OLIGONUCLEOTIDES WITH 1,5-ANHYDROHEXITOL NUCLEOSIDE BUILDING BLOCKS. CRYSTALLIZATION AND PRELIMINARY X-RAY STUDIES OF h(GTGTACAC)

Ruben Declercq¹, Arthur Van Aerschot², Piet Herdewijn² and Luc Van Meervelt¹

¹Laboratory of Macromolecular Structural Chemistry, K.U. Leuven, Celestijnenlaan 200F, B-3001 Heverlee, Belgium
² Laboratory of Medicinal Chemistry, Rega Institute for Medical Research, Minderbroederstraat 10, B-3000 Leuven, Belgium,
Ruben.Declercq@chem.kuleuven.ac.be

HNA, antisense oligonucleotides, 1,5-anhydrohexitol Antisense oligonucleotides can be considered as a new class of potential therapeutic agents. However, modifications of the classical DNA backbone are necessary in order to overcome problems of low stability and cellular uptake. Hexitol nucleic acids (HNA) are oligonucleotides built up from natural nucleobases and phosphorylated 1,5-anhydrohexitol building blocks (1) instead of the normal b-D-2'-deoxyriboses. So far this hexitol modification is one of the strongest hybridizing antisense compounds.

(1)

The anhydrohexitol oligonucleotide h(GTGTACAC) was synthesized using phosphoramidite chemistry and standard protecting groups. Crystals of h(GTGTACAC) were obtained at either 6° or 16°C by the hanging drop vapor-diffusion technique using a 24 matrix screen for nucleic acid fragments. Two distinctive crystal forms were observed: long needles and in the K⁺ containing conditions diamond-like crystals. After some days the morphology of the crystals changed. Fresh diamond-like crystals were grown near the synchrotron site in Trieste. The crystals diffract beyond 2.0 A resolution and belong to the hexagonal space group P6₂22 (or P6₄22) with unit cell parameters a=36.42 and c=63.33 A. Structure determination and further crystallization optimizations are currently in progress.