Thiophosphoramidites are reagents used to synthesize internucleotide linkages that contain two non-bridging sulfurs in place of the oxygens. These PS2 linkages when used in aptamers can result in significantly increased binding affinity and much slower off-rates (See Improve Existing Aptamers & siRNA). When used in siRNA, PS2 linkages can result in increased gene silencing.
AM Biotech sells thiophosphoramidites in 1g, 2g, 5g, 10g, and 20g packages. Smaller quantities are available from Glen Research (www.glenresearch.com).
IMPORTANT: thiophosphoramidites required non-standard synthesis protocols for best results.