Nucleoside–Metallacarborane Conjugates for Base‐Specific Metal Labeling of DNA

A general approach to the synthesis of nucleoside conjugates between derivatives of thymidine (T), 2′‐ O ‐deoxycytidine (dC), 2′‐ O ‐deoxyadenosine (dA), and 2′‐ O ‐deoxyguanosine (dG), and metallacarborane complexes is described. Metallacarborane–nucleoside derivatives are prepared by reaction of the dioxane–metallacarborane adduct with a base‐activated 3′,5′‐protected nucleoside. In the case of T and dG a mixture of regioisomers, which is easily separable by chromatographic methods, is obtained, thus yielding a series of modifications containing metallacarborane groups at the 2‐ O , 3‐ N , 4‐ O and 1‐ N , 2‐ N , 6‐ O locations, respectively; dC and dA are alkylated at the exo ‐amino function. The proposed methodology provides a route for the synthesis and study of nucleic acids modified with metallacarboranes at designated locations and a versatile approach to the incorporation of metals into DNA.