2'-DeoxyXanthosine (dX) is a naturally occurring nucleoside that may be derived from oxidative deamination of 2'-deoxyGuanosine (dG). dX has a similar bonding pattern to thymidine and it may base pair with dA, with such purine-purine interactions causing duplex distortion. dX also featured in attempts to extend the genetic alphabet with a new base pair of dX and pyrimidine-2,4-diamine nucleoside. dX has also interested researchers in the field of DNA damage and repair since it is a product of nitric oxide-induced mutagenesis.
Coupling: No changes needed from standard method recommended by synthesizer manufacturer.
Deprotection: With the oligonucleotide still attached to the support, treat with 1 M DBU in anhydrous ACN for 2-3 minutes, followed by 17 hours using fresh 1 M DBU at room temperature. Rinse support with ACN and then deprotect as required by nucleobases. Note, the dX nucleoside is susceptible to depurination though short exposure to acid is tolerated - e.g. Glen-Pak purification.