For the installation of an amino group at the 3'-terminus of an oligonucleotide, a solid-support-linked monomer with a protected amine and DMT-protected alcohol is required. The amine protecting group is typically removed and acylated with an appropriate NHS ester. The (fluorenylmethyl)carbamoyl (Fmoc) group has been shown to be useful as such an amine protecting group for amine modification of oligonucleotides.⁽¹⁾ It is removed during cleavage/deprotection with ammonium hydroxide. Alternatively, the Fmoc group can be removed before cleavage of the oligonucleotide from the solid support, e.g., with piperidine, simplifying the acylation process. After the acylation is complete, the labeled oligonucleotide can then be cleaved from the support and further deprotected with ammonium hydroxide.⁽²⁾

Both products feature a mixed C/O 7-atom spacer between the amino group and the O-DMT group, which differs slightly in structure from LK2350 which has a fully carbon spacer. 

Ref:

1. Nelson, P. S.; Kent, M.; Muthini, S. Nucl. Acids Res. 1992, 20, 6253-6259.
2. (a) Gartner, Z. J.; Kanan, M. W.; Liu, D. R. J. Am. Chem. Soc. 2002, 124, 10304-10306; see Supporting Information, p. 3. (b) Gartner, Z. J.; Tse, B. N.; Grubina, R.; Doyon, J. B.; Snyder, T. M.; Liu, D. R. Science 2004, 305, 1601-1605; see Supporting Online Material, p. 2.