The use of oxime formation in ligation reactions of oligonucleotides has been widely established in the literature for over a decade.⁽¹⁾ As examples, 5'-aminooxy-modifiers have been used in oxime ligation for peptide-oligonucleotide conjugates,⁽²⁾ attachment of nucleosides to solid supports,⁽³⁾ and head to tail cyclization of oligonucleotides.⁽⁴⁾
The concurrent use of BA0350 at the 5'-terminus and an indole aldehyde modification elsewhere in an oligonucleotide should permit on-support head to tail cyclization upon cleavage of the N-DMT protecting group. See Formylindole-dT-CE Phosphoramidite (BA0301) for an example of an appropriate indole aldehyde.

Ref:

1. For recent reviews see: (a) Zatsepin, T.S.; Stetsenko, D.A.; Gait, M.J.; Oretskaya, T.S. Bioconjugate Chem., 2005, 16(3), 471-89. (b) Singh, Y.; Edupuganti, O.P.; Villen, M.; Defrancq, E.; Dumy, P. Comptes RendusChim., 2005, 8(5), 789-96.
2. (a) Cebon, B.; Lambert, J.N.; Leung, D.; Mackie, K.; McCluskey, K.L.; Nguyen, H.; Tassone, C. Aust J. Chem., 2000, 53, 3333-40. (b) Prater, C.E.; Miller, P.S. Bioconjugate Chem., 2003, 14(2), 320-30. (c) Prater, C.E.; Miller, P.S. Bioconjugate Chem., 2004, 15(2), 498-507.
3. (a) Salo, H.; Virta, P.; Hakala, H.; Prakash, T.P.; Kawasaki, A.M.; Manoharan, M.; Lönnberg, H. Bioconjugate Chem., 1999, 10(5), 815-23. (b) Defrancq, E.; Hoang, a.; Vinet, F.; Dumy, P.; Bioorg. Med. Chem. Lett., 2003, 13, 2683-6. (c) Bincheva, M.; Scheibler, L.; Lincoln, P.; Vogel, H.; Akerman, B. Langmuir, 1999, 15, 4317-20.
4. Edupuganti, O.P.; Defrancq, E.; Dumy, P. J. Org. Chem, 2003, 68, 8708-10.