SYNTHESIS OF 1,N-6-ETHANO-2'-DEOXYADENOSINE, A METABOLIC PRODUCT OF 1,3-BIS(2-CHLOROETHYL)NITROSOUREA, AND ITS INCORPORATION INTO OLIGOMERIC DNA

1,N-6-Ethano-2'-deoxyadenosine (1) is one of the adducts formed during DNA reaction with the antitumor agent, 1,3-bis(2-chloroethyl)nitrosou rea (BCNU), and was synthesized and incorporated into a site-specific deoxyoligonucleotide for the first time. The product 6-chloropurine-2' -deoxyriboside (11) was prepared in high yield by the reaction of 2'-d eoxyinosine (6) with SOCl2, which then was derivatized to give compoun d 12 using tert-butyldimethylsilyl chloride, which was then reacted wi th 2-hydroxyethylamine to produce compound 13 in 86% yield. Reaction o f 13 with (PhO)(8)P+MeI- in DMF gave the cyclized 1,N-6-ethano derivat ive 10 in 67% yield. Desilylation of 10 with triethylamine trihydroflu oride in THF gave 1,N-6-ethano-dA (1) in 91% yield. Tritylation of com pound 1 with DMT+BF4- gave the 5'-O-DMT product 14 in 62% yield, which then was phosphitylated with 2-cyanoethyl N,N-diisopropylchlorophosph oramidite, which yielded a 1:1 mixture of the diastereoisomers 15 in 7 1% yield. This fully protected compound 15 was incorporated site-speci fically into a 25-mer oligonucleotide. The coupling efficiency of etha no-dA phosphoramidite was 93%. Enzymatic hydrolysis and analysis by HP LC confirmed the incorporation of ethano-dA and base composition of th e DNA oligomer. The latter is now under investigation for its biochemi cal and physical properties.