Synthesis of 5LO sequence 5′-GAA GTC ACT GGA ACG-3′ (SEQ ID NO:21) containing 2-octanoxyadenine at specific positions is described. A solution of N6-benzoyl-2′-deoxy-2-methyl-sulfonyladenosine, ethyl diisopropylamine, octanoylamine, and DMF is heated to 100° C. for 30 min and evaporated to dryness under reduced pressure. Recrystallization of the residue affords N6-benzoyl-2′-deoxyadenosine with the carbon chain in the 2-position. This material is converted by procedures of examples 107 and 108 above into its 5′-DMT-3′-β-cyanoethyldiisopropylphosphoramidite derivative which is inserted into the 5LO-sequence 5′-GAA GTC ACT GGA ACG (SEQ ID NO:21) via automated, solid phase DNA synthesis.
