Synthesis of a 2'-Se-thymidine phosphoramidite and its incorporation into oligonucleotides for crystal structure study.

[reaction: see text] To investigate nucleic acids with selenium derivatization for crystallography, we report the first synthesis of 2'-methylseleno-thymidine phosphoramidite and its incorporation into DNAs and RNAs by solid-phase synthesis with over 99% coupling yield. The d(GT(Se)GTACAC)2 crystal structure was also determined at 1.40 A resolution using Se phasing, revealing that this Se derivatization did not cause significant structure perturbation, consistent with our UV melting study. In addition, we observed that the Se modification largely facilitated the crystallization.