Synthesis and incorporation of the phosphoramidite derivative of 2'-O-photocaged 3'-s-thioguanosine into oligoribonucleotides: substrate for probing the mechanism of RNA catalysis.

Oligoribonucleotides containing 3'-S-phosphorothiolate linkages possess properties that can reveal deep mechanistic insights into ribozyme-catalyzed reactions. "Photocaged" 3'-S- RNAs could provide a strategy to stall reactions at the chemical stage and release them after assembly steps have occurred. Toward this end, we describe here an approach for the synthesis of 2'-O-(o-nitrobenzyl)-3'-thioguanosine phosphoramidite starting from N(2)-isobutyrylguanosine in nine steps with 10.2% overall yield. Oligonucleotides containing the 2'-O-(o-nitrobenzyl)-3'-S-guanosine nucleotide were then constructed, characterized, and used in a nuclear pre-mRNA splicing reaction.