Stereospecific Grignard-Activated Solid Phase Synthesis of DNA Methylphosphonate Dimers

Abstract
Stereoregular Rp or Sp DNA methylphosphonate dimers have been synthesized on a solid phase support. A deprotected 5‘-hydroxyl-N2-isobutanoyldeoxyguanosine 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 (Rp or Sp) was added. Coupling of the activated 5‘-hydroxyl to the 3‘-methylphosphonate ensued, releasing nitrophenol, yielding the Rp or Sp dimer, respectively. The dimers were then cleaved from the solid support, deprotected, and purified, yielding methylphosphonate DNA dimers of defined stereochemistry.