Liquid chromatography/electrospray ionization tandem mass spectroscopy (LC/ESI MS/MS) analysis of 1,2-epoxybutene adducts of purine deoxynucleosides.

Calf thymus DNA was reacted with 1,2-epoxybutene (BDO) in phosphate buffered saline at 37 degrees C for 12 h. DNA was ethanol precipitated and hydrolyzed with 1 M HCl to release DNA bases. Adenine (A)-BDO and guanine (Gua)-BDO adducts were analyzed in the ethanol supernatant and DNA hydrolysate using LC/ESI MS/MS. Reaction of BDO with A resulted in the formation of seven A-BDO adducts with MH+ ions at m/z 206. Two of these adducts were observed in the ethanol supernatant. In addition, two formaidopyrimidine (FAPY)-adducts were detected with MH+ ions at m/z 224 in DNA hydrolysate. These data are consistent with formation of regioisomeric N-7 or N-9 adducts which can be released by spontaneous depurination or ring opening. Four other A-BDO adducts were detected in DNA hydrolysate. Similar adducts were observed for Gua. This new methodology permits simultaneous determination of initially formed adducts as well as those arising as a consequence of depurination. The latter adducts provide the opportunity for monitoring exposure to BDO through analysis of N-7 or N-3 adducts excreted in the urine.