Chemical synthesis of 2′-deoxyguanosine-C8 adducts with heterocyclic amines: An application to synthesis of oligonucleotides site-specifically adducted with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

Synthesis of 2′-deoxyguanosine-C8 adducts (dG-C8 adducts) with mutagenic/carcinogenic heterocyclic amines (HCAs) was achieved via the Buchwald-Hartwig arylamination reaction. By using tris-(dibenzylideneacetone) dipalladium (Pd₂dba₃) and 9,9-dimethyl-4,5- bis(diphenylphosphino)xanthene (xantphos) with a cesium carbonate (Cs ₂CO₃) base at a reaction temperature of 100∼120 °C, we obtained derivatives of dG-C8 adducts with 2-amino-3-methylimidazo[4, 5-f]quinoline (IQ), 2-amino-6-methyl-dipyridol [1,2-a:3′,2′-d] imidazole (Glu-P-1), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP) in 69%∼97% yield from the cross-coupling of an 8-bromodeoxyguanosine derivative. In the case of PhIP, it was found that dimethyl sulfoxide (DMSO) was the critical solvent for the arylamination reaction. Subsequent deprotection of the resulting dG-C8 adduct derivatives yielded authentic samples of dG-C8 adducts with HCAs. The dG-C8-PhIP adduct was further converted into a suitably protected phosphoramidite derivative for automated DNA synthesis. Synthesis of oligonucleotides wherein PhIP adducted on each G within a triple G sequence in codon 869 (TCC GGG AAC) of rat Apc genes was performed with a modification in the coupling time and deprotection procedures.