane (8:2) on silica, whereas the products having a basic nitrogen had Rf values around 0.4 in ethyl acetate/ethanol/triethylamine (7:3:0.5). These solvent systems were used to purify all library compounds using FlashTube 2002, which is packed with 2.0g of silica.

The columns were wetted with 0.3ml of eluent and the sample added in ~ 0.2ml of solvent. Another 0.1ml of eluent was added to wash down the sample and finally 2ml of eluent was used to develop the columns. These were subsequently examined in UV light and the position of the product was marked. The piece of column holding the product was cut out using the FlashTube Cutter and left in a plastic reservoir equipped with a filter (<10µ) and a valve. Several purifications were done in parallel and the entire library could thus be purified in less than 2.5 hrs.

The silica plug was allowed to dry over night to simplify removal of the polyethylene tube before extraction with chloroform/methanol (8:2). No suction was applied during filtration in order to avoid particles coming through the filter. The silica can alternatively be removed by centrifugation.

All compounds were obtained completely pure as seen from TLC and in yields between 30 - 50%.

Today purification is a bottleneck in combinatorial chemistry and parallel synthesis. As shown here, FlashTube^TM chromatography offers a simple, rapid and efficient solution. Pure compounds is an important feature of a high quality chemical library.