Boronic acid-modified nucleoside – synthesis and structural characterisation in the solid state

The first structure of a boronic acid-modified nucleoside is elucidated by single-crystal X-ray diffraction and compared to its <i>tert</i>-butyldimethylsilyl-protected nucleoside derivative. Further, we present the synthetic access to boronic acid-modified -nucleosides providing alternative reaction conditions to a reported synthesis. Although the sugar pucker of the boronic acid-modified nucleoside differs slightly from other nucleosides, the geometry around the nucleobase shows a high degree of structural similarity to the nucleosides of the natural nucleobases. Inter- as well as intramolecular hydrogen bonds are present involving the boronic acid residue as donor. The interconnection <i>via</i> hydrogen bonds permits the formation of suprastructures in form of linear zigzag chains in the solid state. In conclusion, the structural influence by the boronic acid residue on the overall nucleoside's geometry was only minor which favours its potential use as functionalised thymidine analogue in deoxyoligonucleotides.