Synthesis and characterization of oligonucleotides containing site-specific bulky N2-aralkylated guanines and N6-aralkylated adenines.

7-Bromomethylbenz[a]anthracene is a known mutagen and carcinogen. The two major DNA adducts produced by this carcinogen, i.e., N2-(benz[a]anthracen-7-ylmethyl)-2'-deoxyguanosine (2, b[a]a2G) and N6-(benz[a]anthracen-7-ylmethyl)-2'-deoxyadenosine (4, b[a]a6A), as well as the simpler benzylated analogs, N2-benzyl-2'-deoxyguanosine (1, bn2G) and N6-benzyl-2'-deoxyadenosine (3, bn6A), were prepared by direct aralkylation of 2'-deoxyguanosine and 2'-deoxyadenosine. To determine the site-specific mutagenicity of these bulky exocyclic amino-substituted adducts, the suitably protected nucleosides were incorporated into 16-base oligodeoxyribonucleotides in place of a normal guanine or adenine residues which respectively are part of the ATG initiation codon for the lac Z' alpha-complementation gene by using an in situ activation approach and automated phosphite triester synthetic methods. The base composition and the incorporation of the bulky adducts into synthetic oligonucleotides were characterized after purification of the modified oligonucleotides by enzymatic digestion and HPLC analysis.