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Six novel keto carotenoids have been isolated from the stick insect. The structure of the pre­dominant red pigment has been assigned to 3,4,3′,4′-tetradehydro-β,β-carotene-2,2′-dione on the basis of electronic, infrared, and mass spectra. Minor pigments are 3,4-didehydro-β,β-carotene-2,2′-dione, 2′-hydroxy-3,4-didehydro-β,β-caroten-2-one, and 2′-hydroxy-β,β-caroten-2-one. Two other com­pounds, β,β-caroten-2-one and β,β carotene-2,2′-dione, have been tentatively identified. The ad­ ditional occurrence of β,β-caroten-2-ol and β,β-carotene-2,2′-diol has been reported recently. All hydroxylated pigments are mainly present as fatty-acid esters. During hydride reduction of the 3,4-didehydro-2-one compounds hydrogenation of the 3,4-double bond was observed as a side reaction.

Metabolites of β, β-Carotene in the Stick Insect, C arausius morosus Br.: Compounds with 2-One and 3,4-Didehydro-2-one Structure