Preparation of Cyclic-1,N2-propano-2′-deoxyguanosine-d7 as an Internal Standard for ESI-MS/MS Determination of DNA Damage from Acetaldehyde

Cyclic-1,N2-propano-2′-deoxyguanosine-d7 (CPr-dG-d7) was prepared as an isotopic internal standard (IS) for electrospray ionization tandem mass spectrometry (ESI-MS/MS) quantification of CPr-dG in DNA as a candidate cancer risk marker of acetaldehyde intake, mainly from drinking. The deuterated compound was reasonably synthesized from acetaldehyde-d4 and 2′-deoxyguanosine in deuterium oxide (D2O), preventing the deuterium atoms of acetaldehyde-d4 from being substituted by hydrogen atoms, which occurred seriously in aqueous synthesis media via keto–enol tautomerism. Furthermore, another deuterium atom was added from D2O to form CPr-dG-d7. After four weeks of storage in H2O at 10°C, CPr-dG-d7 was found to be sufficiently stable for practical use. The calibration curve of CPr-dG by using a hydrophilic interaction chromatography–ESI-MS/MS system with CPr-dG-d7 as the IS showed sufficient linearity from 1.0 × 10−10 to 4.0 × 10−9 M with r2 = 0.998.