Chemically modified oligonucleotides play a significant role for genomic research. Modified nucleosides, such as with a fluorescent dye, can be obtained by chemical synthesis. Site-specifically modified long nucleic acids are obtained by ligation of chemically modified short oligonucleotides with enzyme, photochemistry, or catalytic DNA. The functionality-transfer ODN (FT-ODN), which contains 2'-deoxy-6-thioguanosine (6-thio-dG) functionalized with the 2-methyliden-1,3-diketone group, is hybridized with the target RNA to trigger the selective functionalization of the 4-amino group of the cytosine base at pH 7 or the 2-amino group of the guanine base at pH 9.4 or at pH 7.4 in the presence of NiCl2. In particular, the functionality-transfer reaction (FTR) under the alkaline conditions or neutral conditions in the presence of NiCl2 proceeds rapidly and selectively to lead to the modification of the target guanine. The transfer reaction of the acetylene-containing diketone group produces the acetylene-modified RNA, which can be subjected to the Cu(I)-catalyzed "click chemistry" with a variety of azide compounds for highly specific, internal modification of RNA.
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