Synthesis and crystal structure of 2'-se-modified guanosine containing DNA.

Selenium modification of nucleic acids is of great importance in X-ray crystal structure determination and functional study of nucleic acids. Herein, we describe a convenient synthesis of a new building block, the 2'-SeMe-modified guanosine (G(Se)) phosphoramidite, and report the first incorporation of the 2'-Se-G moiety into DNA. The X-ray crystal structure of the 2'-Se-modified octamer DNA (5'-GTG(Se)TACAC-3') was determined at a resolution of 1.20 A. We also found that the 2'-Se modification points to the minor groove and that the modified and native structures are virtually identical. Furthermore, we observed that the 2'-Se-G modification can significantly facilitate the crystal growth with respect to the corresponding native DNA.