After evaporating the solvent under streaming nitrogen, 200 µl chloroform/N,N-diisopropylethylamine solution and 10 µl pentafluorobenzylbromide solution are added. The sample is incubated at 50 °C for 1 h and then dried under streaming nitrogen. After re-dissolving in 5 ml hexane, the sample is applied to a silica gel column equilibrated with 5 ml hexane. The pentafluorobenzyl esters are eluted with 7 ml hexane/diethylether solution and dried under streaming nitrogen. The pentafluorobenzyl esters are re-dissolved in 100 µl acetonitril and stored under argon atmosphere at -20°C until use.
chloroform/N,N-diisopropylethylamine (1:1, v/v)
2,3,4,5,6-pentafluorobenzyl bromide [ >99 % (GC), SIGMA]
silica gel column:
Bakerbond SPE Silica (3 ml, 500 mg, BAKER)
hexane/diethylether (2:1, v/v)
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