Figure 1.

(A) Formation of M₁G from [1,2a] cyclization of deoxyguanosine by β-hydroxyacrolein. (B) Ring-opening to the N²-(3-oxo-1-propenyl)-dG derivative occurs at basic pH; the ring-opened species equilibrate between the favored amino and the enol tautomers. Note the numbering system for the M₁G protons. In oligodeoxynucleotides, M₁G is designated as M, and N²-(3-oxo-1-propenyl)-dG is designated as X.