Process for oligonucleotide synthesis

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to methods for linking a phosphoramidite nucleoside to a solid support-bound nucleoside.
These methods comprise attaching a first nucleoside having a protected hydroxyl group to a solid support by means of a covalent linkage.
The first nucleoside may be attached to the solid support either directly or via a linker, using standard methods and procedures known in the art.
See, e.
g.
, Oligonucleotides and Analogues: A Practical Approach, Eckstein, F, Ed.
, IRL Press, New York, 1991, hereby incorporated by reference in its entirety.
One example is a long chain alkylamine linker incorporating a carbamate linkage.
The attached protected nucleoside is then deprotected with a deprotecting reagent and coupled with a second phosphoramidite nucleoside to form a phosphorus nucleoside linkage between the first nucleoside and the second nucleoside.
This coupling occurs at the hydroxyl group, of the first nucleoside, which becomes reactive upon deprotection with the deprotecting reagent.
Following this coupling step, the remaining deprotected but uncoupled first nucleoside is optionally capped with a capping reagent.
The resultant phosphorus nucleoside linkage is next oxidized with an oxidizing agent.
According to the methods of the present invention, during the linking of a phosphoramidite nucleoside to a solid support-bound nucleoside, the solid support is washed with acetonitrile prior to or subsequent to at least one of the coupling, capping or oxidizing steps, wherein the acetonitrile has a water content between 30 ppm and about 1250 ppm, or at least one of the capping or oxidizing reagents is in an acetonitrile solvent having a water content of between 30 ppm and about 1250 ppm.
In a preferred embodiment the solid support is washed with acetonitrile prior to or subsequent to at least one of the coupling, capping or oxidizing steps, wherein the acetonitrile has a water content between 30 ppm and about 1250 ppm, and at least one of the capping or oxidizing reagents is in an acetonitrile solvent having a water content of between 30 ppm and about 1250 ppm