Stereospecific Grignard-activated solid phase synthesis of DNA methylphosphonate dimers

Stereoregular R(p) or S-p DNA methylphosphonate dimers have been synthesized on a solid phase support. A deprotected 5'-hydroxyl-N-2-isobutanoyldeoxyguano sine 3'-O-succinate coupled to high-loaded polyethylene glycol (PEG) coated polystyrene beads (HLP) was activated with a Grignard reagent, t-BuMgCl. After activation was complete, a pure diastereoisomer of 5'-(dimethoxytrityl) N-benzoyldeoxynucleoside 3'-(p-nitrophenyl methylphosphonate) p-nitrophenyl ester (R(p) or S-p) was added. Coupling of the activated 5'-hydroxyl to the 3'-methylphosphonate ensued, releasing nitrophenol, yielding the R(p) or S-p dimer, respectively. The dimers were then cleaved from the solid support, deprotected, and purified, yielding methylphosphonate DNA dimers of defined stereochemistry.