Reported here are the syntheses of two thymidine derivatives with an amide-linked 6-carboxyfluorescein residue at their 3′-position that are suitable for the synthesis of fluorophore-labeled oligonucleotides. The first is a 5′-phosphoramidite with a pivaloyl-protected carboxyfluorescein residue in the lactone form. It was prepared from 3′-azido-3′-deoxythymidine (AZT) in three steps and 73% overall yield and coupled on solid support. The second is an imidazolide of thymidine 5′-monophosphate that was obtained from AZT in five steps and 48% overall yield. The imidazolide can be coupled to amino-terminated nucleic acids in aqueous solution.
DNA - nucleosides - oligomerization - oligonucleotides - solid-phase synthesis
