SYNTHESIS AND ASSIGNMENT OF ABSOLUTE-CONFIGURATION TO THE N(6)-DEOXYADENOSINE ADDUCTS RESULTING FROM CIS AND TRANS RING-OPENING OF PHENANTHRENE 9,10-OXIDE

Reaction of calf thymus DNA with phenanthrene 9,10-oxide in vitro resu lts in alkylation of the exocyclic amino groups of the purine bases. A dducts result from both cis and trans opening of the epoxide. In the p resent study, structures of the N-6-deoxyadenosine adducts have been u nequivocally assigned by synthesis from optically pure cis- and trans- 9-amino-10-hydroxy-9,10-dihydrophethrene. Resolution of trans-9-azido- 10-hydroxy-9,10-dihydrophenanthrene as its acetate was achieved on a c hiral. HPLC column. The early-eluting (-)-enantiomer was assigned (9R, 10R)-absolute configuration based on a characteristic negative CD band at 232 nm due to the helicity of its biphenyl chromophore, in combina tion with a H-1 NMR coupling constant that indicated pseudodiaxial ori entation of the substituents at C-9 and C-10. Aminolysis of the ester followed by reduction of the azido group provided the desired, optical ly active trans (9R,10R) amino alcohol. As a starting material for syn thesis of the cis amino alcohol, trans-9-bromo-10-acetoxy-9,10-dihydro phe was resolved by chiral HPLC. As above, the early-eluting (-)-enant iomer was assigned (9R,10R)absolute configuration based on a character istic negative CD band at 234 nm. Displacement of bromine with inversi on of configuration by azide, aminolysis of the ester, and reduction p rovided optically pure ,10R)-9-amino-10-hydroxy-9,10-dihydrophenanthre ne. Coupling of the optically active amino alcohols with 6-fluoro-9-(2 -deoxy-beta-D-erythro-pentofuranosyl) purine (the 6-fluoro analog of d A) yielded the corresponding N-6-deoxyadenosine adducts. Comparison of CD spectra and HPLC retention times of the synthetic adducts with tho se of the adducts obtained from calf thymus DNA make it possible to as sign unambiguously the structures of the DNA adducts.