Structures of the 3,4-Epoxybutene-Derived R- and S-N1-(2-Hydroxy-buten-2-yl) -2' Deoxyinosine DNA Adducts: Regiochemical Control of Glycosidic Torsion Angle Conformation

Abstract

Chemical and Physical Biology

Structures of the 3,4-Epoxybutene-Derived R- and S-N1-(2-Hydroxy-buten-2-yl) -2' Deoxyinosine DNA Adducts: Regiochemical Control of Glycosidic Torsion Angle Conformation Dennis Kuo

Thesis under the direction of Professor Michael P. Stone 1,3-butadiene (BD) is an industrially important chemical obtained from petrochemical extraction and has been classified as a human carcinogen by the National Toxicology Program. EB, the primary metabolite of BD, has two reactive epoxide carbons (Carbon 3 and Carbon 4) that can each react with the N1 of adenine to produce two stereoisomers, leading to a total of four distinct adducts. These adducts can spontaneously deaminate to form deoxyinosine (dI) adducts. The Carbon 3 adducts are observed to induce A to G mutations in COS-7 cells. It has been hypothesized that these A to G mutations are promoted by Hoogsteen base pairing between the modified base and an incoming protonated dCTP. Previously determined solution structures of the Carbon 3 adducts show the modified base in the syn conformation, supporting this hypothesis. The structures of the Carbon 4 adducts, N1-((R-)2-hydroxy-3-buten-2-yl) and N1-((S-)2-hydroxy-3-buten-2-yl), were determined in the ras codon 61 sequence context, using NMR methods. In both stereoisomers, the BD moiety was oriented into the duplex, and the modified base remained in the native anti¬ conformation about the glycosyl bond. These results suggest that the Carbon 4 adducts may be processed differently than the previously investigated Carbon 3 adducts by DNA damage response mechanisms.