Dorte Renneberg

Exploring Hoogsteen and Reversed‐Hoogsteen Duplex and Triplex Formation with Tricyclo‐DNA Purine Sequences

The duplex‐ and triplex‐formation properties of the tricyclo‐DNA purine decamer 5′p‐gagaaggaaa‐3′ as a single strand or as part of a hairpin duplex with corresponding parallel and antiparallel pyrimidine DNA and RNA complements, as well as with antiparallel purine DNA and RNA complements, were investigated by UV melting curve analysis, circular dichroism spectroscopy, and gel mobility shift experiments. It was found that tricyclo‐DNA forms very stable duplexes with the pyrimidine RNA and DNA complements not only in the Watson–Crick pairing mode, but also in the Hoogsteen one. Below pH 6.0, the tc‐DNA/DNA and tc‐DNA/RNA Hoogsteen duplexes were found to be more stable than the corresponding Watson–Crick DNA duplexes. Triplexes of the hairpin structure with parallel pyrimidine complements revealed even stronger Hoogsteen pairing relative to the duplexes, presumably due to structural preorganization phenomena. Triplex formation with antiparallel pyrimidine and purine third strands (reversed‐Hoogsteen motif) could not be observed and seem to be unstable.

Synthesis of the Sugar Building Block of Bicyclo-RNA

We present the novel synthesis of two sugar units that are central intermediates for the formation of members of the bicyclo-DNA and -RNA family. The synthesis starts from commercially available 1,2: 5,6-di-O-isopropylidene-alpha-D-glucofuranose. The key step involves the elaboration of a carbocyclic ring in a furanoside by rhodium(I)-catalyzed hydroacylation. Via this pathway, one of the sugar units is available in 8 steps and in an overall yield of 27%, while its deoxy derivative is obtained in 11 steps, which is 5 steps fewer than in our previous synthesis of this compound.