Azidobutyrate NHS Ester is used1 for azido-modification of amines at either the 3’-end or the 5’-end of an oligo and it can even be used for internal modification on an Amino-Modifier-C6 dX residue within the sequence.
REFERENCES|(1) R. Kumar, et al., Journal of the American Chemical Society, 2007, 129, 6859-6864.
Coupling: For labeling 0.2 umoles of an amino-modified oligonucleotide, dissolve 2.3 mg of Azidobutyrate NHS Ester in 60 uL of ACN (DMSO or DMF are also acceptable). Dissolve the amino-modified oligonucleotide in 500 uL of 0.1 M Carbonate/Bicarbonate buffer (pH 9). Add 12 uL of the Azidobutyrate NHS Ester solution to the dissolved oligonucleotide and let react for 2 hours at room temperature and desalt.