IMPROVED STRATEGIES FOR POSTOLIGOMERIZATION SYNTHESIS OF OLIGODEOXYNUCLEOTIDES BEARING STRUCTURALLY DEFINED ADDUCTS AT THE N-2 POSITION OF DEOXYGUANOSINE

Improved methodology has been developed for preparation of oligodeoxyn ucleotides bearing adducts on the N-2 position of guanine in which the adduction reaction is carried out in homogeneous solution rather than while the oligonucleotide is immobilized on a solid matrix. The metho dology utilizes a new synthon, 2-fluoro-O-6-(trimethylsilylethyl)-2'-d eoxyinosine (3) Nucleoside 3 is stable to the conditions of oligonucle otide synthesis, but the O-6 protection is eliminated under very mild conditions following displacement of the 2-fluoro group by amine nucle ophiles. Oligonucleotides containing 3 could be removed from the solid support by treatment with 0.1 M NaOH (8 h, rt) without disruption of 3. Reaction of the crude, partially deprotected oligonucleotide with ( R)-2-amino-2-phenylethanol in homogeneous solution, followed by remova l of the remaining protective groups with NH4OH (60 degrees C, 8 h) an d then 0.1% acetic acid, gave the adducted oligonucleotide in good pur ity and yield. Alternatively, fully deprotected oligonucleotide contai ning 3 could be prepared by use of labile phenoxyacetyl-type protectin g groups on the exocyclic amino groups.