Detection, quantification, and total synthesis of novel 3-hydroxykynurenine glucoside-derived metabolites present in human lenses

Purpose. 3-Hydroxykynurenine O-β-D-glucoside (3OHKG) protects the lens from UV damage, and novel related species may act analogously. The aim of this study was to detect, quantify, and elucidate the structures of novel 3-hydroxykynurenine glucoside–derived metabolites present in the human lens. Methods. Compounds were detected and quantified by liquid chromatography with tandem mass spectrometry (LC-MS/MS) in 24 human lenses of different ages, of which 22 were normal and two had cataract. Structures of these were confirmed through total synthesis. Results. 3OHKG concentrations decreased with age in the lens nuclei, whereas the levels of three novel species, 4-(2-amino-3-hydroxyphenyl)-2-hydroxy-4-oxobutanoic acid O-β-D-glucoside (3OHKG-W), 3-hydroxykynurenine O-β-D-glucoside yellow (3OHKG-Y), and 2-amino-3-hydroxyacetophenone O-β-D-glucoside (AHAG), increased, though to different extents. In contrast, the concentrations present in the cortex of the lens remained constant with age. Conclusions. Three novel 3OHKG-derived metabolites have been detected in extracts from human lenses.