Large-scale synthesis of antisense oligonucleotides without chlorinated solvents

It is demonstrated that mixed-sequence phosphorothioate oligodeoxyribonucle otides can be synthesized on scales from 1 mu mol up to 80 mmol without usi ng chlorinated solvents such as dichloromethane or dichloroethane, while pr eserving both high yield and purity of the product. A solution of dichloroa cetic acid in organic solvents (e.g., toluene, xylenes, benzotrifluoride) c leanly and efficiently removes the 4,4'-dimethoxytrityl (DMTr) group from t he 5'-terminus of the growing oligonucleotide chain during synthesis on sol id support. We have therefore replaced hazardous dichloromethane, formerly used in oligonucleotide synthesis, as the solvent for DMTr-removal, with to luene.