Characterisation of a novel UV filter in the lens of the thirteen-lined ground squirrel (Ictidomys tridecemlineatus)

•A new UV filter compound has been found in squirrel lenses.•Its structure was elucidated by NMR and mass spectrometry.•It has a maximum UV absorption of 340 nm•It is formed from condensation of proline with N-acetyl 3-hydroxykynurenine.

Structural analysis of a novel UV filter present in the lens of the thirteen-lined ground squirrel has shown that it is related in structure to N-acetyl-3-hydroxykynurenine. This finding is consistent with the fact that the squirrel lenses also contain high levels of this tryptophan metabolite. Analysis of both NMR and mass spectrometric data suggested that the novel UV filter compound forms by condensation of proline with N-acetyl-3-hydroxykynurenine. Its absorption maximum at 340 nm is more than 20 nm lower than that of the kynurenines and it may therefore assist in filtering the more damaging shorter wavelengths of UVA.

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