O(6)-allyl protected deoxyguanosine adducts of polycyclic aromatic hydrocarbons as building blocks for the synthesis of oligonucleotides.

We describe a synthetic strategy for the preparation of oligonucleotides using N(2)-alkylated and O(6)-allyl protected deoxyguanosine phosphoramidite building blocks derived from cis- and trans-opened (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and (+/-)-7beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and from trans-opened (+/-)-3alpha,4beta-dihydroxy-1alpha,2alpha-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene. The appropriately blocked phosphoramidite building blocks were obtained as mixtures of the cis- and trans-opened diol epoxide adducts upon initial reaction of the diol epoxides with O(6)-allyl-3',5'-di-O-(tert-butyldimethylsilyl)-2'-deoxyguanosine. Key to the present approach is the removal of the O(6)-allyl protecting group utilizing a palladium catalyst prior to release of the constructed oligonucleotide with ammonia from the solid support. The methodology described enables a very convenient access to oligonucleotides containing cis- and trans-N(2)-deoxyguanosine adducts of polycyclic aromatic hydrocarbons in different sequence contexts.