Patent ID: 7723511

Claim:
A method for the preparation of a phosphorothioate internucleoside linkage comprising: contacting the 5′ hydroxyl group of a solid support bound nucleic acid moiety with a phosphite moiety in acetonitrile to form a phosphite diester intermediate; said phosphite moiety being bonded to a nucleoside, a nucleotide, an oligonucleoside or an oligonucleotide; and oxidizing said phosphite diester intermediate with an arylacetyl disulfide in a solvent mixture of acetonitrile and a lutidine, acetonitrile and a collidine and/or acetonitrile and a picoline in a ratio of 1.5:1 to 1:1.5, for a time sufficient to effect conversion of said phosphite diester intermediate to said phosphorothioate.