Synthesis of a Thymidine Dimer Containing a Tetrazole‐2,5‐diyl Internucleosidic Linkage and Its Insertion into Oligodeoxynucleotides.

Abstract

Thymidine dimers in which the natural phosphodiester linkage has been replaced by a 2,5-disubstituted tetrazole ring are synthesized and incorporated into oligodeoxynucleotides (ODNs). The synthesis is accomplished by two strategies based on an alkylation of 5′-O-trityl-on and 5′-O-trityl-off 3′-deoxy-3′-(1H-tetrazol-5-yl)thymidines with 5′-iodo-5′-deoxythymidine in the presence of Et3N, and the formation of only 2-substituted tetrazol-5-yl linkages is observed in 89 and 46% yields, respectively. The nucleoside dimer formed is reacted with 4,4′-dimethoxytrityl chloride (DMTCl), followed by treatment with 2-cyanoethyl tetraisopropylphosphordiamidite in the presence of N,N-diisopropylammonium tetrazolide, to afford the 5′-O-DMT-protected dinucleoside phosphoramidite that is used for incorporation into ODNs on an automated DNA synthesizer. The modified ODNs with one and up to five tetrazole internucleosidic linkages are obtained in good yields. The thermal stability of DNA/DNA and DNA/RNA duplexes is studied by UV experiments and reported also.