Premium
Mass spectra of sterically crowded trialkylsilyl derivatives of nucleosides
Author(s) -
Quilliam Michael A.,
Ogilvie Kelvin K.,
Sadana Krishan L.,
Westmore John B.
Publication year - 1980
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210150411
Subject(s) - chemistry , steric effects , mass spectrum , fragmentation (computing) , ion , electron ionization , polyatomic ion , isopropyl , silylation , molecule , trimethylsilyl , mass spectrometry , stereochemistry , photochemistry , computational chemistry , medicinal chemistry , organic chemistry , ionization , chromatography , computer science , catalysis , operating system
The electron impact mass spectra of tert ‐butyldimethylsilyl‐, cyclo ‐tetramethylene‐ tert ‐butylsilyl and cyclo ‐tetramethylene‐isopropylsilyl‐ ether derivatives of ribo‐ and 2′‐deoxyribonucleosides are described in detail. The interpretation of fragmentation pathways of full and mixed derivatives was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements, and spectra of mixed derivatives containing the ‘passive’ (in these spectra) trimethylsilyl group. The sterically crowded silyl groups have a powerful fragmentation directing effect. Elimination of a bulky radical, R˙ ( tert ‐butyl or isopropyl), from the molecular ion produces the siliconium ion [MR] + , which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion center with electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [MR] + ions formed from 2′, 3′ or 5′‐ O ‐silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.