A combination of accurate mass measurement and tandem mass spectrometry (bo
th product ion and precursor ion scans) have been used to characterize the
major fragment ions observed in the EST mass spectrum of kynurenine. Kynure
nine is a metabolite of tryptophan found in the human lens and is thought t
o play a role in protecting the retina from UV-induced damage. Three major
fragmentation pathways were evident, following initial elimination either o
f ammonia, H2O and CO or the imine form of glycine. The latter is proposed
to occur via the formation of an ion-molecule complex. In the case of loss
of H2O and CO from deaminated kynurenine, there is evidence for an acylium
ion intermediate, which is not observed for the loss of H2O and CO directly
from protonated kynurenine. Product ion scans of deuterated kynurenine ena
bled the elucidation of structural rearrangements that were not evident in
the spectra of the native compound. Since UV filter compounds can often onl
y be isolated in small quantities from the lens, this study forms the basis
for the characterization of novel W filter compounds using mass spectromet
ry. The approach presented here may also be useful for the characterization
of related classes of small molecules. (C) 2001 American Society for Mass
Spectrometry.