A Novel Carotenoid with a Unique 2,6-Cyclo-ψ-End Group, Roretziaxanthin, from the Sea Squirt Halocynthia roretzi

A novel carotenoid with a unique 2,6-cyclo-ψ-end group, named roretziaxanthin (1), was isolated from the sea squirt Halocynthia roretzi as a minor carotenoid along with (3S,3′S)-astaxanthin, alloxanthin, halocynthiaxanthin, mytiloxanthin, mytiloxanthinone, etc. This structure was determined to be 3-hydroxy-1′,16′-didehydro-1′,2′-dihydro-2′,6′-cyclo-β,ψ-carotene-4,4′-dione by UV–VIS, MS, and NMR spectral data. The formation mechanism of roretziaxanthin in the sea squirt was discussed.