ELECTRON IONIZATION MASS-SPECTRA OF TRIMETHYLSILYL DERIVATIVES OF NUCLEOSIDES

This chapter discusses electron ionization mass spectra of trimethylsilyl (TMS) derivatives of nucleosides. Trimethylsilyl derivatives of nucleosides have found extensive use for structural characterization by electron ionization (EI) mass spectrometry. Examples of applications include nucleosides from RNA, physiological fluids, nucleoside antibiotics, and nucleoside adduct and DNA damage products. The present chapter principally describes steps and procedures for the interpretation of mass spectra of trimethylsilylated nucleosides. Most examples presented deal with ribonucleosides because they have had the greatest attention in terms of both model studies and applications, but the procedures described are generally relevant to deoxynucleosides, various nucleoside analogs, and mononucleotides. Compared with other approaches based on mass spectrometry, TMS derivatives offer the following advantages: (1) their EI mass spectra produce great structural detail, and models and isotopically labeled analogs have been extensively studied; (2) in terms of increased mass resulting from derivatization, TMS groups produce greater mass dispersion and therefore less chance of overlap when working with mixtures than in the case of the unblocked nucleosides, and result in molecular weights (-500-900) which fall in a generally background-free mass region; (3) the derivatives are easily prepared on a small scale and are sufficiently volatile and thermally stable, so that thermal decomposition during direct-probe vaporization is very unusual; most of the simpler nucleosides are amendable to gas chromatography and thus GC/MS. © 1990, Elsevier Inc. All rights reserved.