We recommend that coupling reactions between BC-PEG-NH2 and NHS esters or activated carboxylic acids take place in anyhydrous N, N-dimethylformamide (DMF) by using triethylamine as a base.
Typical reactions use approximately equimolar quantities of the BC-PEG-NH2 and the desired NHS-label at 5–20 mM final concentration in the presence of a 1.5 fold molar excess of triethylamine in DMF. It is convenient to use similar volumes of the BC-PEG-NH2 and the NHS-label. The reaction is generally performed at 30°C overnight.
The purification strategy will depend on the label used and the reaction scale. Good results have been obtained with both HPLC and silica gel chromatography.