Synthesis and Incorporation of the Phosphoramidite Derivative of 2′-O-Photocaged 3′-S-Thioguanosine into Oligoribonucleotides: Substrate for Probing the Mechanism of RNA Catalysis

[Image: see text] 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.