Animal Carotenoids. 29. New (2R)-2-hydroxy-4-keto-beta-type carotenoids from Daphnia magna (Crustaceae).

Abstract
Two new ketocarotenoids from Daphnia magna (Crustaceae) were assigned the constitutions 2-hydroxyechinenone (2-hydroxy-.beta.,.beta.-caroten-4-one) and 2-hydroxycanthaxanthin (2-hydroxy-.beta.,.beta.-carotene-4,4''-dione) on the basis of 3H NMR, mass spectroscopy and base catalyzed dehydration. Carotenoid ketols with this particular substitution pattern have not previously been identified. 2R-Chiralities were supported by the CD spectra of the dione and of the lithium aluminum hydride reduced derivatives and by the Horeau method. The carbamate method could not be used for determination of the optical purity of .beta.,.beta.-caroten-2-ols. The constitution of 3''-hydroxyechinenone (3''-hydroxy-.beta.,.beta.-caroten-4-one) ex Arthrospira sp. was confirmed by 1H NMR and 3''R-chirality demonstrated by CD.