N-hydroxysuccinimide ester labeling 5'-aminoalkyl DNA oligomers: reaction conditions and purification

Difficulties were encountered in labeling 5'-aminoalkyl DNA oligomers with glycolketo electrophore N-hydroxysuccinimide esters in aqueous sodium bicarbonate (a common base for this purpose), followed by C18-silica reversed-phase high-performance liquid chromatography (HPLC) to achieve purification. The electrophore-labeled oligomers were not separated readily either from the hydrolyzed electrophore or from the starting oligomer. This problem was overcome by conducting the reaction with triethylamine as a base, organic washing the reaction mixtures after evaporation, and separating on a C18-poly(styrene-divinylbenzene) HPLC packing.