Studies on the role of nitrosamines in carcinogenesis. Part I. LC-ESI-MS-MS trace detection of glyoxaldeoxyguanosine and O(6)-hydroxyethyldeoxyguanosine. Part II. Nitrosation reactions of a methaqualone drug analog

Part I. LC-ESI-MS-MS trace detection of glyoxaldeoxy-guanosine and O6-hydroxyethyldeoxyguanosine. N-Nitrosodiethanolamine (NDELA) is a bident carcinogen that undergoes both P-450 mediated α-hydroxylation and β-oxidation, which ultimately lead to glyoxaldeoxyguanosine (gdG) and O6-2-hydroxyethyldeoxyguanosine (OHEdG) adducts in rat liver DNA. In order to develop better methods for the detection of these adducts for mechanistic and possibly human studies, an improved method over 32P-postlabeling or fluorescence was sought for their detection. The pH sensitive gdG adduct was detected by acid catalyzed DNA hydrolysis followed by HPLC electrospray MS-MS (LC-ESI-MS-MS), where the adducted base was monitored after the loss of the deoxyribose fragment. The amount of adduct present was quantified with the use of an isotopically labeled gdG internal standard. This method was also applied to the detection of OHEdG. Quantitative MS-MS detection was linear over a concentration range of 104 and reproducible results were obtained using isotopomer spiking of the DNA prior to hydrolysis. These methods were applied to the determination of DNA adduct levels in rat liver following NDELA administration. Both adducts were detected and quantified successfully although a dose response relationship was not observed.; Part II. Nitrosation reactions of a methaqualone drug analog . In order to test the possible nitrous acid reactivity of compounds structurally related to methaqualone, a widely prescribed CNS drug, the synthesis and reaction of 2-methyl-3-phenyl-4-quinazolone with nitrous acid was undertaken. 2-Methyl-3-phenyl-4-quinazolone was synthesized by a known procedure from the condensation of N-phenylantranilamide with acetylacetone. Nitrosation with six equivalents of sodium nitrite in glacial acetic acid gave two major products, a and b, which were separated by chromatography, crystallized and their structures determined by X-ray crystallography. In a, the methyl group of 2-methyl-3-phenyl-4-quinazolone was converted into a cyano residue, and in b, it has been replaced by a hydrogen. Methaqualone was determined to not be susceptible to gastric nitrosation as most of its structural analogue remained unchanged at high nitrous acid concentrations in vitro.*; *Please refer to dissertation for diagrams.