Synthesis and biochemical application of 2′-O-methyl-3′-thioguanosine as a probe to explore group I intron catalysis

2′-O-Methyl-3′-thioguanosine phosphoramidite was synthesized in eight steps starting from 2′-O-methyl-N2-(isobutyryl) guanosine with 10.4% overall yield. We have also utilized this analogue to investigate a potential hydrogen bond interaction in the Tetrahymena ribozyme reaction. Our results provide evidence against a model in which the guanosine nucleophile 3′-oxygen accepts a hydrogen bond from the adjacent 2′-hydroxyl group.