Replacing two non-bridging oxygen atoms with sulfur atoms in a DNA phosphodiester linkage creates a phosphorodithioate (PS2) linkage.<sup>1</sup> Like natural DNA, the phosphorodithioate linkage is achiral at phosphorus. This analog is completely resistant to nuclease degradation and forms complexes with DNA and RNA with somewhat reduced stabilities.<sup>2</sup> Moreover, it has been found that PS2-ODNs bind proteins with a higher affinity than their phosphodiester analogues<sup>2-6</sup> suggesting that PS2-ODNs may have additional utility in the form of sulfur-modified phosphate ester aptamers (thioaptamers)<sup>3,6-8</sup> for therapeutic and diagnostic applications. Thiophosphoramidites are now commercially available after recent work at AM Biotechnologies (www.thioaptamer.com).
A typical cycle for the solid-phase synthesis of a PS2 linkage is different from a standard cycle for the synthesis of normal phosphate linkages. After coupling, the resulting thiophosphite triester is then sulfurized with DDTT. Capping is carried out AFTER sulfurization. Upon completion of the automated synthesis, deprotection is carried out using a concentrated ammonia:ethanol (3:1, v:v) mix containing 20 mM DTT at 55°C for 15-16 h.
|Diluent||10% (v/v) Anhydrous Dichloromethane in Anhydrous Acetonitrile|
|Storage||Freezer storage, -10 to -30°C, dry|
The table below show pack size data and, for solutions, dilution and approximate coupling based on normal priming procedures.
|Catalog #||Pack Size||Grams/Pack||0.1M Dil. (mL)||Approximate Number of Additions|
|Catalog #||Pack Size||Grams/Pack||Dilution (mL)||Approximate Number of Additions|