Synthesis and binding properties of oligo-2'-deoxyribonucleotides covalently linked to a thiazole orange derivative.

Thiazole orange label was coupled to the eighth phosphate of a pentadeca-2'-deoxyriboadenylate via a phosphoramidate linkage using different linkers. The stereoisomers were separated, and their absolute configurations were determined. Finally, the thiazole orange moiety was also linked to the tenth phosphate of icosathymidylates in both the alpha and the beta series via a phosphoramidate linkage. Once again, the thiazole orange-icosathymidylate conjugates were obtained as pure stereoisomers. The binding properties of these oligo-2'-deoxyribonucleotide-thiazole orange conjugates with their complementary sequences were studied by absorption spectroscopy. The covalent attachment of the thiazole orange derivatives to the oligoadenylates stabilizes the complexes formed with both the DNA and RNA targets. On the contrary, when the thiazole orange is tethered to the oligo-alpha-thymidylate or oligo-beta-thymidylate, no significant stabilization of the duplexes formed with poly r(A) can be observed.