Stereospecific Synthesis of Oligonucleotides Containing Crotonaldehyde Adducts of Deoxyguanosine

Crotonaldehyde reacts with DNA to form two diastereomeric 1,N(2) cyclic adducts of deoxyguanosine. A synthesis of the two diastereomeric deoxynucleosides has been achieved by reaction of mixed diastereomers of 4-amino-1,2-pentanediol with 2-fluoro-O(6)-(trimethylsilylethyl)-deoxyinosine. The resulting N(2)-(1-methyl-3,4-dihydroxybutyl)-deoxyguanosine was treated with NaIO(4), cleaving the vicinal diol to the aldehyde. Spontaneous cyclization gave the two diastereomers of the crotonaldehyde-adducted nucleoside that were readily separated by HPLC. The absolute configurations were assigned by an enantiospecific synthesis of one diastereomer from (S)-3-aminobutanoic acid. The synthetic strategy has been extended to preparation of a site-specifically adducted oligonucleotide by reaction of the mixed diastereomers of 4-amino-1,2-pentanediol with an 8-mer oligonucleotide containing 2-fluoro-O(6)-(trimethylsilylethyl)-deoxyinosine. The diastereomeric oligonucleotides were separated by HPLC and absolute configurations of the adducts were established by enzymatic digestion to the adducted nucleosides.