Bis(2,2,2-trichloroethyl) Phosphorochloridite as a Reagent for the Phosphorylation of Oligonucleotides: Preparation of 5'-Phosphorylated 2',5'-Oligoadenylates

Article abstract of DOI:10.1021/jo00333a016

Bis(2,2,2-trichloroethyl) phosphorochloridite was found to be a useful reagent for the phosphorylation of protected nucleosides and oligonucleotides especially when the phosphate blocking group was 2,2,2-trichloroethyl and the hydroxyl protecting group was tert-butyldimethylsilyl.Thus compounds 2a-c,f,g could be phosphorylated to the corresponding 5'-phosphotriesters 4a-c,f,g in yields of 75-99percent.Removal of the protecting groups (to give the 5'-monophosphates 6a-c,f,g) was achieved by zinc-copper couple/2,4-pentanedione/DMF treatment to remove the 2,2,2-trichloroethyl group and tetrabutylammonium fluoride/THF treatment to remove the tert-butyldimethylsilyl groups.A method was found that permits preparation of reproducibly active zinc-copper couple.As a hydroxyl protecting group, the isopropylidene moiety was somewhat less useful in conjunction with the use of bis(2,2,2-trichloroethyl) phosphorochloridite.Thus, upon phosphorylation of 2d and 2e, the phosphotriesters 4d and 4e were obtained in yields of 83percent and 61percent, respectively.Deblocking of the isopropylidene groups was accomplished with formic acid at room temperature to give 6a and 6b in yields of 74percent and 70percent, respectively.The 5'-phosphorylated 2'-5'-linked oligonucleotides 6f and 6g were converted to the corresponding 5'-triphosphates to give compounds 1a and 1b which are found in extracts of interferon-treated cells upon incubation with double-stranded RNA.