The marked proclivity of 5-S-cysteinyldopa (I) and related phenolic alkylthioethers to undergo UV-induced desulfurization via primary photohomolytic cleavage of the CH2-S bond prompted an investigation of the mass spectrometric behavior of these compds. with a view to obtaining information on the intrinsic susceptibility to dissocn. of the alkylthioether bond under nonirradiative conditions. Dealkylative fission of the CH2-S bond was an important dissociative channel in the fragmentation patterns of 1 and related compds., including cysteinylhydroquinone (II), 4-S-cysteaminylphenol (III) and 4-S-cysteaminylcatechol (IV) under electron impact conditions. The mode of fission and relative susceptibility of the CH2-S bond were, however, profoundly different in cysteaminyl vs. cysteinyl compds. In particular, the former showed a marked tendency to undergo simple homolytic fission, whereas in the latter dealkylative C-S bond cleavage occurred largely via an intramol. rearrangement mechanism, and proved highly sensitive to protonation-induced effects, as evidenced in fast atom bombardment expts. Desulfurization processes with neat loss of the alkylthio residue, like those occurring upon UV irradn., were virtually absent in the fragmentation patterns of III and IV, and provided only a minor contribution to those of I and II. These and other data reported open fresh prospects for future studies on the chem. and mass spectrometric behavior of I and structurally related phenolic compds. of biol. relevance.
Mass spectrometric behavior of 5-S-cysteinyldopa and structurally related phenolic compounds. Fragmentation susceptibility of the alkylthioether bond under electron impact and fast atom bombardment conditions
d'Ischia M.;
1996
Abstract
The marked proclivity of 5-S-cysteinyldopa (I) and related phenolic alkylthioethers to undergo UV-induced desulfurization via primary photohomolytic cleavage of the CH2-S bond prompted an investigation of the mass spectrometric behavior of these compds. with a view to obtaining information on the intrinsic susceptibility to dissocn. of the alkylthioether bond under nonirradiative conditions. Dealkylative fission of the CH2-S bond was an important dissociative channel in the fragmentation patterns of 1 and related compds., including cysteinylhydroquinone (II), 4-S-cysteaminylphenol (III) and 4-S-cysteaminylcatechol (IV) under electron impact conditions. The mode of fission and relative susceptibility of the CH2-S bond were, however, profoundly different in cysteaminyl vs. cysteinyl compds. In particular, the former showed a marked tendency to undergo simple homolytic fission, whereas in the latter dealkylative C-S bond cleavage occurred largely via an intramol. rearrangement mechanism, and proved highly sensitive to protonation-induced effects, as evidenced in fast atom bombardment expts. Desulfurization processes with neat loss of the alkylthio residue, like those occurring upon UV irradn., were virtually absent in the fragmentation patterns of III and IV, and provided only a minor contribution to those of I and II. These and other data reported open fresh prospects for future studies on the chem. and mass spectrometric behavior of I and structurally related phenolic compds. of biol. relevance.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
