DBCO (Figure 1) is usually used in copper-free click reactions, where DBCO-modified oligos and azide modifiers are conjugated in organic solvents, such as DMSO, or aqueous buffers.
Figure 1. Structure of 5'-DBCO (R = sequence).
metabion offers DBCO as a 5'-, 3'- or internal modification in its DNA portfolio:
van Delft P., Meeuwenoord NJ., Hoogendoorn S., Dinkelaar J., Overkleeft HS., van der Marel GA., Filippov DV. Synthesis of oligoribonucleic acid conjugates using a cyclooctyne phosphoramidite. Org Lett. 2010 Dec 3;12(23):5486-9.