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 (), was isolated from the sea squirt as a minor carotenoid along with (3,3')-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.