Improved synthesis of oligonucleoside methylphosphonate analogs

Solid-phase synthesis using pent-4-enoyl nucleoside PNT phosphonamidites allow for the facile preparation of oligonucleoside methylphosphonates, methylphosphonothioates and their chimeric analogs. With PNT phosphonamidites, nucleobase and phosphate deprotection, as well as, cleavage from the support can all be accomplished by treatment of the support-bound oligonucleotide with NH4OH (28%, rt, 1 h).