Characterization of the alkaline degradation products of an oligodeoxynucleotide containing 8-oxo-7,8-dihydro-2'-deoxyguanosine by electrospray ionization mass spectrometry

Oligodeoxynucleotides containing 8-oxo-7,8-dihydro-2'-deoxyguanosine exhibit alkaline sensitivity and undergo cleavage of the phosphodiester backbone. Identification of the major degradation products and unstable intermediates formed in concentrated ammonia was accomplished by HPLC isolation and characterization by electrospray ionization mass spectrometry. Unstable intermediates were reduced in situ with NaBH4 prior to isolation and mass analysis. This technique produced accurate mass data for an oligonucleotide intermediate containing an abasic site, a strand cleavage product containing the 3'-terminus, and two products with the 5'-terminus. 8-Oxoguanine was not present in the product HPLC chromatogram, suggesting rearrangement or degradation of this moiety prior to glycosidic bond cleavage. A scheme for the decomposition of 8-oxo-7,8-dihydro-2'-deoxyguanosine-containing oligonucleotides in 28% ammonia solution is presented.